No. 73 - September 1993

A Message trom the New Editor It is an honourand a pleasure to take on the responsibility of the Editorship ofTHE MESSENGER. The former editors, and in particular Richard West who was editor for two terms (1976-1979 and 1986-1993), made the Messenger an informative and friendly publication. It is therefore clear that no large changes should be brought to the Messenger. However, because of the forthcoming deployment ofthe VLT- VLTI, the ESO observers' community has an increasing need for technical information in all domains: site infrastructure, telescopes, instrumentation and detectors, calibration, data analysis andarchiving. More emphasis will be given to these topics concerning both Paranal and La Silla. The Messenger will also carry articles on the use of the VLT-VLTI for specific astronomical topics. These articles are written byastronomers invited by the Editor to present their views. As before, observational results obtained at La Silla will also be presented. In this area, there will be no attempt at presenting a complete panorama of the observations carried out at ESO, and the numberof articles in the observations section is likely to fluctuate from issue to issue. The mostapparentchange in the look ofthe journal is a division into sections: first the telescopes and instrumentation including detectors. This will be followed byarticles on science with the VLT. Then there will be a section on scientific results obtained at La Silla and a section on otherastronomical news. The last section groups all the announcements of ESO conferences and workshops, some announcements for positions (mostly in the Science Division), the tit/es of the accepted programmes and similar matters. The technical editor of the Messenger remains Kurt Kjär and I look forward to our collaboration in producing the Messenger. Marie-Helene Ulrich email Internet: mulrich eso.org

TELESCOPES AND INSTRUMENTATION

The 8.2-m Primary Mirrors of the VLT R. MUELLER, H. HOENESS, Schott Glaswerke, Mainz, Germany J. ESPIARO, J. PASERI, REOSC, Longjumeau, France P OIERlCKX, ESO

the mirror blank manufacturer, to achieving superb quality. 1. Introduction REOSC, who will polish it and mount its On July 19 at 14:20, Joe was trans­ The 8.2-m Zerodur primary mirrors interfaces. Inspections performed be­ ported to Mainz harbour, a few kilome­ of the VLT telescopes are on their way fore delivery have not only demonstra­ tres away from the SCHOn plant (Fig­ to the observatory. On June 25, the first ted the compliance of the blank with ure 1). At 9 p. m. it was loaded onto the of the four mirror blanks (code name its specifications, but also the perfor­ barge ELDOR. The ELDOR went down Joe Dalton) was delivered by SCHOn, mance of the blank manufacturer in the Rhine to Rotterdam, travelled south to Galais, then up the Seine to Evry after crossing Paris on Friday 23 overnight. On Monday 26 at 10 a. m. it was un­ loaded and placed onto a trailer. The road transport to the REOSG plant started at 0:00 on Tuesday 27 and Joe arrived at REOSG at 02:30 a. m. The container was opened the same day at 14:00'. One of the greatest difficulties in the design of telescopes larger than about 4 01' 5 metres is the manufacturing of the primary mirror blank. The classical de­ sign of a thick and solid mirror would imply enormous masses. First of a long series of problems, the homogeneity of a 200-ton casting is very unlikely to satisfy the stringent requirements ap­ plied to high accuracy optical compo­ nents. Even under the unrealistic assumption that all manufacturing and assembling issues could be solved, an 8-m mirror more than 1 m thick would still deform too much under its own weight. Remember the basic idea: get a surface the size of a small appartment down to sub-micron accuracy, and Figure 1: Joe on its way to Mainz harbour. maintain it. There are three possible diets to get the mass down: reduce its weight, make tial position of the mirror at 150 loca­ of spot images on the GGO. This devia­ it out of segments, 01' get it slim and use tions but aim at providing a force dis­ tion is measured and the wavefront re­ its support to control its shape. The tribution which results in a fully predict­ constructed. The necessary correction three names behind these solutions are: able elastic deformation of the mirror. is translated into a force distribution Palomar, Keck, ND, respectively. How­ With an active mirror, flexibility is used wh ich is applied to the mirror through its ever, in the 8-m range, a Palomar-type to compensate for manufacturing error active support. With active optics the primary mirror still needs some active and for on-line, real-time optimization of frequency of correction is below about control as gravity and thermal loads may the optical properties of the telescope. 1Hz. With its six rings of support the VLT affect the surface accuracy. The effec­ The hydraulic support system is di­ should be able to compensate errors tiveness (with regard to performance vided into three sectors, each of them with spatial frequencies up to about and safety) of very large honeycomb providing a virtual fixed point. Therefore, 1 m-" within an accuracy in the range of structures is still to be proven, while the the axial position and tilt of the mirror is 50 to 100 nm rms, i.e. weil beyond the second 10-m Keck telescope is on its fixed. The actuators interface to the effect of atmospheric turbulence. way, and the ND has al ready provided mirror through axial pads, the geometry On the user's side active optics superb images. Each of the three solu­ of wh ich is a three-Ieg spider. Each leg should be fully automatic, i.e. the only tions has its pros and cons, and the is connected to an invar pad about noticeable effect should be the high trade-off is extremely difficult. There are 50 mm in diameter, wh ich is glued onto quality of the data collected under per­ no miracles, just tremendous efforts to the convex surface. The distribution of manent computerized optimization. Of bring the concepts into operation. the supports has been optimized to pro­ course this situation is quite demanding vide the lowest possible print-through in terms of tuning and reliability, and the on the mirror's surface. Additionally, the concept inevitably requires permanent 2. The Actively Controlled tripods introduce shear forces wh ich re­ maintenance, as any large and complex Meniscus Concept duce local deformations. The residual telescope. On the other side the positive The concept selected by ESO for the error is in the ,J40 rms range, and will be aspects of the active optics concept VLT is an extrapolation of the concept almost totally polished off as the mirrors extend far beyond the potential excel­ demonstrated first with an experimental are figured on their tripods. (See section lence of the optical properties. Indeed it mirror 1 m in diameter and subsequently 4.3, Effectiveness of the FLIP method.) provides far more design and manufac­ with the ND. It consists of a f/1.8, 8.2-m Ouring operation the exact shape of turing perspectives than a passive con­ diameter actively supported Zerodur the mirror will be monitored by Shack­ cept, with positive consequences both meniscus, 175 mm thick. The mirrors Hartmann sensors. These sensors col­ on performance and cost. will be supported axially by 150 hy­ lect the light of an off-axis star to form The fragility of the thin meniscus re­ draulic actuators. These actuators an image of the pupil of the telescope quires particular attention. All supports can be seen as computer-controlled onto a grid of lenses. A GGO camera and auxiliary equipment wh ich will inter­ springs: they do not constrain the spa- records the distribution of the point im­ face to the mirror at one stage 01' the ages provided by the individual micro­ other are designed to keep the probabil­ Ienses. A phase error of the incoming ity of damage under about 10-5 under wavefront would imply a variable incli­ maximum loads. Nevertheless, given I On ESO side the whole process has been exten­ sively recorded by Messrs. Heyer, Madsen and nation of the rays with respect to the the high flexibility of the mirrors and the Zodet. They shall be acknowledged for their ex­ axis of each microlens thus resulting in a highly non-linear relation between dam­ ceptional dedication and efficiency. deviation from the nominal distribution age probability and load parameters

2 (e.g. area of stress fields, magnitude of Table 1. stress, duration, surface finish), trans­ Specifica- Achieve- Parameter port, handling and operation of any tions ment large mirror have to follow strict and rigorous rules. Outer diameter 8200 ± 2 8201.52 mm The mirror itself is made out of a Inner diameter 1000 ± 0.5 999.81 mm highly homogeneous Zerodur sub­ Concentricity 51 0.01 mm 1 strate, with near-zero residual stresses. Thickness 176 + 2-0 177.9 mm 2 Table 1 summarizes the main specifica­ Radius of curvature (concave surface) 28975 28968 mm (convex surface) 28977 289793 mm tions for the mirror blanks, together Profile tolerance (concave surface) 2 0.124 mm with the achievement by SCHOn for (convex surface) 2 0.055 mm the first mirror blank. In many respects Residual stresses (tensile) 50.10 max.0.07 MPa the mirror blank is of exceptional (compressive) 50.60 max.0.08 MPa quality. Coefficient of thermal expansion (mean value) o ± 0.15 -0.043 10-6oK- 1 In addition to the geometrical and (homogeneity) 50.05 0.009 1O-6OK- 1 material properties, the internal quality I Normal to convex suriace, on a diameter of 8160 mm. - 2 Best fitting sphere. - 3 Best fitting sphere. - was specified in terms of maximum • Including the eHect of the 7 mm error on the radius of curvature of the concave suriace. - 5 Including the number of bubbles and inclusions. eHect of the 2 mm error on the radius of curvature of the concex suriace. Again, the result is weil within the specification. The convex surface has two holes (to be compared to 10 allowed), maximum diameter 34.8 mm and maximum depth 40 mm, wh ich re­ specified in such a way that after con­ The issue of matching is less critical sult from the removal of inclusions be­ volution with the atmospheric seeing as weil, as the active support can handle fore ceramization. Local acid etching their effect on the long-exposure image a fairly large error of the conic constant. has been applied and the effect of the will be limited to a maximum decrease Although the option of a pentaprism test holes on stress fields is such that the of 5 % of the peak intensity in stellar on the primary and secondary mirrors probability of breakage is still beyond images, in the visible and with a seeing combination can still be ordered, the 10-5 . angle of 0.4 arcseconds full width at half current strategy for the VLT is to have The optical specifications given to the maximum. It can be easily shown that separate cross-checks performed on optical manufacturer are in line with the the specification ensures simultaneous­ the primary and secondary mirrors. active optics concept and follow the Iy seeing-limited angular resolution and These are direct tests, i.e. they do not formalism developed at ESO to quantify high signal throughput and signal-to­ involve relay lenses which could intro­ optical performance of ground-based noise ratio. duce systematic errors, and they aim at telescopes. A positive consequence of the active ensuring that no significant matching The mirrors will be polished on an optics concept is that it allows the error is left. active support system which interfaces manufacturer to concentrate on high As for any optical component, optical to the tripods. The manufacturer is per­ spatial frequency errors, wh ich have testing is essential as it should ensure mitted to physically remove low spatial usually lower amplitude but much higher that the manufacturing tolerances are frequency errors, provided that he stays slopes and are therefore more detrimen­ fulfilled, and as a proper measurement within the specified budget of ± 120 tal to performance than the low spatial of the surface data (radius of curvature Newton maximum active force. The op­ frequency ones. In other words, an ac­ and conic constant) is requested for the erational performance of the mirrors is tive mirror is likely to be smoother than a calibration of the field aberrations. In­ given by the residual errors after active passive one, and therefore to provide deed, the latter have to be deducted correction. The latter have been better contrast and signal-to-noise ratio. from the off-axis measurement by the wavefront sensors, in order that the ac­ tive system applies the appropriate corrections.

3. Mirror Blanks Large-diameter and medium-thick­ ness menisci are economically manu­ --'- I?'I' ._-.' factured by using the spin casting tech­ ~------nique. This technique was specifically developped by SCHOn in 1986-1987 /"-/ for the production of mirror blanks of the ./ ~./" ./ 8-m class. Contrary to the conventional casting technique, spin casting is able -- to produce a meniscus which ap­ ----- proaches the final shape of the mirror with only small oversizing, thus reduced mass. The meniscus shape is obtained by rotating the mold (wh ich has a spher­ ...... ~..l!<%~/// ical bottom) while the glass is not yet ~ solidified. The spin casting technique has "found another bubble?::J proven successful in the production of several raw blanks of the 8-m class.

3 molten glass from the tank into the cast­ ing mold) to protrude downward from the bottom of the mold. After heating the feeder nose with the help of proper devices, the molten glass flows from the melting tank onto a con­ veyer. Then the mold is progressively low­ ered to keep the feeder nose at a specified distance of the bottom of the casting mold. The discharged glass flow is cut by an appropriate device wh ich allows the casting mold to be filled while it is slowly being lowered. This filling operation lasts approximately 4 hours. After completing the filling operation, the mold is moved from the casting area onto the spinning area with the help of the transfer vehicle.

• Spinning Once the transfer vehicle has been fixed to the spinning unit along with the casting mold, the overhead heating sys­ tem is fastened to and slightly lifted by some hoisting equipment from the cast­ ing mold (Figure 2). This is followed by spinning the casting mold containing the molten glass at a specified rotation rate. A cooling cap is placed above the mold after the concave upper surface of Figura 2: Lifting the overhead heating system. the glass has been produced. The re­ leased radiation energy (20 MW im­ mediately after lifting the heating sys­ tem) is dissipated through the evapora­ After the resolution of start-up prob­ • Pouring of molten glass into the cast­ tion of water. During the spinning phase, lems, several castings could be suc­ ing mold (wh ich has a curved bot­ the molten glass cools down in such a cessfully cooled down to room tempera­ tom). and generation of meniscus by way that the glass surface retains its ture. The subsequent quality inspec­ spinning contour. The spinning process lasts ap­ tions showed that the high requirements • Coarse annealing of vitreous blank to proximately 1 hour. set to the inner quality of ZERODUR are ambient temperature completely fulfilled. • Machining (rough grinding of front All subsequent operations like han­ side, rear and edge) • Annea/ing dling, ceramization and machining were • Transformation into glass ceramic carried out without any problems. The (ceramization) by thermal retreatment After the spinning process, the cast­ first blank is already delivered, and the • Drilling of centre hole ing mold with the raw blank is entered into the annealing furnace. Subsequent­ second blank is currently in the process • Final grinding of being transformed into glass ceram­ The handling and quality controls Iy, the transfer vehicle is moved out and ics in the ceramization furnace. which are necessary between the indi­ the furnace is closed. This is followed by For the spin casting production of vidual production steps are not men­ annealing the vitreous-state raw blank mirror blanks of the 8-m class, all tioned. In the following paragraphs the to ambient temperature. During this pro­ facilities and the respective buildings production process is described in cess, the blank is supported by an were built between June 1989 and some more detail. adaptable support system which follows March 1991. The facilities are entirely the deformation and shrinking of the dedicated to the manufacture of convex surface through the annealing ZERODUR blanks (mirror substrates of • Me/ting process. The annealing period iasts ap­ the 8-m class and smaller blanks of For this purpose, the batch is fed into proximately 3 months. 0.6 m up to 4.4 m in diameter). Produc­ the tank and melted, refined, and subse­ tion structures include new buildings quently homogenized by stirring. A with about 50,000 m3 of enclosed melting cycle lasts 24 days. • Lifting and turn-over space, and modified and enlarged build­ whem• annealing has been completed, ings. the annealing furnace is opened, after • Pouring which the raw blank is lifted from the The casting mold is preheated for casting mold with a vacuum lifter and The main steps ofthe about 2 days, with the overhead heating moved to the turning position by the manufacturing process are: system being lowered. Following this, crane equipment. There it is turned over • Melting of glass in 70-t melting tank the casting mold is lifted to allow the (convex surface up) with the help of the (discontinuous) feeder (platinum tube for feeding the turn-over installation (Figure 3).

4 over the blank again and machining the front side.

• Transformation to a semi­ crystalline state (ceramization) After completing the rough machining the blank is submitted to a thermal after­ treatment in the annealing furnace, which causes the vitreous state to be transformed into a semi-crystalline state. This procedure causes the mate­ rial to acquire its outstanding properties of thermal zero expansion. This crystallization process is exo­ thermic. During crystallization, the vol­ ume shrinks by approximately 3 %. Hence, all efforts should be made to cause crystallization to proceed very slowly, in order to prevent stresses from coming up and leading to the fracture of the disk due to non-controlled crystalli­ Figure 3: Turning the mirrar blank. zation and resultant non-uniform shrink­ age. This is why transformation from the vitreous to the semi-crystalline state During all handling operations, defor­ • Rough machining takes approximately 8 months. mations of the handling equipment During the transformation process, should not be transferred to the blank. After turning over the raw blank, it is the blank is supported by an adaptable Therefore the handling equipment must placed on the support system of the support system within the annealing fur­ have a flexible and adaptable coupling CNC grinding machine. This support nace. to the mirror blank. For this reason hy­ system has a design similar to the de­ draulic cylinders are used. All support sign of the handling equipment. The • Drilling ofthe centre hole and systems are designed in such a way that blank convex surface and edge are final grinding tensile stresses induced in the blank are roughly machined with diamond grind­ kept weil below 1 MPa. ing wheels. This is followed by turning After transformation into a glass

Figure 4: The blank during quality inspection.

5 ceramic, the centre hole is drilled with the CNC grinding machine. The final grinding is also performed on the machine, the accuracy of which is as foliows: Rotating table at 7000 mm diameter: radial (x) runout < 10 ~lm axial (z) runout < 15 ~lm angular positioning < 120 ~lm Positioning in x and z: < 20 ~lm Reproducibility in X and Z < 2 /olm To preserve this accuracy the machine raom has a temperature con­ tral giving spatial temperature homogeneity < ± 1.5°C temporal temperature inertia < ± 1SC/h.

• Qua/ity contro/s Quality controls and acceptance by customers are provided during and be­ Figure 5: The REOSC optical shop. tween the individual production steps (Figure 4). Material characteristics are deter­ 4.1 THE OPTICAL SHOP All this assembly is computer con­ trolled through a unique console. mined by the corporate Service RE­ The new 8-m REOSC shop (Figure 5) SEARCH & OEVELOPMENT. The pro­ was dedicated by the French Minister of jecHied inspection means consist of: Research and Space on April 24, 1992. Po/ishing machine overall geometric testing system This plant is located close to the (theodolite with pracess contraI compu­ The polishing machine (Figure 6) is Seine, in order to optimize the mirror identical to the grinding one but it is not ter), local geometric testing system, ul­ transport. lts total surface is 1100 m2 trasonic thickness gauge system, stress permanently equipped with the milling and its dimensions are: length 70 m, bridge. Furthermore, this machine, 10­ measuring system, video system for width at the tower base 22 m, width of testing and documenting the inner quali­ cated just under the testing tower, is the shop 12.6 m, testing tower height equipped with an axial support of 150 ty. For stress measurements the blank is 32 m. put onto a special quality control pneumatic actuators, each of them is support system that generates extreme­ computer controlled through a Shack Iy low stresses in the blank. Hartmann CCO camera. The force accu­ 4.2 OVERVIEW ON THE TECHNICAL racy delivered by each actuator is better PROCESS FOR FIGURING THE VLT than 2N and this support will be able to • Transfer to transportation system MIRRORS remove physically a large amount of low After final acceptance, the blank is Oue to their huge size and high flexi­ frequency defects. placed onto the transportation system bility, the conventional technique of the The suppport software enables the with the vacuum lifter and the crane. The full sized flexible tool previously used for user to adjust automatically the mirror transportation system (REOSC) is polishing and figuring has been mod­ position and its trim thanks to three assembled beforehand in the produc­ ified in order to obtain a mirrar surface length sensors. This software features tion wing. free of high frequency defects and com­ also the mirror weighting, forces ex­ pliant with the requested aspherical certed by each actuator, mirrar position, etc.... 4. Mirror Figuring and Polishing shape. Thus, the VLT mirrors will be ground On July 25, 1989, REOSC obtained and polished by using tools of adequate 4.3 OVERVIEW OF THE TESTING from ESO the contract for the polishing sizes associated with the REOSC Com­ METHODS of the four VLT mirrors and the following puter Controlled Surfacing (CCS) Pra­ tasks: cess, and axially sustained by a support The testing faci/ities: the tower • design and manufacture of the mirrar which is accurate enough not to bl ur the handling tool and container, mirrar high frequency defects with a As the efficiency of the optical tests • transportation of each VLT mirror large amount of non-axisymmetric low depends on the vibration level, thermal blank fram SCHOn's plant in Mainz frequency defects. stability and on the easiness to pass (Germany) to REOSC's plant, from a polishing run to a testing one, • design, manufacture and assembly REOSC has given particular care in de­ on the mirror of special devices for signing the testing tower wh ich features Grinding machine the mirror fixation in the cell, an external sun shield, a main wall made • grinding, polishing and testing of the The grinding machine is composed of of boarding with a thick lagging, an in­ four VLT mirrors. a ratating table, a removable milling ternal tower totally independent fram One of the governing design drivers in bridge, a couple of two-arm machines the external one, made of a welded this project was the very important flexi­ designed and manufactured according metallic structure which bears a double bility of the VLT mirrors as they feature a to the REOSC requirements and a sim­ walled plastic tent. Thermally contralIed huge diameter of 8.2 m associated to a plified axial support composed of 150 air is inflected between the two walls of very low thickness of only 17.5 cm. pneumatic actuators. this tent. 6 Furthermore, in the testing tower, REOSC has foreseen the possibility to test the matching of a convex mirror associated with a concave mirror by us­ ing the Pentaprism method as already performed for the ESO 3.6-m telescope.

The testing plan Ouring the wh oie surfacing process of the VLT mirrors, the progress of the work is checked by the testing methods summarized in Table 2. The mirror aspherical shape will be generated on the mirror at the rough grinding stage and checked by spherometry. Then the mirror will be moved to the polishing machine located under the tower. Ouring the fine grind­ ing, the mirror surface is tested by IR interferometry. When the mirror surface is smooth enough and about a few mi­ Figure 6: The 8.2-m dummy mirror on the polishing machine, as seen trom the test tower. crons from the requested mirror shape, the polishing and the visible interfero­ metric testing will start. caught in a thousandth of a second with special tripods as interface be­ thanks to the use of an electronic shut­ tween the actuator shaft head and the ter, the disturbing effect of the vibrations mirror, REOSC has figured a Zerodur The spherometer are eliminated. spherical mirror of 1.7 m in diameter, The spherometer body is made of an FLIP is a special software wh ich can 17.5 cm thick and with a radius of curva­ aluminium honeycomb structure. There be used with any interferometer pro­ ture of 28.8 m, the same as the VLT one. are 8 points of measure and about 200 vided it is equipped with a CCO camera This mirror is in fact apart of a whole points of the mirror surface can be and an electronic shutter. REOSC thinks VLT mirror. For the experiment, this test known. The estimated time for perform­ that the FLIP method has the best mirror was resting on seven VLT ac­ ing this measure and processing the money value. tuators, each of them was provided with data is about half an hour. The The interferograms are taken by a tripod. Furthermore, some of them spherometer is carried by the milling batches of 50 units and processed in were equipped with a large dish in order bridge and its position and the position 1 minute for 250 x 250 points with our to compare the residual high frequency of the rotating table are controlled on­ present PC 386 equipped with a frame defects between two kinds of support line by a computerto wh ich are input the graber card, an accelerator card and a for polishing: on the tripod and on the mirror sag measurements. coprocessor. By adding two accelerator dishes. cards, the processing time can be di­ Since the testing tower of the new vided by two. The residual vibrations of plant was not available at the date of Visible interferometry and the Flow the tower combined with the averaging this experiment, the 1.7-m mirror and Interferogram Processing (FLIP) of the results allow the elimination of its support were installed under the The residual vibrations of the tower do irregularities of illumination. REOSC old testing tower of the 4-m not allow the use of the conventional This software delivers the X and Y mirror shop. The light beam was folded phase shift method. The phase method slope error map and the values of the twice. The results obtained with this set­ based on Fourier transforms and the RMS and PN errors, the wavefront error up and the FLIP method are the works of Claude and Franyois Roddier map and the values of the RMS and PN, following: lead to a too long processing time for as weil as the mirror surface profile When the mirror is resting on 7 single averaging a large number of interfero­ when the non-axisymmetric defects points, the measured and computed grams. have been removed. mirror deformations are as shown in In order to overcome this difficulty, The programme is user friendly and it Table 3. REOSC has developed a new algorithm is now currently used in REOSC's opti­ There is a perfect correlation between which allows quick computing of the cal shop. the experiment and the FE computation. phase from only ONE interferogram In order to evaluate the FLIP ability to which must present about 80 fringes detect minute defects among larger Effectiveness ofthe FLIP method inclined at 45° if a CCO camera of ones, we have compared the results 250 x 250 pixels is used for an 8-m In order to test the effectiveness of obtained by finite elements computation mirror. Furthermore, as an image can be the VLT axial support when it is provided and FLIP measurements when the mirror is resting on the tripods. The mirror figure obtained by interfer­ Table2 ometry is the averaging of a batch of 50 Manufacturing Number Absolute Sensitive- Tower interferograms taken by the FLIP Test stage of points accuracy ness PIV requested method to wh ich we have substracted the 1.7-m mirror figure (see Table 4). Rough grinding Spherometry 198 5000 nm 1000nm No The conclusion is that the finite ele­ Fine grinding IR tnterferometry 2000 500nm 300nm Yes ments results are very close to the ex­ Polishing, final figuring FLIP method 250x250 5nm 5nm Yes perimental ones. The difference in the

7 Table3 5. Conclusion Interferometry Computation Joe Dalton was delivered in time and weil within specifications. It is now Iying PIV RMS PIV RMS on the grinding machine at REOSC, Mirror surface 148nm 24 nm 107nm 25nm where everything is ready for the next steps: glueing of the axial interfaces (in August 1993). followed by the exciting PN values comes from the presence in batches of fifty interferograms of the tasks of grinding it aspherical to a few the laser beam of some artefacts wh ich mirror resting on the tripods. The RMS microns accuracy. and then polishing to generate a few local sharp defects. error on the mirror surface error is optical accuracy. Looking forward to It is worth noting that the RMS value 5.6 nm. meeting Bill, William and Averell! of the high frequency defects generated by the axial support is three times lower when the mirror is resting on the tripods. Table4. This factor of three is in very good Interferometry Computation agreement with the computation. In order to evaluate the noise of the PIV RMS PIV RMS measurements. we have computed the Mirror surface 59nm 7.3 nm 37nm 8nm difference between the average of three

Ground-Based Astronomy in the 10 and 20 !lm Atmospheric Windows at ESO - Scientific Potential at Present and in the Future H. u. KÄUFL, ESO

