The pure dipole pulsation mode of the rapidly oscillating Ap star α Cir: determination of the rotation period, and evidence for frequency variability
Open Access
- 1 October 1994
- journal article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 270 (3) , 674-686
- https://doi.org/10.1093/mnras/270.3.674
Abstract
New, multisite observations of the rapidly oscillating Ap star α Cir (HR 5463, HD 128898) show that its principal pulsation mode is a pure oblique dipole mode with a frequency of 2442 μHz. A rotationally split triplet shows the rotation period to be Prot = 4.463 ± 0.010 d. Reanalysis of Johnson B data spanning the years 1981 to 1993 refines the rotation period to Prot = 4.4790 ± 0.0001 d. Four low-amplitude secondary frequencies are present, with separations that are multiples of 25 μHz. From this we suggest that ∆v0 = 50 μHz. The asteroseismological luminosity inferred from this agrees with the luminosity determined independently from the parallax. The principal frequency in α Cir is variable. The available data suggest that this variability is cyclic on a time-scale of hundreds of days. Cyclic frequency variability appears to be the norm in rapidly oscillating Ap stars; since binary motion can be ruled out in some cases, and shown to be extremely unlikely in other cases, this frequency variability is intrinsic to these stars.Keywords
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