Filling the Gaps in the GLIMPSE360 Survey

Abstract:Regarding the GLIMPSE360 Exploration Science project that is mapping the outer Galaxy, wehave some good news and bad news to report. The good news is that the data are proving to bespectacular. Due to the higher dynamic range and the lower confusion compared to the GLIMPSEsurvey (of the inner Galaxy), we can detect stars out to the edge of the Galaxy, PAH bubbles at 3.6microns; and YSO outflows, H II regions, and supernova remnants at 4.5 microns; and we canseparate IR−excess sources in color−magnitude space. The bad news is that due to a variety of conditions we did not fully anticipate, a substantial portionof the survey observed so far (about 1/6 of the entire survey) has narrow gaps in coverage, inbetween AORs. We have corrected the problem and our recent data show no gaps. The complete coverage of this survey is meaningful for several science goals that are based onglobal studies, such as mapping Galactic structure and measuring star formation rate as a functionof Galacto−centric radius. We request additional time to fill in these gaps and to realize the fullpotential of the survey.

Spitzer Space Telescope General Observer Proposal #70072.

Principal Investigator: Barbara A. Whitney

Institution: Space Science Institute

Electronic mail: bwhitney@spacescience.org

Technical Contact: Christer Watson, Manchester College

Co−Investigators: Christer Watson, Manchester College

Edward Churchwell, University of Wisconsin

Robert Benjamin, University of Wisconsin−Whitewater

Marilyn Meade, University of Wisconsin−Madison

Brian Babler, University of Wisconsin−Madison

Matthew Povich, The Pennsylvania State University

Thomas Robitaille, Harvard−Smithsonian Center for Astrophysics

Science Category:Galactic: galactic structure

Observing Modes: IRAC Post−Cryo Mapping

Hours Requested:46.4

Proprietary Period(days): 0

GLIMPSE360 Gaps, B. Whitney et al. 1

1 Science Plan

1.1 Scientific Justification

1.1.1 Overview of GLIMPSE360

GLIMPSE360 is an Exploration Science project that was awarded 1980 hours to map theremaining 183 degrees in longitude of the Galactic plane that have not been mapped by theother Spitzer Galactic Plane surveys (GLIMPSE, GLIMPSE II, GLIMPSE3D, Vela Carina,SMOG, and Cygnus-X). The specific Galactic longitudes covered by GLIMPSE360 are l =65 − 76◦, 82 − 102◦, and 109 − 265◦. Thus GLIMPSE360 will complete the full circle of theGalactic plane. We will refer to the previous suite of surveys as GLIMPSE, and the currentone as GLIMPSE360.

The combined Spitzer surveys of our Galactic plane provide a panoramic view of ourGalaxy that is both visually and scientifically stunning (see our zoomable web browser show-ing the GLIMPSE and MIPSGAL surveys at this website: www.alienearths.org/glimpse).With GLIMPSE (and the MIPSGAL survey) we have calculated the star formation rate ofthe Galaxy (Robitaille & Whitney 2010), refined the dimensions of the Galactic bar (Ben-jamin et al. 2005), studied large star formation regions in detail (Povich et al. 2007, 2009,2010) and cataloged millions of objects, including stars, IR-excess sources, PAH bubbles,outflows from massive young protostars, globular clusters, and external galaxies in the “zoneof avoidance” (see review by Churchwell et al. 2009). Similarly, with GLIMPSE360 we willdetermine the star formation rate of the outer Galaxy, determine the edge of the Galacticdisk, map the Perseus and far outer arm, and look for evidence of star formation in the FarOuter Galaxy. In addition, we and others will catalog many of the same types of objects asfound in GLIMPSE. Following the tradition of the previous GLIMPSE Legacy programs, wewill deliver enhanced data products (sources lists and cleaned mosaics) to the community.The Legacy value of GLIMPSE and GLIMPSE360 are further enhanced by surveys of theGalactic plane at other wavelengths, such as 2MASS and UKIDDs in the near-IR (Skrut-skie et al. 2006, Lucas et al. 2008), WISE at 3-23 µm (at lower resolution than Spitzer),SCUBA-2 in the submm, and the FCRAO CO surveys of the Outer Galaxy (l = 102− 141◦,Heyer et al. 1998; l = 55 − 102◦, Bruno & Heyer, in preparation).