1. Introduction This article is especially written for rotational-vibrational transitions of trace frared astronomical observations are those who have little or no experience moleeules (e.g. CO2,H20, CH 4 , 0 3), In constrained to: with astronomical observations in the in­ some spectral regions these molecular • A= 8-13 ~lm with very good condi­ frared, especially longwards of 2.2 ~lm. transitions blend creating a practically tions In recent issues of the Messenger opaque sky. The region between 8 and • A= 16.5-30 ~m with reasonable to (Käufl et al. 1992, Käufl 1993) there 13 ~m, however, is reasonably free of poor conditions were several reports on instrumentation interfering molecular transitions. Re­ at ESO for observations in the 10 and maining absorption lines in the window 2.2 Wien's Law, Kirchhoff's Law 20 ~m atmospheric windows (N and Q itself and at the "red" edge are rather and their consequences band in Johnson's photometrie system). stable and observations can be easily In this article a description of the per­ corrected for these perturbations. On Wien's law relates the maximum of spectives of ground-based astronomy the "blue" edge H20 is a source of vari­ the Planck curve for black body radia­ in these windows will be given. A special able opacity following the rapid varia­ tion with its temperature focus is set on the astronomical applica­ tions of local humidity. Close to this tions with respect to what is possible edge more careful observing proce­ A = 2898!lm max T[K] (and what not) with the present equip­ dures are required. Beyond = 13.3 ~lm ment; wh ich improvements are antici­ the atmosphere becomes opaque due For a telescope at ambient tempera­ pated at the VLT and how these obser­ to the \/2-band of CO and opens again 2 ture )'max lies exactly in the centre of the vations compare to air-borne and around 16.5 ~m. A forest of lines of H 20. 10 ~lm atmospheric window. Translated space-based infrared astronomy. however. prevents the sky from getting into the words of optical astronomy this clear so that even in the best part of the is equivalent to observing stars from 20 ~m window the average opacity more 2. Targets tor Ground-based within a furnace (Iike the one in wh ich Intrared Observations at or less corresponds to 50 % and is vari­ the VLT blanks have been casted) rather able. Beyond 20 ~m the water vapour Wavelengths longer than 5 f-lm 1 than from a dark astronomical site. lines become a real problem. The term To those readers not familiar with in­ 2.1 Atmospheric constraints "Q-window" is misleading and should frared astronomy it is also useful to re­ be replaced by "Q-venetian-blind". De­ call Kirchhoff's law The terrestrial atmosphere has a sub­ pending on site and local weather, lim­ stantial opacity in the infrared due to ited astronomical observations are pos­ a(A, T) = e(}., T) sible up to 30-35 ~m. Beyond =35 ~m the atmosphere remains opaque until wh ich states that for all wavelengths and 1 Some of the argumentation holds also for the the sub-millimetre region (~ 300~lm) is temperatures the emissivity equals ex­ range of 3-5flm. This transition region between the near infrared and the thermal infrared, how­ reached. actly the absorptivity. For ground-based ever. is outside the scope of this article. In conclusion, long wavelength in- infrared astronomy this means that e.g. a 8 change in opacity from 5 % to 20 % has tronomy. Usually these dust shells pro­ resolved. In AGB objects the molecular the minor effect of reducing the signal by vide for a "calorimeter" which allows to spectra tend to originate from the region = 16 % but increases the background determine bolometric fluxes from the in­ where the dust formation and the accel­ radiation level by a factor of 4. tegrated infrared radiation with very little eration of the outflowing material to its Typical background generated sig­ uncertainties. It is also in many of these terminal velocity takes place. Dust and nals at 10 ~lm are of the order of 1010 objects (especially stars on the 6symp­ parent molecules can be observed electrons/pixel, equivalent to a mag­ totic §iant .!2.ranch, AGB) where the dust simultaneously. Radio observations, on nitude mN = -2.50 (for details of back­ is actually being produced. While the the contrary, are usually restricted to ground noise limited operation see e.g. physics of the mass-Ioss of these ob­ rotational transitions in the vibrational H.U. Käufl et al. 1991). In spite of the jects is poorly understood (see e.g. the ground state and thus to cold material in high background it can be expected review paper by Lafon and Berruyer, regions where the dust formation is (based on experience with today's in­ 1991) it is now clear that they are of completed and the material has been strumentation) that a limiting magnitude some importance for galactic evolution, accelerated to its terminal velocity. Typi­ at N of the order of 12 will be achievable since all stars having main-sequence cal linewidths are of the order of the with ESO's VLT, i.e. 14.5 magnitl:ldes masses :5 8 MG will follow the track sound-speed. The spectral resolution fainter than the background. from a red giant via the AGB to a Planet­ should match this, i.e. approach the At this point the reader may ask the ary Nebula, leaving a white dwarf as km/s realm. question: why bother to try to observe compact remnant and returning the rest Two of the three lowest energy quad­ under such conditions at all? Part of the of the mass to the interstellar medium. rupole transitions of molecular hydrogen answer is again Wien's law: if one wants The 2nd ESO/CTIO workshop held in La in the vibrational ground state (H2 (0,0) to study radiation from the cold universe Serena in 1992 was also entirely de­ S (2) at 12.38~m and H2 (0,0) S (1) at one cannot do it at short wavelengths. voted to this topic (proceedings edited 17.03 ~lm) are observable from ground­ For objects colder than 500 K the radia­ by H.E. Schwarz, now available from based telescopes. Since they are par­ tion is best (I.e. with the highest signal to ESO). Dust is of course also of extreme tially overlapping with telluric lines such noise ratio) detected at wavelengths interest in the context of young stars observations require a spectral resolu­ around 10~lm. Also many objects (most and star formation, especially of low tion high enough to discriminate against stars, galaxies and aSOs) tend to have mass stars. This ranges from Herbig­ the atmosphere, regardless of their in­ mv - mN > O. Usually, however, this is Haro type objects to circumstellar disks strinsic line width. not quite sufficient to outweigh the in young stars. Arecent highlight in this background induced loss in sensitivity context: sub-arcsec spatial resolution 2.5 Ions and atoms compared to visible wavelengths. There 10 ~m images of the disk of ß-Pictoris is, however, a substantial number of in­ obtained with TIMMI at ESO's 3.6-m A variety of atomic lines are acces­ frared bright but obscured sources with telescope (P.O. Lagage, private com­ sible for ground-based observations in mv - mN = 15 to 25. In some of these munication). the 10 and 20 ~m atmospheric win­ cases it is not even sure if the light at V is The PAHs - normally too cold to be dows. Those include normal hydrogen radiation from the object itself or just detectable - are small enough that the recombination lines (H 1(7-6) at 12.36 ~m scattering of interstellar light on the energy of single UV photons hitting or HI (9-7) at 11.30 ~m) and forbidden dust-shell. them raises their temperature to typical­ lines (e.g. [FV] at 13.4~lm, [Nil] at Iy 1000K. The PAHs then cool via their 12.79~m, [NaiV] at 9.04 and 21.3~m, well-known molecular vibrations giving [PIII] at 17.87~lm, [Sill] at 18.68~lm, 2.3 On the scientific interest in dust2 rise to several strong features in the [SIV] at 10.52~m, [CIIV] at 11.76 and By now it is weil known that there is a 10~lm atmospheric window. 20.37~m, [Ar 111] at 8.99 and 21.84~m, lot of dust in the universe wh ich comes The spectroscopic observation of dust [ArV] at 13.07~lm, [KVI] at 8.84~m and in all grain sizes, basically from macro­ in the 10 ~lm atmospheric window is best [CaV] at 11.47~m, for more details as scopic grains to aggregates of several done with a resolution ~\. = 300 because weil as a discussion on the formation of 100 atoms (e.g. the .EolY6romatic ]jy­ only this resolution allows for an unam­ these lines in H 11 regions see e.g. the drocarbonates, PAH). Working at A ;=: biguous discrimination of broad solid­ original article by Simpson 1975). Many 2.2 ~m allows one to actually penetrate state dust features, narrow PAH-tran­ of these lines have al ready been utilized dust aggregations. For a nice example sitions and very narrow emission lines. to assess physical conditions of ionized see e.g. the article by Peletier and Kna­ materials while others still await their pen (1992) who compare V and K im­ discovery in the interstellar medium. Of 2.4 Moleeules ages of the edge-on galaxy NGC 7814. extreme interest for quantitative model­ The strong dust-Iane apparent in the V Many molecules of astrophysical im­ ling in this context is that extinction ~m. image is fairly transparent at 2.2 Ob­ portance (e.g. SiO, CO2 , C2 H2 , C2 H4 , corrections are much simpler or even servation of the dust itself (e.g. to study C2 H6 , SiH 4 or NH3) have rotational-vibra­ not required at all, since most objects its chemical composition) is governed tional transitions between 8 and 13 ~m are practically optically thin at ), = 10 ­ by Wien's law and much of the dust is creating absorption lines in spectra of 20 ~lm. For a very recent example see simply too cold to be observable in cool stars. These spectra contain practi­ e.g. Jennings et al. (1993) who report the infrared, even at the longest cally all information on chemistry and fully resolved spectra of [Co 11] at wavelengths accessible from the physical conditions of photospheres 10.52~m, [Nil] at 11.31 ~lm and [Fell] at ground. But there exist interesting ex­ and circumstellar envelopes. Depending 17.94~lm in SN 1987A, 612 days after ceptions: compact objects and PAHs. on quality (noise, resolution) such spec­ outburst. Many objects are sufficiently compact tra allow to retrieve much of this infor­ Since typical intrinsic linewidths are of so that the dust is hot enough to be mation. Molecular spectra usually form the order of 10-30 km/s they can be observable with ground-based IR as- bands wh ich allow to select "strategic" observed with maximum sensitivity if portions containing transitions sensitive one uses a spectrograph wh ich just not to temperature and/or gradients and resolves these lines. At a spectral reso­

2 This is not al all complete, just a couple 01 ex­ with optical depths close to unity. lution exceeding = 20 km/s kinematic amples. Isotopic shifts of transitions are easily studies inside of objects opaque for visi-

9 ble light become possible. Observing sources and especially on extended copic mode in TIMMI will be done using such lines in external galaxies requires sources at 10 f.lm can only be achieved grisms. These grisms need the grating highest sensitivity and therefore is best with cryogenic telescopes from space; structure to be machined directly into the done with aresolution matching the typ­ but space-based infrared observing base prism material (e.g. Germanium). ical velocity dispersion inside the field of platforms are like apparitions of bright Such devices are not easily available view of one pixel (i.e. resolutions be­ comets: they are rare and short transient commercially. ESO has a contract with tween 10 and 500 km/s are required). things (e.g. 18 months for the case of the Institut für Festkörpertechnologie, ISO). Any form of synoptic observations München, of the Fraunhofer Gesellschaft (e.g. bolometric light curve of aMira) are to produce such prisms. Once they are 2.6 Magnetic fields virtually excluded. Also observations re­ available they can immediately be built The ratio of Zeeman-splitting to Dop­ quiring sub-arcsec spatial resolution into TIMMI to provide for the spectros­ pler-width for atomic lines increases (and consequently telescopes larger copic mode. TIMMI works today with a linearly with the wavelength of observa­ than 4 m) can only be done from ground. 64 x 64-element detector (gallium doped tions, i.e. Zeeman-splitting of lines at In addition, as a rule of the thumb, the silicon) produced by LETI/L1R of Greno­ 10f.lm is 20 times larger than at 0.5f.lm. higher the spectral resolution the less it ble/France. At this laboratory there is, Brault and Noyes (1983) observed and is advantageous to observe from space. also with ESO participation, a new de­ identified for the first time such Zeeman In that sense the working group on in­ vi ce under development wh ich will have splitting of transitions of Mg I at 12 f.lm in frared aspects for the VLT also recom­ both a substantially higher quantum-effi­ 3 solar spectra. Deming at al. (1988) used mended to equip the VLT with in­ ciency and format . Since this new de­ these lines to map with arcsec spatial strumentation wh ich complements the tector will be basically pin-compatible resolution magnetic fields around sun­ performance of space observations (c.f. with the one presently in use in TIMMI, an spots. Applying such techniques on Moorwood, 1986). At this point I would upgrade with this device is feasible. other stars so far is quite difficult be­ also like to add the advice: do not wait While all modes will benefit substantially cause of a lack of suitable instrumenta­ for the VLT. In the following chapters I from the increase in quantum-efficiency tion on large enough telescopes. will describe what is available at ESO and better sampling, the device would now or in the near future and what is also allow to increase the spectral reso­ planned to be available at the VLT. lution for grism spectroscopy to \. "" 3. State ot the Art, 500-600 with 2-pixel sampling per spec­ Now and in the Near Future 3.3 TIMMI, ESO's 10pm Camera/ tral element. Spectrometer 3.1 The IRAS database Recently ESO has complemented its With the publication of the IRAS cata­ 4. Present Plans at ESO tor the 10 suite of infrared instrumentation (the logues a great wealth of precise high and 20 ~m Atmospheric Win­ photometers/bolometers at the 1-m, quality data readily accessible to non­ dow at the VLT 2.2-m and 3.6-m telescopes, IRSPEC, specialists became available to the as­ the 1-5~lm medium resolution spectro­ tronomical community. Thus the scien­ 4. 1 VLT specific aspects graph at the ND, and IRAC2, the 1­ tific value of infrared astronomy became 2.5f.lm near-infrared camera at the Great care is being taken in the VLT recognized in a much broader commun­ 2.2-m telescope) by adding TIMMI (see design to preserve the intrinsic quality of ity than was reached in the pioneering e.g. Käufl et al. 1992 for a detailed de­ the site (Paranal). The design ensures days. Still the IRAS mission had its limi­ scription of the instrument). While this good performance in the infrared (pupil tations: camera has been first offered on a on M2 for a field of up to 3 arcmin, no • being largely a survey-type mission shared risk basis in period 52, ESO has baffles, in-situ mirror cleaning and the sensitivity is not extremely high: already received 24 observing propos­ washing, emissivity at Cassegrain "" 250-1000 mJy at 10-20f.lm (for point ais asking for a total of 85 nights. TIMMI 6 % and provision of a chopping secon­ sourees; equiv. mN = 3.9-5.3, ma = will now be mounted for 2 (out of 6 dary). 2.5-4.0) available) full moon periods in the com­ Extrapolating the Paranal seeing mea­ • spatial resolution is Iimited ("" 25 ing semester. The proposals cover a surements at 500 nm to A"" 10~lm using arcsec) great variety of topics: solar system, Kolmogorov-Taylor theory yields a • spectroscopic data are only available stars (young, old, circumstellar disks, monthly averaged seeing between 0.3 for the brightest sources while the outflow), interstellar medium and galax­ and 0.5 arcsec, i.e. close to the diffrac­ spectral resolution of \; "" 25 allows ies. They involve broad- and narrow­ tion limit of the VLT (1.22b = 0.3 arcsec only for rather restricted investiga­ band imaging and mostly rely on sub­ at 10f.lm at the VLT). According to mea­ tions/conclusions. arcsecond resolution which is only pos­ surements done with a 10f.lm inter­ Just for comparison it should be noted sible from a good 3-4-m-class ground­ ferometer (Bester et al. 1992), this is a that in the 10 ~lm window a bolometer at based telescope. A further increase of conservative extrapolation. Thus the the ESO 1-m telescope would allow for the demand is expected on ce the spec­ spatial resolution will always be close to deeper photometry. troscopic mode ie.\ "" 300, 1-pixel diffraction limited. This image quality sampling in long slit mode) of the cam­ also ensures that unresolved sources 3.2 00 not wait for ISO era is implemented. It should be noted can be observed "" 25 times faster with that there are more than 10 similar cam­ the VLT than with the 3.6-m telescope. "This star is not in the IRAS catalogue, era projects under way or already in use With its fairly dry atmosphere (precipit­ so we have to wait for ISO to settle this worldwide. Still TIMMI is to the best of able H 0 less than 2 mm for half of the question" (quote from a colloquium 2 our knowledge the only system available time in southern winter) Paranal is a speaker at ESO). This is just one exam­ without restrietions to visiting as­ substantial improvement for working at pie of the widely spread belief that tronomers. 20 f.lm when compared to La Silla. follow-up observations in the infrared at long wavelengths need to wait for ISO 3.4 Potential upgrades ofTIMMI (the ESA Infrared Space Observatory). 3 In a lortheoming issue 01 the Messenger there will Clearly ultimate sensitivity on point The implementation of the spectros- be a status report of this projeet. 10 4.2 Anticipated operating modes of the 10/20~lm instrument at the M5~ VLT ; L2 I According to ESO's instrumentation Intermediate plan for the VLT (see e.g. S. D'Odorico, pupil 1992) the Cassegrain focus of unit tele­ scope 2 will carry a dedicated 10/20flm multi-purpose instrument. Installation and commissioning of the instrument is presently scheduled for the second half of 1999. The following operating modes have been identified as the minimum to be implemented to match most scien­ tific objectives addressed above, both for galactic and extragalactic as­ M4 tronomy: • diffraction limited imaging in the 1 N-band with variable magnification Ml for fields as large as 80 x 80 arcsec T with a suite of filters (incl. potentially fixed-spacer Fabry-Perot etalons) • diffraction limited imaging for the part of the Q-band accessible with Ga:Si detectors (16.5 to 17.8 flm) • long slit4 spectroscopy at 7.9-14 flm with - .~i. = 300 - 500 (i.e. covering the entire band in 'one shot') - u~ = 7000 - limited access in spectroscopy to the 16.5-17.8J.lm region at ~,. ~ 3000 additional (optional) observing modes which would be highly desirable: 200mm • high resolution (i.e. 1;;. = 30,000 ­ 50,000, potentially as high as M2 100,000) long-slit spectroscopy mode for 10 J.lm • long slit spectroscopy mode for most of the Q-band (J}. = 3000 at = 17-24flm) Optical Design ofthe 10/20pm Camera/Spectrometer: The instrument is shown in its spectros­ This instrument shall be manufac­ copy mode utilizing the anamorphic beam-expansion for highest resolution (\\ = 30 - 45000, tured by a consortium of institutes in the diffr. limited). The flat entrance window is omitted. M 1 is a cylindrical and M 2 a toroidal mirror. ESO member states. A study contract Whereas the 2-mirror collimator produces a circular beam (diameter = 50 mm) this is changed has been awarded to a team led by PO. to an elliptical beam of 50 x 166 mm 2 by the Germanium prism operating close to the Brewster Lagage at the Service d'Astrophysique angle. Even if no suitable coating for the grazing incidence into Germanium can be found still of CEN-Saclay (France)5. After comple­ an overall efficiency of collimator plus grating exceeding 40 % can be achieved. In the normal tion of the study the operating modes spectroscopy mode the expansion prism will be replaced bya folding mirror which sends the beam to a standard grating uni!. M 3 is a folding mirror. Behind M 3 the intermediate spectrum may be revised. is formed which could be diverted by another kinematic folding mirror (not shown) to feed a dedicated spectroscopic camera for the 20pm atmospheric window. 4.4 Possible embodiments M 4 (kinematic mirror) allows to select between the camera mode (dotted position) and the long slit spectroscopy mode. L 1 is the camera collimator lens (Germanium, f =268 mm, f # = In order to define the scope of the 13.4) which forms an intermediate pupil of20 mm diameter behind the folding mirror M 5. This above-mentioned study contract, pre­ is also the location ofthe filter wheel. L 2 (mounted to a lens wheel) is one of the camera lenses. ec designs were made internally at ESO Shown here is the most critical lens (scale of 6 a't.-'!n ). To achieve background noise limited resulting in two proposals: performance all components before the pupil stop have to be cooled below = 70 K, pupil stop, filter and lens wheel have to be cooled below = SOKo •A dedicated concept for a 10/20 flm instrument taking full advantage of the relaxed optical requirements in the infrared (Käufl and Delabre, 1992). a comparatively moderate size and ment most of the above-defined ob­ All observing modes sketched above complexity. Figure 1 shows this in­ serving modes. Only the implementa­ are feasible with generally close to strument in its high-resolution spec­ tion of high-resolution spectroscopy optimum performance while retaining troscopic mode. needs further studies. • The opto-mechanical concept of The final embodiment will depend on ISAAC, the corresponding instrument the result of the study. The ESO-internal 4 A slil lenglh of lhe order of 30-40 arcsec is for the near-infrared (for a description dedicated design will be used for the considered sufficient. 5 See also The Messenger. 72. p. 44 for some see e.g. Moorwood, 1992), lends it­ sensitivity/performance estimates in the background. self to an easy modification to imple- following chapter.

11 4.5 Sensitivity ofsuch an instrument continuum is of the order of 60 mJansky perform space-based or air-borne ob­ at A = 10urn in an astronornical (7.0 mag) or 2 x 10-18 w, for emission serving platforms. The sensitivity in­ S context ' lines. Galactic PNs (e.g. NCG 7009 or IC crease of such an instrument at the VLT 418) would be observable at 300 to 400 as compared to a 4-m class telescope Broad Band Imaging: The limiting times their distance which will enhance will be substantial and give astronomers flux is expected to be 5.4 x 10-4 Jansky the research capabilities on PNs in the a wide access to objects in the (i.e. 12.1 mag). Operating at the diffrac­ Magellanic Clouds substantially. For Magellanic Clouds for programmes tion limit of the VLT (i.e. 0.33" at lO~m) compact sources, the instrument when wh ich today are restricted to few bright this instrument will allow to image any compared to the IRAS spectroscopic stars (also due to lack of suitable focal celestial object exceeding a brightness channel, will have a 200 times higher plane instrumentation). A big boost is temperature of 90 K, irrespective of its = spectral resolution, will be 100 times especially expected for stars in their distance as long as it is spatially re­ more sensitive and provide 0.3" spatial early and late stages of evolution. In­ solved. For point sources this instru­ resolution along the slit. As e.g. the QSO frared spectroscopy at spectral resolu­ ment will be 3 orders of magnitude = 3C273 exceeds the limiting flux by a tions approaching photospheric sound more sensitive than the IRAS point factor of 8, extragalactic work at this speeds which today are rarely done and source catalogue. spectral resolution even up to cosmo­ restricted to the few brightest stars will Narrow Band Imaging: At a spectral logical distances will become possible. become possible for several 10000 resolution of ~'i 100 the limiting line­ = High Resolution Long Slit Spec­ stars, thus allowing the systematic integrated flux for ionic lines (e.g. [Arlll], troscopy: The limiting flux averaged study of sampies selected with coherent [Ne 11], [SIV] will be 1.3 10-17 ~, per = over one pixel could be of the order of criteria. It is also expected that this in­ 0.3 x 0.3 arcsec pixel. This implies that 300 to 500 mJansky. For point sources strument will contribute enormously to galactic Planetary Nebulae such as this implies that most sources in the research, where a multi-wavelength ap­ NGC 7009 or IC 418 would be detect­ IRAS point source catalogue are bright proach is required or beneficial, e.g. in able up to typically their 150-fold dis­ enough to be detected with a ~ 2: 10 the study of winds in hot stars, Planetary tance, Le. 75 kpc. If the size of = within one hour. This will provide new Nebulae, Herbig-Haro objects or other the intermediate pupil is chosen to be insight into the kinematic and physical forms of low-mass star formation. 20 mm, monochromatic images for a = structure of optically thick or obscured field of 30" with a spectral resolution as compact ionized objects. In stars high as 300 are feasible for selected molecular transitions or Zeeman-sensi­ transitions. Because of the better References tive hydrogen-like metal lines can be background rejection the sensitivity studied with this mode. Particularly in­ M. Bester, W.C. Danchi, C.G. Degiacomi, L.J. limits would then be a factor 3 fainter. Greenhili, C.H. Townes: Astrophysical teresting is also that many Asymptotic Low Resolution Long Slit Spectros­ Journal, 392, p. 357, 1992. Giant Branch objects known in our J.w. Brault, Noyes R.w.: Astrophysical Jour­ copy: In this mode the entire 10~m win­ Galaxy could be observed at LMC/SMC nal Leiters, 269, L61, 1983. dow could be observed in one inte­ distances thus providing for a coherent D. Deming, R.J. Boyle, D.E. Jennings, G. gration with .~i 300-500 to study dust Wiedemann: Astrophysical Journal 333, = sampie of AGB stars where physics of (temperature, composition) and to sur­ p. 978 (1988). mass loss and dust formation could be S. D'Odorico: 1992, proceedings ot the ESO vey emission lines. The limiting con­ studied in an unprecedented way. conterence on Progress in Telescope and tinuum flux for this mode will be 8.7 Instrumentation Technologies, p. 557, M.­ Imaging in the 16.5 to 17.8-~m mJansky (9.0 mag). Spectroscopy of ty­ H. Ulrich editor. passband: It can be expected to reach pical galactic C stars or OH stars will be D.E. Jennings, R.J. Boyle, G.R. Wiedemann, a limiting flux of 13mJy (mo = 7) for this S.H. Moseley: Astrophysical Journal 408 possible even if they were located at mode on point sources. This would ex­ p.277, 1993. distances of 500 to 1000 kpc. Many H.U. Käutl, P. Bouchet, A. van Dijsseldonk, U. ceed the sensitivity of the IRAS 25~lm extragalactic sources are exceeding Weilenmann: Experimental Astronomy 2, channel for point sources with a flat that limiting flux (e.g. the QSO 3C48 at z 1991, p. 115. spectrum by a factor of 10-20. E.g. the H. U. Käutl, B. Delabre: 1992, proceedings ot 0.4 is 8 times brighter than the limiting = above-mentioned QSO 3C48 is 50 % the ESO conterence on Progress in Tele­ flux given above). While 10 ~m spectros­ brighter than the limiting flux. For many scope and Instrumentation Technologies, copy of QSOs will certainly be restricted p. 597, M.-H. Ulrich editor. sources this channel can thus provide to few bright quasars, these spectra will H.U. Käutl, R. Jouan, P.O. Lagage, P. Masse, extremely valuable photometric infor­ P. Mestreau, A. Tarrius: The Messenger, be of extreme interest because they will mation to judge the bolometric 70, 1992, p. 67. allow to study dust (temperature, com­ luminosities. H.U. Käutl, 1993, The Messenger 72, p. 42. position) in these objects and the red­ H.U. Käutl, R. Jouan, P.O. Lagage, P. Masse, Performance in other parts of the Q­ shift will move a variety of interesting P. Mestreau, A. Tarrius: 1993, Infrared band is difficult to judge since one lacks Physics, special issue on CIRP V, in press. atomic emission lines into the observ­ a precise knowledge or models of the J.-P.J. Laton, N. Berruyer: Astron. Astrophys. able window. atmospheric spectrum at the VLT site. Rev. 2, 1991, p. 249. Medium Resolution Long Slit Spec­ P.O. Lagage, R. Jouan, P. Masse, P. Mes­ Furthermore, little is known about de­ troscopy: This mode allows for the ob­ treau, A. Tarrius, H.U. Käutl, 1993, Pro­ tectors wh ich could be available to ESO ceedings SPIE Cont.: Infrared Detectors servation of atomic and ionic emission to be used for this window. and Instrumentation, Orlando, USA, Apnl lines combining highest sensitivity and 1993, Vol 1946 (in press). spectrophotometric precision. Limited 5. Conclusions and Outlook A. Moorwood: "Working Group Report on molecular spectroscopy will be feasible. Infrared Aspects" in proc. ot 2nd Work­ It has been demonstrated that a dedi­ shop on ESO's Very Large Telescope, p. The Iimiting flux for sources emitting a cated 10/20~lm instrument at ESO's 55-82, S. D'Odorico and J.-P. Swings VLT, located on Paranal, certainly an editors, 1986. A. Moorwood: 1992, proceedings ot the ESO 6 Assumptions for sensitivity calculations: excellent site for IR astronomy, will allow conterence on Progress in Telescope and Background !:!mited !::erformance, quantum eHi­ to investigate a significant amount of Instrumentation Technologies, p. 567, M.­ Ciency 30 %, emissivity of sky and telescope 20 % scientific objectives ranging from the H. Ulrich editor. at 273K, transmission of filters 80%, grating eff. solar system to cosmological distances. R.F. Peletier, J.H. Knapen: 1992, The 80 % tor medium resolution and 50 % for high Messenger 70, p. 57. resolution mode. The limiting f1uxes are always tor In the passbands set by the terrestrial J.P. Simpson: Astron. Astrophys. 39, 1975, a ~ ot 10 II in 1 hour in the brightest pixel. atmosphere, it will in many respects out- p.43. 12 On the Linearity of ESO CCD # 9 at CAT + CES E. GOSSETand P MAGAIN, Institut d'Astrophysique, Universite de Liege, Belgium

