First Observing Run with DISCO was SuccessfulF. MAASWINKEL, S. O'OOORICO, F. BORTOLETTO, B. BUZZONI, B. GILLI, C. GOUIFFES,

G. HUSTER, and W. NEES, ESO

The Direct Image Stabilized CameraOption DISCO was tested for the firsttime from 29 November to 5 Decemberat the 2.2-m telescope with a CCD cam­era. The instrument was described inMessenger48, p. 51. It comprises a newadapter for the 2.2-m telescope with anewly designed XYZ oftset guider. Itofters the possibility to observe at theconventional f/8 focus, or alternatively atan f/20 focus. In the latter mode it isPossible to correct the motion of theastronomical image 50 times per sec­ond. DISCO was mounted at the tele­scope with the precious support of theTRS group and operated without prob­lems from the first night. The aim of therun was in particular the test of theimage correction system (fast tiltingmirror, ICCD camera, VME based micro­processor). As had been expected, thesystem gave only minor improvement inmediocre seeing conditions; during verygood seeing, however, it provided arather impressive image improvement.As an illustration, Figure 1 shows aComparison of two exposures of 47 Tucmade without (Ieft picture) and with(right picture) image stabilization. Theexposure time was 45 sec for both and ared gunn filter (I,c = 668 nm) was used.The stellar image diameters withoutstabilization were 1':2 FWHM, withstabilization 0':9 was achieved. Thanksto the superior light concentration thestabilized image reveals more detailsand reaches fainter magnitudes. Duringpart of a night the seeing was so good

that it was possible to improve theFWHM of the stellar images in long in­tegrations from 0':85 (non-stabilized) to0':66 (stabilized). The possibility toswitch remotely in a few minutes fromthe f/8 to the f/20 mode was found

particularly useful. as the seeing wasobserved to change on a rather shorttimescale (- 1 hour).

A more detailed report on this test willbe given at the Very Large TelescopeConference at ESO in March.

New Operational Limits for 1.5-m Danish Telescope. A 14.5 cm thick spacer ring has beenInstalled between the mirror cell and theinstrument adapter. Its purpose is toeliminate residual spherical aberration.Recently analysed Schack-Hartmantests have shown the correction to beComplete.

The longer focal length of the tele­seope has changed the foeal planeseale from 16.07 to 15.83 +/- 0.02aresee/mm.

Unfortunately. the extra length belowthe mirror cell implies restrietions for theuse of eertain pieees of auxiliary equip­ment, in addition to those described inESO Users Manual No. 3 "Danish 1.5-mteleseope and Auxiliary equipment",

pages 4-7. Observers are urged to takethese into aeeount, when planning theirprogramme.

As the telescope can be used eitherwest or east of the base, there are twosets of limits; they are however symme­trie. Telescope operation west of thebase has the advantage that tracking(but not presetting) can be done intopart of the "danger" zone; the observermay override a first warning signal.

The inaccessible corner for the CCDcamera is h.a. > +01 : 10, decl. < -47(telescope west) and h. a. < - 01 : 10,decl. < -47 (telescope east). In the westposition, tracking is allowed to decl.-53, for h.a. > +01 : 10. It is not fea-

sible to reverse the teleseope during thenight, as the CCD electronics wouldhave to be disconnected.

For Coravel. the corner is at h. a.> +00: 10, decl. < -43 (west) and h.a.< -00: 10, deel. < -43 (east). Theselimits appear more restrictive than thosementioned above. However, the controlcable for the Coravel permits the ob­server to reverse the teleseope at night.Objects which are inaccessible fromone side of the base, can therefore beobserved from the other.

A two-channel and a six-channelphotometer have limits whieh are rathersimilar to those of the CCD eamera, andtelescope reversal is possible.

41

Mr. P. Nelrregaard, Brorfelde, has re­programmed the microprocessor-basedsafety-system so that physical collisionsbetween telescope base and auxiliaryequipment remain impossible.