The following sections describe gaps in the initial survey observations (§1.1.2), the needto fill in the gaps (§1.1.3), and preliminary results from GLIMPSE360 showing that thepromise of the survey is exceeding expectations (§1.1.4).

1.1.2 Gaps in the survey

We have completed about 1/3 of our survey as of April 7, 2010, covering ∼ 66◦ of longitude(out of 183◦). Due to different observing modes in the warm mission, to Spitzer ScienceCenter’s (SSC’s) need to have more flexibility in scheduling our observations (less timingconstraints), and to larger roll angle changes in the outer Galaxy than we had seen in theinner Galaxy, our initial observing plan produced some gaps in the survey images. Theseoccur mainly in longitude ranges l = 90 − 102◦, 140 − 150◦, and 170 − 180◦. The Spitzerroll angle changes at 1.0 degree/day at l=90◦. Typical roll angle changes in the originalGLIMPSE survey region were 0.3 degrees/day and were never as high as is common aroundl=90◦. As a result of these quickly changing roll angles, the long strips (used in all theGLIMPSE-related projects) were rotated slightly beyond their tolerance and then gaps be-

GLIMPSE360 Gaps, B. Whitney et al. 2

Figure 1: A 3.1◦ × 2.2◦ region centered at (l = 147◦, b = 0.4◦) showing gaps between AORs in thesurvey coverage at 3.6 µm.

tween the strips resulted. Examples are shown in Figure 1. We did plan 50 extra hours ofcontingency time (3% of the total) to handle situations like this, but they were used to fixsome larger gaps produced by an error in our planning software. Several hours of observingand scheduled observing (that couldn’t be changed) occurred before we saw these problems.We have worked with SSC to adjust our overlaps and timing constraints, and our most recentobservations contain no gaps.

The gaps occurred because we are pushing the limits of efficiency. If we had insured thatthere would be no gaps by increasing overlap between adjacent long strips, our observingefficiency would have decreased, resulting in a smaller survey area. Based on the success ofprevious GLIMPSE-style projects, we were aggressive in using the same overlap despite thequicker roll-angle changes. We regret that we did not anticipate these changes, and humblyask for additional observing time above the original generous allotment that was awardedfor this project. The value added is very high as described in the next section. As describedin §1.2, the observing plan has no timing constraints.

1.1.3 The Need to Fill in the Gaps

A large value of the GLIMPSE surveys has been the complete coverage over the specifiedsurvey area, as the following scientific results illustrate: 1) Counting stars by measuring theslope of logN-logS (source counts vs flux) space allows us to see overdensities of red clumpstars. These are excellent standard candles (M4.5=-1.62+/-0.03), and their over-densitiesare mapping Galactic structure. Benjamin et al. (2005) used this method to map the Long

GLIMPSE360 Gaps, B. Whitney et al. 3

Bar of the Galaxy, the three dimensional structure of the inner bar, and over-densities inthe stellar disk, possibly associated with spiral structure (Benjamin et al., in prep). 2)Robitaille et al. (2008) produced a highly reliable and complete flux-limited catalog of IRexcess sources in GLIMPSE and GLIMPSE II, and identified a likely population of YSOsthrough color-magnitude selections. These were compared to a population synthesis modelof YSOs in the Galaxy to which the same sensitivities, color-magnitude selections, and skycoverage was applied. While we only have a 2-D view of our Galaxy, a population synthesismodel that collapses 3-D information to the same 2-D view as the GLIMPSE survey allowsus to probe the third dimension in a statistical sense. The variable in the model is the starformation rate, which was calculated to be 0.68-1.45M⊙/yr (Robitaille & Whitney 2010).Both of these examples make use of a complete and easily specified survey coverage area,sometimes summing over latitude in the analysis. This can be done with gaps in it but wouldrequire more effort in the analysis to account for them. For example, the YSO populationsynthesis model can use a similar mask for survey coverage area as the GLIMPSE360 data.3) Another example is the set of studies of the M17 star formation region done by Povichet al. (2007, 2009, 2010). These regions cover an area of ∼2 square degrees on the sky. TheM17 molecular cloud is in the process of passing through the Sagittarius spiral arm and isan ideal location to study both local and global triggering of star formation. Povich hasshown that the young stellar populations in three different regions form an age sequenceacross this large complex, as predicted by Elmegreen & Lada (1976). Studies such as thisrequire complete coverage of large areas on the sky. 4) We and others have cataloged globularclusters and external galaxies, outflows from massive young protostars, PAH bubbles frommassive young stars, YSOs and AGB stars, and over 100 million stars. The great value ofthese catalogs is that they are based on complete coverage.

