# Optical and Near-Infrared Photometric Observation during the Superoutburst of the WZ Sge-Type Dwarf Nova, V455 Andromedae

DOI: 10.1093/pasj/61.5.1081 · Source: arXiv
Abstract
We report on optical and infrared photometric observations of a WZ Sge-type dwarf nova, V455 And during a superoutburst in 2007. These observations were performed with the KANATA ($V$, $J$, and $K_{\rm s}$ bands) and MITSuME ($g^\prime$, $R_{\rm C}$, and $I_{\rm C}$ bands) telescopes. Our 6-band simultaneous observations allowed us to investigate the temporal variation of the temperature and the size of the emitting region associated with the superoutburst and short-term modulations, such as early and ordinary superhumps. A hot ($>$11000 K) accretion disk suddenly disappeared when the superoutburst finished, while blackbody emission, probably from the disk, still remained dominant in the optical region with a moderately high temperature ($\sim$8000 K). This indicates that a substantial amount of gas was stored in the disk even after the outburst. This remnant matter may be a sign of an expected mass-reservoir, which can trigger echo outbursts observed in several WZ Sge stars. The color variation associated with superhumps indicates that viscous heating in a superhump source stopped on the way to the superhump maximum, and a subsequent expansion of a low-temperature region made the maximum. The color variation of early superhumps was totally different from that of superhumps: the object was bluest at the early superhump minimum. The temperature of the early superhump light source was lower than that of an underlying component, indicating that the early superhump light source was a vertically expanded low-temperature region at the outermost part of the disk.
• ##### Photometric investigation of V466 And - a new WZ Sge-type dwarf nova
[Show abstract] [Hide abstract] ABSTRACT: We present the UBV(RI)C photometry of a new dwarf nova V466 And, discovered during its superoutburst on Sept. 1.6, 2008 and classified as a WZ Sge-type object. In the first 11 days of the superoutburst, the early superhumps with the period of 0.056383d were found. In days 13 --- 23 of the superoutburst, the ordinary superhumps with the period of 0.05713d were exposed. They were replaced by late superhumps with the period of 0.056d in days 24 --- 33 of the superoutburst. After one month, the dwarf nova returned to its pre-outburst state. A list of known WZ Sge-type dwarf novae, including suspected ones, is presented. We determined a mean value of superhump period excess for WZ Sge-type objects as ε=0.019±0.003. The multicolour photometry of the field stars enables us to conclude that there is no appreciable interstellar extinction in the direction of V466 And.
Full-text · Article · Apr 2010
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• ##### Six years of GRB follow up with MITSuME Okayama Telescope
[Show abstract] [Hide abstract] ABSTRACT: MITSuME Okayama Telescope is an autonomous telescope with a diameter of 50 cm dedicated primarily to follow-up gamma-ray bursts. The telescope has successfully been in operation since 2004. We have made 131 observations of gamma-ray bursts and submitted 47 reports to GCN circulars. In this article, we present an overview of the instrumentation and scientific results obtained so far.
Article · Oct 2010
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• ##### Dwarf novae in the shortest orbital period regime .
[Show abstract] [Hide abstract] ABSTRACT: Dwarf novae (DNe) having very short orbital periods (P_orb) are interesting objects in terms of two points of view: the binary evolution and the physics of accretion disks. They are considered as one of the final evolutionary stages of low-mass binaries. It is well known that the observed P_orb distribution of cataclysmic variables is inconsistent with that expected from population synthesis studies. We evaluate the intrinsic population of low activity DNe in the shortest P_orb regime, which could reconcile the discrepancy between the observation and theory. In the view point of the physics of accretion disks, short P_orb DNe, in particular, WZ Sge stars, have received attention because they exhibit unique variations, like early superhumps. We have recently developed a method to reconstruct the structure of disks using multi-band light curves of early superhumps. Here, we introduce the results of this method using the data of the dwarf nova, V455 And.
Article · Jan 2012
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• ##### Reconstruction of the Structure of Accretion Disks in Dwarf Novae from the Multi-Band Light Curves of Early Superhumps
[Show abstract] [Hide abstract] ABSTRACT: We propose a new method to reconstruct the structure of accretion disks in dwarf novae using multi-band light curves of early superhumps. Our model assumes that early superhumps are caused by the rotation effect of non-axisymmetrically flaring disks. We have developed a Bayesian model for this reconstruction, in which a smoother disk-structure tends to have a higher prior probability. We analyzed simultaneous optical and near-infrared photometric data of early superhumps of the dwarf nova, V455 And using this technique. The reconstructed disk has two flaring parts in the outermost region of the disk. These parts are responsible for the primary and secondary maxima of the light curves. The height-to-radius ratio is h/r=0.20-0.25 in the outermost region. In addition to the outermost flaring structures, flaring arm-like patterns can be seen in an inner region of the reconstructed disk. The overall profile of the reconstructed disk is reminiscent of the disk structure that is deformed by the tidal effect. However, an inner arm-like pattern, which is responsible for the secondary minimum in the light curve, cannot be reproduced only by the tidal effect. It implies the presence of another mechanism that deforms the disk structure. Alternatively, the temperature distribution of the disk could be non-axisymmetric. We demonstrate that the disk structure with weaker arm-like patterns is optimal in the model including the irradiation effect. However, the strongly irradiated disk gives quite blue colors, which may conflict with the observation. Our results suggest that the amplitude of early superhumps depends mainly on the height of the outermost flaring regions of the disk. We predict that early superhumps can be detected with an amplitude of >0.02 mag in about 90% of WZ Sge stars.
Article · Mar 2012
• ##### CC Sculptoris: A superhumping intermediate polar
[Show abstract] [Hide abstract] ABSTRACT: We present high speed optical, spectroscopic and Swift X-ray observations made during the dwarf nova superoutburst of CC Scl in November 2011. An orbital period of 1.383 h and superhump period of 1.443 h were measured, but the principal new finding is that CC Scl is a previously unrecognised intermediate polar, with a white dwarf spin period of 389.49 s which is seen in both optical and Swift X-ray light curves only during the outburst. In this it closely resembles the old nova GK Per, but unlike the latter has one of the shortest orbital periods among intermediate polars.
Full-text · Article · Aug 2012
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• ##### Discovery of Superhumps during a Normal Outburst of SU Ursae Majoris
[Show abstract] [Hide abstract] ABSTRACT: We report on time-resolved photometry during a 2012 January normaloutburst of SU UMa. The light curve shows hump-like modulations with a period of 0.07903(11) d, which coincides with the known superhump period of SU UMa during superoutbursts. We interpret this as superhump, based on the observed periodicity, profiles of the averaged light curve, and the $g'-I_{\rm c}$ variation during the normal outburst. This is the first case that superhumps are detected during an isolated normal outburst of SU UMa-type dwarf novae. The present result strongly suggests that the radius of the accretion disk already reaches the 3:1 resonance even in the midst of the supercycle.
Article · Oct 2012
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