Abstracts: Oral Contributions

ESO Workshop on Scientific Drivers for ESO Future VLT/VLTI Instrumentation


Seeing the Light Through the Dark: From Dark Clouds to Extra-Solar Planets

J. Alves, ESO Garching (Germany)

Star formation is a fundamental astrophysical process which not only determines the origin of the sun and planets but also regulates the structure and evolution of galaxies. Yet our detailed understanding of this process is extremely limited. At a basic level we do not know what mechanism transforms diffuse interstellar gas into condensed hydrogen burning stars and planetary systems. In this contribution we will briefly present results obtained with ESO instruments on our programs on molecular cloud research, very young embedded star clusters, and direct imaging search for extra-solar planets. We will discuss these results from the point of view of technical feasibility at other observatories and conclude with the presentation of future instrumentation dream-list to address the presented open issues on star and planet formation research.


Gamma-ray bursts and Faint Object Spectroscopy

M.I. Andersen, University of Oulu, Finland

Gamma-ray bursts poses one of the most difficult challenges to observational astronomy because of their transient nature. Yet they ultimately promise to deliver the star formation history of the universe, unbiased samples of galaxies with active star formation at all redshifts and direct measurements of the chemical evolution in the infant universe. To reach these goals, we must equip our telescopes with instrumentation which are capable of making optimum use of the photons, because we usually only have "a single shot in the gun". The available faint object spectrographs (at ESO telescopes and most other observatories) is not matching this observational challenge, due to limited spectral coverage, resolution and sensitivity. We discuss the possible design of a faint object spectrograph optimized for the observation of gamma-ray burst afterglows and show that the considerations which leads to its design are in general valid for spectroscopy of faint sources. In this way, gamma-ray burst afterglows highlights the inefficiency with which we in general obtain spectra of faint objects.


Instrumentation for 3D spectroscopic deep field

R. Bacon, Observatoire de Lyon, France

We propose to study a 3D instrument dedicated to the achievement of spectroscopic deep field. It would use a first generation MCAO capability with natural guide stars and tuned to get the maximum encircled energy in a 0.2" aperture within a field of view of 1’x1’. An integral field spectrograph based on the advanced slicer concept will give the required 3D capability with R~1000, 0.5-1 micron simultaneous spectral coverage and 300x300 spatial elements. The instrument will be optimised for maximum throughput and stability (no moving part). A modular approach in designing the spectrograph should keep the costs reasonable. Observing strategy, calibration plan and data reduction software (including 3D deconvolution of multiple datacubes) are part of the study. The instrument would allow exhaustive spectroscopic study of HDF type objects and would also be a revolutionary tool to search for Ly alpha emission objects in the z=[3-7] range.


Identification and study of blue supergiants in nearby galaxies

F. Bresolin (Munich), W. Gieren (Concepcion), R.P. Kudritzki (Hawaii), R. Mendez (Munich) & N. Przbylla (Munich)

We have been using FORS1 on the VLT for an ongoing program of Multi Object Spectroscopy of blue supergiant candidates in a number of late-type galaxies in the "near field" (< 7 Mpc). We report on first results on metallicity determinations, abundance patterns, stellar wind properties and distances derived from the Wind Momentum Luminosity Relationship. Our results demonstrate the excellent capabilities of FORS1+VLT to do quantitative stellar spectroscopy out to several Mpc.


Future VLT Instrumentation: The IoA Perspective

R. Carswell and G. Gilmore

Future very high redshift studies of the first galaxies require discovery of such objects. We propose study of a narrow-band imager, designed to operate between the bright OH lines in the 1-2.5micron region. On the timescale of future VLT instrumentation, NGST will exist: we propose an intermediate dispersion (R~10000) high efficiency spectrograph, providing the whole optical spectrum in a single observation, for internal dynamics and line studies of NGST targets. To complement NGST we consider a wide field optical imager desirable (but note SUBARU and VISTA). For future ISM/IGM studies, we propose a higher dispersion spectrograph than UVES (R=150000+), with stable bench-mount. We also note that efficient and fast access to the archives is as least as important as a new instrument, and propose that this be given appropriate priority.


The formation of elliptical galaxies: future prospects for the VLT

A. Cimatti, Osservatorio Astrofisico di Arcetri, Italy

I will review the most recent results on the search for and understanding of high-z elliptical galaxies and discuss their implications in the framework of massive galaxy formation and evolution. In particular, I will show the main results obtained with the 1st generation VLT instruments and discuss how this crucial research field would benefit from the 2nd generation VLT instruments (optical/near-IR imaging and spectroscopy).


Exploiting the full power of OzPoz

M. Colless, Australian National University

The FLAMES and UVES spectrographs make good use of the OzPoz fibre positioner, but do not exploit its full capabilities. The two existing OzPoz field plates are capable of feeding instruments with twice as many fibres as FLAMES. There are also two additional field plate positions that are currently unused and which could accommodate up to 560 fibres each. This talk will explore ways of harnessing the full power of OzPoz, and examines science drivers and conceptual designs for three possible options: a fibre-fed near-infrared spectrograph, a very high multiplex optical spectrograph, and spectrographs fed by deployable integral field units.


A wide field H+K imager and multi-object spectrograph

J.G. Cuby, ESO Chile

In the current instrumentation plan of the VLT, the "wide field" IR imaging and spectroscopic capabilities covering the 1-2.5 micron region are ISAAC and NIRMOS. ISAAC covers a 2.5 x 2.5 arcmin2 field of view up to the K band, with a single slit spectroscopic capability. NIRMOS has a 14 x 16 arcmin2 field of view in J and H, and a spectroscopic multiplex capability of ~150 in J and part of H. We propose to consider a cryogenic instrument that would cover a field of view of ~ 8 x 8 to 10 x 10 arcmin2, with a separate cryogenic mask cabinet, that would cover the full H and K band in imaging and spectroscopy. The multiplex advantage could range from ~ 120 in medium resolution spectroscopy to ~500 in low resolution spectroscopy (K band only). Such a facility would ideally complement VIMOS and NIRMOS for large, deep surveys and VISTA for massive spectroscopic follow-up, e.g.

- extension of the redshift range from ~ 1.5 to 2.5 for H alpha and 3.4 to 5.5 for [OII]

- deep K band imaging surveys, down to K ~ 27

- H, K band multi-object spectroscopy of nearby and distant galaxy clusters

- H, K band MOS in star forming clusters


Multi-Conjugate Adaptive Optics with Laser Guide Stars

R. Davies (MPE), D. Bonaccini (ESO), S. Rabien (MPE), T. Ott (MPE), W. Hackenberg(ESO), R Genzel (MPE)

The design and construction of PARSEC, the first laser for the VLT, is currently underway and the Laser Guide Star Facility is planned to be commissioned during 2003. This, of course, can only be the first step towards enhancing the scientific output of the VLT through adaptive optics. So in this contribution we propose the development of a multi-conjugate laser guide star adaptive optics system. We provide the rationale by outlining some of the primary science drivers behind such a project. We then consider the technology needed to project up to 5 laser beacons, as well as feasible geometries for an adaptive optic detection and correction system.


