Appearance of Special UGSU-type Phenomenon in the Light Curve of UGZ White Dwarf Nova RX Andromedae

Volume 44 number 1 (2016)

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András Timár

1173 Budapest, Parlagfu u. 10., Hungary; andras.timar@t-online.hu

Abstract

The dwarf nova RX Andromedae was examined using data from the AAVSO International Database. It is classified as a Z Cam (UGZ)-type dwarf nova. The cycle of outbursts is short due to the high accretion rate, approximately 13 days. The object has been in standstill several times over the last two decades, as well observed by the AAVSO. According to previous studies, RX And exhibited VY Scl-type light changes. During the analysis of the AAVSO light curve I established that specific UGSU-type characteristics have also developed in RX And since 5 August 2014. Every fourth outburst is a superoutburst, the period of the supercycle being about 55.5 days. The superoutbursts are brighter and longer than other normal outbursts. The superoutburst itself (~10.7 magnitude) is superpositioned on the precursor normal outburst (~11.0 magnitude). It can be established that the precursor triggers the superoutburst. However, we can find uncertainties in the recently-appearing UGSU-type feature of RX And; the star differs from the behavior of a typical UGSU dwarf nova in a number of aspects. Unlike UGSU stars the orbital period of RX And is above the period gap, and in the light curve of RX And there is not any indication of the presence of superhumps. The amplitude of the superoutburst exceeds that of a normal outburst by about 0.4 to 0.5 magnitude. This value is less than the 2 to 4 magnitudes characteristic of UGSU stars. Also, one should be careful in making conclusions, because the investigated period (from 5 August 2014 to 1 February 2015) is not long enough to judge whether the phenomena appearing in the light curve are really supermaxima. The long orbital period and the lack of superhumps in any case need further explanation. As for whether the supercycle remains stabilized in the star, and whether the UGSU characteristics are a normal stage of development for all UGZ dwarf novae or only typical of RX And, remain to be established by further investigations.