V.P. Goranskij

Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. III: The Third Year (2010-2011)

Continuing the project described by Kato et al. (2009, PASJ 61, S395, arXiv:0905.1757), we collected times of superhump maxima for 51 SU UMa-type dwarf novae mainly observed during the 2010-2011 season. Although most of the new data for systems with short superhump periods basically confirmed the findings by Kato et al. (2009) and Kato et al. (2010, PASJ 62, 1525, arXiv:1009.5444), the long-period system GX Cas showed an exceptionally large positive period derivative. An analysis of public Kepler data of V344 Lyr and V1504 Cyg yielded less striking stage transitions. In V344 Lyr, there was prominent secondary component growing during the late stage of superoutbursts, and the component persisted at least for two more cycles of successive normal outbursts. We also investigated the superoutbursts of two conspicuous eclipsing objects: HT Cas and the WZ Sge-type object SDSS J080434.20+510349.2. Strong beat phenomena were detected in both objects, and late-stage superhumps in the latter object had an almost constant luminosity during the repeated rebrightenings. The WZ Sge-type object SDSS J133941.11+484727.5 showed a phase reversal around the rapid fading from the superoutburst. The object showed a prominent beat phenomenon even after the end of the superoutburst. A pilot study of superhump amplitudes indicated that the amplitudes of superhumps are strongly correlated with orbital periods, and the dependence on the inclination is weak in systems with inclinations smaller than 80 deg.

Subaru and Gemini Observations of SS 433: New Constraint on the Mass of the Compact Object

We present results of optical spectroscopic observations of the mass donor star in SS 433 with Subaru and Gemini, with an aim to best constrain the mass of the compact object. Subaru/Faint Object Camera and Spectrograph observations were performed on four nights of 2007 October 6-8 and 10, covering the orbital phase of = 0.96 – 0.26. We first calculate the cross-correlation function (CCF) of these spectra with that of the reference star HD 9233 in the wavelength range of 4740-4840 A. This region is selected to avoid strong absorption lines accompanied with contaminating emission components, which most probably originate from the surroundings of the donor star, such as the wind and gas stream. The same analysis is applied to archive data of Gemini/GMOS taken at = 0.84 – 0.30 by Hillwig & Gies. From the Subaru and Gemini CCF results, the amplitude of the radial velocity curve of the donor star is determined to be 58.3 ± 3.8 km s–1 with a systemic velocity of 59.2 ± 2.5 km s–1. Together with the radial velocity curve of the compact object, we derive the mass of the donor star and compact object to be M O = 12.4 ± 1.9 M ☉ and M X = 4.3 ± 0.6 M ☉, respectively. We conclude, however, that these values should be taken as upper limits. From the analysis of the averaged absorption line profiles of strong lines (mostly ions) and weak lines (mostly neutrals) observed with Subaru, we find evidence for heating effects from the compact object. Using a simple model, we find that the true radial velocity amplitude of the donor star could be as low as 40 ± 5 km s–1 in order to produce the observed absorption-line profiles. Taking into account the heating of the donor star may lower the derived masses to M O = 10.4+2.3 –1.9 M ☉ and M X = 2.5+0.7 –0.6 M ☉. Our final constraint, 1.9 M ☉ ≤M X≤ 4.9 M ☉, indicates that the compact object in SS 433 is most likely a low mass black hole, although the possibility of a massive neutron star cannot be firmly excluded.

Interacting supernovae and supernova impostors. LSQ13zm: an outburst heralds the death of a massive star

We report photometric and spectroscopic observations of the optical transient LSQ13zm. Historical data reveal the presence of an eruptive episode (that we label as ‘2013a’) followed by a much brighter outburst (‘2013b’) three weeks later, that we argue to be the genuine supernova explosion. This sequence of events closely resemble those observed for SN 2010mc and (in 2012) SN 2009ip. The absolute magnitude reached by LSQ13zm during 2013a (M_R=−14.87±0.25mag) is comparable with those of supernova impostors, while that of the 2013b event (M_R=−18.46±0.21mag) is consistent with those of interacting supernovae. Our spectra reveal the presence of a dense and structured circumstellar medium, probably produced through numerous pre-supernova mass-loss events. In addition, we find evidence for high-velocity ejecta, with a fraction of gas expelled at more than 20000 km s^(−1). The spectra of LSQ13zm show remarkable similarity with those of well-studied core-collapse supernovae. From the analysis of the available photometric and spectroscopic data, we conclude that we first observed the last event of an eruptive sequence from a massive star, likely a Luminous Blue Variable, which a short time later exploded as a core-collapse supernova. The detailed analysis of archival images suggest that the host galaxy is a star-forming Blue Dwarf Compact Galaxy.