1. Introduction The Coude Echelle Spectrograph analysis, to complicated, pernlclous ticular, we waited for the lamp to (CES) is the main facility at ESO for effects related to vignetting or, alterna­ stabilize and the shortest exposure time doing high resolution, high signal-to­ tively, to diffuse light in the spectro­ was chosen to be 5 s in order to avoid noise spectroscopy. The amount and graph. possible problems linked to the preci­ quality of the work done with it clearly Recently, Magain et al. (1992) re­ sion of the shutter at tao short ex­ show its great interest. Reaching such ported problems in the reduction of their posures. In addition, the sequence of high resolution (AIf:1.).. 50,000­ data, including a clear non linearity of exposure times is first decreasing and 100,000) with a conveniently high sig­ CCO#5. Shortly after, J. Surdej, J.P. then increasing in order to check the nal-to-noise ratio would have been Swings and A. Smette took the oppor­ stability of the flat-field lamp. We nearly unfeasible without the availability tunity of an observing run to perform adopted the following sequence: of efficient silicon detectors such as the extensive tests on the CCO#8 mounted 3x140s, 3x120s, 3x100s, 3x80s, CCOs. An RCA SIO 006 EX High Resolu­ at the 2.2-m telescape, wh ich led to the 3x60 s, 3x40 s, 3x20 s, 3x5 s, tion CCO (ESO number 9) is equipping discovery of strang problems. At the 3x10s, 2x30s, 2x50s, 2x70s, the short camera (SC) since 1987, and same time, one of us (E.G.) was observ­ 2x90s, 2x110s, 1x130s (the se­ has equipped the lang one (in alter­ ing with the CAT. Following a telephone quence had been abruptly interrupted nance with the Reticon) from 1987 to conversation with J. Surdej and A. by a switch-off of the remote control line 1992. The CCOs have, compared to old­ Smette, E.G. decided to conduct similar from La Silla). These exposures allow to er detectors (e.g. the photographic tests on CCO#9 in order to further in­ explore the response curve up to 10,000 plates), several advantages such as vestigate the question. After all, al­ AOU. their high quantum efficiency and their though the idea of the existence of non­ The first method (M1) we used to linearity. The linearity is normally better linearities in ESO CCOs could appear as analyse the data is based on the hy­ than 1 per cent, sometimes reaching heresy, a mere lack of linearity would pothesis that the flux rate is constant. If 0.1 per cent, in particular for an RCA naturally explain, at least qualitatively, Fis the received flux integrated over the CCO (McLean, 1989). This latter proper­ all the above-mentioned problems. In­ exposure time f:1. t, then the flux rate FI t ty greatly facilitates the reduction of the deed, quite recently (however not inde­ is independent of the exposure time. If, data while making it more precise. The pendently), Schwarz and Abbott (1993) in addition, the CCO is linear, the ob­ idea that CCOs are linear is so common reported the actual existence of such served flux f should share the same and the manuals are so much dwelling problems. propertyfff:1.t=con~a~. on that, that it became an every day First, a mean bias was subtracted unquestionable evidence. from each flat field exposure. Then, 3 2. Test of the Linearity of CCD # 9 In the course of the reduction of their areas were defined on the CCO (they are data, both authors of the present article At the end of the night 01-02/03/92, given in Table 1) so that the spatiai had sometimes the feeling that some­ we acquired a sequence of triplets and variation of the flux inside them was thing went wrang. A few facts, noticed pairs of internal flat fields with the CES minimal. The observed flux rate fl t is by several users, hinted towards a prob­ in the configuration SC + CCO#9. This plotted in Figure 1 as a function of f. For lem with that instrument: corresponds to sequence number 5 in the sake of clarity, the points coming Table 1. The sequence was designed to from the three zones have been nor­ • the equivalent widths measured at study the linearity of the CCO. In par- malized to the same incident flux. Fig- CAT + CES + SC + CCO#9 are de­ pendent on the exposure level in the continuum; Table 1: Additional information on the different sequences selected for our study (LS: La Si/la; • the equivalent widths measured with RC' Remote Contral fram Garehing) the Reticon are smaller than those measured with the CCO (5 to 15% Central Number of wavelength flat fields Place Selected zone discrepancy); Sequence Date

• the result of the division of two con­ 1 02-03/05/1987 7790A 30 LS X346-X355 Y939-Y995 secutive columns of the CCO has a complicated, spectrum dependent 2 12-13/06/1990 4057 A 18 RC X300-X306 Y200-Y350 shape; 3 12-13/06/1990 3835A 21 RC X300-X306 Y650-Y800 • flat fields at levels differing tao much 4 25-26/05/1991 4057 A 33 RC X418-X423 Y170-Y350 from the science exposure are not 5 01-02/03/1992 4542 A 38 RC X365-X380 Y270-Y330 adequate for flat fielding; X365-X380 Y470-Y530 • flat fields corresponding to different exposure times are not always strictly X365-X380 Y670-Y730 proportional. 6 09-10103/1992 4057 A 33 RC X367-X377 Y040-Y140 The above-mentioned statements are X367-X377 Y300-Y400 not necessarily independent and could X367-X377 Y850-Y950 furthermore represent different aspects of the same effect. Most of the time, 7 21/07/1992 4130A 28 RC X417-X429 Y409-Y754 they were attributed, without further

13 of the response curve or to the presence +. + of an additional, non poissonnian, flux + dependent noise. The discrimination be­ 1. 1 + + tween the two causes is possible by 't + comparing the functions P(f) and Q(f). + If R is the response curve, we have 1. 08 + f= R(F). (2) .,., 1. 06 + We are interested in the reciprocal <1 + response function which is also the --...... linearizing function 1. 0'1 (3)

We fitted the function 1. 02 f P(f) ce t::t. (4)

1.0 F is proportional to t:.. t, so we obtain 0.0 2000.0 '1000.0 6000.0 8000.0 10000.0 the following proportionality f R-1(f) ce _f_ (5) Figure 1: Plot of the normalized observed flux rate fl. t versus the observed flux f. The units are P(f)' AOU. The continuous fine is the fitted function P(f). On the other hand, the variance of the observed flux as a function of the latter is given, in the case of no additional ure 1 shows that f/ t is not constant. A observed flux f. Usually, GGD#9 is op­ noise, by linear increase (i.e. a second order re­ erated at - 7 e-/ADU. sponse curve) is visible up to 3000 ADU; We estimated cd by dividing two flat then, an elbow is present and a second fjelds of the same exposure time (f1 - f2 ) linear increase, with a different slope, and by computing ar Ir. We approxi- 2 2 2 1 2 stands up to - 10,000 ADU. This is mate G, by 0.5 f a',II,. In Figure 2, we To check the equivalence of the two highly suggestive of non-Iinearities with plotted Gr - (RON)2 as a function of f. approaches, we derived the expected ar a rather complex behaviour. Although the first part of the curve is from the fitted function P(f) through Eqs. A function P(f) (fourth order polyno­ compatible with linearity, an elbow is 5 and 6. We found that the expected mial up to 4500 ADU and a straight line again present at about 3000 ADU and, ar - (RON)2 function found in this way beyond, the continuity being imposed beyond, the slope is markedly different. corresponds quite weil to the function up to the first derivative) has been fitted The data have been fitted with a func­ Q(f). Therefore, we conclude that we and is also shown in Figure 1. Unfortu­ tion Q(f) of the same form as P(f) but have to deal with a clear non-linearity nately, this method (M1) suffers from constrained to go through the origin. present in the response curve and not several weaknesses in the form of im­ The lack of linearity of the variance with the apparition of an additional plicit hypotheses not necessarily satis­ could be due either to a lack of linearity strange noise. fied. For example, it assumes the con­ stancy of the flat field lamp emission. A slow drift is effectively present (one can see small oscillations in Figure 1 due to + exposures of the increasing branch al­ 1500.0 + + ternating with exposures of the decreas­ + + ing branch) but the sequence has been :j: designed to minimize the corresponding consequences. Faster variations could also be present and would be more + 1000.0 cumbersome. In particular, uncertainties N 1 ----.. + (particularly systematic ones) in the functioning of the shutter could annihi­ 6 ...... e::: late any confidence in the results. To further ascertain our approach, we N ...... used a second method based on the b 500.0 properties of the variance of a Poisson process. The variance a~ of the flux is given by

a~ = (RON)2 + ~ (1 ) 0.0 where RON is the read-out noise (pos­ 0.0 2000.0 '1000.0 6000.0 8000.0 10000.0 sibly corrected for the effect of the bias f

subtraction) and gis the gain. If the GGD Figure 2: Plot of the variance 0 {- (RONl as a function of the observed flux f. The units are is linear, the law is also valid for the AOU. The continuous line is the fitted function Off). 14 + + 1500.0 + 1992 (5eq.Sl + + 1500.0 + 1992 (5eq.S) + + a + + b + + o 1991 <5eq.4l o 1990 '5eq.3) .... +

+ C'I 1000.0 ~ C'I 1000.0 + %' + ~ .:s

"'b..... SQO.O "'b..... 500.0-

0.0

0.0 2000.0 4000.0 6000.0 8000.0 10000.0 0.0 2000.0 4000.0 6000.0 8000.0 10000.0 f f • + +. 1500.0 + 1992 '5eq.S) + + - 1500.0 + 1992 '5eq.S) + c + + cl +'\ + 1987 (5eq. 1) l> 1990 '5eq.2) $ • $ .... + * .... + * + • + 1000.0 ~ 1000.0 ~ '" + '" + %' 15 .:s .:s

"'b..... "'b..... 500.0 500.0

6000.0 8000.0 10000.0 f f Figure 3: Comparison of the variance plots corresponding to different epochs. The crosses correspond to the 1992 reference data. Panel (a) corresponds to the 1991 data (sequence 4); panel (b) to the 1990 data (sequence 3) and panel (c) to the same year (sequence 2); finally panel (d) corresponds to the 1987 data (sequence 1).

It is rather surprising that we have to deal with the inverse phenomenon of a saturation: the higher the received flux is, the more strongly is the observed flux overestimated. 10.0

3. Persistence of the Phenomenon 8.0 After the existence of a non-Iinearity had been ascertained, we studied its evolution with time. Within our own ar­ L.. 2 6.0 chive, we found a few sequences of flat L.. W fields useful for such an investigation; they were however not designed for that purpose. We found an interesting se­ 4.0 quence on the night 25-26/05/91, and two on the night 12-13/06/90. We can also add an older sequence on 02-03/ 05/87. Additional information is given in 2.0 Table 1. The variance diagram (u? ­ (RON)2 as a function of f) is plotted in ?======- Figure 3 for all the selected sequences along with the 1992 one as a reference. O. 0 L-1.--,--,--l--'-L-l-L-'---'-..I.-L..1--'--'-..L--'-L-l...... L-'-...l.-L-l--'--'--'--J It is seen that sequences 2 and 3 (1990) 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 are in excellent agreement with the re­ eu ference. Concerning the 1991 sequence Figure 4: Relative error on the measured equivalent width, as a function of the equivalent width (4), we had to increase 1/g by 15 % to (expressed in mA), for different levels of the continuum. The continuum va ries from 1000 AOU get the agreement. Most probably, the (Iower curve) to 10,000 AOU (upper curve) by steps of 1000 AOU. The line width remains fixed; gain was different at that time although the line depth va ries from 10 % (Ieft) to 100 % (right) of the continuum level. 15 this was not mentioned in the descrip­ Table 2' Power expansion of the reeiproea/ response funetion R- 1 m(see equation 9). tors (15 % is approximately one e- at 7 Parameter Value 1 :s 4500 Value 1 ~ 4500 e-/ADU). The only slight discrepancy concerns the 1987 data. Clearly, the (,(, 1.00475 1.02824 5 5 non-linearity is already present but (,(2 - 0.7456.10- - 1.4840.10- the elbow could be at somewhat lower 9 10 (,(3 - 1.0272.10- + 2.142.10- counts. In any case, the similarity be­ 13 15 tween the curves is so strong that it (,(4 + 5.0929.10- - 3.09.10- 20 indicates that the non-linearity was (,(5 - 8.0300.10- \7 + 4.5.10- 25 probably there from the beginning. ().7 + 1.9823.10- - After our run (March 2, 1992), we complained about the problem de­ scribed here and the electronic settings fUN oc F (7) have been modified on several occa­ Simulations have been carried out for a sions, therefore changing the response typical case, and show the equivalent can be expressed by curve. The situation after March 2, 1992 widths to be overestimated typically by is described in section 6. 5%, but by more than 10% for weak fUN oc W'(f) (8) lines on a well-exposed continuum (the = 8\ f+ 82f2 + 83f3 + 84f4 + 8 f S + 87f7. (9) 4. Correction of the Non-Linearity s best case for abundance analyses ...). as Before March 2, 1992 Figure 4 exhibits the results of such a The coefficients are given in Table 2. simulation. Strong evidence of the stability of the The high order of the polynomial is basi­ inadequate response curve, at least cally due to the elbow. The correction 6. The Response Curve After since 1990, has been given in section 3. should be applied to the debiased ex­ March 2, 1992 Therefore, we used the reference, se­ posures (science and flat field ones) quence 5, as analysed in section 2, to prior to flat fielding. We had another run from 06/03/92 to derive a response curve and thus a 10/03/92. We took this opportunity to Iinearizing function, adequate for 5. The Scientific Impact of the acquire another sequence of flat fields in correcting data obtained during that Problem order to further study the above-men­ period. tioned problems, particularly, as we From the function P(f) fitted on the On Figures 1 and 2, deviations from knew that the electronic settings were flux rate (Eq. 4), wh ich is perfectly com­ linearity of 5 to 10 % are clearly visible. changed. The variance diagram corre­ patible (through Eqs. 5 and 6) with the fit The observed spectrum changes with sponding to this sequence (numbered 6 Q(f) made on the at - (RON)2 corre­ exposure level and is different from the in Table 1) is given in Figure 5 along with sponding either to sequence 5 alone or correct one. The line profiles are mod­ the curve Q(f) (introduced in section 2) to sequences 2, 3, 4, 5 altogether, we ified, the equivalent widths overesti­ for comparison. The response curve can deduce the reciprocal response mated. clearly changed: the non-linearity is any­ curve function W'(f) (Eq. 5) within a The effect on equivalent widths de­ way still present but to a lesser extent multiplicative factor. Therefore, the pends on the continuum level, on the and the elbow is less obvious than in linearized flux fUN which is directly pro­ shape of the spectrum perpendicular to Figure 2. The variance however behaves portional to F the dispersion and on the line profiles. more Iike a second-degree polynomial which underlines the persistence of the non-linearity. Finally, we could make a last check in July 1992. Sequence 7 was acquired on t:>. 21/07/92; the corresponding variance t:>. t:>. t:>. diagram is also given in the same Fig­ ure 5. The curve is again different from t:>. 1500.0 t:>. 1992 (Seq.6) t:>. all the others shown above. A non­ linearity is still present but its nature o 1992 (Seq.7) t:>. seems more complex. t:>. The conclusion is that, during the l>. B course of 1992, the non-linearity prob­ C'l t:>. lem was not solved at all and that, in ~ 1000.0 >-- addition, variability of the response 0 0::: curve prevents to apply a general '-..../ correction to the data similar to the one proposed in section 4. C'l...... b 500.0 As a last illustration, we decided to use a third method (M3) to investigate the linearity of CCD#9. The principle is that the shape of a spectral feature should remain the same, independently

o. 0 L-..L---L--I....---.l..---'_'--..I..-...L--I....----L---l.----lL-.L..-..L---L--I....----'----'-'--:-..l----:---'-' of the exposure level. So, the profile of a 0.0 2000.0 4000.0 6000.0 8000.0 10000.0 strong line observed with different expo­ f sure times could be used to derive the Figure 5: Plot of the varianee 0 l- (RONf as a funetion of the observed flux 1 for sequenee 6 non-linearity curve. (triang/es) and sequenee 7 (eire/es). The units are AOU. The eontinuous line is the funetion 0(1) Here, we simulated such a broad as introdueed in seetion 2; it is given for eomparison. emission line by narrowing the exit slit of 16 9.5 15000.0 a b

9.0 10000.0 QJ QJ ~ ~ :>'" '":> (ij (ij x x n. n. 5000.0 8.5

0.0 8.0

0.0 200.0 ~oo.o 600.0 800.0 1000.0 0.0 200.0 ~oo.o 600.0 800.0 1000.0 Pos I t Ion POSllJon Figure 6: Ratio of two vignetted flat fields of different exposures. Panel (a) shows the two flat fields (1000 and 120 seconds of exposure) averaged over the slit height. Panel (b) gives the ratio of the two flat fields compared to the ratio of the exposure limes (the straight horizontal line).

the pre-disperser in order to get strong proposed a first order correction to be pertise of Philippe TombaI. We are also vignetting of the flat fields. As an illustra­ applied on the debiased frames. This indebted to Or. Gang Zhao for a prelimi­ tion, two flat fields of different exposure correction is to be considered a first nary look at the 1987 data. This re­ levels are shown in Figure 6. The ratio order one because we do not know the search was supported in part by con­ of the two is clearly flux dependent, exact origin of the problem; the depen­ tract ARC 90/94-140 "Action de re­ showing that the response curve of dency of the response curve on the bias cherche concertee de la Communaute CCO # 9 was still clearly non linear in level, for example, is completely un­ Fran9aise" (Belgium) and by the Belgian July 1992. known. Programme Service Centres and Re­ RCA CCOs are usually thought to be search Networks initiated by the Belgian pretty linear (McLean, 1989). This sug­ State, Prime Minister's Office, Science 7. Conclusion gests that the problem of CCO # 9 Policy Programming. We gave evidence that ESO CCO # 9 originates in fact in the electronics be­ used at CAT + CES has never been hind the CCO itself. This is supported by linear from 1987, shortly after its instal­ the strong dependency of the response References lation at the CES, to 1992. The response curve on the electronic settings as evi­ curve seems to have been rather stable denced after March 2, 1992. Magain, P., Surdej, J., Vanderriest, C., Piren­ ne, S., Hutsemekers, D.: 1992, The from the beginning up to March 2, 1992; Messenge/; 67, 30. this is certainly true during the years Acknowledgements McLean, I.S.: 1989, Electronic and computer­ 1990 and 1991. aided astronomy: from eyes to electronic We briefly analysed the impact of the Calculations on polynomials have sensors, Chichester: Ellis Horwood Ud. problem on abundance analysis works been performed thanks to Mathematica: Schwarz, H.E., Abbott, T.M.C.: 1993, The as those customarily done at CAT. We we would like to acknowledge the ex- Messenger, 71, 53.

CCD Linearity at La Silla - a Status Report IM.C. ABBOTTand P SINCLAIRE, ES0, La Silla

We believe that the non-linearities re­ be related to the age of these devices. tage. It was found that a fraction of a ported above by Gosset and Magain Unfortunately, we do not have adequate volt may have a significant effect on the arise from a combination of two effects. test data to demonstrate that our RCA linearity. All RCA CCOs required adjust­ First are the non-linearities reported in CCOs were ever linear to better than ment, except RCA#13. Schwarz and Abbott (1993), resulting 1 %, but they were certainly non-linear Below is a list of our CCOs and the from a failure in some new ND conver­ to as much as 8 % over their full dy­ most recently measured or most rep­ ter chains in the Generation 111 CCO con­ namic range before March of 1993. At resentative degree of non-linearity. For trollers. Secondly, in the process of re­ this time, we determined that we could the RCA CCOs, data prior to adjustment placing these converters, we discovered reduce these non-linearities to accept­ of the output drain bias voltage is in­ that many of our RCA CCOs exhibited able levels by careful adjustment of the cluded. Non-linearities are expressed as some intrinsic non-linearities wh ich may bias level of the output FET's drain vol- the fractional amplitude of any trends in

17 CCO Telescope & Nonlinearity Range (e-) of Name Instrument Date (%) Measurement Comments

RCA#5 0.9-m 22/2/93 3 180,000 Effect unrepeatable Adapter CCO retired 3/93

GEC#7 0.9-m 3/3/93 1.3 55,000 Adapter CCO retired 12/92

RCA#8 2.2-m 19/3/93 6 75,000 Vod = 17.0V Adapter < 0.6 62,000 VOd = 18.5V

RCA#9 CAT 19/3/93 8 100,000 Vod = 16.0V CES Silort < 0.7 73,000 Vod = 18.0V

RCA#13 1.52-m 6/4/93 < 0.5 120,000 VOd = 21.0V ECHELEC No adjustment necessary

TH#19 2.2-m 18/4/93 < 0.1 60,000 EFOSC 11

FA#24 1.52-m 13/4/93 < 0.5 90,000 S&C

TK#25 NTT 19/6/93 - 1 200,000 SUSI

TK#26 3.6-m 11/8/93 - 0.5 115,000 EFOSC I

TK#28 1.54-m 11/6/93 < 0.5 110,000 Adapter

TK#29 0.9-m 4/8/93 -1 260,000 Adapter Temporary location

FA#30 CAT 11/8/93 < 0.5 47,000 CES Long Non-linear transfer curve'

TK#31 NTT 24/7/93 < 0.2 150,000 EMMI Slue

TK#32 3.6-m 20/12/92 < 0.25 140,000 CASPEC

TK#33 0.9-m 15/5/93 < 0.5 465,000 Adapter Temporarily out of service

LO#34 NTT 6/3/93 < 0.2 42,000 EMMI Red

. Although FA#30 has a linear response to incident light, we have discovered a noise source in this system which is proportional to the signal level; work continues to identify its cause.

count rate over the measured range. served non-linearity. In most cases, the cases where the non-linearity may affect Most of the linearity tests were per­ linearity was measured over the full, observations, work continues to correct formed using a beta light placed in front useful dynamic range of the CCO. The the situation. of the CCO, a few utilized an LEO pre­ extent to which an observer's data will flash light, powered with a stable, low­ be affected is dependent on the fraction noise power supply. of the CCO's dynamic range wh ich was Reference Please note that these results are ex­ used for the observations; normally, the Schwarz, H.E. and Abbott, T.M.C., 1993 The pressed in terms of the maximum ob- effect will be insignificant. In those few Messenger 71, 53.

18 SCIENCE WITH THE VLT

The Magellanic Clouds and the VLT J. LEQUEUX, Observatoire de Paris-Meudon and Ecole Normale Superieure, France

The Magellanic Clouds do not need to Messenger 67, 17 (CONICA, the high­ gramme will supply a data base for our be presented to the readers of the resolution near-IR camera); Appenzeller understanding of the cepheid phenome­ Messenger! I wish however to remind & Ruprecht 1992, The Messenger 67, 18 non. Similar interstellar absorption line them of their interest in general: (FORS, the focal reducer/low dispersion and cepheid studies will also be inter­ (1) they are the closest galaxies of a spectrograph); Moorwood 1992, The esting for the LMC: absorption lines in type different from our own Galaxy; Messenger 70, 10 (ISAAC, the infrared the LMC often show multiple velocity (2) they are sufficiently close for de­ spectrometer and array camera); Dekker components, the origin of which is not tailed studies, similar to many of those & D'Odorico 1992, The Messenger 70, weil understood, and the cepheids will wh ich can be done in our Galaxy; 13 (UVES, the UV-visual echelle spec­ allow a direct measurement of the incli­ (3) they are relatively small systems trograph). The multi-fiber spectrograph nation and of the shape of the disk of compared to their distance, thus all the FUEGOS is in Phase A only and no the LMC. objects they contain are more or less at description is generally available yet. Another topic of great interest is the the same (known) distance; moreover, kinematics of the old populations in the interstellar extinction is generally smalI; Magellanic Clouds. While the kinematics Structure and Kinematics of the these properties make the Magellanic of the young population is weil under­ Magellanic Clouds Clouds especially interesting for study­ stood, that of the older one is much ing objects whose distance is difficult or In spite of much effort, the structure of more difficult to study. Objects like impossible to obtain in our Galaxy (giant the Magellanic Clouds is not yet com­ planetary nebulae and carbon stars will stars, AGB and post-AGB objects in­ pletely understood especially for the yield the kinematics of intermediate-age cluding planetary nebulae, symbiotic SMC which has a very irregular shape. populations: from what we know, they and other strange stars, X-ray binaries, The SMC contains up to 4 different do not seem to differ much from that of novae, etc.); gaseous components with different ra­ the young populations. However the old (4) the abundances of heavy elements dial velocities and associated young clusters of the LMC seem to have a are different from those in our Galaxy; this stellar populations, but their relative 10­ different kinematics from the younger allows to study the formation and evolu­ cation in depth and their distances are clusters, but this observation is at the tion of stars as a function of abundance; not weil known. Interstellar absorption limit of the present telescopes and de­ (5) Iinked to these differences in abun­ lines can show wh ich component is in serves confirmation with the VLT. We dance, the properties of interstellar mat­ front of the studied star, but there are know almost nothing of the kinematics ter (ISM) in the Clouds are strongly dif­ not yet enough such measurements due of the halo stars of both Clouds and this ferent from those of the Galactic ISM. to the faintness of the suitable stars; the will be a new field to open with the VLT. It is obvious that the largest tele­ VLT will allow fast observation of inter­ Presumably FORS and FUEGOS are scopes of the future like the VLT will be stellar lines (especially the sodium lines) most suited for such studies. of much interest for Magellanic Cloud in front of many stars; the most suited Finally the VLT is needed for studying studies, since they will already be of instrument will be UVES and also in detail the stellar population and (via interest for many Galactic studies. My FUEGOS in its high-resolution mode (R observation of interstellar absorption goal in this article is to review some = 30,000, enough for a kinematic study). lines on background objects) the inter­ areas where the VLT will make possible However this does not give distances. stellar matter in the bridge which con­ considerable progress in our under­ They have to be obtained from cepheids nects the two Clouds and in the standing of the Magellanic Clouds. The using their period-Iuminosity relation Magellanic stream. While young stars present study bears heavily upon a preferably in the infrared. Measurement are known to exist in the Bridge, no number of recent reviews by myself and of the mean radial velocity of each bona fide member star has been found by others, and upon the following books cepheid will allow to know to which in the Stream. This may point to different entirely devoted to the Magellanic component it belongs. Present attempts origins, the Bridge being a tidal feature Clouds: lAU Symposium No. 108; lAU at using this method have not been fully or at least having experienced a tidal Symposium No. 148; Recent Develop­ convincing for lack of photometric and perturbation responsible for star forma­ ments of Magellanic Cloud Research radial velocity measurements covering tion, and the Stream being perhaps due (1980, K.S. de Boer, F. Spite & G. evenly the period of the cepheid. While to tidal stripping. Observations with the Stasinska, eds., Observatoire de Paris); the photometry part of this programme VLT should allow to settle this long­ New Aspects of Magellanic Cloud Re­ does not necessarily require a very large debated question. search (1993, B. Baschek, G. Klare & J. telescope, the radial velocity one does, Lequeux, eds. Springer-Verlag, Berlin). I using correlation methods, if one wishes Interstellar Matter will make reference to some of the VLT to observe a large number of cepheids. instrumentation: for a general presenta­ FUEGOS appears most adapted to this Interstellar matter in the Clouds is tion see D'Odorico et al. 1991, The programme wh ich would require an very different from that in our Galaxy: Messenger 65, 10. For the presentation enormous amount of telescope time the abundance of heavy elements is 4 of the 4 instruments under construction with single-object spectrographs. As a and 10 times smaller in the LMC and the see Lenzen & von der Lühe 1992, The very important by-product, this pro- SMC respectively, the dust-to-gas ratio 19 is smaller in the same proportions and One very important goal of Magella­ varied to be discussed here in any de­ the properties of dust are qualitatively nic Cloud stellar observations is to tail. It seems to me that the AGB and different (sm aller absorption bump at help understanding stellar evolution. post-AGB stars are the most interesting 200 nm, higherfar-UVabsorption, small­ While sophisticated models exist for class of such objects. Their evolution is er far-infrared emission by very small this evolution, the physics introduced still very poorly known in spite of much dust particles). The higher far-UV radia­ in these models is to a large extent ar­ effort - in part due to the lack of dis­ tion field together with the lower abun­ bitrary and as a result this evolution tance information in our Galaxy - and dance of dust produce an increased is still very poorly known: for example may depend on metallicity. Once again, photodissociation of molecular hydro­ the evolutionary status of the pro­ a multi-object spectrograph is appropri­ gen, of CO and of other molecules wh ich genitor of SN 1987A is still controver­ ate as the surface density of most affect considerably the properties of the sial. For low- and intermediate-mass classes of such objects (e.g. carbon molecular clouds. I do not clearly see stars, high-quality photometric and stars) is relatively large. observations of the ISM wh ich could be spectroscopic observations of individu­ Finally, observing star formation in a unique to the VLT, but it is clear that the al stars in clusters of different ages and different context than the galactic one is very large sensitivity of this instrument metallicities will help tremendously a very exciting perspective. Already it will allow improvements with respect to understanding their evolution; although has been demonstrated that massive what is done at present, for example by much is presently being done with 4-m stars occur in small compact groups in densifying the observations by FUEGOS class telescopes, the VLT will allow the Clouds, but we would like to know of interstellar absorption lines allowing doing more and better. For massive why and how, and also to know more studies of the fine structure of the ISM, or stars, the observational problem is about the formation of lower-mass by making easier visible and infrared more difficult. The only way to progress stars. For this, one will use the VLT observations of star-forming regions, in­ seems to locate the observed massive mainly in the near- and mid-infrared us­ terfaces between ionized and neutral stars in a "theoretical" (L vs. Tell) HR ing ISAAC and the foreseen mid-IR im­ gas, supernova remnants, etc. The latter diagram, to measure their densities in ager/spectrometer. Such studies are studies will make use of FORS, ISAAC the different parts of the diagram, to still in their infancy in the Magellanic and perhaps CONICA. An interesting study surface abundance anomalies Clouds (only a few images in the K band possibility wh ich requires both high sen­ due to internal mixing, then to confront have been published, for instance). sitivity and excellent image quality is to these observations with the predictions While it is hard to predict what the investigate through extinction (star of models. It is also necessary to outcome of future VLT studies will counts and photometry) the internal measure the strength of the stellar wind be in this field, it would be very sur­ structure of the molecular clouds (not wh ich plays an enormous role in the prising if the results would not be of accessible to the SEST). This will check if evolution. All this should be done for 9reat interest. the properties of the molecular clouds in stars with different metallicities in order the Magellanic Clouds differ from those to understand the role of metallicity in Chemical Abundances in our Galaxy only due to the differences the internal evolution and in the accel­ and Evolution of the Magellanic in photodissociation as explained be­ eration of the wind. The Magellanic Clouds fore, or due to differences in structure. Clouds are ideal places for such inves­ tigations. They contain a sufficient In spite of being a relatively ancient number of massive stars for statistical topic, this is a very controversial one. Stellar Populations and studies, they have very different Determinations of the abundances of Star Formation metallicities and a comparison will be heavy elements in different classes of Due to various causes (not always possible between a complete sampie of young objects in the Magellanic Clouds weil understood) the properties of stellar stars belonging to Galactic open clus­ often give discrepant results: while H 11 populations in the Magellanic Clouds ters and associations. One problem is regions exhibit a remarkable degree of differ from those in our Galaxy. For ex­ to build the sampie, requiring fine spec­ homogeneity in either Cloud, indicating ample, the Clouds like M 33 and a few tral classification of stars first selec­ efficient mixing of the interstellar matter irregular galaxies are known to contain ted by colours, and another one is to during the evolution of the Clouds, young globular clusters which are lack­ secure the high-resolution spectros­ young stars like hot or cold supergiants ing in our Galaxy. The youngest of all copy necessary for determining the have been claimed to have rather differ­ could be the dense clusters of 0 stars abundance of carbon and nitrogen from ent abundances between them and with that ionize the biggest H 1I regions their rather faint lines. It is also the H II regions. If real, this result is very (30 Dor in the LMC and to a lesser desirable to study the HR diagram difficult to understand. However there degree N 66 in the SMC). Of course the down to 6-8 solar masses where the are some doubts about determinations dynamical study of those young clusters transition between the two main re­ of abundances in supergiants, wh ich are and also of those of intermediate age is gimes of stellar evolution occurs. A 6­ made difficult by the strong non-LTE of high interest since in our Galaxy only solar-mass star on the main sequence effects and by problems in measuring old globular clusters are seen. Such has V = 18 in the SMC, and it is clear effective temperature, gravity and inter­ studies have started in particular with that the VLT is necessary for high-reso­ stellar extinction. One would very much the ESO telescopes, but they will be lution, high-quality spectroscopy of like to have such determinations made made considerably easier by the VLT such astar. As one wants to perform in stars with higher gravities. Unfortu­ and will reach stars of earlier spectral this kind of analysis for several hun­ nately these stars are faint in the type for wh ich accurate radial velocities dreds of stars in each cloud, a multi­ Magellanic Clouds and generally out of are more difficult to measure. Due to objet spectrograph is required, once reach of the present telescopes. This crowding one will have to use a again FUEGOS. will be a very important programme for medium-to-high resolution field spec­ Apart from this, the VLT will be ideal the VLT, presumably using UVES or trograph. Once again one will use for detailed observations of all sorts of FUEGOS. I will not specifically discuss FUEGOS in the compact fiber mode for more or less exotic objects whose study the evolution of the Clouds, but it is the centre of the cluster, or in the normal in the Galaxy is hampered by the lack of underlying most of the previous discus­ mode for the rest of the cluster. distance information. This fauna is too sion. 20 Conclusion importantly of stellar evolution in gener­ useful of all the foreseen foca/-plane al: I would like to stress once again how instruments for that purpose appears to I hope to have convinced the reader unique the Clouds are for studying the be FUEGOS, and I very much hope that that the VLT will allow very significant various stages of the evolution of mas­ its construction will not be unduly de­ advances in our knowledge of the sive stars and the late stages of evolu­ layed by budgetary restrictions. Magellanic Clouds, and perhaps more tion of stars of all masses. The most

