A5074635577- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Astronomical Observations and Instrumentation
- Stellar, planetary, and galactic studies
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- SAS software applications and methods
- High-pressure geophysics and materials
- Astrophysics and Star Formation Studies
- Mechanics and Biomechanics Studies
- Astro and Planetary Science
- Laser-Plasma Interactions and Diagnostics
- Advanced Condensed Matter Physics
- Particle Accelerators and Free-Electron Lasers
- Solar and Space Plasma Dynamics
- Computational Physics and Python Applications
- Dark Matter and Cosmic Phenomena
- Geophysics and Gravity Measurements
- Ionosphere and magnetosphere dynamics
- Scientific Measurement and Uncertainty Evaluation
- Infrared Target Detection Methodologies
- Magnetic and transport properties of perovskites and related materials
- Radio Astronomy Observations and Technology
- Shoulder Injury and Treatment
The University of Tokyo
2024
Institute of Astronomy and Astrophysics, Academia Sinica
2014-2023
National Taiwan University
2014-2019
National Astronomical Observatory of Japan
2006-2018
Subaru (Japan)
2006-2018
Theodore Roosevelt High School
2017
Kyoto University
2001-2006
Kyoto Notre Dame University
2002
Abstract 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 superhump is found to be composed three distinct stages: an early evolutionary stage with a longer period, middle varying periods, final shorter, stable period. During stage, systems periods less than 0.08 d show positive derivatives. present observational characteristics these stages give greatly improved...
We present UBVRI light curves of BL Lacertae from May 2000 to January 2001, obtained by 24 telescopes in 11 countries. More than 15000 observations were performed that period, which was the extension Whole Earth Blazar Telescope (WEBT) campaign originally planned for July-August 2000. Rapid flux oscillations are all time, involving variations up a few tenths mag on hour time scales, and witnessing an intense intraday activity this source. Colour indexes have been derived coupling highest...
Abstract Continued from Kato et al. (2009, PASJ, 61, S395), we collected the times of superhump maxima for 68 SU UMa-type dwarf novae, mainly observed during 2009–2010 season. The newly obtained data confirmed basic findings reported in (ibid.): presence stages A–C and predominance positive period derivatives stage B systems with periods shorter than 0.07 d. There was a systematic difference longer 0.075 d between this study (ibid.). We suggest that possibly caused by relative lack...
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 transient such as cataclysmic variables, black hole binaries, supernovae gamma-ray bursts. The VSNET has been playing pioneering role establishing the field "transient object astronomy", by effectively incorporating modern advance observational astronomy electronic network, well collaborative progress theoretical...
BL Lacertae was the target of an extensive multiwavelength monitoring campaign in second half 2000. Simultaneous or quasi-simultaneous observations were taken at radio (UMRAO and Metsaehovi) optical(WEBT collaboration) frequencies, X-rays (BeppoSAX RXTE), VHE gamma-rays (HEGRA). The WEBT optical achieved unprecedented time coverage, virtually continuous over several 10 - 20 hour segments. It revealed intraday variability on scales ~ 1.5 hours evidence for spectral hardening associated with...
We report on time-series photometric observations in the earliest stages of superoutbursts extreme dwarf novae, AL Com and WZ Sge, which started 2001 May after 6 years quiescence July 23 quiescence, respectively. detected growth "early superhumps" during each rising stage. Our reject mass transfer instability for trigger superoutburst Sge stars, show existence some relations between spiral structure, gives a hint origin superhumps."
Abstract We report here on time-resolved photometric observations of the superoutburst a dwarf nova, RZ Leo, which occurred during 2000 December–2001 January. reveal following characteristics outburst based our observations: long duration, large amplitude, and existence two types superhumps — “early superhumps” “normal superhumps”. In addition to extremely low frequency outbursts, strongly indicate that Leo is fifth member WZ Sge-type novae. The orbital period 0.07651 d, remarkably longer...
Abstract We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated remnants the Large Magellanic Cloud: 0519–69.0, 0505–67.9 (DEM L71), and 0548–70.4. In first method, we use Hubble Space Telescope photometric measurements stars construct color–magnitude diagrams (CMDs) compare positions CMDs with those expected from theoretical post-impact evolution main-sequence or helium star companions. No obvious candidates are identified this...
Abstract We revealed that the dwarf nova 1RXS J232953.9+062814 is an SU UMa-type system with a superhump period of $ 66.774\pm 0.010 \,\mathrm{min}$. The short strongly indicates orbital this object below minimum cataclysmic variables. 4.04\pm 0.02$% longer than photometric during quiescence ($ 64.184\pm 0.003 \,\mathrm{min}$), which probably associated period. Although standard evolutionary scenario variables predicts lower mass-transfer rates in systems shorter periods, we found firm...
We report optical photometric observations of four superoutbursts the short-period dwarf nova TV Crv. This object experiences two types superoutbursts; one with a precursor and other without. The superhump period excess Crv are accurately determined to be d , respectively. large implies relatively mass ratio binary components (), though it has short orbital period. can explained by thermal-tidal instability model for systems having ratios. Our reveal that derivatives variable in distinct...
Abstract We observed RZ LMi, which is renowned for its extremely short (∼19 d) supercycle and a member of small, unusual class cataclysmic variables called ER UMa-type dwarf novae, in 2013 2016. In 2016, the supercycles this object substantially lengthened comparison to previous measurements 35, 32, 60 d three consecutive superoutbursts. consider that virtually experienced transition nova-like state (permanent superhumper). This behavior reproduced prediction thermal-tidal instability model...
