[vsnet-chat 5769] Re: More on flare stars

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

Re: More on flare stars

Hi Federico,

   I hope that someone could comment on the physical mechanism of stellar
flares, but I would like to make some comments related to Stan's comment.

> These stars are usually spotty so there was some success at obtaining
> rotation periods of many - BY Draconis variables I think - but the
> variations are usually too small for eyeball photometry. The radio people
> are still working on some similar objects - RS CVn stars with short
> periods - CC Eridani is one, where the visual measures in the form of CCD
> measures provide light curves to help interpret their long wavelength
> observations. This is probably a more useful area that the classical flare
> stars - the RS CVn stars seem to have flares as well - but needs to be
> organised. Random data is useless.

   Multiwavelength data are most useful.  In recent interpretations of
stellar flares (see e.g. ApJ 580, L73, 2002), the increase of optical
continuum light is considered to reflect an increase of high-energy
electrons.  The evaporated matter originating from the stellar choromosphere
(where these electrons inject energy) is responsible for late-time
soft X-ray increase.  Correlated optical and X-ray studies are a key to
understanding the physics of stellar flares.  A search for stellar actibvity
cycle would be another interesting field, but this study would require
years- or decades-long patience using the same instrument...

   To add to the list given by Stan, T Tau stars (pre-main sequence stars)
are known to show strong flares.  It still controversial whether the
same mechanism is responsible for flares in these systems.  A correrated
X-ray and optical studies would be helpful in solving the problem.

> But, again from memory, one of the stars in the field of
> HL CMa is reputed to be a flare star and was used in the original AAVSO
> sequence.

   This is HM CMa.  Discussed in vsnet-chat 4415, 4417, 4423, 4424.
To my knowledge, there is no confirmatory observation of the flare-star
nature of this object.

Regards,
Taichi Kato

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