Discovery of A New Class of Pulsating Stars: Gravity-mode Pulsators among Subdwarf B Stars

TL;DR

This paper reports the discovery of a new class of low-amplitude, gravity-mode pulsating subdwarf B stars with longer periods, mainly found among cooler sdB stars, revealing a different pulsation mechanism.

Contribution

It introduces a new class of sdB pulsators with longer periods driven by gravity modes, expanding understanding of stellar pulsation phenomena.

Findings

Discovered a new class of sdB pulsators with ~hour-long periods

Longer periods are associated with cooler sdB stars

The driving mechanism for these gravity modes is currently unknown

Abstract

During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, we have serendipitously discovered a new class of low amplitude, multimode sdB pulsators with periods of the order of an hour. These periods are more than a factor of ten longer than those of previously known multimode sdB pulsators (EC 14026 stars), implying that they are due to gravity modes rather than pressure modes. The longer period pulsators are found only among cooler sdB stars, where they are surprisingly common. The iron opacity instability that drives the short period EC 14026 stars is effective only in hot sdB's, leaving the driving mechanism for the deeper gravity modes in cool sdB's currently unknown. We present the first observational results for our newly identified sdB variables, and discuss possible implications.