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

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The winds and mass-ejections from luminous stars strongly
influence the evolution of massive stars and their
surrounding circumstellar and interstellar matter. We propose to
study the stellar winds and their circumstellar envelopes
in a few stars of different sequential evolutionary stages by
means of ISO spectroscopic, photometric and imaging observations.
The stages are: O-supergiants,   B-supergiants, Luminous Blue
Variables and rapidly rotating B[e]-supergiants.

The stellar winds of hot stars are characterized by high terminal
velocities (10^3 to 3.5 10^3 km/s) and a rapid acceleration. The
SWS grating will resolve the line profiles in hot supergiants and so the
velocity field can be studied. The
infrared Hydrogen and Helium recombination lines are formed in
layers of the wind where the acceleration takes place and therefore
offer an opportunity to study the radiation driven wind mechanism in
detail. This information cannot be obtained from UV
observations because the UV resonance lines are often saturated near
line centre. Also the IR recombination lines are much easier to model
than the Balmer emission lines in the optical.

The IR emission lines also provide a measurement of the mass loss rate
of the star which does not depend strongly on the details of the
ionisation structure of the wind. Therefore these data will give more
accurate determinations of the mass loss rate than the UV resonance lines of
ions of trace elements as C IV and Si IV. Furthermore it is expected
that forbidden lines are present in the IR spectra which will allow an
abundance study of the ejecta. Evolutionary calculations predict that
the surface abundance of He and N increase as the star strips more and
more of its envelope by means of mass loss. Therefore abundance
determinations provide a critical test of these evolutionary calculations and
of the mass loss history of the star.
These measurements are especially meaningful for the ejecta around
Luminous Blue Variables (LBV's) since these objects are thought to be
the immediate progenitors of Wolf-Rayet stars.


We plan to observe HI and HeI recombination lines and forbidden line
transitions in our targets using SWS grating AOT06 and in four objects
AOT01 for full grating scans at reduced resolution. In addition we request
PHT-S spectra for all targets. We also request PHT-C measurements at
selected wavelengths (60, 90, 160 and 200 microns) of several stars. Finally
we request a CAM  AOT01 observation of P Cygni using the CVF at the [Ne II]
12.8 mu line with a 6" p.f.o.v..

Linelist for the AOT06 observations:

4.0512	HI  5-4  Br alfa
4.652   HI  7-5  Pf beta
7.4579	HI  6-5  Pf alfa
7.5005	HI  8-6  Hu beta
8.7577	HI 10-7
11.3056	HI  9-7
12.3685 HI  7-6  Hu alfa
12.3838 HI 11-8
16.2047 HI 10-8
16.8760 HI 12-9
19.0569 HI  8-7
22.3344 HI 11-9
27.7958 HI  9-8
38.8593 HI 10-9
4.243	HeI 5-4
4.2947  HeI 5-3
4.6053	HeI 5-4
4.6936	HeI 5-4
7.4351	HeI 3-3
10.88	HeI 4-4
12.37	HeI 7-6
18.095	HeI 4-4
43.944	HeI 4-4
4.652	HeII 14-10
7.205	HeII 14-11
9.114	HeII 15-12
12.367	HeII 14-12
13.128	HeII 11-10
17.261	HeII 12-11
22.180	HeII 13-12
34.649	HeII 15-14

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