Search

We report on the masses ($M_\mathrm{WD}$), effective temperatures ($T_\mathrm{eff}$) and secular mean accretion rates ($\langle \dot{M} \rangle$) of 43 cataclysmic variable (CV) white dwarfs, 42 of which were obtained from the combined analysis of their $\mathit{Hubble~Space~Telescope}$ ultraviolet data with the parallaxes provided by the Early Third Data Release of the $\mathit{Gaia}$ space mission, and one from the white dwarf gravitational redshift. Our results double the number of CV white dwarfs with an accurate mass measurement, bringing the total census to 89 systems. From the study of the mass distribution, we derive $\langle M_\mathrm{WD} \rangle = 0.81^{+0.16}_{-0.20}\,\mathrm{M_\odot}$, in perfect agreement with previous results, and find no evidence of any evolution of the mass with orbital period. Moreover, we identify five systems with $M_\mathrm{WD} < 0.5\mathrm{M_\odot}$, which are most likely representative of helium-core white dwarfs, showing that these CVs are present in the overall population. We reveal the presence of an anti-correlation between the average accretion rates and the white dwarf masses for the systems below the $2-3\,$h period gap. Since $\langle \dot{M} \rangle$ reflects the rate of system angular momentum loss, this correlation suggests the presence of an additional mechanism of angular momentum loss that is more efficient at low white dwarf masses. This is the fundamental concept of the recently proposed empirical prescription of consequential angular momentum loss (eCAML) and our results provide observational support for it, although we also highlight how its current recipe needs to be refined to better reproduce the observed scatter in $T_\mathrm{eff}$ and $\langle \dot{M} \rangle$, and the presence of helium-core white dwarfs., Comment: Accepted for publication in MNRAS. 22 pages of main body (6 tables and 14 figures) and 54 pages of appendices. Appendix B includes the best-fitting parameters and models to the HST data

We present HST spectroscopy for 45 cataclysmic variables (CVs), observed with HST/COS and HST/STIS. For 36 CVs, the white dwarf is recognisable through its broad Ly$\alpha$ absorption profile and we measure the white dwarf effective temperatures ($T_{\mathrm{eff}}$) by fitting the HST data assuming $\log\,g=8.35$, which corresponds to the average mass for CV white dwarfs ($\simeq\,0.8\,\mathrm{M}_\odot$). Our results nearly double the number of CV white dwarfs with an accurate temperature measurement. We find that CVs above the period gap have, on average, higher temperatures ($\langle T_{\mathrm{eff}} \rangle \simeq 23\,000\,$K) and exhibit much more scatter compared to those below the gap ($\langle T_{\mathrm{eff}} \rangle \simeq 15\,000\,$K). While this behaviour broadly agrees with theoretical predictions, some discrepancies are present: (i) all our new measurements above the gap are characterised by lower temperatures ($T_{\mathrm{eff}} \simeq 16\,000 - 26\,000\,$K) than predicted by the present day CV population models ($T_{\mathrm{eff}} \simeq 38\,000 - 43\,000\,$K); (ii) our results below the gap are not clustered in the predicted narrow track and exhibit in particular a relatively large spread near the period minimum, which may point to some shortcomings in the CV evolutionary models. Finally, in the standard model of CV evolution, reaching the minimum period, CVs are expected to evolve back towards longer periods with mean accretion rates $\dot{M}\lesssim 2 \times 10^{-11}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$, corresponding to $T_\mathrm{eff}\lesssim 11\,500\,$K. We do not unambiguously identify any such system in our survey, suggesting that this major component of the predicted CV population still remains elusive to observations., Comment: 26 pages, 21 figures. Published in MNRAS

