To be published in:
Astronomy & Astrophysics
Early-type stars in the young open cluster IC 1805
I. The SB2 system BD+60° 497 and the probably single stars
BD+60° 501 and BD+60° 513 +
G. Rauw1,* and
M. De Becker1
1 Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (Sart Tilman), Belgium
* Research Associate FNRS, Belgium
+ Based on observations collected at the Observatoire de Haute Provence (France).
We investigate the multiplicity of three O-type stars in the very young open
cluster IC 1805. All our targets were previously considered as spectroscopic
binaries, but no orbital solution was available for any of them. Our results
confirm the binarity of BD+60° 497 and we provide the very first orbital
solution for this double-lined spectroscopic binary. This is only the second
O-star binary in IC 1805, and the first SB2 system, for which an orbital
solution is now available. BD+60° 497 has an orbital period of 3.96 days
and consists of an evolved O6.5V((f)) primary and an O8.5-9.5V((f))
secondary with minimum masses of
m1 sin3i = 13.9 M and
m2 sin3i = 10.9 M.
The observed primary/secondary mass ratio (1.28) appears lower than expected
from a comparison with single star evolutionary models (1.60 - 1.74). For the
other two stars, BD+60° 501 and BD+60° 513, we find no significant
radial velocity variations, suggesting that they are most probably single.
Although a fraction of binaries among the early-type stars of IC 1805 as high
as 80% has been advocated in the literature, our results suggest that this
number might be overestimated.
binaries: spectroscopic -- stars: early-type --
stars: fundamental parameters --
stars: individual: BD+60° 497, BD+60° 501, BD+60° 513