Stellar Radio Astronomy: Probing Stellar Atmospheres from Protostars to Giants

Guêdel, M.

doi:10.1146/annurev.astro.40.060401.093806

Cited by 331 publications

(368 citation statements)

References 267 publications

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“…Both X-ray (Favata & Micela 2003) and radio (Güdel 2002) stellar peak flare properties show that magnetic loop scaling relationships can be derived from the corresponding solar flare properties. We use here the work of Shibata & Yokoyama (1999 which is based on a scaling law relation for the maximum temperature of reconnection heated plasma and magnetic field strength derived from MHD simulations (Yokoyama & Shibata 1998, 2001).…”

Section: Peak Propertiesmentioning

confidence: 99%

Chandra observation of an unusually long and intense X-ray flare from a young solar-like star in M 78

Grosso

Montmerle

Feigelson

et al. 2004

A&A

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Abstract. LkHα 312 has been observed serendipitously with the ACIS-I detector on board the Chandra X-ray Observatory with a 26 h continuous exposure. This Hα emission line star belongs to M 78 (NGC 2068), one of the star-forming regions of the Orion B giant molecular cloud at a distance of 400 pc. From the optical and the near-infrared (NIR) data, we show that LkHα 312 is a pre-main sequence (PMS) low-mass star with a weak NIR excess. This genuine T Tauri star displayed an X-ray flare with an unusually long rise phase (∼8 h). The X-ray emission was nearly constant during the first 18 h of the observation, and then increased by a factor of 13 during a fast rise phase (∼2 h), and reached a factor of 16 above the quiescent X-ray level at the end of a gradual phase (∼6 h) showing a slower rise. To our knowledge this flare, with ∼0.4-0.5 cts s −1 , has the highest count rate observed so far with Chandra from a PMS low-mass star. By chance, the source position, 8.2 off-axis, protected this observation from pile-up. We make a spectral analysis of the X-ray emission versus time, showing that the plasma temperature of the quiescent phase and the flare peak reaches 29 MK and 88 MK, respectively. The quiescent and flare luminosities in the energy range 0.5-8 keV corrected from absorption (N H ≈ 1.7 × 10 21 cm −2 ) are 6 × 10 30 erg s −1 and ∼10 32 erg s −1 , respectively. The ratio of the quiescent X-ray luminosity on the LkHα 312 bolometric luminosity is very high with log(L X /L bol ) = −2.9, implying that the corona of LkHα 312 reached the "saturation" level. The X-ray luminosity of the flare peak reaches ∼2% of the stellar bolometric luminosity. The different phases of this flare are finally discussed in the framework of solar flares, which leads to the magnetic loop height from 3.1 × 10 10 to 10 11 cm (0.2-0.5 R , i.e., 0.5-1.3 R ).

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Section: Peak Propertiesmentioning

confidence: 99%

Chandra observation of an unusually long and intense X-ray flare from a young solar-like star in M 78

Grosso

Montmerle

Feigelson

et al. 2004

A&A

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“…However, coronal emission from stars can also be observed in the radio range (e.g. Berger 2002or Güdel 2002 and in the optical (Schmitt & Wichmann 2001). Coronal observations at those latter wavebands are Send offprint requests to: B. Fuhrmeister, e-mail: bfuhrmeister@hs.uni-hamburg.…”

Section: Introductionmentioning

confidence: 99%

Fe XIII coronal line emission in cool M dwarfs

Fuhrmeister

Schmitt

Wichmann

2004

A&A

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Abstract. We report on a search for the Fe  forbidden coronal line at 3388.1 Å in a sample of 15 M-type dwarf stars covering the whole spectral class as well as different levels of activity. A clear detection was achieved for LHS 2076 during a major flare and for CN Leo, where the line had been discovered before. For some other stars the situation is not quite clear. For CN Leo we investigated the timing behaviour of the Fe  line and report a high level of variability on a timescale of hours which we ascribe to microflare heating.

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“…The mechanisms generally invoked to account for the observed radio emission are gyrosynchrotron, synchrotron and coherent (electron-cyclotron maser or plasma radiation) processes. For reviews on these radio emission mechanisms see, for instance, Dulk (1985) and Güdel (2002).…”

Section: Introductionmentioning

confidence: 99%

VLA multifrequency observations of RS CVn binaries

Garcia-Sanchez¹,

Paredes²,

Ribó³

2003

A&A

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Abstract. We present multiepoch Very Large Array (VLA) observations at 1.4 GHz, 4.9 GHz, 8.5 GHz and 14.9 GHz for a sample of eight RS CVn binary systems. Circular polarization measurements of these systems are also reported. Most of the fluxes observed are consistent with incoherent emission from mildly relativistic electrons. Several systems show an increase of the degree of circular polarization with increasing frequency in the optically thin regime, in conflict with predictions by gyrosynchrotron models. We observed a reversal in the sense of circular polarization with increasing frequency in three noneclipsing systems: EI Eri, DM UMa and HD 8358. We find clear evidence for coherent plasma emission at 1.4 GHz in the quiescent spectrum of HD 8358 during the helicity reversal. The degrees of polarization of the other two systems could also be accounted for by a coherent emission process. The observations of ER Vul revealed two U-shaped flux spectra at the highest frequencies. The U-shape of the spectra may be accounted for by an optically thin gyrosynchrotron source for the low frequency part whereas the high frequency part is dominated by a thermal emission component.

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Stellar Radio Astronomy: Probing Stellar Atmospheres from Protostars to Giants

Cited by 331 publications

References 267 publications

Chandra observation of an unusually long and intense X-ray flare from a young solar-like star in M 78

Chandra observation of an unusually long and intense X-ray flare from a young solar-like star in M 78

Fe XIII coronal line emission in cool M dwarfs

VLA multifrequency observations of RS CVn binaries

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