Discovery of a new class of pulsating stars: gravity-mode pulsators among subdwarf B stars

Green, EM; Fontaine, G; Reed, MD; Callerame, K; Seitenzahl, IR; White, BA; Hyde, EA; Ostensen, Roy; Cordes, O; Brassard, P; Falter, S; Jeffery, EJ; Dreizler, S; Schuh, SL; Giovanni, M; Edelmann, H; Rigby, J; Bronowska, A

doi:10.1086/367929

Discovery of a new class of pulsating stars: gravity-mode pulsators among subdwarf B stars

Author:

Green, EM

Fontaine, G ; Reed, MD ; Callerame, K ; Seitenzahl, IR ; White, BA ; Hyde, EA ; Ostensen, Roy ; Cordes, O ; Brassard, P ; Falter, S ; Jeffery, EJ ; Dreizler, S ; Schuh, SL ; Giovanni, M ; Edelmann, H ; Rigby, J ; Bronowska, A

Keywords:

stars : horizontal, branch, stars : individual (pg 1716+426), stars : oscillations, subdwarfs, ec-14026 stars, palomar-green, white-dwarf, mechanism, hot, Science & Technology, Physical Sciences, Astronomy & Astrophysics, stars : individual (PG 1716+426), EC-14026 STARS, PALOMAR-GREEN, WHITE-DWARF, MECHANISM, HOT, 0201 Astronomical and Space Sciences, 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics, 0306 Physical Chemistry (incl. Structural), 5101 Astronomical sciences, 5107 Particle and high energy physics, 5109 Space sciences

Abstract:

During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf (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 10 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 stars, leaving the driving mechanism for the deeper gravity modes in cool sdB stars currently unknown. We present the first observational results for our newly identified sdB variables and discuss possible implications.