Seiichiro Kiyota - VSOLJ

Seiichiro Kiyota
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Seiichiro Kiyota
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VSOLJ
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Solar and Stellar Astrophysics (20)
 
Astrophysics (8)
 
High Energy Astrophysical Phenomena (3)

Publications Authored By Seiichiro Kiyota

We observed RZ LMi, which is renowned for the extremely (~19d) short supercycle and is a member of a small, unusual class of cataclysmic variables called ER UMa-type dwarf novae, in 2013 and 2016. In 2016, the supercycles of this object substantially lengthened in comparison to the previous measurements to 35, 32, 60d for three consecutive superoutbursts. We consider that the object virtually experienced a transition to the novalike state (permanent superhumper). Read More

How black holes accrete surrounding matter is a fundamental, yet unsolved question in astrophysics. It is generally believed that matter is absorbed into black holes via accretion disks, the state of which depends primarily on the mass-accretion rate. When this rate approaches the critical rate (the Eddington limit), thermal instability is supposed to occur in the inner disc, causing repetitive patterns of large-amplitude X-ray variability (oscillations) on timescales of minutes to hours. Read More

Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 128 SU UMa-type dwarf novae observed mainly during the 2015-2016 season and characterized these objects. Read More

We observed the first-ever recorded outburst of PM J03338+3320, the cataclysmic variable selected by proper-motion survey. The outburst was composed of a precursor and the main superoutburst. The precursor outburst occurred at least 5 d before the maximum of the main superoutburst. Read More

In 2015 March, the notable WZ Sge-type dwarf nova AL Com exhibited an unusual outburst with a recurrence time of ${\sim}$1.5 yr, which is the shortest interval of superoutbursts among WZ Sge-type dwarf novae. Early superhumps in the superoutburst light curve were absent, and a precursor was observed at the onset of the superoutburst for the first time in WZ Sge-type dwarf novae. Read More

The recurrent nova U Scorpii most recently erupted in 2010. Our collaboration observed the eruption in bands ranging from the Swift XRT and UVOT w2 (193 nm) to K-band (2200 nm), with a few serendipitous observations stretching down to WISE W2 (4600 nm). Considering the time and wavelength coverage, this is the most comprehensively observed nova eruption to date. Read More

2015Jul
Authors: Taichi Kato, Franz-Josef Hambsch, Pavol A. Dubovsky, Igor Kudzej, Berto Monard, Ian Miller, Hiroshi Itoh, Seiichiro Kiyota, Kazunari Masumoto, Daiki Fukushima, Hiroki Kinoshita, Kazuki Maeda, Jyunya Mikami, Risa Matsuda, Naoto Kojiguchi, Miho Kawabata, Megumi Takenaka, Katsura Matsumoto, Enrique de Miguel, Yutaka Maeda, Tomohito Ohshima, Keisuke Isogai, Roger D. Pickard, Arne Henden, Stella Kafka, Hidehiko Akazawa, Noritoshi Otani, Sakiko Ishibashi, Minako Ogi, Kenji Tanabe, Kazuyoshi Imamura, William Stein, Kiyoshi Kasai, Tonny Vanmunster, Peter Starr, Elena P. Pavlenko, Oksana I. Antonyuk, Kirill A. Antonyuk, Aleksei A. Sosnovskij, Nikolaj V. Pit, Julia V. Babina, Aleksandr Sklyanov, Rudolf Novak, Arto Oksanen, Shawn Dvorak, Raul Michel, Gianluca Masi, Colin Littlefield, Joseph Ulowetz, Sergey Yu. Shugarov, Polina Yu. Golysheva, Drahomir Chochol, Viktoriia Krushevska, Javier Ruiz, Tamas Tordai, Etienne Morelle, Richard Sabo, Hiroyuki Maehara, Michael Richmond, Natalia Katysheva, Kenji Hirosawa, William N. Goff, Franky Dubois, Ludwig Logie, Steve Rau, Irina B. Voloshina, Maksim V. Andreev, Kazuhiko Shiokawa, Vitaly V. Neustroev, George Sjoberg, Sergey Zharikov, Nick James, Greg Bolt, Tim Crawford, Denis Buczynski, Lewis M. Cook, Christopher S. Kochanek, Benjamin Shappee, Krzysztof Z. Stanek, Jose L. Prieto, Denis Denisenko, Hideo Nishimura, Masaru Mukai, Shizuo Kaneko, Seiji Ueda, Rod Stubbings, Masayuki Moriyama, Patrick Schmeer, Eddy Muyllaert, Jeremy Shears, Robert J. Modic, Kevin B. Paxson

Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during the 2014-2015 season and characterized these objects. Read More

2014Jun
Affiliations: 1Kyoto U

Continuing the project described by Kato et al. (2009, PASJ, 61, S395, arXiv:0905.1757), we collected times of superhump maxima for 56 SU UMa-type dwarf novae mainly observed during the 2013-2014 season and characterized these objects. Read More

2013Oct

Continuing the project described by Kato et al. (2009a, arXiv:0905.1757), we collected times of superhump maxima for SU UMa-type dwarf novae mainly observed during the 2012-2013 season. Read More

