scholarly journals Extreme‐Ultraviolet Flare Activity in Late‐Type Stars

2000 ◽  
Vol 541 (1) ◽  
pp. 396-409 ◽  
Author(s):  
Marc Audard ◽  
Manuel Gudel ◽  
Jeremy J. Drake ◽  
Vinay L. Kashyap
Keyword(s):  
Extreme Ultraviolet ◽  
Flare Activity ◽  
Late Type

scholarly journals IUE Observations of the Chromospheric Activity-Age Relation in Young Solar-Type Stars

1983 ◽  
Vol 102 ◽  
pp. 161-164
Author(s):  
Theodore Simon ◽  
Ann Merchant Boesgaard
Keyword(s):  
Magnetic Fields ◽  
Flare Activity ◽  
The Sun ◽  
Late Type ◽  
Cool Star ◽  
Opportune Time ◽  
Solar Type ◽  
Age Relation ◽  
Relationship Of ◽  
The Relationship

The difficulties of measuring magnetic fields in late-type stars other than the sun are well known, as one is reminded by other contributions to these Proceedings. This Symposium nevertheless comes at a very opportune time, as we are now at the point where we can begin to explore the relationship of stellar magnetism to flare activity and quiescent cool star chromospheres, transition regions (TRs), and coronae.

scholarly journals Rosat WFC EUV Observations of Ab Dor (And other Local Group Stars)

1993 ◽  
Vol 137 ◽  
pp. 658-661
Author(s):  
Barry J. Kellett ◽  
Gordon E. Bromage
Keyword(s):  
Energy Range ◽  
Local Group ◽  
Extreme Ultraviolet ◽  
Broad Band ◽  
Full Description ◽  
Wide Field ◽  
Late Type ◽  
Rutherford Appleton Laboratory ◽  
Sky Survey ◽  
The Uk

The Rosat Observatory was launched on June 1st, 1990, and after a brief Performance Verification phase, performed an almost complete sky survey. One of the two main telescopes on the Observatory is the UK Wide Field Camera (WFC). The WFC is the first extreme ultraviolet (EUV) instrument to survey the whole sky, and during the survey detected several hundred active late-type stars.The WFC (Wells et al., 1990) was built by a consortium of five UK institutes, four Universities and the Rutherford Appleton Laboratory. During the all-sky survey, two filters were used. These allow broad-band photometry to be performed. The SIA filter (lexan/carbon/boron) and S2A filter (lexan/beryllium) were alternated on a one day basis. The SIA filter covers the energy range 0.085-0.180 KeV, centred on 0.124 KeV, while the softer S2A filter covers the range 0.070-0.110 KeV (centred on 0.090 KeV) (10% efficiency) [see Kent et al. (1990) for a full description of the WFC filters].

scholarly journals EUVE Spectra of Coronae and Flares

1996 ◽  
Vol 152 ◽  
pp. 81-88 ◽  
Author(s):  
Carole Jordan
Keyword(s):  
Short Wavelength ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Wavelength Region ◽  
Late Type ◽  
Short Wavelength Region ◽  
Plane Parallel ◽  
Parallel Geometry ◽  
Measure Distribution

Following a summary of early solar EUV spectroscopy the spectra of some late-type stars obtained with the Extreme Ultraviolet Explorer (EUVE) are briefly surveyed. Some transitions which are not included in current emissivity codes but could lead to numerous weak lines, and an apparent continuum in the EUVE short wavelength region, are discussed. The importance of the geometry adopted when interpreting the emission measure distribution is stressed, since radial factors can lead to an apparent emission measure distribution gradient that is steeper than the value of 3/2 expected in plane parallel geometry.

scholarly journals The Secrets of EUVE J2056-17.1

1996 ◽  
Vol 152 ◽  
pp. 475-479
Author(s):  
M. Mathioudakis ◽  
J.J. Drake ◽  
N. Craig ◽  
D. Kilkenny ◽  
J.G. Doyle ◽  
...  
Keyword(s):  
Optical Spectrum ◽  
Flare Activity ◽  
Late Type ◽  
Spallation Reactions ◽  
Deep Survey ◽  
Large Flare

EUVE J2056-17.1 is one of the brightest sources in the First EUVE Source Catalog with 0.24 counts s−1 in the Deep Survey Lexan/B band. We present optical and EUV results that show this source is one of the most active late-type dwarfs. EUVE observed a large flare with energy in excess of 1035 ergs in its Lexan/B band. The quiescent optical spectrum of the source reveals strong hydrogen Balmer and Ca II H and K emission. A strong Li I 6707 Å line is also present in the spectrum. We have estimated a Li abundance of log N(Li) = 2.5±0.4. The high Li abundance and the high flare activity favors an interpretation where the enhanced Li is sustained by spallation reactions.

scholarly journals High-Resolution Optical Observations of Extreme-Ultraviolet–selected Active Late-Type Stars

