Nova-like cataclysmic variable TT Arietis

Abstract

Aims. We study the variability of the nova-like cataclysmic variable TT Ari, on time-scales of between minutes and months. Methods. The observations in the filter R were obtained at the 40-cm telescope of the Chungbuk National University (Korea), 51 observational runs cover 226 h. The table of individual observations is available electronically. In our analysis, we applied several methods: periodogram, wavelet, and scalegram analysis. Results. TT Ari remained in a "negative superhump" state after its return from the "positive superhump" state, which lasted for 8 years.The ephemeris for 12 of the best pronounced minima is T min = BJD 2 453 747.0700(47) + 0.132322(53)E. The phases of minima may reach 0.2, which reflects the non-eclipse nature of these minima. The quasi-periodic oscillations (QPO) are present with a mean "period" of 21.6 min and mean semi-amplitude of 36 mmag. This value is consistent with the range 15−25 min reported for previous "negative superhump" states and does not support the hypothesis of secular decrease in the QPO period. Either the period, or the semi-amplitude show significant night-to-night variations. According to the position at the two-parameter diagrams (i.e. diagrams of pairs of parameters: time, mean brightness of the system, brightness of the source of QPO, amplitude, and timescale of the QPOs), the interval of observations was divided into 5 parts, showing different characteristics: 1) the "pre-outburst" stage; 2) the "rise to outburst"; 3) "top of the outbursts"; 4) "post-outburst QPO" state; and 5) "slow brightening". The the QPO source was significantly brighter during the 10-day outburst, than during the preceding interval. However, after the outburst, the large brightness of the QPO source still existed for about 30 days, producing the stage "4". The diagram for m QPO (m) exhibits two groups in the brightness range 10. m 6−10. m 8, which correspond to larger and smaller amplitudes of the QPO. For the group "5" only, statistically significant correlations were found, for which, with increasing mean brightness, the period, amplitude, and brightness of the of QPO source also increase. The mean brightness at the "negative superhump state" varies within 10. m 3−11. m 2, so the system is brighter than at the "positive superhump" (11. m 3), therefore the "negative superhump" phenomenon may be interpreted by a larger accretion rate. The system is an excellent laboratory for studying processes resulting in variations on timescales of between seconds and decades and needs further monitoring at various states of activity.

A photometric study of the nova‐like variable TT Arietis with the MOST satellite

“…7, lower entire run, nor in limited time intervals, could we identify significant QPOs. Kim et al (2009) found occasional QPOs with mean semi-amplitudes between 1.4 and 8.2 % in the period range between 10 and 27 minutes, which apparently were not present in our MOST observations. They only show random variability in typical time scales of a about 10-20 minutes with amplitudes up to 0.1 mag (flickering).…”

“…Between 1986 and 1996 several authors (Skillman et al 1998;Andronov et al 1999;Kraicheva et al 1999) (Skillman et al 1998;Wu et al 2002;Andronov et al 2005). In October 2005 the negative superhumps had reappeared: Kim et al (2009) A preliminary analysis of these data reveals a rather stable superhump period P S = 0.132883±0.000003 d (Vogt et al, in preparation), within the range of the historical observations between 1961 and 1988. Therefore, the superhump period presented here for October/November 2007 is larger than any other value known before or after the MOST run.…”

57-second oscillations in Nova Centauri 1986 (V842 Cen)

“…BT Mon and V533 Her; Warner 2004). But here again there is similarity between V842 Cen and TT Ari – the latter has QPOs extending over the range 900–1500 s (Kim et al 2009).…”

Spectral and photometric observations of TT Ari. III.

“…Photometric observations at the beginning of July 2009 show that the star's brightness, R~11 m .21 [20], corresponds to the normal brightness of the star in its "negative superhump" phase [21]. [13,14].…”