Nuclei of Non-Active Galaxies with the VLT M. STIAVELLI, Scuola Normale Superiore, Pisa, Italy

1. The Physical Properties 01 hand the red herring of isothermal cores equilibrium configurations and the Galactic Cores and Nuclei was brought up and followed by several availability of powerful and flexible mod­ Since the very beginning of ex­ investigators, who found less and less elling techniques, makes it difficult to tragalactic studies it was realized that truly isothermal cores as the resolution obtain an irrefutable proof of the exist­ galaxies have very compact central increased. Even in the late 80s it was ence of a black hole in any given galaxy parts. However, only in the last decades possible to find statements concerning (see, e.g., Kormendy 1993). Although it has been fully appreciated that atmo­ a broad subdivision of galaxies into the central black hole hypothesis is spheric seeing was the major limiting those with isothermal cores and those probably the simplest to explain objects factor for the angular resolution that without. On the other hand, dynamicists like M87, it is important to obtain such a could be achieved from the ground and were able to produce (often contrived) proof by improving resolution and accu­ that, in turn, the observed core proper­ models able to fit the observed kinema­ racy of observations. ties were often just artifacts of the Iim­ tic and photometric profiles of galaxies Galaxy cores are also important as ited resolution available (Hoyle 1965; without the need of a supermassive benchmarks for theories of galaxy for­ Schweizer 1979, 1981). Of the two black hole. Unfortunately, the intrinsic mation. Great progress has been made galaxies known in the late 1970s with freedom allowed by stellar dynamics in this field, often guided by our interpre- truly resolved cores, one, M31, had a nuclear, very dense, spike roughly in the centre of its broader core, while the other, the radio galaxy M87, presented a central spike in the light profile, wh ich was interpreted as due to an unresolved 7 0 non-stellar point source. Despite this, the notion of isothermal cares was intro­ duced, i.e. of cores with a light profile that flattens to a plateau at small radii. This was partly inspired by theoretical 6 arguments, in practice it reflected pre­ ".--...., o C':> cisely the kind of profile that seeing I o effects were producing. On the other C) hand, spectacular phenomena like the ~ M87 optical jet opened up the issue of ~5 the nature of the nuclear energy sources .....::l o in galaxies and of the possible existence of nuclear supermassive black holes. It ----...... ,0 is very intuitive that a supermassive o black hole would affect the stellar orbits Q.(J 0 in the core, producing spikes in velocity 0 4 dispersion and nuclear rotation curves .....::l with steep gradients. Theoretical argu­ ments showed that a black hole would o influence also the core light profile, by capturing stars in a very concentrated 3 o cusp detectable in the light profile. In­ deed, both indicators were used by o Young and collaborators (1978, 1979) to claim the existence of a central black hole in M87. Unfortunately, even models o 1 2 without a central black hole can be con­ structed able to give adequate fit to the Log D(Mpc) data (Binney and Mamon 1982). Figure 1: The apparent centrallight density of galaxies appears to anticorrelate with galactic Developments in the following years distance. This is aresolution effect also present in Hubble Space Telescope data (Crane et al. were in a way frustrating. On the one 1993). 21 tation of what the core properties were and how they originated. For instance, the discovery of counter-rotating and decoupled cores was seen as a proof that merging and accretion is occurring, with the remnants of tidally destroyed companions settling into the cores of larger galaxies with their residual angu­ lar momentum. Better data and new in­ dicators have shown that this is prob­ ably not the case, since (at least some of) these decoupled nuclei turn out to be much more metal rich than the main galactic body (Bender and Surma 1992, Davies et al. 1993), in opposition to the dissipationless merging prediction. Should all decoupled cores have the same property, what was seen as a suc­ cessful prediction of late-time merging would turn into a fatal blow to this idea. Most likely, further strong constraints on the formation of galaxies will come from deeper studies of their cores.

2. Progress with the Current Figure 2: Hubble Space Telescope FOG image at 3420 A of the core of the Sombrero Galaxy Generation of Telescopes (NGG 4594). Visible are the point-Iike nucleus as weil as the dust lanes and patches (from Grane et al. 1993). Gores are the brightest parts of galax­ ies. In addition, the desire of having a spatial resolution as high as possible forces us to consider relatively nearby objects. Why then should one use a are just the result of a finite resolution analyses involving the study of line pro­ large telescope? Shouldn't telescopes effect, we have to conclude that even at files. The latter will probably be funda­ of the 3.6-m class or even smaller be their resolution of about 0.05 arcsec mental in proving the existence of a adequate? This question has two oppo­ FWHM the derived core properties are black hole in a given galaxy since they site aspects. strongly affected by resolution. It is un­ probe directly the stellar distribution Experience shows that typical inte­ likely that this will be changed signifi­ function. Another example is the rotat­ gration times with e.g. the SUSI camera cantly by GOSTAR, since the gain in ing gas disk in the nucleus of NGG 3557 at the 3.5-m ND or the standy-by cam­ resolution will only be moderate. In addi­ identified by Zeilinger et al. (1993). The era at the 2.5-m NOT are, respectively, 2 tion, some cores, and perhaps the most disk was detected in a spectrum taken and 5 minutes. Therefore, the use of interesting ones, like those of NGG 4261 at the ESO 3.6-m telescope with a reso­ these cameras often leads to low-effi­ (Ford et al. 1993), of Sombrero (NGG lution of 1 Aper pixel, by resolving the ciency observations, since the integra­ 4594, Grane et al. 1993, see also Figure [N 11] (), 6583.4 A) into two wings both tion time is shorter or comparable to the 2), and of NGG 3557 (Zeilinger et al. appearing in the core of the galaxy. East read-out time. From this point of view, 1993), contain dust. This is a reason to and west of the nucleus only the ap­ and considering that so far the angular shift the preferred observational proaching and receding wings, respec­ resolution wh ich could be obtained was wavelengths to the Near Infrared. Note tively, are observed, thus producing a dictated by atmospheric seeing rather that after GOSTAR only the UV (and typical-Iooking rotation curve. This than telescope diffraction limit, a large dust!) sensitive FOG will sampie the Hub­ spectrum al ready gives strong hints for telescope does not seem to be ble Space Telescope PSF properly. the existence of a central black hole in necessary. In fact, at the GFHT it is a Not only direct images but also long this galaxy (Zeilinger et. al. 1993). A fur­ weil established procedure to dia­ slit spectra are desired. Indeed, spectra ther attempt to derive more accurate phragm the main mirror reducing its size allow one to derive stellar kinematical line shapes by using the echelle spec­ to 1.8 m to improve optical quality and information, stellar line-strengths, and trograph GASPEG at the 3.6-metre tele­ angular resolution. ionized gas kinematics and metal con­ scope failed because even with 4 hours From what we have seen, one could tent. These data are essential in under­ of integration not enough photons therefore argue that a small telescope in standing dynamics and formation of were collected. For very high resolution space would be better than a large tele­ cores. work, a 3.6-metre-class telescope is scope on the ground. This is not true. The need of both high spatial and simply too small to observe galaxy Indeed, it is now becoming apparent that wavelength resolution forces one to use cores with typical B surface brightness many galaxy cores remain unresolved very narrow slits and high dispersions, of 17 magnitudes/arcsec2 or more. even at the HST resolution. Grane et al. at the price of reducing the signal to (1993) have observed a sampie of 10 noise. As an example, a one-hour spec­ 3. Developments with the VLT objects with the FOG camera. They find trum of the core of NGG 1399 with an anticorrelation between the central EMMI Red Arm at the ND, with 0.5 A A number of factors concur to make density and the distance of the galaxy resolution, only yields a signal to noise the VLT (see Figure 3) a superb tele­ (see Figure 1), weil described by apower of about 30 in the core, adequate to scope for a variety of applications: the law with power 1.8. Since apower of 2 derive kinematical information but not site, the size of the unit telescope, the would indicate that the core properties enough to carry out more sophisticated instrumental developments. Here we 22 will consider separately the contribution Layout of the VLT Observatory that CONICA, FüRS, ISAAC, and UVES will make to the study of galaxy cores.

VLTI 3.1 CON/CA CONICA is the Coude Near-Infrared Camera (Lenzen and von der Lühe 1992). It is the prime instrument for ex­ ploiting the high resolution potentially available at the single VLT unit. In fact, the diffraction limit of a single VLT mirror is for a given wavelength almost 4 times VLT unil VLT unil VLT unit VLT unil as small as for the Hubble Space Tele­ - scope. With adaptive optics it is ex­ 1 2 3 4 CIlv pected that the diffraction limit will be 0.. 0 reached in the Near Infrared for A. > 2.2 CJ CIl II II micron and that partial correction will be V V attempted at 1.25 micron. The PSF for - -' FORS ISAAC UVES FORS UVES :>, the case of partial correction is charac­ ~ terized by a diffraction limited core with ~ 'x most of the power in the PSF wings, i.e., :J a situation similar to that of the pre­ co CONICA COSTAR HST, so that one will be able - to exploit all techniques developed for HST data. The CONICA Camera will be CONICA : Coude' Near Infrared Camera able to sampie with 0.012 arcsec pixels FORS : Focal Reducer/low dispersion Speclrograph the PSF at 1.25 micron, yielding a reso­ lution of 0.032 arcsec FWHM, and with ISAAC : Infrared Speclrometer And Array Camera 0.024 arcsec pixels the PSF at 2.2 mi­ UVES : UV-Visual Echelle Speclrograph cron, yielding a (fully corrected) resolu­ VLTI : VLT Inlerferometer tion of 0.057 arcsec FWHM. Thus effec­ tively exceeding, with weil sampled im­ Figure 3: Schematic drawing of the VLT with the instruments considered in the text. ages, the spatial resolution provided by HST at optical wavelengths. The gain of a factor 2 in resolution over HST is cer­ tainly welcome, but very important is also the ability to take such high resolu­ "shift and add" operation. A typical ellip­ olution achieved, these wavelengths will tion images in the Near Infrared, where tical galaxy core with surface brightness allow unique opportunities for those ob­ the effects of obscuration by dust are PJ = 13.8 and PK = 12.7 will be detected jects with cores obscured by dust lanes, much less important. as 20 photons/sec/pixel (0.012 arcsec/ like, e.g., NGC 5128. The major problem of adaptive optics pixel) in the J band and as 110 photons/ at the VLT, at least until the technique of sec/pixel (0.024 arcsec/pixel) in the K 3.2 FORS artificial reference stars will be intro­ band. These fluxes are too small to use duced, is that only a small fraction of sampling rates larger than 10Hz. How­ FORS is a focal reducer with parallel galaxies will be suitable for such a ever, many galaxies turn out to be brigh­ beams (Appenzeller and Rupprecht study, since adaptive optics requires the ter by about a factor 10 at milliarcsec 1992). For imaging application the setup presence of a reference star (brighter scales compared to the aresec scales; of choice will be the High Resolution than about 15) within the isoplanatic in addition, many contain point sources mode with 0.1 arcsec/pixel. Such a pixel patch, i.e. at, say, less than 10 arcsec brighter than 20 in V. The latter are usu­ size should allow a suitable sampie of from the target. Luckily, many galaxies ally too faint to serve as reference stars the typical seeing conditions at the VLT turn out to have central point sources for adaptive optics but can be used to Observatory. The large collecting area (Lauer et al. 1991, Crane et al. 1993). align the images. Globular clusters may of the VLT unit however would imply For a number of objects including, e.g. also be suitable for similar purposes, very short exposure times and therefore M87, the central (non-thermal) point provided some are present in the re­ inefficient observations. Apart from the source is bright enough to serve as a stricted FOV of 3 arcsec in J and 6 resolution benefits in using very short reference star. When this is possible, arcsec in K. exposures, we therefore expect that the this is an optimal observing mode since At lower resolution, the capability of use of FORS in the study of cores will reference star and target coincide in po­ extending the observing wavelength to primarily be spectroscopic. With a grism sition. CONICA offers other possibilities 5 micron is also very important, espe­ and narrow slits, it will be possible to for galaxies without a suitable reference cially since no high-resolution data are obtain spectra with aresolution of about star near the core. These techniques available for galaxies at these 100 Nmm of the core regions of galax­ include speckle imaging and various wavelengths. In the Land M bands re­ ies. In good seeing, with a 004 arcsec forms of coaddition. Abasie require­ spectively, a diffraction-limited resolu­ slit, spectra with 2.5 Aper pixel and S/N ment is that an object in the field of view tion 0.093 and 0.12 arcsec FWHM will 200 in the centre will be obtained in one is bright enough to get enough photons be obtained for a significant fraction of hour for typical galaxy cores. Such a in a very short integration time to, e.g., the sky, thanks to the less demanding resolution is adequate for deriving accu­ allow for the measurement of the frame requirements of adaptive optics at these rate kinematical properties (errors smal­ reference coordinates and carry out a wavelengths. In addition to the high res- ler than 20 km/s in radial velocity and 23 velocity dispersion), line profiles, and In good seeing, with a 0.4 arcsec slit 4. Further Desirable Instruments absorption line strengths. Therefore, exploiting the 0.19 arcsec/pixel of the The VLT interferometer (Beckers and with a moderate amount of telescope blue arm, one will be able to obtain high Merkle 1991) would represent another time, it will be possible to make a com­ spatial and spectral resolution. Stellar step further in terms of angular resolu­ plete two-dimensional mapping with kinematics in the blue arm will be carried tion, since it should allow aresolution of high spatial resolution of the cores of out preferably on the Ca 1I H + K band about 0.004 arcsec, corresponding to nearby galaxies. Such a mapping will and on the G band. The slit length will about a factor 10 improvement over allow us to construct an accurate dy­ have to be limited at 8 arcsec to avoid HST. It is very hard at this stage to namical model for the core and also to order overlapping. The overall efficiency predict the kind of impact that such an infer its stellar population properties and should be around 8 per cent. For a instrument would allow. It is perhaps possibly its star formation history. galaxy of typical surface brightness Ila = significant to note that it would allow for 17.6, a signal-to-noise of 20 will be galaxies in the Virgo Cluster aresolution reached with two hours of integration. 3.3/SAAC in physical distance scales comparable Such a signal to noise would be ade­ to what can be obtained now with the The Infrared Spectrometer and Array quate to derive kinematical information. Hubble Space Telescope on M32. If Camera (Moorwood 1992) is another It appears that several galaxy cores may M32 remains unresolved with HST, it is Near-IR instrument for the VLT. The in­ have low velocity dispersions in the extremely important to understand if it is strument has a relatively large field (up range of the few tens km/s (see, e.g., an extreme, not too significant, object to 2 arcmin) and medium spectral reso­ M33), such cores would require the use or, rather, a typical core for low mass lution capabilities. In imaging applica­ of UVES to be detected outside the local galaxies. 00 NGC 7457 (Lauer et al. tions, particularly interesting would be group. 1991) and NGC 4621 (Crane et al. 1993), the inclusion of the tip-tilt option of the The red arm would allow for a higher both unresolved with HST, have similar­ secondary mirror. Such control should sensitivity. With a 0.7 arcsec slit and Iy compact nuclei? The major limitation allow diffraction limited imaging in the L 0.31 arcsec/pixel one could obtain high for such a study will again be the availa­ and M bands, where the images would resolution spectra of the Mg I blend and bility of a suitable reference star. It however be undersampled by the 0.125 of the Ca + Fe E band, which are the should be noted that the quasi point-like arcsec pixels. Despite the problems of standard regions used for stellar source in M87, for instance, is partially undersampling (possibly cured by a re­ kinematical measurements. A signal to resolved by HST and therefore cannot duction in pixel size with the use of noise exceeding 30 should be obtained be used for this application. detectors of a new generation) imaging with two hours of integration. As we have seen, the instruments al­ at these wavelengths, and also in J and Longer integrations will probably be ready foreseen for the VLT guarantee K, with ISAAC can be an important com­ of interest to improve the accuracy of enormous improvements with respect plement to CONICA given the larger the measurement but also to allow for a to what can be done now from the field and the higher sensitivity resulting more reliable determination of the line ground or from space. Is there any other from being at the Nasmyth focus rather profiles, which will give a direct observa­ improvement possible? The need of be­ than at the COUdEL The use of a shift­ tional constraint on the stellar distribu­ ing able to take high spatial and fre­ and-add technique should in any case tion function in the parent galaxy. Such quency resolution spectra could be guarantee very good spatial resolution a measurement will have an impact both satisfied with a Fabry-Perot spectro­ at the longer wavelengths. The ex­ on the problem of galaxy formation and graph. Such an instrument could allow pected count rates from a typical galaxy on that of the presence of central black for the measurement of the velocity dis­ core are 4000 and 5600 counts/pixel/ holes, since the various models make persion and rotation velocity fields of second, respectively in the J and K very clear and specific predictions on galaxy cores. This kind of instruments bands. They should allow integration the distribution function properties. has been so far limited by technical times shorter than 0.1 second. One possible additional application reasons and by their relatively low sen­ Especially interesting is the possibility for such an instrument is in the direct sitivity, requiring the use of a very large of obtaining long-slit spectra at a resolu­ measurement of the gravitational poten­ telescope. tion of 5000 (for a 1 arcsec wide slit). tial in galaxy cores. Such a measure­ Indeed, Near-IR spectroscopy of galax­ ment is made possible by gravitational ies is a relatively new field which will redshift, wh ich for a big galaxy is ex­ benefit considerably from the availability pected to be of the order of 10 km/so of ISAAC at the VLT. The observation of The effect has already been detected in References CO lines is perhaps the only way to accurate radial velocity profiles (Stiavelli derive central velocity dispersions for and Setti 1993) but it would require a Appenzeller, 1., Rupprecht, G., 1992, The Messenger, 67, 18. heavily obscured cores like NGC 5128. very high resolution and signal to noise Bender, R., Surma, P., 1992, M 258, 250. In addition, important applications will to actually measure the potential varia­ Beckers, J.M., Merkle, F., 1991, The be possible also in stellar population tion in the core, i.e. reach a velocity Messenger, 66, 5. studies. resolution below 1 km/so Binney, J., Mamon, G., 1982, MNRAS 200, In addition to stellar kinematics, gas 361. Crane, P., Stiavelli, M., King, I.R., et al., 1993, 3.4 UVES emission lines will also be measured and used to derive information on the A.J. in press. The prime instrument for the study with physical properties of gas in the dust Davies, R., Sadler, E.M., Peletier, R., 1993, high wavelength resolution of both line and gas disks often seen in the centres . MNRAS 262, 650. Dekker, H., D'Odorico, S., 1992, The profiles from stellar absorption lines and of ellipticals. This is especially important Messenger, 70, 13. ionized gas emission lines will be rep­ since these dust rings appear to be in­ Ford, H., Jaffe, W, Ferrarese, L., van den resented by the UV-Visual Echelle Spec­ volved in the fuelling of nuclear activity Bosch, F., O'Connell, R.W, 1993, STSC/ trograph (Dekker and D'Odorico 1992). in normal galaxies and could also be the News/etter, 10, 1. This instrument will profit from the size of progenitors of the kinematically decou­ Hoyle, F., 1965, Nature 208, 111. the VLT and allow for observations which pled stellar disks observed in some Kormendy, J., 1993, in The Nearest Active have not been possible so far. galaxies. Ga/axies, J.E. Beckman et al. Eds. 24 Lauer, T.R., Faber, S.M., Lynds, C.R., et al., Schweizer, F., 1981, AJ 86, 662. son, C.P., Landauer, F.P., 1978, ApJ 221, 1991, ApJ Lett 369, L 41. Stiavelli, M., M011er, P., Zeilinger, WW, 1993, 721. Lenzen, R., von der Lühe, 0., 1992, The AA in press. 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From Planets to the Big Bang with High-Resolution Spectroscopy at the VLT R. FERLET, Institut d'Astrophysique de Paris, France

