scholarly journals Time-resolved spectroscopy and photometry of M dwarf flare star YZ Canis Minoris with OISTER and TESS: Blue asymmetry in the Hα line during the non-white light flare

2020 ◽  
Author(s):  
Hiroyuki Maehara ◽  
Yuta Notsu ◽  
Kousuke Namekata ◽  
Satoshi Honda ◽  
Adam F Kowalski ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
White Light ◽  
Near Infrared ◽  
Empirical Relation ◽  
Flare Star ◽  
Time Resolved ◽  
X Ray ◽  
Stellar Flares ◽  
The Difference ◽  
Upward Moving

Abstract In this paper, we present the results from spectroscopic and photometric observations of the M-type flare star YZ CMi in the framework of the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) collaborations during the Transiting Exoplanet Survey Satellite (TESS) observation period. We detected 145 white-light flares from the TESS light-curve and four Hα flares from the OISTER observations performed between 2019 January 16 and 18. Among them, three Hα flares were associated with white-light flares. However, one of them did not show clear brightening in the continuum; during this flare, the Hα line exhibited blue asymmetry which lasted for ∼60 min. The line-of-sight velocity of the blueshifted component is in the range from −80 to −100 km s−1. This suggests that there can be upward flows of chromospheric cool plasma even without detectable red/near-infrared (NIR) continuum brightening. By assuming that the blue asymmetry in the Hα line was caused by a prominence eruption on YZ CMi, we estimated the mass and kinetic energy of the upward-moving material to be 1016–1018 g and 1029.5–1031.5 erg, respectively. The estimated mass is comparable to expectations from the empirical relation between the flare X-ray energy and mass of upward-moving material for stellar flares and solar coronal mass ejections (CMEs). In contrast, the estimated kinetic energy for the non-white-light flare on YZ CMi is roughly two orders of magnitude smaller than that expected from the relation between flare X-ray energy and kinetic energy for solar CMEs. This could be understood by the difference in the velocity between CMEs and prominence eruptions.

scholarly journals The Future of X-Ray Time-Domain Surveys

2011 ◽  
Vol 7 (S285) ◽  
pp. 199-206
Author(s):  
Daryl Haggard ◽  
Gregory R. Sivakoff
Keyword(s):  
Time Domain ◽  
Gamma Ray ◽  
High Energy ◽  
Galactic Centre ◽  
Time Resolved ◽  
X Ray ◽  
Stellar Flares ◽  
Time Domain Data ◽  
Deep Fields ◽  
Energy Dependent

AbstractModern X-ray observatories yield unique insight into the astrophysical time domain. Each X-ray photon can be assigned an arrival time, an energy and a sky position, yielding sensitive, energy-dependent light curves and enabling time-resolved spectra down to millisecond time-scales. Combining those with multiple views of the same patch of sky (e.g., in the Chandra and XMM-Newton deep fields) so as to extend variability studies over longer baselines, the spectral timing capacity of X-ray observatories then stretch over 10 orders of magnitude at spatial resolutions of arcseconds, and 13 orders of magnitude at spatial resolutions of a degree. A wealth of high-energy time-domain data already exists, and indicates variability on timescales ranging from microseconds to years in a wide variety of objects, including numerous classes of AGN, high-energy phenomena at the Galactic centre, Galactic and extra-Galactic X-ray binaries, supernovæ, gamma-ray bursts, stellar flares, tidal disruption flares, and as-yet unknown X-ray variables. This workshop explored the potential of strategic X-ray surveys to probe a broad range of astrophysical sources and phenomena. Here we present the highlights, with an emphasis on the science topics and mission designs that will drive future discovery in the X-ray time domain.

scholarly journals A statistical study of plasmoids associated with a post-CME current sheet

2020 ◽  
Vol 644 ◽  
pp. A158
Author(s):  
Ritesh Patel ◽  
Vaibhav Pant ◽  
Kalugodu Chandrashekhar ◽  
Dipankar Banerjee
Keyword(s):  
Current Sheet ◽  
White Light ◽  
Extreme Ultraviolet ◽  
Empirical Relation ◽  
Pass Band ◽  
Diffusion Region ◽  
Average Width ◽  
Average Speed ◽  
Mean Width ◽  
Upward Moving

