University of Texas McDonald Observatory Department of ......Barbara, 5/15– 6/15/96. On August 31,...

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University of TexasMcDonald Observatory

Department of AstronomyAustin, Texas 78712

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This report covers the period 1 September 1995–31 Aug1996.

1. ORGANIZATION, STAFF, AND ACTIVITIES

1.1 Description of Facilities

The astronomical components of the University of Texat Austin are the Department of Astronomy, the CenterAdvanced Studies in Astronomy, and McDonald Obsertory at Mount Locke. Faculty, research, and administratstaff offices of all components are located on the campuAustin. The Department of Astronomy operates a 23-cmfractor and a 41-cm reflector on the Austin campus forstructional, test, and research purposes.

McDonald Observatory is in West Texas, near Fort Davon Mount Locke and Mount Fowlkes. The primary instrments are 2.7-m, 2.1-m, 91-cm, and 76-cm reflecting tescopes and a 76-cm telescope dedicated to laser ranginthe moon and artificial satellites.

McDonald Observatory is also a partner in the CalteSubmillimeter Observatory on Mauna Kea, Hawaii.

1.2 Administration

William H. Jefferys is Chair of the Department of Astronomy, with EthanVishniac as Assistant Chair. Frank NBash is the Director of McDonald Observatory and the Ceter for Advanced Studies in Astronomy, Thomas G.BarnesIII is Associate Director, and Phillip W.Kelton is AssistantDirector. MarkAdams is the resident Superintendent.

1.3 Teaching and Research Personnel

~In the lists that follow, asterisks denote Mount Locresidents.! Academic

Named Professors: Frank N. Bash ~Frank N. EdmondsRegents Professor in Astronomy!; Gerard H. de Vau-couleurs ~Jane and Roland Blumberg Professor EmeritusAstronomy, deceased September 1995!; David S. Evans~Jack S. Josey Centennial Professor Emeritus in Astronom!;Neal J.Evans II ~Edward Randall, Jr. Centennial Professo!,William H. Jefferys ~Harlan J. Smith Centennial Professin Astronomy!; David L. Lambert ~Isabel McCutcheonHarte Centennial Chair in Astronomy!; R. EdwardNather~Rex G. Baker, Jr. and McDonald Observatory CentennResearch Professor in Astronomy!; Edward L. Robinson~William B. Blakemore II Regents Professor in Astronomy!;John M.Scalo ~Jack S. Josey Centennial Professor in Atronomy!; Gregory A.Shields ~Jane and Roland BlumberCentennial Professor in Astronomy!; StevenWeinberg ~Re-gents Professor and Jack S. Josey–Welch Foundation Cin Science!; and J. CraigWheeler ~Samuel T. and FernYanagisawa Regents Professorship in Astronomy!. Profes-

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sors: Michel Breger ~adjunct!, James N.Douglas, PaulSha-piro , RomanSmoluchowski ~emeritus, deceased Janua1996!, ChrisSneden, Paul A.Vanden Bout ~adjunct!, EthanVishniac, DerekWills , and DonWinget.

Associate Professors: Harriet Dinerstein, Paul M.Har-vey, DanJaffe, JohnLacy, and R. RobertRobbins, Jr.Non-Academic

Senior Research Scientists: Thomas G.Barnes III, Lau-rence M.Trafton , and Robert G.Tull .

Research Scientists: Edwin S.Barker , George F.Bene-dict, Anita L. Cochran, William D. Cochran, RobertDun-can, Artie P.Hatzes, Paul D.Hemenway, GaryHill , AlexeiKhokhlov , Daniel F. Lester, FrankRay, Peter J.Shelus,Verne Smith, JocelynTomkin , Arthur L. Whipple, andBeverley J.Wills . Research Associates: Mark Cornell, Wil-lamGressler, Mary KayHemenway, Victor Krabbendam,Larry Long, Phillip MacQueen, Hugo Martel , Alvin L.Mitchell , EdNelan, and DarrellStory.

Postdoctoral Research Associates and Other VisitStaff: JannaAnossova, Eric Bakker, DonBarry , GuillermoGonzalez, William Hix , ChristopherJohns-Krull , IngerJo”rgensen, Soon-WookKim , JeremyKing , ChrisKoresko,MasaakiKusunose, Kepler Oliveira , Matt Richter, JuditGyorgyey Ries, Yaron Sheffer, JosefStein, Keith L. Th-ompson, Lifan Wang, and ChunyanWei.

1.4 Senior Research Support and Administration

HET Project Manager: Tom Sebring.Special Assistant to the Director (Development): Joyce C.

Sampson~departed January 1996! and JoelBarna.Associated member of another department: Raynor L.

Duncombe, Professor of Aerospace Engineering and Enneering Mechanics.

Director of the McDonald Public Information Office: San-dra L.Barnes.

McDonald supervisors: GordonWesley ~mechanical en-gineering, departed September 1995!, EdwardDutchover,Jr.* ~administrative support!, Earl Green* ~observing sup-port!, George E.Grubb* ~physical plant!, Mark Cornell~computing systems!, Phillip MacQueen ~CCD develop-ment!, Alvin L. Mitchell ~engineering support!, and Jerry R.Wiant* ~MLRS!.

Administrative Services Officer: CecilioMartinez

1.5 Board of Visitors

GeorgeChristian was Chair of the McDonald Observatory and Department of Astronomy Board of Visitors, wiMark Bivins Vice Chair and FrancisWright Secretary.

Members of the Board of Visitors: LucyAlexander,GrantBillingsley, Mark Bivins, William Block, Wm. TerryBray, J.P.Bryan, GeorgeChristian , JosephCialone, Anne

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Dickson, Marshall Doke, GeorgeFinley, William Guest,HenryHamman, PaulHobby, KatherineJohnson, HerbertKelleher, GarlandLasater, ThomasLink , JamesMcCart-ney, ArthurMiller , BradfordMoody, Lillian Murray , JudyNewton, PikePowers, William Ratz, JonRuff , CarlRyan,Karen Skelton, F. Ford Smith, Marshall Steves, CurtisVaughan, David Weeks, Gene Wiggins, and FrancisWright .

1.6 Visitors and Affiliations

Dr. James E. Peebles received the Antoinette de Vcouleurs Medal. He presented the Antoinette de VaucouleLecture on October 31, 1995 entitled ‘‘Is the Universe Opor Closed? Comments on the Ideas and the Evidence.addition, on November 1 he presented a popular lecturetitled ‘‘Images of the Physical Universe.’’

The following people were visitors to the departmeverse C. Colome, Universidad Nacional Autonoma dMexico A. Davidsen, Johns Hopkins University D.Dey-oung, National Optical Astronomy Observatories G.Fer-land, University of Kentucky C.Heiles, University of Cali-fornia, Berkeley P. Hoflich, Harvard University M.Kaufman, Ohio State University A.Klypin , New MexicoState University B.Milvang-Jensen, Copenhagen University Observatory J.Moran , Smithsonian Astrophysical Observatory F.Shu, University of California, Berkeley SStarrfield , Arizona State University J.Stein, Hebrew Uni-versity of Jerusalem D.Turnshek, University of PittsburghC.Wei, China verse

G. Shields spent 7/15–8/7/96 at the Center for Astrophics and Space Science~CASS! at the University of Californiaat San Diego, formulating plans to study QSO chemiabundances with F. Hamman, V. Junkkarinen, and other

P. Shapiro was an invited member of the InstituteTheoretical Physics Workshop on Galaxy Formation anddiation Backgrounds at the University of California at SanBarbara, 5/15– 6/15/96.

On August 31, 1996, E. Barker completed a three-yIntergovernment Personnel Act~IPA! assignment to the Office of Space Science at NASA Headquarters where hethe Discipline Scientist for Planetary Astronomy. He noreturns full-time to his position as Research Scientist atUniversity of Texas.

C. Sneden was on research leave from the AstronoDepartment, spending the academic year at NOAO/KP~Tucson!.

1.7 Awards, Honors, and Special Activities

Robert Tull won the Astronomical Society of the Pacific1996 Maria and Eric Muhlmann Award. This award is givfor ‘‘recent significant observational results made possiby innovative advances in astronomical instrumentatisoftware, or observational infrastructure.’’ In Tull’s case,is being recognized for his designs of spectrographs, inticular the coude´ spectrographs of the 2.7-m telescope at MDonald Observatory, and for pioneering work in solid-staimage detectors and computer automation in astronomobservations.

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Lifan Wang received a Hubble Postdoctoral Fellowshwhich he will use to remain in Texas and work on supernospectra and polarimetry.

Mike Brotherton was awarded an AAS InternationTravel Grant to attend IAU Colloquium No. 159, heldShanghai, China, June 17–20, 1996.

Anita Cochran was Chair of the Division for PlanetaSciences of the American Astronomical Society. Mary KHemenway served as the Education Officer for the AmeriAstronomical Society. Frank Bash was elected to the Couof the American Astronomical Society, and he is a memof the Board of Directors of the Astronomical Society of thPacific. Anita Cochran was elected to the U.S. NatioCommittee, IAU. Craig Wheeler was a member of the Tinley Prize Committee and the Committee on the StatusWomen in Astronomy for the American Astronomical Socety.

Judit Ries served on the Committee of the AAS Division Dynamical Astronomy; Peter Shelus served as its trsurer. Art Whipple was secretary of the Division on Dynamcal Astronomy. In this capacity, he was a member oforganizing committee for the 27th meeting of the DDA,the U.S. Naval Observatory in Washington, DC.

Frank Bash is the Member Representative from the Uversity of Texas to AURA, the AURA Coordinating Councof Observatory Research Directors, and the Council ofrectors of Independent Astronomical Observatories.

Peter Shelus was elected as LLR Vice-Chairman ofSLR Subcommittee within the international fundamental rerence system working group, CSTG. Mary Kay Hemenwserved on the American Institute of Physics CommitteePhysics Education~term 1992–8!. She also was the Directofor the Steering Committee of the Coalition for Earth Sence Education~1995–6!.

Craig Wheeler was Chair, Panel on Stars and Stellar Elution, National Academy of Science Task Group on SpaAstronomy and Astrophysics.

Bev Wills finished a term on the Hubble Space Tescope’s User Committee. She was also on the AGN Panethe HST Cycle 6 Proposal review. Harriet Dinerstein servon the Interstellar Medium Panel for the HST Cycle 6 prposal review.

William Cochran served on the NASA Origins Subcommittee and the NASA Keck TAC.

Paul Shapiro served on the NASA Review Panels forHPCC Grand Challenge Program and the Long-Term SpAstrophysics Program.

Mary Kay Hemenway served on the following organizincommittees at the University of Texas: 1996 Conferencethe Advancement of Science Teaching of the State ScieTeachers Association of Texas; College of Natural Sciencmeeting on Discovery Learning; 1996 Summer AdvancPlacement Institute.

Phillip MacQueen won the University President’s Excelence Award, and Cleota Gambino won the College of Naral Sciences Staff Excellence Award.

Peter Shelus, Randall Ricklefs, and Jerry Wiant eachceived a Productivity Group Award from the Goddard Spa

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616 ANNUAL REPORT

Flight Center as members of the NASA Satellite Laser Raing Network Engineering Team.