2013Jul
Affiliations: 1Kyoto U., 2Center for Backyard Astronomy Kleinkaroo, 3Vereniging Voor Sterrenkunde, 4VSOLJ, 5U. of Tokyo

We observed the 2012-2013 superoutburst of the newly identified transient SSS J122221.7-311523 and found that this object showed successive two superoutbursts. Superhumps grew in amplitude during the second superoutburst and showed a characteristic pattern of period change reflecting the growth of the superhump. Read More

2012Oct

Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we studied 86 SU UMa-type dwarf novae. Read More

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. Read More

We report on the spectral evolution of the enigmatic, very slow nova V5558 Sgr, based on the low-resolution spectra obtained at the Fujii-Bisei Observatory and the Bisei Astronomical Observatory, Japan during a period of 2007 April 6 to 2008 May 3. V5558 Sgr shows a pre-maximum halt and then several flare-like rebrightenings, which is similar to another very slow nova V723 Cas. In our observations, the spectral type of V5558 Sgr evolved from the He/N type toward the Fe II type during the pre-maximum halt, and then toward the He/N type again. Read More

We present optical and near-infrared (NIR) photometry of a classical nova, V2362 Cyg (= Nova Cygni 2006). V2362 Cyg experienced a peculiar rebrightening with a long duration from 100 to 240 d after the maximum of the nova. Our multicolor observation indicates an emergence of a pseudophotosphere with an effective temperature of 9000 K at the rebrightening maximum. Read More

We have observed the fast nova V5583 Sagittarii with five B, V, y, R_C, and I_C bands, and found that these multi-band light curves are almost identical with those of V382 Vel 1999 until at least 100 days after outburst. A supersoft X-ray phase of V382 Vel was detected with BeppoSAX about six months after outburst. V5583 Sgr outbursted a few days ago the discovery on 2009 August 6. Read More

We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of superhump period are found to be composed of three distinct stages: early evolutionary stage with a longer superhump period, middle stage with systematically varying periods, final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods less than 0. Read More

Two classical novae V1493 Aql and V2362 Cyg were known to exhibit unprecedented large-amplitude rebrightening during the late stage of their evolution. We analyzed common properties in these two light curves. We show that these unusual light curves are very well expressed by a combination of power-law decline, omnipresent in fast novae, and exponential brightening. Read More

We report a coordinated multi-band photometry of the RS Oph 2006 outburst and highlight the emission line free y-band photometry that shows a mid-plateau phase at y ~ 10.2 mag from day 40 to day 75 after the discovery followed by a sharp drop of the final decline. Such mid-plateau phases are observed in other two recurrent novae, U Sco and CI Aql, and are interpreted as a bright disk irradiated by the white dwarf. Read More

We report time-resolved CCD photometry of the cataclysmic variable EG Aquarii during the 2006 November outburst During the outburst, superhumps were unambiguously detected with a mean period of 0.078828(6) days, firstly classifying the object as an SU UMa-type dwarf nova. It also turned out that the outburst contained a precursor. Read More

V445 Pup (2000) is a unique object identified as a helium nova. Color indexes during the outburst are consistent with those of free-free emission. We present a free-free emission dominated light curve model of V445 Pup on the basis of the optically thick wind theory. Read More

2006Jul
Affiliations: 1Univ. of Tokyo, 2Kieo Univ., 3VSOLJ, 4VSOLJ, 5VSOLJ, 6VSOLJ, 7Osaka Kyoiku Univ., 8Osaka Kyoiku Univ., 9Osaka Kyoiku Univ., 10Osaka Kyoiku Univ., 11Osaka Kyoiku Univ., 12Osaka Kyoiku Univ., 13Osaka Kyoiku Univ., 14Osaka Kyoiku Univ.
Category: Astrophysics

We report a coordinated multi-band photometry of the RS Oph 2006 outburst and highlight the emission line free y-band photometry that shows a mid-plateau phase at y ~ 10.2 mag from day 40 to day 75 after the discovery followed by a sharp drop of the final decline. Such mid-plateau phases are observed in other two recurrent novae, U Sco and CI Aql, and are interpreted as a bright disk irradiated by the white dwarf. Read More

2002Aug
Affiliations: 1Kyoto University, 2Kyoto University, 3Kyoto University, 4Okayama University of Science
Category: Astrophysics

We report on unprecedented short-term variations detected in the optical flux from the black hole binary system, V4641 Sgr. Amplitudes of the optical fluctuations were larger at longer time scales, and surprisingly reached ~60% around a period of ~10 min. The power spectra of fluctuations are characterized by a power law. Read More

We report on time-series photometric observations in the earliest stages of superoutbursts of the extreme dwarf novae, AL Com and WZ Sge, which started on 2001 May after the 6 years quiescence and on 2001 July after the 23 years quiescence, respectively. We detected growth of ``early superhumps'' during the each rising stage. Our observations reject the mass transfer instability for the trigger of the superoutburst of WZ Sge stars, and show the existence of some relations between the ``early superhumps'' and the spiral structure, which give a hint of the origin of the ``early superhumps. Read More

We observed the 1998 November superoutburst of WX Cet, a dwarf nova originally proposed as a WZ Sge-like system. The observation established that WX Cet is an SU UMa-type dwarf nova with a mean superhump period of 0.05949(1) d, which is 2. Read More