NTT ProgressFigure 2: The NTT building on La Silla (Arch. U. To!omeo).

Since the last issue of the Messenger,the mechanical pre-assembly of theND at INNSE Brescia (Italy) has beencompleted and the electronic hardwareand software integration has started.

Figure 1 shows the telescope struc­ture. The optical elements are beingpolished at Carl Zeiss and completion isexpected by summer 1988. In the mean­time, the primary, secondary and tertiary

mirrors are substituted by steel concretedummies while the telescope enters aphase of functional tests. It is expectedto be shipped to Chile in March 1988.

Major advances have been made inthe sphere of building activities and sitepreparation in the civil engineering workhas begun on La Silla (construction ofroad, concrete base and service annex).The rotating building has been manufac-

tured in Europe and is expected to beshipped to Chile in October 1987.

Figure 2 shows an artist's impressionof the ND building in its future locationon La Silla. The innovative design of thebuilding distinguishes it from the tradi­tional dome structures.

80th building and telescope are man­ufactured in such a way as to facilitatemounting and dismounting. M. Tarenghi

Site Evaluation for the VLT: a Status ReportM. SARAZIN, ESO

The instrumentation for the VLT siteseeing evaluation programme has beenprogressively installed at La Silla andtested there during the course of 1986.Part of it was calibrated during theLassca campaign against various opti­cal measurements made on the La S~lIa

telescopes (The Messenger No. 44).It includes a 35-cm diameter optical

telescope equipped with the differentialmotion monitor, an acoustic sounder(sodar) to probe the atmospheric turbu­lence up to 800 m above the site, ascintillometer which delivers informationabout the turbulence in the high atmos­phere and a local turbulence monitoringsystem using fast temperature and windSpeed sensors. Figure 1: Trailed Sodar, Seeing monitor and contra! raom shelter.

37

N: 26 APRIL 1987

IGHT EEIN· AVERA E: 0.91"

• - WI D 5 T lO M/8

. -

• UNIVERSAL TIME (ha ur)L-----+------:i-----+-------.&------;11O

~.l\l

0

cÜ

u .... !\<ll •"' ....u...~

~ l\l

::I: ~

~....•

ci

.,0

Figure 2: The Seeing monitor telescope.

Figure 3: Paranal contral room.

Figure 4: Example of a Full Width Half Maximum record.

Ouring that time, the cloud cover andwater vapour survey undertaken fouryears ago was continuously confirmingthe superior quality of the Atacama de­sert area and in particular of coastalsummits between Taltal and Antofagas­tao Gerra Paranal was picked up as thebest candidate and after the construc­tion of an access road and the erectionof a 5 metre high tower, measurementscould start in April 1987.

The instruments are gathered at theNorthern edge of the summit (Fig. 1).Assuming that most short-scale varia­tions of seeing quality would be mainlyproduced by boundary layer effects, theacoustic sounder was made easily mov­able to evaluate the suitability of themountain slope for long-baseline 'inter­ferometry. It is also aimed to probe sev­eral closeby summits and establish thetotal housing capacity of the site forother telescopes. It is also of prime in­terest to use the redundancy of theinstruments to check fram time totime that the total seeing measuredat the telescope corresponds to thesum of the three other specialized in­struments.

The type of optical measurements touse for site evaluation has been exten­sively discussed during the meetings ofthe Site Evaluation Working Group in1984-1985 and the best choice formobile instrumentation appeared to bethe differential motion monitor. Such asystem does not need a large telescope,neither a very stable mount and is notsensitive to optical quality, It performs astatistical measure of the wavefrontquality by comparing the local slopes ontwo 5-cm diameter apertures, 20 cmapart. The variations of the slope of thewavefront are responsible for the motionof the star image. The image corre­sponding to each subaperture are phys­ically separated on the intensified GGOdetector, and their relative positions aremeasured in real time at a rate of five10-ms exposures per second. The bet­ter the seeing is, the smaller will be thewavefront distortions and consequentlythe differential motion of the two im­ages.

The telescope (Fig. 2) is placed a fewmetres above graund to escape framgraund turbulence, dust and humanhazards. It works in the open air tominimize self-induced seeing. Apartfram the fine centring of the star in thefinder, the experiment is remotely oper­ated from the control raom (Fig. 3)where the observer checks the tele­scope guiding and is informed everyminute of the seeing variations, as weilas of the local turbulence and thescintillation (measured on the sameobject).