Tom Barnes served on the Organizing CommitteeCommission 27~Variable Stars! of the IAU this year andwrote the triennial summary of research on field RR Lyrstars for the commission.

Larry Trafton, Tom Barnes, and Anita Cochran servedthe Local Organizing Committee for the January 1996 meing of the American Astronomical Society in San Antonio

Craig Wheeler served as a General Member, BoardTrustees, Aspen Center for Physics. He was a Co-Chathe Organizing Committee for the Aspen Winter Workshon Black Hole X-Ray Transients and on the OrganiziCommittee for the Texas Symposium on Relativistic Astphysics. Craig Wheeler is on the organizing committeethe International Astronomical Union Commission 42–CloBinary Systems.

Chris Sneden is an associate editor ofThe AstrophysicalJournal. Larry Trafton is an Associate Editor ofIcarus.Ethan Vishniac served as a Divisional Associate EditorThe Physical Review Letters. Tom Barnes was a technicaeditor for StarDate Radio andStarDatemagazine. DerekWills was a technical editor for the popular science progr‘‘Earth and Sky’’ on National Public Radio.

2. ACADEMIC AND EDUCATIONAL PROGRAM

2.1 Graduate Program

The Graduate Studies Committee Chairman was EtVishniac, with Graduate Advisor Neal Evans. The FredGoetting, Jr. Memorial Endowed Presidential Scholarswas awarded to ByronMattingly . The David Alan BenfieldMemorial Fellowship was awarded to JamesDi Francesco.The Frank N. Edmonds, Jr. Memorial Fellowship wawarded to WenbinLi . The Board of Visitors second-yeaproject award was given to VincentWoolf. Graduate stu-dents in 1995–1996 were JayBoisseau, Michael Brother-ton, David Chappell, JungyeonCho, Cecilia Colome,JamesDi Francesco, GregoryDoppmann, CynthiaFron-ing, Niall Gaffney, Youxin Gao, Erik Gregersen, RodneyHeyd, Daniel Hiltgen, D. Andrew Howell, Renee James,Antonio Kanaan-Neto, LukeKeller , ScotKleinmann, EricKlumpe, PaulKornreich , AnandKudari , WenbinLi , Zhi-qing Li , FengMa, Byron Mattingly , RebeccaMcQuitty ,Michael Montgomery, Micahel Moscoso, Atsuko Nitta ,SoojongPak, ChristinePulliam, DivasSanwal, JoeWang,QiangguoWang, VincentWoolf, Bingrong Xie, and EricZink .

Doctoral Dissertations:Eight Ph.D. degrees in astronomwere awarded in 1995–1996:

Cecilia Colome ~Supervisor P. Harvey!: ‘‘Far-InfraredPhotometry and Near-Infrared Polarimetry of High-MaStar-Forming Regions: Diagnosing Their Density Structur

PaulKornreich ~Supervisor J. Scalo!: ‘‘Vorticity Genera-tion by Shocks in the Interstellar Medium’’

ScotKleinmann ~Supervisor R.E. Nather!: ‘‘G29-38 andthe Advent of Cool DAV Asteroseismology’’

JohnBoisseau~Supervisor J.C. Wheeler!: ‘‘The Multidi-mensional Structure of Detonations in Type IA Supernova

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Niall Gaffney ~Supervisor C. Sneden!: ‘‘Near-InfraredMeasurements of Kinematics in Infrared Bright Galaxies’

MichaelBrotherton ~Supervisor B. Wills!: ‘‘The Natureof QSO Emission-Line Regions’’

Daniel Hiltgen ~Supervisor C. Sneden!: ‘‘Lithium inEvolved Stars’’

Antonio Kanaan-Neto ~Supervisor D. Winget!: ‘‘Magne-tism and Pulsating Stars’’

Master’s Theses:Five Master’s degrees in astronomwere earned in 1995–1996:

Erik Gregersen~Supervisor N. Evans!: ‘‘New Protostel-lar Collapse Candidates: An HCO1 Survey of the Class OSources’’

Anand Kudari ~Supervisor E. Vishniac!: ‘‘Thermody-namics and Radiative Transfer in Highly Magnetized PPlasmas: A Model of Soft Gamma Repeaters’’

CynthiaFroning ~Supervisor E. Robinson!: ‘‘The Infra-red Properties of a Compact Binary Accretion Disk in Quescence’’

Eric Klumpe ~Supervisor D. Winget!: ‘‘Carbon/OxygenPhase Separation and Its Non-Influence on White DwCosmochronology’’

Eric Zink ~Supervisor P. Harvey!: ‘‘High Resolution 100Micron Observations of Far-Infrared Luminous Galaxies’’

2.2 Undergraduate Program

Derek Wills is the chair of the Undergraduate StudCommittee; Dan Jaffe served as undergraduate advThere were 31 astronomy majors this year, and sevendents received BAs.

Sonali Kolhatkar was awarded the Outstanding Graduing Senior Award. She will be entering graduate schoolastronomy at the University of Hawaii in the fall of 1996Benjamin Shaw was the winner of the Karl G. Henize Mmorial Scholarship in Astronomy. Bianca Basso is the recent of this award for 1996–97. Audress Johnson is the wner of the Board of Visitors Undergraduate ScholarshipAstronomy.

2.3 Educational Services

The Painter Hall observatory, a 9-inch refractor telescowas operated by Antoˆnio Kanaan-Neto, Anand Kudari, anFeng Ma. From September 1995 through the end of Aug1996, the observatory hosted 29 public nights with 670 vtors and 29 ‘‘UT’’ nights with 170 visitors. Thirteen groutours were arranged for 260 visitors.

The Educational Office of the Department hosted star pties every Wednesday, weather permitting, on the 14th flobserving deck of the Astronomy Department building.large number of those were cancelled due to bad weathera total of 200 visitors participated. In March, we had 1visitors at two special star parties to view Comet Hyakutaand a total lunar eclipse. 300 elementary school studentsited the department during the twelve specially arrangedlar tours.

In the course of theTexas Energy Symposium for HigSchool Students and Teachers, Judit Ries hosted two speciaastronomy laboratory sessions for the participants.

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Ethan Vishniac and Judit Ries participated in the AnnHonors Colloquium, giving a lecture and an informal discusion session. A special viewing session was also arrangeJudit Ries and Lara Eakins, with the help of the astronograduate students, for 70 high school students.

Lara Eakins and Judit Ries created a Web site for Edution Office Services as a part of the departmental Web sInformation about tours, star parties, educational resourand equipment is now available on line.

2.4 Public Information Office

The StarDate radio program continues to broadcast toaudience of 2.5 million daily on over 200 radio stationsthe U.S. Universo, the Spanish-language version of StarDbroadcasts on over 150 radio stations. It is heard in 40 oftop 50 markets in the U.S. Universo also broadcastsMexico, Venezuela, and South Africa. Sternzeit, StarDaGerman counterpart, continues to broadcast on DeutschRadio throughout Germany.StarDatemagazine continues tobe very popular among radio listeners and others in the U

Universo was also made available to 60 school teachfor use in the classroom. A survey of these teachers indicthe need for a teacher guide to accompany the programshowed that each teacher exposed the program to an avof 77 students. The National Science Foundation hasvided supplemental funds for the guide. Estrada Commucations Group joined the Universo team to syndicate theries, search for corporate sponsorship, and provide purelations in the Hispanic community.

The W.L. Moody, Jr. Visitors’ Information Center serveover 130,000 visitors. Improvements were made that enlive video of the sun and the planets to be shown ontelevision screen inside the Visitors’ Center. A volunteprogram was successfully implemented by the Visitors’ Cter team. Staff uniforms were also added to the improments made at the Center this year.

The project for a major expansion of the visitors’ prgrams and facilities at McDonald Observatory was namthe Texas Astronomy Education Center. The Texastronomy Education Center is a six-phase, $7.7-million-doproject ~including a $2 million endowment!. It has been de-clared one of the top priority fundraising projects for tUniversity of Texas by the Vice President for DevelopmeA grant from the National Science Foundation totalli$943,000 was awarded for an interactive science exhibittitled Fingerprinting the Universe. The Texas DepartmenTransportation awarded $420,000 for transportationhancements in association with the expansion. Togetherthe private funds raised, the $2 million fundraising milestofor the Texas Astronomy Education Center was achievefiscal 1995–1996.

3. RESEARCH PROGRAM

3.1 The 9.2-Meter HobbydEberly Telescope„HET …

In August, 1995, Phase II of construction of the het facity commenced. This included build-out of the interior, afollowed installation of the telescope structure and the doenclosure. In September 1995, problems with the structu

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air bearing azimuth rotation system were debugged. An orwas placed for the Segment Positioning System which csists of 273 linear actuators under computer control.

In October, final acceptance testing of the structure aazimuth rotation system was completed. Fabrication ofULE blanks for the four spherical aberration corrector mrors was procured from Corning Glass. Production of pmary mirror segments~96 total, 1-m hexagons 50 mm thickmade of Zerodur! by Eastman Kodak went well, with fousegments completed in October.

All 96 Primary Mirror segment blanks were received bKodak from Schott Glass in November. Following a chanin management, construction activities reached their bpace with regard to schedule. Development of electronand software subsystems proceeded on schedule. Detdesign of the Prime Focus Instrument Platform commenc

In December, two crates of completed primary mirrsegments were delivered to Denton Vacuum for coating wprotected silver. Work on the tracker system by Orbital Sences Corporation continued, albeit at a slow pace. By Jaary 1996, construction activities were virtually complete,cluding interior finishes, the large glycol/water aconditioning system, and landscaping. Additional develoment work was performed on the Hindle type primary mirrsegment mounting system, resulting in fully acceptable pformance.

In March, HET personnel began increasing their on-sparticipation. Previously, most work had been performedcontractors, but integration of mirrors, software, electronitracker, and instruments is to be performed byHET person-nel.

In April, weather station installation was completed, ainstallation of software controls for dome rotation and struture interface were completed.

In May 1996, a contract was let to Space Optics ReseaLab to fabricate three of the four radical aspheres ofSpherical Aberration Corrector. The fourth mirror was cotracted to Tinsley Optical. The first two primary mirror sements were successfully coated at Denton, and a total oman–days ofHET personnel time was spent at the site.

Eleven completed primary mirror segments were receion site, and components were received to assemble quanof the primary segment mounts. A surrogate, single-podiamond turned aluminum spherical aberration correctorsembly was received from II–IV Optical. This surrogate alows first light and telescope debug prior to completionthe Prime Focus Instrument Package.

In June, the first three primary mirror segments werestalled, and the Center of Curvature Alignment Sen~CCAS! was installed atop the 90-foot-tall tower providefor it. The CCAS is a polarization shearing interferomeused to sense segment tip, tilt, and piston positions for alment.

In July, demonstration of the CCAS was accomplishensuring that interferometry could be performed overlong, exposed optical path. Initial final acceptance testingthe Tracker system was performed, and development othermal control algorithm for coarse segment position crection was in work.

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As of August, theHET awaits installation of the Trackerdelivery of which is expected in September. The facility~in-cluding HVAC and downdraft ventilation system!, the struc-ture ~including azimuth rotation system!, the dome, and theCCAS instrument are all operational under full compucontrol. It is expected that first light will be achievedNovember 1996, three months behind the schedule datetablished in August of 1992 at the inception of the projectis expected that theHET will be fully operational by August1997 and will be completed for the originally budgeted cof $13.5 million.

