5,876 research outputs found
On the Formation of Runaway Stars BN and x in the Orion Nebula Cluster
We explore scenarios for the dynamical ejection of stars BN and x from source
I in the Kleinmann-Low nebula of the Orion Nebula Cluster (ONC), which is
important for being the closest region of massive star formation. This ejection
would cause source I to become a close binary or a merger product of two stars.
We thus consider binary-binary encounters as the mechanism to produce this
event. By running a large suite of -body simulations, we find that it is
nearly impossible to match the observations when using the commonly adopted
masses for the participants, especially a source I mass of .
The only way to recreate the event is if source I is more massive, i.e.,
. However, even in this case, the likelihood of
reproducing the observed system is low. We discuss the implications of these
results for understanding this important star-forming region.Comment: 7 pages, 4 figures, 1 table. Accepted by A&A Letter
Star Cluster Formation from Turbulent Clumps. I. The Fast Formation Limit
We investigate the formation and early evolution of star clusters assuming
that they form from a turbulent starless clump of given mass bounded inside a
parent self-gravitating molecular cloud characterized by a particular mass
surface density. As a first step we assume instantaneous star cluster formation
and gas expulsion. We draw our initial conditions from observed properties of
starless clumps. We follow the early evolution of the clusters up to 20 Myr,
investigating effects of different star formation efficiencies, primordial
binary fractions and eccentricities and primordial mass segregation levels. We
investigate clumps with initial masses of
embedded in ambient cloud environments with mass surface densities,
and . We show that these models
of fast star cluster formation result, in the fiducial case, in clusters that
expand rapidly, even considering only the bound members. Clusters formed from
higher environments tend to expand more quickly, so are
soon larger than clusters born from lower conditions. To
form a young cluster of a given age, stellar mass and mass surface density,
these models need to assume a parent molecular clump that is many times denser,
which is unrealistic compared to observed systems. We also show that in these
models the initial binary properties are only slightly modified by
interactions, meaning that binary properties, e.g., at 20 Myr, are very similar
to those at birth. With this study we set up the basis of future work where we
will investigate more realistic models of star formation compared to this
instantaneous, baseline case.Comment: 25 pages, 19 figures. Accepted by Ap
Hunting for Runaways from the Orion Nebula Cluster
We use Gaia DR2 to hunt for runaway stars from the Orion Nebula Cluster
(ONC). We search a region extending 45{\deg} around the ONC and out to 1 kpc to
find sources that overlapped in angular position with the cluster in the last
~10 Myr. We find ~17,000 runaway/walkaway candidates satisfy this 2D traceback
condition. Most of these are expected to be contaminants, e.g., caused by
Galactic streaming motions of stars at different distances. We thus examine six
further tests to help identify real runaways, namely: (1) possessing young
stellar object (YSO) colors and magnitudes based on Gaia optical photometry;
(2) having IR excess consistent with YSOs based on 2MASS and WISE photometry;
(3) having a high degree of optical variability; (4) having closest approach
distances well constrained to within the cluster half-mass radius; (5) having
ejection directions that avoid the main Galactic streaming contamination zone;
and (6) having a required radial velocity (RV) for 3D overlap of reasonable
magnitude (or, for the 7% of candidates with measured RVs, satisfying 3D
traceback). Thirteen sources, not previously noted as Orion members, pass all
these tests, while another twelve are similarly promising, except they are in
the main Galactic streaming contamination zone. Among these 25 ejection
candidates, ten with measured RVs pass the most restrictive 3D traceback
condition. We present full lists of runaway/walkaway candidates, estimate the
high-velocity population ejected from the ONC and discuss its implications for
cluster formation theories via comparison with numerical simulations.Comment: 22 pages, 10 figures, and 5 tables. Accepted for publication in Ap
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