78 research outputs found
A Chandra ACIS Study of the Young Star Cluster Trumpler 15 in Carina and Correlation with Near-infrared Sources
Using the highest-resolution X-ray observation of the Trumpler 15 star
cluster taken by the Chandra X-ray Observatory, we estimate the total size of
its stellar population by comparing the X-ray luminosity function of the
detected sources to a calibrator cluster, and identify for the first time a
significant fraction (~14%) of its individual members. The highest-resolution
near-IR observation of Trumpler 15 (taken by the HAWK-I instrument on the VLT)
was found to detect most of our X-ray selected sample of cluster members, with
a K-excess disk frequency of 3.8+-0.7%. The near-IR data, X-ray luminosity
function, and published spectral types of the brightest members support a
cluster age estimate (5-10 Myr) that is older than those for the nearby
Trumpler 14 and Trumpler 16 clusters, and suggest that high-mass members may
have already exploded as supernovae. The morphology of the inner ~0.7 pc core
of the cluster is found to be spherical. However, the outer regions (beyond 2
pc) are elongated, forming an `envelope' of stars that, in projection, appears
to connect Trumpler 15 to Trumpler 14; this morphology supports the view that
these clusters are physically associated. Clear evidence of mass segregation is
seen. This study appears in a Special Issue of the ApJS devoted to the Chandra
Carina Complex Project (CCCP), a 1.42 square degree Chandra X-ray survey of the
Great Nebula in Carina.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
least. 30 pages; 8 figures; 3 table
Global X-ray properties of the Orion Nebula region
Based on the Chandra Orion Ultradeep Project (COUP) observation, we establish
the global X-ray properties of the stellar population associated with the Orion
Nebula. Three components contribute roughly equally to the integrated COUP
luminosity in the hard (2-8 keV) X-ray band: several OB stars, 822 lightly
obscured cool stars in the Orion Nebula Cluster (ONC), and 559 heavily obscured
stars. ONC stars 0.5-2 pc from the center show a spatial asymmetry consistent
with violent relaxation in the stellar dynamics. The obscured COUP sources
concentrate around both OMC-1 molecular cores; these small-scale structures
indicate ages t < 0.1 Myr. The X-ray luminosity function (XLF) of the lightly
obscured sample is roughly lognormal in shape. The obscured population is
deficient in lower-luminosity stars, perhaps due to localized circumstellar
material. Mass-stratified XLFs show that one-third of the Orion Nebula region
hard-band emission is produced by the bright O6 star theta-1 Ori C and half is
produced by lower mass pre-main sequence stars with masses 0.3 < M < 3 Mo. Very
low mass stars contribute little to the cluster X-ray emission.
Using the hard band emission, we show that young stellar clusters like the
ONC can be readily detected and resolved with Chandra across the Galactic disk,
even in the presence of heavy obscuration. The Orion Nebula sample is a
valuable template for studies of distant clusters. For example, the peak of the
XLF shape can serve as a standard candle for a new distance measure to distant
young stellar clusters, and the presence of a neon emission line complex around
1 keV can serve as a diagnostic for young stars.Comment: Accepted for publication in the Astrophysical Journal Supplements,
Special Issue on the Chandra Orion Ultradeep Project (COUP). 11 pages, 7
figures. See http://www.astro.psu.edu/coup for an overview of COU
A Catalog of Chandra X-ray Sources in the Carina Nebula
We present a catalog of ~14,000 X-ray sources observed by the ACIS instrument
on the Chandra X-ray Observatory within a 1.42 square degree survey of the
Great Nebula in Carina, known as the Chandra Carina Complex Project (CCCP).
This study appears in a Special Issue of the ApJS devoted to the CCCP. Here, we
describe the data reduction and analysis procedures performed on the X-ray
observations, including calibration and cleaning of the X-ray event data, point
source detection, and source extraction. The catalog appears to be complete
across most of the field to an absorption-corrected total-band luminosity of
~10^{30.7} erg/s for a typical low-mass pre-main sequence star. Counterparts to
the X-ray sources are identified in a variety of visual, near-infrared, and
mid-infrared surveys. The X-ray and infrared source properties presented here
form the basis of many CCCP studies of the young stellar populations in Carina.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
least. 29 pages, 11 figure
Spitzer Imaging of the Nearby Rich Young Cluster, Cep OB3b
We map the full extent of a rich massive young cluster in the Cep OB3b
association with the IRAC and MIPS instruments aboard the {\it Spitzer} Space
Telescope and the ACIS instrument aboard the X-Ray Observatory.