Observations of extragalactic novae with VLT

M. Della Valle (Arcetri, Firenze) and R. Gilmozzi (ESO)

Nova outbursts are the result of strong thermonuclear runaways on the surface of a white dwarf accreting H-rich material from a low mass sequence star companion. Despite their scientific interest, surveys of novae in extragalactic systems have not been popular among astronomers (remarkable exceptions are M31 and, marginally, LMC and M33). The major reason for this is probably the unpredictable nature of these events, which make nova surveys considerably (telescope) time consuming. As a consequence, very little is known about the nova populations in extragalactic systems. In particular, almost nothing is known about the properties of nova explosions in different metallicity environments. This is an uncomfortable situation if one wishes to use novae as standard candles aimed at providing a valuable alternative to Cepheids calibrations of the absolute magnitude at maximum of type Ia SNe.

In addition, VLT observations of extragalactic novae will help to address several "hot" questions inherent to nova theory, such as: 1) what is the effect of the metallicity on the characteristics of a nova? 2) what is the chemical composition of the shells ejected by novae originated in different Hubble type galaxies? 3) is there any dependence of the nova rate on the Hubble type and/or class of luminosity of the parent galaxy? 4) are nova and SNI-a consistent?

The recent discovery of four novae in one galaxy in the Fornax cluster with only 3 hours of observing time, has clearly shown that the VLT + FORS are able to improve the efficiency of nova searches in extragalactic systems by a factor ~ 10, as compared to previous searches with 4-m telescopes. This will help transforming the use of novae as distance indicators from a curiosity to a mature field of research.


Spectroscopy of faint emission line nebulae

R.-J. Dettmar, Ruhr-University Bochum (Germany)

Based on results obtained with FORS1 in long-slit mode we demonstrate the power of the VLT for the spectroscopy of faint emission line nebulae such as the gaseous halos of diffuse ionized gas (DIG) in spiral galaxies. It is shown that VLT spectra of this DIG allow us to address the metallicity and energy budgets of the interstellar medium on galactic scales and that DIG kinematics may even provide a new tool to constrain the distribution of dark matter.

The currently available instrumentation with regard to this application is compared to other possible designs and efficiencies for integral field spectrographs, e.g. Fabry-Perot systems.


A high resolution visible and infrared spectropolarimeter for the ESO Very Large Telescope

J.F. Donati, C. Catala (OMP, France), A. Kaufer, G. Mathys (ESO, Chile)

We propose to build a high resolution spectropolarimeter as a new generation VLT instrument, for studies of stellar magnetic fields throughout the HR diagram. With both a visible and an infrared arm, this high resolution spectropolarimeter will enable us to address with unprecedented accuracy not only the important issue of the origin of stellar magnetic fields (i.e. whether they are fossil remnants of an earlier evolutionary stage, or amplified in situ by MHD processes like the dynamo field of the Sun), but also the crucial question of the impact of magnetic fields on the transport processes operating within or in the immediate surrounding of the star (e.g. rotation, convection, diffusion, circulation, pulsation, mass loss, accretion) and thus on the chemical and rotational evolution of stars. This instrument will be the only such tool available worldwide on very large telescopes.


VLT/VLTI Mid-Infrared Heterodyne Observations

A. Eckart & R. Schieder, I.Physikalisches Institut, Universität zu Köln (Germany)

Heterodyne receivers are versatile instruments for very high frequency resolution and sensitivity at the same time. Mid-infrared heterodyne receivers are well established with fixed frequency CO2 lasers as local oscillators. A new heterodyne system with tunable solid-state IR-Lasers as local oscillator has been developed at the Cologne Observatory for Sub-millimeter Astronomy (KOSMA) with very high stability and noise temperatures in the range of only a few times the quantum limit. A HgCdTe-photovoltaic mixer provides an IF-bandwidth of about 2 GHz which is spectrally analyzed by means of a large bandwidth acousto-optical spectrometer. Presently the system is usable at any desired wavelength between 11 and 8 micron, but progress is being made towards longer wavelength regions.

Targets for these instruments are the observations of narrow lines of molecules without permanent dipole moment such as CO2, CH4, C2H2, C2H4, ... Narrow lines are expected to be detectable in absorption against strong IR-sources for example while probing the composition of the cold interstellar medium. For this the availability of telescopes with highest angular resolution is a decisive assumption in order to access a sufficient number of possible targets. The present developments are directed towards the observation of molecular hydrogen through its vibrational-rotational quadrupole transitions between 28 and 10 micron - some of which can be reached from the ground. The goal is to determine the content of molecular hydrogen in the interstellar medium at highest angular and spectral resolution together with the important determination of abundances in the para- and ortho-states of the molecule.

A mobile instrument is already in observatory test, and fully radiometric performance within many hours of operation has been verified. We propose to increase the effort of this development for a future use at the VLT. The uniqueness of the instrument makes it a very promising tool to expand and increase the future scientific yield of the VLT. In general, the heterodyne principle is also well suited for an interferometric combination of 2 or more telescopes to increase the angular resolution. Target sources would be comets, solar system planets and moons (i.e. Titan), proto-planetary systems, circumstellar atmospheres of evolved stellar systems and infrared bright continuum sources to carry out detailed studies of the molecular interstellar medium.


Scientific Potential of an Enhancement of the Integral Field Spectrometer SPIFFI with a Large Detector and High Spectral Resolution

F. Eisenhauer (1), P. van der Werf (2), N. Thatte (1), T. de Zeeuw (2), M. Tecza (1), M. Franx(2)

(1) MPI für extraterrestrische Physik / (2) Leiden Observatory

SPIFFI is the near infrared integral field spectrometer for the VLT. It is supported by the adaptive optics system MACAO — the combination being named SINFONI - and will be offered to the astronomical community starting in 2002. After two years of operation, SPIFFI will be enhanced with the most recent detector, and its spectral resolution will be enhanced to about 10000. In this presentation we will outline the scientific rationale for infrared field spectroscopy at the VLT. We will give examples for a broad variety of astronomical research which will gain specifically from the high angular and spectral resolution provided by SPIFFI, including high-z galaxies, active galactic nuclei, starburst and ultra-luminous galaxies, super star clusters, ultra-compact HII regions, circumstellar discs, extra solar planets, and solar system objects.


A Differential Imager for Adaptive Optics

J. Eislöffel1, A. Hatzes1, T. Henning2, B. Stecklum1

1Thüringer Landessternwarte, Tautenburg (Germany)

2Astrophysikalisches Institut und Universitäts-Sternwarte, Jena (Germany)

The detection of two very closely spaced sources with larger brightness difference is difficult even with modern adaptive optics systems. For sources with different spectral characteristics, however, a substantial increase in dynamic range can be achieved by differential imaging (Beckers 1983, Lowell Observatory Bulletin 167, 165; Hebden, Hege & Beckers 1986, in "Advanced technology optical telescopes III", SPIE 628, 42). The suppression of residuals and speckle noise in adaptive optics images can improve their dynamic range by factors of ~ 104 (Marois et al. 2000, PASP 112,91). While this technique can be applied favorably to various classes of astrophysical objects (e.g., binaries, environments of young stars, UCHII regions, planetary nebulae, AGN) the most promising prospect would be the direct imaging of extrasolar planets. Such an instrument should therefore be considered for the 2nd generation of VLT instruments.


