Radial Pulsation and the Rotation Period of the Rapidly Oscillating Ap-Star Alpha-Circini HR:5463 HD128898

Details Radial Pulsation and the Rotation Period of the Rapidly Oscillating Ap-Star Alpha-Circini HR:5463 HD128898 Radial Pulsation and the Rotation Period of the Rapidly Oscillating Ap-Star Alpha-Circini HR:5463 HD128898

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.264..529k&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 264, NO. 3/OCT1, P. 529, 1993

Astronomy and Astrophysics

Astronomy

4

Stars: Chemically Peculiar - Stars: Individual: Α Cir - Stars: Oscillations

Scientific paper

A frequency analysis of 211 h of high-speed photometric observations obtained in 1981, 1983 and 1992 shows that α Cir pulsates in two modes with frequencies ν1 =2442.023±0.016 μHz and ν2 =2439.427±0.016 μHz, separated by ν1-ν2 = 2.60±0.02 μHz. This separation suggests that ν1 is a mode of overtone n ≍ =35-40 and degree l=0, while ν2 has overtone and degree of n-1 and l=2. The principal frequency, ν1, however, is phase-modulated. The modulation period may be 524.2 d, in which case α Cir is a binary star with a reasonable probability that the secondary is of substellar mass. The modulation period may be 0.995 350 d, which is then the rotation period, in which case it can be shown that the principal frequency cannot be represented purely by a radial spherical harmonic pulsation mode. A decomposition of a derived frequency triplet indicates that, for most values of the rotational inclination i and the magnetic obliquity β, the mode is mostly a radial mode with a smaller dipole distortion. We suggest that the rotational inclination i ≤ 12° and the magnetic obliquity is large, which means that the magnetic field is seen always from an unfavourable aspect. The suggested rotation period, Prot=0.995350±0.000005 d, is so close to one sidereal day that it must be confirmed with multisite observations. If it is not confirmed, then the binary model becomes more attractive.

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