At 700 pc, it is revealed to be the second nearest large ( member),
young ( Myr) cluster known. In contrast to the nearest large cluster, the
Orion Nebula Cluster, Cep OB3b is only lightly obscured and is mostly located
in a large cavity carved out of the surrounding molecular cloud. Our infrared
and X-ray datasets, as well as visible photometry from the literature, are used
to take a census of the young stars in Cep OB3b. We find that the young stars
within the cluster are concentrated in two sub-clusters; an eastern
sub-cluster, near the Cep B molecular clump, and a western sub-cluster, near
the Cep F molecular clump. Using our census of young stars, we examine the
fraction of young stars with infrared excesses indicative of circumstellar
disks. We create a map of the disk fraction throughout the cluster and find
that it is spatially variable. Due to these spatial variations, the two
sub-clusters exhibit substantially different average disk fractions from each
other: and . We discuss whether the discrepant disk
fractions are due to the photodestruction of disks by the high mass members of
the cluster or whether they result from differences in the ages of the
sub-clusters. We conclude that the discrepant disk fractions are most likely
due to differences in the ages.Comment: 48 Pages, 12 figures, 6 table
2-[(1-{[3-(dimethylazaniumyl)propyl]methylamino}ethylidene)azaniumyl]nonahydro-closo-decaborate dimethyl sulfoxide disolvate
The title compound, 2-B10H9NH=C(CH3)N(CH3)CH2CH2CH2N(CH3)2H·2C2H6OS or C8H29B10N3·2C2H6OS, is zwitterionic with the negative charge localized on the decaborate cage and the positive charge on the terminal ammonium group. Two molecules of dimethyl sulfoxide (DMSO) and one molecule of the title compound constitute the asymmetric unit. One DMSO molecule is disordered [ratio 0.739 (3):0.261 (3)]. The bonds and angles within the decaborate cage are within the normal ranges. The amidine fragment of the ligand, which is expected to be planar, is significantly distorted from planarity as exemplified by four torsion angles [B—N—C—C = 8.4 (3), H—N—C—N = 5(2), N—C—N—C = 7.3 (3) and C—C—N—C = 14.8 (3)°] found within this portion of the molecule. The crystal packing consists of head-to-tail-arranged dimers of the title molecule held together by four molecules of DMSO which are attached via strong N—H⋯O and weak C—H⋯O hydrogen bonds
X-ray emission from young brown dwarfs in the Orion Nebula Cluster
We use the sensitive X-ray data from the Chandra Orion Ultradeep Project
(COUP) to study the X-ray properties of 34 spectroscopically-identified brown
dwarfs with near-infrared spectral types between M6 and M9 in the core of the
Orion Nebula Cluster. Nine of the 34 objects are clearly detected as X-ray
sources. The apparently low detection rate is in many cases related to the
substantial extinction of these brown dwarfs; considering only the BDs with
mag, nearly half of the objects (7 out of 16) are detected in
X-rays. Our 10-day long X-ray lightcurves of these objects exhibit strong
variability, including numerous flares. While one of the objects was only
detected during a short flare, a statistical analysis of the lightcurves
provides evidence for continuous (`quiescent') emission in addition to flares
for all other objects. Of these, the M9 brown dwarf COUP 1255 = HC 212
is one of the coolest known objects with a clear detection of quiescent X-ray
emission. The X-ray properties (spectra, fractional X-ray luminosities, flare
rates) of these young brown dwarfs are similar to those of the low-mass stars
in the ONC, and thus there is no evidence for changes in the magnetic activity
around the stellar/substellar boundary, which lies at M6 for ONC
sources. Since the X-ray properties of the young brown dwarfs are also similar
to those of M6--M9 field stars, the key to the magnetic activity in very cool
objects seems to be the effective temperature, which determines the degree of
ionization in the atmosphere.Comment: accepted for ApJS, COUP special issu
An Introduction to the Chandra Carina Complex Project
The Great Nebula in Carina provides an exceptional view into the violent
massive star formation and feedback that typifies giant HII regions and
starburst galaxies. We have mapped the Carina star-forming complex in X-rays,
using archival Chandra data and a mosaic of 20 new 60ks pointings using the
Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for
understanding recent and ongoing star formation and to probe Carina's regions
of bright diffuse X-ray emission. This study has yielded a catalog of