Abstract We report on the evolution of superhumps and late in an ultrashort period dwarf nova, 1RXS J232953.9$+$062814, during superoutburst 2001 November. Ordinary were observed throughout a plateau phase, rapid fading rebrightening phase. During superhump increased with time at large rate $P_\mathrm{dot} = 1.19 \pm 0.24 \times 10^{-4}$. In conjunction phenomenon, these characteristics indicate that accretion disk expanded further outward from $3:1$ resonance radius, which caused amount...
The layered honeycomb magnet $\alpha$-RuCl$_3$ is the most promising candidate for a Kitaev quantum spin liquid (KQSL) that can host charge-neutral Majorana fermions. Recent studies have shown significant sample dependence of thermal transport properties, which are key probe quasiparticles in KQSL state, highlighting importance preparing high-quality single crystals $\alpha$-RuCl$_3$. Here, we present relatively simple and reliable method to grow We use two-step crystal growth consisting...
We report on the first time-series observations of a short outburst proposed intermediate polar HT Cam ($=$ RX J0757.0$+$6306). On 2001 December 29, we detected that object was undergoing bright at magnitude $m_\mathrm{vis}=12.2$. Following this detection, started international joint through VSNET. The light curve showed gradual decline for 0.5 d. plateau phase, rate dramatically increased to more than $4 \,\mathrm{mag} \,\mathrm{d}^{-1}$. Within 1.5 d from almost declined quiescent level....
We examined the VSNET light curve of unusual SU UMa-type dwarf nova V503 Cyg which is known to show a short (89 d) supercycle length and exceptionally small (a few) normal outbursts within supercycle. In 1999-2000, displayed frequent with typical recurrence times 7-9 d. The behavior during this period characteristic an usual length. On other hand, showed very infrequent in 2001-2002. Some superoutbursts were observed shorter than usual. remarkable alternations outbursting states support...
Abstract We report on optical observations during the first hour of gamma-ray burst (GRB) afterglow GRB 021004. Our revealed existence a short plateau phase, in which remained at almost constant brightness, before an ordinary rapid-fading phase. This phase lasted for about 2 hours from 0.024 to 0.10 d after burst, corresponds missing blank early light curve 990123. propose that can be interpreted as being natural evolution synchrotron emission forward shock region blast wave. The time when...
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 October, December and The recurrence cycle superoutburst (supercycle) is indicated be ~60 d, shortest among values known so far UMa stars close those ER stars. superhump periods measured during first two were 0.104885(93) 0.10623(16) respectively. A 0.10424(3)-d periodicity detected quiescence. change...
We present near-infrared spectra for five dwarf novae with short orbital periods. performed fittings of the spectral energy distributions (SEDs) by assuming a power-law distribution accretion disk and using template late-type dwarfs secondary star. Two are WZ Sge–or WX Cet-type stars, whose show water absorption features, one them shows K$\;$ I Na$\;$ lines in $J$-band. find that contributions to overall SED larger Sge stars than ER UMa stars. The fitting suggests M9 L1 type companions our...
We photometrically observed the VY Scl-type cataclysmic variable KR Aurigae after its final rise from fading episode in 2000-2001. Time-resolved observation revealed that light curve is dominated by persistent short-term variation with time-scales of minutes to tens minutes. On some nights, quasi-periodic variations periods 10--15 min were observed. No coherent was detected. The power spectral density has a law component (f^(-1.63)). temporal properties Aur present additional support for...
After 10 years of quiescence, HV Vir underwent a superoutburst in January 2002. We report time-series observations clearly revealing the period change ordinary superhumps during superoutburst. derived mean superhump 0.058260 d and positive derivative $7 \times 10^{-5}$. These results are good agreement with value obtained from 1992 also detected early superhumps, which were not recognized past outburst, possible rebrightening. Both them common characteristics WZ Sge-type stars.
We report on time-resolved CCD photometry of four outbursts a short-period SU UMa-type dwarf nova, V844 Herculis. successfully determined the mean superhump periods to be 0.05584(64) days, and 0.055883(3) for 2002 May superoutburst, 2006 April-May respectively. During October observations, we confirmed that outburst is normal outburst, which first recorded in Her. also examined period changes during superoutbursts, both showed increasing over course plateau stage. In order examine long-term...
Abstract We report on unprecedented short-term variations detected in the optical flux from black hole binary system, V4641 Sgr. The amplitudes of fluctuations were larger at longer time scales, and surprisingly reached $ \sim 60\%$ around a period \sim10 \,\mathrm{min}$. power spectra are characterized by law ($ \propto f^{-\alpha},\; \alpha \sim-1.7$). It is first case for binaries that emission was revealed to show large-amplitude given such spectrum. generally dominated outer portion an...
Abstract We report on photometric and spectroscopic observations of a possible halo black-hole X-ray nova, XTE J1118$ +$480 ($ =$ KV UMa) during outburst. Our monitoring the main outburst revealed that optical maximum as well onset precede those in region. This indicates event was an “outside-in” type its flux dominated by viscous heating, itself, not effect irradiation. Based these results, we suggest scenario analogous to superoutbursts SU UMa-type dwarf novae. predicts superhump...