139 research outputs found
Spitzer IRAC and MIPS Imaging of Clusters and Outflows in 9 High-mass Star Forming Regions
We present Spitzer Space Telescope IRAC and MIPS observations toward a sample
of nine high-mass star forming regions at a distance of around 2 kpc. Based on
IRAC and MIPS 24 m photometric results and 2MASS JHKs data, we carry out a
census of young stellar objects (YSOs) in a 5' by 5' field toward each region.
Toward seven out of the nine regions, we detect parsec sized clusters with
around 20 YSOs surrounded by a more extended and sparse distribution of young
stars and protostars. For the other two regions, IRAS 20126+4104 and IRAS
22172+5549, the former has the lowest number of YSOs in the sample and shows no
obvious cluster, and the latter appears to be part of a larger, potentially
more evolved cluster. The deep IRAC imaging reveals at least twelve outflows in
eight out of the nine regions, with nine outflows prominent in the 4.5 m
band most probably attributed to shocked H emission, two outflows dominated
by scattered light in the 3.6 and 4.5 m bands, and one outflow standing
out from its hydrocarbon emission in the 8.0 m band. In comparison with
previous ground-based observations, our IRAC observations reveal new outflow
structures in five regions. The dramatically different morphologies of detected
outflows can be tentatively interpreted in terms of possible evolution of
massive outflows. The driving sources of these outflows are deeply embedded in
dense dusty cores revealed by previous millimeter interferometric observations.
We detect infrared counterparts of these dusty cores in the IRAC or MIPS 24
m bands. Reflection nebulae dominated by the emission from UV heated
hydrocarbons in the 8 m band can be found in most regions and they may
imply the presence of young B stars.Comment: 76 pages, 25 figures and 5 tables, ApJ in press, a full resolution
version available at http://www.cfa.harvard.edu/~kqiu/spitzer.pd
The Molecular Gas Environment around Two Herbig Ae/Be Stars: Resolving the Outflows of LkHa 198 and LkHa 225S
Observations of outflows associated with pre-main-sequence stars reveal
details about morphology, binarity and evolutionary states of young stellar
objects. We present molecular line data from the Berkeley-Illinois-Maryland
Association array and Five Colleges Radio Astronomical Observatory toward the
regions containing the Herbig Ae/Be stars LkHa 198 and LkHa 225S. Single dish
observations of 12CO 1-0, 13CO 1-0, N2H+ 1-0 and CS 2-1 were made over a field
of 4.3' x 4.3' for each species. 12CO data from FCRAO were combined with high
resolution BIMA array data to achieve a naturally-weighted synthesized beam of
6.75'' x 5.5'' toward LkHa 198 and 5.7'' x 3.95'' toward LkHa 225S,
representing resolution improvements of factors of approximately 10 and 5 over
existing data. By using uniform weighting, we achieved another factor of two
improvement. The outflow around LkHa 198 resolves into at least four outflows,
none of which are centered on LkHa 198-IR, but even at our resolution, we
cannot exclude the possibility of an outflow associated with this source. In
the LkHa 225S region, we find evidence for two outflows associated with LkHa
225S itself and a third outflow is likely driven by this source. Identification
of the driving sources is still resolution-limited and is also complicated by
the presence of three clouds along the line of sight toward the Cygnus
molecular cloud. 13CO is present in the environments of both stars along with
cold, dense gas as traced by CS and (in LkHa 225S) N2H+. No 2.6 mm continuum is
detected in either region in relatively shallow maps compared to existing
continuum observations.Comment: 14 pages, 10 figures (5 color), accepted for publication in Ap
Chandra Study of Young Stellar Objects in the NGC 1333 Star-forming Cloud
NGC 1333, a highly active star formation region within the Perseus molecular
cloud complex, has been observed with the ACIS-I detector on board the Chandra
X-ray Observatory. In our image with a sensitivity limit of ~ 1e28 erg/s, we
detect 127 X-ray sources, of which, 95 are known cluster members. The X-ray
luminosity function of the discovered YSO population spans a range of
1e28-3.2e31 erg/s in the 0.5-8 keV band. Comparison with K-band source counts
indicates that we detect all of the known cluster members with K < 12, and
about half of members with K > 12. We detect seven X-ray emitting YSOs which
drive optically visible jets as well as one deeply embedded object that has not
been detected in near-IR observations. The presence or absence of an outflows
does not appear to produce any difference in X-ray properties of YSOs. We also
find no systematic differences in X-ray luminosity distributions between two
complete subsamples of CTTs and WTTs. That suggests that there is no difference
in the astrophysical mechanism of WTT and CTT X-ray emission production.