Bright stars less then 30 degrees from

38

the zenith are used, three objects arenecessary to cover a full night. Resultsup to now confirm that, as at La Silla, theseeing may vary much during the nightand from one night to the other. A typi­cal example is presented in Figure 4where the data have been averaged with

MIDAS MemoESO Image Processing Group

1. Application Developments

An optimized digital filter to removecosmic ray events from single CCD ex­posures is being developed in collab­oration with M. Deleuil. The filter locatespossible cosmic ray events and com­pares them with the point spread func­tion to determine the probability of itbeing a cosmic ray. At a given probabili­ty level, pixels effected by such eventscan then be replaced either by a NULLor on interpolated value.

The FITS input/output commands cannow also work directly on disk files. Thismakes it possible to transfer data files inFITS format over a Local Area Networkto workstations which do not have theirown tape unit.

The table file editor, one of the favour­ite commands, has been extended; nowit is possible to create and delete col­umns during the editing session and tosearch for an entry in a given column. Anew command allows the interpolationof data using splines; this command,working both on images and/or tables,complements the capabilities al readyprovided by the rebin operator.

a 5-mn moving window. Due to prob­able seasonal effects, a full year will benecessary to present a preliminaryassessment of the quality of Paranal. Atthe end of July, thanks to the efforts ofthe Paranal team and to the technicalsupport of La Silla, more than 70 % of

The plotting facilities have been furth­er upgraded with some new featuresand commands. The ASSIGN/PLOTcommand has been redefined to make itmore consistent with the other ASSIGNcommands in the system; the old func­tionality of this command has been ta­ken over by a new SEND/PLOT com­mand. Also, some new OVERPLOTcommands have been added. Amongthe new features the most importantones are: the possibility to specifyscales, the support to different linetypes, and the separate manual specifi­cation of the x- and y axis.

2. Communication

The number of computers connectedto the ESO Local Area Network is stead­ily increasing. In order to provide ahomogeneous interface to external insti­tutes a dedicated communication pro­cessor (Bull SPS 7/300) has been pur­chased. This processor is connected tothe ESO network and will act both as agateway to external electronic networksand provide general services to the ESO

the photometric nights had been moni­tored. The unique data base thus cre­ated will also permit a better parametricanalysis and thus a first step towardsthe ultimate goal for flexible scheduling:the prediction of observing condi­tions ...

community such as bulletin boards. Thespecial computer for communicationmakes internal changes to the ESOcomputer systems transparent to exter­nal users and should therefore utilize aneasier communication between ESOand the user community. The implemen­tation of this system has already beenstarted and is expected to be termi­nated in the spring of 1988.

3. MIDAS Hot-Une 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.

Five Nights on a Bare Mountain - an Outsider's Lookat La SillaG. SCHILLING, Utrecht, the Netherlands

The person in front of me is nearlyunrecognizable. In the first place, it isvery dark around uso Secondly, he iscompletely wrapped up in a fur jacket,with a cap around his head. The airtemperature is just below zero, but thatisn't the worst. It's the icy northern windthat blows literally through everything,and that's chilling you to the bone. Theperson's hands are uncovered, becausehe has to write, push buttons, turn dials,etc. His fingers must be frozen to death.He has already been working for about

six hours, and after a short break for asandwich and a cup of coffee, he hasanother six hours to go. This goes on forseveral nights, all of them cold and win­dy. No labour union would tolerate suchsevere working conditions. Neverthe­less, this person doesn't complain. Heloves his work. He is an astronomer. Weare not at the South Pole, but at La Silla,the site of the European Southern Ob­servatory.

Since I am a science journalist ratherthan a professional astronomer, I have

little experience with the way of life at abig observatory. In my home country,the Netherlands, only some small histor­ical observatories exist (apart from theWesterbork Radio Synthesis Telescopeof course), and Dutch astronomers areused to do their observational workabroad. For instance at the EuropeanSouthern Observatory in Chile. TheNetherlands has been a member coun­try of ESO since the establishment ofthe organization in 1962, and alwaysplayed an important roje, not only scien-

39