54 research outputs found
X Marks the Spot: Nexus of Filaments, Cores, and Outflows in a Young Star-Forming Region
We present a multiwavelength investigation of a region of a nearby giant
molecular cloud that is distinguished by a minimal level of star formation
activity. With our new 12CO(J=2-1) and 13CO(J=2-1) observations of a remote
region within the middle of the California molecular cloud, we aim to
investigate the relationship between filaments, cores, and a molecular outflow
in a relatively pristine environment. An extinction map of the region from
Herschel Space Observatory observations reveals the presence of two 2-pc-long
filaments radiating from a high-extinction clump. Using the 13CO observations,
we show that the filaments have coherent velocity gradients and that their
mass-per-unit-lengths may exceed the critical value above which filaments are
gravitationally unstable. The region exhibits structure with eight cores, at
least one of which is a starless, prestellar core. We identify a low-velocity,
low-mass molecular outflow that may be driven by a flat spectrum protostar. The
outflow does not appear to be responsible for driving the turbulence in the
core with which it is associated, nor does it provide significant support
against gravitational collapse.Comment: Accepted for publication in the Astrophysical Journa
Star formation in W3 - AFGL333: Young stellar content, properties and roles of external feedback
One of the key questions in the field of star formation is the role of
stellar feedback on subsequent star formation process. The W3 giant molecular
cloud complex at the western border of the W4 super bubble is thought to be
influenced by the stellar winds of the massive stars in W4. AFGL333 is a ~10^4
Msun cloud within W3. This paper presents a study of the star formation
activity within AFGL333 using deep JHKs photometry obtained from the NOAO
Extremely Wide-Field Infrared Imager combined with Spitzer-IRAC-MIPS
photometry. Based on the infrared excess, we identify 812 candidate young
stellar objects in the complex, of which 99 are classified as Class I and 713
are classified as Class II sources. The stellar density analysis of young
stellar objects reveals three major stellar aggregates within AFGL333, named
here AFGL333-main, AFGL333-NW1 and AFGL333-NW2. The disk fraction within
AFGL333 is estimated to be ~50-60%. We use the extinction map made from the
H-Ks colors of the background stars to understand the cloud structure and to
estimate the cloud mass. The CO-derived extinction map corroborates the cloud
structure and mass estimates from NIR color method. From the stellar mass and
cloud mass associated with AFGL333, we infer that the region is currently
forming stars with an efficiency of ~4.5% and at a rate of ~2 - 3 Msun
Myr-1pc-2. In general, the star formation activity within AFGL333 is comparable
to that of nearby low mass star-forming regions. We do not find any strong
evidence to suggest that the stellar feedback from the massive stars of nearby
W4 super bubble has affected the global star formation properties of the
AFGL333 region.Comment: 17 pages, 9 figures, Accepted for publication in Ap
Observational Constraints on Submillimeter Dust Opacity
Infrared extinction maps and submillimeter dust continuum maps are powerful probes of the density structure in the envelope of star-forming cores. We make a direct comparison between infrared and submillimeter dust continuum observations of the low-mass Class 0 core, B335, to constrain the ratio of submillimeter to infrared opacity (Îș_(smm)/Îș_(ir)) and the submillimeter opacity power-law index (Îș â λâÎČ). Using the average value of theoretical dust opacity models at 2.2 ÎŒm, we constrain the dust opacity at 850 and 450 ÎŒm. Using new dust continuum models based upon the broken power-law density structure derived from interferometric observations of B335 and the infall model derived from molecular line observations of B335, we find that the opacity ratios are ^Îș_(850)_Îș_(2.2) = (3.21 - 4.80)^(+0.44)_(-0.30) x 10^(-4) ^Îș_(450)_Îș(2.0) = (12.8-24.8)^(+2.4)_(-1.3) x 10^(-4) with a submillimeter opacity power-law index of ÎČ_(smm) = (2.18-2.58)^(+0.30)_(â0.30). The range of quoted values is determined from the uncertainty in the physical model for B335. For an average 2.2 ÎŒm opacity of 3800 ± 700 cm^2 g^(â1), we find a dust opacity at 850 and 450 ÎŒm of Îș_(850) = (1.18-1.77)^9+0.36)_(â0.24) and Îș_(450) = (4.72-9.13)^(+1.9)_(â0.98) cm^2 g^(â1) of dust. These opacities are from (0.65-0.97)Îș^(OH5)_(850) of the widely used theoretical opacities of Ossenkopf and Henning for coagulated ice grains with thin mantles at 850 ÎŒm
A CO Line and Infrared Continuum Study of the Active Star-Forming Complex W51
We present the results of an extensive observational study of the active
star-forming complex W51 that was observed in the J=2-1 transition of the 12CO
and 13CO molecules over a 1.25 deg x 1.00 deg region with the University of
Arizona Heinrich Hertz Submillimeter Telescope. We use a statistical
equilibrium code to estimate physical properties of the molecular gas. We
compare the molecular cloud morphology with the distribution of infrared (IR)
and radio continuum sources, and find associations between molecular clouds and
young stellar objects (YSOs) listed in Spitzer IR catalogs. The ratios of CO
lines associated with HII regions are different from the ratios outside the
active star-forming regions. We present evidence of star formation triggered by
the expansion of the HII regions and by cloud-cloud collisions. We estimate
that about 1% of the cloud mass is currently in YSOs.Comment: 18 pages, 29 figures; accepted for publication in ApJ
The distribution of H13CN in the circumstellar envelope around IRC+10216
H13CN J=8-7 sub-millimetre line emission produced in the circumstellar
envelope around the extreme carbon star IRC+10216 has been imaged at
sub-arcsecond angular resolution using the SMA. Supplemented by a detailed
excitation analysis the average fractional abundance of H13CN in the inner wind
(< 5E15 cm) is estimated to be about 4E-7, translating into a total HCN
fractional abundance of 2E-5 using the isotopic ratio 12C/13C=50.