We could replan the rest of our survey to make it narrower in latitude, and use the extratime to fill in the gaps. We have already done this when we discovered our earlier, largergaps. Our survey width is now 2.58◦, compared to the original 3.1◦ proposed. The outerGalaxy is thicker than the inner and we are very reluctant to make the survey any narrower(the original GLIMPSE width is 2◦ from |l| = 5 − 65◦ and up to 8◦ at the Galactic center).

Finally, the images are much more beautiful without gaps in them, and this has intrinsicvalue to us and to the general public.

1.1.4 GLIMPSE360 Preliminary Results

The GLIMPSE360 observing strategy differs from GLIMPSE in that we observe with only 3.6and 4.5 IRAC bands, and we observe each portion of the sky 3 times in High-Dynamic-Range(HDR) mode (12 sec and 0.6 sec frametime). The total exposure time on each position in thesky is 13 times longer than the GLIMPSE 2-visit 2-sec frametime exposures. The effectivemagnitude ranges, based on our recently processed catalogs, are 6.0-18.5 at 3.6 µm, and5.5-17.8 for 4.5 µm. Note: These are based on single-frame photometry and will go deeperwhen we do mosaic photometry. We expect those catalogs to be about 2.5 mags deeper and1 mag brighter than the GLIMPSE survey catalogs.

Figure 2 shows updated logN-logS slope plots including the processed portion of theGLIMPSE360 survey. GLIMPSE360 shows preliminary evidence for a slope change coherentin longitude-magnitude space from l = 109 − 90◦ at m = 12.6 − 13.2. If this is due to redclump stars, it indicates a region of stellar overdensity that is 7-9 kpc distant, consistentwith the distance of the Outer Arm. Modelling is in progress to test this interpretation.

GLIMPSE360 Gaps, B. Whitney et al. 4

Figure 2: Identifying red clump star overdensities in the Galaxy using 4.5 µm star counts. Theseshow up as changes in the slope of the logN-logS histograms. The apparent magnitude of theseinflection points maps to distance. The region highlighted by the yellow question mark maps to adistance of 7-9 kpc. The Perseus arm at 2-4 kpc is not apparent. It will be very interesting to seewhat more complete coverage will show us. Other features in the GLIMPSE survey are indicatedat center.

Interestingly, there is no clear feature at the expected distance of the Perseus Arm; furtherdata will shed more light on these surprising results.

Figure 3 shows images of star forming regions. These show two important effects of valueto our science goals: 1) Protostellar outflows are detected as excess 4.5 µm emission in 2- or3-color image displays (IRAC 3.6 µm + 4.5 µm, or K + IRAC 3.6 µm + 4.5 µm, respectively).These show up as smallish (∼ 10′′) green objects in 3-color displays (3.6 µm in blue, 4.5 µmin green, 8.0 µm in red) in the GLIMPSE survey. Cyganowski et al. (2008) has published acatalog of over 300 of these “Extended Green Objects” (EGOs) and confirmed in followupsubmm observations that they are outflows from massive YSOs in their earliest stages offormation. This is a rare stage to observe because it is so short-lived. Thus identifying theseoutflows provides a way to locate these rare objects, and do detailed followup studies to learnmore about their physical properties. Using the GLIMPSE360 data, where we do not have8 µm images, we display the 4.5 µm image in the red channel (Figure 3) so the outflows willhave to be renamed to be “Extended Red Objects.” The image at left in Figure 3 shows oneprobable outflow (at center in red) and one possible (at the left of the image) from the starforming region WB89 43 (Wouterloot & Brand 1989; also IRAS21078+521). This is locatedat l = 92.67◦, b = 3.07◦, at a kinematic distance of 1.5 kpc. The image at right shows severaloutflows near the well-studied intermediate-mass protostar GL 490. These outflows are allnew discoveries, except one that was discovered in the radio (top right) (Lyder, Belton, &Gower 1998). These also show a second feature of our survey that will enable great science:2) The higher sensitivity of GLIMPSE360 and the lower backgrounds allow detection offainter outflows such as these. It also allows detection of PAH bubbles in the 3.6 µm band,as shown in Figure 4, left panel. Churchwell et al. (2006, 2007) identified almost 600 PAHbubbles using the 8 µm images. These are signposts of recent massive star formation and