We present simultaneous optical and near-infrared (NIR) polarimetric results for the black hole binary V404 Cygni spanning the duration of its 7-day long optically-brightest phase of its 2015 June outburst. The simultaneous R and Ks-band light curves showed almost the same temporal variation except for the isolated (~30 min duration) orphan Ks-band flare observed at MJD 57193.54. We did not find any significant temporal variation of polarization degree (PD) and position angle (PA) in both R and Ks bands throughout our observations, including the duration of the orphan NIR flare. We show that the observed PD and PA are predominantly interstellar in origin by comparing the V404 Cyg polarimetric results with those of the surrounding sources within the 7'x7' field-of-view. The low intrinsic PD (less than a few percent) implies that the optical and NIR emissions are dominated by either disk or optically-thick synchrotron emission, or both. We also present the broadband spectra of V404 Cyg during the orphan NIR flare and a relatively faint and steady state by including quasi-simultaneous Swift/XRT and INTEGRAL fluxes. By adopting a single-zone synchrotron plus inverse-Compton model as widely used in modeling of blazars, we constrained the parameters of a putative jet. Because the jet synchrotron component cannot exceed the Swift/XRT disk/corona flux, the cutoff Lorentz factor in the electron energy distribution is constrained to be <10^2, suggesting particle acceleration is less efficient in this microquasar jet outburst compared to AGN jets. We also suggest that the loading of the baryon component inside the jet is inevitable based on energetic arguments., Comment: 8 pages, 6 figures, 2 tables. Accepted by ApJ

Na I D absorbing systems toward Type Ia supernovae (SNe Ia) have been intensively studied over the last decade with the aim of finding circumstellar material (CSM), which is an indirect probe of the progenitor system. However, it is difficult to deconvolve CSM components from non-variable, and often dominant, components created by interstellar material (ISM). We present a series of high-resolution spectra of SN Ia 2014J from before maximum brightness to ~250 days after maximum brightness. The late-time spectrum provides unique information for determining the origin of the Na I D absorption systems. The deep late-time observation allows us to probe the environment around the SN at a large scale, extending to ~40 pc. We find that a spectrum of diffuse light in the vicinity, but not directly in the line-of-sight, of the SN has absorbing systems nearly identical to those obtained for the "pure" SN line-of-sight. Therefore, basically all Na I D systems seen toward SN 2014J must originate from foreground material that extends to at least ~40 pc in projection and none at the CSM scale. A fluctuation in the column densities at a scale of ~20 pc is also identified. After subtracting the diffuse, "background" spectrum, the late-time SN Na I D profile along the SN line-of-sight is consistent with the profile in the near-maximum brightness spectra. The lack of variability on a ~1 year timescale is consistent with the ISM interpretation for the gas., Comment: 20 pages, 17 figures, 1 table. Accepted for publication in ApJ

We presented optical and near-infrared multi-band linear polarimetry of the highly reddened Type Ia SN~2014J appeared in M82. SN~2014J exhibits large polarization at shorter wavelengths, e.g., $4.8$\% in $B$ band, and the polarization decreases rapidly at longer wavelengths, with the position angle of the polarization remaining at approximately $40^{\circ}$ over the observed wavelength range. These polarimetric properties suggest that the observed polarization is likely to be caused predominantly by the interstellar dust within M82. Further analysis shows that the polarization peaks at a wavelengths much shorter than those obtained for the Galactic dust. The wavelength dependence of the polarization can be better described by an inverse power law rather than by Serkowski law for Galactic interstellar polarization. These suggests that the nature of the dust in M82 may be different from that in our Galaxy, with polarizing dust grains having a mean radius of $<0.1\ \mu$m., Comment: 8 pages, 4 figures, accepted for publication in ApJ Letters

WZ Sge-type dwarf novae are characterized by long recurrence times of outbursts (~10 yr) and short orbital periods (<~ 85 min). A significant part of WZ Sge stars may remain undiscovered because of low outburst activity. Recently, the observed orbital period distribution of cataclysmic variables (CVs) has changed partly because outbursts of new WZ Sge stars have been discovered routinely. Hence, the estimation of the intrinsic population of WZ Sge stars is important for the study of the population and evolution of CVs. In this paper, we present a Bayesian approach to estimate the intrinsic period distribution of dwarf novae from observed samples. In this Bayesian model, we assumed a simple relationship between the recurrence time and the orbital period which is consistent with observations of WZ Sge stars and other dwarf novae. As a result, the minimum orbital period was estimated to be ~70 min. The population of WZ Sge stars exhibited a spike-like feature at the shortest period regime in the orbital period distribution. These features are consistent with the orbital period distribution previously predicted by population synthesis studies. We propose that WZ Sge stars and CVs with a low mass-transfer rate are excellent candidates for the missing population predicted by the evolution theory of CVs., Comment: 9 pages, 5 figures, accepted for publication in PASJ

