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TwitterA&A 430, 303-311 (2005)
DOI: 10.1051/0004-6361:20041440
Mg II chromospheric radiative loss rates in cool active and quiet stars
D. CardiniIstituto di Astrofisica Spaziale e Fisica Cosmica, CNR, via del Fosso del Cavaliere 100, 00133 Roma, Italy
e-mail: cardini@rm.iasf.cnr.it
(Received 9 June 2004 / Accepted 14 September 2004)
Abstract
The
k emission line is a good indicator of the level of
chromospheric activity in late-type stars.
We investigate the dependence of this activity indicator on fundamental
stellar parameters.
To this purpose we use IUE observations of the
k line in 225 late-type stars of luminosity classes I-V,
with different levels of chromospheric activity.
We first re-analyse the relation between
k line luminosity
and stellar absolute magnitude,
performing linear fits to the points.
The ratio of
surface flux to total surface flux is
found to be independent of stellar luminosity for evolved stars
and to increase with decreasing luminosity for dwarfs.
We also analyse the
k line surface flux-metallicity
connection. The
k emission level turns out to be
not dependent on metallicity.
Finally, the
k line surface flux-temperature relation
is investigated by treating separately, for the first time, a large sample of
very active and normal stars.
The stellar surface fluxes in the k line of normal stars are
found to be strongly dependent on the temperature and slightly dependent
on the gravity,
thus confirming the validity of recently proposed models.
In contrast, data relative to RS CVn binaries and BY Dra stars,
which show very
strong chromospheric activity, are not justified in the framework
of a description based only on acoustic waves and uniformly distributed
magnetic flux tubes so that they require more detailed models.
Key words: stars: late-type -- stars: chromospheres -- stars: activity -- ultraviolet: general -- line: profiles
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© ESO 2005