Laurens B. F. M. Waters

Ten-micron instrument MIDI: getting ready for observations on the VLTI

The mid-infrared interferometric instrument MIDI is currently undergoing testing in preparation for commissioning on the Very Large Telescope Interferometer VLTI at the end of this year 2002. It will perform interferometric observations over the 8 μm - 13 μm wavelength range, with a spatial resolution of 20 milliarcsec, a spectral resolution of up to 250, and an anticipated point source sensitivity of N = 4 mag or 1 Jy for self-fringe tracking, which will be the only observing mode during the first months of operation. We describe the layout of the instrument and the performance during laboratory tests, both for broadband and spectrally resolved observing modes. We also briefly outline the planned guaranteed time observations.

The Mineralogy of Interstellar and Circumstellar Dust

The study of dust in space was for a long time hampered by the lack of resolution and wavelength coverage in the infrared. The launch of the Infrared Space Observatory (ISO) changed this dramatically. Its unprecedented wavelength range (2.4 - 200 μm) together with its relatively high spectral resolution (λ/Δλ = 2000–150) made this instrument ideal to study dust in space. Many new dust species have been found, in particular of oxygen-rich species. The quality of the data allows a detailed mineralogy of individual species. The ISO database can be used to carry out an inventory of the occurrence of dust species in various circumstellar and interstellar environments. The picture that emerges is that of a very rich circumstellar dust mineralogy, while the interstellar medium shows only a limited amount of species. We present an overview of this inventory, as well as of the mineralogy of the dust species found. The implications for our understanding of dust processing in different astrophysical environments are also discussed.

10-μm interferometry on the VLTI with the MIDI instrument : a preview

We describe principles, design and present status of MIDI, the mid-infrared interferometric instrument for the VLTI, which is planned to come into operation at the ESO Very Large Telescope Interferometer during the second half of 2001.

The Structure of the Circumstellar Material in Be Stars

We review observations that are relevant for the determination of the structure and geometry of the circumstellar envelopes of Be stars. Evidence is summarized suggesting that Be stars have rotating discs. Infrared and radio continuum and line measurements and their interpretation are discussed.

MIDI, the 10 mu m interferometer of the VLT

Abstract We report in this paper on the current status of the mid-infrared beam combiner of the VLTI: MIDI. We explain the interest of VLTI for this range of wavelentghs and give an overview of the main characteristics of MIDI and present its scientific targets.

The astrophysical potentials of the MIDI VLTI instrument

The mid-infrared interferometric instrument (MIDI) is planned to become operative at the ESO Very Large Telescope Interferometer (VLTI) during the year 2001. The first version of MIDI is designed for use of two telescope beams at 10 micrometers wavelength. We here present an overview of some of the scientific objectives. The preparatory work under progress, before first VLTI observations, consists in studying the feasibility of different astrophysical projects (expected visibility, required absolute accuracy of the measurement, required observing time, procedure of observation, and VLTI baseline configuration). As examples we will discuss the observations of disks around young stellar objects, of active galactic nuclei, of extrasolar planets and of some evolved stars.

Infrared, submillimeter, and millimeter observations of the soft gamma-ray repeaters

Abstract The Soft Gamma-Ray Repeaters appear to be a completely new manifestation of neutron stars. SGR 1806-20 and SGR 1900+14 may have highly unusual stellar counterparts, whose spectra peak in the far infrared. They have not been detected at submillimeter or millimeter wavelengths. Their infrared spectra appear to contain several components: the photospheric emission from star(s) dominates at shorter wavelengths, a bright point source dominates at 25 μm, while an extended source dominates at 60 μm. Their spectra are inconsistent with monoenergetic synchrotron and black body radiation models, but are consistent with simple dust models. We briefly review here our latest millimeter, submillimeter, and infrared observations. We include new upper limits at 235 GHz (1.3 mm) for SGR 1806-20 and SGR 0525-66. The extended IRAS emission detected for SGR 0525-66 is consistent with that expected from heated dust in the supernova remnant N49. Here we show a preliminary analysis of our recent 9.862 μm imaging of the region around SGR 0525-66. We do not detect any point sources, at flux limits lower than would be expected if the other two SGR were placed at the distance of the LMC.

The asymptotic giant branch in the LMC, SMC and the Galactic Centre

Mass loss on the AGB is extremely important for galactic chemical evolution but is poorly understood. A data set of a coherently selected sample of AGB stars is required to resolve this issue. The VLT with its suite of infrared instruments allows the Large Magellanic Cloud, the Small Magellanic Cloud and the Galactic Center to be completely surveyed for AGB stars. The survey could be done using only morning and evening twilight, which is of no use to other programs. The limiting flux for this survey is expected to be 2–3 orders of magnitude fainter than that of the IRAS 12.5 μm channel. The survey will result in the first complete catalog of AGB stars at a known distance. The objects would then be studied more in depth, employing high spatial resolution IR imaging and medium to high resolution spectroscopy with a special emphasis on rotational-vibrational molecular transitions. This program could lead to an understanding of this important but as yet enigmatic phase of stellar evolution, especially the physics of mass loss and the thermonuclear evolution of AGB stellar cores.

ISO-SWS spectroscopy of B[e] stars

We present ISO-SWS spectra of B[e] stars. We find a wide diversity of spectral characteristics of B[e] stars, suggesting different origins for the circumstellar matter. Most B[e] supergiants show hot dust with weak amorphous silicate emission. MWC 300 has a warm dust shell with strong crystalline silicate emission; its evolutionary status is unclear.

SCUBA sub-millimeter observations of gamma-ray burst counterparts

SCUBA is a new sub-millimeter instrument on the James Clerk Maxwell Telescope. It can use two arrays of bolometers to simultaneously map the same patch of sky (∼2.3′ in diameter) at 850 and 450 microns. The field of view and sensitivity make it a good instrument to use in the sub-millimeter on arcminute sized gamma-ray burst error boxes. For well-localized radio and optical counterparts, sensitive pointed observations can be made using the central pixel of these arrays, or using the dedicated photometry pixels at 1100, 1350, and 2000 microns. We have an ongoing program of Target of Opportunity GRB observations. As a test run, we observed GRB970508 on May 26 using the 1350 μm pixel. No sources were detected, consistent with other millimeter observations.