Bibcode
Gvaramadze, V. V.; Weidner, C.; Kroupa, P.; Pflamm-Altenburg, J.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 424, Issue 4, pp. 3037-3049.
Advertised on:
8
2012
Citations
86
Refereed citations
77
Description
A significant fraction of massive stars in the Milky Way and other
galaxies are located far from star clusters and star-forming regions. It
is known that some of these stars are runaways, i.e. possess high space
velocities (determined through the proper motion and/or radial velocity
measurements), and therefore most likely were formed in embedded
clusters and then ejected into the field because of dynamical few-body
interactions or binary-supernova explosions. However, there exists a
group of field O stars whose runaway status is difficult to prove via
direct proper motion measurements (e.g. in the Magellanic Clouds) or
whose (measured) low space velocities and/or young ages appear to be
incompatible with their large separation from known star clusters. The
existence of this group led some authors to believe that field O stars
can form in situ. Since the question of whether or not O stars can form
in isolation is of crucial importance for star formation theory, it is
important to thoroughly test candidates of such stars in order to
improve the theory. In this paper, we examine the runaway status of the
best candidates for isolated formation of massive stars in the Milky Way
and the Magellanic Clouds by searching for bow shocks around them, by
using the new reduction of the Hipparcos data, and by searching for
stellar systems from which they could originate within their lifetimes.
We show that most of the known O stars thought to have formed in
isolation are instead very likely runaways. We show also that the field
must contain a population of O stars whose low space velocities and/or
young ages are in apparent contradiction to the large separation of
these stars from their parent clusters and/or the ages of these
clusters. These stars (the descendants of runaway massive binaries)
cannot be traced back to their parent clusters and therefore can be
mistakenly considered as having formed in situ. We argue also that some
field O stars could be detected in optical wavelengths only because they
are runaways, while their cousins residing in the deeply embedded parent
clusters might still remain totally obscured. The main conclusion of our
study is that there is no significant evidence whatsoever in support of
the in situ proposal on the origin of massive stars.
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