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

Publications- Astronomical Society of Japan (Impact Factor: 2.01). 08/2009; 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_s bands) and MITSuME (g', Rc, and Ic 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 (~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. Comment: 14 pages, 12 figures, PASJ accepted

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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.
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    Makoto Uemura · Taichi Kato · Tomohito Ohshima · Hiroyuki Maehara
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    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.
    Publications- Astronomical Society of Japan 03/2012; 64(5). DOI:10.1093/pasj/64.5.92 · 2.01 Impact Factor
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