We report on optical high-dispersion spectroscopic monitoring observations of the Be/X-ray binary A0535+26/V725 Tau, carried out from November 2005 to March 2009. The main aim of these monitoring observations is to study spectral variabilities in the Be disc, on both the short (a week or so) and long (more than hundreds of days) timescales, by taking long-term frequent observations. Our four-year spectroscopic observations indicate that the V/R ratio, i.e., the relative intensity of the violet (V) peak to the red (R) one, of the double-peaked H-alpha line profile varies with a period of 500 days. The H-beta line profile also varies in phase with the H-alpha profile. With these observations covering two full cycles of the V/R variability, we reconstruct the 2-D structure of the Be disc by applying the Doppler tomography method to the H-alpha and H-beta emission line profiles, using a rigidly rotating frame with the V/R variability period. The resulting disc structure reveals non-axisymmetric features, which can be explained by a one-armed perturbation in the Be disc. It is the first time that an eccentric disc structure is directly detected by using a method other than the interferometric one., Comment: (10 pages, 9 figures, accepted to MNRAS)

We carried out intensive spectroscopic observations of two WZ Sge-type dwarf novae, GW Lib, and V455 And during their superoutbursts in 2007, at 6 observatories. The observations covered the whole of both superoutbursts from the very maximum to the fading tail. We found evidence of the winds having a speed of $\sim$1000 km s$^{-1}$ which blew in GW Lib during the rising phase. The evolution of the hydrogen, helium, and carbon lines suggests flaring of the accretion disk and emergence of the temperature inversion layer on the disk., Comment: 5 pages, to be published in the proceedings of the 8th Pacific Rim Conference on Stellar Astrophysics

We present the results of photometric observations of SDSS J080434.20+510349.2 in its low state and during an outburst and spectroscopy during the outburst. We found such peculiarities as a long-term outburst with amplitude probably not less than 6m, rarity of the outbursts, eleven rebrightenings, and a short (0.059713(7) d) superhump period. We conclude that this star belongs to the WZ Sge-type subclass of cataclysmic variables. The spectrum shows both emission and absorption lines of H and He superimposed on the blue continuum. We also found 8 -- 9 min. brightness variations during the end of the super-outburst plateau that could be related to pulsations of the white dwarf in the binary., Comment: Published in 15th European Workshop on White Dwarfs ASP Conference Series, Vol. 372, proceedings of the conference held 7-11 August, 2006 in Leicester, United Kingdom. Edited by Ralf Napiwotzki and Matthew R. Burleigh. San Francisco: Astronomical Society of the Pacific, 2007., p.511

Several SU UMa-type dwarf novae, in particular, WZ Sge-type stars tend to exhibit rebrightenings after superoutbursts. The rebrightening phenomenon is problematic for the disk instability theory of dwarf novae since it requires a large amount of remnant matter in the disk even after superoutbursts. Here, we report our optical and infrared observations during the first-ever outburst of a new dwarf nova, SDSS J102146.44+234926.3. During the outburst, we detected superhumps with a period of 0.056281 +/- 0.000015 d, which is typical for superhump periods in WZ Sge stars. In conjunction with the appearance of a long-lived rebrightening, we conclude that the object is a new member of WZ Sge stars. Our observations, furthermore, revealed infrared behaviors for the first time in the rebrightening phase of WZ Sge stars. We discovered prominent infrared superhumps. We calculate the color temperature of the infrared superhump source to be 4600-6400 K. These temperatures are too low to be explained with a fully-ionized disk appearing during dwarf nova outbursts. We also found a Ks-band excess over the hot disk component. These unprecedented infrared activities provide evidence for the presence of mass reservoir at the outermost part of the accretion disk. We propose that a moderately high mass-accretion rate at this infrared active region leads to the long-lived rebrightening observed in SDSS J102146.44+234926.3., Comment: 11 pages, 10 figures. Accepted for publication in PASJ

