Fu-Yuan Xiang

Orbital period changes of the W UMa binary YY Eri

The orbital period changes of the W UMa-type binary, YY Eri, are analyzed by using all pe and ccd times of light minimum. The results show that its orbital period is undergoing a secular increase superposed on two cyclic oscillations. The continuous increase at the rate of dP/dt = 6.3806 × 10 d yr may be accounted for the mass transfer from the less massive companion to the more massive one. Two periodic variations with the periods of 38.6192 and 22.3573 yr may be attributed to the light-time effect of a faint third star and the cyclic magnetic activity of the system, respectively.

Reanalysis of the orbital period variations of two DLMR overcontact binaries: FG Hya and GR Vir

We investigate orbital period changes of two deep, low mass ratio (DLMR) overcontact W UMa-type binaries, FG Hya and GR Vir. It is found that the orbital period of FG Hya shows a cyclic change with a period of P mod = 54.44 yr. The cyclic oscillation may be due to a third body in an eccentric orbit, while the orbital period of GR Vir shows a periodic variation with a period of P mod = 28.56 yr and an amplitude of A = 0.0352 d. The periodic variation of GR Vir can be interpreted as a result of either the light-time effect of an unseen third body or the magnetic activity cycle.

Orbital Period Investigations of Two W UMa-type Binaries: AH Aur and V728 Her

The orbital period changes of two W UMa-type binaries, AH Aur and V728 Her, are investigated based on all available times of the light minimum taken from the databases and literature. It is revealed that the orbital period of AH Aur shows a long-term decrease at a rate of days yr−1. For V728 Her, we find that the orbital period exhibits a secular increase at a rate of days yr−1. The secular period changes suggest that AH Aur and V728 Her are undergoing rapid mass transfer between the primary star and the secondary companion.

Vector Magnetic Field Measurement of NOAA AR 10197

A set of two-dimensional Stokes spectral data of NOAA AR 10197 obtained by the Solar Stokes Spectral Telescope ((ST)-T-3) at the Yunnan Observatory are qualitatively analyzed. The three components of the vector magnetic field, the strength H, inclination gamma and azimuth chi, are derived. Based on the three components, we contour the distributions of the longitudinal magnetic field and transverse magnetic field. The active region (AR) has two different magnetic polarities apparent in the longitudinal magnetic map due to projection effect. There is a basic agreement on the longitudinal magnetic fields between the (ST)-T-3 and SOHO/MDI magnetograms, with a correlation coefficient rho(Bl) = 0.911. The transverse magnetic field of the AR has a radial distribution from a center located in the southwest of the AR. It is also found that the transverse magnetic fields obtained by Huairou Solar Observing Station (HRSOS) have a similar radial distribution. The distributions of transverse magnetic field obtained by (ST)-T-3 and HRSOS have correlation coefficients, rho(Azimu) = 0.86 and rho(Bt) = 0.883, in regard to the azimuthal angle and intensity.