properties of >14,000 X-ray point sources; >9800 of them have multiwavelength
counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have
separated these point sources from the extensive, spatially-complex diffuse
emission that pervades the region; X-ray properties of this diffuse emission
suggest that it traces feedback from Carina's massive stars. In this
introductory paper, we motivate the survey design, describe the Chandra
observations, and present some simple results, providing a foundation for the
15 papers that follow in this Special Issue and that present detailed catalogs,
methods, and science results.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
least. 43 pages; 18 figure
Candidate X-ray-Emitting OB Stars in the Carina Nebula Identified Via Infrared Spectral Energy Distributions
We report the results of a new survey of massive, OB stars throughout the
Carina Nebula using the X-ray point source catalog provided by the Chandra
Carina Complex Project (CCCP) in conjunction with infrared (IR) photometry from
the Two Micron All-Sky Survey and the Spitzer Space Telescope Vela--Carina
survey. Mid-IR photometry is relatively unaffected by extinction, hence it
provides strong constraints on the luminosities of OB stars, assuming that
their association with the Carina Nebula, and hence their distance, is
confirmed. We fit model stellar atmospheres to the optical (UBV) and IR
spectral energy distributions (SEDs) of 182 OB stars with known spectral types
and measure the bolometric luminosity and extinction for each star. We find
that the extinction law measured toward the OB stars has two components:
Av=1--1.5 mag produced by foreground dust with a ratio of total-to-selective
absorption Rv=3.1 plus a contribution from local dust with Rv>4.0 in the Carina
molecular clouds that increases as Av increases. Using X-ray emission as a
strong indicator of association with Carina, we identify 94 candidate OB stars
with Lbol\geq10^4 Lsun by fitting their IR SEDs. If the candidate OB stars are
eventually confirmed by follow-up spectroscopic observations, the number of
cataloged OB stars in the Carina Nebula will increase by ~50%. Correcting for
incompleteness due to OB stars falling below the Lbol cutoff or the CCCP
detection limit, these results potentially double the size of the young massive
stellar population.Comment: 19 pages, 8 figures, accepted for the ApJS Special Issue on the
Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011.
All 16 CCCP Special Issue papers, including a version of this article with
high-quality figures, are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html (through 2011
at least
Excess AGN Activity in the z=2.30 Protocluster in HS 1700+64
We present the results of spectroscopic, narrow-band and X-ray observations
of a z=2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of
BX/MD galaxies, which are selected to be at z~2.2-2.7 by their rest-frame
ultraviolet colours, we find that there are 5 protocluster AGN which have been
identified by characteristic emission-lines in their optical/near-IR spectra;
this represents an enhancement over the field significant at ~98.5 per cent
confidence. Using a ~200 ks Chandra/ACIS-I observation of this field we detect
a total of 161 X-ray point sources to a Poissonian false-probability limit of
4x10^{-6} and identify 8 of these with BX/MD galaxies. Two of these are
spectroscopically confirmed protocluster members and are also classified as
emission-line AGN. When compared to a similarly selected field sample the
analysis indicates this is also evidence for an enhancement of X-ray selected
BX/MD AGN over the field, significant at ~99 per cent confidence. Deep Lya
narrow-band imaging reveals that a total of 4/123 Lya emitters (LAEs) are found
to be associated with X-ray sources, with two of these confirmed protocluster
members and one highly likely member. We do not find a significant enhancement
of AGN activity in this LAE sample over that of the field (result significant
at only 87 per cent confidence). The X-ray emitting AGN fractions for the BX/MD
and LAE samples are found to be 6.9_{-4.4}^{+9.2} and 2.9_{-1.6}^{+2.9} per
cent, respectively, for protocluster AGN with L_{2-10 keV}>4.6x10^{43} erg
s^{-1} at z=2.30. These findings are similar to results from the z=3.09
protocluster in the SSA 22 field found by Lehmer et al. (2009), in that both
suggest AGN activity is favoured in dense environments at z>2.Comment: 8 pages, 2 figures. Accepted for publication in MNRAS
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