We report the observation of the first gravitational microlensing event in a sparse stellar field, involving the brightest (V=11.4 mag) andclosest (~ 1 kpc) source star to date. This event was discovered by an amateurastronomer, A. Tago, on 2006 October 31 as a transient brightening, by ~4.5 mag during a ~15 day period, of a normal A-type star (GSC 3656-1328) in the Cassiopeia constellation. Analysis of both spectroscopic observations and the light curve indicates that this event was caused by gravitational microlensing rather than an intrinsically variable star. Discovery of this single event over a 30 year period is roughly consistent with the expected microlensing rate for the whole sky down to V = 12 mag stars. However, the probability for finding events with such a high magnification (~ 50) is much smaller, by a factor ~1/50, which implies that the true event rate may be higher than expected. This discovery indicates the potential of all sky variability surveys, employing frequent sampling by telescopes with small apertures and wide fields of view, for finding such rare transient events, and using the observations to explore galactic disk structure and search for exo-planets., Comment: 13 pages, 2 tables, 3 figures, accepted by ApJ

We report the discovery of five new dwarf novae from the Hamburg Quasar Survey (HQS), and discuss the properties of the sample of dwarf novae in the HQS. The orbital periods of the new dwarf novae are ~105.1 min or ~109.9 min, 114.3+-2.7 min, 92.66+-0.17 min, 272.317+-0.001 min, 258.02+-0.56 min for HS0417+7445, HS1016+3412, HS1340+1524, HS1857+7127, and HS2214+2845, respectively. HS1857+7127 is found to be partially eclipsing. In HS2214+2845 the secondary star of spectral type M3+-1 is clearly detected, and we estimate the distance to the system to be d=390+-40 pc. We recorded one superoutburst of the SU UMa system HS0417+7445. HS1016+3412 and HS1340+1524 have rare outbursts, and their subtype is yet undetermined. HS1857+7127 frequently varies in brightness and may be a Z Cam-type dwarf nova. HS2214+2845 is a U Gem-type dwarf nova with a most likely cycle length of 71 d. To date, 14 new dwarf novae have been identified in the HQS. The ratio of short-period (<3 h) to long-period (>3 h) systems of this sample is 1.3, much smaller compared to the ratio of 2.7 found for all known dwarf novae. The HQS dwarf novae display typically infrequent or low-amplitude outburst activity, underlining the strength of spectroscopic selection in identifying new CVs independently of their variability. The spectroscopic properties of short-period CVs in the HQS suggest that most of them are still evolving towards the minimum period. Their total number agrees with the predictions of population models within an order of magnitude. However, the bulk of all CVs is predicted to have evolved past the minimum period, and those systems remain unidentified. Those post-bounce systems may have markedly weaker Hbeta emission lines compared to the average known short-period CVs, and probably undergo no or extremely rare outbursts., Comment: accepted for publication in A&A, 17 pages, 18 figures, low-quality figures to comply with astro-ph size limit

Our research on variable objects based on the VSNET collaborations has achieved much progress in understanding the nature of many kinds of phenomena. Many problems have appeared, instead. Among them, we here review three newly arising problems in the research of SU UMa-type dwarf novae: 1) how do EI Psc and V485 Cen evolve as a cataclysmic variable?, 2) is the early superhump a particular phenomenon for WZ Sge-type dwarf novae?, and 3) what parameters determine variations of the superhump period?, Comment: 5 pages, no figure, to appear in the proceedings of the 7th Pacific-Rim Conference on Stellar Astrophysics

