1,260 research outputs found
Fundamental Parameters of 4 Massive Eclipsing Binaries in Westerlund 1
Westerlund 1 is one of the most massive young clusters known in the Local
Group, with an age of 3-5 Myr. It contains an assortment of rare evolved
massive stars, such as blue, yellow and red supergiants, Wolf-Rayet stars, a
luminous blue variable, and a magnetar, as well as 4 massive eclipsing binary
systems (Wddeb, Wd13, Wd36, WR77o, see Bonanos 2007). The eclipsing binaries
present a rare opportunity to constrain evolutionary models of massive stars,
the distance to the cluster and furthermore, to determine a dynamical lower
limit for the mass of a magnetar progenitor. Wddeb, being a detached system, is
of great interest as it allows determination of the masses of 2 of the most
massive unevolved stars in the cluster. We have analyzed spectra of all 4
eclipsing binaries, taken in 2007-2008 with the 6.5 meter Magellan telescope at
Las Campanas Observatory, Chile, and present fundamental parameters (masses,
radii) for their component stars.Comment: 2 pages, to appear in the proceedings of the IAUS 272 on "Active OB
stars: structure, evolution, mass loss and critical limits" (Paris, July
19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G.
Meynet and G. Peter
The open cluster Pismis 11 and the very luminous blue supergiant HD 80077
(Abridged) The very luminous blue supergiant HD 80077 has been claimed to be
a member of the young open cluster Pismis 11, and hence a hypergiant. We
obtained UBVRI photometry of the cluster field and low-resolution spectroscopy
of a number of putative members. We derive spectral types from the spectra and
determine that the reddening in this direction is standard. We then carry out a
careful photometric analysis that allows us to determine individual reddening
values, deriving unreddened parameters that are used for the main sequence fit.
We identify 43 likely members of Pismis 11. We study the variation of
extinction across the face of the cluster and find some dispersion, with a
trend to higher values in the immediate neighbourhood of HD 80077. We estimate
a distance of 3.6 kpc for the cluster. If HD 80077 is a member, it has
M_bol<-10.5 and it is one of the three visually brightest stars in the Galaxy.
Several early type stars in the vicinity of Pismis~11 fit well the cluster
sequence and are likely to represent an extended population at the same
distance. About 18 arcmin to the North of Pismis 11, we find a small
concentration of stars, which form a clear sequence. We identify this group as
a previously uncatalogued open cluster, which we provisionally call Alicante 5.
The distance to Alicante 5 is also 3.6 kpc, suggesting that these two clusters
and neighbouring early-type stars form a small association. Based on its proper
motion, HD 80077 is not a runaway star and may be a member of the cluster. If
this is the case, it would be one of the brightest stars in the Galaxy.Comment: 25 pages. It contains many figures and tables. Accepted for
publication in Astronomy and Astrophysic
Open clusters in AurOB2
We study the area around the HII region Sh 2-234, including the young open
cluster Stock 8, to investigate the extent and definition of the association
Aur OB2 and the possible role of triggering in massive cluster formation. We
obtained Str\"omgren and J,H,Ks photometry for Stock 8 and Str\"omgren
photometry for two other cluster candidates in the area, which we confirm as
young open clusters and name Alicante 11 and Alicante 12. We took spectroscopy
of 33 early-type stars in the area, including the brightest cluster members. We
calculate a common distance of kpc for the three open
clusters and surrounding association. We derive an age 4-6 Ma for Stock 8, and
do not find a significantly different age for the other clusters or the
association. The star LSV +34 23, with spectral type O8 II(f), is likely the
main source of ionization of Sh 2-234. We observe an important population of
pre-main sequence stars, some of them with disks, associated with the B-type
members lying on the main-sequence. We interpret the region as an area of
recent star formation with some residual and very localized ongoing star
formation. We do not find evidence for sequential star formation on a large
scale. The classical definition of Aur OB2 has to be reconsidered, because its
two main open clusters, Stock 8 and NGC 1893, are not at the same distance.
Stock 8 is probably located in the Perseus arm, but other nearby HII regions
whose distances also place them in this arm show quite different distances and
radial velocities and, therefore, are not connected.Comment: 29 pages, 17 figures Accepted for publication in MNRA
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