VARIATION OF THE LIGHT AND PERIOD OF THE MAGNETIC CATACLYSMIC VARIABLE AM Her

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) × 10 −9 days yr −1 , with a mass transfer rate ofṀ = 8(2) × 10 −9 M yr −1 , in agreement with the previous findings by a different method.

Angular Momentum Loss in Polars

“…The effect of angular momentum loss (AML) in a short period binary star evolution was discussed in details in many papers (e.g., Paczyński 1967, Chau 1978, Verbunt & Zwaan 1981, Patterson 1984, Yakut et al 2008. We assumed that the AML driven by magnetic braking (MB) and gravitational radiation (GR) will result in AML from the binary (see Verbunt & Zwaan 1981).…”

“…Cyclotron spectra of polars have been the subject of many studies (Campbell et al 2008, Kalomeni et al 2005a and references therein). Polars show short term and long term light variations (Kalomeni et al 2005b, Kalomeni & Yakut 2008 and references therein). The knowledge of fundamental parameters of binary stars is of importance for formation and evolution studies of them to determine their possible evolutionary tracks (see King et al 1994, Baraffe & Kolb 2000.…”

Magnetic Cataclysmic Variables

“…In polars mass transfer between the components occurs by removing angular momentum, mainly driven by magnetic braking and by gravitational radiation. Observed mass accretion rates in polars are relatively low in comparison with the binaries consisting of non-degenerate components (see [1]). Occasionally, mass transfer between the components either reduces or ceases.…”

“…Occasionally, mass transfer between the components either reduces or ceases. This state of polars can last from days to years (see [2], [1]). …”

Long-Term Monitoring of Polars

“…AM Her 4.2-4.7 minutes (Bonnet-Bidaud et al 1991, Kalomeni et al 2005) and V1309 Ori 10 minutes (Katajainen et al 2003)). In the literature especially during the last decade long period observations of polars have been intensively studied (Hessman et al 2000, Wu & Kiss 2008, Kalomeni & Yakut 2008, Kafka & Hoard 2009, Sanad 2010. Studies of the long term variations are especially important to reveal any characteristics based on stellar activity and/or mass transfer.…”