Issue |
A&A
Volume 458, Number 1, October IV 2006
|
|
---|---|---|
Page(s) | 293 - 296 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20064889 | |
Published online | 16 October 2006 |
An empirical temperature calibration for the
photometric system
II. The A-type and mid F-type stars
Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria e-mail: Ernst.Paunzen@univie.ac.at
Received:
21
January
2006
Accepted:
22
June
2006
Context.With the photometric system, it is possible to
study very distant galactic and even extragalactic clusters
with a high level of accuracy. This can be done with a classical
color-magnitude diagram and appropriate isochrones. The new
calibration presented in this paper is a powerful extension.
Aims.For open clusters, the reddening is straightforward for
an estimation via Isochrone fitting and is needed in order
to calculate the
reddening-free, temperature sensitive, index . As a last
step, the calibration can be applied to individual stars.
Methods.Because no a priori reddening-free photometric parameters are
available for the investigated spectral range, we have applied
the dereddening calibrations of the Strömgren
system and compared them with extinction models for the Milky Way.
As expected from the sample of bright stars, the extinction is
negligible for almost all objects. As a next step,
already established calibrations within
the Strömgren
, Geneva 7-color, and Johnson
systems were
applied to a sample of 282 normal stars to derive
a polynomial fit of the third degree for the averaged effective temperatures to
the individual
values.
Results.We derived an empirical temperature calibration for the
photometric system for A-type to mid F-type with a
mean of the error for the whole sample of
is 134 K, which is lower than the value
in Paper I for hotter stars. No
statistically significant effect
of the rotational velocity on the precision
of the calibration was found.
Conclusions.We have derived a new
intrinsically consistent, empirical, effective temperature calibration
for a spectral range from early B-type to mid F-type, luminosity class V to III
stars within the photometric system. The statistical
mean error over the complete spectral range of about 140 to 240 K will allow to
individual objects of far distant galactic be studied as well as extragalactic
clusters with high accuracy.
Key words: stars: early-type / techniques: photometric
© ESO, 2006
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