ZZ Ceti white dwarfs and candidates in Gaia survey
Short Name:
J/AJ/160/252
Date:
09 Mar 2022 22:00:00
Publisher:
CDS
Description:
The Gaia satellite recently released parallax measurements for ~260000 high-confidence white dwarf candidates, allowing for precise measurements of their physical parameters. By combining these parallaxes with Pan-STARRS and u-band photometry, we measured the effective temperature and stellar mass for all white dwarfs in the Northern Hemisphere within 100pc of the Sun, and identified a sample of ZZ-Ceti white dwarf candidates within the so-called instability strip. We acquired high-speed photometric observations for 90 candidates using the PESTO camera attached to the 1.6m telescope at the Mont-Megantic Observatory. We report the discovery of 38 new ZZ-Ceti stars, including two very rare ultramassive pulsators. We also identified five possibly variable stars within the strip, in addition to 47 objects that do not appear to show any photometric variability. However, several of those could be variable with an amplitude below our detection threshold, or could be located outside the instability strip due to errors in their photometric parameters. In the light of our results, we explore the trends of the dominant period and amplitude in the M--Teff plane, and briefly discuss the question of the purity of the ZZ-Ceti instability strip (i.e., a region devoid of non-variable stars).
We present new photometry of the eclipsing binary ZZ Cyg. From all accumulated eclipsing times, we constructed the (O-C) curve, which can be described by a downward parabola with a possible light-time orbit. The period decrease rate is source dP/dt=-5.73(+/-0.18)d/yr. The modulated period, semi-amplitude and eccentricity for the light-time orbit are Pmod=71.4(+/-1.1)yr, A=0.0071(+/-0.0005)day and e=0.420(+/-0.053), respectively. After removing effects of the magnetic activity, this kind of cyclic oscillation may be attributed to light-time effect via an additional companion. By using the W-D code, the photometric model was updated, which identified that ZZ Cyg is a near-contact binary. We find that a hot spot may occur on the primary that explains the asymmetric light curve. The secular period decrease may possibly cause the fill-out factor of the primary to increase. Finally it will finally fill its Roche lobe. This kind of binary, ZZ Cyg, may evolve into contact binary star.