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| Paper: |
The Long Secondary Periods in Semi-regular Variables |
| Volume: |
310, Variable Stars in the Local Group (IAU Colloquium 193) |
| Page: |
322 |
| Authors: |
Wood, P.R.; Olivier, A.E.; Kawaler, S.D. |
| Abstract: |
About 25% of variable asymptotic giant branch stars in th 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 asymmetricand of small amplitude (~3−5 kms−1). Possible explanations for the photometric and radial velocity variations include: eccentric motion of an orbiting companion of mass ~0.1 MSolar; radial and nonradial pulsation; roration 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. |
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