K2 observations of the pulsating subdwarf B star EQ Piscium: an sdB+dM binary

TL;DR

This paper reports K2 space telescope observations of the pulsating subdwarf B star EQ Psc, revealing pulsation frequencies and a 19.2-hour light variation likely caused by a cool companion, contributing to understanding binary evolution.

Contribution

First detection of pulsations and a long-period reflection effect in EQ Psc, establishing it as a key sdB+dM binary for studying common-envelope ejection.

Findings

Detected rich g-mode pulsations.

Identified 19.2-hour light variation likely due to a cool companion.

Established EQ Psc as the longest-period sdB+dM binary.

Abstract

K2, the two-wheel mission of the Kepler space telescope, observed the pulsating subdwarf B star EQ Psc during engineering tests in 2014 February. In addition to a rich spectrum of g-mode pulsation frequencies, the observations demonstrate a light variation with a period of 19.2 h and a full amplitude of 2%. We suggest that this is due to reflection from a cool companion, making EQ\,Psc the longest-period member of some 30 binaries comprising a hot subdwarf and a cool dwarf companion (sdB+dM), and hence useful for exploring the common-envelope ejection mechanism in low-mass binaries.