Contents of: VI/111/./abstract/PWESSELI_YSOAEBE2.abs

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SCIENTIFIC ABSTRACT

We want to study young intermediate mass stars, in two stages: the
youngest completely embedded `YSO' stage, and the very young, already
visible, Herbig Ae/Be stars with sizable dust envelopes still around
them. These stars have masses of 2 to 10 Msun, and ages up to a few
million years.  It is generally assumed that disks play a pivotal role
in the earliest evolution of very young stars, and indeed several
authors make models for Herbig Ae/Be stars that include disks (e.g.
Hillenbrand et al. 1992), but a few authors have recently shown that
dusty envelopes alone may suffice to explain their near-infrared
emission (e.g. Hartmann, Kenyon and Calvet 1993).

Our goal is to determine whether intermediate mass YSO's and Herbig
Ae/Be stars  have disks, and to study the geometry and physical
conditions of their extended atmospheres, winds and infalling material,
if any. The program stars are in different stages  of their evolution:
massive envelopes (and disks?) close to the star, less massive extended
envelopes, and stars that are still recognizably young by their extended
atmosphere.

All of ISO's instruments are used to study these objects. This proposal
emphasizes the SWS. Commonality between similar proposals of LWS, PHT
and CAM has been sought.  Apart from images with CAM, and full spectra
with PHT-S, SWS and LWS, important lines are studied with a higher  S/N
using SWS-AOT2, and occasionally SWS-AOT3.

We expect that these observations and the application of recently
published models will lead to a three-dimensional picture of the
complicated surroundings of young stars in the mass range 2 to 10 Msun.

The sources are well-spread in priority and location on the sky such
that even observing a small sample will  further the goals of the
program.

OBSERVATION SUMMARY

For some objects we perform complete scans of the SWS and/or LWS range
using SWS-AOT1 and LWS-AOT1. The length of the planned SWS-AOT1
observation gives implicitly the spectral resolution  (see SWS Observers
Manual).

The lines we wish to observe in the SWS and LWS range are listed
completely in the `scientific justification' section.

Very recently it has become apparent that both YSO's and Herbig Ae/Be
stars have often complicated surroundings with a few  sources in an area
of 10 by 10 arcsec. We perform therefore three CAM observations with the
highest spatial resolution (2 minutes per exposure) for each object
using the filters LW4, 8, 9 at about 6, 11.5 and 15 micrometer, unless
CAM plans to observe these objects already.

For efficiency reasons, the observations of other groups have been
merged with ours, for a few objects.  This concerns the SWS proposal of
van Dishoeck et al.  for T Tau and R CrA, that of Whittet et al. for
Elias 1 and IRAS 12496-7650 and the water lines for a few stars in
collaboration with Ceccarelli of LWS.

Research using ground-based facilities is vigorously being pursued by
many astronomers on these objects. The identification of IRAS sources
evolves with time for some sources.  It may be anticipated that the
coordinates selected for the objects of this proposal have to be adapted
just before the launch of ISO.



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