3.2 Observing Conditions at McDonald Observatory

A summary of the hours scheduled, hours lost to pweather, hours lost to telescope/instrument problems,hours assigned to maintenance is given below. Availahours are measured from civil twilight to civil twilight, pluany especially scheduled daytime hours.~The daytime hoursfor all four telescopes together total only 21 hours.! Category‘‘Other’’ is comprised primarily of time when the telescopwas not scheduled or no program object was available.

The 2.7-m telescope records may be used to infer antimate of the fraction of time the sky was suitable for spetrometry or imaging. After correcting for downtime duemaintenance, equipment, etc., the usable time is estimate67% for the last fiscal year. This value may be compawith 65% for the previous year and 62.4% for a fifteen-yemean. Until recently, the 0.9-m telescope was used predonately for photometry, so its usage can be used to inferphotometric weather statistic. From the 0.9-m telescopetistics for 1981–1992, the photometric weather at McDonObservatory has averaged 39.8% of the available ho~Since then, the 0.9-m telescope has been used only forcial programs without sufficient statistics to infer thweather.!

3.3 Scientific Results

3.3.1 Instrumentation:D. Lester has been active on theSOFIA Science Working

Group and in activities to develop this important new obs

TABLE 1. Utilization Statistics for McDonald Observatory Optical Telscopes~1995–1996! ~hours!

2.1-m 0.9-m 0.8-m

a! 4034 4025 4020 4020

b! 2406 ~60%! 2402 ~60%! 666 ~16%! 1650 ~41%!

c! 1203 ~30%! 1410 ~35%! 751 ~19%! 851 ~21%!

d! 35 ~1%! 54 ~1%! 104 ~3%! 15 ~1%!

e! 217 ~5%! 1 ~0%! 158 ~4%! 49 ~1%!

f! 173 ~4%! 158 ~4%! 2341 ~58%! 1455 ~36%!

a!Available; b!Observed; c! Lost to weather;d! Lost to telescope/instrument problems;e! Scheduled maintenance; f! Other

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vatory. He has been a leader in efforts to privatizeSOFIA inorder to achieve lower costs to the government by comptive procurement of the entire facility for development aoperations. The University of Texas has played a major rin developing partnerships that are necessary for this eff

R. Tull and colleagues are continuing the planning adesign of a high-resolution fiber-fed broad-band optical sptrometer for theHET. The spectrograph will work in therange of resolving powers 30,000<R<120,000, using anR-4 echelle mosaic with cross-dispersing gratings. The loteam includes P. MacQueen, C. Sneden, W. CochranLambert, A. Hatzes, D. Barry, and J. Good. The internatioteam includes members at theHET member organizations aPenn State University and the University of Munich. Fufunding has been obtained through an NSF grant togewith private gifts, a State of Texas appropriation, andNASA enhancement of an existing grant, plus UniversityTexas matching funds. Many of the major optical compnents have been ordered, and the all-refracting camercurrently under design by H. Epps~Lick Observatory!.Completion is planned for the autumn of 1998.

D. Lester, G. Hill, and P. Harvey, with graduate studeG. Doppmann and C. Froning, are finishing constructionthe CoolSpec near-infrared spectrometer for use on theDonald Observatory 2.7-m telescope. This spectrometertheROKCAM HgCdTe camera as a detector which is mateda spectrometer that can be cooled to 150 K to reduce bground emission out to three microns. This instrumeshould see first light on the telescope in 1997.

The University of Texas Fabry–Perot Spectrometerbeen upgraded. S. Pak and D. Jaffe have built a Fabry–Pcooling box for the instrument. The low and stable tempeture of the Fabry–Perot Etalon can reduce the backgrosignal by a factor of two to four and stabilize the alignmeof the Fabry–Perot mirrors. E. Klumpe and Jaffe havesigned and built a 6-inch ‘‘mini-telescope’’ that will be integrated with the University of Texas Near-IR Fabry–Pespectrometer. They will use this system to survey molecuclouds both near the solar circle and in the inner GalaCurrently, they are in the process of evaluating the pointperformance of the telescope.

L. Keller, T. Benedict, and D. Jaffe have improved theprocessing technique for fabrication of chemically etch~micromachined! diffraction gratings in silicon. They havedone extensive testing on a prototype immersion echellefound that the diffraction efficiency suffers from scatterlight due to defects produced in the fabrication proceKeller has begun a design for installing an etched immersechelle and a 2563256 near-IR~InSb! detector array into anexisting spectrograph~IRSHELL, built by J. Lacy!. The newspectrograph will have a resolving power ofR5100,000 inthe 1–5mm spectral region. Keller is also working witLacy, Jaffe, and M. Richter on a mid-IR spectrograph desfor SOFIA.

W. Wren and J.C. Wheeler have put into operationnovel new telescope at McDonald Observatory to be useda visual search for nearby supernovae. This telescope sitan optical bench with a fixed 18-inch primary mounted wits optical axis horizontal. The only moving part is a flat

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the opposite end of the optical bench. Comparison imaare stored and accessed by a hyperlink connected to theware that selects the next closest galaxy to the last obseand slews the telescope accordingly. The rapid slewingthe Supernova Search Telescope caused some initial poiproblems. These were solved by Wayne Rosing of thebotic Telescope Company by remachining both bearings~al-titude and azimuth! and writing custom software to meet thunique optical and mechanical needs of this instrument.Supernova Search Telescope became operational in M1996. In April, the telescope set a program record of 2,5observations for a single month. A lighting strike disablthe telescope for two weeks in July, and summer weahindered observations. Totals for the Supernova Search Tscope as of September 29, 1996 are 8,704 observation2095 galaxies, one near miss, no discoveries~yet!.

F. Bash, T. Sebring~HET Project Manager!, L. Ramsey~Penn State andHET Project Scientist!, and F. Ray~HET LeadEngineer! have examined the design of a telescope patteron the HobbydEberly Telescope but with a diameter of 2meters. The preliminary design allows cost estimates whsuggest that the telescope with initial instruments couldbuilt for less than $200 million.

3.3.2 Solar System:

The McDonald Observatory Planetary Search~MOPS!program~W. Cochran and A. Hatzes! continued survey ob-servations designed to detect planetary systems in oaround nearby solar type stars. Extremely high-precismeasurements are obtained of radial velocity variationssample of 36 dwarfs and subgiants of spectral types Fand K. A time series of such observations will reveal torbital motion of the star around the star–planet barycenAn I2 gas absorption cell placed in front of the 2.7-m tescope coude´ spectrograph allows velocity precision of abo5–10 m s21 to be achieved. A companion southern hemsphere survey is being conducted at the European SoutObservatory in collaboration with M. Ku¨rster, K. Dennerl,and S. Do¨bereiner~MPI Garching!. The eso survey uses an

2 absorption cell at the 1.4m CAT. Four years of data froeso have demonstrated a long-term precision of better10 m s21.

The Hubble Space Telescope Astrometry Science Tecontinued to monitor the nearby stars Proxima CentauriBarnard’s Star for low-mass companions~investigation ledby G.F. Benedict!, and this year it added L726-8AB~P.J.Shelus, lead!. Ten new data sets for Proxima Centauri weacquired this year with which to either confirm or refute tweak perturbation detected at P;80 days. They continue toanalyze the astrometric residuals for the signature of a cpanion. With 35 observation sets acquired over three yethere are no obvious brown dwarf companions to BarnaStar. Present companion mass detection limits for bProxima Cen and Barnard’s Star vary from 0.3 to one Jupmass for periods ranging from 100 to 600 days. Theepochs for L726-8AB already yield a companion lower malimit of two Jupiter masses for periods less than one-hyear. Eight more epochs will be secured this year.

A. Cochran, along with H. Levison, S.A. Stern~both of

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SwRI!, and M. Duncan~Queens University! continued theirinvestigations of the structure of the Kuiper belt by studyithe comet-sized bodies. They analyzed images of an ational field obtained with the HST WFPC2, but increasnoise in the images~over the first field in August 1994! didnot allow faint enough limiting magnitudes to detect tsmall objects. The lack of detected objects is consistent wthe limiting magnitudes if the population was identicalthat observed in the first hst field.

Comets deVico and Hyakutake~1996B2! were observedwith theR560,000 andR5200,000 modes of the 2DCoud´spectrograph and theR560,000 Cassegrain Echelle spetrograph by J. Tomkin, W. Cochran, D. Lambert, C. JohnKrull, and A. Hatzes. These spectra are being processedanalyzed by A. Cochran. With the highest resolution dathey are studying the line widths of the O (1D!, O (1S! and Ha lines along with single lines from NH2, C2 , and CN. Alllines are spectrally resolved. The NH2 line is the narrowest,while all of the other lines except Ha are about the samewidth. The Ha line width is consistent with excess ejectiovelocity from photodissociation of H2O. The modeling ofthese line widths is being performed by M. Combi~Michi-gan! using his Monte Carlo Particle Trajectory Mode

W. Cochran, A. Cochran, and K. Baines~JPL! obtainedspectra of Jupiter to investigate a weak absorption ban920–940 nm which Karkoschka~Icarus111, 174, 1994! sug-gested might be due to H2O. High-resolution (R5200,000!spectra with the 2.7-m telescope 2DCoude´ spectrograph re-vealed several absorption features from this band. Thesesorptions, however, do not coincide with the wavelengthsexpected H2O absorptions. The identification of the band rmains uncertain, but the band morphology and the tendeof the features to weaken near the limb of the planetsuggest NH3 as the most likely candidate.

L. Trafton and S.A. Stern~SwRI! completed their analysisof Pluto’s UV light curve down to 2500 Å obtained with thHubble Space Telescope. The absolute amplitude was foto vary little with wavelength from the visual to 2500 Å , butthe relative light curve amplitude was found to increase40% over this range. Below 3100 Å , the light curve profilesand albedos are nearly independent of wavelength. No strgaseous absorbers were found. They established an ulimit on the haze optical depth at 2600 Å of 0.54, or 0.extrapolated to the visual, which is still too high to rule oatmospheric haze as the cause of the sudden drop-off instellar occultation light curve.

With S.A. Stern ~SwRI! and M.W. Buie ~Lowell!, L.Trafton analyzed high-resolution images of Pluto taken whst to obtain albedo maps of Pluto’s surface. These mreveal that Pluto has a highly variegated surface, with extsive bright but asymmetric polar regions, large mid-latituand equatorial spots, and possible linear features hundredkilometers in extent. Regions of fresh ice deposits werecated. These maps will be useful for constraining modelsPluto’s volatile transport, and for comparative studiesPluto and Triton.

L. Trafton reduced spectra of Uranus’ H2 and H31 emis-

sions obtained with the UKIRT CGS4 and IRTF CSHELA variation with Uranus’ rotational phase was noted for bo

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620 ANNUAL REPORT

species. This was attributed to the localization of auroemission from the planet’s tilted magnetic pole, and toglobal ionospheric emission component which is relativstrong. This is different than Jupiter’s case, where the nauroral emission is quite weak. Comparative auroral studare expected to elucidate the reasons for the different extions on the two planets.

