Variation of the Light and Period of the Magnetic Cataclysmic Variable Am Her

TL;DR

This study analyzes long-term optical variability of the magnetic cataclysmic variable AM Her, revealing short-term brightness fluctuations, long-term period changes, and estimating mass transfer rates over a 30-year span.

Contribution

It provides new long-term observational data and period variation analysis of AM Her, including estimates of period increase and mass transfer rate, using combined historical and recent minima timings.

Findings

Detected short-term low-amplitude brightness variations of 0.02-0.03 mag.

Observed brightness variations of 0.7-2 mag likely due to stellar activity.

Estimated period increase rate of 7.5(1.2)×10^{-9} days/year.

Abstract

Ground-based long-term optic variability of AM Her, covering the period between 2003-2008, has been conducted to study the features seen in both low and high states of the system. Low-state analysis shows the presence of short-term, low-amplitude light variations of about 0.02-0.03 mag with a mean power time between 16 s and 226 s. Brightness variations on the order of 0.7--2 mag, which could be due to the stellar activity of the component in the system, are also detected. A total of 30 years times of minimum light given in the literature are combined with nine times of minima obtained in this study. We represented the (observed--calculated) diagram by a parabolic curve and also by two broken lines. Under the assumption of a parabolic variation, we estimate an increase in period, dP/dt=7.5(1.2)x10^{-9} days yr^{-1}, with a mass transfer rate of dM/dt = 8(2)x10^{-9} M_{\odot} yr^{-1}, in agreement with the previous findings by a different method.