Issue |
A&A
Volume 366, Number 1, January IV 2001
|
|
---|---|---|
Page(s) | 241 - 253 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20000212 | |
Published online | 15 January 2001 |
Infrared spectral classification of OB stars with ISO-SWS
1
Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2
Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, 3001 Heverlee, Belgium
Corresponding author: A. de Koter, dekoter@astro.uva.nl
Received:
4
November
1999
Accepted:
6
November
2000
We present observations of the Brα, Brβand Pfαlines of 16 dwarf
and (sub)giant stars in the spectral range O9-B3. The observations were
done using the Short Wavelength Spectrometer on board the Infrared Space
Observatory, and have a signal-to-noise of ∼20 to > 150 and a
resolving power varying from ∼1400 to 2100. We compare the equivalent
widths of these lines with predictions using non-LTE model atmospheres
to investigate to what extent these infrared lines can be used to derive
effective temperatures. We find that Pfαis a sensitive Teff
diagnostic for the range of spectral types investigated, and Brαfor
types O9-B2, yielding agreement with optical results to within 1-4
kK or one-three spectral sub-types.
We find evidence for a gradient in the turbulent velocity, increasing
from 5 km s-1for the atmospheric region in which Brαis formed
to ∼15 km s-1for the regime where Pfαoriginates. When this
gradient in turbulent velocity is taken into account, the accuracy of the
spectral type calibration is improved to ∼1 kK or one spectral
sub-type.
The gravity dependence of the strengths of the
investigated infrared lines is relatively weak, and could not be used
to constrain luminosity class. This failure is in part a result of the
modest
and resolution and in part a result of a cancelation of
gravity effects in the line core and line wing. Our line predictions
show that Hei
λ 2.058is relatively unsuited for spectral classification
of O9-B3 stars. Huα, however, is expected to be an even better
diagnostic as are Pfαand Brα. This line may be observed with the VLT
Imager and Spectrometer for mid InfraRed when it is installed on the
Very Large Telescope.
Key words: line: formation / radiative transfer / stars: atmospheres / stars: early-type / stars: fundamental parameters / infrared: stars
© ESO, 2001
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