Cyclic Frequency Variability in the Rapidly Oscillating Ap-Star HD3831

Details Cyclic Frequency Variability in the Rapidly Oscillating Ap-Star HD3831 Cyclic Frequency Variability in the Rapidly Oscillating Ap-Star HD3831

Jun 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994mnras.268..641k&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 268, NO. 3/JUN1, P. 641, 1994

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24

Binaries: Visual - Stars: Chemically Peculiar - Stars: Individual: Hr 3831 - Stars: Magnetic Fields - Stars: Oscillations - Stars: Variables: Other

Scientific paper

HR 3831 is an A7p SrCrEu magnetic star with an effective temperature of Teff = 8000±200 K a radius of R=1.9±0.1 Rsun and an absolute magnitude of Mbol = 2.0±0.3. It has a polarity-reversing magnetic field which ranges from about +780 to -740 G with the rotation period of Prot = 2.851 982±0.000005 d. It is a visual binary with a separation of 3.29 arcsec; the secondary is a G2V star. The distance is about 66 pc. HR 3831 is a singly periodic rapidly oscillating Ap(roAp) star which pulsates with a frequency of ν ≍ 1428 μHz (P = 700 s = 11.67 min). We have 666 h of photometric observations of HR 3831 obtained in 1981, 1985, 1986, 1990, 1991, 1992 and 1993, which show that the frequency of the pulsation mode varies cyclically with a peak-to-peak amplitude of 0.12 μHz on a time-scale of 1.6 yr. A Doppler shift of the pulsation frequency caused by binary motion is ruled out by a lack of radial velocity variation. Variations over the solar magnetic cycle have recently been detected in the frequencies of global solar oscillations, with a peak-to-peak amplitude of about 4 times that seen in HR 3831. This suggests that the cyclic frequency variability in HR 3831 may be caused by a cyclic modulation of the magnetic field. If so, this is the first evidence of magnetic variations on a time-scale other than the rotation period in the magnetic stars of the upper main sequence. Other roAp stars also show cyclic frequency variations, as does one ZZ Ceti star.

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