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Register a new userOn the superhumps and mass ratio of CzeV404
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Taichi Kato
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CzeV404 is an SU UMa-type dwarf nova in the period gap. Kara et al. (2021) (arXiv:2107.02664) recently published photometric and spectroscopic observations and obtained a mass ratio q=0.16, which is in severe disagreement of q~0.32 estimated from superhump observations (Bakowska et al., 2014). I here present what analysis was wrong or outdated in Bakowska et al. (2014) and provide a new value of q=0.247(5), consistent with the known behavior of superhumps and the evolution of cataclysmic variables. CzeV404 does not look like an unusual dwarf nova as suggested by Kara et al. (2021) and I discuss that the link between SW Sex and SU UMa systems suggested by Kara et al. (2021) is not supported.
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We report on two superoutbursts of the AM CVn-type object CR Boo in 2014 April--March and 2015 May--June. A precursor outburst acompanied both of these superoutbursts. During the rising branch of the main superoutburst in 2014, we detected growing superhumps (stage A superhumps) whose period was $0.017669(24)$ d. Assuming that this period reflects the dynamical precession rate at the radius of the 3:1 resonance, we could estimate the mass ratio ($q=M_2/M_1$) of 0.101(4) by using the stage A superhump period and the orbital one of 0.0170290(6) d. This mass ratio is consistent with that expected by the theoretical evolutionary model of AM CVn-type objects. The detection of precursor outbursts and stage A superhumps is the second case in AM CVn-type objects. There are two interpretations of the outbursts of AM CVn-type objects. One is a dwarf nova (DN) outbursts analogy, which is caused by thermal and tidal instabilities. Another is the VY Scl-type variation, which is caused by the variation of the mass-transfer rate of the secondary. This detection of the superhump variations strongly suggests the former interpretation.
We present simultaneous $g$, $R_{rm c}$, and $I_{rm c}$ photometry of the notable dwarf nova ER UMa during the 2011 season. Our photometry revealed that the brightness maxima of negative superhumps coincide with the bluest peaks in $g - I_{rm c}$ colour variations. We also found that the amplitudes of negative superhumps are the largest in the $g$ band. These observed properties are significantly different from those observed in early and positive superhumps. Our findings are consistent with a tilted disk model as the light source of negative superhumps.
We report on a superoutburst of the AM CVn-type object SDSS J090221.35+381941.9 [J0902; orbital period 0.03355(6) d] in 2014 March-April. The entire outburst consisted of a precursor outburst and the main superoutburst, followed by a short rebrightening. During the rising branch of the main superoutburst, we detected growing superhumps (stage A superhumps) with a period of 0.03409(1) d. During the plateau phase of the superoutburst, superhumps with a shorter period (stage B superhumps) were observed. Using the orbital period and the period of the stage A superhumps, we were able to measure the dynamical precession rate of the accretion disk at the 3:1 resonance, and obtained a mass ratio (q) of 0.041(7). This is the first successful measurement of the mass ratio in an AM CVn-type object using the recently developed stage A superhump method. The value is generally in good agreement with the theoretical evolutionary model. The orbital period of J0902 is the longest among the outbursting AM CVn-type objects, and the borderline between the outbursting systems and systems with stable cool disks appears to be longer than had been supposed.
We propose a new dynamical method to estimate binary mass ratios by using the period of superhumps in SU UMa-type dwarf novae during the growing stage (the stage A superhumps). This method is based on a working hypothesis in which the period of the superhumps at the growing stage is determined by the dynamical precession rate at the 3:1 resonance radius, a picture suggested in our new interpretation of the superhump period evolution during the superoutburst (Osaki, Kato 2013, arXiv:1305.5877). By comparison with the objects with known mass ratios, we show that our method can provide sufficiently accurate mass ratios comparable to those obtained by quiescent eclipse observations. This method is very advantageous in that it requires neither eclipses, nor an experimental calibration. It is particularly suited for exploring the low mass-ratio end of the evolution of cataclysmic variables, where the secondary is undetectable by conventional methods. Our analysis suggests that previous estimates of mass ratios using superhump periods during superoutburst were systematically underestimated for low mass-ratio systems and we provided a new calibration. It suggests that most of WZ Sge-type dwarf novae have secondaries close to the border of the lower main-sequence and brown dwarfs, and most of the objects have not yet reached the evolutionary stage of period bouncers. Our result is not in contradiction with an assumption that the observed minimum period (~77 min) of ordinary hydrogen-rich cataclysmic variables is indeed the period minimum. We highlight the importance of early observation of stage A superhumps and propose a future desirable strategy of observation.
We report CCD photometry of the cataclysmic variable V1113 Cygni. During two campaigns, lasting from May to August 2003 and from March to June 2005, we recorded two superoutburst. In the obtained light curves we detected clear superhumps with a mean period 0.07891(3) days (113.63(4) min). That fact confirms that the star is a member of SU UMa class of dwarf novae. During the first observed superoutburst the superhump period was decreasing with an enormous rate of $dot P = -4.5(8)times 10^{-4}$ which is one of the highest values ever observed in SU UMa systems.
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