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

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(Impact Factor: 2.07). 08/2009; 61(5). 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.

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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.
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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.
No preview · Article · Jan 2012