Cosmology and Large Scale Structure studies with GRB afterglows

F. Fiore, S. Savaglio, A. Fontana, L. Stella, Osservatorio Astronomico di Roma

GRB afterglows close to their peak intensity are among the brightest sources in the sky. When fluxes are integrated from minutes to hours after the GRB, the corresponding logN-logPh exceeds that of any other z>0.5 source. Optical afterglows can be as bright as R=16-19 2-3 hours after the GRB event, reaching R~14 15 min. after the burst. We discuss how to take advantage with the VLT of the accurate (within 10 arcsec) and nearly real-time GRB positioning that HETE2 and Swift will provide. In addition to the study of the fireball itself, this will allow studies of unprecedented quality on: i) high redshift (host) galaxies and in particular on their interstellar material and its connection with nebular emission. Absorption lines will provide information on the metal abundances and dust depletion; emission lines can be used for reddening determination, star formation rate and metallicity of forming stars. ii) The metal enrichment and heating histories of the intergalactic matter in filaments and outskirts of clusters of galaxies along the line of sight. The key points of the proposed observation strategy are: 1) prompt GRB observations (within tens of minutes), 2) high resolution spectroscopy (R>10,000), and 3) coordinated X-ray observations with high throughput, high resolution instruments such those on board of XMM-Newton.


Galaxy Evolution from Ultradeep Multicolor Imaging

A. Fontana, Osservatorio Astronomico di Roma

I will first review the results from our VLT multicolor imaging surveys aimed at studying the physical evolution of high z galaxies, such as the z distribution of K-selected samples, the luminosity destiny up to z~6 and the faint side of the LF at intermediate and large z. These surveys require a combination of area + wavelength coverage + throughput and would largely benefit from improved VLT capabilities. In particular, efficient and wide imagers in the more extreme spectral bands (UV/nearIR) would be ideal to match the depth achieved with FORS/VIMOS in the optical bands. Current and planned ESO imaging instrumentation will be discussed in this context, as well as the motivations for complementing UV and IR spectrographs.


Very rapid follow up of Gamma-Ray Bursts: very-high redshift GRBs (z > 5) and the physics of the reverse shock

T. Galama & P. Vreeswijk (Caltech & University of Amsterdam)

We now know that Gamma-Ray Bursts (GRBs) lie at cosmological distances, with optical afterglow that can be a million times brighter than supernovae. Currently, accurate localizations are available to observers within 3-8 hours of the event. The recent launch of HETE-2 and the future launch of NASA's MIDEX mission Swift (2003) will offer localizations without delay, allowing for studies of GRBs within minutes of the event. At early times, as the example of GRB 990123 has shown, GRBs may be very bright (GRB 990123, at z = 1.6, peaked at V = 9 30 seconds after the event, and subsequently decayed to V = 15 at 15 minutes); a million times brighter than supernovae. Observations within the first few hours allow for studies of the reverse shock (the regular afterglow arises from the forward shock) and may be used to probe Very High Redshifts (VHRs; z > 5). It is estimated that above HETE-2's detection limit, about 20% of GRBs should be at VHRs, and by selecting faint GRBs near HETE-2's detection limit, this fraction may be as high as 50%. Hence, GRBs may be invaluable and powerful probes of the very early universe (e.g., the star formation and metallicity histories of the universe, large-scale structure, and the epoch of re-ionization out to z ~ 6-7. We will discuss how the VLT can be used to perform such studies.


Growing up - the completion of the VLTI

A. Glindemann, J. Alatalo, B. Bauvir, R. van Boekel, F. Delplancke, F. Derie, E. di Folco, A. Gennai, P. Gitton, A. Huxley, P. Kervella, B. Koehler, S. Leveque, S. Menardi, S. Morel, F. Paresce, T. Phan Duc, A. Richichi, M. Schoeller, M. Tarenghi, A. Wallander, R. Wilhelm, M. Wittkowski

The completed VLTI with eight Delay Lines and eight ATs forms the base for the second generation instrumentation. We describe the impact of eight telescopes on observing strategies and performance. Boot strapping with several telescopes will be discussed as well as multi beam combination for `smoother images'. The impact of multi baseline interferometry with dual feed will be investigated. New technological developments like fiber optics amplifiers and integrated optics in combination with STJ open the door for a new type of interferometric arrays. Baselines as long as a a few kilometres come into reach. Examples of these second generation interferometers will be discussed.


Multi-Object and multi-Conjugate Adaptive optics (MOCA): the FALCON concept

F. Hammer, F. Sayede, E. Gendron

Current theories predict that galaxies are hierarchically formed through merging of smaller entities. Deepest surveys (CFRS & HDF) show that galaxies beyond z=0.5 were smaller, more irregular and had higher star formation than present-day galaxies. Merging rate was much more important at high z than today, following (1+z)4, and 50% of the IR background has been resolved by ISO and isdominated by large disks at z=0.5-1.5, generally found in interacting systems. The way galaxies are assembling, and how they are re-distributing their masses, velocities and angular momentum, are largely unknown. Cinematics and chemistry of galaxies should be studied at different redshifts, on large samples, to determine how important is the merging phenomenon, to know the distribution of disks and spheroids at various times, and to firmly establish the origin of the Hubble sequence. An important redshift range for studying galaxy formation is from z=0.5 to z=2-3, covering epochs for which most of the present-day stars have been formed and for which the important spectral features ([OII]3727 to H alpha, stellar absorption lines) are redshifted to a wavelength range from 0.6 to 2 microns. An ideal instrument to study physics of galaxy/star formation, has to include the following properties:

- adaptive optics correction to 0".15-0".25 to detail 1-2kpc sizes,

- spectral resolutions ranging from R=3000 to R=25000 (sigma from 10 to 100km/s),

- 3 dimensional spectroscopy using mosaics of microlenses (integral field units, IFUs, 2-3 arcsec in diameter),

- multi-object spectroscopy within the field offered by the Nasmyth focus (25 arcminute diameter).

In other words, it would be a Fiber-spectrograph with Adaptative-optics on Large-fields to Correct at Optical and Near-infrared (FALCON). The major constraint of adaptive optics is the small field of view. For the specific use of a multi-IFU spectrograph in near IR, this can be overcome because the correction is only needed on a discrete number of small areas (the IFUs) in a large field, and also because a partial correction can satisfy the scientific needs. Our preliminary simulations based on MCAO softwares are very encouraging and will be presented. The FALCON concept will be briefly discussed, including its preliminary technical aspects. Ground-based instruments based on such a concept could become major competitors to NGST.


Astrophysical imaging interferometry - experience from COAST and its implications for the next phase of the VLTI

C. Haniff and D. Buscher

Astrophysics Group, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, England

Model-independent imaging of complex astrophysical sources is one of the key challenges for the latest generation of optical/IR interferometers such as the VLTI. Two main issues are likely to shape the architecture of these arrays: first, their proposed science programme, and second, the technical "rules of thumb" established through the operation of existing imaging arrays. We present an overview of both of these critical questions, with particular emphasis on the experience gained through 7 years of astronomical observations with the world's first optical/IR imaging interferometer, the 5-element 100m-baseline Cambridge Optical Aperture Synthesis Telescope (COAST). We review the key functional requirements for useful model-independent imaging with the VLTI, and outline the strategy needed to ensure its scientific success in the face of competing facilities such as the Keck and CHARA arrays.


The evolution of dwarf galaxies: the VLT perspective

E.V. Held, I. Saviane, Y. Momany, L. Rizzi, G. Bertelli

We present some recent results and projects of our group that have been made possible with the opening of the VLT. Our contribution will address the following topics:

1) deep imaging of distant Local Group galaxies -- we present our results and discuss the degree to which VLT imaging can be competitive with HST/WFPC2 observations;

2) measurements of radial velocities in resolved LG dwarfs. The main goal is studying their internal kinematics and M/L ratios. Also, precise measurements of the systemic radial velocity are important to establish the physical association between gas and stellar populations, and to investigate the Local Group dynamics.