H. Pedersen, ESO

MIDAS MemoESO Image Processing Group

1. Application Developments

An extended CCD reduction packagemade by S. Jörsäter, Stockholm Obser­vatory, has been implemented inMIDAS. This package includes tools forstandard reductions of CCD framessuch as dark current and sensitivitycorrections. A set of sophisticated rou­tines also allows the user to makemosaics of several frames includingphotometric adjustments of the indi­vidual exposures.

A calibration directory structure is be­ing created. This will contain generalcalibration data useful for reduction ofdata from La Silla. The first data to beincluded are tables of spectral lines,flux of standard stars, and extinctiondata. Information on filter transmissioncurves, performance of ESO CCD chips,

gratings efficiencies, etc. will be addedlater.

2. Portable MIDAS

The developments of the portableversion of MIDAS are proceedingaccording to schedule. The portablemonitor has been tested successfully onallVAX ULTRIX system while internalverifications on a SUN and Bull SPS 7system are in progress. The full TableFile System has been ported using thenew set of table interface routines. TheFortran application code has been con­verted from VAXNMS Fortran to stan­dard Fortran with 5 simple extensions(i. e. INCLUDE, IMPUCIT NONE, !-com­ments, ENDDO and long internalnames). A preprocessor was made forFortran compilers which do not supportthese extensions.

We are also happy to announce that anew UNIX system programmer, CarlosGuirao Sanchez, has joined the IPG.One of his main responsibilities is todevelop and maintain the system de­pendent interfaces of MIDAS. He willtherefore be strongly involved in the im­plementation of MIDAS on new sys­tems.

3. MIDAS Workshop

The next Data Analysis Workshop,arranged by the ST-ECF, will be held onthe 26th and 27th April, 1988. For the

convenience of people who also want toparticipate in the MIDAS workshop, theImage Processing Group has scheduledthis workshop for 28th April, 1988. Theprogramme will include sessions ongeneral developments and new applica­tions. Since the Portable version ofMIDAS will be made available duringthis summer, a significant part of theMIDAS Workshop will be devoted to thistopic. We anticipate giving a demon­stration of a prototype of the PortableMIDAS during the workshop. A tentativeagenda will be sent out to all MIDASsites together with other material for theData Analysis Workshop. People in­terested in participating in the Work­shop should contact either the IPG orthe ST-ECF.

4. MIDAS Hot-Line Service

The following MIDAS Support ser­vices can be used in case of problemsto obtain fast help:• EARN: MIDAS DGAES051• SPAN: ESOMC1 ::MIDAS• Tlx.: 52828222 eso d, attn.: MIDAS

HOT-UNE• Tel.: +49-89-32006-456

Also, users are invited to send us anysuggestions or comments. Although atelephone service is provided, we preferthat requests are submitted in writtenform through either electronic networksor telex. This makes it easier for us toprocess the requests properly.

Unusual Building for the ESO NTT Arrivesat the La Silla Observatory

Early in February, M/S Cervo arrivedin the harbour of Valparaiso, Chile, withthe packaged parts for the buildingwhich will house the ESO New Technol­ogy Telescope (NTT). Soon thereafter,the 350 ton load was hauled by road tothe ESO La Silla observatory in theAtacama desert, same 600 km north ofSantiago de Chile. Here, at one of thebest astronomical sites on earth, thegiant mechanical puzzle will now be puttagether to form one of the strangesttelescope domes ever seen.

The ND will be mounted in a rotatingbuilding with an unusual octagonalshape. It has been designed to ensuremaximum exposure of the telescape tothe external environment during obser­vation, while protecting the structurefrom strong winds and dust. Further­more, the floor of the building is activelycooled and the temperature in the tele­scope room and in the instrumentrooms is maintained at the level of the The 3.58-m NTT main mirror being polished at Zeiss, Oberkochen, F.R.G.

42