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Are the stars of a new class of variability detected in NGC 3766 fast rotating SPB stars?

Published online by Cambridge University Press:  23 January 2015

S. J. A. J. Salmon ,
J. Montalbán ,
D. R. Reese ,
M.-A. Dupret  and
P. Eggenberger
S. J. A. J. Salmon
Affiliation:
Département d'Astrophysique, Géophysique et Océanographie, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium email: salmon@astro.ulg.ac.be
J. Montalbán
Affiliation:
Département d'Astrophysique, Géophysique et Océanographie, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium email: salmon@astro.ulg.ac.be
D. R. Reese
Affiliation:
School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
M.-A. Dupret
Affiliation:
Département d'Astrophysique, Géophysique et Océanographie, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium email: salmon@astro.ulg.ac.be
P. Eggenberger
Affiliation:
Observatoire de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
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Abstract

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A recent photometric survey in the NGC 3766 cluster led to the detection of stars presenting an unexpected variability. They lie in a region of the Hertzsprung-Russell (HR) diagram where no pulsation are theoretically expected, in between the δ Scuti and slowly pulsating B (SPB) star instability domains. Their variability periods, between ~0.1–0.7 d, are outside the expected domains of these well-known pulsators. The NCG 3766 cluster is known to host fast rotating stars. Rotation can significantly affect the pulsation properties of stars and alter their apparent luminosity through gravity darkening. Therefore we inspect if the new variable stars could correspond to fast rotating SPB stars. We carry out instability and visibility analysis of SPB pulsation modes within the frame of the traditional approximation. The effects of gravity darkening on typical SPB models are next studied. We find that at the red border of the SPB instability strip, prograde sectoral (PS) modes are preferentially excited, with periods shifted in the 0.2–0.5 d range due to the Coriolis effect. These modes are best seen when the star is seen equator-on. For such inclinations, low-mass SPB models can appear fainter due to gravity darkening and as if they were located between the δ Scuti and SPB instability strips.

Keywords

stars: rotationstars: variables: otherstars: early-type
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 9 , Issue S307: New windows on massive stars: asteroseismology, interferometry, and spectropolarimetry , June 2014 , pp. 188 - 193
Copyright
Copyright © International Astronomical Union 2015 

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