3) measurements of individual stellar abundances. We will discuss the role of VLT's medium-resolution spectroscopy in deriving the metallicity distributions for distant LG dwarfs.

We will briefly comment on some aspects of future instrumental developments that may be advantageous for research on the evolution of low-mass galaxies.


MCAO and associated instrumentation for the VLT

N. Hubin, M.Kissler-Patig — ESO Garching (Germany), E.Marchetti

This paper will describe the current Multi-Conjugate Adaptive Optics MCAO) concepts and performances which can be expected from MCAO techniques both in the visible and in the IR. We will present some of the scientific drivers such as star-formation histories of our and nearby galaxies via deep CMDs, dynamics of stellar clusters by combining astrometry with radial velocities, and the evolution of galaxies in high-redshift clusters by means of integral field spectroscopy. This will introduce a quick overview of the potential instrumentation to be coupled with MCAO. We will emphasize the need for multi-LGS to significantly improve the efficiency of this technique for 8m-class telescopes.

The collaborative efforts between European astronomical Institutes and ESO for the development of a VLT MCAO demonstrator coupled with an imager will be described and goal performances will be presented.


Astrophysical Applications of Tunable Imaging Filters

H. Jones, ESO

The past five years have seen a rapid rise in the use of tunable imaging filters in many diverse areas of astronomy, through the Taurus Tunable Filter (TTF) instruments at the Anglo-Australian and William Herschel Telescopes. Low-redshift science undertaken with these instruments includes studies of brown dwarf atmospheric variability and the identification of optical counterparts to Galactic x-ray sources. High-redshift science has included measurement of the cosmic star-formation history, identification of galaxy clustering around high-redshift QSOs, deep imaging of jet-cloud interactions in powerful radio galaxies, and the detection of a large ionized nebula around a nearby QSO.

In this contribution I will describe the characteristics of these novel devices and the future role they could play at the VLT. I will also review the wide range of potential science, both Galactic and extragalactic, that could be undertaken with a tunable filter on an 8-m class telescope.


Stellar Oscillations studies with STOMACH

A. Kaufer, O. Marco, M. Kürster - ESO, Santiago (Chile)

Asteroseismology has for a long time been proposed as the key for future progress in the understanding of stellar evolution. Indeed, for the Sun the complex multi-periodic oscillation spectra provide profound insight into the stellar interior which otherwise stays inaccessible to any other observational technique. On the other hand, the application of asteroseismological techniques to other normal main sequence stars is still at its beginning - in our understanding mostly due to the lack of dedicated instrumentation at telescopes of high photon-collecting power like the VLT. The basic instrumental requirements include very high resolution (~106) together with large wavelength coverage in the optical range, very high short-term (~days) radial-velocity accuracy (~0.2 m/s), and high time resolution (<1 minute). A possible future instrument with these specifications might also have a strong scientific impact on research in the fields of stellar atmosphere- chromosphere dynamics and extrasolar planets (e.g. bi-sector studies).

Therefore, we envision a dedicated STellar Oscillation MACHine ("STOMACH") at the VLT based on a low-order Adaptive Optics (AO) system working in the optical regime (delivering 0.1" single star images or 90% of the energy in 50 micron diameter at a VLT f/15 focus station) which feeds via near-monomode optical fibers a very high resolution (R=500000) f/10 echelle spectrograph. High spectral resolution with 10-m class telescopes can only efficiently be achieved by reducing image- and therefore slit-size by means of adaptive optics. A small (fiber-)slit size (33 micron in our proposal) further allows to keep the size of optics and the overall spectrograph reasonably small. A compact instrument on the other hand is the prerequisite for the required instrument and PSF stability and allows active temperature and pressure/vacuum control. The STOMACH spectrograph follows the very successful design principles of FEROS/UVES with a bench-mounted crossdispersed echelle spectrograph in white-pupil configuration. Using a R4 echelle grating with 16 grooves/mm, 206 mm beam size and a BK7 crossdisperser prism of 50 degree apex angle it is possible to cover the spectral range from 380-840 nm on 175 spectral orders with a resolving power of R=500000. The complete spectrum can be recorded on a 4kx8k CCD detector with 9 micron pixels with 2.5 pixels per resolution element. The crossdispersion is sufficiently high to accept a feed with three stacked fibers, i.e., for the object, the sky, and for a simultaneous reference spectrum. The spectrograph should operate in fixed configuration for maximum stability; an active, closed-loop stabilization of the opto-mechanical system has been considered, too.


UVES vs. FEROS vs. FOCES: comparing the rectification qualities

A.J. Korn, Inst. für Astron. & Astrophys., Ludwig-Maximilians-Univ., München (Germany)

One of the main uncertainties in high-precision spectroscopic studies comes from the placement of the continuum. This is particularly true if a) you analyse regions of high line density (as generally found in cool metal-rich stars) or b) you want to utilize lines which span across several orders of echelle spectrograms (e.g. Balmer lines). From the point of view of the optical design, fibre-fed spectrographs have the advantage of identical slit illumination for the calibration lamp and the stellar source. Thus, after blaze correction, only small residuals ought to be present within an echelle order and a steady behaviour of these residuals from order to order is expected. Unfortunately, this is not always the case: FEROS shows a non-uniform variation of the continuum shape with order number, UVES is more steady from order to order, but (by design: no fibre) has stronger residuals within the order. I will show that both these drawbacks are absent in FOCES, the Fibre Optics Cassegrain Echelle Spectrograph at the Calar Alto 2.2m [1]. By comparing spectra of one and the same (metal-poor) star taken with the respective spectrograph, it becomes evident that it is possible to design fibre-fed echelle spectrographs which allow you to rectify e.g. Ha (spanning 300 Å or 5 orders!) of stars like Vega to within 0.5%.

For high-precision abundance studies of faint objects (mV < 11m, e.g. metal-poor stars, DA white dwarfs, DLAs...), such an instrument attached to a VLT would be highly desirable.

[1] Pfeiffer, M.J., Frank, C., Baumüller, D., Fuhrmann, K., Gehren, T., 1998, A&AS, 130,381; can be downloaded from http://www.usm.uni-muenchen.de/people/gehren/coolgroup.html


Faint multi-object spectroscopy, present and future

O. Le Fèvre, Laboratoire d'Astrophysique de Marseille (France)

Multi-object spectroscopy is a major tool at the VLT as in most major observatories. I will present a comparison of the current combined capability of the VLT instrumentation with similar instrumentation worldwide. While the VLT fares well in this comparison, many on-going projects will challenge this leadership in the future. Expending from the VIRMOS project experience, I will identify avenues for future multi-object spectroscopy instrumentation at the VLT, in particular expending access to the K band, and high spatial resolution spectroscopy behind adaptive optics.