Introduction Sufficient resolution is required to re­ an 8-m-c1ass one will so much increase Some years ago, M. Harwit showed solve the velocity structure of the lines the number of potential targets that that most cosmic discoveries were con­ of sight. This is the only way to gain many stars more deeply embedded in nected with the occurrence of a signifi­ information on individual clouds, on av­ cloud cores will become accessible, cant technical step or the opening of a erage separated by a few km/s, that is allowing thus to link the properties of the new window on the Universe. Without now badly needed instead of integrated diffuse clouds currently studied in ab­ question, high-resolution spectroscopy properties. Amongst physical parame­ sorption to those of the denser and associated with very large collecting ters, temperature is directly accessible colder regions detected in the IR or area will be such a major tool to attack only through the intrinsic width of the mm radio range. vital astrophysical problems. Beside lines. For purely thermal broadening, the A more specific programme would be serendipitous discoveries, there are width increases with decreasing mass the measurements of the IS abundances several areas of research to be investi­ of the studied ions, and the lightest ele­ of light elements, in particular beryllium gated with a high-resolution VLT ment having an observable resonance and lithium wh ich are only observable in spectrographic capability. The VLT line in the visible is lithium (the lighter the visible range around 3130 A and should not miss the opportunity to ven­ elements hydrogen, deuterium and 6707 Arespectively. The knowledge of ture into an almost virgin universe and helium show up in the currently unac­ their present-day abundances, and even 7 make discoveries. cessible far UV, except Lya observable more uniquely of the ratios Be/Li and Li / 6 Here, we are tal king about resolving with the Hubble Space Telescope but Li , is a key-milestone to severely con­ 5 power R of at least 1-1.5x10 , simply wh ich is always heavily saturated and strain cosmological scenarios and because many important pending prob­ blended). Nevertheless, even through galactic chemical evolution models. This lems cannot be tackled with lower reso­ the Li I doublet, IS gas at 1000 K gives a kind of observations needs extremely lution. Many of these are reviewed in the full width at half maximum of 2.57 km/s, high S/N ratios. For instance, IS Li 6 has 5 proceedings of the ESO Workshop on requiring already R > 1.2-10 . Higher been recently detected for the first time "High Resolution Spectroscopy with the resolution is mandatory in order to de­ towards Q Oph (Lemoine et al., 1993), VLT" held in Garching in 1992. We will rive true b-values from cooler IS gas, thanks to a S/N ratio 2:: 2700 per pixel, briefly give here only a few exciting ex­ even though careful profile fitting analy­ implying a limiting detectable equivalent 7 amples of potential achievements in var­ sis of several lines may help to artificially width of 0.043 mA (3 a). The resulting Li / ious fields through high-resolution ab­ increase the resolution by a factor of Li 6 ratio - 12.5 is in strikingly good sorption spectroscopy at the VLT. perhaps 2 or so depending on the sig­ agreement with the meteoritic value nal-to-noise ratio. Moreover, using lines wh ich is thought to be representative of of different ions in the same velocity the early solar system, and cannot as yet Technical Advances components will allow to also determine be explained by the most recent and Measurements of equivalent widths of any turbulent velocity, another impor­ elaborated evolutionary models. This interstellar lines (IS) are indeed quite in­ tant and poorly known parameter for the has been achieved after 13 hours of dependent of the resolution. However, it dynamics of the interstellar medium. integration time with the CES linked to is weil known that they can yield very the ESO 3.6-m telescope via fiber optics, large errors on column densities when on a m - 5.0 star. The same measure­ Astrophysical Considerations: v multiple components are present on the ment is going to be published for ~ Oph Interstellar Medium line of sight and when lines are satu­ (m v =2.7) with a S/N ratio above - 7000! rated (on the flat part of the curve of The Li 7 equivalent width for IS diffuse (see Figures 1 and 2). However, this is growth). The former situation appears clouds such as those in front of ~Oph or restricted to the 4-5 stars on the whole very general, even for the short lines of Q Oph in wh ich typical temperature is sky which are bright enough but still sight of the solar neighbourhood. The very likely below 100 K, is of the order of shining through a dense cloud to en­ latter one is less common, at least for the mÄ, claiming thus for S/N ratios weil hance the expected column density. It part of the IS lines in the visible spec­ above 100. Because both stars are should be done in many individual clouds trum. But both cases will become se­ bright enough, these two lines of sight in order to statistically establish the sig­ vere limitations when probing the diffuse are weil studied with the ESO CES at La nificance of the first results and to direct­ IS medium beyond what is currently Silla, wh ich has provided R= 105 for Iy test the cosmic ray production of Li; reachable in the galactic plane with the more than ten years. The CES is usually the gain from one VLT unit should even available telescopes. fed by a 1.4-m telescope. The jump to allow to see possible variations in the 25 supernova rate through IS clouds in allow a much more complete mapping same order as kTCBR at z > 0.5, when CI other galactic spiral arms. of the Clouds, yielding in particular the Iines show up in the visible range. At Measurements in the visible range of still poorly known depth structure of the such epochs, contrary to the galactic molecules Iike CH, CH+, co+ or C2 are Clouds. ISM where collisions are much more also of prime importance for interstellar efficient, CI should be appreciably ex­ cited by the CBR. Up to now, because chemistry; they can also yield the car­ Astrophysical Considerations: 12 13 of the lack of resolution available even bon isotopic ratio C /C and the dark Extragalactic c10uds temperature (see e.g. Black and for the brightest asos to resolve the CI Van Dishoek, 1988; Crane et al., 1991; Another example of the need for reso­ line splitting, only an upper limit of 16 K Hobbs, 1973, Vladilo et al. , 1993). In lution in the 105 range at the VLT is the at z=1.776 has been assigned by Meyer fact, requiring very high spectral resolu­ study of the narrow absorption lines in et al. (1986). Such measurements in tion and S/N ratios, all these abundance quasar spectra. Just to give two exciting several asos' absorption systems at studies need to be performed towards cases, one can first mention the mea­ different z are waiting for the VLT. more and more distant targets, in very surement of the cosmic background The second case is the measurement different environments or where galactic radiation temperature, TCBR, at high red­ of the deuterium abundance in ade­ gradients become sensitive, or in other shifts. Besides black body microwave quate absorption components of the so­ spiral arms. In several hours of integra­ observations, IS lines from the lowest called Lya forest in quasar spectra. Only tion time with the VLT, the most abun­ rotational levels of the CN molecule directly observable in the far UV, the dant of these species might be detect­ around 3875 A have been used for many present-day IS value of the D/H ratio is able in the Magellanic Clouds, which years to derive the precise CBR temper­ still controversial since variations might would give access to less processed ature at the present epoch (e.g. Palazzi exist in the very local ISM (see e.g. Fer­ extragalactic material, to be compared et al. , 1992). However, this is the only let, 1992). New determinations are to the more extreme metaliicity towards point determined up to now. According under way with HST, but restricted to the galactic centre. Equivalent widths of to the Big Bang theory, TCBR depends in very short lines of sight. Furthermore, to several tens of mA in neutral IS sodium a simple way upon the redshift, and its go from the IS value to the primordial at 5890 A, good tracer of H I, are already determination at different z would really one - wh ich is of major cosmological gathered at R= 105 towards the very be a new extremely strong observation­ significance since it is highly sensitive to brightest Magellanic supergiants with al argument in favour of the Big Bang. A the universal baryon density and thus the 3.6-m telescope, but Call at 3930 A, convenient radiometer for directly can constrain the density parameter ­ providing information on ionization, is measuring the background radiation at requires very uncertain evolutionary just barely feasible at that resolution earlier epochs would be neutral carbon. models. While early models suggested a (Molaro et al. and Vladilo et al., 1993). The ground state of CI splits into three relatively low astration of deuterium (a The use of an 8-m telescope would levels separated by energies of the factor 2-3), the accumulation of obser-

7+6Lil (" Oph 6 Lil (" Oph 1.0005 f- I I 1- f- IlII ...... 998 ·r············· / 1{ .996 I I I .9995 I-- .\ -

.994 I - .999 I-- - .992

I I I I 6707.5 6708 6708.5 6707.5 6708 6708.5 Wavelength (Ä) Wavelength (Ä)

Figure 1: Interstellar 6. 7U I absorption doublets toward S Oph. The Figure 2: Same as Figure 1, but the calculated 7U absorption was data were gathered in June 1990 and June 1992 at ESO using the subtracted from the data points. These residuals thus reveal clearly CES linked to the 3.6-m telescope via a fiber link. The total integra­ the 6U absorption doublet. The depth of this doublet is less than tion time is 15h., the resolution is Al6-).. =100,000, and the signal-to­ 0.1 % of the continuum (see ordinates). The solid line represents the noise ratio 7500 per pixel, 01' 11 per resolution element, giving a 30 previously calculated 6U fit to this profile. Error bars are 1 o. limiting detectable equivalent width of 18 W~! The solid line represents the fit to the data with two interstellar absorbing clouds on the line of sight, and ta king 6U and 7U absorp­ tions into account. Ordinates are arbitrary units; error bars are 1 o. 26 vational data made apparent that fac­ The search for extra-solar giant mode, some examples having been tors of 10-50 are needed if the standard planets through extremely precise radial pointed out in e.g. Ferlet (1993) and Big Bang nucleosynthesis predictions velocity measurements is also now en­ Dravins (1993). It has to be noted also are to remain consistent with the obser­ tering the discovery phase, since a ± 5 that for both modes, a small spectral vations (see e.g. Audouze, 1987). The m/s sensitivity has been reached for range, say few tens of Ato record simul­ idea is therefore to evaluate D/H in very bright stars by two techniques: taneously both lines of the Call doublet, media as primordial as possible, and in Fabry-Perot and gas absorption cell. It is often sufficient. It would be advisable absorption systems having a wide range has been vigorously put forward as part to implement these modes at the VLT in abundances to be able to discrimi­ of the first stage of the recently coude focus, in order to provide enough nate between theoretical models of announced TOPS Program of NASA: room and stability, and avoid the field galactic chemical evolution. Toward Other Planetary Systems. For rotation of the Nasmyth focus. This will The feasibility of such measurements instance, Jupiter induces an amplitude moreover leave open the future possibil­ has been last explored by Webb et al. variation of 13 m/s in the radial velocity ity to dedicate a 4-m class "Auxiliary" (1991), assuming existing possibilities: of the Sun over aperiod of 11.9 years. telescope for high-resolution spectros­ 10 km/s resolution, 10 hours integration The limits for such long-term follow-up copy. time with a 4-m telescope on a mv of very many stars are more imposed by -17.5 aso (i.e. S/N=15), and the first 5 the apparent brightness of the observed Lyman lines are observed, implying zabs stars. This is why TOPS is intended to References ~ 2.6. Deuterium appears detectable be performed in partnership with the Audouze, J., 1987, in Observational Cosmol­ only as an extension in some of the Keck Observatory. ogy, lAU Symp. 124, Dordrecht: Reidel, Lyman line wings, but the DI line is not p.89. resolved and D/H very difficult to mea­ Black, J., van Dishoek, E., 1988, Astrophys. Astrophysical Considerations: sure, although some particular ranges of J, 331, 986. Stars Grane, P., Hegyi, D., Lambert, D., 1991, As­ values for the crucial velocity dispersion trophys. J, 378, 181. band for the HI column density may Last, in the field of stellar research, Dravins, D., 1993, in High Resolution Spec­ increase the chances of making cos­ one can briefly mention the study of non troscopy with the VLT, ESO Workshop, mologically significant measurements. radial pulsation in early-type stars. For Garehing, p. 55. Obviously, the VLT will make these D/H cooler stars, again the determination of Ferlet, R., 1992, in Astrochemistry of Cosmic analysis not only easier but also, as for the Li isotopic ratio, the measurements Phenomena, lAU Symp. 150, Dordrecht: the TCBR determination, more numerous: of surface magnetic fields from the Zee­ Reidel, p. 85. Webb et al. (1991) identify about 35 man broadening, the separation of dif­ Ferlet, R., 1993, in High Resolution Spectros­ suitable absorption systems with high ferent broadening mechanisms such as copy with the VLT, ESO Workshop, Gareh­ ing, p. 97. enough N I in the around 30 known H rotation and macroturbulence in G and Hobbs, L, 1973, Astrophys. J., 181, 795. ~ asos with z 2.6 and mv ::5 17.5; about K stars, time-resolved spectroscopy (on Lagrange-Henri, A.M., Gosset, E., Beust, H., 10 times more potential asos as yet time scales as low as -1 sec) of flares, Ferlet, R., Vidal-Madjar, A., 1992, Astron. undiscovered are expected with these the mapping of stellar surface features Astrophys., 264, 637. characteristics. It will thus be possible to (spots) through Doppler imaging tech­ Lemoine, M., Ferlet, R., Vidal-Madjar, A., perform a more extensive statistical in­ niques, and an approach to astroseis­ Emerich, G., Bertin, P., 1993, Astron. As­ vestigation in order to place tight con­ mology, etc. This kind of problems, that trophys., 269, 469. straints on chemical evolution models we have limited to those really needing Meyer, D., Black, J., Ghaffee, F., Foltz, G., York, D., 1986, Astrophys. J Lett., 308, and the Big Bang itself. spectral resolution in the 105 range and/ L37. or time resolution, are currently tackled Molaro, P., Vladilo, G., Monai, S., D'Odorico, at ESO; but the small aperture of the Astrophysical Considerations: S., Ferlet, R., Vidal-Madjar, A., Dennefeld, available telescopes simply prevents Planetary Systems M., 1993, Astron. Astrophys., in press; most interesting targets to be reached, ESO Preprint 907. The study of protoplanetary systems e.g. M dwarfs, T-Tauri stars, stars in Palazzi, E., Mandolesi, N., Grane, P., 1992, is another field of research we would like clusters, Pop II stars, etc. A new poten­ Astrophys. J., 398, 53. to mention here. The ß Pictoris disk is tially also very interesting case is the TOPS, AReport by the Solar System Explo­ the prototype of this new area which will study of the remnants of the AGB winds ration Division, Ed. B. Burke, NASA. Vladilo, G., Centurion, M., Cassola, G., 1993, surely become more and more impor­ during the post-AGB stellar evolutionary Astron. Astrophys., 273, 239. tant in the near future with the discovery phase towards planetary nebulae. Here Vladilo, G., Molaro, P., Monai, S., D'Odorico, of other systems. As for the previous again, all the targets are very obscured S., Ferlet, R., Vidal-Madjar, A., Dennefeld, fields, this asks for high spectral resolu­ and optically very faint. M., 1993, Astron. Astrophys., in press; tion at high S/N ratios, but also for high ESO Preprint 907. temporal resolution. In the case of Pie, Webb, J., Carswell, R., Irwin, M., Penston, ß Condusion the very large UV and visual circumstel­ M., 1991, MNRAS, 250, 657. lar absorption data base is presently It is obvious that the jump from 4-m to interpreted as the signature of comet­ 8-m (and a fortiori from 2-m) class tele­ ary-like bodies evaporating when graz­ scopes will very much increase the ing and falling onto the star, perhaps number of observable targets so that through perturbations of a huge small entirely new results will undoubtedly bodies reservoir by an already formed come up. The type of scientific ques­ planet orbiting ß Pie. Such events last tions we have discussed here are only few hours and have to be spectroscopi­ tractable with a spectral resolution VLT cally followed in velocity and equivalent mode in the 1-2 x 105 range. It does not width simultaneously in different lines at all mean that an ultra-high resolution 5 (Iike the Call doublet), or as close as mode (R ~ 3 x 10 ) would be useless; an possible in time (see e.g. Lagrange­ enormous amount of information on Henri et al., 1992). physical processes is waiting for that 27 REPORTS FROM OBSERVERS Probing the Properties of Elliptical Galaxy Cores: Analysis of High Angular Resolution Data 1 2 3 W W ZEIUNGER , P M0LLER and M. STIAVELU 1ST-ECF, Garching, Germany: 2ESA STScl Baltimore, Md, U.SA, 3Scuola Normale Superiore, Pisa, Italy

Introduction decoupled fram the main body of the alignment of the angular momentum The cores of elliptical galaxies provide galaxy are known to exist in many ellipti­ vectors of the stellar component in the important clues to the formation and cals and are widely interpreted as evi­ central region with respect to the main dynamical evolution of the parent galax­ dence for galactic cannibalism. How­ galaxy body, and finally core radio sour­ ies, e.g. recent episodes of star forma­ ever, different signatures of the de­ ces and X-ray emission found in ellipti­ tion, merging and cannibalism and pos­ coupling have been found wh ich may cals may indicate the presence of a sible presence of black holes. Many not necessarily be related to each other: (super) massive central object. More re­ "features" are observed in the central central light excess (Kormendy 1985), cently, unresolved nuclei have been dis­ region of ellipticals: Gores kinematically kinematically decoupled cores, i.e. mis- covered in many ellipticals and seem to be a much more common phenomenon than previously thought as also pointed out by the HST observations of the core of the early-type galaxy NGG 7457 (Lauer et al. 1991). Grane et al. (1993) reported central mass densities in ex­ 3 3 cess of 10 MQ /pc for several galaxies. Despite the fact that a wide range of core properties has been found in ellipti­ cal galaxies, no homogeneous survey 20 has been carried out so far with the necessary high resolution. Therefore, nature and physical interpretation of galaxy cores are still subjects of discus­ sion. The largest sampie published so far is the compilation by Lauer (1985) of CIl .;.J surface photometry for the cores of 42 C) (l) 15 early-type galaxies. Lauer's sam pie, '''-' ..0 however, is not complete and based on o single waveband observations carried out at a 1-m telescope with a medium seeing of about 1.7 arcsec FWHM and no comparable kinematic survey exists in the literature. 10 The Survey On the basis of the morphological classifications in the "Gatalogue of Prin­ cipal Galaxies" (Paturel et al. 1989) and the "Third Reference Gatalogue of Bright Galaxies" (de Vaucouleurs et al. 5 1991) all elliptical galaxies within a red­ shift of 3000 km/s were selected for the present survey, in total about 230 galax­ ies. The aim of the survey is to obtain a homogeneous set of high-resolution multi-colour surface photometry data and major-axis long-slit spectra for the whole sampie. As a first step VRI images 0.3 0.6 0.9 1.2 were obtained at the 2.5-m Nordic Tele­ scope (NOT) for the northern hemi­ Seeing FWHM [arcsec] sphere and at the ESO 3.5-m ND using Figure 1: Distribution of best seeing values of a sampie of 69 galaxies. The shaded area the direct imaging facility SUSI for indicates objects observed at the NOT. The remaining data are from the NTT using SUSI. southern hemisphere objects. In addi- 28 tion, using the ESO Archive Database I I facility within STARCAT, the ND data archive was systematically searched for adequate galaxy images. Long-slit I - spectra for southern hemisphere ob­ jects were obtained using the ESO 1.5-m telescope during several observ­ ing runs. For a sub-sampie of objects, images and spectra were obtained at 0.8 - - the ESO/MPI 2.2-m equipped with , , , , EFOSC2 and IRAC2 and also at the ND , with EMMI. The long-slit spectra should , , , provide information on global kinematic , (.J 0.6 I- ' - properties on the (ionized) gas and stars (~ , , I, , and identify candidates for high-resolu­ ,, tion studies. , , , , 100 Most of the effort so far has been put , , , in performing surface photometry and 0.4 I- ', , , ,'70 - further analysis of the images. The reso­ , , , 50 lution of the NOT and ND-SUSI data ,, ,, are of comparable order. The respective , , ," H1i'35 , " scales on the detector are 0.20 and 0.13 , ',20 arcsec/pixel. In Figure 1 the best-see­ 0.2 -,: I - ing values for 69 galaxies are presented ,," '10

wh ich have been analysed so far from :I 5 , the VRI data sampie. The seeing was '2 measured on stellar-like images in the I I respective frames. A data base of im­ ages obtained at very good (exception­ 0.5 1 al) seeing conditions is an essential in­ gredient for this project. However, in order to take full advantage of the high­ Figure 2: Gore resolution diagram for a sampie of21 galaxies observed at the NOT. The galaxy resolution data one needs also take into data are plotted with 10 error bars. The uppermost dotted line indicates the location of account effects of seeing, telescope isothermal cores. The other dotted curves represent non-isothermal cores with their respective spikyness lT . The units oflT are parts per thousand of the underlying core flux. Resolved cores guiding, etc. which affect the image e e will lie in the left part of the diagram, unresolved ones in the right part. quality. Some experiences on handling and analysing such images are pre­ sented in the following sections.

As shown by Meiler, Stiavelli & Zeilinger namely = seeing FWHMI Rn and Parametrization of the 2,w (1992 a, 1992 b), deconvolution of (Photometrie) Core Properties Re = Re/Rn with Re being the observed luminosity profiles cannot in general core radius and Rn the Petrosian radius The "classical" galaxy core parame­ compensate for lack of resolution (Iike as previously defined. Re is an isother­ ters are the central surface brightness bad seeing) and seeing corrections us­ mality measure, i.e. for an isothermal and the core radius (i.e. radius of the ing light profiles derived from galaxy Gare Re = 1, while ±,w represents an in­ isophote at wh ich the surface bright­ models are necessarily model-depen­ verse resolution measure, 2,w = 0 indi­ ness has decreased by a factor of two dent (i.e. one has to know in advance cates a fully resolved core and becomes with respect to the central surface properties and structure of the core and larger when the same core is observed brightness). It is immediately evident the underlying galaxy, to be able to de­ with worse seeing. The i:,w versus Re that these parameters depend crucially termine them). plane {core resolution diagram is there­ on the seeing conditions during the ob­ In order to reduce the seeing depend­ fore a useful tool for the first direct anal­ servations, and several studies have ad­ ence of the classical core parameters ysis of the observed data and their qual­ dressed the problem of how to consis­ we have introduced a new type of core ity. As a first step of analysing the single tently correct the parameters for these radius, wh ich for an isothermal (Hubble galaxy data and their location in the core seeing effects. The most commonly law) core is identical to the classical resolution diagram, one may quantify used methods of seeing correction have core radius but which does not depend the non-isothermality of the core in been to firstly extract the luminosity pro­ strongly on the core structure (e.g. pres­ terms of "equivalent point-source flux­ file of the galaxy, and then either (i) ence of a central point source). The Pe­ fraction" (spikyness parameter .iTe). Such deconvolve the profile directly with an trosian core radius (Petrosian 1976), an example is shown in Figure 2 using a appropriate PSF (Lauer 1985, (ii) mea­ wh ich is defined as the distance from sub-sampie of 21 galaxies observed at sure the core parameters of the ex­ the centre at wh ich the local surface the NOT. As a next step one may apply tracted luminosity profile and apply see­ brightness has fallen to some fraction of analytical models using parametrized ing corrections found by convolution of the mean surface brightness inside that central point sources, power laws or core models with a PSF (Kormendy radius, will reduce the influence of the central cusps introduced by a black hole 1985), or (iii) use directly the core para­ seeing since it depends only on the total to interpret the data. Such a study has meters derived from galaxy models fit­ flux inside the radius irrespective of its been carried out for the elliptical NGC ted to the luminosity profile (Kormendy distribution. Two core resolution para­ 1399 (Stiavelli, M011er & Zeilinger 1993). & Richstone 1992). It is evident that meters were introduced in order to A more detailed introduction to the these methods all have their limitations: quantify the observed core properties, core resolution technique together with 29 Figure 3: (a) R band image of NGC 4261 obtained with NTT-SUSI (exposure time 120 seconds). The frame has been aligned with the HST-PC image and rebinned to the PC detector scale. The seeing FWHM is 0.63 arcsec. (b) F555W band HST-PC image of NGC 4261 (exposure time 1700 seconds). The image is rotated 68° counter-clockwise with respect to the astronomical convention. (c) Combined SUSI and PC image using the co-addition technique after applying 150 iterations of the Richardson-Lucy restauration algorithm. (See also the at1icle on page 37 of this issue.)

a presentation of the first scientific re­ From star-like images a seeing FWHM central dust lane profit however from the sults and implications is given by M011er, of 0.63 arcsec was determined. An HST better signal-to-noise ratio of the Stiavelli & Zeilinger (1992a, 1992b). Planetary Camera (PC) image of NGC ground-based image. 4261 (detector scale 0.0439 arcsec/pix­ In the context of studying core re­ el) is shown in Figure 3 b as comparison. gions of elliptical galaxies at high spatial The frame was extracted from the HST resolution, one of the main open issues The Search tor Sub-Components Data Archive. The SUSI image was re­ is the question of the (non) presence of in the Nuclear Region binned to the scale and then aligned central black holes. There have been The use of image restoration tech­ with the PC frame. Because of missing extensive studies in this field (e.g. Kor­ niques becomes more and more popu­ field stars, the alignment of the two im­ mendy 1993, Nieto 1992) pointing out, lar not only in relation with HST data. ages was done using the (bright) galaxy however, mostly circumstantial evi­ One of the most versatile tools is the nucleus as reference point. Therefore dence like (radio) jets, compact (unre­ Richardson-Lucy technique whose al­ the accuracy of the alignment of the two solved) radio sources or core fluxes in gorithm is now part of major image pro­ images is only at the level of 1 (PC) pixel. excess of an isothermal galaxy core. cessing packages like IRAF and MIDAS. The selection of the "right" PSF is a The nearby elliptical NGC 4486 (M87) The straightforward application of this crucial part for the image restauration illustrates very weil the problem (Zeilin­ algorithm enables the correction of ear­ and subsequent co-addition. A well-ex­ ger, M011er & Stiavelli 1993). Despite its lier mentioned impairments of the image posed star within the frame was used for obvious signatures of nuclear activity quality by means of an appropriate PSF the SUSI image of NGC 4261. In the and non-isothermal core, it was up to and allows enhancements of faint struc­ case of the PC image the situation is now not possible to pinpoint the nature tures. The study of the nuclear gas and much more difficult. Given the fact, that of the central source. The kinematics in dust disk in NGC 3557 is such an exam­ the shape of the PSF varies as a func­ the nucleus is a key element in this pie (Zeilinger, Stiavelli & M011er 1993). tion of the location in the frame, one study. It is by now a well-established An interesting option of the method is needs to know the PSF in position of the fact that, in general, giant (high-Iumi­ the possibility to combine images hav­ observed object. Useful stellar images, nosity) ellipticals are not rotationally ing different PSFs (resolutions). The co­ repeating the exact instrument config­ flattened systems. Therefore, in order to adding technique, using the Richard­ uration, are therefore almost never avail­ account for their tri axial shape, they son-Lucy algorithm, consolidates the able. A solution to this problem gives the must have an anisotropic velocity dis­ signal of different images but conserves software tool TINYTIM (Kirst 1992) tribution. It has been shown that most of the resolution of the sharpest one. A wh ich can calculate an "artificial" PSF the light contribution in excess of an more detailed description of the method for a given observation date and instru­ isothermal model can be explained by is given by Lucy (1991) and Hook & Lucy ment configuration. The usage of the an even modest anisotropy in the veloci­ (1992). One is now in the position to take package is straightforward, however, ty field (Binney & Mamon 1982). The full advantage of the high-resolution im­ one has to be aware that TINYTIM is kinematic signature of a central dark ages in the HST Data Archive, by co­ only a tool based on current best fits of mass concentration, however, is very adding them with (high signal-to-noise) aberration values for the various mirror difficult to detect since it requires spec­ ground-based data. In order to illustrate positions and current best estimates of troscopic data with aresolution at the the capabilities of this method the well­ the obscuration positions and sizes subarcsecond level. NGC 1399 is such a known elliptical NGC 4261 (Ford et al. wh ich may still not describe the HST case where the combination of radio, 1993) has been chosen. The core region PSF exactly. After applying 150 itera­ photometric and (stellar) kinematic sig­ of this galaxy is characterized by a dust tions the deconvolved image was con­ natures (each of them alone would not lane (radial extent less than 2 arcsec) volved again with the appropriate PSF. have been conclusive) has led to the and a point source. Figure 3a shows an The result is shown in Figure 3 c. The confirmation of a central black hole of ND image of NGC 4261 obtained with resolution of the PC image has been about 6 x 109 MG (Stiavelli, M011er & SUSI (detector scale 0.13 arcsec/pixel). retained, shape and structure of the Zeilinger 1993). 30 References Kormendy, J., 1985, Astrophys. J. (Lett.), 1992b, Mon. Not. R. Astr. Soc., submitted. 292, L9. Nieto, J.-L., 1992, in Morphological and Kormendy, J., 1993, in High Energy Neutrino Physical Classification of Galaxies, ed. G. Binney, J. & Mamon, GA, 1982, Mon. Not. Astrophysics, ed. V.J. Stenger et al. (World Longo et al. (Kluwer). R. Astr. Soc., 200, 361. Seientifie). Paturel, G., Fouque, P., Bottinelli, L. &Gou­ Crane, P., et al. 1993, Astr. J., in press. Kormendy, J. & Riehstone, D., 1992, Astro­ guenheim, L., 1989, "Catalogue of Princi­ de Vaueouleurs, G., et al., 1991, "Third Refer­ phys. J., 393, 559. pal Galaxies" (Lyon). ence Catalogue of Bright Galaxies" Lauer, T.R., 1985, Astrophys. J., 292, 104. Petrosian, v., 1976, Astrophys. J. (Lett.), 209, (Springer). Lauer, T.A., et al, 1991, Astrophys. J. (Lett), L1. Ford, H., Jaffe, W, Ferrarese, L., van den 369, L41. Stiavelli, M., Moller, P. &Zeilinger, WW, Boseh, F. &O'Connell, R.w., 1993, STScl Luey, L.B., 1991, ST-ECF Newsletter, 16, 6. 1993, Astr. Astrophys., in press. Newsletter, 10, 1. M0l1er, P., Stiavelli, M. &Zeilinger, WW, Zeilinger, WW, M0l1er, P. & Stiavelli, M., Hook, R. & Luey, L., 1992, ST-ECF Newslet­ 1992a, in Structure, Dynamics and Chemi­ 1993, Mon. Not. R. Astr. Soc., 261,175. ter, 17, 10. cal Evolution of Ellipticaf Galaxies, ed. I. J. Zeilinger, WW, Stiavelli, M. & Moller, j'., Kirst, J., 1992, "The TinyTim User's Manual" Danziger et al. (ESO). 1993, Nature, submitted. (STSel). M011er, P., Stiavelli, M. &Zeilinger, WW,

Light Curves of Miras Towards the Galactic Centre 2 1 c. ALARO 1, A. TERZAN , J. GUIBERT lCentre d'Analyse des Images, Observatoire de Paris, France; 20bservatoire de Lyon, France

105 years, is a complex process and the Introduction A First Step in the Inventory object of many investigations. For in­ Long Period Variables represent a late stance, Vassiliadis and Woods (1993) Here we present the first results of a stage in the evolution of stars of inter­ suggest that mass loss could occur in systematic study of variable objects in a mediate masses. Mass loss, wh ich brief superwind phases separated by field of about 10 x 10 degrees towards leads them to planetary nebulae in a few long quiescent periods. the Gaiactic Centre. The first step of our

I * 422.654 * * * ~ * ~ (a) N - N * • (b)

* * * ~ '

424.1 62 1II (C) (d) ~ • 0.018

Cl 0.047 0.12

Cl 0.285

8 I~ ~ IA o o IM IM o 2xl0-, 4xl0-, 6xl0 8xl0,-> o 2xl0 4xl0- 6xl0- 8xl0n-J

Figure 1: Example of light curve derived from ESO Schmidt plate measurements. (a) time sampling of R magnitudes; (b) derived light curve; (c) Renson's method; (d) periodogram with Scargle's false alarm probability

31 investigation deals with the thousands of not being too sensitive to gaps in the better knowledge of the period-Iuminos­ of variable stars discovered by Terzan data. The periodogramme yields an esti­ ity relations for various kinds of objects, (Terzan, 1982, Terzan, 1990 and ref. mate of the probability of false periodici­ and understanding of the relations be­ therein) on ESO Schmidt plates. We ty detection. Both methods lead to simi­ tween the shape of the light curves, have scanned 22 ESO Red Schmidt lar results in most cases, as exemplified mass loss and other properties of vari­ plates centred on the star 45 Oph., with by Figure 1. As a result, we have ob­ able objects. the MAMA measuring machine (e.g. tained light curves for 118 variables Guibert and Moreau, 1991). In this field, (80 % of the stars under investigation). we have selected 150 variables with 6.mR > 2. The plates were calibrated Developments in Progress Referen ces with 55 photometrie standards. This programme is being continued A. Vassiliadis, P.R. Wood, 1993, Astrophys. by a systematic search for variables in J. in press. Light Curves A. Terzan, 1982, Astron. Astrophys. Suppt. the whole 100-square-degree field. It 49,715. Two methods have been imple­ will require additional plates to cover the A. Terzan, 1990, The Messenger, 59, 41. mented to derive the light curves from whole range of periods, as weil as near J. Guibert, O. Moreau, 1991, The Messen­ the time sampling series. The first one infrared and radio measurements. In­ ger, 64, 69. (Renson, 1978), presents the advantage terpretation of these data will lead to a P. Renson, 1978, Astron. Astrophys. 63, 125.