GLIMPSE360 Gaps, B. Whitney et al. 5

Figure 3: Left. The star formation region WB89 43 showing at least one outflow from a massiveyoung protostar, in red at the center. Right: Star formation near GL 490 (which is the saturatedsource at l = 142.09◦, b = 1.93◦) showing previously undiscovered outflows (encircled in green). Inboth images, K (2.2 µm) is displayed in blue, 3.6 µm in green, 4.5 µm in red.

good places to study triggering of current star formation (Watson et al. 2008, 2009). InGLIMPSE, the bubbles are not as apparent at 3.6 µm as at 8 µm. In GLIMPSE360, due tothe higher sensitivity (more and deeper exposures) and lower Galactic background emission,the PAH bubbles are very apparent at 3.6 µm. Again, this identifies interesting regions thatcan be studied further.

Figure 4 shows the supernova remnant HB3 in red emission in the right panel. Severalstar clusters are present throughout the images (e.g., Figure 4, left panel, at right in theimage). A search for new clusters is in progress.

Figure 5 shows that we can separate IR-excess sources from naked stellar atmospheresin color-magnitude space. These IR-excess sources consist primarily of YSOs, evolved stars,and unresolved galaxies. Because of the lower confusion in the outer Galaxy compared toGLIMPSE, the IR-excess sources identified in a given star forming region are more likelyto be YSOs and to be associated with that star forming region. In the GLIMPSE survey(of the inner Galaxy), there is more confusion with background and foreground YSOs aswell as evolved stars (mainly Asymptotic Giant Branch, or AGB stars). Not shown here,we examined a (GLIMPSE360) region with an overdensity of resolved galaxies. This alsoshowed a large population of IR-excess sources compared to an empty region, likely due tounresolved galaxies in a cluster. The population of IR-excess sources in the “empty” regionsis most likely AGB stars. These are distributed more uniformly in space than YSOs andgalaxies, and their source density can be used to study their properties and to estimate theircontamination to star forming regions and galaxy clusters.

In our YSO population synthesis model, we can make the same color-magnitude selectionsand sensitivity cuts to our model as the GLIMPSE360 data and compare the results modeland data catalogs. We can estimate the galaxy contamination using the SWIRE survey

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Figure 4: Left. PAH “bubbles” seen at 3.6 µm in green (K in blue, 4.5 µm in red). Right. Asupernova remnant seen at 4.5 µm in red (3.6 µm shows PAHs in green, and K is blue).

Figure 5: Left. Color-magnitude diagram of an “empty” field region. The purple points are fromthe GLIMPSE360 catalog. The greyscale is expected colors of YSOs at the distance of the starforming region GL490 (d = 1 kpc). The black line shows the probable dividing line between nakedstar colors and those with dusty envelope producing an IR excess (the purple sources to the rightare probably galaxies). Right: Color-magnitude diagram of the region surrounding GL 490. Thepurple points to the right of the black line are probable YSOs.

GLIMPSE360 Gaps, B. Whitney et al. 7

and the AGB contamination from source counts in “empty” regions (after galaxy removal).The main variable of the model will again be the star formation rate. By comparing thelongitudinal distribution of the model and data, we’ll constrain the Galacto-centric radialdistribution of YSOs.

As discussed in the original GLIMPSE360 proposal, we have several other science goalsthat we are confident will be achievable, including finding Infrared Dark Clouds using ex-tinction mapping from SED (Spectral Energy Distribution) fits to catalog stars; searchingfor supernovae remnants, star clusters, planetary nebulae; and studying the AGB and YSOpopulation in the Outer Galaxy. Since these are global studies, they will benefit from acomplete and uniformly sampled survey.

We have discussed just a few of the science goals that our particular group is mostinterested in. We have treated the GLIMPSE360 project similar to the previous GLIMPSElegacy projects in that we are making our processed images and catalogs publicly available.The legacy value of the project will be greatly enhanced by filling in the gaps.