Scientific potential of MIDI at the VLTI in the 20 micron region

Ch. Leinert1, U. Graser1, L.B.F.M. Waters2, G. Perrin3, B. Lopez4, W. Jaffe5, J.-W. Pel6

1Max Planck Institut fuer Astronomie Heidelberg, Germany
2Astronomical Institute, University of Amsterdam, The Netherlands
3DESPA, Observatoire de Paris, Paris, France
4Observatoire de la Cote d'Azur, Nice, France
5Leiden Observatory, Leiden, The Netherlands
6Kapteyn Astronomical Institute, University of Groningen, The Netherlands

The Mid-Infrared Interferometric Instrument (MIDI) will become operational at the VLT Interferometer in 2002. The instrument will observe in the 10 micron atmospheric window and will reach a spatial resolution of up to 10-20 milliarcsec in combination with a spectral resolution up to 250. MIDI has been designed to also allow operation in the 20 micron atmospheric window. This wavelength region contains important diagnostic spectral features of gas and dust, for which MIDI has the potential to provide unprecedented spatial information. The 20 micron region allows access to solid state bands from amorphous silicates, crystalline silicates, SiO2, TiC, FeS, FeO, MgO, etc. In addition, fine-structure lines from e.g. [SIII] and [FeII] allow studies of ionized gas. When combined with observations at shorter wavelengths this will lead to strong constraints on the spatial structure of objects such as disks around young stars, the stellar winds of evolved stars and the cores of AGN. For instance, the infrared emission of young pre-main-sequence stars is dominated by circumstellar dust which is probably in a disk. It is believed that these disks are the site of planet formation. A key question is the structure of the disk; we mention the possible presence of disk gaps resulting from orbiting proto-planets. The 20 micron region will probe a much cooler part of the disk than accessible at 10 microns. This is important since the bulk of the mass in these disks is dominated by cold dust.


VLTI Wide-Field Imager

R. Le Poole, Sterrewacht Leiden (The Netherlands)

It is proposed that it is the right time to elaborate the installation of a homothetic mapping facility in the central "pit" in the interferometric laboratory. With an appropriate cophasing strategy for all beams this shall prove to be the most sensitive interferometric imager ever. System parameters and tolerances will be addressed in connection with proposals for implementation of required subsystems. Expected (limiting) performance will be indicated.

Delivery of such a system is of course still far away in time, as it must follow an extensive exploitation period for the instruments that are going to be commissioned shortly. However, the complexity of such an imager, and the planning for the future of the interferometric laboratory make the onset of studies for this unique European facility rather important at this time.


A super-imaging Fourier Transform Spectrometer for the VLT

J.-P. Maillard (IAP), R. Bacon (Obs. de Lyon)

A visible, imaging FTS (dual input, dual output design) is proposed for a Nasmyth focus without adaptive optics, of one 8-m VLT. Such an instrument is characterized by a continuously chooseable spectral resolution. The proposed maximum resolution is chosen equal to ~ 2x104 at 0.6 micron (15 kms–1), which corresponds to a maximum optical path difference of only 8 mm. With a 4Kx4K CCD camera on each output port, which provides a wavelength coverage of 3500 to 10000Å, and a scale factor of 0.15"/pxl, a full 10x10 arcmin field is covered. For lower image sampling, a factor 2 variable focal enlarger at the entrance makes it possible to achieve IFS on a field as large as 20x20 arcmin. At the highest spectral resolutions the spectral range must be limited by narrow-band filters (down to 0.05% relative width) in order to keep the interferogram data cubes of comparable size with the resolution. This is obtained by switching a 4x4 mosaic of 100x100 microlens at the entrance focal plane of the interferometer and a reflective prism on each output beam to disperse the full spectral range from each microlens, over 20 pixels onto the detector arrays. Hence, the instrument can work with a wide spectral coverage (3500–10000 Å), either at low resolution over a large field, in a survey mode, or on a smaller field (80x80 arcsec) and high sensitivity, at high spectral resolution. Compared to a long slit solution, a complete flexibility is obtained, making it possible to adapt field size, spatial and spectral resolution to various astrophysics problems, going from full analysis of clusters of galaxies, of star clusters, to detailed kinematic studies of particular nearby galaxies and planetary nebulae. By replacing the 4Kx4K CCD cameras by 4Kx4K HgCdTe cameras, the same concept could be extended to the near infrared. We will present the performances and the main science drivers of this instrument.


VLTI imaging instrument using the full potential of the interferometric array

Malbet, Kern, Perraut, Berger, Haguenauer, Perrier, Monin, Chelli, Bouveir, Fraix-Burnet (LAOG - Observatoire de Grenoble)

With a milli-arcsecond spatial resolution, many scientific topics like dust torus around AGN, disks around young stars, envelopes around AGBs, require imaging. The current VLTI instruments (AMBER and MIDI) will give access to information at high angular resolution without actual imaging. Since as a rule of thumb, the field and the image quality that is accessible with an optical interferometer is roughly proportional to the number of telescopes used simultaneously, the more numerous the apertures, the better the reconstructed field. We propose the interferometric beam combination of N telescopes (4 <= N <= 8) thanks to the integrated optics (IO) technology: 4 Unit telescopes in the short term and/or 8 Auxiliary telescopes in the medium term. The goal is to achieve an instrument whose image quality is equivalent to the IRAM Plateau de Bure interferometer with a spatial resolution better than the one foreseen with ALMA, either in the visible and/or in the near infrared. This instrument would be able to acquire routinely images with 1 mas resolution with a 14-to 20-mag sensitivity in the NIR with a spectral range from 0.5 to 2.5 microns.


Second-generation VLT/VLTI instrumentation requirements for star and planet formation studies

M. McCaughrean, Astrophysikalisches Institut Potsdam

T. Henning, Universität Jena

The VLT and VLTI provide extraordinary observational capabilities across a wide range of astrophysical problems. However, the most important capabilities for a given class of problem may differ, and the study of galactic star and planet formation is more often limited by the available spatial resolution than by a lack of photons. Important issues include resolving rings and gaps in circumstellar disks and measuring their spatial and dynamical structure, separating individual stars and planets in densely-clustered regions to obtain accurate photometry and spectroscopy, and accurate astrometric monitoring of stars with invisible companions, directly-detected planets, and knots in collimated jets. Spatial resolution also plays an important role in the battle to reduce the effects of the strong thermal background seen beyond 2.5 micron, a vital region for studying early embedded phases of star and planet evolution.

In this contribution, we shall outline the important requirements imposed by star/planet formation studies on instruments for the VLT and VLTI, and which crucial areas must be addressed in second-generation instrumentation, in particular those covering the infrared from 1—20 micron. These include wide-field imaging, filled-aperture clean-PSF imaging with the possible inclusion of coronography and polarimetry, high spatial resolution integral field spectroscopy at medium and high spectral resolution, simultaneous multi-colour imaging, and dilute-aperture interferometric imaging and spectroscopy with the VLTI, with maximum possible u,v plane coverage. We end using these requirements to propose some specific recommendations for new VLT/VLTI instruments, with close attention to synergy with instrumentation planned or foreseen for complementary facilities over the present decade, including ALMA and the NGST.


Star formation with the 2nd generation instruments of the VLT and VLTI

Monin, Malbet, Menard, Mouillet, Bouvier, Beuzit et al.

The first generation of the VLT & VLTI instruments cover a wide range in the "angular resolution / wavelength domain" parameter space. However, large gaps remain in this coverage that could be filled by second generation instruments devoted to star formation study. Among others, filling these gaps includes an extension of the diffraction-limited capability of the VLT and the VLTI toward the visible domain.

In this paper, we will explore the breakthrough results that would be expected from an extended coverage of current VLT & VLTI capabilities, in the field of star formation research.


