ray and optical, to further study this veryunusual object.

References1. Giaconni, R, Gursky, H., Paolini, F., and

Rossi, B.: 1962, Phys. Rev. Lett. 9, 439.2. Schreier, E., Levinson, R., Gursky, H.,

Kellogg, E., Tananbaum, H., andGiaconni, R.: 1972, Ap. J. 172, L79.

3. While, N.E.: 1989, EXOSAT preprinlno. 103, 10 appear in Vol. 1 01 The As­tronomy and Astrophysics Review.

4. Van Paradijs, J.: 1983, in Accretiondriven stellar X-ray sources, Eds. Lewin,W. H. G. and Van den Heuvel, E. P. J.Cambridge Universily press, p.189.

5. McClinlock, J. R, Canizares, C. R, andTarter, C.B.: 1975, Ap. J. 198, 641.

6. Molch, C., and Pakull, M. W.: 1989, pre­prinl, 10 appear in Astron. Astrophys.

7. Shapiro, S.L., and Teukolsky, S.A.:1983, in Black holes, white dwarfs andneutron stars, John Wiley-Inlerscience,N.Y.

8. Cowley, A.P., Cramplon, D., Hulchings,J. B., Remillard, K., and Penlold, J. E.:1983, Ap. J. 272, 118.

9. Gies, D.R., and BoiIon, C.T.: 1986, Ap.J. 304, 371.

10. McClinlock, J. E. and Remillard, RA.:1986,Ap. J. 308,110.

11. HUlchings, J. B., Cramplon, D., Cowley,A.P., Bianclli, L., Thompson, I.B.: 1987,Astron. J. 94, 340.

12. Kuiper, L., Van Paradijs, J., and Van derKlis, M.: 1988, Astron. Astrophys. 203, 79.

13. Mason, K.O.: 1986, in The physics ofaccretion onto a compact object, Eds.Mason, K.O., Walson, M. G. and While,N. E. Springer-Verlag Berlin, p. 29.

14. Parmar, A. N., While, N. E., Giommi, P.,and Haberl, F.: 1985, lAU Circ. no. 4039.

15. Parmar, A. N., While, N. E., Giommi, P.,and Gottwald, M.: 1986, Ap. J. 308,189.

16. Van Paradijs, J., Van der Klis, M., andPedersen, H.: 1988, Aslron. Astrophys.Suppl. 76, 185.

17. Pedersen, H., Van Paradijs, J., Molch,C., Cominsky, L., Lawrence, A., Lewin,W. H. G., Oda, M., Ohashi, T., and Mal­suoka, M.: 1982, Ap. J. 263, 340.

18. Gotlwald, M., Haberl, F., Parmar, A. N.,and While, N. E.: 1986, Ap. J. 308, 213.

--L-

1.84xl0 71.82xl0 7

in the Figure) of the night. Following thepicture given above, this is in turn fullyconsistent with the idea that the diskradiates through reprocessing of X-rays,giving a rise in the optical emission witha rise in the X-ray flux also when only theside of the companion turned away fromthe X-ray source and (part) of the diskare visible. The depth of the eclipse alsoshows that the disk is a major source ofoptical light in the system.

To look further into the relation be­tween optical and X-ray behaviour ofthis source, aseparate night of observa­tions, simultaneous with the X-raysatellite GINGA, was made on March 25this year. Unfortunately, only threehours of data cou1d be collected and afirst quick look at the data did not showany special activity of the source,though a closer look, also at the X-raydata, will be necessary.

However, it still would be very inter­esting to follow this source closely in thefuture, if possible simultaneously in X-

1.78xl07

1000 [~

soorDA 'ISH 1.54 m 13-1 '89

~ EX00748 676

\~I......III

~ 600

~ ~\i II~\~~'rl IM~-> rMMI\~ifl~'~1~ I I tl~it~\~ :~~f~~rr~YI~i~jl~~~ V~ ~/~t1lI..

c:: 400:J0

l.J

1.8; J 0 7

Time (ms)

Figure 2: The light curve of a burst from UY Vol, observed on January 13, 1989. The axes havethe same definition as in Figure 1. Each point is a one-second integration. The sky counts areCorrected for the difference in sensitivity of the two detectors.

t:-v0 fOliowing nights the count rates hadnsen to between - 400 and - 600 cis. Inthis respect it is interesting to note thatthe shape of the "first" burst in'Figure 2 isvery simular to the "slow" X-ray burstprofile seen in the low X-ray state.