NGC4636 - a Rich Globular Cluster System in aNormal Elliptical Galaxy 1 1 2 4 M. KISSLER , T RICHTLER , E. V HEL0 , E.K. GREBEL 3, S. WAGNER , M. CAPACCIOL/5 lSternwat1e der Universität Bonn, Germany; 20sservatorio Astronomico di Bologna, Italy; 3ESO, La Silla, Chile; 4Landessternwat1e Heidelberg, Germany; 50ipat1imento di Astronomia, Universita di Padova, Italy

1. What Drives the Investigations clusters, colour, and spatial distribution) for ellipticals in the rich Virgo cluster it is of Globular Cluster Systems of to those of their host galaxies, the study about 6. The interpretation of this ten­ Elliptical Galaxies? of extragalactic GCSs leads to a new dency is far from being unambiguous, level of problems, which could not be but the dependence on the environment In 1918 Shapley started to use the foreseen by the study of the galactic suggests that interaction between galactic globular clusters to explore the GCS alone. One of the systematic galaxies may playa role. spatial dimensions of our Milky Way. patterns emerging from all previous Other morphological properties, for Three quarters of a century later, we still studies is that the richness of a GCS example the relation between the spatial cannot claim to have understood the depends somehow on the environment distribution of clusters and the light pro­ properties of our globular cluster system of the host galaxy. M87 became the first file of the host galaxy, or the luminosity (GCS) in the context of the early evo­ example of a giant elliptical galaxy, 10­ function of globular clusters, also bear lution of the Galaxy. This is mainly cated in the dynamical centre of a rich potential information wh ich may finally due to the fact that there are severe galaxy cluster, found to be surrounded lead us to an understanding of the for­ problems in disentangling age and by a huge number of globular clusters mation history of GCSs and thus to gain metallicity, wh ich are the most signifi­ (Baum 1955, Sandage 1961). Later on, deeper insight in the formation and cant parameters in theories of galaxy very rich GCSs have been also discov­ structure of the host galaxies them­ evolution. ered in the central giant ellipticals NGC selves. This field is still in the phase Given these problems with weil ob­ 1399 in the Fornax cluster (e.g. Wagner where the investigation of individual gal­ servable clusters, what can we hope to et al. 1991), NGC 3311 in the Hydra axies provides interesting and useful learn from the study of faint images of cluster (Harris et al. 1983), and NGC contributions to the general knowledge. globular clusters around distant galax­ 4874 in the Centaurus cluster (Harris The elliptical galaxy NGC 4636 appears ies, where individual clusters appear 1987). Harris and van den Bergh (1981) to violate these general properties. NGC star-like and only integrated magnitudes introduced the "specific frequency" S 4636 is supposed to be a member of the can be determined? as a quantitative measure: S = N. Virgo cluster of galaxies though it is Research on GCSs over the past 20 1Q0.4(Mv+15), where N is the total number Iying weil outside the main body of the years showed that there is an amazing of globular clusters and Mv the absolute cluster, in a region where the density of variety in the morphologies of GCSs visual brightness of the host galaxy. The galaxies is quite low. Using photo­ (see Harris 1991 for a review). Most above mentioned galaxies have S val­ graphie plates, Hanes (1977) deter­ studies refer to elliptical galaxies, be­ ues between 12 and 18. mined a specific frequency of 9.9 ± 3 cause globular clusters in spirals are All galaxies that do not occupy central for the GCS of this galaxy, wh ich is a normally much less numerous and they positions in galaxy clusters possess surprisingly high value considering loca­ are difficult to identify due to the in­ poorer GCSs, but a relation with the tion and environment of NGC4636. We homogeneous background of bright environment persists: e.g., the normal reobserved NGC4636 using CCO imag­ stars or H I1 regions. Relating the proper­ elliptical galaxies in the sparse Fornax ing to investigate the properties of its ties of GCSs (such as total number of cluster have a mean S value of 3, while GCS with higher accuracy. 32 Figure 1: Six N7T frames combined to a single image of one hour Figure 2: The image shown above results from subtracting a model of effective exposure time. The frame shows a 7.5' x 7.5' field north­ the galaxy light, which has been obtained by a median filtering east of NGC 4636. technique. This is the frame on which we performed our search and photometry of globular cluster candidates. The crowding of stellar­ like images near the galaxy centre is striking.

2. Our NTT Observations 3. The Specific Frequency 1992), it may indicate a large total mass ofNGC4636 ofNGC4636 which in combination with a rich envi­ ronment causes effective accretion of NGC 4636 was observed at the ND To calculate the total number of matter. This matter could be for exam­ using EMMI and a 1k Thomson chip in globular clusters, we had to correct for pie in the form of dwarf galaxies. We July 1992, in the context of a collabora­ the incomplete spatial coverage of the recall in this respect that the dwarf tion between German and Italian groups galaxy and for the fact that we only see spheroidal in the constellation Fornax interested in the GCS problem. The see­ the brightest part of the luminosity func­ possesses 5 globular clusters. Adding ing during our run was only moderate tion (see below). After all corrections, we 500 dwarf spheroidals of the Fornax (1.5") and this prevented an investiga­ obtained a total number of 3500 ± 200 type to NGC4636 could account for tion of the luminosity function beyond its globular clusters around NGC 4636, 2500 clusters, but would increase its turnover (see section 4). but the data wh ich corresponds to a specific fre­ totalluminosity by only 0.1 mag. quality turned out to suffice for a study quency of $ = 7.3 ± 2.0, if (m - M) of the main properties of the GCS of = 31.2 and Mv = -21.7 ± 0.3 are NGC 4636. We combined six frames in adopted. As can be noticed, the error in 4. The Luminosity Function of the the V filter of 10 minutes each to a frame $ is quite substantial. This is the conse­ GCS: Gaussian or Power Law? of an effective exposure time of one quence of the fact that $ is very sensi­ hour (Figure 1). We modelIed the galaxy tive to the absolute brightness of the Apparently, globular cluster luminosi­ light by a median filtering technique and galaxy, and an error of 0.1 in (m - M) ty functions (GCLFs) exhibit a nearly uni­ subtracted it from the original frame to implies an error of 10% in $. versal shape, wh ich in the past has been obtain a homogeneous background. We This $ value of 7.3 ± 2.0 for NGC represented by Gaussians with disper­ then ran DAOPHOT on the resulting im­ 4636 is marginally below the one found sions of 1.3 mag and a peak or "turn­ age (Figure 2). About 1500 point sour­ by Hanes (1977), and slightly higher over" of Mv = -7.1 ± 0.3 mag, as de­ ces down to a magnitude of 24.5 were than the mean value for elliptical galax­ rived for several ellipticals in the Virgo identified. At the faint magnitude limit ies in the Virgo cluster. It is thus at the cluster (Secker & Harris 1993). For we reached a completeness in finding upper limit of what can be considered a NGC 4636, we find the turnover to be at point sources of 60%. "normal" specific frequency. However, Mv = 24.1. This corresponds to a dis­ We calibrated our data by simulating the question remains what distinguishes tance modulus of (m - M) = 31.2 ± 0.3, aperture photometry on a frame centred NGC 4636 for example from NGC 4697, which is in good agreement with previ­ on NGC 4636. The zeropoint has been another Virgo elliptical with $ = 3.5, but ously determined distances of NGC obtained from the photometry published almost twice as bright. There is much 4636 (31.1 ± 0.4 using the supernova by Poulain (1988). and we estimate a room for speculation. NGC 4636 has an 1993a, Capaccioli et al. 1990; zeropoint error of 0.05 mag. X-ray luminosity ten times as high as 30.96 ± 0.08 by surface brightness fluc­ To account for contamination with NGC 4697 (Roberts et al. 1991) and tuation, Tonry et al. 1990). background objects we statistically sub­ presumably a high dark matter content We believe that the choice of a Gaus­ tracted the objects found on a frame 7' (Saglia et al. 1992). While the X-ray flux sian for a GCLF does not bear any phys­ away from the galaxy centre, and con­ is not generally correlated with $, as the ical significance. In particular, the possi­ sidered the remaining objects as globu­ pair NGC 1399 and NGC 1404 in the ble existence of a universal turnover lar clusters belonging to NGC4636. Fornax cluster shows (Richtler et al. magnitude does not mean that there is a

33 2 NGC 4365 and 4649, Harris et al. 1991). while in poorer systems the GCSs seem to follow the light of the host galaxy cD (NGC 3379, Pritchet & van den Bergh, ., 1985; NGC 1404, Richtler et al. 1992). " Again, this can be understood as an 1.5 indication that rich cluster systems " might be partially formed through ", merger er accretion processes. -."

1 6. Concluding Remarks o 1 g This investigation of GCS of NGC 4636 demonstrates that more questions are open than answered. The . fundamental problem of what deter­ . 5 .. mines the total number of globular clus­ .. ters in a galaxy is still open, but the first .. ' steps to an answer point in directions that are closely connected with general problems of galaxy structure and evolu­ tion. Moreover, the use of globular clus­ ter luminosity functions as distance indi­ 1.5 1. 75 2 2,25 2.5 cators will perhaps play an important log(rad1us["]) role in the forthcoming VLT era. A huge potential of information about the phys­ Figure 3: This plot compares the profile of the sur1ace density ofglobular clusters with the light ics of galaxies and their stellar popula­ of NGC 4636. The abscissa is the logarithm of the galactocentric radius (arcsec) along the major axis. The ordinate is the logarithm of the number ofglobular clusters per square arcmin. tions awaits its exploitation. Open circles represent the globular cluster profile. The small dots are measurements of the galaxy light. The density profile ofglobular clusters is flatter than the galaxy light. This suggests that the globular clusters do not share the dynamical history of the field population.

References Baum, WA., 1955, PASp, 67, 328. Capaccioli, M., Cappellaro, E., Della Valle, characteristic mass among globular clusters decreases with increasing M., D'Onofrio, M., Rosino, L. and Turatto, clusters connected with this charac­ galactocentric distance in the same way M., 1990, ApJ 350, 110. Cohen, J., 1988, AJ 95, 682. teristic magnitude. Richtler (1993) and as the galaxy light itself. If it does, this Fischer, P., Hesser, J.E., Harris, H.C., Harris & Pudritz (1993) show that the would indicate that globular clusters Bothun, G.D., 1990, PASP 102, 5. mass distribution of globular clusters in and field population behave dynamically Hanes, DA, 1977, MemRAS 84,45. the Milky Way, M31, and some Virgo in the same way and probably date from Harris, WE., van den Bergh, S., 1981, AJ 86, galaxies is weil described by apower the same epoch of formation. For many 1627. law ~~ - m-ü where a is about -1.7. In galaxies this is not easy to investigate Harris, WE., Smith, M.G., Myra, E.S., 1983, the Milky Way and M31, i.e. in those due to the large scatter in the globular ApJ 272, 456. galaxies where the luminosity function cluster counts in small number statis­ Harris, WE., 1986, AJ 91, 822. can be followed weil beyond the turn­ tics. In case of rich systems like the one Harris, WE., 1987, ApJ Lett. 315, L29. Harris, WE., 1991, ARM 29,543. over magnitude, this power law con­ discussed, the statistics are more trust­ Harris, WE., Allwright, J.WB., Pritchet, C.J., tinues beyond the turnover magnitude worthy. We find the density profile of the van den Bergh, S., 1991, ApJS 76, 115. and has a cut-off at very low mas­ GCS of NGC 4636 to be flatter than the Harris, WE., Pudritz, A.E., 1993, AJ, in press. ses, probably due to the dissolution of galaxy halo light itself. If we represent Mandushev, G., Spassova, N., Staneva, A., less massive clusters. Concerning NGC both pofiles by apower law Q - r-(t., 1991, A & A 252, 94. 4636, we transformed the luminosities where Q is the surface density of globu­ Poulain, P., 1988, A& AS 72, 215. of globular cluster candidates to lar clusters and r the projected ga- Pritchet, C.J., van den Bergh, S., 1985, AJ masses using the relation given by lactocentric distance, we get 90, 2027. Mandushev et al. (1991), and calculated a=-1.0±0.1 for the GCS and Richtler, 1., Grebel, E.K., Domgörgen, H., Hilker, M., Kissler, M., 1992, A&A 264,25. the mass distribution of the globular a = -1.5 ± 0.1 for the galaxy light. The Richtler, 1., 1993, 11 '11 Santa Cruz Sommer cluster in NGC 4636. We found b = -1.9 density profile is plotted in Figure 3, Workshop proceedings, The globular clus­ which fits weil to the Milky Way system. where the ordinate is the logarithm of ter-galaxy connection, in press. The existence of a power-Iaw (wh ich is the number of globular clusters per Sandage, A., 1961 The Hubble Atlas of equivalent to the absence of a charac­ square arcminute. The abscissa is the Galaxies, Carnegie Inst. Washington Publ. teristic mass scale) and its apparently logarithm of the galactocentric radius in N.618. universal shape are remarkable fea­ arcseconds along the major axis. The Saglia, R.P., Bertini, G., Stiavelli, M. 1992, tures. A satisfactory explanation has yet small dots are measurements of the ApJ, 384, 433. to be found. galaxy light with an arbitrary offset. The Shapley, H., 1918, ApJ 48,89. Secker, J., Harris, WE., 1993, AJ 105, 1358. four open circles represent the globular Tonry, J.L., Ajhar, E.A., Luppino, GA, 1990, cluster density profile. Interestingly, this 5. The Density Profile AJ 100, 1416. has also been found in other rich globu­ Tu 11 y, R.B., Shaya, E.J., 1984, ApJ 281, 31. A further interesting question is lar cluster systems (NGC 1399, Wagner Wagner, S., Richtler, T., Hoop, U., 1991, whether the surface density of globular et al. 1991; NGC 4472, Cohen 1988; A&A241,399.

34 Imaging the Globules in the Core of the Helix Nebula (NGC 7293) J. R. WALSH, ST-ECF, ESO J. MEABURN, Oept. ofAstronomy, University ofManchester, England

Introduction though higher velocity structures have dark. Of the knots observed by Meaburn NGC 7293 is one of the closest been found ([5], [3)). et al. [7] the one with the highest ab­ planetary nebulae and the only one in sorption had a central extinction of 0.5 wh ich small scale structures can be Knots and Tails mag. and a projected diameter of 1.4" easily resolved on ground-based im­ (3 x 1015 cm). If such a globule were ages. The distance is about 130 pc [1] Around the periphery of the inner low spherical and had a dust content typical and the central star has an effective ionization shell there are numerous of interstellar gas and with interstellar temperature of - 120,000 K [2] making small (- 1") emission knots, some with gas-to-dust mass ratio then the density it a typical high ionization planetary tails pointing radially away from the star is - 5 x 105 cm-3 and its total mass nebula with emission lines of He 11 and [6J. With the ND and EFOSC2 in 1990 :::: 10-5 MG). higher ionization species. On account of (before the commissioning of EMMI) we its proximity the projected size of the obtained CCO images in low (Ha + [N 11)) New Observations nebula is very large - the bright inner and high ([0111)) ionization emission in rings are 13' in diameter but there is a good seeing of some of these knots. With the new large CCO chips and the prominent ring structure of radius 10' The result was unexpected: whilst in low big field available for imaging at the and faint extensions, clearly belonging ionization emission the knots show up Cassegrain focus of the ND with EMMI to the nebula, out to at least 15'; the as bow-shaped structures with a bright we can obtain in one image the whole of projected size is thus at least half a tip on the side of the globule nearer to the central region of the Helix nebula degree (eg. [3)). On the large scale, the the central star and a tail extending ra­ and examine in detail all the knots and nebula shows some resemblances to a dially outwards, at [0111] no emission tails. This was done in August 1992 and helix (hence its name) in the low ioniza­ was seen, only a depression in the local some of the spectacular images are tion emission (eg [N 11)) but in high ioniza­ smooth [0111]; the knots were thus seen shown here. Figure 1 shows the whole tion emission a central, nearly spherical, in absorption. On consideration, this is of an Ha + [Nil] Thomson 10242 CCO volume [4] is seen. Some attempts have not so surprising if the knots are dusty image covering the central 7.5' of been made to understand the velocity and are seen against background [0111] NGC 7293. The star at the centre is the structure in terms of a radially expand­ emission [7]. If a dense dusty knot lies ionizing star of the nebula. In Figure 2 is ing helix but the real 3-D structure is on the near side of the central emitting shown the corresponding [0111] image. probably more barrel-shaped with an [0111] volume then it will absorb the Comparison of Figure 1 and 2 shows expansion velocity of - 25 km/s, al- background [0111] radiation and appear that not all the globules seen in emission

Figura 1: A photographic representation of the NTT + EMMI GGO Figure 2: A photographic print of the NTT + EMMI GGO image of the image of the core of NGG 7293 taken with an Ha + [N 11] filter. A Helix nebula taken with an [OIl1j5007A. filter is shown at the same logarithmic intensity scale was used and the size of the field is scale and orientation as Figure 1. 450 x 450" (10" = 1.9 x 10/6 cm); north is at the top and east to the left. 35 Figure 3: An enlarged view of both the Ha + [NI/] (upper) and [01/1] Figure 4: An enlarged view of both the Ha + [NI/] (upper) and [01/1] (Iower) images of the globules and tails in the north-east corner of (Iower) images of the region of extended dust absorption to the Figure 1 is shown. The bright globule which shows both Ha + [N 1/] south-east of the core of the Helix nebula. The largest globule with and [01/1] emission is arrowed. the deepest absorption is indicated.

on Figure 1 are found on Figure 2. This surroundings. Figure 4 shows an en­ neutral globules and producing a bow can be simply understood in terms of largement of the large scale dust feature shock around the globule. In addition, if the globules being distributed along the to the south-east. The globule in the the globules are stationary then there line of sight through the nebula, some centre of this field (arrowed), which will be ionized gas streaming past at being on the near side of the [0111] zone, appears to have no low ionization emis­ - 20 km/s from the expanding nebula. some on the far side; only those on the sion, is the largest found with a max­ All these effects may contrive to drag near side give rise to observed absorb­ imum diameter of 4" and also has the material off the globule and entrain it in a ing globules. Of the - 600 globules deepest absorption. radial tail as observed. Meaburn et al. [7] counted in emission on Figure 1, some showed that the size and density of the 40 % are found in absorption in Figure 2, globules are such that they could sur­ Nature of the Globules consistent with this hypothesis. Only vive long enough for such ablation pro­ three globules were seen with [0111] The low ionization crescent-shaped cesses to be important. emission from the bow-shaped heads, heads to the globules are presumably One of the abiding puzzles is the ioni­ and one of these is seen in the lower left attributable to radiative ionization by the zation mechanisms for the tails. Early of Figure 3 (arrowed), which is an en­ photons from the central star, with most work ([8], [9]) suggested they could be largement of a region to the north-east globules being beyond the 0++ ionizing ionized by the diffuse radiation field of the central star. The three globules zone where the photons have lower since they are shadowed by the optical­ with [0111] emission are also those Glos­ energy. However, central stars of Iy thick globule from the direct ionizing est in projected distance to the central planetary nebulae are known to have radiation of the central star. Hartquist & star; presumably they must be embed­ high velocity winds (typically 2000 km/s Dyson [10] and Dyson, Hartquist & Biro 8 1 ded in the [0111] zone whilst the other and mass loss rates -10- MG) yr- ) so [11] suggest that the material in the tail globules are in lower ionization that there may be wind impacting the could be a low Mach number shock 36 ionized flow caused by interaction with a the globules themselves [13]. The CO 3 Walsh, J.R. & Meaburn, J., 1987, low velocity wind, perhaps arising in the linewidths are small suggesting molecu­ MNRAS, 224, 885. expanding ionized gas rather than in the lar gas at - 25 K. Further observations at 4 Meaburn, J. &White, N.J., 1986, ASS, 82, stellar wind itself. Clearly the ionization high spatial resolution in the optical and 423. mechanism in the vicinity of these millimetre will enable the parameters of 5 Meaburn, J. & Walsh, J.R., 1980, Astro­ phys. Letl., 21, 53. globules and their tails need to be ex­ the globules, such as the gas and dust 6 Vorontsov-Velyaminov, BA, 1968. In plored more closely and NGC 7293 pro­ content, to be determined and their for­ Planetary Nebulae. lAU Symp. No. 34 vides an excellent site. mation and evolution to be more eds. Osterbrock, D.E. & O'Dell, G.R., Where do the globules come from? thoroughly investigated. So far no other Reidel, p.256. Perhaps they represent clumpy ejecta planetary nebulae with similar small­ 7 Meaburn, J., Walsh, J.R., Glegg, R.E.S., from the progenitor asymptotic giant scale structures have been observed Walton, NA, Taylor, D. & Berry, D.S., branch (AGB) star ejecta during a phase but there is no reason to think that the 1992, MNRAS, 255, 177. of mass loss or are formed through in­ Helix is atypical and such structures 8 Kirkpatrick, J.P., 1972, MNRAS, 176, stabilities when the hot fast wind from probably exist in all planetary nebulae. 381. the central star collides with the slow Until more are found the Helix will con­ 9 Van BIerkom, D. & Arny, 1., 1972, MNRAS, 156, 91. higher density red giant wind. Dyson et tinue to be an ideal laboratory for the 10 Hartquist, T.W. & Dyson, J.E., 1993, al. [12] have suggested that the knots study of these ionized-neutral/dusty in­ QJRAS, 34, 57. could be remnants of SiO maser spots terfaces. 11 Dyson, J.E., Hartquist, T.w. & Biro, S., wh ich were formed in the atmosphere of 1993, MNRAS, 261, 430. the AGB star and have survived ejection References 12 Dyson, J.E., Hartquist, T.w., Pettini, M. & and photoionization. CO emission has 1 Daub, G.T., 1982, ApJ, 260, 612. Smit'" L.J., 1989, MNRAS, 241, 625. been detected from some of the glob­ 2 Bohlin, R., Harrington, J.P. & Stecher, 13 Huggins, P.J., Bachiller, R., Gox, P. & ules even though the beam is larger than T.P., 1982, ApJ, 255, 87. Forveille, T., 1992, ApJ, 300, L17.