L. Trafton extended his FUV analysis of HST spectrathe G impact zone from comet SL9 by attempting to moand remove the Lyman H2 band emissions to search for Cand other emissions. No such emissions were found. Stsaturation in the 4th positive CO bands limited their visibilrelative to the large CO abundance derived from mm-wobservations; hence the weak FUV emissions appear nobe inconsistent with the large mm-wave CO column abdance.

3.3.3 Stars and Stellar Systems, Stellar Ejecta:

Using HST FGS astrometry data, it was determined tBarnard’s Star is a periodic photometric variable, with a priod clearly different than that found by HST for ProximCentauri. G.F. Benedict~assisted by P. Shelus, A. Whippland D. Cornell! has instigated a ground-based photomemonitoring program to confirm or refute the period indicatby HST for Barnard’s star. They used the McDonald Obsvatory Prime Focus Camera. The wide field allows for dferential photometry with a large number of reference staThey achieved 0.008 magnitude~one-sigma! precision, butonly during photometric conditions. The data in hand aconsistent with the variation found with HST but spaninsufficient time interval to confirm the period.

J. Fernley~ESA-Vilspa! and T. Barnes completed theprogram on the metal abundances and radial velocitiefield RR Lyrae stars. High resolution metal abundancesnine stars have permitted a recalibration of the relati@Fe/H#520.1620.195DS. The velocities will be combinedwith HIPPARCOSproper motions for a new determinationthe mean absolute magnitudes of RR Lyraes.

In collaboration with E. Luck~Case Western ReservUniversity! and T. Moffett~Purdue University!, T. Barnes isinvestigating the metallicities of Magellanic Cloud CepheidA successful observing run by Moffett at the CTIO 4-m tescope led to collection of spectra of 16 Cepheids for tprogram. The spectra are in reduction by Luck. Thesenot only clarify the abundance anomalies noted by Luck aD. Lambert in Magellanic Cloud Cepheids, they are aneeded for the application of the surface brightness metto determination of these Cepheids’ distances. The lawork is in collaboration with W. Gieren~Catholic Universityof Chile!.

G. Gonza´lez has been studying the photospheric abdances of field RV Tau variables since 1993 in collaboratwith D.L. Lambert and S. Giridhar~Indian Institute of As-trophysics!. The field RV Tau’s have been found to exhibabundance patterns similar to that seen in the ISM, whereabundances of the elements correlate with their condensatemperatures.

G. Gonza´lez has also been studying the spectra ofrecently discovered extra-solar planetary systems. The

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sults of the analyses show that the stars in these systemmetal-rich. This finding might have far-reaching impact nonly in planet formation studies, but also on stellar andlactic chemical evolution.

A. Hatzes, W. Cochran, and C. Johns-Krull searchedvariability in the spectral line profiles of 51 Pegasi to detmine whether the radial velocity variability discovered bMayor and Queloz~Nature378, 355, 1995! is really due to aplanetary companion or might, instead, be a result of stepulsations. They found no evidence for line variability athus excluded the presence of nonradial sectoral modesl>4. They did not find any variation in the equivalent widof spectral lines, thus placing a limit ofDT 5 4 K for anydisk-integrated temperature variations of the stellar surfaThe projected rotational velocity was also measured usnine spectral lines, yielding a mean value ofvsin i52.356 0.1 km sec21. This along with the published rotation period of 37 d yields a minimum stellar radius of 1.7R( . Theplanetary companion hypothesis is still the most likely eplanation for the radial velocity variations.

A. Hatzes and W. Cochran conducted further higprecision radial velocity measurements of the K-giantbOph. These data show radial velocity variations with a priod of 13.05 days. Rotational modulation, low-mass copanions, and radial velocity variations can be excluded asexplanation for these variations. Most likely this period rsults from a nonradialg-mode. A period analysis of the residual radial velocities after subtracting the contributionthe dominant period yields a long-term period of 142.3 daand a short-term period of 0.258960.005 days. The latter isconsistent with previous work by Hatzes and Cochran. Tlong-term period, if real, most likely arises from rotationmodulation of surface features, although the presenceplanetary companion cannot be excluded at the present t

C. Sneden, J. Cowan~University of Oklahoma!, and J.Truran~University of Chicago! have strengthened the usethorium ~Th, z590) as a cosmochronometer in ultra-metpoor stars by combining ground based data andHST ghrsspectra of the bright metal-poor stars HD 126238 and122563 to demonstrate that a solar-systemr -process abun-dance distribution persists in metal-poor stars out to elem~Os, Pt, and Pb! of the ‘‘3rd neutron-capture peak.’’

C. Sneden, G. Preston and A. McWilliam~Carnegie Ob-servatories!, J. Cowan and D.L. Burris~University of Okla-homa!, and B. Armosky have continued their detailed expration of the spectrum of the ultra-metal-poor, but neutrocapture-rich, halo giant star CS 22892-052. Abundances20 neutron-capture elements from over 200 spectral feathave been deduced. Element abundances in the ra56<Z<76 match the scaled solar systemr -process abun-dance distribution very well and bear little relation to thscaled solars-process distribution. Thisr -process abundancpattern could only have been generated in the explosivecleosynthesis of a prior supernova~surely one of the veryearliest element donors of our Galaxy!. The depressed abundance of the radioactive element Th in CS 22892-052 signa large age for the progenitor to this star; a lower limit for t‘‘age’’ of its supernova precursor (. the Galactic halo age!is 15.263.7 Gyr from the Th abundance. In related wor

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this group has considered the Th-based age in more deInvestigation of effects of nucleosynthesis and galacchemical evolution mainly push the implied age of C22892-052 material to higher values, with a likely maximuage of about 18 Gyr.

For more ordinary metal-poor stars~@Fe/H# ;22), C.Sneden, J. Wright, and B. Carney~University of North Caro-lina! have recently completed a study of five stars fromCarney-Latham metal-poor star sample that might havelactic disk kinematics. One candidate star~BD180 245! hasa nearly unique abundance signature among metal-poor~@Fe/H# . –1.9! stars. It isa-capture-poor:@Mg, Si, or Ca/Fe#. –0.2. This is a vivid exception to the standard assumpof a-rich metal-poor star material. They are currently gaering further spectra of this star to provide a complete abdance distribution.

C. Sneden, R. Kraft~UCSC!, E. Langer~Colorado Col-lege!, and C. Pilachowski~NOAO/ KPNO! have been deriv-ing light element abundances from echelle spectra of lastellar samples~typically >10! on the upper red gianbranches (RGBs! of globular clusters spanning the metalliity range –0.8> @Fe/H# > –2.3. They find that the verylarge star-to-star variations of the light elements C, N, O,Mg, and Al are linked via the common culprit of high temperature proton-capture fusion. At some time~s!, in someplace~s! in cluster evolution, advanced proton captures hareshuffled substantial numbers of light element abundanvia C,O→N, Ne→Na, and Mg→Al synthesis chains. Research this past year has concentrated on M13. First,abundances for 130 giants with luminosities extending doto the level of theHB (M v510.3! were derived; the datawere moderate-resolution spectra from the kpno/wiyn Hymulti-object spectrograph. The Na abundances are alwhigh in stars near theRGB tip (M v , –1.7 or logg,1.0),and many lower luminosityRGB stars have Na abundancesimilar to those of field metal-poor stars. However, high Nabundance stars occur at all M13RGB positions, indicatingeither a! that there were indeed primordial star-to-starabundance variations, or b! that high-temperature protoncapture nucleosynthesis and convective envelope mixinprocessed material happened quite early in the stars’ evtion after leaving the main sequence. Second, they obse11 lower luminosity M13RGB stars at high resolution withthe Keck I HIRES spectrograph, and combined these swith 23 others previously and newly observed with the LiHamilton Echelle spectrograph. This 34-star sample demstrates that the O–Na, O–Al anticorrelations and O–MNa–Al correlations do not depend onRGB positions.

Detailed studies have been made of the photospherethe circumstellar environment of several candidate poAGB stars by E. Bakker. A survey has been initiated~withD.L. Lambert! which aims at detecting at ultra-highresolution (R5200,000! molecular absorption lines in optical spectra obtained using the 2.7-m telescope at McDoObservatory. They find complex line profiles and line widtsignificantly broader than expected from thermal broaden

H. Dinerstein and C. Sneden have been studying the ntral envelopes of planetary nebulae by observing resonaabsorption lines from species such as Na I, which arise

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these layers and can be seen against the optical continuuthe central star; such lines offer a new probe of these phdissociation regions, which appear to be a major mass cstituent of most planetary nebulae. Their earlier survey ofplanetary nebulae in the Na I D lines~5889.95 Å! at a spec-tral resolving power of 30,000~Dinerstein, Sneden, and Uglum 1995, ApJ 447, 262! revealed that over 50% of thsample showed evidence for Na I, and hence for neutralterial in the circumnebular environment. They are currenextending this work by observing a larger number of nebuat higher spectral resolution with the 2DCoude´ spectrographon the McDonald Observatory 2.7-m. In addition to improing the statistics on the prevalence of the neutral envelothe new work aims at measuring additional, weaker linwhich provide diagnostics of the chemical and thermal strture of these regions. An initial result from the new observtions, undertaken in collaboration with K. Volk~Universityof Calgary!, is that the weakness of the Ca II emission linnear 7300 Å implies very severe depletion of calcium indust grains and sets strong limits on the extent of duststruction in these regions of planetary nebulae.

H. Dinerstein, with graduate student C. Pulliam andGarnett~University of Minnesota!, has begun a new obsevational study of faint optical emission lines from recombiing oxygen atoms in planetary nebulae. Since the emissties of these lines have similar, weak dependences on thetemperature as those of recombination lines of hydrogenhelium, the ratios among these lines should yield reliaO/H abundances for the ionized gas, avoiding the uncertties due to the strong dependences of the collisionaexcited forbidden@O III # lines on electron temperature. However, recent results from other groups have yieldsurprisingly large O/H values, some greater than solar,large discrepancies between O/H as determined from thekinds of lines in the same nebulae. Observations of abouplanetary nebulae at a spectral resolving power of 2000 wobtained at McDonald Observatory on the 2.7-m in the sumer of 1996 and are being analyzed and combined withhigher-resolution coude´ data of Dinerstein, Sneden, anVolk. This study should yield accurate new fluxes for therecombination lines in several nebulae, and enable us tothe claims of high O/H values.

M. Adams, W. Wren, M. Ward, L. Wang, and J.CWheeler have begun a search program for supernovaclusters with redshift in the rangeZ50.03–0.15. This searchwill take advantage of the wide field of view of the PrimFocus Camera on the 0.76-m telescope to survey entire Aclusters in a single image. Search software provided bySchmidt ~Mt. Stromlo! has been configured for the McDonald instrumentation, and a large collection of comparisimages have been obtained. Graduate student A. Howelljoined the project and was instrumental in customizingsearch software. The search will resume in the fall.