We have identified a new intermediate polar, HS 0943+1404, as part of our ongoing search for cataclysmic variables in the Hamburg Quasar Survey. The orbital and white dwarf spin periods determined from time-resolved photometry and spectroscopy are Porb ~= 250 min and Pspin = 69.171 +- 0.001 min, respectively. The combination of a large ratio Pspin/Porb ~= 0.3 and a long orbital period is very unusual compared to the other known intermediate polars. The magnetic moment of the white dwarf is estimated to be mu1 ~ 10^{34} G cm^3, which is in the typical range of polars. Our extensive photometry shows that HS 0943+1404 enters into deep (~ 3 mag) low states, which are also a characteristic feature of polars. We therefore suggest that the system is a true ``intermediate'' polar that will eventually synchronise, that is, a transitional object between intermediate polars and polars. The optical spectrum of HS 0943+1404 also exhibits a number of unusual emission lines, most noticeably NII 5680, which is likely to reflect enhanced nitrogen abundances in the envelope of the secondary., Comment: LaTeX, 10 pages, 11 figures, accepted for publication in A&A

We report optical photometric observations of four superoutbursts of the short-period dwarf nova TV Crv. This object experiences two types of superoutbursts; one with a precursor and the other without. The superhump period and period excess of TV Crv are accurately determined to be 0.065028 +/- 0.000008 d and 0.0342 +/- 0.0021, respectively. This large excess implies a relatively large mass ratio of the binary components (M_2/M_1), though it has a short orbital period. The two types of superoutbursts can be explained by the thermal-tidal instability model for systems having large mass ratios. Our observations reveal that superhump period derivatives are variable in distinct superoutbursts. The variation is apparently related to the presence or absence of a precursor. We propose that the superhump period derivative depends on the maximum disk radius during outbursts. We investigate the relationship of the type of superoutbursts and the superhump period derivative for known sources. In the case of superoutbursts without a precursor, superhump period derivatives tend to be larger than those in precursor-main type superoutbursts, which is consistent with our scenario., Comment: 13 pages, 11 figures, accepted for publication in A&A

We conducted a time-resolved photometric campaign of the helium dwarf nova, 2003aw in 2004 May--June. 2003aw stayed at 14.7--15.7 mag for the first several days during this campaign, which is the plateau phase of this superoutburst. This variable then rapidly decayed to $\sim$18.0 mag, still brighter by about 2 mag than its quiescence magnitude, and maintained this brightness for about 20 days, having short flares of $\sim$2 mag. A long fading tail followed it. We detected superhumps with a period of 0.02357(4) d [= 2036(3) s] during the plateau phase. The whole light curve of the superoutburst in 2003aw, taking into account the present data and those in the literature, perfectly resembles that of the 1996-1997 superoutburst of the peculiar WZ Sge-type hydrogen-rich dwarf nova, EG Cnc., Comment: 5 pages, 4 figures, PASJ Letter in press

We carried out optical spectroscopic observations of the most enigmatic dwarf nova WZ Sge in 11 nights during the 2001 superoutburst. Our observations covered the period from the initial phase, several hours before the maximum, to the ninth maximum of the rebrightening phase. The first spectrum shows absorption lines of H I (except for Halpha), He I, and Na I, as well as emission lines of He\II, C III/N III, and Halpha in doubly-peaked shapes. The same spectrum shows the emission lines of C IV and N IV which are the first detection in dwarf novae. The spectral features dramatically changed in various time scales. For example, the peak separations of the emission lines of H I and He II changed from ~700 km/s to 1300 km/s, and one of the peaks dominated over an orbital period in the genuine-superhump era, but the dominant peak interchanged with the orbital phase in the early-superhump era. The lines of H I and He I were in emission at minima of the rebrightening phase (with no high-excitation lines, nor Na I), while they became in absorption at maxima. We report on these observational results in detail and their implications concerning the outburst mechanism, two types of superhumps, and variation of the disk structure., Comment: 22 pages, 17 figures, to appear in the VSNET special issue of PASJ

