A5056061558- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- High-pressure geophysics and materials
- Particle Accelerators and Free-Electron Lasers
- Astro and Planetary Science
- Laser-Plasma Interactions and Diagnostics
- Atomic and Molecular Physics
- Solar and Space Plasma Dynamics
- Galaxies: Formation, Evolution, Phenomena
- Ophthalmology and Visual Health Research
- Historical Astronomy and Related Studies
- Adaptive optics and wavefront sensing
- Particle physics theoretical and experimental studies
- Epilepsy research and treatment
- Geological Studies and Exploration
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- X-ray Spectroscopy and Fluorescence Analysis
- Geophysics and Gravity Measurements
- Superconducting Materials and Applications
- Spacecraft and Cryogenic Technologies
Kyoto University
2019-2025
University of Cape Town
2024-2025
South African Radio Astronomy Observatory
2024-2025
Astronomical Observatory
2025
University of Southampton
2024
Tohoku University
2020
We report multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with Seimei Telescope (6150--7930 {\AA}), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700--7500 NICER (Neutron Star Interior Composition Explorer; 0.2--12.0 keV), and collaborations OISTER (Optical Infrared Synergetic Telescopes for Education Research) program. Twelve flares are detected in total which include ten H$\alpha$, four X-ray, optical-continuum flares; one them is a superflare the...
Abstract Rapidly evolving transients form a new class of that show shorter timescales light curves than those typical core-collapse and thermonuclear supernovae. We performed systematic search for rapidly using deep data taken with the Hyper Suprime-Cam Subaru Strategic Program Transient Survey. By measuring 1824 transients, we identified five transients. Our samples are found in wide range redshifts (0.3 ≤ z 1.5) peak absolute magnitudes (−17 ≥ M i −20). The light-curve properties similar...
WZ Sge stars are highly evolved accreting white dwarf systems (AWDs) exhibiting remarkably large amplitude outbursts (a.k.a. super-outbursts), typically followed by short rebrightenings/echo outbursts. These have some of the lowest mass transfer rates among AWDs, making even low magnetic fields dynamically important. Such often invoked to explain phenomenology observed in these systems, such as their X-ray luminosity and long periods quiescence (30+ years). However, detection is very elusive...
Abstract Studying the early stages of transient events provides crucial information about fundamental physical processes in cataclysmic variables (CVs). However, determining an appropriate observation mode immediately after discovery a new presents challenges due to significant uncertainties regarding its nature. We developed framework designed for autonomous decision-making prompt follow-up observations CVs using Kanata $1.5$ m telescope. The system, named Smart Kanata, first estimates...
There remains debate over whether the accretion disk survives or is entirely disrupted after nova eruption. In our previous paper, Muraoka et al. (2024, PASJ, 76, 293) have photometrically demonstrated that surviving was expanded close to L1 point during optical plateau stage and then drastically shrank tidal truncation radius ended. To approach clarification of physical mechanism drives these structural changes, we conducted systematic analyses spectral evolution narrow emission line...
Abstract WZ Sge stars are highly evolved accreting white dwarf systems (AWDs) exhibiting remarkably large amplitude outbursts (a.k.a. super-outbursts), typically followed by short rebrightenings/echo outbursts. These have some of the lowest mass transfer rates among AWDs, making even low magnetic fields dynamically important. Such often invoked to explain phenomenology observed in these systems, such as their X-ray luminosity and long periods quiescence (30+ years). However, detection is...
Abstract We present our optical photometric observations of the 2022 eruption recurrent nova U Scorpii (U Sco) using 49152 data points over 70 d following peak. have also analyzed its soft X-ray (0.3–1 keV) light curve by Neil Gehrels Swift Observatory. During eruption, plateau stage started 13.8–15.0 and ended 23.8–25.0 after The 14.6–15.3 38.7–39.5 Both stages later had shorter durations, peaked earlier was less luminous compared to those during Sco 2010 eruption. These suggest that there...
