New Light Curves and Spectra of the close PG1159 Binary System SDSSJ212531.92-010745.9

TL;DR

This study presents new light curves and spectra of the close PG1159 binary system SDSSJ212531.92-010745.9, aiming to enable the first dynamical mass measurement to test stellar evolution models.

Contribution

It provides extended photometric and spectroscopic observations of the binary system, improving orbital parameters and setting the stage for a direct mass determination.

Findings

Refined orbital period of 6.95573 hours.

New phase-resolved spectra obtained.

Preparation for radial velocity and spectral analysis.

Abstract

Methods to measure masses of PG1159 stars in order to test evolutionary scenarios are currently based on spectroscopic masses or asteroseismological mass determinations. SDSSJ212531.92-010745.9, a recently discovered PG1159 star in a close binary system, may finally allow the first dynamical mass determination, and has so far been analysed on the basis of one SDSS spectrum and photometric monitoring. In order to be able to phase radial velocity measurements of the system SDSSJ212531.92-010745.9, we have followed up the photometric monitoring of this system. New white light time series of the brightness variation of SDSSJ212531.92-010745.9 with the Tuebingen 80cm and Goettingen 50cm telescopes extend the monitoring into a second season (2006). We give the improved ephemeris for the orbital motion of the system, based on a sine fit which now results in a period of 6.95573(5)h. In 2007, we have obtained a series of phase-resolved medium-resolution spectra with the TWIN spectrograph at the 3.5m telescope at Calar Alto, which will allow us to derive the radial velocity curves for both components of the system, and to perform spectral analyses of the irradiating and irradiated components at different phases. We briefly describe the newly obtained spectra. The light curve and radial velocities combined will allow us to carry out a mass determination.