Variations in the Period of Negative Superhumps in SU UMa-Type Dwarf Novae. I. Mn Dra (2012-2017)

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. This is a photometric study of the dwarf nova MN Dra made during 2012-2017 on nine telescopes over 152 nights. Overall, the observations covered 4 superoutbursts, 7 normal outbursts and the quiescent state. The interval between neighboring superoutbursts in 2017 was 65 days, and between neighboring normal bursts, 15 days. During the superoutbursts of 2012 and 2017, positive superhumps with a period of 0.10558(6) and 0.10500(2) days, respectively, were observed and in the quiescent state, negative superhumps with an average period of 0.095921(3) days, It is shown that the period of the negative superhumps varied cyclically between normal outbursts: sharply decreasing during an outburst and gradually increasing toward the onset of the next outburst. This feature of the variation in the period of the negative superhumps may correspond to a rapid increase in the radius of the accretion disk during the time of an outburst followed by a slow decrease, in agreement with the theory of thermal-tidal instability

First detection of two superoutbursts during the rebrightening phase of a WZ Sge-Type dwarf nova: TCP J21040470+4631129

© 2020 The Author(s) 2020. Published by Oxford University Press on behalf of the Astronomical Society of Japan. We report on photometric and spectroscopic observations and analysis of the 2019 superoutburst of TCP J21040470+4631129. This object showed a 9 mag superoutburst with early superhumps and ordinary superhumps, which are the features of WZ Sge-Type dwarf novae. Five rebrightenings were observed after the main superoutburst. The spectra during the post-superoutburst stage showed Balmer, He i, and possible sodium doublet features. The mass ratio is derived as 0.0880(9) from the period of the superhump. During the third and fifth rebrightenings, growing superhumps and superoutbursts were observed, which have never been detected during a rebrightening phase among WZ Sge-Type dwarf novae with multiple rebrightenings. To induce a superoutburst during the brightening phase, the accretion disk needs to have expanded beyond the 3: 1 resonance radius of the system again after the main superoutburst. These peculiar phenomena can be explained by the enhanced viscosity and large radius of the accretion disk suggested by the higher luminosity and the presence of late-stage superhumps during the post-superoutburst stage, plus by more mass supply from the cool mass reservoir and/or from the secondary because of the enhanced mass transfer than those of other WZ Sge-Type dwarf novae

Survey of period variations of superhumps in SU UMa-type dwarf novae. X. The tenth year (2017)

© 2020 The Author(s) 2020. Published by Oxford University Press on behalf of the Astronomical Society of Japan. Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during the 2017 season, and characterized these objects. WZ Sge-type stars identified in this study are PT And, ASASSN-17ei, ASASSN-17el, ASASSN-17es, ASASSN-17fn, ASASSN-17fz, ASASSN-17hw, ASASSN-17kd, ASASSN-17la, PNV J20205397+2508145, and TCP J00332502-3518565. We obtained new mass ratios for seven objects using growing superhumps (stage A). ASASSN-17gf is an EI Psc-type object below the period minimum. CRTS J080941.3+171528 and DDE 51 are objects in the period gap, and both showed a long-lasting phase of stage A superhumps. We also summarize the recent advances in understanding of SU UMa-type and WZ Sge-type dwarf novae