L. Wang and J.C. Wheeler have continued their progrof supernova polarimetry. They showed that a classic Typsupernovae is polarized before maximum at about the opercent level, similar to all other well-observed Type IIlater times. These early observations constrain modelswhich the polarization is due to asymmetric distributions

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622 ANNUAL REPORT

radioactive elements, because it is less likely that theyeffect the results before the envelope becomes thin. Thisimply that some asymmetry in the outer envelope is presWang, Wheeler, and P. Ho¨flich established that the Type Isupernova SN 1996X is polarized at about the level ofpercent, roughly consistent with the upper limits placedother Type Ia. The polarization spectrum is much mowavelength-dependent than the total flux spectrum due todominance of scattering lines as confirmed by atmosphmodels. More thorough study of the cause of this polarition is underway. A principle candidate is composition inhmogeneity at the iron/silicon interface.

3.3.4 Interstellar Medium, Compact Regions, ProtostellaDisks, Star-Forming Regions:

J. Scalo and M. Miesch~University of Colorado! contin-ued their investigation of the statistics of the Bell La13CO survey of local star-forming regions. Previous resudemonstrated near-exponential tails in the probability disbution of centroid velocities of many of the regions. A neresult is that the probability distributions of linewidths apear uniformly exponential or possibly log normal, an unepected and unexplained result. One possible complicatioleast for the velocity centroids, is that the statistics mayaffected by the fact that filtering is unable to convert tobservations into a statistically homogeneous field: larscale structure remains. Coupled with an observational spling that is biased to large signal strengths, the net effecfor much of the tail distribution to arise from spatial outliethat are sampling regions where the large-scale velocityfers from that in the densely sampled regions. The imptance of this effect is being investigated. Interpretationsterms of physical processes are also underway.

J. Scalo and A. Lazarian~Princeton University! investi-gated the effects of cloud occlusion~blocking of one cloudby a larger foreground cloud! on observational estimates othe cloud size and mass spectra in order to understanddiscrepancy between size and mass spectra derived fromtinction and from spectral line surveys. The effect is of tright magnitude, but only if the surveys span a sufficierange in size or mass. The range of most observed surveinsufficient for a clear resolution of the discrepancy.

A group comprised of N. Evans, D. Jaffe, J. Di FrancisW. Li, S. Pak, E. Gregersen, L. Keller, and E. Klumpe cotinues to study star formation on scales ranging from gimolecular cloud complexes to molecular cores forming clters and to cores forming individual or binary low-mastars. Their primary tools are the Caltech Submillimeter Oservatory, including a re-imaging device, and the Universof Texas Near-IR Fabry–Perot Spectrometer. They alsodata from many other telescopes, including ISO. Theseare then modeled with 1-D and 2-D Monte Carlo radiattransfer codes.

N. Evans, collaborating with E. Lada~University ofFlorida! and E. Falgarone~Ecole Normal Superieure! hascompleted a multitransition CS study of the cores in L16for the physical conditions in the star-forming cores.Gregersen, Evans, and S. Zhou and M. Choi~Institute forAstronomy and Astrophysics, Taiwan! have surveyed 23

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Class 0 sources in HCO1 to study the density, temperaturand velocity structure. They found that nine sources hline asymmetries~skewed to the blue! characteristic of col-lapse. W. Li, Evans, and Lada have surveyed a large regof the L1630 cloud in the near-IR. They found very feobjects with a color excess outside the known cluster, sgesting that there is very little recent star formation distruted through the cloud.

S. Pak and D. Jaffe have finished observations of neaH2 emission lines in the Magellanic Clouds using the UFabry–Perot Spectrometer. The H2 molecule is excited byfar-UV radiation, and the emission will trace the photdissociation regions~PDRs! in the clouds. Pak and Jaffecollaborating with G. Stacey~Cornell!, have also observedthe H2 lines from the central regions of nearby gas-rich gaxies~M82 and IC 342!.

J. Di Francesco, N. Evans, and P. Harvey have analynew high-resolution, far-infrared continuum kao maps of tintermediate-mass, pre-main-sequence Herbig Ae/Be sand found further evidence for extended envelope strucaround these sources. These results suggest that theevance of disk structures at far-infrared wavelengths isduced. In addition, similar observations have been analyof ten highly-embedded IRAS sources that may be precsors to the Herbig Ae/Be stars, revealing that this sammostly exhibits extended emission indicative of envelostructure. Comparison of these samples will probe howvelope structures evolve with their young central objectswards the main-sequence.

J. Di Francesco, N. Evans, and C. Chandler~Mullard Ra-dio Astronomy Observatory! observed two Herbig Ae/Bestars at the VLA in the 7-mm, 1.3-cm, and 3.6-cm continuuto constrain the contribution of free-free emission from thmal dust emission to the detected emission at 2.7 mm.source~Elias 3-1! was detected at all three wavelengths,lowing better-constrained models of its small-scale circumtellar structure. J. Di Francesco and collaborators have ctinued their large-scale mapping of regions surroundHerbig Ae/Be stars in theJ5 3–2 line of both12CO and13CO, allowing them to compare the gas and dust enveloof these pre-main-sequence objects.

3.3.5 Extragalactic:

G. Shields continued a study of chemical abundanceextragalactic H II regions using theHST. With D. Garnett andE. Skillman~University of Minnesota! and R. Dufour~RiceUniversity!, he found log C/O5 –0.66 0.1 in I Zw 18, themost metal-poor galaxy known. This value is lower thanthe sun, but it departs from a trend of decreasing C/O wdecreasing O/H shown by other metal poor galaxies. Tsuggests that I Zw 18 experienced an earlier burst offormation and is not a ‘‘primeval galaxy,’’ despite its lowabundance of heavy elements.

H. Dinerstein has begun a program of optical spectrcopy of H II regions in the sample of galaxies observedthe ISO Key Project on ‘‘The Interstellar Medium of NormGalaxies.’’ This project, which involves 11 co-investigato~G. Helou of Caltech/IPAC is the Principal Investigator!, in-cludes a survey of about 60 galaxies of a wide range

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morphological types and infrared emission characteristThe iso observations include measurements of the infradust continuum and far-infrared emission lines from diffuionized and neutral gas. Ground-based observations of tgalaxies at McDonald Observatory and elsewhere~by othermembers of the Key Project team! will provide measure-ments of the metallicity~e.g., O/H! in the ISM of these gal-axies and will enable us to examine relationships betwmetallicity and other properties of the galaxies, particulathose determined from the iso observations.

D. Lester, with graduate student E. Zink, has been copleting a high-spatial resolution study of the distributionfar-infrared continuum emission around luminous galaxiThis study has been completed using the Kuiper AirboObservatory, with diffraction-limited detector arrays. Thwork shows that in many of theL.1011L( galaxies thatwere observed, the far-infrared emission is significantlytended on kiloparsec scales. This work helps in the undstanding of the distribution of luminosity in interacting pairwhich constitute a large fraction of these luminous sourcTheir sample size of fifteen galaxies appears to offer a rresentative picture of the far infrared structure of distaluminous galaxies.

D. Lester, N. Gaffney, and G. Doppmann have been alyzing the kinematics of starburst galaxies using infraredcombination lines and the 2.3-micron CO bandhead fromcool stellar component in these galaxies. This work has bdone using the IRTF CSHELL infrared spectrometer. Twork has identified differences in the kinematics of ionizgas and red starlight. It is presumably the latter that brepresents the dynamical properties of these galaxies.study of M82 is complete, while the data on NGC4736 aNGC3256 is still being analyzed.

I. Jo”rgensen and M. Franx~Kapteyn Institute, GroningenHolland! have continued the study of elliptical and lenticulgalaxies in nearby clusters. Analysis of absorption lstrengths shows that a large fraction of the galaxies habundance ratios of magnesium relative to iron abovesolar value. Further, the abundances of magnesium andas well as the abundance ratio of magnesium relative todepend on the density of the cluster environment. To furtunderstand the stellar populations of nearby cluster elliptand lenticular galaxies Jo”rgensen, B. Milvang-Jense~Copenhagen University!, and Franx have obtained data flarge magnitude-limited samples of galaxies in four neaclusters.

I. Jo”rgensen, M. Franx, and J. Hjorth~NORDITA, Den-mark! have established the fundamental plane~FP! for twogalaxy clusters atz50.2. The FP is a tight relation betweeeffective radius, surface brightness, and velocity dispersfor the galaxies. It is possible to use the FP to quantifyluminosity evolution of elliptical and lenticular galaxies. Thevolution implied from the FP for the two clustersz50.2 is consistent with a passive luminosity evolution aa formation redshift for the galaxies of four or larger. S. LuH. Martel, and E.T. Vishniac have continued to study theof statistical measures to categorize galaxy clustering. Thave applied these statistics to a set of numerical simulatand found that they are a robust means of distinguish

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between models with similar correlation functions. Applieto real galaxy catalogs, they find significant differencestween the CfA and Perseus–Pisces catalogs, implyingneither is a fair sample of the universe.

G.F. Benedict obtained two orbits of HST WFPC2 da~V- and I-band! on NGC 7479 on 16 October 1995 and isthe process of analyzing the frames. He obtained five or(U, B, V, I , H-alpha bandpasses! of WFPC2 data of NGC4314 on 29 December 1995. All data have been reducedthe team~I. Jo”rgensen, D. Cornell, A. Whipple, D. ChappeB. Smith ~IPAC!, J. Kenney~Yale University!, and S. Laine~University of Florida!! has only partially analyzed the NGC7479 images. NGC 7479 has asymmetric spiral armsstrong star formation along its bar, yet has no observed cpanions~confirmed with digitally stacked PFC data obtainthis year!, suggesting that it has recently undergone a merwith a low-mass galaxy. Our HSTV and I images of thissystem show a galactic core with high extinction. In the cetral 19 of this galaxy, three distinct sources are observsimilar to those of the super star clusters found in mergand starburst galaxies. Once fully analyzed, these obsetions will aid in understanding the feeding of nuclear enginby bars, the evolution of bar-driven nuclear structure, andgenesis of pathological grand-design spiral galaxies.

G. Shields proposed an explanation of the observed habundances of heavy elements in the broad absorption~BAL ! gas of QSOs. Several workers have found abundanof C, N, O, and Si one to two orders of magnitude highthan solar, and Junkkarinenet al. ~1995! reported P/C'65~P/C!( . Shields showed that these abundances resemthose of classical novae. He suggested that the BAL gasfact nova material accelerated to high outflow velocitiesthe QSO radiation pressure or a wind. Accretion of gas osingle white dwarfs passing through an accretion disk aroa supermassive black hole can result in a large rate of nexplosions in QSOs.

M. Brotherton undertook statistical investigations of tbroad emission lines in several samples of intermediaredshift QSOs and discovered strong relationships amline ratios, widths, asymmetries, and redshifts of Lya, thel1400 feature, C IVl1549, C III# l1909, and other weakeUV lines characterizing a range of excitation conditionThese relationships, together with photoionization modeliled to the derivation of rather different physical and chemiproperties for gas with lower (;2000 km s21) and highervelocity dispersion (;7000 km s21) ~Brotherton, Wills,Francis, and Steidel,ApJ430, 495, 1994!. This was the firstinvestigation to show highly significant differences in themission-line spectra of radio-loud and radio-quiet QS~C IV l1549 and C III# l1909 are narrower in radio-loudQSOs! ~Brotherton, Wills, Steidel, and Sargent,ApJ 423,131, 1994!. The Hb profile shows clear dependences on tdominance of a compact radio core, an indicator of oriention of the central engine’s rotation axis. Several relatiosuggested a strong link between the;2000 km s21 gas onscales of;1 pc, and that of the narrow line region at ditances of. several pc from the nucleus. This was cofirmed by obtaining and measuring IR spectra in theb – @O III # l region in the same QSOs for which C IV

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624 ANNUAL REPORT

l1549, C III# l1909, or Mg II l2798 data were availableThe main collaborators on some aspects of the above intigations were P.J. Francis~University of Melbourne!, B.Wills, D. Wills, and F. Ma.

