160 research outputs found
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
A WN4 companion to BD +62 2296 in Cas OB5
I report observations of the triple system BD +62 2296 showing that all its
components are early-type stars, most likely physically related. The faintest
component BD +62 2296B is a hitherto uncatalogued Wolf-Rayet star. The
brightest component, star A, is shown to be a seemingly normal B2.5Ia
supergiant. Long-slit spectroscopy of BD +62 2296B shows it to be a
narrow-lined WN4 star. Given the spatial separation, the two objects are
unlikely to form a physical binary. Spectra of the third visual component, BD
+62 2296C, allow its classification as a B0III star. Such concentration of
massive stars strongly suggests that BD +62 2296 is in reality a very compact
young open cluster in the area of the OB association Cas OB5.Comment: Research Note accepted for publication in Astronomy & Astrophysics. 5
pages, 4 figures; uses new A&A style (included
High-mass stars in clusters and associations
High-mass stars are major players in the chemical and dynamical evolution of
galaxies. Open clusters and associations represent the natural laboratories to
study their evolution. In this review, I will present a personal selection of
current research topics that highlight the use of open clusters to constrain
different properties of high-mass stars, such as the possible existence of an
upper limit for the mass of a star, the evolutionary stage of blue supergiants
or the characterisation of supernova progenitors.Comment: Invited review presented at "Stellar Clusters and Associations - A
RIA workshop on GAIA", 23-27 May 2011, Granada, Spai
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