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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Preprint E/03

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

Green E.M. (1), Fontaine G. (2), Reed M.D. (3), Callerame K. (1), Seitenzahl R. (1),White B.A. (1), Hyde E.A. (1), Oestensen R. (4), Cordes O. (5), Brassard P. (2), Falter S. (6), Jeffery E.J. (7), Dreizler S. (8), Schuh S.L. (8), Giovanni M. (1), Edelmann H. (6), Rigby J. (1), Bronowska A. (4)

(1)Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721
(2)Departement de Physique, Universite de Montreal, CP6128, Station Centreville, Montreal, QC H3C 3J7, Canada
(3)Department of Physics, Astronomy, and Materials Science, Southwest Missouri State University, 901 South National Avenue, Springfield, MO 65804
(4)Isaac Newton Gruop of telescopes, Apartado de Correos 321, 37800 Santa Cruz de La Palma, Canary Islands, Spain
(5)Sternwarte der Universitaet Bonn, Auf dem Huegel 71, D-53123 Bonn, Germany
(6)Dr. Karl-Remeis Sternwarte University Erlangen-Nuernberg, Sternwartstrasse 7, D-96049 Bamberg, Germany
(7)Brigham Young University, Provo, UT 84602
(8)Institut fuer Astronomie und Astrophysik, Universitaet Tuebingen, Sand 1, D-72076 Tuebingen, germany

ApJL 583, 31 (2003)

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 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 periods 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 effctive 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.

Key words: stars: horizontal-branch - stras: individual (PG 1716+426) - stars: oszillations


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