Abstract

HD 188112, a He-core white dwarf in a binary system, pre-SN Ia candidate ?

Marilyn Latour (Dr. Karl Remeis-Sternwarte)

U. Heber, H. Edelmann, V. Schaffenroth (Dr. Karl Remeis-Sternwarte) & S. Geier (ESO Garching)

HD 188112 is a bright (V=10.2) and nearby star (~80 pc, Hipparcos parallax) that is found below the Extreme Horizontal Branch in the log g - Teff plane (21 500 K, log g = 5.6). The spectroscopic parameters, combined with the parallax distance allowed to determine a mass of 0.24 Msun for the star, thus making it an ELM WD. Indeed its rather plain optical spectra, showing only two weak lines of He and Mg (at high resolution) besides the strong Balmer lines, is somewhat similar to those of DA WD. HD 188112 is part of a binary system with an orbital period of ~ 14.5 hr and a semi-amplitude of 188 km/s, so the lower limit for the mass of the unseen companion is 0.73 Msun. If the total mass of the system is high enough, it would qualify as a pre-supernovae Ia candidate. I will present our updated radial velocity curve as well as preliminary results from the analysis of the STIS FUV and NUV spectra of HD 188112. The UV spectra should allow us to determine the abundances of the few metallic species seen and also the mass and nature of the invisible companion.

Mode of presentation: oral