Issue |
A&A
Volume 509, January 2010
|
|
---|---|---|
Article Number | A65 | |
Number of page(s) | 21 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/200811602 | |
Published online | 20 January 2010 |
Observation and modelling of main-sequence star chromospheres*
IX. Two-component model chromospheres for nine M1 dwarfs
25 rue du Dr. Laulaigne, 49670 Valanjou, France e-mail: eric_houdebine@yahoo.fr
Received:
30
December
2008
Accepted:
21
April
2009
Aims.
We aim to constrain the H, CaII H and CaII K line profiles of
quiescent and active regions of nine dM1 stars of near solar metallicity:
Gl 2, GJ 1010A, Gl 49, Gl 150.1B, Gl 205, Gl 229, Gl 526, G192-11A, and
Gl 880.
Methods. We propose a new method for building two-component model chromospheres for
dM1 stars-based on simple constraints and a grid of model atmospheres
developed by
Houdebine & Stempels. This method is based on the
measurements of the equivalent width of H and CaII H & K.
Based on the peculiar relationship between these two equivalent
widths in the model atmospheres, our solutions provide an exact match of
these equivalent widths.
Results. We obtain two component (quiescent and active region) model chromospheres
for our nine target stars. We fit the H, CaII H, and CaII K
profiles
for these stars. These models show that seven of these stars lie in the
intermediate activity range between H
maximum absorption
and emission. Two stars (Gl 49 and G192-11A) are quite active with
H
emission profiles in plages. As far as the CaII emission is
concerned, these two stars are almost as active as dM1e stars. Two stars
(GJ 1010A and Gl 526) have lower activity levels with narrower and weaker
H
profiles. The range of activity covered by these stars is a
factor of 13 in the CaII lines, from low activity to activity
levels almost as high as those of dM1e stars.
Our method sometimes provides two solutions of the observed H
equivalent width as a function of the quiescent region H
equivalent width. For Gl 205, one of the solutions is shown to be impossible
for the assumptions that we use. For Gl 49 and G192-11A,
two solutions are possible; a low solution (low CaII EW) and a high solution
(high CaII EW). The difference between these two solutions is mainly in the
plage-filling factor. The two solutions give almost identical H
and CaII profiles. We prefer the low solutions because the filling factors are
in closer agreement with those of other stars. We find plage-filling
factors typically in the range 20%-40%. We also find that it is the
chromospheric pressure rather than the filling factor that increases with
increasing activity.
We define a minimum theoretical H
equivalent width as a function
of the mean CaII H & K equivalent width. We show that our observations
agree well with this lower limit. We also show that the properties of the
chromosphere in quiescent and active regions correlate with
the mean CaII H & K equivalent width. This could be useful in future studies
to derive an estimate of the chromospheric properties from the observed
mean CaII H & K equivalent width.
Key words: line: formation / radiative transfer / stars: activity / stars: low-mass / stars: chromospheres / stars: late-type
© ESO, 2010
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