In-the-gap SU UMa-type dwarf nova, Var73 Dra with a supercycle of about 60 days

An intensive photometric-observation campaign of the recently discovered SU UMa-type dwarf nova, Var73 Dra was conducted from 2002 August to 2003 February. We caught three superoutbursts in 2002 October, December and 2003 February. The recurrence cycle of the superoutburst (supercycle) is indicated to be60 d, the shortest among the values known so far in SU UMa stars and close to those of ER UMa stars. The superhump periods measured during the first two superoutbursts were 0.104885(93) d, and 0.10623(16) d, respectively. A 0.10424(3)-d periodicity was detected in quiescence. The change rate of the superhump period during the second superoutburst was 1:7 10 3 , which is an order of magnitude larger than the largest value ever known. Outburst activity has changed from a phase of frequent normal outbursts and infrequent superoutbursts in 2001 to a phase of infrequent normal outbursts and frequent superoutbursts in 2002. Our observations are negative to an idea that this star is an related object to ER UMa stars in terms of the duty cycle of the superoutburst and the recurrence cycle of the normal outburst. However, to trace the superhump evolution throughout a superoutburst, and from quiescence more eectively, may give a fruitful result on this matter.

The Mode Change of the RR Lyrae Variable V79 in M3

The RR Lyrae variable V79 in M3 has been studied on approximately 1000 photographs in the Sternberg Observatory plate collection and on 126 CCD frames. The photographs were obtained over the interval 1949-1992, and the CCD observations were made in 1998. A comparison of our data with observations made in 1992, 1993, and 1996 indicates that V79 changed its pulsation mode in 1992. Before 1992, it was a fundamental mode pulsator (RRab star) with an irregular light curve, but since then it has been a double-mode pulsator (RRd star) with the first overtone the dominant mode. Prior to the mode change, there were sporadic episodes when pulsation in the first overtone mode occurred, for example, for a few days in 1976 and again in 1989. In each case, however, the fundamental mode pulsation resumed afterward. During the first two weeks in April of 1989, the star appeared to stop varying, and when it began again, the period of the fundamental mode pulsation had decreased substantially, from 0.483 to 0.480 days. Although the first overtone has been the dominant mode of pulsation for V79 since 1992 when it became an RRd star, our 1998 observations show that the amplitude of the fundamental mode is greater than it was in 1996. Previously published investigations of the Oosterhoff type II cluster M15 indicate that some of its RRd stars have exhibited irregular behavior, but no mode switches have been observed. In addition, there are some short period RRab stars in other Oosterhoff type I clusters that have changed their light curve amplitude and shape on a timescale of years, but up to now, none of these have been shown to be RRd stars.

M31N 2008-12a—THE REMARKABLE RECURRENT NOVA IN M31: PANCHROMATIC OBSERVATIONS OF THE 2015 ERUPTION

The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption ten times, including yearly eruptions from 2008-2014. With a measured recurrence period of

Discovery of a WZ Sge-Type Dwarf Nova, SDSS J102146.44+234926.3: Unprecedented Infrared Activity during a Rebrightening Phase

P_\mathrm{rec}=351\pm13

Photometric and spectroscopic study of nova Cassiopeiae 1995 (V723 Cas)

days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground and space-based follow-up programs. In this paper we present the 2015 detection; visible to near-infrared photometry and visible spectroscopy; and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2m (Hawaii) discovered the 2015 eruption, estimated to have commenced at Aug.

Spectral variability of LBV star V 532 (Romano’s star)

28.28\pm0.12

Photometry and spectroscopy of the luminous red nova PSNJ14021678+5426205 in the galaxy M101

UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities