2003A&A...397.1019H


C.D.S. - SIMBAD4 rel 1.7 - 2019.12.10CET05:58:41

2003A&A...397.1019H - Astronomy and Astrophysics, volume 397, 1019-1034 (2003/1-3)

Dynamics of flares on late type dMe stars. IV. Constraints from spectrophotometry in the visible.

HOUDEBINE E.R.

Abstract (from CDS):

We investigate the spectral signatures of stellar flares in the wavelength range 3600Å to 4500Å 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 Hγ line is well correlated to the rise time in the Caii K line, and that the Caii K line is 1.63 times slower to rise than the Hγ 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 Hγ 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 Hγ and Caii 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 Caii 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 15Å, which indicates that emission in the Balmer lines is then dominated by kernel emission, and (iii) for large flares the widths decrease with increasing U-band flux, which suggests that the Balmer line emission is then increasingly dominated by a radiative pumping process between the white light and the Balmer lines. Finally, we remark that the Balmer line fluxes are well correlated to the white light flux during the impulsive phase of flares, and not only at flare maximum. We obtain a power law correlation between the Balmer line and U-band fluxes that is evidence for either a common source (``kernels'') or strongly related flare components.

Abstract Copyright:

Journal keyword(s): stars: flare - stars: activity - stars: late-type

CDS comments: In table 1, T48 = HPRA 48.

Simbad objects: 15

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Number of rows : 15

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 G 272-61A Fl* 01 39 01.3765356886 -17 57 02.399297242     12.7     M5.5V 95 0
2 G 272-61B Fl* 01 39 01.6334059022 -17 57 01.121866655     13.2     M6V 782 0
3 V* V781 Ori Fl* 05 34 52.4027104523 -06 11 56.981763177   17.34 16.213   13.926 M1.9 14 0
4 V* YZ CMi BY* 07 44 40.1726285952 +03 33 08.877830321 13.761 12.831 11.225 9.958 8.263 M4.0Ve 770 0
5 BD+20 2465 ** 10 19 36.2808024653 +19 52 12.014037746   10.82 9.52 9.19   M4Vae 1118 0
6 Wolf 424 ** 12 33 17.361480 +09 01 15.79224 15.398 14.313 12.467 10.937 8.988 M5.5V 292 0
7 V* V645 Cen Fl* 14 29 42.9451234609 -62 40 46.170818907 14.21 12.95 11.13 9.45 7.41 M5.5Ve 899 0
8 V* BY Dra BY* 18 33 55.7719224141 +51 43 08.903033617 10.22 9.23   8.733   K4Ve+K7.5Ve 592 0
9 V* AT Mic ** 20 41 51.15925 -32 26 06.8283 12.753 11.909 10.343 9.098 7.383 M4.5Ve+M4.5Ve 320 0
10 V* AU Mic BY* 20 45 09.5323695486 -31 20 27.241710746   10.05 8.627 9.078 6.593 M1VeBa1 874 0
11 V* EZ Aqr BY* 22 38 33.576000 -15 17 59.75700 15.762 14.33 12.38 12.12 8.677 M5V 279 1
12 V* EV Lac Fl* 22 46 49.7311740821 +44 20 02.372223230   11.85 10.26 9.89   M4.0V 780 2
13 BD+19 5116 ** 23 31 52.17898 +19 56 14.1505 12.737 11.749 10.165 8.982 7.446 M4+M5 416 0
14 BD+19 5116B Fl* 23 31 52.5741250923 +19 56 14.004074575   14.8 12.4 12.165   M4.0Ve 167 0
15 HD 224085 RS* 23 55 04.0516465022 +28 38 01.248194500 8.88 8.20   6.9   K2+IVeFe-1 675 0

    Equat.    Gal    SGal    Ecl

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2019.12.10-05:58:41

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