ABSTRACT Many high-state cataclysmic variables (CVs) exhibit blue-shifted absorption features in their ultraviolet (UV) spectra – a smoking-gun signature of outflows. However, the impact these outflows on optical remains much more uncertain. During its recent outburst, eclipsing dwarf nova V455 And displayed strong emission lines whose cores were narrower than expected from Keplerian disc. Here, we explore whether disc + wind models developed for matching UV observations CVs can also account...
We present timing and spectral analysis results of the {\it NICER} NuSTAR} observations dwarf nova MASTER OT J030227.28$+$191754.5 during 2021--2022 outburst. The soft X-ray component was found to be dominated by blackbody radiation with a temperature $\sim$30 eV also showed prominent oxygen neon emission lines. luminosity exceeded 10$^{34}$ ergs s$^{-1}$, which is consistent theoretical predictions, then decreased more than an order magnitude in 3.5 days. inferred abundances optically-thin...
Abstract The lowest possible mass of ONeMg white dwarfs (WDs) has not been clarified despite its importance in the formation and evolution WDs. We tackle this issue by studying properties V1405 Cas (Nova Cassiopeiae 2021), which is an outlier given a combination very slow light-curve recently reported neon-nova identification. report rapid spectral initial phase, covering 9.88, 23.77, 33.94, 53.53, 71.79, 81.90 hr after discovery. first spectrum characterized lines from highly ionized...
IW And stars are a recently recognized subgroup of dwarf novae which characterized by (often repetitive) slowly rising standstills terminated brightening, but the exact mechanism for this variation is not yet identified. We have identified BO Cet, had been considered as novalike cataclysmic variable, new member based on behavior in 2019-2020. In addition to this, object showed nova-type outbursts 2020-2021, and superhumps having period 7.8% longer than orbital one developed at least during...
We report photometric and spectroscopic observations analysis of the 2019 superoutburst TCP J21040470+4631129. This object showed a 9-mag with early superhumps ordinary superhumps, which are features WZ Sge-type dwarf novae. Five rebrightenings were observed after main superoutburst. The spectra during post-superoutburst stage Balmer, He I possible sodium doublet features. mass ratio is derived as 0.0880(9) from period superhump. During third fifth rebrightenings, growing superoutbursts...
Many high-state cataclysmic variables (CVs) exhibit blue-shifted absorption features in their ultraviolet (UV) spectra -- a smoking-gun signature of outflows. However, the impact these outflows on {\em optical} remains much more uncertain. During its recent outburst, eclipsing dwarf nova V455 And displayed strong optical emission lines whose cores were narrower than expected from Keplerian disc. Here, we explore whether disc + wind models developed for matching UV observations CVs can also...
We present spectroscopic and photometric observations of 17 dwarf-nova superoutbursts obtained by KOOLS-IFU mounted on the 3.8 m telescope Seimei at Okayama Observatory Kyoto University through VSNET collaboration. Our for six outbursts were performed within 1 d from their optical peak. 11 objects (TCP J00590972+3438357. ASASSN-19ado, TCP J06073081-0101501, ZTF20aavnpug, ASASSN-19ady, MASTER OT J061642.05+435617.9, J20034647+1335125, ASASSN-20kv, ASASSN-20kw, J213908.79+161240.2,...
Abstract We present our spectroscopic observations of V455 Andromedae during the 2007 superoutburst. Our cover this superoutburst from around optical peak outburst to post-superoutburst stage. During early superhump phase, emission lines Balmer series, He i, ii, Bowen blend, and C iv/N iv blend were detected. The ii 4686 line exhibited a double-peaked profile, where single-peaked, which is unexpected its high inclination. In ordinary series transitioned profiles, high-ionization...
