| Issue |
A&A
Volume 411, Number 3, December I 2003
|
|
|---|---|---|
| Page(s) | L477 - L480 | |
| Section | Letters | |
| DOI | https://doi.org/10.1051/0004-6361:20031553 | |
| Published online | 17 November 2003 | |
Letter to the Editor
Discovery of a helium-core white dwarf progenitor *,**
Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
Corresponding author: U. Heber, This email address is being protected from spambots. You need JavaScript enabled to view it.
Received:
5
August
2003
Accepted:
5
October
2003
Abstract
We discovered that HD 188112, a bright (V = 
), nearby (80 pc)
B-type star, is a unique subluminous B (sdB) star.
SdB stars are usually identified with models of
core helium burning Extreme Horizontal-Branch (EHB) stars
of half a solar mass.
A spectral analysis of the hydrogen and helium lines resulted in
K, 
placing the
star below the EHB.
HD 188112 was found to be radial velocity (RV) variable and the RV curve
has been measured to be perfectly
sinusoidal with a period of 0.606585 days and a semi-amplitude
of 188.3 km s-1 indicating that it is a close binary system.
From the atmospheric parameters and the Hipparcos parallax we
conclude that the sdB star is of low mass (0.24 
).
The mass of the sdB is too low to sustain core helium burning
and it is now evolving into a
helium core white dwarf.
A lower limit to the mass of its unseen companion of 0.73
is derived from the mass function.
Because the companion does not contribute to the spectral energy
distribution from the UV to the infrared
it
cannot be a main sequence star but
must be a white dwarf (WD), a
neutron star (NS) or a black hole.
The system would
qualify as pre-supernova Ia candidate (sdB+WD) if its total mass is above
the Chandrasekhar limit (1.4 ), or as post-supernova (sdB+NS)
if the companion mass is above that limit, requiring the inclination angle
to be lower than 51° or 48°, respectively.
Key words: binaries: spectroscopic / stars: early-type / stars: fundamental parameters / stars: individual: HD 188112
Based on observations collected at the German-Spanish Astronomical Center (DSAZ), Calar Alto, operated by the Max-Planck-Institut für Astronomie, Heidelberg jointly with the Spanish National Commission for Astronomy.
Based on observations collected at the European Southern Observatory (ESO proposal No. 65.H-0341(A) and 69.D-0016(A)).
© ESO, 2003
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