A5013891205- Stellar, planetary, and galactic studies
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Astrophysics and Star Formation Studies
- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- High-pressure geophysics and materials
- Historical Astronomy and Related Studies
- History and Developments in Astronomy
- Planetary Science and Exploration
- Atmospheric Ozone and Climate
- Adaptive optics and wavefront sensing
- CCD and CMOS Imaging Sensors
- Ionosphere and magnetosphere dynamics
- Heat Transfer and Boiling Studies
- Laser-Plasma Interactions and Diagnostics
- Geophysics and Gravity Measurements
- Heat Transfer and Optimization
- Calibration and Measurement Techniques
- Law, logistics, and international trade
Subaru (Japan)
2019-2025
National Astronomical Observatory of Japan
2016-2025
National Institutes of Natural Sciences
2017-2025
Kyoto University
2013-2024
Tokyo Institute of Technology
2024
Okayama University
2019-2022
The University of Tokyo
1987-2017
Kumamoto University
2013-2015
Institute of Astronomy
2013-2014
National Research Institute of Astronomy and Geophysics
2014
Recent observations of solar type stars with the Kepler satellite by Maehara et al. have revealed existence superflares (with energy 10^33 - 10^35 erg) on Sun-like stars, which are similar to our Sun in their surface temperature (5600 K 6000 K) and slow rotation (rotational period > 10 days). From statistical analysis these superflares, it was found that 10^34 erg occur once 800 years 5000 stars. In this paper, we examine whether could present through use simple order-of-magnitude estimates...
By extending our previous study by Maehara et al., we searched for superflares on G-type dwarfs (solar-type stars) using Kepler data a longer period (500 days) than that (120 in study. As result, found 1547 279 dwarfs, which is much more the 365 148 stars. Using these new data, studied statistical properties of occurrence rate superflares, and confirmed results, i.e., (dN/dE) versus flare energy (E) shows power-law distribution with dN/dE∝E−α, where α ∼ 2. It interesting this roughly similar...
We searched for superflares on solar-type stars using Kepler data with 1 min sampling in order to detect short duration. found 187 23 whose bolometric energy ranges from the of $10^{32}$ erg $10^{36}$ erg. Some show multiple peaks peak separation $100$-$1000$ seconds which is comparable periods quasi-periodic pulsations solar and stellar flares. Using these new combined results 30 sampling, we occurrence frequency ($dN/dE$) as a function flare ($E$) shows power-law distribution ($dN/dE...
Abstract We report the latest view of Kepler solar-type (G-type main-sequence) superflare stars, including recent updates with Apache Point Observatory (APO) 3.5 m telescope spectroscopic observations and Gaia -DR2 data. First, we newly conducted APO 18 stars found from 1-minute time-cadence More than half (43 stars) are confirmed to be “single” among 64 in total that have been spectroscopically investigated so far this our previous Subaru/HDS observations. The measurements v sin i...
Young solar-type stars frequently produce superflares, serving as a unique window into the young Sun-Earth environments. Large solar flares are closely linked to coronal mass ejections (CMEs) associated with filament/prominence eruptions, but its observational evidence for stellar superflares remains scarce. Here, we present 12-day multi-wavelength campaign observation of star EK Draconis (G1.5V, 50-120 Myr age) utilizing TESS, NICER, and Seimei telescope. The has previously exhibited...
Abstract We conducted the time-resolved simultaneous optical spectroscopic and photometric observations of mid-M-dwarf flare stars YZ CMi, EV Lac, AD Leo. Spectroscopic were obtained using Apache Point Observatory 3.5 m Small Moderate Aperture Research Telescope System 1.5 telescopes during 31 nights. Among 41 detected flares, seven flares showed clear blue wing asymmetries in H α line, with various correspondences properties. The duration range from 20 minutes to 2.5 hr, including a showing...
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...
Abstract Recently, many superflares on solar-type stars have been discovered as white-light flares (WLFs). The statistical study found a correlation between their energies ( E ) and durations τ ): <?CDATA $\tau \propto {E}^{0.39}$?> , similar to those of solar hard/soft X-ray flares, {E}^{0.2\mbox{--}0.33}$?> . This indicates universal mechanism energy release stellar i.e., magnetic reconnection. We here carried out research 50 WLFs observed with Solar Dynamics Observatory /HMI examined the...
Kepler data from G-, K-, and M-type stars are used to study conditions that lead superflares with energies above 1034 erg. From the 117,661 included, 380 show a total of 1690 such events. We whether parameters, like effective temperature or rotation rate, have any effect on superflare occurrence rate energy. With increasing we observe decrease in which is analogous previous findings dynamo activity temperature. For slowly rotating stars, find quadratic increase mean up critical point, after...
We report the latest statistical analyses of superflares on solar-type (G-type main-sequence; effective temperature is 5100 - 6000 K) stars using all $Kepler$ primary mission data, and $Gaia$-DR2 (Data Release 2) catalog. updated flare detection method from our previous studies by high-pass filter to remove rotational variations caused starspots. also examined sample biases frequency superflares, taking into account gyrochronology completeness. The size Sun-like (effective 5600 K rotation...
