Boudreault, S.; Bailer-Jones, C. A. L.
Referencia bibliográfica
The Astrophysical Journal, Volume 706, Issue 2, pp. 1484-1503 (2009).
Fecha de publicación:
12
2009
Revista
Número de citas
18
Número de citas referidas
14
Descripción
We present the stellar and substellar mass function (MF) of the open
cluster IC 2391, plus its radial dependence, and use this to put
constraints on the formation mechanism of brown dwarfs (BDs). Our
multi-band optical and infrared photometric survey with spectroscopic
follow-up covers 11 deg2, making it the largest survey of
this cluster to date. We observe a radial variation in the MF over the
range 0.072-0.3 M sun, but no significant variation in the MF
below the substellar boundary at the three cluster radius intervals is
analyzed. This lack of radial variation for low masses is what we would
expect with the ejection scenario for BD formation, although considering
that IC 2391 has an age about three times older than its crossing time,
we expect that BDs with a velocity greater than the escape velocity have
already escaped the cluster. Alternatively, the variation in the MF of
the stellar objects could be an indication that they have undergone mass
segregation via dynamical evolution. We also observe a significant
variation across the cluster in the color of the (background) field star
locus in color-magnitude diagrams and conclude that this is due to
variable background extinction in the Galactic plane. From our
preliminary spectroscopic follow-up, to confirm BD status and cluster
membership, we find that all candidates are M dwarfs (in either the
field or the cluster), demonstrating the efficiency of our photometric
selection method in avoiding contaminants (e.g., red giants). About half
of our photometric candidates for which we have spectra are
spectroscopically confirmed as cluster members; two are new
spectroscopically confirmed BD members of IC 2391.