Additional results include: the X-ray emission from two late-B stars which
illuminate the reflection nebula originates from unresolved late-type
companions; two T Tauri stars are discovered as previously unknown components
of visual binaries; and the X-ray counterpart of SVS 16 has the column density
much lower than that expected from near-IR photometry and thus its X-ray
luminosity is not anomalously high, as has been previously suggested.Comment: 53 pages, 14 figures, 3 tables. To appear in the Astrophysical
Journal; scheduled for 2002, ApJ, 575 (August 10th). High quality copy
available at ftp://ftp.astro.psu.edu/pub/gkosta/ngc1333
Chandra Observations of High Mass Young Stellar Objects in the Monoceros R2 molecular cloud
We observed the Monoceros R2 molecular cloud with the ACIS-I array onboard
the Chandra X-ray Observatory. From the central 3.2' x 3.2' region, we detect
154 sources above the detection limit of ~5x10^-16 ergs s^-1 cm^-2 with a 100
ks-exposure. About 85% of the X-ray sources are identified with an infrared
counterpart, including four high mass stars in zero age main sequence (ZAMS)
and/or pre main sequence (PMS) phase. The X-ray spectra of the high mass ZAMS
and PMS stars are represented with a thin thermal plasma model of a temperature
above 2 keV. The X-rays are time-variable and exhibit rapid flares. These high
temperature plasma and flaring activity are similar to those seen in low mass
PMS stars and contrary to the behavior observed in high mass main sequence
stars. The X-ray luminosity increases as the intrinsic K-band flux increases.
However, the X-ray luminosity saturates at a level of ~10^31 ergs s^-1. We
conclude that high mass ZAMS and PMS emit X-rays, possibly due to the magnetic
activity like those of low mass stars.Comment: 12 pages, 10 figures, accepted for publication in Ap
High-velocity collimated outflows in planetary nebulae: NGC 6337, He 2-186, and K 4-47
We have obtained narrow-band images and high-resolution spectra of the
planetary nebulae NGC 6337, He 2-186, and K 4-47, with the aim of investigating
the relation between their main morphological components and several
low-ionization features present in these nebulae. The data suggest that NGC
6337 is a bipolar PN seen almost pole on, with polar velocities higher than 200
km/s. The bright inner ring of the nebula is interpreted to be the "equatorial"
density enhancement. It contains a number of low-ionization knots and outward
tails that we ascribe to dynamical instabilities leading to fragmentation of
the ring or transient density enhancements due to the interaction of the
ionization front with previous density fluctuations in the ISM. The lobes show
a pronounced point-symmetric morphology and two peculiar low-ionization
filaments whose nature remains unclear. The most notable characteristic of He
2-186 is the presence of two high-velocity (higher than 135 km/s) knots from
which an S-shaped lane of emission departs toward the central star. K 4-47 is
composed of a compact core and two high-velocity, low-ionization blobs. We
interpret the substantial broadening of line emission from the blobs as a
signature of bow shocks, and using the modeling of Hartigan, Raymond, & Hartman
(1987), we derive a shock velocity of 150 km/s and a mild inclination of the
outflow on the plane of the sky. We discuss possible scenarios for the
formation of these nebulae and their low-ionization features. In particular,
the morphology of K 4-47 hardly fits into any of the usually adopted mass-loss
geometries for single AGB stars. Finally, we discuss the possibility that
point-symmetric morphologies in the lobes of NGC 6337 and the knots of He 2-186
are the result of precessing outflows from the central stars.Comment: 16 pages plus 7 figures, ApJ accepted. Also available at
http://www.iac.es/publicaciones/preprints.htm
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