A&A 411, L477-L480 (2003)
Discovery of a
helium-core white dwarf progenitor
U. Heber, H. Edelmann, T. Lisker and R. Napiwotzki
Dr. Remeis-Sternwarte, Astronomisches Institut der Universität
Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
(Received 5 August 2003 / Accepted 5 October 2003 )
We discovered that HD 188112, a bright (
), 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
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
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
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
binaries: spectroscopic --
stars: early-type --
stars: fundamental parameters --
stars: individual: HD 188112
Offprint request: U. Heber, firstname.lastname@example.orgSIMBAD Objects
© ESO 2003