73 research outputs found
The Massive Star-forming Regions Omnibus X-ray Catalog
We present the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog
(MOXC), a compendium of X-ray point sources from {\em Chandra}/ACIS
observations of a selection of MSFRs across the Galaxy, plus 30 Doradus in the
Large Magellanic Cloud. MOXC consists of 20,623 X-ray point sources from 12
MSFRs with distances ranging from 1.7 kpc to 50 kpc. Additionally, we show the
morphology of the unresolved X-ray emission that remains after the catalogued
X-ray point sources are excised from the ACIS data, in the context of \Spitzer\
and {\em WISE} observations that trace the bubbles, ionization fronts, and
photon-dominated regions that characterize MSFRs. In previous work, we have
found that this unresolved X-ray emission is dominated by hot plasma from
massive star wind shocks. This diffuse X-ray emission is found in every MOXC
MSFR, clearly demonstrating that massive star feedback (and the
several-million-degree plasmas that it generates) is an integral component of
MSFR physics.Comment: Accepted to ApJS, March 3, 2014. 51 pages, 25 figure
Rapid Circumstellar Disk Evolution and an Accelerating Star Formation Rate in the Infrared Dark Cloud M17 SWex
We present a catalog of 840 X-ray sources and first results from a 100 ks
Chandra X-ray Observatory imaging study of the filamentary infrared dark cloud
G014.22500.506, which forms the central regions of a larger cloud complex
known as the M17 southwest extension (M17 SWex). In addition to the rich
population of protostars and young stellar objects with dusty circumstellar
disks revealed by Spitzer Space Telescope archival data, we discover a
population of X-ray-emitting, intermediate-mass pre--main-sequence stars (IMPS)
that lack infrared excess emission from circumstellar disks. We model the
infrared spectral energy distributions of this source population to measure its
mass function and place new constraints on the inner dust disk destruction
timescales for 2-8 stars. We also place a lower limit on the star
formation rate (SFR) and find that it is quite high ( yr), equivalent to several Orion Nebula Clusters in
G14.2250.506 alone, and likely accelerating. The cloud complex has not
produced a population of massive, O-type stars commensurate with its SFR. This
absence of very massive () stars suggests that either (1)
M17 SWex is an example of a distributed mode of star formation that will
produce a large OB association dominated by intermediate-mass stars but
relatively few massive clusters, or (2) the massive cores are still in the
process of accreting sufficient mass to form massive clusters hosting O stars.Comment: 29 pages, 9 figures, accepted to Ap
The Diverse Stellar Populations of the W3 Star Forming Complex
An 800 sq-arcmin mosaic image of the W3 star forming complex obtained with
the Chandra X-ray Observatory gives a valuable new view of the spatial
structure of its young stellar populations. The Chandra image reveals about
1300 faint X-ray sources, most of which are PMS stars in the cloud. Some, but
not all, of the high-mass stars producing hypercompact and ultracompact H II
(UCHII) regions are also seen, as reported in a previous study.
The Chandra images reveal three dramatically different embedded stellar
populations. The W3 Main cluster extends over 7 pc with about 900 X-ray stars
in a nearly-spherical distribution centered on the well-studied UCHII regions
and high-mass protostars. The cluster surrounding the prototypical UCHII region
W3(OH) shows a much smaller (<0.6 pc), asymmetrical, and clumpy distribution of
about 50 PMS stars. The massive star ionizing the W3 North H II region is
completely isolated without any accompanying PMS stars. In W3 Main, the
inferred ages of the widely distributed PMS stars are significantly older than
the inferred ages of the central OB stars illuminating the UCHIIs. We suggest
that different formation mechanisms are necessary to explain the diversity of
the W3 stellar populations: cluster-wide gravitational collapse with delayed OB
star formation in W3 Main, collect-and-collapse triggering by shock fronts in
W3(OH), and a runaway O star or isolated massive star formation in W3 North.Comment: To appear in the Astrophysical Journal. 21 pages, 5 figures. A
version with high-quality figures is available at
http://www.astro.psu.edu/users/edf/W3_Chandra.pd
Membership of the Orion Nebula Population from the Chandra Orion Ultradeep Project
The Chandra Orion Ultradeep project (COUP) observation described in a
companion paper by Getman et al. provides an exceptionally deep X-ray survey of
the Orion Nebula Cluster and associated embedded young stellar objects.
Membership of the region is important for studies of the stellar IMF, cluster
dynamics, and star formation. The COUP study detected 1616 X-ray sources. In
this study we confirm cloud membership for 1315 stars, identify 16 probable
foreground field stars having optical counterparts with discrepant proper
motions, and classify the remaining 285 X-ray sources, of which 51 are lightly
and 234 heavily obscured. The 51 lightly obscured sources without known
counterparts fall into three groups. (i) Sixteen are likely new members of the
Orion Nebula Cluster. (ii) Two with unusually soft and non-flaring X-ray
emission appear to be associated with nebular shocks, and may be new examples
of X-rays produced at the bow shocks of Herbig-Haro outflows. (iii) The
remaining thirty three are very weak uncertain sources, possibly spurious. Out
of 234 heavily absorbed sources without optical or near-infrared counterparts
75 COUP sources are likely new embedded cloud members (with membership for 42
confirmed by powerful X-ray flares), and the remaining 159 are likely
extragalactic AGN seen through the molecular cloud, as argued by a careful
simulation of the extragalactic background population. Finally, a few new
binary companions to Orion stars may have been found, but most cases of
proximate COUP sources can be attributed to chance superpositions in this
crowded field.Comment: 49 pages, 6 figures, 5 tables. Accepted for publication in ApJS,
special issue dedicated to Chandra Orion Ultradeep Project. A version with
high quality figures can be found at
http://www.astro.psu.edu/users/gkosta/COUP_Membership.pd
- …