OTHER ASTRONOMICAL NEWS Detection of Faint Extended Structures by Multiresolution Wavelet Analysis 1 1 2 3 F MURTAGH , WW ZEILINGER , J.-L. STARCK and H. BÖHNHARDT

1ST-ECF; 2ESO, OCA Nice, Cisi-/ngfmierie Va/bonne; 3University ofMunich

1. Introduction It has been known for a long time that alignments or to develop useful The wavelet transform, in common multiresolution approaches to images strategies for image compression. An with other image transforms such as the allow an image to be interpreted as a isotropic wavelet appears to be a good Fourier or the Haar transforms, can be sum of details wh ich appear at different choice for the investigation of astronom­ used to produce insightful perspectives resolutions. Furthermore, each scale of ical objects. on image data. Some particular at­ resolution may pick up different types of The natural incorporation of a suite of tributes of the wavelet transform will be structure in the image. For example, a resolution scales in the wavelet trans­ discussed in the next section, which coarse resolution may pick up gross form has been beneficially used in differ­ seem to make it very appropriate for structure, and finer resolutions allow ent application fields. Such multiresolu­ astronomical image data. Two illustra­ progressive insights into faint and tex­ tion analysis is particularly appropriate tive examples will be used, where the tured structures. for astronomical data since the struc­ original images do not provide much Consider the convolution of an image tu res we want to recognize have very indication of underlying faint extended with a Gaussian. The effect is to smooth different scales. Apriori we cannot structure. The wavelet transform can the image. Now consider that Gaussian know the size of a local neighbourhood effectively uncover such faint structure. to have a scale parameter, a function of where contrast should be enhanced, i.e. It is a new mathematical tool which the standard deviation (e.g. 1s, 2s, 3s, we cannot define in advance an optimal ought to be kept in mind when exploring ..., where s is the standard deviation). resolution level for analysing an image. and analysing image data. By varying the scale parameter, a se­ The wavelet transform implicitly caters quence of Gaussian-filtered images is for a more sophisticated astronomical arrived at. These provide a sequence of 2. Multiresolution Analysis with image model than the simple resolution scales. The Gaussian func­ "background plus objects" image mod­ the Wavelet Transform tion is not a wavelet; for the latter certain el. The latter, implicitly, is very widely We will briefly motivate the use of properties are required, such as transla­ used: object detection packages esti­ wavelets by making reference to (i) the tion invariance, and a "scaling property" mate the local background, and then property of multiresolution usually - a dilation invariance property - wh ich define protrusions from this as objects; associated with the wavelet transform; relates the filtered images at two or in image restoration, a two-channel and (ii) the perspective of the wavelet successive scales. The wavelet used in algorithm regularizes the background transform as a discrete convolution this article is isotropic, wh ich is unlike differently from non-background ob­ filter. some other wavelets used to enhance jects. In practice, astronomical images 37 often encapsulate more complex, lution levels of the image, - wh ich are Compared to other methods for the superimposed objects and/or structures sensitive to faint structures, and wh ich coma structure enhancement (see Lar­ than is allowed for by the traditional are produced and output in the new son and Sekanina, 1984; A'Hearn et al., image model. MIDAS wavelet package. Thus, what 1986; Schulz, 1990; Boehnhardt and Let us take image restoration as an may be referred to as a "level 1" image Kohoutek, 1992) the wavelet analysis example. There are different ways of is the difference between the original can be applied in a very convenient and enforcing, e.g., the smoothness of the image and the first wavelet-transformed straightforward way to cometary coma background, or of planetary objects, by image; the "level 2" image is the differ­ images. Most importantly, it does not adapting the widely-used Richardson­ ence between the first and the second depend on the accurate determination Lucy (RL) method. A good alternative is wavelet-transformed images; etc. Simi­ of the nucleus position as a reference de-noising through shrinking noisy lar objectives have also been pursued point for angular or radial shifts (method wavelet coefficients. The latter define using another wavelet-based approach, of Larson and Sekanina, and of Schulz) the wavelet-transformed image. Fur­ the H-transform. The latter is available in or for the alignment of the images ana­ thermore wavelet coefficients are ob­ MIDAS as a command FILTER/ Iysed (allother methods). Therefore, the tained wh ich define the transformed im­ ADAPTIV. interpretation of the wavelet analysed age at varying levels of resolution. The coma structures should not suffer from original image may be reconstructed 3. Cometary Coma Analysis the presence of image processing ar­ from the series of wavelet-transformed tifacts or "diseases" (artificial structures, images. A noise-removal strategy is The abilities of the wavelet transform modified geometry, "blindness" as re­ based on the wavelet coefficients being to provide insight on cometary comas gards ring structures) as do each of the clipped in value if they are considered to was tested with images of the periodic previous methods. be associated with noise. Such an ap­ comet P/Swift-Tuttle. The data were In summary, the wavelet analysis of proach has been pursued by various collected with the 1.2-m telescope at cometary images promises to become a authors. This strategy was investigated the Calar Alto Observatory in Spain in very useful tool for the enhancement of by Starck and Murtagh (1993) with the October and November 1992 and were faint coma and tail structures. The iden­ conclusion that such de-noising, in the kindly provided by Dr. K. Birkle of the tification of jets, fans, shells and bright­ framework of RL restoration, leads to Max-Planck-Institut für Astronomie, ness excess areas, and the derivation of significantly improved detection of faint Heidelberg. their characteristics from such images objects. This de-noised RL image resto­ Figure 1 shows the cometary coma of can be used for the determination of ration method, used in the preparation P/Swift-Tuttle observed through the CN important properties of cometary nuclei of some of the images discussed below, molecule filter of the IHW filter set. The (rotation motion and axis, nucleography is available in the MIDAS image pro­ isophote pattern is asymmetric with re­ of activity centres) from ground-based cessing system (version N093). spect to the nucleus (= central bright­ observations. In this article we wish to see what ness peak) and highly irregular wh ich insights the wavelet transform, at some usually indicates the presence of jets in 4. Physical Processes around the coma. Figure 2 gives the level 4 appropriate resolution level, can offer in Elliptical Galaxies terms of uncovering faint extended wavelet transform result for the CN im­ structures and physical processes. age. Three jets can clearly be identified. The HST PC (Planetary Camera) im­ Differing structures, wh ich are not at all It is also easily possible to determine the age of elliptical galaxy NGC 4261, and apparent in the given image, may be­ geometry, the curvature and the ap­ the NTT SUSI image of the same object, come salient at other resolution scales. proximate position angles of the jets at as described in Zeilinger et al. (1993), We select a range of differences of reso- the nucleus from the wavelet image. were used. The objective was to uncov-

Figure 1: Gomet P/Swift-Tuttle, October-November 1992. Figure 2: Wavelet transform of Figure 1 image, enhancing coma. 38 • • • •

Figure 3: Wavelet transform of the SUSI im­ Figure 4: Wavelet transform of the PC image Figure 5: Wavelet transform of the PC image age of NGC 4261. of NGC 4261 (level 4). of NGC 4261 (level 3).

er the morphological characteristics of restored PC image. A rather severe in­ ing in terms of image pre-preparation or infalling matter in the central region of tensity transfer function has been used modelling. If faint and complex features the galaxy. The original images provided to emphasize the faint features external are present, then it offers an excellent no direct clues. Availability of a pair of to, and closely adjacent to, the central way of heuristically demarcating them. images from different instruments with dust lane of the galaxy. In the ground­ very different resolutions and signal based and level 3 space-born images levels affords a very good framework for one notices a clear protrusion to the validating the faint structures uncovered right-hand side (which is far less pro­ by the wavelet transform, as will be nounced in the level 4 PC image). Simi­ References seen. (See also p. 28 of this issue.) larly, much of the detail in the upper left­ To lessen the impact of different hand side is common to these images. A'Hearn, M.F.S., Hoban, S., Birch, P.V., Bow­ ers, C., Martin, R. and Klinglesmith 111, DA, effects due to image borders and image These features may be interpreted in 1990, Nature, 324, 649. resolution, the SUSI image was re­ terms of a warp related to the central Boehnhardt, H. and Kohoutek, L., 1992, binned to the scale of, and rotated to be disko Emphasized features in the Icarus, 99, 106. aligned with, the PC image. Both im­ background, and towards the image Larson, S.M. and Sekanina, Z., 1984 Astron. ages are shown in Zeilinger et al. (1993). borders, are artifacts which are of J., 89, 571. The SUSI image was sharpened, and course uninteresting. Schulz, R., 1990, PhD thesis, University of the PC image was restored, using 40 Bochum. Starck, J.-L., 1993, "The wavelet transfarm", iterations of the de-noising RL method 5. Conclusion referenced in Section 1 above. MIDAS Manual, Version N093. Starck, J.-L. and Murtagh, F., 1993, "Image Figure 3 shows a wavelet transform The wavelet transform provides a restaration or sharpening with noise sup­ image (level 4) of the de-noised and powerful exploratory tool for the analy­ pression using the wavelet transfarm", sharpened SUSI image. Figures 4 and 5 sis of faint features associated with pro­ submitted. show two wavelet transform images cesses which are superimposed and/or Zeilinger, w.w., M011er, P. and Stiavelli, M., (levels 3 and 4) of the de-noised and not easily distinguished. It is undemand- 1993, The Messenger, this issue.

StarGates and StarWords AN ON-UNE YELLOW PAGES DIRECTORY FOR ASTRONOMY M. A. ALBRECHT, ESO, and A. HECK, Observatoire Astronomique, Strasbourg, France

1. General base of acronyms and abbreviations 1989a), IDPAI (Heck, 1989b) and Two new databases have been made used in astronomy and related sciences. ASpScROW (Heck, 1991 a&b), and cur­ available at ESO under Starcat (Pirenne rently available under the homogenized et al. , 1993). They are products of the name of StarGuides (Heck, 1993 a&b). 2. StarGates Star's Family encompassing databases, StarGates has however the advantage data sets, dictionaries, directories, mail­ StarGates is an on-line database of of being permanently updated. To date, ing labels, and so on, compiled by the astronomy, space sciences, and related more than 6,000 entries from about 100 second author (see Heck, 1991 cl. They organizations in the world. It offers countries are accessible. offer a comprehensive yellow pages essentially the information listed in di­ Besides astronomy and space sci­ service of astronomical institutions rectories on paper published previously ences, related fields, such as aeronau­ world-wide as weil as a lookup data- under the acronyms IDAAS (Heck, tics, aeronomy, astronautics, atmo- 39 spheric sciences, chemistry, communi­ within a given radius. Any string of ous ways to compile and update the cations, computer sciences, data pro­ characters can also be searched in any information presented in StarGates and cessing, education, electronics, energe­ field. It is also possible to search by StarWords. tics, engineering, environment, geod­ keywords such as places, etc. Part of the processing involved in this esy, geophysics, information handling, work has been carried out on the IBM management, mathematics, meteorolo­ 3. StarWords 3090 of the CNRS Strasbourg-Cronen­ gy, optics, physics, remote sensing, and StarWords is an on-line database of bourg Computer Centre (France). so son, are also covered when approp­ abbreviations, acronyms, contractions, Feedback from users on possible riate. and symbols in astronomy, space sci­ modifications and/or additions to the StarGates gathers all practical data ences, and related fields. It offers essen­ data provided in StarGates and Star­ available on associations, societies, sci­ tially the updated information listed in Words would be highly appreciated in entific committees, agencies, com­ the dictionary StarBriefs (Heck, 1993 order to ensure endured accuracy of the master files. panies, institutions, universities, etc., c&d). To date, about 60,000 entries are and more generally organizations in­ accessible. volved in astronomy and space sci­ The field coverage is 1he same as for References ences. StarGates. Abbreviations, acronyms, 1. Heck, A. 1989a, International Oirectory of Many other related types of entries contractions and symbols in common Astronomical Associations and Societies to­ have also been included, such as use and/or of general interest have also gether with related items of interest. IOAAS academies, bibliographical services, been included when appropriate. The 1990, CDS Special Publ. 13, vi+716 pp. data centres, and also distributors, travelling scientist has not been for­ (ISSN 0764-9614 - ISBN 2-908064-11-1). 2. Heck, A. 1989b, International Oirectory of funding organizations, IAU-adhering or­ gotten either (codes of airlines, loca­ Professional Astronomical Institutions to­ ganizations, journals, manufacturers, tions, currencies, and so on). meteorological services, national norms gether with related items of interest. IOPAI and standards institutes, parent associ­ 1990, CDS Special Publ. 14, vi+658 pp. 4. How to Access It? (ISSN 0764-9614 - ISBN 2-908064-12-X). ations and societies, publishers, soft­ Access to StarGates and StarWords 3. Heck, A. 1991 a, Astronomy, space sci­ ware producers, and so on. ences and related organizations of the world The information is given in an uncoded is included in Starcat which can be run from any computer within ESO or - ASpScROW 1991, CDS Special Publ. 16, x way for easy and direct use. For each + 1182 pp. (ISSN 0764-9614 - ISBN 2­ entry, all practical data returned by the through the standard Starcat account 908064-14-6) (two volumes). organizations are available: city, postal reachable 4. Heck, A. 1991 b, Astron. Astrophys. and electronic-mail addresses; tele­ •• through Internet: $ telnet Suppl. 90,103-104. phone, telex and telefax numbers; stesis.hq.eso.org (134.171.8.100), 5. Heck, A. 1991c, CDS Inform. Bull. 40, foundation years; numbers of members •• through SPAN: $ set host stesis 139-141. 6. Heck, A. 1993a, StarGuides, a directory or staff; main activities; titles, frequen­ From the top level menu, select the ESO option. The successive menus are of astronomy, space seiences, and related cies, ISS-Numbers and circulations of organizations of the world, CDS Special Publ. periodicals produced; names and geo­ then setf-explanatory. On-line help and documentation is also available, as weil 20, x + 1174 pp. (ISSN 0764-9614 - ISBN 2­ graphical coordinates of observing sites; 908064-18-9) (two volumes). names of planetariums; awards, prizes as a dedicated user report system. 7. Heck, A. 1993b, CDS Inform. Bull. 42, or distinctions granted; and so on. More details on Starcat can be ob­ 71-72. StarGates points to the various en­ tained by contacting S. Hili at ESO or 8. Heck, A. 1993c, StarBriefs, a dictionary of tries not only by their different designa­ archeso a eso.org (Internet) or abbreviations, acronyms, and symbols in as­ tions and acronyms, but also by loca­ ESO::ARCHESO (SPAN). tronomy, space sciences, and related fields CDS Special Publ. 21, xxxiv + 778 pp. (ISSN tions and major terms in names. Setec­ Acknowledgements 0764-9614 - ISBN 2-908064-19-7). tion criteria are also available, such as 9. Heck, A. 1993 d, CDS Inform. Bull. 42, the geographical coordinates of a loca­ It is a very pleasant duty to express 73-74. tion around which one would like to list here our gratitude to the organizations 10. Pirenne, B. and Albrecht, M.A. 1993, ECF the entries (with available coordinates) and individuals who have helped in vari- Newsletter19,16-17.

• ~ .... III ,*

Summary of StarGates Oatabase Entries Org Title: Max-Planck-Institut fuer Astronomie (MP1AL Heidelberg Address: Koenigstuhl 17

City: 0-69117 Heidelberg Country: Gerlllany Tel: 6221-5280 Fax: 6221-528246 [-Mall :

40 ANNOUNCEMENTS Programmes Approved tor Period 52 KEY PROGRAMMES

ESO No. Principal Investigator Title of submitted programme Telescope

1-003-43K de Lapparent et al. A redshift survey of galaxies with z S 0.6 using multi-slil spectroscopy NTT 1-005-43K Rhee/Katgert et al. Peculiar motions of rich clusters of galaxies 3.6m 1-012-43K Bergeron et al. Identification of high redshift galaxies with very large gaseous halos NTT 1-014-43K Mazure et al. Structure and dynamical state of nearby clusters of galaxies 3.6m 1-019-47K Vettolani et al. A galaxy redshift survey over a fair sampie of the Universe 3.6m 1-022-47K Tammann et al. The distance of the Centaurus Group: A test for various distance NTT indicators 1-023-49K Böhringer et al. Redshift survey of ROSAT clusters of galaxies 3.6m, 202m, 1.5m 2-001-43K Mileyet al. A study of the most distant radio galaxies 3.6m, NTT 2-007-43K Cristiani et al. A homogeneous bright quasar survey 2.2m,1.5m,lm 2-009-45K Reimers et al. A wide angle objective prism survey for bright asos 3.6m, 1.5m, 0.9mDu 2-013-49K D'Odorico et al. A statistical study of the intergalactic medium at high redshifts NTT 3-001-43K Israel et al. CO as a tracer for the molecular content of the Magellanic Clouds SEST 4-004-45/51 K Turatto et al. A photometric and spectroscopic study of supernovae of all types 3.6m, NTT, 2.2m, 0.9Du 5-001-43K Mayor et al. Radial velocity survey of southern late-type Hipparcos stars 1.5m Danish 5-004-43K Gerbaldi et al. Astrophysical fundamental parameters of early-type stars of the Hip­ 1.5m parcos Survey 5-005-45K Hensberge et al. High-precision radial velocity determinations for the study of the inter­ 3.6m nal kinematical and dynamical structure and evolution of young stellar groups 6-003-45K Danziger et al. Optical identification content in selected regions of ROSAT All Sky 3.6m, 2.2m, 1.5m X-Ray Survey 7-008-51 K Habing et al. Infrared standards for ISO NTT, 2.2m, 1m 7-009-49K Oblak et al. CCD and conventional photometry of components of visual binaries 1m, 50cm, 0.9mDu 9-002-49K Epchtein et al. Deep near infrared survey of the southern sky (DEN IS) 1m 9-004-51 K Ferletet al. Is our halo dark matter made of compact objects? GPO, 1.5m Danish

Name(s) ESO No. Title of submitted programme and telescope(s)

Abbott/Pasquini/Fleming 07127 Time-series CCD photometry of cataclysmic variables discovered by ROSAT (0.9m Dutch). AbbottiShafter 07125 Time series CCD photometry of old novae (0.9m Dutch). Acker/Cuisinier/Gesicki/GornylTylenda 04035 WR nuclei of planetary nebulae: physical and chemical properties (1.5m). Acker/Cuisinier/Gesicki/GornylTylenda 04034 Wolf-Rayet nuclei of planetary nebulae: distances and expansion (104m CAll. AlcalWCovino/KrautterlTerranegraIWichmann 07121 Spectroscopic and photometric monitoring of strongly variable weak-Iine T Tauri stars (0.5m, 3.6m). Alloin/Blietz/Cameron/Rouan 01002 Diffraction limited broad-band studies of the Seyfert galaxies NGC 7469 and NGC 1068 (3.6m). Andreani/La FrancaiMilier/Cristiani/ 02026 The cosmological evolution of the clustering of quasars (3.6m). Goldschmidl/Read Antonello/MantegazzaiPoretti 03012 First overtone mode Cepheids in Magellanic Clouds (0.9m Dutch). Appenzeller/Beckmann/Nussbaum/Schoeller/ 02036 Speckle imaging and speckle spectroscopy of nearby Seyfert galaxies (2.2m). Van Elst/WagnerlWeigelt Azzopardi/Breysacher/LequeuxiMuratorio 01078 Final search and spectroscopic study of Wolf-Rayet stars in NGC 300 (3.5m NTl"). Baessgen/Bremer/Diesch/Grewing 04043 Detailed studies of old, extended planetary nebulae (1.5m). BarthellHes 02050 The high-redshift nature of GPS radio sources: searching for the most distant quasars (2.2m) Bergeron/Le Brun 01082 Identification of the gaseous systems detected by their CIV and Ly 0. in the quasar spectra of the HST KP (3.5m NTl"). BertauxiLallementiBeust 07115 Search for cometary water vapour towards ß Pictoris (104m CAll. BertolaiPersic/PizzellaiSalucci 01020 Modelling the dark matter component in Sa galaxies (1.5m). Beuermann/GrupelThomas H.lReinsch/Fink 02006 Spectroscopic indicators for the soft X-ray excess in AGN (2.2m). BeuzitiLagrangelTessierNidal-Madjar/Ferlet 07098 IR Observations of the ß-Pictoris disk with adaptive optics (3.6m). Blaauw/Srinivasan-Sahu 04052 The Distance of the Vela molecular ridge (104m CAll. Bockelee-Morvan/Gautier/Owen 07131 Search for cometary gas around ß Pic and Fomalhaut (SESll. Bouvier/BeuzitiPerrier/Sams 07114 High angular resolution imaging of close pre-main sequence binaries (3.6m) Bower/Böhringer/Ellis/Castander/Couch 01074 The dynamical structure of galaxy clusters at z=0.5 (3.6m). Brandner/Zinnecker 07058 Component colours and spectroscopy of low-main-sequence (PMS) binaries (0.9m Dutch, 1.5m, 3.5m NTl").

41 Name(s) ESO No. Title of submitted programme and telescope(s)

BroadhurstlMoeller/Szalay 01031 Cluster mass profiles via amplification of background galaxy fluxes (305m NTT). Bues/Karl 07081 Spectral variability of single magnetic white dwarfs (1.5m). BuonannoNietrilMarconi 05008 Young globular clusters in the Milky Way (2.2m). CabritlCesarsky/Lagage/Olofsson/Pantin 07096 10 micron spectro-imaging of young outflow sources (3.6m). Cacciari/BragagliaiFusi Pecci/Carretta 05010 Spectroscopic study of blue horizontal branch stars in globular clusters (1.5m). CalvanilSulentic/Marziani 02052 Orientation effects in radio loud AGN (1.5). CapacciolilFreeman/Ford/HuilArnaboldi 01086 Dynamics of the outer halos of elliptical galaxies (3.5m NTT) Caraveo/Bignami/Mereghetti/MignanilGol­ 06018 Optical studies of isolated neutron stars detected as X1gamma-ray sources doni/Pacini/Salvati (3.5m NTT). Carollo/Danziger/De Zeeuwn 01116 Linking stellar population and orbital structure in elliptical galaxies (2.2m). Carrasco G.lLoyola 07060 UBVRI photometry of FK5 faint stars (0.5m). Casoli/Boselli/Braine/Combes/Fouquei 01003 The CO emission of isolated spirals (SEST). Gavazzi/KarachetsevaiKazes/Lequeux Castellani/Brocato/Piotto 05027 White dwarfs in old open clusters (3.5m NTT). CauletlHasinger/Pietsch/Smith 03033 Probing the IS gas of the superbubble LMC2 (3.6m). Cayrel/Nissen/Beers/Spite F./Spite M.lAn­ 07029 Survey of very metal-poor stars and nucleosynthesis in the galaxy (1.5m). dersen J.lNordstroem/Barbuy Char/LabraiBerrios/MaldinilJankov/Foingl 07132 Survey de la variabilite chromospherique d'etoiles ci. rotation rapide (0.5m, Neff/Di-Sheng 1.4m CAT). Chiosi/Ortolani/BertelliNallenari 03037 Star formation I,istory of the Magellanic Clouds (2.2m). Cimatti/Freudling 02016 A millimetric view of distant radio galaxies (z>1) (SEST). Clausen/StormlTobin/Hilditch/Hill/Gimenez 03025 Eclipsing binaries in the Magellanic Clouds - distances and absolute dimensions (3.5m NTT). Collins/Nichol/Guzzo 01045 Multiobject spectroscopy of distant clusters of galaxies (3.6m). Combes/Saint-PelTomasko/Demaillyl 08014 Very high spatial resolution study of Titan in the near IR (3.6m). Faucherre/Encrenaz Corradi/Schwarz H. 04046 00 bipolar nebulae have the hottest central stars of PNe? (1.5m). CostaiGrebel/Macconnell/RobertslWing 07052 Red supergiants as tracers of Galactic spiral arms (1.5m). Courvoisier/BouchetlBlechaiPaltani 02046 Coordinated observations of 3C 273 (1.5m, SEST). Cox/Bronfman/Roelfsema 04047 A study of the photon dominated region facing Trumpier 14 (SEST). Cunow/Naumann/Ungruhe/Sommer 01040 Magnitude calibration for homogeneity studies of the Universe (0.9m Dutch). Danks/Sembach/Caulet 04048 Gas kinematics and physical conditions in the Vela supernova remnant (1.4m CAT). Danziger/Baade/Della Valle 07023 Optical spectroscopy of the visible counterpart of the bright radio millisecond pulsar J0437-4715 (3.6m). Danziger/Baade/Gouiffes/Della Valle 07022 Fast photometry of the millisecond pulsar candidate (3.6m). Danziger/BouchetlGouiffes/Lucy/Franssonl 03005 SN 1987A (SEST, 1.5m Danish 2.2m, 3.6m). Mazzali/Della Valle Danziger/Carollo 01117 Optical and infrared colour gradients in early-type galaxies (2.2m, 1.5m Danish). Danziger/Liu 04049 Observations of molecular hydrogen emission from planetary nebulae (305m ND, 1.5m). Danziger/MendeziKudritzki/Mazzali/Lucy/Ciar­ 01053 Determining distances to galaxies with well-studied SN la's using the PNLF dullo/Jacoby/Roth/Soffner method (3.5m NTT). Oe Angelis 08023 Asteroid photometry for pole and shape determination (0.9m Dutch). Oe BoerlWill/Bomans/Seggewiss 03006 Spectroscopic improvement of the age determination of NGC 1948 (105m). Oe Medeiros/Lebre/Charbonnel 07107 Lithium and rotation in subgiant stars (1.4m CAT). Oe Ruiter/Lub 02075 Variations of emission line and continuum intensities in Seyfert nuclei (0.9m Dutch,105m). Oe WinterlThe 07137 Detection of mass-outflow indicators of newly discovered young stellar objects of intermediate mass (0.9m Dutch). Oe WinterNan den Ancker 07135 Astrophysical properties of newly found early-type young stars associated with strong IRAS-sources (0.5m Danish, 1.5m, 0.5m). Della Valle/Bianchini/Duerbeck/Oegelman/Orio 07025 Novae as standard candles: calibrations of nova shells (3.6m). Dennefeld/Bertin/Boulanger/Moshir 01050 The nature of the faintestlRAS galaxies and galaxy evolution (3.6m). DietersNan der Klis 07138 Spectrophotometry of CP Pub: Weighing the white dwarf (1.5m). Doyle/Houdebine/Gunn 07033 Eclipse imaging of active binaries: coronal mass ejections & related phenomena (1.4m CAT). DrossartiForni/BenitlBibring/Lellouch/Rosen­ 08013 Observations of the Jovian system at4 microns with COME-ON PLUS (3.6 m). qvist Dürbeck/Seitter 07046 Accretion disk properties and masses of bright exnovae (1.5 m). Duquennoy/Mariolti/Mayor/Perrier 07104 Infrared imaging of very low mass companions to nearby stars (3.6 m). Duquennoy/Mayor 07103 Stellar duplicity of very low mass stars (1.5 m Danish). Eist 08010 L5 Trojan search (Schmidt). Falomo/PescelTreves 02005 The environment of BL Lacertae objects (3.5 m NTT). FavataiBarberaiMicelaiSciortino 07042 Lithium abundance determination in a sampie of volume-limited main-sequence K stars (1.4 m CAT). FavataiBarberaiMicelaiSciortino/Schachter 06004 Identification and classification of candidate stellar Einstein Siew Survey sources (1.4m CAT, 1.5 m). FavataiMicelaiSciortino 07041 Lithium abundance in a sampie of active binaries with known levels of X-ray emission (1.4 m CAT). Felenbok/JablonkalAlloi nlAri moto/BicaiBal­ 01062 1. Spectropl,otometric properties of spiral galaxies; 2. Search in the Galactic kowski/Cayatte/Kraan-Korteweg plane toward the Great Attractor (3.6 m).