1.2 Technical Plan

1.2.1 Observing Plan

The regions to be observed consist of thin strips (typically less than 100′′ in width) andof variable length (between a ∼ 1′ to ∼1◦). Our observing strategy makes exclusive useof the fixed cluster-position observing mode. By using positions on the sky offset alonga line in increments of 2.4′, we are able to assure full coverage (1-3 times) of thin stripsregardless of roll angle. This last quality allows our observing strategy to be implementedwith efficiency and without any observing constraints of any kind, a marked contrast fromprevious GLIMPSE-style proposals.

Some gaps in the GLIMPSE360 survey resulted from AORs of adjacent segments notoverlapping, resulting in a gap that is more square-shaped than the slivers between adjacentAORs within a single segment. These areas are covered in this proposal by AORs designedby hand to be nearly square-shaped and will cover the gap at any roll angle or observingdate. We have placed no constraints on these AORs.

Our exposure times are the same as for the GLIMPSE360 project (12 second HDR frames)with 1-3 visits on each sky position, depending on roll angle (2-3 visits in most cases).

1.2.2 Management Plan

The observations have been planned by co-I Watson. Watson will also oversee the data-taking. The data will be processed by co-Is Meade and Babler. The gap data will be addedinto the previous data, and the regions will be reprocessed as a set. PI Whitney will managethe project as a whole. The other co-Is (Churchwell, Povich, Robitaille) are science users ofthe data (along with Watson and Whitney). Their heavy use of the data helps to improvethe products.

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1.3 References

Benjamin, R. A. et al. 2005, ApJL, 630, L149

Cyganowski, C. et al. 2008, AJ, 136, 2391

Churchwell, E. et al. 2006, ApJ, 649, 759

Churchwell, E. et al. 2007, ApJ, 670, 428

Churchwell, E. et al. 2009, PASP, 121, 213

Elmegreen, B. G. & Lada, C. J. 1976, AJ, 81, 1089

Heyer, M., et al. 1998, ApJS, 115, 241

Lucas, P., et al. 2008, MNRAS, 391, 136

Lyder, D. A., Belton, D. S., & Gower, A. C. 1998, AJ, 116, 840

Povich, M. S. et al. 2007, ApJ, 660, 346

Povich, M. S. et al. 2009, ApJ, 696, 1278

Povich, M. S. & Whitney, B. A. 2010, ApJL, 714, L285

Robitaille, T. P. et al. 2008, AJ, 136, 2413

Robitaille, T. P., & Whitney, B. A. 2010 ApJL, 710, L11

Skrutskie, M., et al. 2006, AJ, 131, 1163

Watson, C. et al. 2008, ApJ, 681, 1341

Watson, C. et al. 2009, ApJ, 694, 546

Wouterloot, J. G. A., & Brand, J. 1989, A&AS, 80, 149

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2 Brief Team Resume

PI B. Whitney, Senior Research Scientist at Space Science Institute, is PI of the GO6Exploration Science program GLIMPSE360, a member of the GLIMPSE and SAGE legacyteams, and one of the developers of the GLIMPSE data processing pipeline. She developed amulti-dimensional radiation transfer code that has been used to model the SEDs of thousandsof YSOs observed by Spitzer.Co-I C. Watson, Associate Professor at Manchester College, member of the GLIMPSEteams and designer of their observing programs. He studies feedback in massive star formingregions.Co-I E. Churchwell, Professor Emeritus at the University of Wisconsin, is PI of theGLIMPSE I and GLIMPSE II legacy projects, and is an expert in massive star formation.Co-I R. Benjamin, Associate Professor at University of Wisconsin-Whitewater, is a mem-ber of the original GLIMPSE team, and the PI for GLIMPSE-3D Legacy project. He hasled the effort to use GLIMPSE data to constrain the stellar structure of the Galaxy.Co-I M. Meade is a member of the GLIMPSE and SAGE legacy teams, and one of thedevelopers of the Wisconsin IRAC pipeline. She has run the IRAC pipeline on the GLIMPSEand SAGE data, producing source lists and images for the astronomical community.Co-I B. Babler is a member of the GLIMPSE and SAGE legacy teams, and is our experton photometry, source catalogs and errors.Co-I M. Povich is an NSF Astronomy & Astrophysics Postdoctoral Fellow at the Penn-sylvania State University. He has analyzed several massive star forming regions in theGLIMPSE and Vela-Carina surveys using YSO radiation transfer models.Co-I T. Robitaille is a Spitzer Postdoctoral Fellow at Harvard- Smithsonian Center forAstrophysics. He developed a large grid of YSO models and a YSO population synthesismodel to calculate the star formation rate of our Galaxy. He produced a GLIMPSE catalogof 20,000 IR-excess sources.