The HST team~B. Wills, D. Wills, K. Thompson, M.Brotherton, J. Baldwin~CTIO!, H. Netzer~Tel Aviv Univer-sity!, G. Ferland~University of Kentucky!, R. Caswell~In-stitute of Astronomy, Cambridge University!, and I. Browne~Jodrell Bank Observatory!! continued investigations of relationships among line, continuum, and radio-structure msurements on the complete dataset of spectra from belowa to beyond Hb for almost 60 radio-loud QSOs. SpectrPrincipal Component Analyses show that ratios of broad-strengths, and their profiles, are quite similar from one Qto another. However there are relationships between ctinuum shape and narrow line emission that we are stillvestigating. With C. Wei, a comparison is being made wthe HST archival Faint Object Spectrograph data for bradio-loud and radio-quiet QSOs, and we are making specprincipal component analyses for both the HST radio-loQSO sample and archival spectral data.

B. Wills and F. Ma are investigating the meaning of tnew core-dominance factor~the ratio of relativisticallybeamed radio-core flux to optical or near-infrared nosynchrotron flux!. This core-dominance factor is likely to buseful as an indicator of orientation of the spin-axis of tcentral engine in radio-loud QSOs~Wills and Brotherton,ApJ448, L81, 1995!.

In collaboration with A. Laor~Technion, Israel!, B.J.Wilkes ~Harvard–Smithsonian Center for Astrophysics!, G.Ferland ~Kentucky!, D. Wills, and M. Brotherton~now atLLNL !, B. Wills is investigating relations of UV and opticabroad emission lines, absorption lines, and continua withROSAT X-ray spectra. This is for a complete subset of 23the Palomar–Green~B–V selected! sample having redshif,0.4 and Galactic hydrogen columns,1.931021 cm22

~Laor, Fiore, Elvis, Wilkes, and McDowell,ApJ 435, 611,1995!. With respect to data, the project is half compleWhen completed, it will provide a valuable comparison wsamples of different luminosity, radio and X-ray and infrarselection criteria.

B. Wills, B. Xie, and M. Brotherton are investigating thdependence of narrow@O III # l5007 profile parameters oROSAT X-ray spectra using the above subset of thesample. This investigation was suggested by Brotherto~1996! finding that @O III # profiles are broader when thoptical-to-X-ray spectra are steeper.

D.C. Hines~University of Arizona! and B. Wills, alongwith G. Schmidt, P. Smith, R. Allen~Steward Observatory!,and M. Sitko ~University of Cincinnatti!, have made spectropolarimetric measurements of the UV emission from tIRAS-selected QSOs. The rapid rise in polarization obserin the optical becomes independent of wavelength (p'1012%! for l&3000 Å ~rest!. The spectrum of polarizedlight peaks nearl;3000 Å ~rest! and decreases rapidly foshorter wavelengths. This behavior is similar to that seenhigh redshift radio galaxies and some BALQSOs, andbeen interpreted as evidence for dust scattering.

D.C. Hines~University of Arizona! and B. Wills, along

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with G. Schmidt, P. Smith,~Steward Observatory!, R. Goo-drich ~Keck!, and M. Sitko~University of Cincinnatti! haveused the WFPC2 on HST to obtain images in polarized liof the hyperluminous infrared galaxy IRAS P0910414109.A highly polarized biconical structure centered on tnucleus is revealed. This strongly reinforces the spectroprimetry results of Hines and Wills~1993! which suggestedthat P0910414109 is a misdirected QSO that would appeas a typical luminous QSO if viewed from the directionthe scattering~polarizing! material.

F. Bash participated in a research project which discered and analyzed a radio-frequency jet or arc found nearcenter of M81. The arc extends 0.9 kpc in the plane ofsky and has no apparent optical counterpart. The archighly polarized and, most likely, is highly inclined to thplane of the galaxy.

The Texas Survey of discrete radio sources is based365 MHz observations made at the University of Texas Rdio Astronomy Observatory~UTRAO! during the period1974–1983. After an extended period of data reductioncalibration, the final version of the Texas Survey, listing asecond positions, flux densities, and structure models66841 discrete radio sources between –35 and171 degreesdeclination, was published in theAstronomical JournalinMay 1996 by J.N. Douglas, F.N. Bash, and former depament members F.A. Bozyan, G.W. Torrence, and C. WoDouglas continues to reduce post-survey observations totend the time-base and precision of flux density variabidata on the approximately 1000 variable sources discoveby the Survey. The Survey may be accessed on the WoWide Web: http://utrao.as.utexas.edu/txs.html.

3.3.6 Theory:

R. Duncan, in collaboration with C. Thompson~Univer-sity of North Carolina at Chapel Hill!, studied the evolutionof neutron stars with very strong magnetic fieldBdipole;1014–1015 G andBinternal;1015–1016 G. The mag-netic field, rather than the rotation, is the main source of fenergy in such ‘‘magnetars.’’ These stars might be obseras soft gamma repeaters~SGRs!, anomalous X-ray pulsars~AXPs! like 1E 22591586, and/or gamma-ray burst sourceTheir fields evolve primarily via ambipolar diffusion in thliquid interior and Hall drift in the crust. Magnetic dissipation heats the nuclear fluid, powering steady, thermal X-emissions, as observed in SGRs and AXPs. Magneticainduced crust fractures also occur, and could power Sbursts. Such fractures drive pulses of Alfve´n waves into themagnetosphere which undergo nonlinear damping, creatimagnetically-confined thermal pair plasma with a trace ctamination of baryons. The pair plasma cools via hypEddington thermal X-ray emissions with little spectral evlution, as observed in SGR bursts and in the soft-specttail of the exceptional 1979 March 5th gamma-ray burst.Kudari and Duncan studied radiative transfer in the oulayers of these confined pair bubbles. Absorption and emsion processes are suppressed because of the large Lalevel energy, but magnetic photon–electron scattering mtains energy equipartion. Photon number-changing occprimarily via the exotic QED processes of photon mergi

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and splitting in the strong magnetic field. In his Mastethesis, Kudari calculated the Bose–Einstein photon spectat the E-mode scattering photosphere. Further photon sting occurs outside this photosphere and must be includerealistic calcuations of SGR burst spectra.

R. Duncan and H. Li~Los Alamos National Laboratory!made Monte Carlo models of the distribution of higvelocity neutron stars in the halo of our Galaxy, in ordertest halo gamma-ray burst models. In particular, they conered a ‘‘halo beaming model’’~HBM! in which emergentgamma rays are beamed along a magnetic axis which isrectionally correlated with the peculiar velocity of a bursescaping from the galaxy. Such conditions occur in the mnetar theory of GRBs. The HBM gives an adequate fitGRB observations for a range of beam widths of about 1to 30°. In this scenario, GRBs are magnetic reconnecevents, like stellar flares.

J. Scalo and P. Kornreich examined the vorticity producby shocks propagating through the interstellar medium. Geral analytic results were derived for three cases: 1. Curshock propagating through a uniform medium; 2. Plashock encountering a general density inhomogeneity; 3.nar shock encountering a general velocity inhomogeneityeach case the vorticity generation has two components:! akinematic vorticity production just behind the shock, whiarises purely because of the nature of the shock jump cotions and does not involve any dynamical or thermal effesuch as baroclinic vorticity production; 2! a dynamical vor-ticity production downstream from the shock, which repsents the amplification or destruction of vorticity due to tvelocity, density, and pressure gradients in the post-shflow. Explicit analytical results are found for the kinematcomponent and numerical solutions are presented for thenamical component.

J. Scalo and P. Kornreich applied their analytic derivtions of vorticity production behind shocks to the case oplanar shock encountering a spherically symmetric, densstratified cloud. The results show that, at large Mach nubers, the kinematic vorticity generation dominates overdynamical production, the induced vortical velocities~and bysymmetry, the induced compressional velocities! are a sig-nificant fraction of the shock speed, and the induced veloties depend on the inverse square root of the cloud intedensity. The results were supported by lattice gas simulatof a shock-cloud encounter at mildly supersonic shospeeds. The induced vortical motions should rapidly be cverted into comperessible or MHD modes with accompaing density fluctuations. The results suggest that the soof the supersonic linewidths and internal density structseen in interstellar clouds is shock waves, which providmeans of generating internal density and velocity structwithout any source of instabilities.

D. Chappell and J. Scalo investigated the questionwhether the behavior of ‘‘one-zone’’ models for star formtion activity in galaxies, including self-regulating stabilitlimit cycles, or chaos, would survive when spatial degreesfreedom were included in the models. A two-dimensionlattice simulation of local and nonlocal heating or stirringstar formation, which inhibits further star formation, alon

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with dissipation due to gas interactions at a subgrid scwas studied. Star formation is assumed to occur atToomre condition threshold and at a rate correspondingthe fastest growing mode. A linear stability analysis of tsystem with and without spatial couplings was also pformed. The results show that at least five distinct modesbehavior can be found in the~coupling parameter–gas coumn density! phase diagram. These phases include stebehavior, small isolated patches of star formation, cohepropagating waves of star formation, and synchronizedhavior of the entire lattice, with star formation occuringhuge ‘‘cloudy’’ structures. The synchronized behavior apears to be an emergent property of the model and wouldbe expected given the long timescales for communicaacross the lattice. This work demonstrates the possibilitycoherent self-organized behavior of star formation can ocover large scales without the presence of organizing forsuch as self-gravity, spiral waves, etc., and that the behaof galactic disk gas may proceed through phases as theerage column density changes. Whether or not this repersists in the presence of hydrodynamical spatial coupliremains to be seen.

D. Chappell and J. Scalo studied simulations of the spastructure and temporal behavior of a model interstellar mdium. The simulations are intermediate-level representatiin which stellar/cluster winds and hydrodynamical advectare the dominant processes, but thermal pressure is ignoas if the effective ratio of specific heats were zero. The mels can also be thought of as simulations of a driven quBurgers equation that includes the mass conservationstraint. The simulations are two-dimensional, aincorporate a finite difference representation of advectionmomentum-conserving model for the action of cluster winand a threshold gravitational instability criterion for star fomation in the shells generated by the winds. The simulatigenerally evolve by a bottom-up hierarchical agglomeratof interacting wind-driven shells, generating a highly filmentary spatial structure over a range of scales. The pospectrum of the velocity field, the mass spectrum of coher‘‘clouds,’’ the probability distribution of velocity, and thetemporal behavior of the star formation rate are examinOne interesting result is that the velocity distribution of gin dense shells is non-Gaussian and often nearly exponenA cloud mass spectrum with a power law index of arou–1.5 is found, similar to predictions of coalescence modbut with no assumptions about cross section or velocity dtribution, which arise from the simulated hydrodynamicHowever, the index appears to vary with the star formatactivity. A simple ‘‘one-zone’’ model is found to accounsatisfactorily for the scaling of the velocity dispersion wiother parameters for the simulations.