Context. Coronal mass ejections (CMEs) are often observed to be accompanied by flare, current sheets, and plasmoids/plasma blobs. 2D and 3D numerical simulations and observations reported plasmoids moving upward as well as downward along the current sheet. Aims. We aim to investigate the properties of plasmoids observed in the current sheet formed after an X-8.3 flare and followed by a fast CME eruption on September 10, 2017 using extreme-ultraviolet (EUV) and white-light coronagraph images. The main goal is to understand the evolution of plasmoids in different spatio-temporal scales using existing ground- and space-based instruments. Methods. We identified the plasmoids manually and tracked them along the current sheet in the successive images of Atmospheric Imaging Assembly (AIA) taken at the 131 Å pass band and in running difference images of the white-light coronagraphs, K-Cor and LASCO/C2. The location and size of the plasmoids in each image were recorded and analyzed, covering the current sheet from the inner to outer corona. Results. We find that the observed current sheet has an Alfvén Mach number of 0.018−0.35. The fast reconnection is also accompanied by plasmoids moving upward and downward. We identified 20 downward-moving and 16 upward-moving plasmoids using AIA 131 Å images. In white-light coronagraph images, only upward-moving plasmoids are observed. Our analysis shows that the downward-moving plasmoids have an average width of 5.92 Mm, whereas upward-moving blobs have an average size of 5.65 Mm in the AIA field of view (FOV). The upward-moving plasmoids, when observed in the white-light images, have an average width of 64 Mm in the K-Cor, which evolves to a mean width of 510 Mm in the LASCO/C2 FOV. Upon tracking the plasmoids in successive images, we find that downward- and upward-moving plasmoids have average speeds of ∼272 km s−1 and ∼191 km s−1, respectively in the EUV channels of observation. The average speed of plasmoids increases to ∼671 km s−1 and ∼1080 km s−1 in the K-Cor and LASCO/C2 FOVs, respectively, implying that the plasmoids become super-Alfvénic when they propagate outward. The downward-moving plasmoids show an acceleration in the range of −11 km s−1 to over 8 km s−1. We also find that the null point of the current sheet is located at ≈1.15 R⊙, where bidirectional plasmoid motion is observed. Conclusions. The width distribution of plasmoids formed during the reconnection process is governed by a power law with an index of −1.12. Unlike previous studies, there is no difference in trend for small- and large-scale plasmoids. The evolution of width W of the plasmoids moving at an average speed V along the current sheet is governed by an empirical relation: V = 115.69W0.37. The presence of accelerating plasmoids near the neutral point indicates a longer diffusion region as predicted by MHD models.

scholarly journals Estimating signal and noise of time-resolved X-ray solution scattering data at synchrotrons and XFELs

2020 ◽  
Vol 27 (3) ◽  
pp. 633-645
Author(s):  
Jungmin Kim ◽  
Jong Goo Kim ◽  
Hosung Ki ◽  
Chi Woo Ahn ◽  
Hyotcherl Ihee
Keyword(s):  
Quantum Noise ◽  
Structural Information ◽  
Signal To Noise Ratio ◽  
Liquid Solution ◽  
Solution Phase ◽  
Scattering Data ◽  
Time Resolved ◽  
X Ray ◽  
The Future ◽  
The Difference

Elucidating the structural dynamics of small molecules and proteins in the liquid solution phase is essential to ensure a fundamental understanding of their reaction mechanisms. In this regard, time-resolved X-ray solution scattering (TRXSS), also known as time-resolved X-ray liquidography (TRXL), has been established as a powerful technique for obtaining the structural information of reaction intermediates and products in the liquid solution phase and is expected to be applied to a wider range of molecules in the future. A TRXL experiment is generally performed at the beamline of a synchrotron or an X-ray free-electron laser (XFEL) to provide intense and short X-ray pulses. Considering the limited opportunities to use these facilities, it is necessary to verify the plausibility of a target experiment prior to the actual experiment. For this purpose, a program has been developed, referred to as S-cube, which is short for a Solution Scattering Simulator. This code allows the routine estimation of the shape and signal-to-noise ratio (SNR) of TRXL data from known experimental parameters. Specifically, S-cube calculates the difference scattering curve and the associated quantum noise on the basis of the molecular structure of the target reactant and product, the target solvent, the energy of the pump laser pulse and the specifications of the beamline to be used. Employing a simplified form for the pair-distribution function required to calculate the solute–solvent cross term greatly increases the calculation speed as compared with a typical TRXL data analysis. Demonstrative applications of S-cube are presented, including the estimation of the expected TRXL data and SNR level for the future LCLS-II HE beamlines.

