96 research outputs found
X-rays from HH210 in the Orion nebula
We report the detection during the Chandra Orion Ultradeep Project (COUP) of
two soft, constant, and faint X-ray sources associated with the Herbig-Haro
object HH210. HH210 is located at the tip of the NNE finger of the emission
line system bursting out of the BN-KL complex, northwest of the Trapezium
cluster in the OMC-1 molecular cloud. Using a recent Halpha image obtained with
the ACS imager on board HST, and taking into account the known proper motions
of HH210 emission knots, we show that the position of the brightest X-ray
source, COUP703, coincides with the emission knot 154-040a of HH210, which is
the emission knot of HH210 having the highest tangential velocity (425 km/s).
The second X-ray source, COUP704, is located on the complicated emission tail
of HH210 close to an emission line filament and has no obvious optical/infrared
counterpart. Spectral fitting indicates for both sources a plasma temperature
of ~0.8 MK and absorption-corrected X-ray luminosities of about 1E30 erg/s
(0.5-2.0 keV). These X-ray sources are well explained by a model invoking a
fast-moving, radiative bow shock in a neutral medium with a density of ~12000
cm^{-3}. The X-ray detection of COUP704 therefore reveals, in the complicated
HH210 region, an energetic shock not yet identified at other wavelengths.Comment: 5 pages, 3 figures; accepted for publication in A&A Letter
The Spatial Structure of Young Stellar Clusters. III. Physical Properties and Evolutionary States
We analyze the physical properties of stellar clusters that are detected in
massive star-forming regions in the MYStIX project--a comparative,
multiwavelength study of young stellar clusters within 3.6 kpc that contain at
least one O-type star. Tabulated properties of subclusters in these regions
include physical sizes and shapes, intrinsic numbers of stars, absorptions by
the molecular clouds, and median subcluster ages. Physical signs of dynamical
evolution are present in the relations of these properties, including
statistically significant correlations between subcluster size, central
density, and age, which are likely the result of cluster expansion after gas
removal. We argue that many of the subclusters identified in Paper I are
gravitationally bound because their radii are significantly less than what
would be expected from freely expanding clumps of stars with a typical initial
stellar velocity dispersion of ~3 km/s for star-forming regions. We explore a
model for cluster formation in which structurally simpler clusters are built up
hierarchically through the mergers of subclusters--subcluster mergers are
indicated by an inverse relation between the numbers of stars in a subcluster
and their central densities (also seen as a density vs. radius relation that is
less steep than would be expected from pure expansion). We discuss implications
of these effects for the dynamical relaxation of young stellar clusters.Comment: Accepted for publication in The Astrophysical Journal ; 48 pages, 13
figures, and 6 table
The Elephant Trunk Nebula and the Trumpler 37 cluster: Contribution of triggered star formation to the total population of an HII region
Rich young stellar clusters produce HII regions whose expansion into the
nearby molecular cloud is thought to trigger the formation of new stars.
However, the importance of this mode of star formation is uncertain. This
investigation seeks to quantify triggered star formation (TSF) in IC 1396A
(a.k.a., the Elephant Trunk Nebula), a bright rimmed cloud (BRC) on the
periphery of the nearby giant HII region IC 1396 produced by the Trumpler 37
cluster. X-ray selection of young stars from Chandra X-ray Observatory data is
combined with existing optical and infrared surveys to give a more complete
census of the TSF population. Over 250 young stars in and around IC 1396A are
identified; this doubles the previously known population. A spatio-temporal
gradient of stars from the IC 1396A cloud toward the primary ionizing star HD
206267 is found. We argue that the TSF mechanism in IC 1396A is the
radiation-driven implosion process persisting over several million years.
Analysis of the X-ray luminosity and initial mass functions indicates that >140
stars down to 0.1 Msun were formed by TSF. Considering other BRCs in the IC
1396 HII region, we estimate the TSF contribution for the entire HII region
exceeds 14-25% today, and may be higher over the lifetime of the HII region.
Such triggering on the periphery of HII regions may be a significant mode of
star formation in the Galaxy.Comment: Accepted for publication in MNRAS; 28 pages, 18 figure
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