MEIFUS (Million Element IFU Spectrograph)

S. Morris, R. Content, R. Bower, R. Davies, R. Sharples (University of Durham, UK)

We will describe an instrument concept that will provide simultaneous spectra for over 1 million spatial samples on the sky. With the proposed field of view and spectral resolution, it will be able to measure redshifts and line strengths for around 1000 z~3 galaxies in a six hour exposure. The main science driver is to obtain a complete census of the star formation properties of galaxies with 2.3<z<4.75 as a function of luminosity, environment, morphology and redshift. This redshift survey will also allow us to study the evolution of the 3 dimensional power spectrum and hence test the connection between these early galaxies and the large scale structure of the Ly-alpha forest.


Interest in very accurate imaging of the close environment of bright objects in visible and near-infrared wavelengths

D. Mouillet, J.L. Beuzit, G. Chauvin, A.M. Lagrange, et al.

The latest decade has demonstrated the instrumental capability to control, up to now mostly in near IR, the wavefront coming through atmosphere so as to provide accurate spatial information on astronomical objects (with AO or long baseline interferometry).

We emphasize that still better imaging capabilities, both for VLT (with very high Sr AO) and VLTI (towards real imaging with a large number of simultaneous baselines), would dramatically benefit a large number of astrophysical topics: environment of young stellar objects, evolved stars, binary or multiple systems, planetary disks and low mass companions down to brown dwarves or hot planets. In particular, the very accurate control of wavefront would very interestingly open the possibility to use new instrumentation dedicated to very high dynamic observations and/or to extend the wavelength range from near-IR to visible.

Most of the mentioned astrophysical interests can be reached with moderate limiting magnitude and moderate field of view. For these topics, and if instrumental developments imply compromises, very high angular resolution and dynamic down to visible wavelength appear in priority before sensitivity and field. Concerning spectral resolution, a large number of topics will need only broad and narrow filters. A significant number of studies will also benefit from medium and high spectral resolution.


Scientific motivations for an Adaptive Optics Visual Echelle Spectrograph and Imager-Coronograph for the VLT NAOS Visitor Focus

R. Pallavicini1, A.-M. Lagrange2, P. Molaro3, L. Pasquin4, J.-L. Beuzit5, B. Delabre4, F.M. Zerbi5, P. Santin3, G. Bonanno6 and the AVES-IMCO team

1) Osservatorio Astronomico di Palermo, Italy, 2) Laboratoire d'Astrophysique, Observatoire de Grenoble, France, 3) Osservatorio Astronomico di Trieste, Italy, 4) European Southern Observatory, Garching, Germany, 5) Osservatorio Astronomico di Brera, Merate (LC), Italy, 6) Osservatorio Astrofisico di Catania, Italy

We present the scientific motivations for an adaptive optics visual echelle spectrograph and imager-coronograph for use as a visitor instrument at the secondary port of NAOS on unit UT4 (Yepun) of the VLT. We demonstrate that such an instrument would be ideal for intermediate-resolution (R=16,000) spectroscopy of sky-limited observations of weak objects, down to a limiting magnitude of V=22.5, and will complement very effectively the near-IR imaging capabilities of CONICA. We present examples of science programs that could be carried out with such an instrument and which cannot be addressed with existing VLT instruments. We also report on the results of a two-year design study of the instrument, with specific reference to its use as parallel instrument of NAOS.


The VLTI adulthood: plans for second generation instrumentation and scientific opportunities

F. Paresce, A. Richichi, M. Schoeller et al. (ESO)

We present some of the ideas currently being discussed for second generation VLTI instrumentation, which could be made available when the facility will have reached a mature phase of routine interferometric observations with all of the planned subsystems, telescopes and delay lines integrated. At that stage, the VLTI will have probably outgrown the capabilities of the AMBER and MIDI instruments, which could be joined by one or more additional instruments to exploit the full potential of wavelenght range and beam combinations of the VLTI. In particular, the possibility of combining several baselines simultaneously (up to eight) will permit to achieve actual imaging capability. This, in combination with the flexibility of baseline combinations offered by the VLTI, will in turn open the door to studies of rather complex objects with unprecedented detail. Examples include the circumstellar environment of young stars, in particular with regard to the imaging of disks and jets, and extragalactic objects such as AGNs and their nuclear region.


Massive Spectroscopy of Stellar Fields

L. Pasquini, M. Kissler-Patig — ESO Garching (Germany)

Large photometric surveys, like microlensing experiments or DENIS are bringing new, exciting results about the Galaxy and the LMCs structure and composition. We will present the scientific cases for the spectroscopic equivalent of those surveys, which will require the extension of multi-object spectroscopic capabilities at the VLT. Dynamics and metallicity of Magellanic Clouds, Bulge, local group and nearby galaxies are the most obvious candidates. To achieve such an ambitious goal several avenues can be explored, like a full completion of the FLAMES facility or a new, large field 3D instrument. We will briefly explore the advantages and the disadvantages of both concepts.


Advanced Tele-robotic Field Spectrometer

H. Pedersen, Copenhagen University Observatory (Denmark)

M.I. Andersen, University of Oulu (Finland)

Three decades after the discovery of Gamma-Ray Bursts, the basic energy source remains to be found. Alone for that reason the phenomenon presents a formidable challenge to astrophysics.

During the last few years considerable progress has been made on the physics of the burst outflow, and its interaction with circumstellar matter. This was achieved through optical (and IR, radio) observations of more than 20 rapidly fading sources for which accurate positions were available sufficiently early from space-borne, high-energy detectors. The optical data have proven useful also for cosmological studies, e.g. of intervening inter- galactic space. These investigations are facilitated by the large red-shifts measured to many sources (up to z~4.5), in conjunction with their apparent optical peak brightness (reaching m~9).

While the VLT is well equipped to exploit these research opportunities, a separate piece of equipment is required to optimize the observing strategy. We intend to describe an instrument, called the Advanced Tele-robotic Field Spectrometer (ATFS), which takes input from a range of spacecraft, performs the optical/near-IR identification, estimates the red-shift, and decides which observation, if any, should be requested from the VLT, - and all within 60 seconds of time. Through application of elaborate image-analysis and control software the need for humans in the loop will be eliminated, which is a prerequisite for efficient VLT observations of the fading optical sources.

The ATFS will monitor the temporal development of the counterpart brightness and optical spectrum in the time-interval starting about 2 seconds after receipt of trigger command from space, and until the VLT can start observation, typically after 3 minutes. For many bursts, the high-energy emission will peak during this time interval. It is therefore plausible that comparison of the time-resolved optical spectrum with the gamma- radiation time profile will lead to a better understanding of the basic emission process. The ATFS will thus have an important task in its own right.

For best synergetic value, the ATFS must be installed at Paranal, where it will share sky coverage and general observing conditions with the VLT. We shall give details of the instrument performance as derived from numerical simulations, and outline a scenario for its realization.


3D Mapping of the intergalactic medium

P. Petitjean and E. Rollinde, Institut d'Astrophysique de Paris

Recent N-body simulations have shown that Ly alpha absorption line systems can be used as luminosity unbiased tracers of the spatial distribution of baryons over most of the history of the Universe. This opens the exciting prospect to map in 3D the spatial structures of the inter-galactic medium. For this, a dense network of background QSOs must be observed in the same field in order to correlate the absorptions observed along the different lines of sight. This project needs multi-object (~20—50 objects) intermediate resolution (3000-10000) spectroscopy in the blue (3200-4000Å) with a large field (~20 arcmin). The corresponding instrument does not exist at the moment and should interest a large community.


