Contents of: VI/111/./abstract/ASARGENT_PPDISKS.abs

The following document lists the file abstract/ASARGENT_PPDISKS.abs from catalogue VI/111.
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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.
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.

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