We report the photometric observations of an SU UMa-type dwarf nova VW CrB during two superoutbursts in 2001 and 2003 and a normal outburst in 2003. Superhumps with a period of 0.07287(1) d were observed during the 2003 superoutburst. The change rate of the superhump period was positive. During the normal outburst, there are some hint of modulation up to a 0.2-mag amplitude. However, any periodicity was not found. The recurrence cycles of the normal outburst and the superoutburst, and the distance were estimated to be > ~50 d, 270-500 d, and 690(+230, -170) pc, respectively. These recurrence cycles are usual values for an SU UMa-type dwarf nova having this superhump period. The superhump period of VW CrB was the longest among those of the SU UMa stars with positive derivatives of the superhump period. The coverage of our observations was, however, not enough, and the variation of the Psh change rate of VW CrB is still unknown. A superhump regrowth and a brightening were seen near the end of the plateau phase. Measuring the deviation of the start timings of the brightening and the superhump regrowth (>2 days in VW CrB) will be a key to reveal the mechanism of these phenomena., Comment: 7 pages, 8 figures, to appear in PASJ

We report on time-resolved photometric observations of the WZ Sge-type dwarf nova, EG Cnc (Huruhata's variable, see also http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/egcnc.html), during its superoutburst in 1996-1997. EG Cnc, after the main superoutburst accompanied with development of superhumps typical of a WZ Sge-type dwarf nova, exhibited a series of six major rebrightenings. During these rebrightenings and the following long fading tail, EG Cnc persistently showed superhumps having a period equal to the superhump period observed during the main superoutburst. The persistent superhumps had a constant superhump flux with respect to the rebrightening phase. These findings suggest the superhumps observed during the rebrightening stage and the fading tail are a "remnant" of usual superhumps, and are not newly triggered by rebrightenings. By comparison with the 1977 outburst of this object and outbursts of other WZ Sge-type dwarf novae, we propose an activity sequence of WZ Sge-type superoutbursts, in which the current outburst of EG Cnc is placed between a single-rebrightening event and distinct outbursts separated by a dip. The post-superoutburst behavior of WZ Sge-type dwarf novae can be understood in the presence of considerable amount of remnant matter behind the cooling front in the outer accretion disk, even after the main superoutburst. We consider the premature quenching of the hot state due to the weak tidal effect under the extreme mass ratio of the WZ Sge-type binary is responsible for the origin of the remnant mass., Comment: 16 pages, 15 figures, to appear in PASJ (special issue on VSNET), for more information, see http://www.kusastro.kyoto-u.ac.jp/vsnet/

We report on the results of the QW Ser campaign which has been continued from 2000 to 2003 by the VSNET collaboration team. Four long outbursts and many short ones were caught during this period. Our intensive photometric observations revealed superhumps with a period of 0.07700(4) d during all four superoutbursts, proving the SU UMa nature of this star. The recurrence cycles of the normal outbursts and the superoutbursts were measured to be $\sim$50 days and 240(30) days, respectively. The change rate of the superhump period was -5.8x10^{-5}. The distance and the X-ray luminosity in the range of 0.5-2.4 keV are estimated to be 380(60) pc and log L_x = 31.0 \pm 0.1 erg s^{-1}. These properties have typical values for an SU UMa-type dwarf nova with this superhump period., Comment: 9 pages, 12 figures, to appear in the VSNET special issue of PASJ

Variable Star Network (VSNET, http://www.kusastro.kyoto-u.ac.jp/vsnet/) is a global professional-amateur network of researchers in variable stars and related objects, particularly in transient objects, such as cataclysmic variables, black hole binaries, supernovae and gamma-ray bursts. The VSNET has been playing a pioneering role in establishing the field of "transient object astronomy", by effectively incorporating modern advance in observational astronomy and global electronic network, as well as collaborative progress in theoretical astronomy and astronomical computing. The VSNET is now one of the best-featured global networks in this field of astronomy. We review on the historical progress, design concept, associated technology, and a wealth of scientific achievements powered by the VSNET., Comment: 57 pages, 21 figures, to appear in PASJ (special issue on VSNET), for more information and a full resolution version, see http://www.kusastro.kyoto-u.ac.jp/vsnet/