Optimizing a Differential Interferometric Instrument

M. Vannier, R.G. Petrov, B. Lopez, et al.

From its conception, AMBER has been designed to measure the variation of interferometric phase with wavelength. This measure has applications in most of Amber astrophysical programs including the detection and spectroscopy of hot giant extra solar planets. However, in the design of Amber it has been necessary to make several trade off which might limit the ultimate performances of this mode, mainly because all causes for rapidly variable nanometric differential dispersion could not be eliminated. This paper summarizes this limitations and analyzes ideas to build a VLTI instrument dedicated to the measure of differential phases with accuracy down to the photon noise limit which can be as low as a 10-6 fringes in the K band. Such a performance should allow, for example, high SNR medium resolution spectroscopy of more distant or smaller giant extra solar planets.


Imaging Spectroscopy for a Multi-Telescope Interferometer

R.G. Petrov, et al.

The current study of the first generation VLTI instruments AMBER and MIDI as well as the preparation of their scientific program very clearly underlined the crucial importance of spectrally resolved interferometric observations. On the other hand, a strong trend for future interferometric instruments is to improve the imaging capability by an increase of the number of apertures and also of the available field. Combining all this constraints has been a classical problem for spectrally resolved speckle interferometry or multi speckle long baseline interferometry. It is the very standard problem of what is called "3D spectroscopy". The solutions can be roughly grouped in three classes. One way is to use classical spectroscopy with a slit fed by a field reorganized by image slicers or combinations of micro lenses and fibers: the spectral resolution can be good but the number of spatial resolution is limited. A second solution is to use a "Courtes" type multichromator. Then the field can be extended and well sampled but the spectral resolution is very limited. The third class of solutions is to boost the performances of a multichromator with an adjustable filter such as a Perot-Fabry. This combines high spectral and spatial resolution but implies using time to fully explore the data cube. This paper is intended to synthesize and summarize the key parameters which can allow to select the optimum possibility and to size it for a given application. The analysis will be made for a VLT interferometer with 4 to 8 beams.


Proposal for a single mode medium resolution spectrometer with a wide optical spectral coverage

M.A. Prieto, ESO Garching (Germany)

Gaseous nebulae are ionized regions of low-density plasma associated with a great variety of astronomical objects, from HII regions, to AGN, to supernova remnants. It is impressive that despite the very different conditions associated with each of those object types, their basic nebular spectra is a characteristic one that in the optical range is usually dominated by the typical forbidden lines of common elements as O, N, S and by the permitted lines of H and He. Yet, besides these usually strong optical lines, there is a large number of much weaker ones which are generally missed with current instrumentation but that are fundamental for a correct diagnosis of the physics of nebular gas.

Some of the most important missing optical lines will be briefly reviewed and their scientific applications discussed. Because most of these lines are basically spatially unresolved, it is argued that a dramatic improvement in detection and reliable measurement of these lines can be achieved by combining medium resolution spectroscopy and high spatial resolution. To that aim, a single-purpose, high throughput, medium resolution (R~5000 - 8000) integral field spectrometer adapted to high spatial resolution scales in the 3000-10000Å waveband is envisaged.


The capability of the VLT and the VLTI instrumentation will be reviewed in the context of the search and the characterization of extra-solar planets

D. Queloz, M. Mayor — Obs. de Genève (Switzerland)

Now, successful radial velocity surveys are conducted as well as observations of planet transit. Many attempts to directly measure some spectral features from a planet have also be made. It should eventually be successful. New instruments, optimized for accurate radial velocity measurements, like HARPS, should bring the radial velocity technique to its limits. However the high resolution IR capability of CRIRES and the Interferometric combination of VLTs will open up new prospects for direct detection of planets. We plan to review our current knowledge on extra-solar planets and to extrapolate on future observations with the VLT/VLTI planned instrumentation. We shall also identify new needs and possible improvements and new developments.


Achromatic Interfero Coronography and VLT

Y. Rabbia (OCA, France), P. Baudoz (IfA, Honolulu, USA), J. Gay (OCA, France)

Achromatic Interfero Coronograph (AIC ), works on a single aperture in near IR and achieves extinction of an on-axis point-like object by destructive interference. It is a compact device and have already been tested on the sky: good agreement has been found between expected and effective performances. It allows sensing the vicinity of a star, as close as one third of the Airy angular radius. Extinction capability of astrophysical interest requires a high performance adaptive optics system. It is thus inviting to consider the insertion of AIC between NAOS and CONICA, taking advantage of both a large aperture and high performance focal devices. With AIC, extinction is achromatic and makes much versatile the choice of the spectral band of work (center and width). In particular, the possibility offered by AIC to record, simultaneously, images in two separated spectral bands is enhancing the extinction performance, by better removal of residual light. We present the compact AIC device and images recently obtained on stars and we describe a technical solution to insert AIC (switch of a mirror) between NAOS and CONICA without changing the optical configuration seen by CONICA. Critical points are discussed and scientific goals are outlined.


Coronography with sectorised phase masks

D. Rouan (Observatoire de Paris), P. Riaud (OHP), A. Labeyrie (OHP), A. Boccalletti (Obs. de Paris and Caltech), Y. Clénet (Observatoire de Paris)

Coronography is essential when looking at faint structures nearby a bright object (star, AGN, planet...). It appears that the performances of classical amplitude coronography (focal plane diaphragm + Lyot stop) can be largely surpassed when one modifies the phase rather than the amplitude of the wavefront in order to produce destructive interferences of the coherent PSF of the bright source - obtained thanks to adaptive optics-. This nulling interference can be produced with a phase mask in the focal plane, as proposed by Roddier, or by interferometric combination in the pupil plane, as proposed by Gay and Rabbia. Both concepts are interesting.

We explore here the feasibility of a phase mask solution for a VLT instrument based on a new design of the mask, while, in a symmetric paper, Rabbia et al. develop the interferometric concept.

We have recently proposed a genuine design (Rouan et al., in press) of the geometry of a phase mask, which is especially efficient because a) of its reduced sensitivity to tip-tilt residuals and b) it makes the residuals of speckles symmetrical, so that an additional gain is obtained by subtraction of this symmetrical pattern when asymmetric structures are looked for (faint companion for instance). A contrast as large as 1.E5 can be reached in principle at an angular distance 0.8 lambda/D, in excellent conditions of seeing. A fairly good adaptive optics correction is required and NAOS/CONICA is clearly the target instrument that could benefit from such a device. Such a mask just need to be inserted on one position of the focal plane wheel of Conica. It must be completed by a classical Lyot stop, that does exist anyhow in Conica. Simulation of performances on a VLT class telescope in different conditions of turbulence will be presented for two types of sectorised masks we propose. We will discuss the scientific goals that this instrument could aim at, especially in the field of AGNs environment and extrasolar planets imaging. Manufacturing of achromatic masks, an important issue, will also be discussed.


Constraining the formation epoch of the first stars

D. Schaerer, R. Pello — Obs. Midi-Pyrénées, Toulouse (France)

Based on new pop III stellar tracks, new state-of-the art non-LTE model atmospheres, and existing models at low metallicity we construct a grid of starburst models for metal-free and low metallicity galaxies. The dependence of their properties on the IMF, upper mass limit for star formation and dust reddening is studied. The emerging synthetic spectra are used to discuss the implications on different observational features, which could be addressed through wide and narrow band photometry and spectroscopy. Our simulations aim at exploring possible constraints on the formation epoch of the first stars in galaxies.


