A pulsation analysis of K2 observations of the subdwarf B star PG1142-037 during Campaign 1: A subsynchronously rotating ellipsoidal variable

TL;DR

This study reports the discovery and analysis of a new subdwarf B star, PG1142-037, observed by K2, revealing its pulsation modes, binary nature, and a surprising slow rotation period despite a close binary orbit.

Contribution

It presents the first detailed pulsation and binary analysis of PG1142-037, highlighting its subsynchronous rotation and tidal distortion features.

Findings

14 pulsation periods detected between 0.9 and 2.5 hours

Binary period of 0.54 days with ellipsoidal variations

Rotation period longer than 45 days despite close binary orbit

Abstract

We report a new subdwarf B (sdB) pulsator, PG1142-037, discovered during the first full-length campaign of K2, the two-gyro mission of the Kepler space telescope. Fourteen periodicities have been detected between 0.9 and 2.5 hours with amplitudes below 0.35 ppt. We have been able to associate all of the pulsations with low-degree, ell<=2 modes. Follow-up spectroscopy of PG1142 has revealed it to be in a binary with a period of 0.54 days. Phase-folding the K2 photometry reveals a two-component variation including both Doppler boosting and ellipsoidal deformation. Perhaps the most surprising and interesting result is the detection of an ellipsoidal, tidally distorted variable with no indication of rotationally-induced pulsation multiplets. This indicates that the rotation period is longer than 45 days, even though the binary period is near 13 hours.