42 Name(s) ESO No. Tille 01 submitted programme and telescope(s)

FerletJHobbs/Wallerstein 04023 Variable interstellar absorption within the Vela supernova remnant (1.4 m CAT). Ferrari/Bucciarelli/Massone/Pizzuti/Koornneef/ 05030 Photometrie calibrations lor the southern sky surveys (0.9 m Outeh). Lattanzi/Lasker/Postman/Siciliano/Le Poole Forni/Bibring/Benit 08012 Observations of the Jovian system at 2 microns with COME-ON-PLUS (3.6 m). Freudling/Alonso/Da CostaIWegner 01090 The peculiar motion 01 galaxies and the density 01 the Universe (1.5m Danish, 1.5m). Fusi Pecci/Cacciari/Bragaglia/Ferraro/Carretta 05009 UV survey 01 Galactic globular clusters (1.5 m Danish). Gahm/CarlqvistJMattila/Kaas 04025 Serpentine structures in the Chamaeleon Dark Clouds (Schmidt). Galletta/PiccolilTomadini 09001 A search for Sun companions (1.4 m CAT). Gehren/Baumüller/Fuhrmann/Reetz 07026 CNO abundances in metal-poor stars (3.6 m). Gemmo 07039 An inlrared search lor companions to white dwarfs (2.2 m). Genzel/Beckers/LEma/Sams/Brandl 01066 Diffraction Iimited K-band studies 01 high-z galaxy evolution and morphology (3.6m). GochermannlTappert 03018 Physical and chemical parameters 01 LMC supergiants Irom medium-resolution spectroscopy (1.5 m). GochermannlTappert 03017 Physical parameters 01 LMC supergiants Irom UBVRI-JHKL photometry (1 m). Gochermann/ZaumlTappert 03019 UBV photometry 01 LMC galactic loreground and member stars (0.5 m). GossetJManlroidNreux/Smette 07013 Study 01 eclipses of the SB1 system WR22 (0.5 m Danish). GossetJMoreau 02031 A multi-technique quasar survey: the variability criterion (Schmidt). GossetJMoreau 02030 An objective-prism survey for high redshift quasars: a feasibility test (Schmidt). Gouiffes/Oegelmann/Augusteijn/Bouchet 03030 Optical search for the pulsar in SN1987A. (3.6 m). Gredel 04017 Narrow band imaging 01 Herbig-Haro objects and jets in Hand K (2.2 m). Gredel 04016 Near-inlrared spectroscopy of Herbig-Haro objects and jets (3.5 m NTT). Gredel/Kopp 04018 Interstellar molecular absorption lines towards southern OB associations (1.4 m CAT). Grenier/Gouiffes/Oegelman 07139 Fast photometry 01 the Vela gamma-ray pulsar (3.6 m). Griffin R.E.lGriffin R.E.M.lMayor/Clube 05017 Radial velocities 01 stars in the Clube selected areas (1.5 m Danish). Gustalsson/Andersen J.lEdvardsson/Nissen 05031 The transition Irom the thick to the thin galactic disk (1.4 m CAT). Henning/Launhardt 05001 A 1.3mm continuum and CO outflow search lor extreme class I sources (SEST). Hensberge/DavidNerschueren 05032 Study 01 the double-Iined eclipsing binary NGC 2244-200 =V578 Mon (0.5 m Danish) HES/Barthel/Peletier 02028 Inlrared imaging 01 hotspots in radio sources (2.2 m). Heydari-Malayeri/Rigaut 03008 High resolution investigation 01 the most massive stars in the Magellanic Clouds (3.6 m). Hillier/Kudritzki/Lennon/Butler/Hamann/ 07141 Constraints on massive star evolution from abundances in LMC WC stars Wessolowski (3.5 m NTT). Hoffmann 08001 Structure 01 suspected composite asteroids (1.5 m Danish). HutsemekersNan Drom/Remy 02021 Polarization properties 01 BAL QSOs (3.6 m). Infante/Fouque/Richller/Quintana 01017 The distribution 01 dwarf galaxies in the Fornax Cluster (3.6 m). lovino/Chincarini/Garilli/Maccagni/Saracco 01093 K-band galaxy counts: the way to QO? (2.2 m). Israel/Oe GraauwNan der HulstJLacy/Kelly 01095 Low resolution spectroscopy of galactic nuclei in the near-IR (3.5 m NTT) Ivison/SeaquistJHughes/Schwarz H. 07001 A simultaneous multi-Irequency study 01 symbiotic stars: The cm-mm continuum (SEST). Jerjen/Binggeli 01096 Exploring the spatial structure 01 the Centaurus Cluster by surface photometry 01 its dwarf galaxies (1.5 m Danish). Jorissen/Mayor/North 07050 The evolutionary status of S stars and dwarf Barium stars (1.5 m Danish). Jüttner/Baschek/Stahl/Wolf 03011 Abundances from early B-type giants in selected regions 01 the Magellanic Clouds (3.6m). Kaper/Hammerschlag/Blondin 06010 Simultaneous optical, UV, and X-ray observations of HMXRB Vela X-1 (1.4 m CAT). Kneer/Bender/Krautter 01015 Spectroscopy 01 distant, laint clusters 01 galaxies (3.6 m). Knude/Bowyer 04053 Distances 01 local EUV shadowing clouds (0.5 m Danish). Kopp/Smette 02048 Search lor CO in quasar absorption lines (SEST). Kostiuk/Käull/Livengood 08021 Morphology 01 Jupiter's thermal inlrared aurorae (3.6 m). Krautter/AlcalaiSchmittlMundtIWichmann/ 07071 Search lor weak-line T Tauri stars in Chamaeleon and Lupus (1.5 m). Zinnecker Kudritzki/MendeziGabler/Puls/Roth 07090 Mass loss rates 01 central stars 01 planetary nebulae (3.5 m NTT). Kürster/Hatzes/Cochran/Dennerl/Döbereiner 07002 High precision stellar radial velocities, part 111 (1.4 m CAT). Kürster/Schmitt 07143 Towards a butterfly diagram for AB Dor (1.4 m CAT). Lagage/Pantin 07095 Prolile and composition 01 the inner dust disk of tl1e ß-Pictoris star (3.6 m). LagerkvistJMagnusson/Erikson 08005 Pole orientations and shapes 01 asteroids (1 m). LagrangeNidal-Madjar/FerletJCorporon/De­ 07116 High resolution survey 01 ß Pictoris with the CES (1.4 m CAT). leuil/GrylTobin Lamers/De Graauw/Waters/LoupNan Hool 07144 Inlrared spectroscopy and imaging of LBV's (3.5 m NTT). Lennon/Kudritzki/Dufton 03041 An intermediate dispersion spectroscopic survey 01 B-supergiants in the SMC (3.5 m NTT). Lennon/Kudritzki/Husleld/Herrero/Gabler 07016 Spectroscopy of luminous blue stars in the Local Group galaxies NGC 6822, IC 1613 and WLM (3.5 m NTT). Liller/Alcaino/Alvarado/Wenderoth 03002 UBVRI photometry of Magellanic Clouds cluster standards (1 m). Lin Yun 07091 Near-inlrared imaging 01 young stellar objects in Bok globules (2.2m). Lin Yun 07019 Narrow-Band imaging ofT Tauri stars associated with Bok globules (0.9m OuteIl). Lin Yun/Clemens 07047 Spectral energy distributions of young stellar objects in Bok globules: millimeter Iluxes (SEST).

43 Name(s) ESO No. Tille of submitted programme and telescope(s)

Lin Yun/Clemens 07028 HCN survey of physical conditions in cores of star-forming Bok globules (SEST). Lindblad PAB.lLindblad/Joersaeter 01036 Photometry of nearby barred spiral galaxies (1.5m Danish). Lindblad/JoersaeterNaesterberg/Lindblad 02029 Active nuclei of NGC 613 and NGC 1365 (1.5m). PAB. Loiseau/Combes 01097 CO observations of active interacting galaxies -111 (SEST). Lorenzetti/Moneti/Spinoglio/Liseau 07066 The initialluminosity function in the Vela star forming region (2.2m). Loup/Hron/Kerschbaum/ZijlstraiWaters 07145 Oxygen-rich AGB-stars willl 60 micron excess (1 m, 1.5m). Macchetto/Giavalisco/SteidellSparks 01098 Optical and near-infrared spectroscopy of radio-quiet galaxy candidates at z>3 (3.5m NTT). Magnan/De Laverny/Mennessier 07021 UBVRI photometry of Mira variables during a whole cycle and study of the light curve in different cycles (0.5m). Mandolesi/CranelAttolinilPalazzi 04054 Small scale structure of diffuse interstellar clouds (104m CAT). MaranolZamorani/Zitelli/Cimatti/Giacconil 02038 Deep multi-colour imaging for faint X-ray sources and a search for faint quasar Hasinger candidates (22.0

44 Name(s) ESO No. Title of submitted programme and telescope(s)

Röttgering/Bremer 02065 Compact radio galaxies and the continuum alignment effect (2.2m). Roueff/Kopp/Le BourloVGerin 04059 Search for CS and CN in the diffuse clouds close to ~ Oph (SEST). Rutten/Harlaftis/OhilionNan Paradijs 06002 Spatially-resolved spectra of accretion disks in cataclysmic variables (2.2m) SaglialOavies/Baggley/Colless/Burstein/ 01007 Peculiar velocities of galaxy clusters in the Pisces-Cetus supercluster (3.6m) Bertschinger/McMahan/Wegner 3 SchildlTennyson/Miller 04006 Search for the moieculaI' ion H + in Orion (2.2m). SchildNogel/Nußbaumer/MürseVSchmid 07040 Symbiotic stars in the Magellanic Clouds (2.2m, 3.6m). Schober 08019 Variable lightcurves of asteroids 258, 369 and 582 (0.5m). SchutteNan Oishoeck/HelmichlTielens/Gredel 04004 Interstellar ice composition toward southern infrared sources (305m NTT). Seaquistllvison/Evans/Schwarz H. 07034 A maser survey of symbiotic Miras (SEST). Shaver/Wall/Kellermann 02001 A search for radio-Ioud quasars at z>5 (3.6m). Siebenmorgen/ZijlstraiGredel 04032 The dust composition in Herbig-Haro objects (305m NTT). Simon/Saleck/Stutzki/Winnewisser 04038 Abundance and excitation of CN, 13CN and CiS N in OMC1 (SEST). Sivan/Perrin 04002 Spectrophotometry of reflection nebulae illuminated by late type stars (1.5m). Sommer-Larsen/Christensen/Beers/Flynn 05007 Bright blue horizontal branch field stars in the inner galactic halo (1.5m). Soucall/Kneib/FortlMellier 01027 Spectroscopic survey of the galaxies in S295, and redshift determination of the arcs in MS2137-23 (3.5m NTT). Spite F./Spite M.lFran«ois/Hill 05026 Abundances of Lithium and heavy elements in NGC 2004 (3.5m NTT). Stark/Gredel 04011 MoieculaI' absorption lines toward cometary interstellar cirrus clouds (104m CAT). Stecklum/EckartlHenning/Fischer 07102 High angular resolution observations of Herbig Ae/Be and Vega-like stars (3.6m) Stecklum/Henning/Pfau 07086 NIR photometry of candidate pre-main sequence stars (1 m). Sterken 07015 Long-term photometry of variables (O.5m Oanish) Sterken 07014 Pulsating B stars in NGC 3293 (O.5m Oanish). Stirpe/Gianuzzo 02037 Are narrow line Seyfert 1 nuclei variable? (1.5m) Surdej etal. 02047 Spectroscopic identification of gravitationallens candidates (3.5m NTT). Telles/KotilainenlTerlevich 01075 High resolution near-infrared imaging of H 11 galaxies (2.2m). The/Grady/Perez 07051 High resolution and S/N spectroscopy of edge-on proto-planetary disk systems (104m CAT). TM/Moister 07010 Planet formation in proto-planetary dust clouds of Herbig Ae/Be stellar systems (O.5m). Theuns/Warren 01056 Search and identification of intergalactic planetary nebulae in galaxy clusters (3.5m NTT). Thomas H.lTrümper/Beuermann/Reinsch/ 06013 Spectroscopic identification of ROSAT X-ray sources near the South Ecliptic Pole Simon (SEP) (1.5m) Tinney 07070 A spectral atlas for the latest M-dwarfs (3.5m NTT). Tinney 07069 Parallaxes of VLM stars (202m). Tinney/Mould/Reid 05016 The kinematics of stars at the bottom of the main sequence (3.6m). ToussaintlReimers/Hünsch 07106 A high resolution study of short-lived absorption in three M giants (104m CAT). Turon/Mermilliod/Gomez/Sellier/Guibertl 05006 The core-halo structure of open clusters observed with Hipparcos (Schmidt). Robicllon Van de Steene/Sahai/Pottasch 07111 A search for moieculaI' envelopes in newly discovered planetary nebulae (SEST). Van der Bliek/Gustafsson 07053 Chemical abundan ces analysis of the royal standard stars for ISO (104m CAT). Van der HülsWan der Werf/Oe Graauw/Israel/ 03026 Excitation of H 11 regions in the Magellanic Clouds (3.6m). Joubert/Baluteau Van der KruitlOe Grijs/Peletier 01021 Optical surface photometry of edge-on spiral galaxies (1.5m Oanish). Van der WerfNan der Hülst 03027 Excitation of moieculaI' and ionized gas in the Magellanic Clouds (202m). Van Oishoeck/Helmich/Hogerheijde 04005 The chemical state of southern star-forming regions (SEST). Van Oishoeck/Langevelde/Hogerheijde 04009 The nature and dust content of young stellar objects in Chamaeleon (SEST). Van Winckel/Balm/Waelkens 07048 CW of the Red Rectangle Nebula (104m CAT). Vidal-Madjar et al. 09002 is our halo dark matter made of compact objects? (Schmidt). Waelkens 07030 110rionis (104m CAT). Waelkens/Mayor 07031 Radial-Velocity variations in post-AGB stars (1.5m Oanish). Wagner 02035 High resolution spectroscopy of the NLRS of NGC 1068 and NGC 1386 (3.6m). Walsh/Walton/Pottasch 04015 Spectral classification and distances for binary star planetary nebulae (2.2m). Wampler/HazardlTurnshek 02044 An absorption-line study of chemical abundances in quasar nuclei (3.5m ND, 3.6m). Wampler/Wang 03035 The SN 1987A environment (3.5m NTT). Wanders/Bergvali/OestiinNan Groningen/ 02071 Host galaxies of intermediate-redshift quasars (3.5m NTT). Roennback/Olofsson/Oerndahl Warren/lovino/Shaver 01055 The evolution of the galaxy correlation function (3.6m). Warren/Pownall/Hewett 01113 Ha emission from galaxies at z>2 (2.2m). Waters/ZijlstralKäuflNan Winckel/Meixner 07093 10 micron direct imaging of detached envelopes around post-AGB stars (3.6m). Way/Quintanallnfante 02073 A spectrophotometric survey of AGN in rich clusters of galaxies (2.2m). WeigeIVBeckmann/Oavidson/Kohl/Nußbaum/ 07101 Speckle masking and speckle spectroscopy observations of stellar objects Schöller/SeggewissNan Eist (2.2m). West M.J.lBothum 01057 Globular cluster populations in Hickson compact groups (3.5m NTT). West R.lHainautlMarsden/Meech/Smette 08017 Activity in very distant comets (3.5m NTT). Westerlund/Azzopardi/Breysacher 03004 Low-Iuminosity carbon stars in the Large Magellanic Cloud (2.2m). Wild/Cameron/EckartlRothermel 02025 12CO/C180 ratio in the nucleus of Centaurus A (SEST). Wild/Eckart 01028 The moieculaI' ISM ofthe starburst galaxy NGC 5188 (SEST). WolflKaufer/Mandel/Stahl/Gaeng/Gummers­ 07017 Structure and variability of the winds of A-type supergiants (O.5m). bach/Sterken

45 Name(s) ESO No. Title of submitted programme and telescope(s)

Wolter/Maccacaro/Ciliegi 06014 Search for distant clusters of unusual objects among unidentified EMSS sources (2.2m). Zamorani/Giacconi/Hasinger/Marano/Mignoli/ 06015 Spectroscopic follow-up of ROSAT discovered X-ray sources in the "Marano Zitelli Field" (3.6m). ZijlstraiLoup/WaterslTinney/Groenewegen 03028 TIMMI observations and infrared photometry of obscured AGB stars in the LMC (3.6m). Zinnecker/McCaughrean/Meylan 03031 Testing the starburst paradigm in 30 Ooradus (2.2m).

ANNOUNCEMENT ANNOUNCEMENT ESOIEIpe Workshop on ESO Workshop on The Light Element Abundances aso Absorption Lines

Marciana Marina, Isola d'Elba ESO, Garehing 22-28 May 1994 21-24 November 1994 A joint ESO/EIPC workshop on the Light Element Abun­ An ESO workshop on aso absorption lines will be held from dances will be held from 22 to 28 May 1994, at the Elba 21 to 24 November 1994, at the Headquarters of the European International Physics Center, Marciana Marina, Isola d'Elba, Southern Observatory, Garching bei München, Germany. Italy. The workshop is intended to discuss the theory and observa- The workshop is intended to discuss the theory and observa­ tions of aso absorption lines in relation to the following topics: tions of the light elements (z<5) in relation to the following topics: • Galactic halo and interstellar medium • Low-redshift systems • Primordial Abundances • Intrinsic absorption Iines and BAL systems • Elements at High Redshift • Ly-alpha clouds • Stellar Processes • Interstellar Processes • Oamped systems • Metal systems • Galactic Evolution • Probing the large scale structure • Isotopic effects • Probing the Universe at high redshifts Organizing Committee: P. Crane (ESO), R. Ferlet (Paris), F. Ferrini (Pisa), O.L. Lambert Organizing Committee: (Austin), P. Molaro (Trieste), P. Nissen (Aarhus), B. Pagel (NOR­ S. O'Odorico, G. Meylan, P. Petitjean, P. Shaver, J. Wampler, OITA), L. Pasquini (La Silla), G. Steigman (Columbus). ESO. Contact Address: Contact Address: Phil Crane, European Southern Observatory Georges Meylan, European Southern Observatory Karl-Schwarzschild-Str.2, 0-85748 Garching bei München, Karl-Schwarzschild-Str.2, 0-85748 Garching bei Müncllen, Germany Germany e-mail: crane CI eso.org fax: +4989320-06-480/320-23-62 e-mail: gmeylan aeso.org fax: +4989320-06-480/320-23-62

The European Southern Observatory (ESO) is an intergovernmental organization responsible for astronomical research in the southern hemisphere. The eight member States of ESO are Belgium, Denmark, France, Germany, Italy, the Netherlands, Sweden and Switzerland. As the prime European astronomical centre, ESO occupies a leading position in the world's scientific community. Its research work is of great value to many areas of science and industry. Applications are invited for the position of (m/~:

Associate Director tor Science (ref. ESD205) within the Science Division at the ESO Headquarters, in Garching near Munich, Germany. Assignment: a strong research-orientated scientific staff with diverse expertise is essential if ESO is to fulfil its mandate of providing and maintaining an international competitive multi-telescope observatory for its community of users. Within this framework, the Associate Oirector for Science will be responsible to the Oirector General for the overall quality of scientific research at ESO, for guiding the rebuilding and expansion of the scientific staff in anticipation of the Very Large Telescope era, for coordinating the participation of the scientific staff in the VLT project and for revitalizing the ESO Fellowship and Studentship programmes. A further responsibility will be to ensure the broad participation of the European astronomical community in all ESO activities and in particular in the VLTNLT Interferometer programme. Experience: the chosen candidate will have an outstanding record of achievement in one or more areas of modern astrophysics and will be widely experienced in the use of large ground-based optical telescopes. This will be combined with excellent management and leadership skills. Contractual conditions: the Associate Oirectorship is intended as a tenured staff appointment. Nevertheless, serious consideration will be given to outstanding candidates willing to be seconded to ESO on extended leaves from their home institutions. ESO remuneration and conditions: remuneration will be commensurate with background, experience and family status of the incumbent. The basic tax-free monthly salary will not be less than DM 12,402.-. To this may be added an expatriation allowance and other allowances depending on family status. ESO staff enjoy highly-favourable working conditions and have every opportunity to demonstrate their skills in an international and creative environment equipped with advanced technologies. Applications should specify the job reference and be submilted before October 31, 1993 to: The Oirector General, Prof. R. Giacconi, European Southern Observatory, Karl-Schwarzschild-Straße 2, 0-85748 Garching near Munich, Germany. Tel. (089) 32006250.

46 ESO Studentship Programme Tentative Time-Table

The European Southern Observatory has positions available of Council Sessions and for 12 research students. Six of these positions are at the ESO Committee Meetings HQ in Garching, the other six at the Observatory, La Silla, Chile. Since students normally stay approximately 2 years, this means November 4-5 Seientifie Technieal Committee that each year a total of 6 students (3 at each location) may be November 8-9 Finanee Committee accepted. These are applicable to any student enrolled in a November 25-26 Observing Programmes Committee Ph.O. (or equivalent) programme in institutions in the member Oecember 1-2 Council states. All meetings will take plaee in Garching. Potential candidates or their supervisors may obtain detailed information about the programme by requesting the updated brochure and application forms from the Personnel Administra­ tion and General Services at ESO HQ, Karl-Schwarzschild­ The Proceedings of the Second ESO/CTIO Workshop on Str. 2, 0-85748 Garching bei München, Germany. There is now an annual closing date of 15 October for appli­ cations. Mass Loss on the AGB and Beyond (ESO Conference and Workshop Proceedings No. 46) have now been published. The 479-p. volume, edited by H.E. Schwarz, is available at a price of DM 70,- (prepayment re­ ESO Users Manual 1993 quired). Payments have to be made to the ESO bank aceount 2102002 The new (1993) edition of the ESO Users Manual has just with Commerzbank München or by cheque, addressed to the become available and been distributed to Institutes in the ESO attention of member States. Institutes wh ich have not received a copy ESO, Financial Services many obtain one on request addressed to the Karl-Sehwarzschild-Str. 2 ESO Visiting Astronomers Service 0-85748 Garching b. München, Germany Karl-Schwarzschild-Str. 2 Please do not forget to indicate your eomplete address and the 0-85748 Garching b. München, Germany title of the Proceedings.

New ESO Preprints STAFF MOVEMENTS June-August 1993 Arrivals Scientific Preprints Europe SIML, Erieh (0), Clerk (General Services) 920. T.R. Bedding: The Orbit of the Binary Star Delta Scorpii. TEUPKE, Svea (0). Secretary Astronomical Journal. ZELLER; Kurt (CH), Head of Personnel 921. F. Matteucci: lron and Magnesium Evolution in Giant Elliptical HUBERT, Georgette (0), Secretary Galaxies. A Cimatti and S. di Serego Alighieri: Stellar and CUMANI, Claudio (I), Assoeiate Scattered Light in a Radio Galaxy at z=2.63. HUIZINGA, Edwin (NL), Fellow G. Marconi et al.: Chemical Evolution of Blue Compact Galaxies. AUSSEM, Alexandre (F), Cooperant Papers presented at the Kiel Conferenee "Panchromatic View of PETERSON, Bruce (Aus), Guest Professor Galaxies: their evolutionary puzzle". PETITJEAN, Patrick (F), Associate 922. C.M. Carollo et al.: Metallicity Gradients in Early-Type Galaxies. Chile Monthly Notices of the Royal Astronomical Society. 923. P. Crane et al.: High Resolution Imaging of Galaxy Cores. KNEE, Lewis B.G. (Can.), Fellow (SEST) Astronomical Journal. MANFROIO, Jean (B), Associate (Senior Visitor Progr.) 924. N. Meyssonnier and M. Azzopardi: A New Catalogue of Ha CLAESKENS, Jean-Franyois (B), Cooperant Emission-Line Stars and Sm all Nebulae in the Small Magellanie BRANONER, Wolfgang (0), Student Cloud. Astronomy and Astrophysics Suppl. 925. H. van Winckel et al.: An Atlas of High Resolution Line Profiles of Symbiotie Stars. Part I: Coude Echelle Spectrometry of South­ Departures ern Objects and a Classification System of Ha Line Profiles. Europe Astronomy and Astrophysics. 926. Bo Reipurth and H. Zinnecker: Visual Binaries Among Pre-Main BEELEN, Marion (NL), Secretary Sequenee Stars. Astronomy and Astrophysics. PLÖTZ, Franz (0), Electro-Mechanieal Engineer 927. M. Heydari-Malayeri et al.: HOE 269828: A Reddened Massive BECKERS, Jacques (USA), VLT Programme Scientist Star Cluster. Astronomy and Astrophysics. ZAGO, Lorenzo (I), Engineer/Physieist 928. M. Stiavelli et al.: Core Sub-Structure of Elliptical Galaxies: the SIEBENMORGEN, Ralf (0), Fellow Core Resolution Technique Applied to NGC 1399. Astronomy and Astrophysics. Chile 929. J.K. Kotilainen and M.J. Ward: The Host Galaxies of Seyfert WILD, Wolfgang (0), Fellow Type 1 Nuclei. Monthly Notices of the Royal Astronomical SMETIE, Alain (B), CooperantiAssociate Society. 930. A.F.M. Moorwood and E. Oliva: Infrared Spectroscopy of Star­ burst and Seyfert Galaxies. Invited paper to appear in CIRP5: Topical Conference on Infrared Astrophysics. Infrared Physics (ed. F.K. Kneubühl). 931. M.A. Prieto and W. Freudling: New Evidenee for an Anisotropie: 933. M.H.O. Ulrich: The Energy Budget on the Irradiation Model of Radiation Field in NGC 5252. The Astrophysical Journal. Quasars. 2nd Workshop on Theory of Aecretion Oisks, MPI 932. S.G. Ojorgovski and G. Meylan: Appendices and Tables to Garehing, March 1993. appear in Structure and Dynamics of Globular Clusters - Pro­ 934. F. Murtagh and M. Sarazin: Nowcasting Astronomical Seeing: a ceedings of a Workshop held in Berkeley, California, July 15th to Study of ESO La Silla and Paranal. Publications of the 17th, 1992, to honour the 65th birthday of Ivan King. Astronomical Society of the Pacific.

47 935. C. Aspin et al.: Near-IR Spectroscopy and Imaging Photometry of M1-16: Bipolar H2 Jets in a Post-AGB Transition Object. Astronomy and Astrophysics. 936. G. Meylan: Some Clues About the Dynamics of Globular Clusters from High-Resolution Observations. Invited review in Ergodie Concepts in Stellar Dynamies, eds. D. Pfenniger and v.G. Gurzadyan (Berlin: Springer), in press. 937. L. Origlia et al.: The 1.5-1.7 Microns spectrum of Cool Stars: Une Identifications, Indices for Spectral Classification and the Stellar Content of the Seyfert Galaxy NGC 1068. Astronomy and Astrophysics. 938. L.F. Rodriguez and Bo Reipurth: the Exciting Source of the Herbig-Haro 111 Jet Complex: VLA Detection of a One-Sided Radio Jet. Astronomy and Astrophysics.

Technical Preprints 52. A.F.M. Moorwood: IR Instrumentation for the VLT. To appear in Proceedings of SPIE Conference No. 1946 on Infrared Detectors and Instrumentation (ed. A. Fowler), Orlando, April 1993. 53. G. Finger et al.: Image Sharpening by On-Chip Tracking in IRAC2. To appear in Proc. of SPIE Conference No. 1946 in Infrared Detectors and Instrumentation (ed. A. Fowler), Orlando, April 1993. 54. J.M. Beckers: Progress in High Resolution Astronomical Imaging Including Active and Adaptive Optics. Invited lecture at the 16th meeting of the International Commission for Optics, August 9-13,1993, Budapest. 55. N. Hubin et al.: Results of a System Study for the ESO Very Large Telescope Adaptive Optics. To be published in the Proc. ICO-16 Satellite Conf. on "Active and Adaptive Optics", Garching, August 2-5, 1993.

Contents

M.-H. Ulrich: A Message from the New Editor .

TELESCOPES AND INSTRUMENTATION R. Mueller, H. Hoeness, J. Espiard, J. Paseri, P. Dierickx: The 8.2-m Primary Mirrors of the VLT . H.U. Käufl: Ground-Based Astronomy in the 10 and 20 ~lm Atmospheric Windows at ESO - Scientific Potential at Present and in the Future 8 E. Gosset, P. Magain: On the Linearity of ESO CCD # 9 at CAT + CES 13 1. M. C. Abbott, P. Sinclaire: CCD Linearity at La Silla - a Status Report ...... 17

SCIENCE WITH THE VLT J. Lequeux: The Magellanic Clouds and the VLT 19 M. Stiavelli: Nuclei of Non-Active Galaxies with the VLT ...... 21 R. Ferlet: From Planets to the Big Bang with High-Resolution Spectroscopy at the VLT ...... 25

REPORTS FROM OBSERVERS W. W. Zeilinger, P. M0l1er, M. Stiavelli: Probing the Properties of Elliptical Galaxy Cores: Analysis of High Angular Resolution Observational Data .. .. 28 C. Alard, A. Terzan, ,I. Guibert: Light Curves of Miras Towards the Galactic Centre...... 31 M. Kissler, 1. Richtler: E. V. Held, E. K. Grebel, S. Wagner, M. Capaccioli: NGC 4636 - a Rich Globular Cluster System in aNormal Elliptical Galaxy ...... 32 J. R. Walsh, J. Meaburn: Imaging the Globules in the Core of the Helix Nebula (NGC 7293) ...... 35

OTHER ASTRONOMICAL NEWS F. Murtagh, W. W. Zeilinger, J.-L. Starck, H. Böhnhardt: Detection of Faint Extended Structures by Multiresolution Wavelet Analysis ...... 37 M.A. Albrecht, A. Heck: StarGates and StarWords - an On-Line Yellow Pages Directory for Astronomy ...... 39

ANNOUNCEMENTS Programmes Approved for Period 52 ...... 41 Announcement of ESO/EIPC Workshop on "The Light Element Abundances" .. 46 Announcement of ESO Workshop on "OSO Absorption Lines" ...... 46 Associate Director for Science ...... 46 ESO Studentship Programme...... 46 ESO Users Manual 1993 ...... 46 Tentative Time-Table of Council Sessions and Committee Meetings...... 46 Proceedings of Second ESO/CTIO Workshop on "Mass Loss on the AGB and Beyond" ...... 46 New ESO Preprints (June-August 1993) 47 Staff Movements ...... 47 48