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The long secondary periods in semi-regular variables

Published online by Cambridge University Press:  12 April 2016

P.R. Wood ,
A.E. Olivier  and
S.D. Kawaler
P.R. Wood
Affiliation:
Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston Creek ACT 2611, Australia
A.E. Olivier
Affiliation:
Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston Creek ACT 2611, Australia
S.D. Kawaler
Affiliation:
Department of Physics and Astronomy, Iowa State University, Ames IA 50011, USA

Abstract

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About 25% of variable asymptotic giant branch stars in the LMC have light curves that are modulated by a long secondary period of length ~ 1–4 yr. Solar-vicinity analogs of these stars show radial velocity curves that are asymmetric and of small amplitude (~3–5km s−1). Possible explanations for the photometric and radial velocity variations include: eccentric motion of an orbiting companion of mass ~0.1 M⊙; radial and nonradial pulsation; rotation of an ellipsoidal-shaped red giant; episodic dust ejection; and star spot cycles. We find that there are severe difficulties with each of these models. Thus, the long secondary periods are the only unexplained type of large-amplitude stellar variability known at this time.

Type
Part 5. Red Giants, Miras, post-AGB stars and proto-planetary nebulae
Information
International Astronomical Union Colloquium , Volume 193: Variable Stars in the Local Group , 2004 , pp. 322 - 326
Copyright
Copyright © Astronomical Society of the Pacific 2004

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