Imaging of Polarimetry and Spectropolarimetry of Bright Objects

H.M. Schmid, I. Appenzeller, Landessternwarte Heidelberg, Germany

J.O. Stenflo, Institute of Astronomy, ETH Zürich, Switzerland

A. Kaufer, ESO Santiago, Chile

The VLT and FORS1 instrument configuration provides spectropolarimetry of bright active galactic nuclei (AGN) with an accuracy in p of about 0.1%. We present such data and discuss the new diagnostic potential opened up for these targets by high signal-to-noise (S/N) spectropolarimetry with large telescopes. The observations show that it is now possible for bright AGN to measure accurately the polarization structure in different spectral components.

For bright AGN the achieved S/N level with the VLT is photon noise limited. But for objects brighter than about m=14 in spectropolarimetric mode or about m=16 in polarimetric mode the S/N is dominated with the traditional measuring technique as used in FORS1 by systematic errors due to e.g. seeing, varying background polarization and flat-fielding. For solar physics an instrument (ZIMPOL) for imaging polarimetry and spectropolarimetry has been built, which overcomes these limitations for objects with high photon flux. The ZIMPOL-technology pushes the systematic errors down by at least two orders of magnitudes. Thus, it is technically possible to reach with the VLT for bright stars of about m=5 an accuracy in p of about 0.001% with medium resolution (R=1000) spectropolarimetry.

A whole range of new types of astronomical investigations would be possible with such a device. Any type of scattered radiation from asymmetrically distributed circumstellar material, like stellar wind or proto-planetary disks, could be studied in much more detail. Also the scattered radiation from short period extra-solar planets could be measurable for the determination of orbit inclinations and planetary atmosphere chemistry. Combined with high resolution spectroscopy magnetic fields in many different types of stars could be thoroughly investigated. Further the interstellar magnetic fields, e.g. in star forming regions, could be studied with much higher sensitivity in the Milky Way and local group galaxies.


Extension of the Near Infrared Instrument Amber in the visible: a giant step in the astrophysics at low cost

Ph. Stee, D. Mourard et al.

We will focus on particular proposals that are already defined to be run within the Amber guarantee time such as stellar surfaces of AGB stars, dust shells of stars in late phases of stellar evolution, circumstellar environment of Be and B[e] stars, survey of inner disks in T Tauri stars as well as Seyfert galaxies or radio jets and broad line regions of active galactic nuclei. We will show that the AMBER extension in the visible can put strong constraints on the understanding of the physics of these complicated objects since physical conditions that produce visible photons are very different from those in the IR. Finally we will illustrate these new possibilities through recent results obtained with the GI2T interferometer in the visible.


A cryogenic near infrared multi-object spectrograph for the VLT

N. Thatte, R. Hofmann, M. Tecza, F. Eisenhauer, R. Genzel — MPI für extraterrestrische Physik, Garching (Germany)

Spatially resolved spectra of high redshift galaxies are crucial to unraveling the nature of these objects. Emission and absorption line kinematics and dynamics will enable measurements of mass, stellar population, chemical composition and spatially resolved star formation histories. Most familiar rest-frame visible diagnostic spectral features are shifted to the near infrared at moderate redshifts, requiring cryogenic instrumentation at wavelengths longer than 1.6 micron.

We propose to build a cryogenic near infrared multi-object spectrograph equipped with deployable mini-integral field units (IFU) with 0.3" pixels. Each mini-IFU will obtain spectra of ~25 field points, and 20 such units will be deployable within a 4’x4’ field of view using a cryogenic robotic positioner. Besides providing spatially resoled spectra, the mini-IFUs will require low positioning accuracies and prevent slit-losses while providing high spectral resolution. In addition, no a priori knowledge of galaxy major axes or orientation is required, improving observing efficiency. The fully cryogenic design is optimized for observations up to 2.5 micron. Spectral resolutions of ~5000 will be realised to enable the use of OH avoidance techniques. First light is foreseen in 2004.


VLTI studies of optical jets from AGN

S. Wagner, Landessternwarte Heidelberg (German)

Radio-VLBI observations allow AGN studies with highest angular resolution, approaching the size of the solar system in nearby, radio-loud sources. Recent Chandra-Observations confirm that the non-thermal radiation emitted from radio-jets can be detected to very high energies. Correlated optical- and high energy - variability studies illustrate that significant fractions of the OPTICAL non-thermal emission from Blazars are emitted from a compact jet on linear size scales corresponding to the angular resolution of the VLTI. High photon-densities in the compact optical jets will enable detections of extended jets with optical interferometry. The photon densities exceed estimates for high-resolution studies of thermally emitting components of AGN by orders of magnitude. We will discuss technical requirements and expected scientific breakthroughs.


Polarization - and variability studies - Understanding non-thermal emission from compact objects

S. Wagner, Landessternwarte Heidelberg (German)

VLT polarization observations and variability studies have led to important constraints on the nature of particle acceleration and emission processes. Polarization studies of extended jets illustrate the call for in-situ particle acceleration up to very high energies throughout extended regions, even in highly redshifted AGN. Magnetic fields traced in plerionic SN remnants by VLT polarization studies coincide with bright X-ray features, indicating distinct topologies for regions accelerating particles to different energies. Circular polarization in radio-loud AGN question the paradigm of isotropic particle distribution functions, and variable signals in pulsars trace feeding processes in pulsar magnetospheres. We review the new questions emerging from studies of non-thermal emission from compact objects and possible ways of addressing them.


Integral Field Spectroscopy

G. Wright, R. Ivison, A. Russell

In order to fully exploit the superb image quality of the VLT telescopes, the most effective spectroscopic mode will often be integral field spectroscopy from which the associated, often complex, image morphology can be reconstructed with the same angular resolution as that of the spectroscopic data. We will discuss science drivers and requirements for multiple deployable integral fields for spectroscopy in the near infrared. We will describe an instrument concept to achieve such a capability with up to 32 integral fields deployable over a 10 arcmin field.


Characteristics and status of the REM telescope

F.M. Zerbi(1), G. Chincarini(1), G. Ghisellini(1), M. Rodonò(2), A. Antonelli(3), P. Conconi(1), S. Covino(1), G. Cutispoto(2), E. Molinari(1), on behalf of the REM team

(1)Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate (Lc), Italy

(2)Osservatorio Astrofisico di Catania, Via S.Sofia 78, I-95123 Catania, Italy

(3)Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (Roma), Italy

We present REM, a fully robotized fast slewing telescope equipped with a NIR (Z', J, H, K') camera dedicated to the monitoring of the prompt IR afterglow of GRBs. REM has been designed as the NIR complement to the SWIFT observatory, scheduled to fly in 2003, which has on-board a gamma ray detector system, an X-ray and a UV-Visible telescope. REM is designed to arrive on-target in a few tens of seconds after receiving the trigger information. Through the extension at the NIR wavelength of the prompt afterglow measuring, REM can discover objects at extremely high red--shift and it can trigger large telescopes to observe them. The possible location of REM at la Silla Observatory is currently under discussion and would make VLT the preferential partner for receiving REM output. This would possibly give to the VLT Observatory the chance to record spectra of the most distant sources observed so far.