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

2021 ◽  
Author(s):  
Kosuke Namekata ◽  
Hiroyuki Maehara ◽  
Ryo Sasaki ◽  
Hiroki Kawai ◽  
Yuta Notsu ◽  
...  
Keyword(s):  
X Ray ◽  
Stellar Flares ◽  
M Dwarf

scholarly journals X-Ray Emission from Stellar Flares: Exosat Results

1989 ◽  
Vol 104 (2) ◽  
pp. 17-20 ◽  
Author(s):  
R. Pallavicini ◽  
G. Tagliaferri
Keyword(s):  
Main Sequence ◽  
Late Type ◽  
X Ray ◽  
Visual Binary ◽  
Stellar Flares ◽  
Flare Stars ◽  
M Dwarf

AbstractWe present an overview of recent observations of stellar X-ray flares obtained with the EXOSAT Observatory. We discuss a few examples of flares from M dwarf flare stars, from RS CVn and Algol-type binaries, from single late-type stars (including a G0 dwarf and an A-type visual binary), and from pre-main-sequence objects. We also draw some general conclusions from the pieliminary analysis of the EXOSAT data sample.

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 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.

scholarly journals Stellar Flares: Observations and Theory

1989 ◽  
Vol 104 (2) ◽  
pp. 49-52
Author(s):  
Suzanne L. Hawley
Keyword(s):  
Scaling Law ◽  
Dynamic Scaling ◽  
X Ray ◽  
Temperature Distributions ◽  
Photometric And Spectroscopic Observations ◽  
Stellar Flares ◽  
Consistent Model ◽  
Self Consistent ◽  
Flare Model ◽  
Large Flare

AbstractPhotometric and spectroscopic observations of a very large flare on AD Leo are presented. A self consistent model of a flare corona, transition region and chromosphere is developed; in particular the chromospheric temperature distributions resulting from X-ray and EUV irradiation by coronae of various temperatures are determined. The predicted line fluxes in Hγ are compared to the observed line fluxes to find the coronal temperature as a function of time during the flare. This run of temperature with time is then compared with the predictions of an independent theoretical flare model based on a dynamic scaling law (see paper by Fisher and Hawley, these proceedings).

scholarly journals Hydrodynamic Models of Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 289-298
Author(s):  
Giovanni Peres
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Solar Flares ◽  
Impulsive Phase ◽  
Light Curves ◽  
Physical Parameters ◽  
The Sun ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

scholarly journals White-light continuum in stellar flares

2015 ◽  
Vol 11 (S320) ◽  
pp. 259-267 ◽  
Author(s):  
Adam F. Kowalski
Keyword(s):  
White Light ◽  
High Energy ◽  
Continuum Emission ◽  
Nonthermal Electrons ◽  
White Light Continuum ◽  
Optical Wavelength ◽  
Near Ultraviolet ◽  
Stellar Flares ◽  
Optical Continuum ◽  
M Dwarf

AbstractIn this talk, we discuss the formation of the near-ultraviolet and optical continuum emission in M dwarf flares through the formation of a dense, heated chromospheric condensation. Results are used from a recent radiative-hydrodynamic model of the response of an M dwarf atmosphere to a high energy flux of nonthermal electrons. These models are used to infer the charge density and optical depth in continuum emitting flare layers from spectra covering the Balmer jump and optical wavelength regimes. Future modeling and observational directions are discussed.

scholarly journals GJ 357 b

2020 ◽  
Vol 641 ◽  
pp. A113
Author(s):  
D. Modirrousta-Galian ◽  
B. Stelzer ◽  
E. Magaudda ◽  
J. Maldonado ◽  
M. Güdel ◽  
...  
Keyword(s):  
Large Scale ◽  
Systematic Errors ◽  
Small Mass ◽  
Activity Levels ◽  
M Dwarfs ◽  
X Ray ◽  
History Of ◽  
Age Relations ◽  
M Dwarf ◽  
Atmospheric Mass