We observed the 1994, 1996 and 2001 outbursts of HO Del. From the detection of secure superhumps, HO Del is confirmed to be an SU UMa-type dwarf nova with a superhump period of 0.06453(6) d. Based on the recent observations and the past records, the outbursts of HO Del are found to be relatively rare, with the shortest intervals of superoutbursts being ~740 d. Among SU UMa-type dwarf novae with similar outburst intervals, the outburst amplitude (~5.0 mag) is unusually small. HO Del showed a rather rapid decay of the superhump amplitudes, and no regrowth of the amplitudes during the later stage, in contrast to the commonly observed behavior in SU UMa-type dwarf novae with long outburst intervals. We positively identified HO Del with a ROSAT X-ray source, and obtained a relatively large X-ray luminosity of 10^(31.1+/-0.2) erg/s. We also performed a literature survey of SU UMa-type dwarf novae, and presented a new set of basic statistics. The SU UMa-type dwarf novae with a brightening trend or with a regrowth of superhumps near the termination of a superoutburst are found to be rather tightly confined in a small region on the (superhump period-supercycle length) plane. These features may provide a better observational distinction for the previously claimed subgroup of dwarf novae (Tremendous Outburst Amplitude Dwarf Novae)., Comment: 17 pages, 12 figures, accepted for publication in PASJ

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 be $\sim$60 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 $1.7\times10^{-3}$, 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 effectively, may give a fruitful result on this matter., Comment: 9 pages, 8 figures, submitted to A&A

We observed the 2002 October-November outburst of the dwarf nova CW Mon. The outburst showed a clear signature of a premaximum halt, and a more rapid decline after reaching the outburst maximum. On two separate occasions, during the premaximum stage and near the outburst maximum, shallow eclipses were recorded. This finding confirms the previously suggested possibility of the grazing eclipsing nature of this system. The separate occurrence of the eclipses and the premaximum halt can be understood as a result of a combination of two-step ignition of an outburst and the inside-out propagation of the heating wave. We detected a coherent short-period (0.02549 d) signal on two subsequent nights around the optical maximum. This signal was likely present during the maximum phase of the 2000 January outburst. We interpret this signal as a signature of the intermediate polar (IP) type pulses. The rather strange outburst properties, strong and hard X-ray emission, and the low luminosity of the outburst maximum might be understood as consequences of the supposed IP nature. The ratio between the suggested spin period and the orbital period, however, is rather unusual for a system having an orbital period of ~0.176 d., Comment: 11 pages, 11 figures, to appear in PASJ

We carried out time-resolved $V$-band photometry of DM Lyr during long outbursts in 1996 July and in 1996 February-March at Ouda Station, Kyoto University and at Osaka Kyoiku University. Since superhumps were clearly detected in the light curves, DM Lyr was first identified with an SU UMa-type dwarf nova. The superhump period is 0.0673(2) d, and the superhump excess is 2.8(3) %. The duration of the superoutburst, the outburst amplitude, the decline rate in the plateau phase, and the superhump excess were typical values for a usual SU UMa star. According to visual and CCD observations reported to VSNET, this star has experienced a dramatic change of the outburst pattern from a superoutburst phase to a normal outburst phase. There may exist mechanisms to decrease the number of the normal outburst between two successive superoutbursts and to elongate the recurrence cycle of the superoutburst., Comment: 6 pages, 5 figures, accepted for publication in PASJ

We studied the evolution of superhumps in the peculiar SU UMa-type dwarf nova, ER UMa. Contrary to the canonical picture of the SU UMa-type superhump phenomena, the superhumps of ER UMa show an unexpected phase reversal during the very early stage (~5 d after the superoutburst maximum). We interpret that a sudden switch to so-called late superhumps occurs during the very early stage of a superoutburst. What had been believed to be (ordinary) superhumps during the superoutburst plateau of ER UMa were actually late superhumps. The implication of this discovery is briefly discussed., Comment: 4 pages, 5 figures, submitted to Publ. Astron. Soc. Japan

