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 Rosat Observations of Stellar Flares

1994 ◽  
Vol 142 ◽  
pp. 735-742
Author(s):  
J. H. M. M. Schmitt
Keyword(s):  
Time Variability ◽  
X Rays ◽  
Late Type ◽  
X Ray ◽  
Stellar Flares ◽  
Long Duration ◽  
Sky Survey ◽  
Pointed Observation ◽  
Flare Stars ◽  
First Time

AbstractX-ray observations of stellar flares obtained during the ROSAT all-sky survey as well as in the ROSAT pointing program are discussed. The ROSAT all-sky survey allowed—for the first time—an unbiased search for stellar flares among all types of stars. A fundamentally new result obtained is that flares can occur on all types of late-type stars, thus supporting the view that the X-ray emission from these stars is controlled by magnetic processes. Long-duration flares can be studied with the all-sky survey data particularly well, and an especially well-observed long-duration flare event on the flare star EV Lacertae is presented and discussed in detail. Finally, the issue of time variability on the shortest detectable timescales and the question of microflaring is discussed using ROSAT data from a pointed observation of UV Ceti.Subject headings: stars: coronae — stars: flare — stars: late-type — X-rays: stars

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 Activity and rotation of the X-ray emitting Kepler stars

2019 ◽  
Vol 628 ◽  
pp. A41 ◽  
Author(s):  
D. Pizzocaro ◽  
B. Stelzer ◽  
E. Poretti ◽  
S. Raetz ◽  
G. Micela ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Light Curves ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photometric Variability ◽  
X Ray ◽  
Rotation Periods ◽  
Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

scholarly journals X-ray Flare Rate of T Tauri Stars in Taurus

1995 ◽  
Vol 151 ◽  
pp. 216-217
Author(s):  
R. Neuhäuser ◽  
Th. Preibisch
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
T Tauri Stars ◽  
Medium Size ◽  
Late Type ◽  
Large Sample ◽  
X Ray ◽  
T Tauri ◽  
Sky Survey ◽  
Low Mass

AbstractWe study the X-ray emission of several hundred (young, low-mass, late-type, pre-main sequence) T Tauri stars (TTS) in the Taurus T association, a nearby well-studied region of ongoing star formation. We report on X-ray emission variability of TTS as observed with the flux-limited ROSAT All-Sky Survey (RASS). Since RASS observations are spatially unbiased, we can investigate the X-ray flare rate of TTS on a large sample. We find that large flares are very rare (once per year), while medium-size flares can occur once in ∼ 40 days.

scholarly journals Evolution of Stellar Activity in Early Post-Main-Sequence Phases

1993 ◽  
Vol 137 ◽  
pp. 648-650
Author(s):  
A. Maggio ◽  
S. Sciortino ◽  
L. Bianchi ◽  
F.R. Harnden ◽  
R. Rosner
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Activity Level ◽  
Sensitivity Threshold ◽  
Moderate Increase ◽  
X Rays ◽  
Late Type ◽  
Lower Mass ◽  
X Ray ◽  
Radiative Emission

We present preliminary observational evidences on the variation of the activity level in late type stars, during the evolutionary phases on the main sequence and beyond. We have selected a sample of 51 stars (Fig. 1), lying mostly along evolutionary tracks between 1.3 and 1.7 solar masses, which have been observed in soft X-rays with the Einstein Observatory, and in UV with IUE (Maggio et al. 1990; Haisch et al.1990). Two ROSAT targets, and four new IUE observations are also included.We find that the radiative emission from the outer atmospheres of stars with M > 1.6M⊙ seems to behave differently than for stars with lower mass.On the main sequence, the X-ray luminosity of most stars with B-V < 0.42 (spectral type F3) is relatively low, at Lx ~ 3 × 1028erg s-1 (Fig. 2). In the early evolutionary phases beyond the main sequence, the X-ray luminosity of the higher mass stars tend to increase sistematically up to ~ 1030erg s-1, while the lower mass stars show an initial moderate increase followed by a drop, at B-V ~ 0.6, below our sensitivity threshold.

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 Cool Stars in the EUV: Spectral and Structural Variability

1996 ◽  
Vol 152 ◽  
pp. 89-96
Author(s):  
Alexander Brown
Keyword(s):  
Spectral Region ◽  
Coronal Temperature ◽  
Coronal Emission ◽  
X Ray ◽  
Cool Stars ◽  
Flare Stars ◽  
M Dwarf ◽  
Coronal Electron ◽  
Very High ◽  
Combined Data

EUV observations of RS CVn binaries and M dwarf flare stars are used to illustrate the variability of coronal emission seen in EUVE spectra and photometry. The EUVE emission line spectra show that the quiescent coronae of active stars are extremely hot (≥10 million K) and flares, which are even hotter, are common. Spectral sequences showing the evolution of flare temperature and density are presented. Very high coronal electron densities (log Ne ~ 13) have been detected during M dwarf flares. EUVE data for the RS CVn binary HR1099 are compared with those from simultaneous observations in other spectral regions, including X-ray (ASCA), ultraviolet (IUE), and radio (VLA, AT) data. These combined data show that the peak coronal temperature is above the sensitivity of EUVE and that the time of maximum flare brightness is spectral region dependent.

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.

scholarly journals A Mass-Eccentricity Correlation in Spectroscopic and Visual Binary Orbits

1982 ◽  
Vol 69 ◽  
pp. 119-122
Author(s):  
J. Dommanget
Keyword(s):  
Mass Loss ◽  
Total Mass ◽  
Main Sequence ◽  
Orbital Evolution ◽  
Late Type ◽  
Orbital Eccentricity ◽  
Main Sequence Stars ◽  
Visual Binary ◽  
Mass Eccentricity

Looking for a possible explanation for the debated existence of a correlation between period and eccentricity in binary orbits [of which a diagramme is given in fig. 1.) we made the assumption that the orbital evolution of the binaries could be the consequence of a substantial mass-loss of their components even when these components are late type main sequence stars.This led first to the consideration of various classes of the areal constant. But it.immediately appeared much better to consider for each of such classes, the total mass of each system instead of its orbital eccentricity and thus to consider the mass-period diagramme rather than the period-eccentricity diagramme. Eleven such diagrammes were considered.

scholarly journals A giant X-ray flare from a B9 + Post-T Tauri system detected by EXOSAT

1989 ◽  
Vol 104 (2) ◽  
pp. 131-134
Author(s):  
G. Tagliaferri ◽  
P. Giommi ◽  
L. Angelini ◽  
J.P. Osborne ◽  
R. Pallavicini
Keyword(s):  
Tauri Star ◽  
Optical Methods ◽  
Type I ◽  
Late Type ◽  
Optical Studies ◽  
X Ray ◽  
Visual Binary ◽  
T Tauri ◽  
Seyfert Type

AbstractWe report the serendipitous discovery by EXOSAT of a flaring X-ray source in the field of the Seyfert type I galaxy III ZW 2. We identify this source with the visual binary HD 560 (B9V + G5Ve) and argue that virtually all of the observed X-ray flux, including the flare, came from its late-type component (HD 560 B). Optical studies have lead to the identification of HD 560 B as a post-T Tauri star. Since these stars are difficult to detect by optical methods, X-ray observations may prove to be the best way to identify them.

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