Aims. In this paper we present a deep X-ray observation of the nearby M dwarf GJ 357 and use it to put constraints on the atmospheric evolution of its planet, GJ 357 b. We also analyse the systematic errors in the stellar parameters of GJ 357 in order to see how they affect the perceived planetary properties. Methods. By comparing the observed X-ray luminosity of its host star, we estimate the age of GJ 357 b as derived from a recent XMM-Newton observation (log Lx [erg s−1] = 25.73), with Lx− age relations for M dwarfs. We find that GJ 357 presents one of the lowest X-ray activity levels ever measured for an M dwarf, and we put a lower limit on its age of 5 Gyr. Using this age limit, we performed a backwards reconstruction of the original primordial atmospheric reservoir. Furthermore, by considering the systematic errors in the stellar parameters, we find a range of possible planetary masses, radii, and densities. Results. From the backwards reconstruction of the irradiation history of GJ 357 b’s we find that the upper limit of its initial primordial atmospheric mass is ~38 M⊕. An initial atmospheric reservoir significantly larger than this may have survived through the X-ray and ultraviolet irradiation history, which would not be consistent with current observations that suggest a telluric composition. However, given the relatively small mass of GJ 357 b, even accreting a primordial envelope ≳10 M⊕ would have been improbable as an unusually low protoplanetary disc opacity, large-scale migration, and a weak interior luminosity would have been required. For this reason, we discard the possibility that GJ 357 b was born as a Neptunian- or Jovian-sized body. In spite of the unlikelihood of a currently existing primordial envelope, volcanism and outgassing may have contributed to a secondary atmosphere. Under this assumption, we present three different synthetic IR spectra for GJ 357 b that one might expect, consisting of 100% CO2, 100% SO2, and 75% N2, 24% CO2 and 1% H2O, respectively. Future observations with space-based IR spectroscopy missions will be able to test these models. Finally, we show that the uncertainties in the stellar and planetary quantities do not have a significant effect on the estimated mass or radius of GJ 357 b.

scholarly journals Short-Duration X-ray Transients Observed With WATCH on Granat: Are Some of Them Related to Stellar Flares?

1995 ◽  
Vol 151 ◽  
pp. 158-163
Author(s):  
Alberto J. Castro-Tirado ◽  
Søren Brandt ◽  
Niels Lund ◽  
Igor Lapshov ◽  
Rashid Sunyaev
Keyword(s):  
Short Duration ◽  
Tauri Star ◽  
X Ray ◽  
T Tauri ◽  
Stellar Flares ◽  
Peculiar Stars

AbstractDuring 1990-92, the WATCH all-sky X-ray monitor on GRANAT has discovered 6 short-duration X-ray transients. We discuss their possible relationship to peculiar stars. Only one source, GRS 1100-77 seems to be related to a T Tauri star.

X-ray Spectral Synthesis in Hydrodynamic Flare Models

1990 ◽  
Vol 115 ◽  
pp. 126-131
Author(s):  
S. Serio ◽  
E. Antonucci ◽  
M.A. Dodero ◽  
G. Peres ◽  
F. Reale
Keyword(s):  
Solar Flares ◽  
Energy Deposition ◽  
Electron Beams ◽  
Spectral Synthesis ◽  
Theoretical Models ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Relativistic Electron Beams ◽  
Stellar Flares ◽  
Magnetically Confined

AbstractCompact solar flares are triggered by sudden energy release in magnetically confined plasma. This class of flares is well suited to be studied with numerical hydrodynamic models. In particular, one can compare the evolution of observed and synthetic X-ray spectra, computed under various assumptions for the mechanism of impulsive energy deposition, to constrain theoretical models and their parameter space. We discuss recent results on solar flares along this line, non thermal to models of energy depositions by relativistic electron beams. We shall also discuss possible applications of X-ray spectral synthesis to stellar flares.

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