Periods of magnetic field variations in the Ap star $\gamma$ Equulei (HD 201601)

Abstract

This paper presents a series of 95 new measurements of the longitudinal (effective) magnetic field $B_e$ of the Ap star $\gamma$ Equ (HD 201601). Observations were obtained at the coudé focus of the 1-m reflector at the Special Astrophysical Observatory (SAO RAS) in Russia over a time period of 4190 days (more than 11 years). We compiled a long record of $B_e$ points, adding our measurements to all published data. The time series of magnetic data consists of 395 $B_e$ points extending for 24488 days, or over 67 years. Various methods of period determination were examined for the case in which the length of the observed time series is rather short and amounts only to ~69 percent of the period. We argue that the fitting of a sine wave to the observed $B_e$ points by least squares yields the most reliable period in the case of $\gamma$ Equ. Therefore, the best period for long-term magnetic variations of $\gamma$ Equ, and hence the rotational period, is $P_{\mathrm{rot}}=35462.5\pm 1149$ days $=97.16\pm 3.15$ years.

7 pages, 6 figures, accepted for publication in MNRAS

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• An Inexpensive Liquid Crystal Spectropolarimeter for the Dominion Astrophysical Observatory Plaskett Telescope

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