2002 ◽  
Vol 123 (5) ◽  
pp. 2796-2805 ◽  
Author(s):  
Damian J. Christian ◽  
Mihalis Mathioudakis
Keyword(s):  
High Resolution ◽  
Extreme Ultraviolet ◽  
Optical Observations ◽  
Late Type

scholarly journals Temporal Behaviour of Sources in the ROSAT Extreme-Ultraviolet All-Sky Survey

1996 ◽  
Vol 152 ◽  
pp. 15-19
Author(s):  
Paul McGale ◽  
J.P. Pye ◽  
C.R. Barber ◽  
C.G. Page
Keyword(s):  
Extreme Ultraviolet ◽  
Cataclysmic Variables ◽  
Eclipsing Binaries ◽  
High Mass ◽  
Late Type ◽  
Temporal Behaviour ◽  
Source Type ◽  
Luminosity Functions ◽  
Sky Survey ◽  
M Stars

From a total catalogue of 479 2RE sources, 31 have been found to be variable. All the variable sources are optically identified, with a breakdown by source type as follows: cataclysmic variables 9, late-type (F-M) stars 18, the high-mass X-ray binary Her X-1, the eclipsing binaries Algol and V471 Tau, and the active galaxy Mkn 478. The most highly variable objects in the EUV band are cataclysmic variables. The survey was sensitive to timescales from ~ 1.5 h to ~ 5 d, and observed variability ranges from flare-like events lasting < 1.5 h to irregular and periodic flux changes over ~ 0.5–2 d. With the exception of the cataclysmic variables, and possibly a few late-type dK-dMe stars with large flares, the observed variability levels should not substantially affect EUV luminosity functions

Extreme ultraviolet emission from late-type stars - Initial results from Extreme Ultraviolet Explorer

1993 ◽  
Vol 414 ◽  
pp. L61 ◽  
Author(s):  
Peter W. Vedder ◽  
Robert J. Patterer ◽  
Patrick Jelinsky ◽  
Alex Brown ◽  
Stuart Bowyer
Keyword(s):  
Extreme Ultraviolet ◽  
Late Type ◽  
Ultraviolet Emission ◽  
Initial Results

scholarly journals Flare Activity in Algol-type Binaries

1995 ◽  
Vol 151 ◽  
pp. 193-194
Author(s):  
Izold Pustylnik
Keyword(s):  
Convection Zone ◽  
Scale Height ◽  
The Other ◽  
Flare Activity ◽  
Low Density ◽  
Late Type ◽  
X Ray ◽  
Relative Contribution ◽  
Shock Region ◽  
Solar Type

Two sites of flare activity have been identified in Algol-type binaiies. One is associated with the shock region from the accretion on B-A type primary, another, predominant one is apparently connected with coronal mass ejections (CME) from the late-type, Roche lobe filling secondary. The relative contribution from both sources of activity is still to be found. According to Peters & Polidan (1984), a moderately hot (105 K) and low density ne ≃ 109 cm−3 high turbulent accretion region (HTAR) surrounding the hot component has been discovered. Typical dimensions of HTAR agree with the scale height of the X-ray source HX ≃ 1.2 · 1011 · T7 cm (Harnden et al 1977), where T7 is the temperature in units of 107 K. But the decay time of the HTAR, comparable to the orbital period, more favourably agrees with the idea of CME as deduced from Ginga observations of X-ray flares on Algol (Stern et al. 1992). One solution of the controversy as to the contribution from HTAR would be to concentrate on X-ray observations of systems like u Her and U CrB, where the secondary is possibly earlier than FO (thus, is not expected to possess an extensive convection zone) and on the other hand on systems like U Cep, where during periods of high activity Ṁ ≃ 10−6M⊙ per year. Thus, the accretion luminosity must be at least by two orders of magnitude higher than in Algol. At present the analysis of X-ray flares is based upon the solar type CME assuming different scenarios of radiative and/or conductive cooling (see Stern et al. 1992). However, the current models of CME do not take into account the binary nature of the flaring object.

scholarly journals Active Late-Type Stellar Coronae: Hints for Flare Heating?

2000 ◽  
Vol 195 ◽  
pp. 377-378 ◽  
Author(s):  
M. Audard ◽  
M. Güdel ◽  
J. J. Drake ◽  
V. Kashyap ◽  
E. F. Guinan
Keyword(s):  
Thermal Energy ◽  
Spectral Type ◽  
Extreme Ultraviolet ◽  
Coronal Heating ◽  
Data Archive ◽  
Late Type ◽  
Energy Distributions ◽  
X Ray ◽  
Type Classification

The Extreme Ultraviolet Explorer data archive has been used to study flare energy distributions and infer the role of flares in coronal heating. We have constructed flare number distributions as a function of observed EUV and X-ray emitted thermal energy. We find cumulative flare distributions of the form N(> E) ∝ E−α+1 with α ≍ 1.5–2.6. We present results in the context of spectral type classification.

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