Also, the source intensity during thesecond part of the third night was higherthan during the first part. This can beseen by comparing the lower curve ofFigure 1, wh ich was observed duringthe fc Irst part of that night, and the upperurve, observed in the second part of

;~at night, wh ich is higher by more tllane upward shift of +70 cis. This would

then also indicate an increase in thep~rSistent X-ray flux and naturally ex­P alns the detection of only one burst atthe be' .glnnlng of that night and the lack

tOf any further detection for the rest ofhe night.

In Figure 1 it can be seen that alsoduri~g the X-ray eclipse the optical in­tenslty of the Source is significantly in­creased in the second part (upper curve

. , . . : ~ . .. . . ,

'NEW,S ON ESO IN.STRUMENTATION, .

The VLT Adaptive Optics Prototype System: Status July 1989F. MERKLE, ESO

th In June 1986 the conceptual design of

te VLT Adaptive Optics Prototype sys­

em was started, based on the collab­Oratio bp . n etween the Observatoire det ans (Meudon), ONERA, the Labora­Olres de Marcoussis, and ESO after

funding was assured by ESO andsupporting French authorities.

In August 1987 began the construc­tion of the major components. 1I wascompleted at the facilities of the variouspartners in May 1988. The major com-

ponents are the 19-actuator deformablemirror (LdM), the Shack-Hartmannwavefront sensor (ESO), the wavefrontcomputer and control electronics (ON­ERA, LdM), the tip/tilt mirror (OdM), theopto-mechanical support structure

63

Figure 1: The adaptive optics prototype system in the laboratory. The opticallight pass is indicated. The major components are the deformablemirror (DM), the tip/tilt mirror (TM), the off-axis parabola (PM), the dichroic beamsplitter (85), the field selection mirror for the wavefront sensor(FM), the wavefront sensor (WS), the chopping mirror (CM), and the infrared camera (IC). The electronics, including computers, occupy twostandard racks and are not shown. The light path from the dichroic beam splitter to the wavefront sensor is indicated in red.

Table: Major parameters of the adaptive optics prototype system

wavelengths and the visible, to mentiononly a few of them.

This prototype system is ESO's firstmajor step towards the adaptive opticssystems required for the VLT. As a test­bench it allows to investigate the per­formance of all components and in par­ticular of the control strategy. Alreadyduring the design and construction itbecame obvious that the computingpower necessary in order to achieve thereal-time control with the required band­width is the major constraint. A possible

(OdM, CNRS), and the IR array camera(OdM).

Meanwhile the system has been com­pletely integrated at Observatoire deMeudon. First successful static testshave been performed in the laboratoryand dynamic operation is under prepa­ration. Figure 1 shows the prototypesystem at Meudon in June 1989. It isplanned that the alignment and tuning ofthe system will be finished by mid-Sep­tember. The major characteristics aresummarized in the Table.

The first, closed-Ioop operation isscheduled for October 12 to 23, 1989,followed by a second observing run inNovember. These observations will takeplace at the Observatoire de Haute­Provence at the coude focus of the1.52-metre telescope. Currently theOHP is preparing the installation of theadaptive system in October.

Early 1990 the system will go fromGarching to La Silla, after the necessarymodifications for adaptation to the 3.6­metre telescope, and aseries of finallaboratory tests and improvements, ifrequired. During the observations, awhole set of technical programmes willbe carried out, like seeing and isoplanic­ity measurements in the IR and visible,partial adaptive correction at shorter

64

Wavelength range:

Deformable mirror:Tip/tilt mirror:

Wavefront sensor:

Wavefront computer:

Control algorithm:

Camera:

upgrade of the system with a mirror ofapproximately 64 actuators will be animportant intermediate step for thespecification of the VLT systems. Forthe VLT the current plans envisage ap­proximately 250 actuators.

Acknowledgements

The author's thanks are due to manycolleagues contributing to ESO's ac­tivities in the field of adaptive optics,particularly J. C. Fontanella (ONERA),

3 to 5 micrometre (3.6-m telescope)partial correction for 11. < 3 micrometre19 piezoelectric actuators +/- 7.5 micrometre strokegimbal mountpiezoelectric actuatorsShack-Hartmann principle5 x 5 and 10 x 10 subapertures100 x 100 intensified Reticon detectorbuilt-in reference sourceadditional fjeld selection mirrordedicated electronicshost computer based on Motorola 68020modal correction schememirror eigenmodes32 x 32 InSb array camera (SAT detector)additional chopping mirror

J. P. Gaffard (CGE), P. Kern (Obs. deMeudon), P. Lena (Obs. de Meudon),J.C. de Miscault (CGE), G. Rousset(ONERA), and to many colleagues atESO for stimulating discussions.

