Astronomy and Astrophysics, volume 448, L25-28 (2006/3-3)
SDSS J212531.92-010745.9 - the first definite PG 1159 close binary system.
NAGEL T., SCHUH S., KUSTERER D.-J., STAHN T., HUEGELMEYER S.D., DREIZLER S., GAENSICKE B.T. and SCHREIBER M.R.
Abstract (from CDS):
The archival spectrum of SDSSJ212531.92-010745.9 shows not only the typical signature of a PG1159 star, but also indicates the presence of a companion. Our aim was the proof of the binary nature of this object and the determination of its orbital period.We performed time-series photometry of SDSSJ212531.92-010745.9. We observed the object during 10 nights, spread over one month, with the Tuebingen 80cm and the Goettingen 50cm telescopes. We fitted the observed light curve with a sine and simulated the light curve of this system with the nightfall program. Furthermore, we compared the spectrum of SDSSJ212531.92-010745.9 with NLTE models, the results of which also constrain the light curve solution. An orbital period of 6.95616(33)h with an amplitude of 0.354(3)mag is derived from our observations. A pulsation period could not be detected. For the PG1159 star we found, as preliminary results from comparison with our NLTE models, Teff∼90000K, logg∼7.60, and the abundance ratio C/He∼0.05 by number fraction. For the companion we obtained with a mean radius of 0.4±0.1R☉, a mass of 0.4±0.1M☉, and a temperature of 8200K on the irradiated side, good agreement between the observed light curve and the nightfall simulation, but we do not regard those values as final.
stars: AGB and post-AGB - white dwarfs - binaries: close
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