Solar flares are often accompanied by filament/prominence eruptions ($\sim10^{4}$ K and $\sim 10^{10-11}$ cm$^{-3}$), sometimes leading to coronal mass ejections (CMEs) that directly affect the Earth's environment. `Superflares' found on some active solar-type (G-type main-sequence) stars, but association of filament eruptions/CMEs has not been established. Here we show our optical spectroscopic observation young star EK Draconis reveals evidence for a stellar eruption associated with...
In this paper, we present the results from spectroscopic and photometric observations of M-type flare star YZ CMi in framework Optical Infrared Synergetic Telescopes for Education Research (OISTER) collaborations during Transiting Exoplanet Survey Satellite (TESS) observation period. We detected 145 white-light flares TESS light curve 4 H$\alpha$ OISTER performed between 2019-01-16 2019-01-18. Among them, 3 were associated with flares. However, one them did not show clear brightening...
Abstract The Carrington flare in 1859 September is a benchmark, as the earliest reported solar and an event with one of greatest terrestrial impacts. To date, no rigorous estimate energy this has been made on basis only direct observation available, its white-light emission. Here, we exploit historical observations to obtain magnitude express it terms GOES soft X-ray class. From Carrington’s original drawings, estimated area flaring region be 116 ± 25 msh. account allows us blackbody...
Abstract We conducted four-night multiwavelength observations of an active M-dwarf star EV Lacertae on 2022 October 24–27 with simultaneous coverage soft X-rays (NICER; 0.2–12 keV, Swift XRT; 0.2–10 keV), near-ultraviolet (Swift UVOT/UVW2; 1600–3500 Å), optical photometry (TESS; 6000–10000 and spectroscopy (Nayuta/MALLS; 6350–6800 Å). During the campaign, we detected a flare starting at 12:28 UTC 25 white-light bolometric energy 3.4 × 1032 erg. At about 1 h after this peak, our Hα spectrum...
We performed simple spot-model calculations for quasi-periodic brightness variations of solar-type stars showing superflares, by using Kepler photometric data. Most superflare show modulations with the typical period one to a few tens days. Our results indicate that these can be explained rotation star fairly large starspots. Using result analysis, we investigated relation between energy and frequency superflares period. Stars relatively slower rates still produce flares are as energetic...
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...
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we studied 86 SU UMa-type dwarf novae. We confirmed general trends such as relation between period derivatives and orbital periods. There are some systems showing positive despite long observed 2011 outburst of WZ Sge-type nova BW Scl, recorded an O-C diagram similar to those previously known The OT J184228.1+483742 showed unusual pattern double outbursts composed with early superhumps one ordinary superhumps. propose...
Stellar coronal mass ejections (CMEs) have recently received much attention for their impacts on exoplanets and stellar evolution. Detecting prominence eruptions, the initial phase of CMEs, as blue-shifted excess component Balmer lines is a technique to capture CMEs. However, most eruptions identified thus far been slow less than surface escape velocity. Therefore, whether these were developing into CMEs remained unknown. In this study, we conducted simultaneous optical photometric...
Starspots and stellar flares are indicators of magnetic activity.The energy stored around spots is thought to be the origin flares, but connection not completely understood. To investigate relation between spot locations deduced from light curves occurrence therein, we perform starspot modeling for TESS three M-dwarf flare stars, AU Mic, YZ CMi, EV Lac, using code implemented in Paper I. The enables deduce multiple stellar/spot parameters by adaptive parallel tempering algorithm efficiently....
Abstract Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 51 SU UMa-type dwarf novae, mainly observed during 2010–2011 season. Although most new data systems with short periods basically confirmed findings (ibid.) and (2010, 62, 1525), long-period system GX Cas showed an exceptionally large positive-period derivative. An analysis public Kepler V344 Lyr V1504 Cyg yielded less-striking stage transitions. In Lyr, there was a...
We report on the results of high dispersion spectroscopy two `superflare stars', KIC 9766237, and 9944137 with Subaru/HDS. Superflare stars are G-type main sequence stars, but show gigantic flares compared to Sun, which have been recently discovered in data obtained Kepler spacecraft. Though most these thought a rotation period shorter than 10 days basis photometric variabilities, targets present paper estimated 21.8 d, 25.3 d. Our spectroscopic clarified that stellar parameters similar...
ABSTRACT The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption 10 times, including yearly eruptions from 2008 to 2014. With a measured recurrence period of <?CDATA ${P}_{\mathrm{rec}}=351\pm 13$?> days (we believe the true value be half this) and white dwarf very close Chandrasekhar limit, has become leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations 2013 2014 eruptions, we initiated campaign ensure early...
The current progress in the detection of terrestrial type exoplanets has opened a new avenue characterization exoplanetary atmospheres and search for biosignatures life with upcoming ground-based space missions. To specify conditions favorable origin, development sustainment as we know it other worlds, need to understand nature astrospheric, atmospheric surface environments habitable zones around G-K-M dwarfs including our young Sun. Global environment is formed by propagated disturbances...
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...