New Pulse Timing Measurements of the sdBV Star CS 1246

TL;DR

This study presents eight years of pulse timing data for the sdBV star CS 1246, revealing nonlinear amplitude decay and potential evidence for a circumbinary planet, while highlighting the challenges of distinguishing intrinsic variability from orbital effects.

Contribution

It provides updated pulse timing measurements and analysis of amplitude decay, and suggests possible detection of a circumbinary planet through O-C diagram analysis.

Findings

Pulsation amplitude of CS 1246 is decaying nonlinearly.

Updated O-C diagram indicates a potential 2.09-year orbital oscillation.

Possible evidence for a circumbinary planet with minimum mass ~3.3 Jupiter masses.

Abstract

CS 1246 is a hot subdwarf B star discovered in 2009 to exhibit a single, large-amplitude radial pulsation. An O-C diagram constructed from this mode revealed reflex motion due to the presence of a low-mass M dwarf, as well as a long-term trend consistent with a decrease in the pulsational period. The orbital reflex motion was later confirmed with radial velocity measurements. Using eight years of data collected with the Skynet Robotic Telescope Network, we show that the pulsation amplitude of CS 1246 is decaying nonlinearly. We also present an updated O-C diagram, which might now indicate a positive $\dot P$ and a new $2.09 \pm 0.05$ yr oscillation consistent with orbital reflex motion of the entire inner sdB+dM binary, possibly due to the gravitational influence of a circumbinary planet with minimum mass $m\sin i = 3.3 \, \pm \, ^{2.1}_{1.2}$ $M_{\rm Jup}$. However, unlike the presence of the M dwarf, we hesitate to claim this object as a definitive detection since intrinsic variability of the pulsation phase could theoretically produce a similar effect.