scholarly journals X-Ray Observations Of Stellar Flares

1983 ◽  
Vol 71 ◽  
pp. 255-272 ◽  
Author(s):  
Bernhard M. Haisch
Keyword(s):  
Optical Emission ◽  
Light Curves ◽  
Data Set ◽  
Time Resolved ◽  
X Ray ◽  
Uv Emission ◽  
Stellar Flares ◽  
History Of ◽  
Relationship Of ◽  
Lower Limits

ABSTRACTThe history of stellar X-ray flare observations prior to EINSTEIN is reviewed. X-ray light curves as measured by the IPC are then presented for all time resolved flare events discovered as of July 1982 in the EINSTEIN data set. These light curves are analyzed in terms of solar-like loop models to derive densities, temperatures, loop lengths, magnetic field strength lower limits, etc. The failure of the model to adequately represent the observations in the case of the YZ CMi flares is discussed. The relationship of X-ray to optical emission and X-ray to UV emission is considered from both an observational and a theoretical viewpoint. It is concluded that the characterization of a flare by a single, time averaged ratio, Lx /Lopt , is not physically significant.

scholarly journals Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER

2020 ◽  
Vol 72 (4) ◽  
Author(s):  
Kosuke Namekata ◽  
Hiroyuki Maehara ◽  
Ryo Sasaki ◽  
Hiroki Kawai ◽  
Yuta Notsu ◽  
...  
Keyword(s):  
Emission Line ◽  
White Light ◽  
High Energy ◽  
Lower Atmosphere ◽  
Line Profiles ◽  
X Ray ◽  
Energy Beam ◽  
Stellar Flares ◽  
Optical Continuum ◽  
M Dwarf

Abstract We report on multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with the Seimei Telescope (6150–7930 Å), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700–7500 Å), and NICER (Neutron Star Interior Composition Explorer; 0.2–12.0 keV), with the collaboration of the OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) program. Twelve flares are detected in total, including ten Hα, four X-ray, and four optical-continuum flares; one of them is a superflare with a total energy of ∼2.0 × 1033 erg. We found that: (1) during the superflare, the Hα emission line full width at 1/8 maximum dramatically increases to 14 Å from 8 Å in the low-resolution spectra (R ∼ 2000) accompanied by large white-light flares, (2) some weak Hα/X-ray flares are not accompanied by white-light emissions, and (3) the non-flaring emissions show clear rotational modulations in X-ray and Hα intensity in the same phase. To understand these observational features, one-dimensional hydrodynamic flare simulations are performed using the RADYN code. We find the simulated Hα line profiles with hard and high-energy non-thermal electron beams to be consistent with the initial phase line profiles of the superflares, while those with a softer and/or weak-energy beam are consistent with those in decay phases, indicating the changes in the energy fluxes injected to the lower atmosphere. Also, we find that the relation between the optical continuum and Hα intensity is nonlinear, which can be one cause of the non-white-light flares. The flare energy budget exhibits diversity in the observations and models, and more observations of stellar flares are necessary for constraining the occurrence of various emission line phenomena in stellar flares.

scholarly journals State-of-the-Art Observations and Modeling of Stellar Flares

2012 ◽  
Vol 10 (H16) ◽  
pp. 99-100
Author(s):  
Adam F. Kowalski ◽  
Suzanne L. Hawley
Keyword(s):  
White Light ◽  
Binary Systems ◽  
Light Emission ◽  
Continuum Emission ◽  
M Dwarfs ◽  
Time Resolved ◽  
Color Distribution ◽  
Nonthermal Electrons ◽  
White Light Continuum ◽  
Stellar Flares

Flares are observed on a wide variety of stellar types, ranging from closely orbiting binary systems consisting of an evolved member (RS CVn's) and young, nearby super-active M dwarfs (dMe's). The timescales and energies of flares span many orders of magnitude and typically far exceed the scales of even the largest solar flares observed. In particular, the active M dwarfs produce an energetic signature in the near-UV and optical continuum, which is often referred to as the white-light continuum. White-light emission has been studied in Johnson UBVR filters during a few large-amplitude flares, and the best emission mechanism that fits the broadband color distribution is a T~104 K blackbody (Hawley & Fisher 1992). Time-resolved blue spectra have revealed a consistent picture, with little or no Balmer jump and a smoothly rising continuum toward the near-UV (Hawley & Pettersen 1991). However, the most recent self-consistent radiative-hydrodynamic (RHD) models, which use a solar-type flare heating function from accelerated, nonthermal electrons, do not reproduce this emission spectrum. Instead, these models predict that the white-light is dominated by Balmer continuum emission from Hydrogen recombination in the chromosphere (Allred et al. 2006). Moreover, Allred et al. (2006) showed that the Johnson colors of the model prediction exhibit a broadband distribution similar to a blackbody with T~9000 K.