J. Scalo continued an investigation of models for the slar and ‘‘cloud’’ initial mass spectrum~IMF!, emphasizingmodels that couple the IMF to the statistics of the velocfield, such as velocity fields dominated by stellar or cluswinds, by externally-driven shock waves, or by some sortmore traditional ‘‘turbulence’’ or motions driven by MHDwaves. The main goal is to understand how differentsumptions about the dominant physics affects the predic

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626 ANNUAL REPORT

degree of universality and variations in the IMF, and to eamine whether meaningful choices between theoriespresently be made, given the range of possible physicalnarios and the weakness of observational constraints. A nber of simplified models for the gas velocity distributiofunction have been examined: an ensemble of stellar or cter winds, a Fokker–Planck approach to the energy-inpcloud collision model, and the statistical mechanics of stems in which momentum, but not energy, is conservWith D. Chappell, quasi-hydrodynamical simulations areing examined in which the velocity field is calculated explitly and the mass spectrum is allowed to feed back on its

A. Khokhlov, E. Oran~Naval Research Laboratory!, andJ.C. Wheeler developed a theory of deflagration to detotion transition in unconfined flames based on the Zel’dovgradient mechanism. They proposed that the necessarydient in conditions of compostion and temperature is pduced by turbulence and local quenching of any laminarturbulent flame. They derived a criterion for the minimulength scale of the premixed turbulent region which shoapply both to chemical terrestrial and nuclear astrophysflames. This theory can be applied to thermonuclear exsions in white dwarfs to predict the needed strength ofbulent premixing and the critical density for the transitiowhich should be a little in excess of 107 gm cm23. Thistheory will be incorporated in future three-dimensional moels of the dynamics of Type Ia supernovae.

A. Khokhlov, I. Lichtenstadt ~Hebrew University ofJerusalem!, and J.C. Wheeler continued to work on the dvelopment of the multi-energy multi-dimensional neutritransport and fluid dynamics model for Type II supernoexplosions. Preliminary calculations in the core of a star15 solar masses revealed convection in the proto-neustar, but no explosion. Other masses are being explored

A. Clocchiatti ~CTIO! and J.C. Wheeler analyzed the aymptotic behavior of supernova light curves to show ththere can be a convergence of slopes for ejecta massesrange 1–2 solar masses that do not require precisely idenconditions. The time when the asymptotic regime is reacdepends on the mass of the ejecta and the gamma ray oity, but the slope subsequent to that does not depend on tquantities. This may help to explain the category of supervae with common late time light curve behavior, but diffeent spectral classification.

Y. Stein, Z. Barkat~Hebrew University of Jerusalem!, andJ.C. Wheeler continued to study the vexing problem ofconvective Urca neutrino process in carbon/oxygen whdwarfs. The previous study by Barkat and Wheeler ccluded that when gradients in mean molecular weight andassociated currents in composition are properly takenaccount, the convective Urca process will lead to cooling,control of the carbon burning, and associated instabilidisplayed by computer simulations. New work suggestsaccount must also be taken of the kinetic energy associwith the convective flow. Although nominally small, the efect of the kinetic energy is to ensure that while the convtive Urca process will result in less thermonuclear heatthan would be the case without it, there can be no decreaentropy. This will mean that the convective Urca process

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Y. Stein and J.C. Wheeler explored, for the first time wmulti-dimensional calculations, the process of quasi-stacarbon burning in carbon/oxygen white dwarfs near theChandrasekhar limit. This is a particularly difficult calcultion because the stars are very close to the limits of dynaand thermal instability. Preliminary models show thplumes of burning carbon form which penetrate beyondregion that is nominally convectively stable. Such behavnot seen in previous one-dimensional computations, cosubstantially affect the nature of the ultimate dynamical ruaway in Type Ia supernovae, whether they develop subsdeflagrations or supersonic detonations, and how sensthe results of the explosion are to initial conditions.

W.R. Hix has constructed a reduced reaction rate netwconsisting of only six or seven effective nuclei that captuthe basic energetics and composition shift due to burningthe alpha chain and the silicon quasi-equilibrium bottle neThis routine will be very valuable for use in threedimensional computations of the reactive flow of modelsType Ia supernova where both speed and memory arepremium.

J. Wang has developed a model for convection in odimensional core-collapse calculations, a ‘‘two-stream’’ fomalism to simulate the effects of convection and overshoSuch a code will allow a study of a broader range of paraeter space than full multi-dimensional models. Wang is adeveloping a semi-analytic model of core collapse showaves to establish the criteria under which such shockssuccessful. The post-shock entropy seems to be more imtant than the neutrino flux.

S.-W. Kim and J.C. Wheeler have continued to stutime-dependent irradiated disk models for black hole X-rtransients. Of particular interest are the limits for exposureirradiation that will cause the disks to remain in a hot steastate when non-irradiated disks could not, and whetherlimit is different for steady state and for time-dependedisks which are subject to shadowing of the outer disk byinner disk. Another key issue is the role of nearly radtwo-temperature advection flow which may be able tocount for the observed X-ray flux, but which is not eascompatible with the outer Keplerian disk, especially the codisks with low flow rate predicted by the disk instabilitmodels for the outbursts.

M. Moscoso has continued work to develop a code tcan compute the radiation-induced pair wind expected todriven from a pair-dominated corona around a black hole

I. Yi ~Institute for Advanced Study!, E. Vishniac, and J.C.Wheeler have developed a theory for the newly discovesymmetry in spin up and spin down of accreting X-ray psars. This observation is a challenge to standard theoriemagnetic accretion which would predict a strong asymmein spin up and spin-down torque. The new theory invokeschanges in the disk state that accompany the onset of raadvective, high temperature flow at a critical accretion raThis transition shifts the inner edge of the Keplerian disk ahence alters the torque.

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E.T. Vishniac and C. Zhang have studied the parametidal instability in accretion disks. They have derived geneformulae for calculating growth rates in disks with arbitravertical structure, including the effects of tidally inducepressure perturbations. They have shown that this menism is extremely effective in producing torque and geneing internal waves from the radius of the vertical resona~between the 4:1 and 5:1 orbital resonances! on out. A sig-nificant, but smaller, growth rate appears at smaller radiia related piece of work, D. Ryu~Chungnam University!, J.Goodman~Princeton!, and Vishniac have shown that thtidal instability is completely insensitive to boundary condtions and can produce waves with a range of azimuwavenumbers.

E.T. Vishniac and J.C. Wheeler have produced a ntheory of the propagation of cooling waves in accretidisks. This work reproduces the computational resultsCannizzoet al.and shows that the exponential decline of tluminosity of soft X-ray transients is a direct measure offunctional form of the viscosity in the hot part of the disThe results are consistent with the wave-driven dynamodel for accretion disk viscosity.

G. Shields and D. Husfeld~Munich University Observa-tory! continued work on the energy distribution and polariztion of thermal continuum from accretion disks around spermassive black holes in AGN. Models of the diatmosphere were improved to include a hydrostatic denlaw and an exact calculation of the polarization due to eltron scattering. Results confirm the recent discovery by Bland Agol ~ApJL, submitted, 1996! of an abrupt rise in thepolarization in the Lyman continuum region of the spectrufor certain disk parameters. Shields and Husfeld also fothat similar polarization features can occur in the Lymcontinua of He I and He II for hotter accretion disks. A quatatively similar polarization rise has been observed inLyman continuum of a few QSOs~Koratkaret al., ApJ450,501, 1995! and may provide an important clue to the natuof AGN.

E.T. Vishniac has continued to work on the formationflux tubes in turbulent magnetized plasmas. S.J. Park~KoreaAstronomy Observatory! and he have shown that as a cosequence of this process, accretion disks tend to push pdal magnetic field lines outward. In radiation pressure donated accretion disks this process overwhelms the inwmotion of field lines due to the accretion process.

E.T. Vishniac and A. Brandenburg~University of New-castle! have discovered a new kind of magnetic dynamwhich can occur in a differentially rotating system and donot require any loss of symmetry in the underlying turblence. Applied to accretion disks it predicts a dimensionlviscosity which will scale as (h/r )2, which is a steeper dependence than is seen in most systems. This suggeststhis is not usually the dominant dynamo mechanism inaccretion disks in binary systems. However, it may playrole in systems which seem to show an anomalouslyviscosity.

P. Shapiro and H. Martel continued their developmenta new and improved version of the numerical gas dynammethod known as Smoothed Particles Hydrodynam

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~SPH!, with application to cosmology. As a Lagrangiamethod, SPH is well-suited to the simulation of galaxy fomation by the growth of cosmological density fluctuatiosince it uses particles which move with the flow as centersinterpolation and which replace the fixed grid pointsfinite-difference codes, thereby increasing its resolvpower in high density regions as density contrasts arise.standard version of SPH, however, suffers from two deciencies which are particularly acute in cosmology simutions: ~1! the smoothing, or interpolation, of particle datwhich is at the heart of the method, uses an isotropic inpolation kernel which is parametrized by a scalar smoothlength, even though the gravitational collapse and shwaves which dominate the flows involve highly anisotropvolume changes; and~2! shocks are handled by artificial viscosity which causes widespread, spurious viscous heatincompressing regions far from any shocks. The new methAdaptive SPH~ASPH!, solves these problems by introduing an anisotropic interpolation kernel and a tensor smooing length which automatically adjust the resolving powertime, in space, and indirectionby tracking the mean particlespacing along different directions around each particle inflow. In addition, shock-tracking is accomplished using ttensor smoothing lengths to predict the occurrence of dencaustics and thereby to restrict viscous heating to gascountering a shock. As a result, the new ASPH method haleast an order of magnitude better resolving power than sdard SPH. Collaborators include J. Owen~Ohio State Uni-versity! and J. Villumsen~Max Planck Institute for Theoreti-cal Astrophysics!.

P. Shapiro, H. Martel, and A. Valinia applied their neASPH numerical gas dynamics method to simulate themation of the large-scale structure and evolution of the ingalactic medium~IGM! in cosmology models including ColdDark Matter ~CDM! and to address the problem of madeterminations of X-ray clusters. Observed X-ray surfabrightness profiles of galaxy clusters have been used receto measure the cluster total mass and the baryonic gastion, by assuming the cluster is an isothermal sphere indrostatic equilibrium. This has led to claims of a so-call‘‘baryon catastrophe,’’ since the results indicate that tcluster baryon mass fraction is significantly higher thanmean value allowed by Big Bang nucleosynthesis abundaconstraints if the total universal mean density is enoughmake the Universe flat. They have used their simulationsflat models of cosmology to test the assumptions underlythe analysis which leads to the baryon catastrophe. Theythat clusters are not relaxed, virialized, and in hydrostaequilibrium but are, instead, comprised of merging subclters. Mergers and projection effects are found to causestandard mass determinations to underestimate the totaland overestimate the gas fraction. Their results help resthe baryon catastrophe.

