The following document lists the file abstract/ASARGENT_PPDISKS.abs
from catalogue VI/111.
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SCIENTIFIC ABSTRACT: The presence of circumstellar dust around main-sequence stars such as Vega and Beta Pictoris was inferred from strong infrared excesses measured by the IRAS satellite. Follow-up observations of a few objects suggested extended emission. For Beta Pic, coronagraph images show disk-like morphology. It seems likely that the IR excesses imply the presence of disks. Disk properties may be critical to understanding the origin and evolution of the solar system. With the enhanced sensitivity of ISOCAM, the nature and morphology of the material around a larger sample of Vega-type stars will be studied. The infrared emission from the Vega-type stars alpha Lyrae, alpha Piscis Austrinus, beta Pictoris and, perhaps, epsilon Eridani has been resolved (c.f. Backman & Paresce 1993, Protostars & Planets III, p.1253). Optical coronagraph measures of beta Pictoris have demonstrated that the circumstellar dust is distributed in a disk-like structure(e.g. Smith & Terrille 1984). Until very recently, there were no other direct images of the material around Vega-like stars. However, the successful imaging of the beta Pictoris system by Lagage & Pantin (Proceedings: IR Astronomy with Array 1993) encourages us to believe that the sensitivity of ISOCAM will enable direct imaging of a number of Vega-type systems. The morphology and properties of the circumstellar dust are of critical importance for understanding the evolution of stars and possibly planetary subsystems. Objects to be observed have been selected from the extensive literature on Vega-type candidate systems and are listed below. OBSERVATION SUMMARY: These are obviously most difficult observations with ISOCAM. We intend to use for all observations the Beam Switching mode, with only one excursion between source and background, and much time allowed for detector stabilization. For PSF determination, we intend to study two stars. The main filter will be LW9 (14-16 microns); some stars will also be observed with LW8 (10.75-12 microns). For Beta Pic we will also attempt an observation with LW7 (8.5-10.75 microns). Beta Pic, Alpha Psa, Epsilon Eri and Vega are too bright to be observed with an individual integration time longer than 0.28 sec; total spacecraft times on a given observations will be of order 20 minutes. For the other stars, we will use individual integration times of 2 sec and total spacecraft time of 30 minutes (source plus background on one filter). The results will depend on the detailed behaviour of ISO and ISOCAM in flight conditions; we aim at detected extended emission close to the stars at the level of 100 microJansky/arcsec2, with a S/N of order 5. For a spring launch, both reference stars are close to Beta Pic; the observations will be concatenated to those on Beta Pic itself. For an autumn launch, one of the reference stars will be close to Vega and it is concatenated to the Vega observation.