Abstract This study provides the results of simultaneous multicolor observations for first Visorsat (STARLINK-1436) and ordinary Starlink satellite (STARLINK-1113) in U, B, V, g′, r, i, RC, IC, $z$, J, H, Ks bands to quantitatively investigate extent which reduces its reflected light. Our are as follows: (1) most cases, is fainter than STARLINK-1113, sunshade on therefore contributes reduction sunlight; (2) magnitude at 550 km altitude (normalized magnitude) both satellites often reaches...
Superoutbursts in WZ Sge-type dwarf novae (DNe) are characterized by both early superhumps and ordinary originating from the 2:1 3:1 resonances, respectively. However, some DNe show a superoutburst lacking superhumps; it is not well established how these differ superoutbursts with an superhump phase. We report time-resolved photometric observations of DN V627 Peg during its 2021 superoutburst. The detection before peak highlights that this Peg, like {in} 2014, did feature duration stage B...
ABSTRACT The population of optical transients evolving within a time-scale few hours or day (so-called fast transients, FOTs) has recently been debated extensively. In particular, our understanding extragalactic FOTs and their rates is limited. We present search for with the Tomo-e Gozen high-cadence survey. Using data taken from 2019 August to 2022 June, we obtain 113 FOT candidates. Through light curve analysis cross-matching other survey data, find that most these candidates are in fact...
We present our optical photometric observations of the 2022 eruption recurrent nova U Scorpii (U Sco) using 49,152 data points over 70 d following peak. have also analyzed its soft X-ray (0.3--1 keV) light curve by Neil Gehrels Swift Observatory. During eruption, plateau stage started 13.8--15.0 and ended 23.8--25.0 after The 14.6--15.3 38.7--39.5 Both stages later had shorter durations, peaked earlier was less luminous compared to those during Sco 2010 eruption. These suggest that there...
We present a detailed study of the MASTER OT J030227.28+191754.5 outburst in 2021-2022, reaching an amplitude 10.2 mag and duration 60 d. The detections (1) double-peaked optical emission lines, (2) early ordinary superhumps, established that is extremely energetic WZ Sge-type dwarf nova (DN). Based on superhump observations, we obtained its orbital period mass ratio as 0.05986(1) d 0.063(1), respectively. These are within typical range low-mass-ratio DNe. According to binary parameters...
Abstract We present a detailed study of the MASTER OT J030227.28$+$191754.5 outburst in 2021–2022, which reached an amplitude $10.2\:$mag and duration $60\:$d. The detections (1) double-peaked optical emission lines, (2) early ordinary superhumps, established that is extremely energetic WZ Sge-type dwarf nova (DN). Based on superhump observations, we obtained its orbital period mass ratio as $0.05986(1)\:$d 0.063(1), respectively. These values are within typical range for low-mass-ratio DNe....
Studying the early stages of transient events provides crucial information about fundamental physical processes in cataclysmic variables (CVs). However, determining an appropriate observation mode immediately after discovery a new presents challenges due to significant uncertainties regarding its nature. We developed framework designed for autonomous decision making prompt follow-up observations CVs using Kanata 1.5-m telescope. The system, named Smart Kanata, first estimates class...
We made a time-resolved photometric campaign of the bright cataclysmic variable ASAS J071404+7004.3 in 2020. Inight et al. (2022, arXiv/2109.14514) recently published optical spectroscopy, X-ray observations and long- short-term variations. Although their results were correct many parts, they classified as VY Scl-type novalike object. By comparing ASAS-SN data this object IW And-type HO Pup, we showed that type classification was incorrect. outbursts from standstill followed by shallow dips,...
In the first days of WZ Sge-type dwarf nova (DN) outbursts, 2:1 resonance induces a spiral arm structure in accretion disk, which is observed as early superhumps optical light curves. This paper reports our observations an eclipsing DN PNV J00444033+4113068 during its 2021 superoutburst with 3.8m Seimei telescope and through VSNET collaboration. The eclipse analysis gave orbital period 0.055425534(1) d. Our confirmed amplitude 0.7 mag, largest among known DNe. More interestingly, became...