P. Shapiro has continued his study of the re-ionizationthe intergalactic medium~IGM! and of quasar absorptioline clouds~QALCs!. Recent observations of QALCs havdetected heavy elements for the first time in high-redsclouds with neutral hydrogen column densities at the low eof the column density distribution known as the Lyman alp

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628 ANNUAL REPORT

forest ~LF!. In addition, new measurements of He II Lymaalpha absorption in quasar spectra have led to an interption in terms of unresolved absorption lines by theQALCs. In collaboration with Y. Gao and A. Davidse~Johns Hopkins University!, photoionized cloud models oLF QALCs were used to make a detailed set of predictionsdetectable absorption lines by heavy elements, consiswith other known constraints on the LF, including the Heopacity.

P. Shapiro and H. Martel considered the feedback onIGM and on the rate of formation of new objects due to tionizing energy released by the first generation of bouobjects to form by condensing out of the IGM. If energyreleased at a rate high enough to re-ionize the IGM,reheats and raises the Jeans mass of the uncollapsedwhich suppresses and delays the growth of the collapfraction. In order to investigate the importance of the feeback effect of this reionization and reheating of the IGMthe rate of formation of galaxies and QALCs out of the IGMShapiro and Martel have applied their ASPH methodsimulate the gas dynamical response of the IGM to sreheating, and to determine the consequences for the raformation of galaxy-sized and subgalactic gas clouds. Thresults indicate that the observed amount of baryonic malready formed into QALCs by redshift 3 is too high to bconsistent with predictions of the Cold1Hot Dark Matter~CHDM! model, while the CDM model is consistent if eithephoto-heatingalonereheats the IGM, or if explosive heatinoccurs as well and this heating is accompanied by very ecient radiative cooling.

R. Benjamin~University of Texas and University of Minnesota! and P. Shapiro continued their modeling of hot gwhich cools radiatively in the Galactic halo as in the Galacfountain model. Their calculations of a steady-state, 1D flof gas cooling from close to 106 K to below 104 K, includingnonequilibrium ionization, radiative cooling, and radiatitransfer, make detailed predictions for comparison with Glactic halo ISM observations. They show that UV emissiand absorption lines from highly ionized species in our Glactic halo, observed with iue,HST, and various other spaceborne detectors, can be self-consistently explained by suGalactic fountain flow when the self-illumination of thcooling gas by the radiation emitted by the hotter part offlow is properly taken into account. These calculations hbeen generalized to describe steady-state, radiative Mshocks. They have also been applied successfully to preand explain the metal lines observed in quasar Lyman-liabsorption-line systems, believed to originate in galacticlos over a range of earlier redshifts.

A. Valinia, P. Shapiro, H. Martel, and E. Vishniac havstudied the gravitational instability of cosmological pacakes. They have modeled these pancakes as 1D, plane-density fluctuations in a collisionless gas, which collapse isheets along the planes of each density maximum andsubjected the pancakes to transverse perturbations whiceither symmetric ~density! or antisymmetric ~bending!modes. They have shown by high-resolution 2D, gravtional N-body simulations by the Particle-Mesh~PM!method that pancakes are unstable to the formation

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clumps for perturbations of any wavelength roughly less thor equal to the pancake mode wavelength. Numericaldynamical simulations using the new ASPH method devoped here have also been performed, revealing similar inbilities when a collisional gaseous component is includedaddition, this gaseous component develops significant voity, which may be important in explaining the origin of galactic rotation.

H. Martel, P. Shapiro, and P.J.E. Peebles~Princeton! usedhigh-resolution, 2D Particle-Mesh~PM! simulations of thegrowth of cosmological density fluctations to answer tquestion, ‘‘How generic is pancake formation when densfluctuations arise from Gaussian random noise with a powlaw power spectrum?’’ They find that pancakes are gento a wide range of initial conditions.

S. Weinberg, P. Shapiro, and H. Martel have appliedanthropic principle to explain why the cosmological constain our observed universe has a value as small as it doeswhy it is likely that this small value is, nevertheless, nonzeThey show, using the CDM model, that a value of the cmological constant that is currently favored by several obsvational constraints~i.e., a vacuum energy density abothree times as large as the matter density, in a flat unive!is close to the median value expected to be observed inensemble of universes in which the constant is equally likto have any~positive! value.

3.3.7 Laser Ranging:

The McDonald Laser Ranging Station~MLRS! is a fun-damental station in the world-wide laser ranging networkconsists of a 0.76-m reflecting telescope and a very-shpulse, frequency-doubled, 532-nm wavelength, neodymiuYAG laser, with ancilliary computer, electronic, and timinhardware. The station is located at McDonald Observaton Mt. Fowlkes, to the northeast of Mt. Locke in WeTexas, and shares the mountaintop with the new HodEberly Telescope. With a two-crew observing operatiolaser ranging is carried on to a host of artificial satellit~Fizeau, ERS-1, ERS-2, Tips, Starlette, Stella, Meteor-3, Asai, TOPEX/Poseidon, LAGEOS-1, LAGEOS-2, Etalon-Etalon-2, GPS-35, GPS-36, and GLONASS! as well as themoon. The MLRS is the only lunar-capable laser rangstation in the United States and only one of two luncapable stations in the entire world. By measuring the timtakes for a laser pulse to leave a ground station, bounce otargeted reflector array, and return to the ground station,can measure very precisely the distance between the stand the reflector array. Comparing a series of measurem~almost 30 years of lunar laser ranging observations hnow been accumulated, together with more than 10 yearartificial satellite data!, scientific results are obtained in foubroad areas: solar system ephemeris development, gerelativity and gravitational physics, lunar science, and gdynamics.

Lunar and artificial satellite laser ranging, with ProjeDirector P.J. Shelus and staff members R.L. Ricklefs, JRies, A.L. Whipple, and J.R. Wiant, continued under tsupport of NASA. A new five-year laser ranging operatiocontract from the Goddard Space Flight Center was awar

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continuing nearly three decades of effort along this avenuobservation and research. Support for lunar laser rangingforts comes from the Ultraviolet, Visible, and GravitationAstrophysics Research and Analysis Program at NAHeadquarters.

Lunar and artificial satellite laser ranging observatiowere obtained with the MLRS at record setting levels forseventh straight year, as personnel cooperated withleagues around the world, making maximum use of the dtype in earth, moon, and solar system related dynamics1995, for the first time ever, the MLRS attained lunar ddensities that surpassed that obtained during the veryyears of 2.7-m telescope system operation, but at levelaccuracy and precision more than five times better. Princresearch activity included monitoring the exchange of anlar momentum between the solid earth and its atmosphthe principal geopotential terms, plate tectonic activity, tiddissipation in the lunar orbit, the lunar free libration, and tequivalence principle of general relativity.

In a service capacity, the project serves as Observing Cter and Analysis Center in the International Earth RotatService~IERS!, obtaining millisecond accuracy estimatesthe constant of precession, coefficients of nutation, polartion, and Earth rotation. This constitutes the only near-retime source of this information that includes the lunar laranging data type.

The MLRS Auto-Guiding and Imaging System~AGIS!has approached full integration in virtually all facets of tlunar laser ranging operation. The AGIS is an integrahardware and software system that accepts real-time vsignals as input, i.e., highly magnified images of a smportion of the lunar surface, or stellar or artificial satellpoint-source images. It performs real-time image processand allows a user to select among various levels and typeimage enhancement. The AGIS also produces raw andtered tracking error signals, that under user selection,communicated to a control computer for guiding control.this time, most use of the AGIS is applied to the lunar effoproducing a marked increase in the volume of LLR data. Tproject is beginning to investigate ways of using the AGISthe artificial satellite ranging portion of the operation.

An improved Avalanche Photo-Diode~APD! was re-ceived from the Wettzell, Germany laser ranging site toplace the MLRS Varian high quantum efficiency photomtiplier tube in lunar laser ranging operations. An APdetector now in use at the LLR station in the south of Frahas exhibited a significant increase in sensitivity andproved accuracy and precision. Similar devices are usedartificial satellite laser ranging operations around the woThe first test results on the moon have been very encouing.

The replacement of the MLRS’s 15-year-old Data Geeral NOVA control computer system with a LynxOS-baseX-Windows, real-time Unix system running on PC hardwais now completed. This has been coordinated with simupgrades at other NASA-based laser ranging systems. Itcreated a system having highly compatible, transportaand transferable hardware and software architecture inopen-systems~POSIX! environment. The approach has a

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lowed a maximum amount of software portability and shing. All MLRS data, both lunar and artificial satellite, arnow being obtained with this system.

3.3.8 Astrometry:

The Hubble Space Telescope Astrometry Science Teabased at the University of Texas. Local members incluG.F. Benedict~Deputy P.I.!, R. Duncombe~Aerospace En-gineering!, W. Jefferys~P.I.!, B. McArthur, P. Hemenway,E. Nelan~STScI!, P. Shelus, D. Story~Goddard SpaceflighCenter!, and A. Whipple. The team continued reducing aanalyzing data bearing on planet searches~seeSolar System,above!, hipparcos-quasar reference frame tie-in, and palaxes of astrophysically interesting objects~Delta Cephei,RR Lyrae, Feige 24, planetary nebulae central stars, theades, and low-mass M-dwarfs!. All data are obtained withFine Guidance Sensor 3 aboard HST. Precision of 1–2 mliarcsecond per measurement is obtained. This year theence pipeline was modified to deal with nearly simultaneotransfer scan and position mode astrometry withFGS3. Thiscapability will be used to obtain precise orbits, parallaxand masses for close binary stars difficult or impossiblestudy from the ground.

P. Shelus and A. Whipple continue their astrometric oservations of faint solar system objects. This effort has copletely moved from the photographic process to a CCD usthe Prime Focus Corrector~PFC! on the McDonald 0.76-mreflector. The f/3 PFC is ideal for astrometric observationsfaint solar system objects. The PFC is capable of reachR522, with more than three sigma significance on steobjects, in co-added integrations. Software has been deoped within IRAF to perform routine, real-time processingCCD frames taken with the PFC~or any other CCD!, iden-tify star fields and solar system objects within the fielddigitally determine the centers and intensities for all idenfied objects within the fields, and then process the measto obtain astrometric positions and magnitudes. The totaltrometric system is fully functional and excellent results abeing obtained. It is routine to have a night’s worth of minplanet and cometary positional observations electronicsent to the Minor Planet Center the morning after the obsvations were taken.

A. Whipple and P. Shelus also obtained observationsthe satellites of Jupiter, Saturn, Neptune, and Uranus wthe PFC. Many of these objects that they observe have, inpast, been grossly underobserved. Orbit refinements reqthat a continuous set of precise and accurate positionalservations be maintained. Positions of all target objectsdetermined in a standard reference frame. Many of thobservations are crucial for spacecraft trajectories.

3.3.9 History of Astronomy:

D.S. Evans has continued his interest in astronomicaltory. In addition to contributions to the forthcoming GarlanEncyclopedia of the History of Astronomy, the new~British!Dictionary of National Biography, and the new HandbookTexas, he is revising his personal memoir of the lateArthur Eddington and preparing a contribution on J.-

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Houzeau, the celebrated Belgian astronomical bibliograpwho spent several of his earlier adventurous years in Te

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