References

For additional relerences the lollowing pa­pers are recommended:- F. Merkle (1988), "Adaptive Optics De­

velopment at ESO", Proceedings 01 theESO Conlerence on "Very Large Tele-

scopes and their Instrumentation", Garch­ing 21-24 March, 1988.

- P. Kern, P. Uma, G. Rousset, J.C. Fon­tanella, F. Merkle, J. P. Gaffard (1988),"Prototype 01 on adaptive optical systemlor inlrared astronomy", rel. as above.

- F. Merkle (1988), in SPIE Proceedings1013: "Optical Design Methods, Applica­tions and Large Optics", Hamburg, F. R. G.,September 1988.

- P. Kern, P. Lena, J. C. Fontanella, G.Rousset, F. Merkle, J. P. Gaffard (1989) inSPIE Proceedings 1114: Symposium on"Aerospace Sensing", Orlando, FI, March1989.

LATEST NEWSIR Observers at the 3.6-m telescope areinormed that the new F/35 chopping sec­ondary mirror is now available.

The F/35 chopping secondary mirrorwas reinstalled in August 1989 and testedwith the IR Photometer/Spectrophotome­ter. The performance 01 the systemproved at least identical to the onequoted in Messenger 39, 1, 1985. ESO'sIR Specklegraph (see Messenger 45, 29,1986) was also successlully used in its F/35 conliguration.

A. van Dijsseldonk (ESO)

Telescope Alignment Procedures: Improved Technique in theOpticalldentification of Mechanical AxesP. GIOROANO, ESO

Introduction

. In the article concerning "First Light"In the ND in the Messenger No. 56, abnef de . .scnptlon was given on page 2 ofthe b .aStC steps of the alignment proce-dure Ad . s was stated there, the proce-

ure used in the ND was essentiallyonly a somewhat more refined form of astandard procedure which had been~UcceSsfully used on a number of LaI lila telescopes. The first - and mostt~~damental - step is the optical iden-

at/on of the altitude axis (alt-az tele­~Clopes) or declination axis (equatoriale escopes).

The set-up for this step in the ND isshow'. n In Figure 1. ST 1 and ST2 are two~ghting telescopes mounted at the twot~smyth foci. Target mirrors tM1 C1 andI 2C2 were mounted on the fixed parts

o the fork. The observation of a centralc~oss on these target mirrors and theo s.ervation of the ST graticule in auto-collimat' .Ion agalnst the plane faces of~he target mirrors enables the two ST to

e. placed on the mechanical altitudeaXIS, thereby establishing a basic refer­~nce for the whole operation. However,pace reasons dictated in this case that

one had to "look through" tM2C2 toobserve tM 1C1 with ST1 and converselyw~S~ Th . .. . e conventlonal solution us-Ing "h3j. all-coated" mirrors leads to loss ofh~ ~f the light and ghost images with

9 er Intenslty than the required im­ages.

thThe selected solution was based one Co b' .

tric .m Inatlon of narrow band dielec-i mlrrors and Illumination of the sight­I~~t telescope with the corresponding

t USlng narrow band interference lil­ers We t·

irnu' ge In S~1, for example, a max-rn of reflectlvlty from M2C2, in spite

of 2 passages through M1 C1 (seeFig.1).

The wavelengths chosen in the reali­zation of the 2 beams were in accor­dance with the laser light currently usedin our laboratory:Red beam Ac = 632,8 nm HeNe laserGreen beam AC = 543,5 nm HeNe laser

Realization

The dielectric mirrors were realizedand delivered on time by MELLES

Figure 1.

GRIOT (France), who, after a first studyand a computer simulation, achieved inpractice an excellent confirmation of thetheoretical values. The front surface,with the cross-hair, is coated with thedielectric layer, while the back surface iscoated with a broad band antireflectivecoating.

The interference filters were selectedcarefully from the ESO La Silla cata­logue, in order to optimize the total effi­ciency of the delivered version of thedielectric mirrors.

65