Relevant Publications

2010 M. S. Povich & B. A. Whitney, “Evidence for Delayed Massive Star Formation in theM17 Proto-OB Association,” ApJL, 714, L285

2010 T. P. Robitaille & B. A. Whitney, “The Present-Day Star Formation Rate of the MilkyWay Determined from Spitzer-Detected Young Stellar Objects,” ApJL, 710, L11

2009 E. Churchwell, B. L. Babler, M. R. Meade, B. A. Whitney, R. Benjamin et al. “TheSpitzer/GLIMPSE Surveys: A New View of the Milky Way,” PASP, 121, 213

2008 C. Watson et al., “IR Dust Bubbles: Probing the Detailed Structure and Young MassiveStellar Populations of Galactic H II Regions,” ApJ, 681, 1341

2008 T. P. Robitaille, M. R. Meade, B. L. Babler, B. A. Whitney et al. “Intrinsically RedSources observed by Spitzer in the Galactic Mid-Plane”, AJ, 136, 2413

2006 E. Churchwell, M. S. Povich, D. Allen, M. R. Meade, B. L. Babler, R. Indebetouw, B.A. Whitney et al., “The Bubbling Galactic Disk,” ApJ, 649, 759-778.

2005 R. A. Benjamin, E. Churchwell, B. L. Babler, R. Indebetouw, M. R. Meade, B. A.Whitney, C. Watson et al. “First GLIMPSE Results on the Stellar Structure of theGalaxy,” ApJ, 630, L149

2004 B. A. Whitney, et al., “A GLIMPSE of Star Formation in the Giant H II Region RCW49,” ApJS, 154, 315

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3 Summary of Existing Programs

PI. B. Whitney is PI of Cycle-3 and Cycle-4 Theory proposals (PID 30467 & 40794) tomake a large YSO grid and SED fitter publicly available and to modify the codes and producethe next generation grid of models. The tasks for the first proposal are finished, we havepublished 18 papers, and are currently running the new grid of models. Whitney is also PIof the Cycle-6 GLIMPSE360 Exploration Science program (PID 60020). Data taking startedin Sept. 2009, is continuing through 2010, and we are processing the data as it comes in.

Co-I E. Churchwell is PI of 4 Spitzer programs. The GLIMPSE I & II programsare completed, with final data products released to the community. 59 papers have beenpublished by the GLIMPSE team, with at least another 143 by the community. For PID40002, data have been reduced, and a publication is in preparation. Data for proposal 50130,data have been reduced and a publication is in prep.

Co-I B. Benjamin is PI of the Cycle-3 GLIMPSE-3D Legacy project (30570), whichcompleted all required data delivery last year. A paper is in preparation.

4 Observation Summary Table

Below is a table outlining our observations. Note that we did use the Perl script to generateinformation from the AOR file but that created a table 4000 lines long. The Spitzer helpdesk advised us that this smaller table would be sufficient.

Longitude range Number of AORs observing time (hrs)90-102 38 10.9

110-140 26 3.3140-150 46 18.2170-180 31 14.0

The total time to image the gaps is 46.4 hours. The AORs we are submitting are final.

5 Modification of the Proprietary Period

We waive the proprietary period. This is an add-on to the GLIMPSE360 project which weview as a legacy project.

6 Summary of Duplicate Observations

The GLIMPSE360 project overlaps several large surveys at the boundaries (SMOG, Cygnus-X, and Vela Carina). There are multiple smaller programs that were reobserved by GLIMPSE360,because avoiding them would make the survey very inefficient. These include the ARGUSprogram (of sufficiently different sensitivity to not be considered a duplicate), W5, and theGalactic First Look Survey. Our gap observations may overlap some of these, as well asoverlapping the GLIMPSE360 survey, which is intentional for full coverage.

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7 Summary of Scheduling Constraints/ToOs

There are no scheduling constraints on our observations.