scholarly journals Analysis and modeling of the dynamics of the glow of calcium and hydrogen lines in solar and stellar flares

2021 ◽  
Vol 30 (1) ◽  
pp. 91-95
Author(s):  
Yurij Alekseevich Kupryakov ◽  
Konstantin Veniaminovich Bychkov ◽  
Oksana Mikhailovna Belova ◽  
Alexey Borisovich Gorshkov ◽  
Petr Heinzel ◽  
...  
Keyword(s):  
Solar Flares ◽  
Radiation Flux ◽  
Temporal Variations ◽  
Slow Heating ◽  
X Ray ◽  
Stellar Flares ◽  
Flare Stars ◽  
The Difference ◽  
Ev Lac ◽  
Hydrogen Lines

Abstract We present intensity curves of solar flares obtained in the Hα hydrogen line and CaII H, CaIR 8542Å lines using multichannel spectrographs of Ondřejov Observatory (Czech Republic) for the period 2000–2012. The general behavior of observed intensity curves is practically the same for all flares and is consistent with temporal variations of X-ray emission. However, our results differ significantly from those obtained by other authors for selected flare stars, for example, AD Leo; EV Lac; YZ CMi. We tried to explain the difference in the behavior of Ca II and Hα radiation flux by appearance of a shock wave during a flare and slow heating of the plasma.

Relationship between Changes in Cerebral Blood Volume During Hypoxic-ischemic Insult and Early Period after Insult

2021 ◽  
Author(s):  
Tsutomu Mitsuie ◽  
Shinji Nakamura ◽  
Yinmon Htun ◽  
Yasuhiro Nakao ◽  
Makoto Arioka ◽  
...  
Keyword(s):  
Blood Volume ◽  
Near Infrared ◽  
Cerebral Blood Volume ◽  
Brain Injuries ◽  
Treatment Strategies ◽  
Early Period ◽  
Additional Treatment ◽  
Time Resolved ◽  
Precise Prediction ◽  
The Difference

Abstract To achieve better outcomes in hypoxic-ischemic encephalopathy, categorizing the degree of the hypoxia-ischemia (HI) is important for selecting suitable candidates for therapeutic hypothermia and any additional treatment strategies. We previously developed a novel model of asphyxiated piglets with a uniform degree of histopathological brain injuries that survived for 5 days after insult and showed changes in cerebral blood volume (CBV) that reflected the severity of the brain injuries. However, little is known about the relationship between changes in CBV during and after insult. In this study, an HI event was induced by low inspired oxygen in 23 anesthetized newborn piglets, including three sham controls. CBV was measured using near-infrared time-resolved spectroscopy (TRS). Data were collected before, during, and 6 h after insult. The change in CBV was calculated as the difference between the peak CBV value during insult and the value at the end of insult. The decrease in CBV during insult was found to correlate with the increase in CBV within 6 h after insult. Heart rate exhibited a similar tendency to CBV but blood pressure did not. The CBV increment immediately after resuscitation provides a relatively precise prediction of the severity of HI insult.

scholarly journals Independence of Chromospheric Activity and Soft X-Ray Flaring on the Flare Star EV Lacertae

1989 ◽  
Vol 104 (2) ◽  
pp. 27-31
Author(s):  
C.W. Ambruster ◽  
B.R. Pettersen ◽  
S.L. Hawley ◽  
L.A. Coleman ◽  
S. Sciortino
Keyword(s):  
Flare Star ◽  
The Other ◽  
Significant Fraction ◽  
X Ray ◽  
Long Period ◽  
Chromospheric Activity ◽  
Other Hand ◽  
Stellar Flares ◽  
M Dwarf ◽  
Band Activity

AbstractEXOSAT observed the flare star EV Lacertae for 17 hr over 2 days in October 1985. Two flaring episodes were recorded. During a significant fraction of these observations, IUE, photometric and spectroscopic coverage was available. A 2-hour long period of X-ray flaring was observed during which there was no U-band activity and almost no chromospheric activity. On the other hand, two ΔU ~ 1° m° 5 optical flares produced normal chromospheric enhancements, but only a weak X-ray response. We suggest that these and a few other observations of stellar flares may imply the occasional existence of magnetically isolated regions in M-dwarf atmospheres.

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