New Insights into the Large 1992 July 15–17 Flare on AU Microscopii: The First Detection of Posteruptive Energy Release on a Red Dwarf Star

Katsova, M. M.; Drake, J. J.; Livshits, M. A.

doi:10.1086/306587

Cited by 38 publications

(35 citation statements)

References 45 publications

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“…Numerous investigations and reviews have targeted the three stars, which are among the youngest pre-main sequence stars in the solar neighbourhood. They display X-ray emission, flaring activity, flux excess in the infrared due to a circumstellar disc (AU Mic), photometric variability (of BY Dra type), active coronae, Ca ii H+K in emission, and other properties typical of young stars (Linsky et al 1982;Kundu et al 1987;Pallavicini et al 1990;Batalha et al 1996;Barrado y Navascués et al 1999;Katsova et al 1999;Zuckerman et al 2001;Kalas et al 2004). There is a difference between Hipparcos heliocentric distances of 0.8 ± 0.4 pc, which could be real (as in the case of α Cen AB and Proxima) or stem from a poor accuracy in the parallax measurement (e.g.…”

Section: Wds 20452-3120 (Au Mic and At Mic Ab)mentioning

confidence: 99%

Reaching the boundary between stellar kinematic groups and very wide binaries

Caballero¹

2009

A&A

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Aims. I look for and characterise very wide binaries and multiple systems with projected physical separations larger than s = 0.1 pc, which is generally believed to be a sharp upper limit to the distribution of wide binary semimajor axes. Methods. I investigated in detail 30 Washington double stars with angular separations of ρ > 1000 arcsec. I discarded 23 of them as probably unbound systems based on discordant astrometry, photometry, spectral types, and radial velocities. The remaining seven systems were subject to a comprehensive data compilation and derivation (multi-wavelength photometry, heliocentric distance, multiplicity, age, mass, metallicity, membership in a young kinematic group). Results. Of the seven very wide systems, six have projected physical separations greater than the hypothetical cutoff at s = 0.1 pc and four have separations s > 0.2 pc. Although there are two systems in young kinematic groups (namely HD 136654 and BD+32 2572 in the Hyades Supercluster, and AU Mic and AT Mic AB in the β Pictoris moving group), there is no clear prevalence of young systems (τ < 1 Ga) among these very wide binaries. Finally, I compare the binding energies of the seven systems with those of other weakly bound systems in the field.

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Section: Wds 20452-3120 (Au Mic and At Mic Ab)mentioning

confidence: 99%

Reaching the boundary between stellar kinematic groups and very wide binaries

Caballero¹

2009

A&A

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“…A massive flare was observed by EUVE on this object in July 1992, and is discussed by various authors, including Cully et al (1994) who modelled the slow decay phase as being due to the ejection of a magnetically confined plasmoid, an event similar to a solar coronal mass ejection. The time-varying UV spectral lines during this event were discussed by Monsignori Fossi et al (1996) and also by Katsova et al (1999). The quiescent UV spectrum was studied by Pagano et al (2000), who derived an emission measure distribution and compared the conditions to those on the Sun.…”

Section: Target Objectsmentioning

confidence: 99%

Flares observed with XMM-Newton and the VLA

Smith

Güdel²,

Audard³

2005

A&A

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Abstract. We present lightcurves obtained in X-ray by the XMM-Newton EPIC cameras and simultaneous radio lightcurves obtained with the VLA for five active M-type flare stars. A number of flare events were observed, and by comparing radio with X-ray data, we consider various possible flare mechanisms. In cases where there seems to be a clear correlation between radio and X-ray activity, we use an energy budget argument to show that the heating which leads to the X-ray emission could be due to the same particles emitting in the radio. In cases where there is radio activity without corresponding X-ray activity, we argue that the radio emission is likely to arise from coherent processes involving comparatively few particles. In one case, we are able to show from polarization of the radio emission that this is almost certainly the case. Cases for which X-ray activity is seen without corresponding radio activity are more difficult to explain. We suggest that the heating particles may be accelerated to very high energy, and the resulting synchrotron radio emission may be beamed in directions other than the line of sight.

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“…Flares exhibit quite different spectroscopic behaviour from one flare to another; some evolve on time scales of tens of seconds whereas others may last for a day or more (Katsova et al 1999;Foing et al 1994). First, one should distinguish between solar-type flares that evolve typically on time scales shorter than a few tens of minutes and "RS CVn" type flares that last typically more than a couple of hours (Baliunas et al 1984;Linsky et al 1989;Foing et al 1994).…”

Section: Flux Time Profilesmentioning

confidence: 99%

Dynamics of flares on late type dMe stars

Houdebine

2003

A&A

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Abstract.We investigate the spectral signatures of stellar flares in the wavelength range 3600 Å to 4500 Å and in broad band photometry. We study the phenomenology of the spectral signatures and we found that flares are best described by two main phases; an impulsive phase and a gradual phase, for which the physical properties are different. Important spectral differences between flares lead us to distinguish four main classes: (i) solar-like chromospheric or two-ribbon flares, (ii) white-light flares, (iii) combined white-light flares with distinct impulsive and gradual phases, and (iv) non solar-like flares (usually occuring on RS CVn type stars). We show how this classification corresponds to substantial differences in the physical properties of the flare components. We compiled all available spectroscopic data for stellar flares. We found several new empirical correlations between the time lags in the spectral lines (rise and decay times). We found for instance that during the gradual phase, the rise time in the H γ line is well correlated to the rise time in the Ca  K line, and that the Ca  K line is 1.63 times slower to rise than the H γ line. Similar correlations were found between the rise and decay times in these lines. These correlations are evidence that there is a dominant mechanism commanding the temporal flux evolutions during the gradual phase of flares. This mechanism applies on time scales ranging from one minute to more than a hundred minutes. We found correlations between the time lags and the maximum fluxes in the Johnson U-band and the spectral lines. These correlations show that the larger the flare the longer it takes to evolve. We show that the maximum flux in the Johnson U-band correlates well, but not linearly with the maximum flux in the H γ line during the impulsive phase, and over five orders of magnitude. We argue how this correlation can provide constraints on the currently available models. The spectral line maximum fluxes during the gradual phase also correlate with the Johnson U-band flux, which demonstrates that somehow the impulsive and gradual phases are physically linked. The correlation between the H γ and Ca K line fluxes during the gradual phase and the lack of dependence of the flux ratio of those lines on flare magnitude reveal that larger flares are not "hotter" than smaller flares during the gradual phase. We examine the behaviour of the spectral line widths: While the Ca  K line width shows essentially no detectable variation, the Balmer line widths show a complex dependency on the white light intensity. We distinguish three energy domains where the Balmer line widths exhibit a different behaviour: (i) for small flares, the widths remain rather constant as a function of white light intensity, which suggests that in this energy range the U-band is not a good diagnostic of the total energy release and that dense "kernels" do not dominate the Balmer emission, (ii) for medium size flares, the widths rapidly increase with the U-band flux up to about 15 Å, which in...

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New Insights into the Large 1992 July 15–17 Flare on AU Microscopii: The First Detection of Posteruptive Energy Release on a Red Dwarf Star

Cited by 38 publications

References 45 publications

Reaching the boundary between stellar kinematic groups and very wide binaries

Reaching the boundary between stellar kinematic groups and very wide binaries

Flares observed with XMM-Newton and the VLA

Dynamics of flares on late type dMe stars

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