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A Spectroscopic Search for Non-Radial Pulsations in Early B-Type Stars

Published online by Cambridge University Press:  12 April 2016

C. Schrijvers
Affiliation:
Astronomical Institute Anton Pannekoek, University of Amsterdam, and Center for High Energy Astrophysics, Amsterdam, Netherlands
J.H. Telting
Affiliation:
Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma, Spain; jht@not.iac.es
J. De Ridder
Affiliation:
Instituut voor Sterrenkunde, Katholieke Univ. Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium; joris@ster.kuleuven.ac.be

Extract

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It is known that early-B type main-sequence stars can be unstable against pulsations induced by the κ mechanism. Traditionally, radial and low-degree non-radial β Cephei-like pulsations have been detected photometrically; nowadays radial, low-degree and intermediate-degree pulsations can be detected spectroscopically through line-profile variations (LPVs). Whereas most of the brightest early-B type stars have been photometrically monitored for variability (72 of the 541 O9.5-B3 III-V stars in the BSC are classified as β Cephei stars), a systematic LPV survey to look for pulsational behaviour was lacking. Here we present some preliminary results of the southern part of our Spectroscopic survey of early-B type stars. We have made a high spectral resolution survey of the Si III λ 4552, 4567, 4574 Å triplet in early-B type stars in order to look for LPVs due to non-radial pulsation (NRP). Our sample consists of 82 southern O9.5-B3 stars with spectral classes III-V, taken from the BSC; 27% of all O9.5-B2.5 III-V stars in the BSC were sampled. This sample is not fully representative for all nearby early-B stars, because we concentrated on stars with high rotational velocities, because many of the stars are members of the Sco-Cen associations, and because we focused on the β Cephei stars in the BSC. As much as 40% of the β Cephei stars in the BSC with v sin г ≥ 25 km s-1 were sampled. The observations were carried out with the ESO CAT telescope at resolution R∼65000. Our targets were observed during 6 runs in September 1995 – June 1998. Some stars were observed many times, but most targets were observed only once or twice.

Type
Part 2.2. B-Type Stars
Copyright
Copyright © Astronomical Society of the Pacific 2002