SETI bioastro: The brightest stars of the sigma Orionis cluster

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Astrophysics, abstract
astro-ph/0701067

From: Jos\'e A. Caballero [view email]

Date: Wed, 3 Jan 2007 19:04:22 GMT (359kb)

The brightest stars of the sigma Orionis cluster

Authors: J. A. Caballero

Comments: Accepted by A&A Chief Editor. Sent to language editor. Tables A.1
and A.2 will be only available in electronic form

Context: The very young sigma Orionis cluster (about 3 Ma) is a cornerstone
for the understanding of the formation of stars and substellar objects down
to planetary masses. However, its stellar population is far to be completely
known. Aims: This study has the purpose of identyfing and characterising the
most massive stars of sigma Orionis to complement current and future deep
searches for brown dwarfs and planetary-mass objects in the cluster.
Methods: I have cross-correlated the sources in the Tycho and 2MASS
catalogues in a region of 30 arcmin radius with centre in the O-type star
sigma Ori A. In the area, I have studied the membership in the Ori OB 1b
Association of the brightest stars in the optical using astrometric, X-ray
and infrared and optical photometric data from public catalogues and
spectroscopic data from the literature. Results: A list of 26 young stars,
four candidate young stars and 16 probable foreground stars has arised from
the study. Seven young stars probably harbour discs (four are new). There is
no mass-dependence of the disc frequency in the cluster. I have derived for
the first time the mass spectrum in sigma Orionis from 1.1 to 24 Msol (alpha
= +2.0+0.2-0.1; roughly Salpeter-like). I have also provided additional
proofs on the existence of several spatially superimposed stellar
populations in the direction of sigma Orionis. Finally, the cluster may be
closer and older than previously considered.

http://arxiv.org/abs/astro-ph/0701067

Astrophysics, abstract
astro-ph/0701066

From: Paul Hodge [view email]

Date: Wed, 3 Jan 2007 18:46:43 GMT (617kb)

An HST Survey of the Disk Cluster Population of M31. I. WFPC2 Pointings

Authors: O. K. Krienke, P.W. Hodge

Comments: 24 pages, 13 figures

A survey of 49 HST WFPC2 pointings in M31 has resulted in a photometric
catalog of 344 disk clusters ("open clusters"). We have analyzed the
color-magnitude diagram, the luminosity function, the size distribution and
the age distribution of the clusters, together with correlations between
these characteristics and the environment of the clusters within M31's
spiral structure.

http://arxiv.org/abs/astro-ph/0701066

• Previous message: LARRY KLAES: "SETI bioastro: Dava Sobel article on sundials new and old in the January Smithsonian Magazine"

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