A new period determination for the close PG1159 binary SDSSJ212531.92-010745.9

TL;DR

This paper refines the orbital period of the close PG1159 binary SDSSJ212531.92-010745.9 through extended photometric monitoring, enabling future dynamical mass measurements to test stellar evolution models.

Contribution

It provides an improved orbital ephemeris for the binary system based on new, longer-term photometric data, facilitating dynamical mass determination of the PG1159 star.

Findings

Orbital period determined as 6.95573 hours.

Enhanced accuracy of the ephemeris by over an order of magnitude.

Extended observational data set covering two seasons.

Abstract

Methods to measure masses of PG1159 stars in order to test evolutionary scenarios are currently based on spectroscopic masses or asteroseismological mass determinations. One recently discovered PG1159 star in a close binary system may finally allow the first dynamical mass determination, which has so far been analysed on the basis of one SDSS spectrum and photometric monitoring. In order to be able to phase future radial velocity measurements of the system SDSSJ212531.92-010745.9, we follow up on the photometric monitoring of this system to provide a solid observational basis for an improved orbital ephemeris determination. 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), tripling the length of overall observational data available, and significantly increasing the time base covered. We give the ephemeris for the orbital motion of the system, based on a sine fit which now results in a period of 6.95573(5)h, and discuss the associated new amplitude determination in the context of the phased light curve variation profile. The accuracy of the ephemeris has been improved by more than one order of magnitude compared to that previously published for 2005 alone.