GK Per is a unique cataclysmic variable star which has showed a nova explosion as well as dwarf nova-type outbursts, and has the intermediate-polar nature. We carried out V-band time-resolved photometry and B-band monitoring during the 1996 outburst. This outburst lasted about 60 d and is divided into three parts: the slow rise branch for 35 d, the gradual decay branch with a decay rate of 20.0 d/mag for ~16 d, and the rapid decline branch with a rate of 5.6 d/mag for ~10 d. The $B-V$ color became bluest (B-V~0.18) about 10 d before the outburst maximum, which supports an idea that the outburst in GK Per is of the inside-out type. The spin pulse, 440-s quasi periodic oscillations (QPOs), and ~5,000-s QPOs were detected in our light curve, as previously seen in X-ray and optical observations. In addition, we report the discovery of ~300-s periodicity, which is shorter than the spin period., Comment: 12 pages, 7 figures, To appear in PASJ, vol. 54, No. 6

We discovered that RX And, one of prototypical Z Cam-type dwarf novae, underwent a deep, extended faint state in 1996-1997. Time-resolved photometry at the bottom of the fading revealed the presence of strong flickering, and the absence of detectable orbital modulation. This finding indicates that the mass-transfer remained even at the deepest minimum of the fading, contrary to what was observed in a deep minimum of a VY Scl-type star, MV Lyr. RX And subsequently underwent a brightening (outburst) during its recovery stage. The photometric and spectroscopic characteristics of the brightening significantly differed from those of ordinary outbursts of RX And, and are considered to resemble an inside-out type outburst of a long-period dwarf nova. An examination of historical visual observations revealed the possible presence of \~10-yr periodicity, which is close to what has been proposed for MV Lyr. The common observed features between RX And and VY Scl-type stars may suggest a common underlying mechanism for producing temporary deep fadings. The departure from the disk instability model, as observed in VY Scl-type stars, was not apparent in the present fading of RX And. In conjunction with the recently published Hubble Space Telescope observation during the same fading, we can conclude that the phenomenological difference from the VY Scl-type fading is understood as a smaller effect of irradiation on the accretion disk in RX And., Comment: 7 pages, 5 figures, accepted for publication in PASJ

We report time-resolved photometric observations of the Hamburg Quasar Survey-selected dwarf nova HS 1449+6415 (= RX J1450.5+6403) during the interval from JD 2451672 to 2451724. During a long outburst with a duration of ~12 days, we detected superhumps with a period of 0.0601(5) d, revealing that this star is an SU UMa star. A short outburst which lasted 3 days was found about 40 days after the onset of the superoutburst. From quiescence observations, we determine an orbital period of 0.05898(2) d. The small outburst amplitude of \~3.5 mag, the short orbital period, and the normal outburst cycle length suggest that HS 1449+6415 is an intermediate object between ER UMa stars with high mass-transfer rates and WZ Sge stars with very low mass-transfer rates., Comment: 5 pages, 6 figures, submitted to A&A

We report on follow-up spectroscopy and photometry of the cataclysmic variable candidate HS0907+1902 selected from the Hamburg Quasar Survey. B, V, and R photometry obtained during the first observed outburst of HS0907+1902 (V~13) reveals deep eclipses (DeltaV~2.1-2.8) and an orbital period Porb=4.2h with the eclipse depth decreasing to the red. The outburst eclipse profiles are symmetric, indicating an axisymmetrical brightness distribution in the accretion disc. We derive an inclination i~73deg-79deg from the eclipse duration. The quiescent spectrum obtained with the Hobby-Eberly Telescope shows double peaked emission lines of HI, HeI and FeI,II and clearly identifies the system as a dwarf nova. Absorption features of the secondary star are detected at red wavelengths from which a spectral class M3+-1.5 and a distance of d=320+-100pc are derived., Comment: 4 pages A&A-PSLatex, 5 Figures, accepted for publication in A&A Letters