Multi-transitional single-dish observations further requires the H13CN
fractional abundance to remain more or less constant in the envelope out to a
radius of about 4E16 cm, where the HCN molecules are effectively destroyed,
most probably, by photodissociation. The large amount of HCN present in the
inner wind provides effective line cooling that can dominate over that
generated from CO line emission. It is also shown that great care needs to be
taken in the radiative transfer modelling where non-local, and non-LTE, effects
are important and where the radiation field from thermal dust grains plays a
major role in exciting the HCN molecules. The amount of HCN present in the
circumstellar envelope around IRC+10216 is consistent with predicted
photospheric values based on equilibrium chemical models and indicates that any
non-equilibrium chemistry occurring in the extended pulsating atmosphere has no
drastic net effect on the fractional abundance of HCN molecules that enters the
outer envelope. It further suggests that few HCN molecules are incorporated
into dust grains.Comment: Accepted for publication in ApJ. 20 pages, 7 figure
Submillimeter Observations of Dense Clumps in the Infrared Dark Cloud G049.40-00.01
We obtained 350 and 850 micron continuum maps of the infrared dark cloud
G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01
based on the 350 micron continuum map with an angular resolution of about 9.6".
We present submillimeter continuum maps and report physical properties of the
clumps. The masses of clumps range from 50 to 600 M_sun. About 70% of the
clumps are associated with bright 24 micron emission sources, and they may
contain protostars. The most massive two clumps show extended, enhanced 4.5
micron emission indicating vigorous star-forming activity. The clump size-mass
distribution suggests that many of them are forming high mass stars.
G049.40-00.01 contains numerous objects in various evolutionary stages of star
formation, from pre-protostellar clumps to HII regions.Comment: 6 pages, 3 figures; accepted for publication in Ap
Mid- CO Line Observations of Protostellar Outflows in the Orion Molecular Clouds
Ten protostellar outflows in the Orion molecular clouds were mapped in the
CO/CO and CO
lines. The maps of these mid- CO lines have an angular resolution of about
10 and a typical field size of about 100. Physical parameters of the
molecular outflows were derived, including mass transfer rates, kinetic
luminosities, and outflow forces. The outflow sample was expanded by
re-analyzing archival data of nearby low-luminosity protostars, to cover a wide
range of bolometric luminosities. Outflow parameters derived from other
transitions of CO were compared. The mid- () and
low- () CO line wings trace essentially the same outflow
component. By contrast, the high- (up to )
line-emission luminosity of CO shows little correlation with the kinetic
luminosity from the line, which suggests that they trace
distinct components. The low/mid- CO line wings trace long-term outflow
behaviors while the high- CO lines are sensitive to short-term activities.
The correlations between the outflow parameters and protostellar properties are
presented, which shows that the strengths of molecular outflows increase with
bolometric luminosity and envelope mass.Comment: 31 pages, 16 figures, Accepted for publication in ApJ
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The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds. VI. The Cep OB3 Cloud (Cepheus B and C) in CO J=2-1, (CO)-C-13 J=2-1, and CO J=3-2
We present (1) new fully sampled maps of CO and (CO)-C-13 J = 2-1 emission and CO J = 3-2 emission toward the molecular clouds Cep B and C, associated with the Cep OB3 association; (2) a map of extinction, A(V), derived from IR colors of background stars; and (3) the distribution of young stellar objects (YSOs) over the same field as the molecular maps. An LTE analysis of the CO and (CO)-C-13. maps yields the distribution of molecular column densities and temperatures. Substantial variations are evident across the clouds; smaller subregions show correlations between molecular properties and dust extinction, consistent with a picture of outer photodissociation regions with a layer of CO-dark molecular gas, a CO self-shielded interior, and an inner cold dense region where CO is largely depleted onto grains. Comparing the distribution of YSOs with molecular gas surface density shows a power-law relation very similar in slope to that for the giant molecular cloud associated with the H II region Sh2-235 from a previous paper in this series that employed the same methodology. We note the presence of several compact, isolated CO emission sources in the J = 3-2 maps. The gas temperature and (CO)-C-13. velocity dispersion yield a map of the sonic Mach number, which varies across the cloud but always exceeds unity, confirming the pervasiveness of supersonic turbulence over length scales greater than or similar to 0.1 pc (the map resolution). We also compute a J = 2-1 CO X-factor that varies with position but is, on average, within. 20% of the Galactic average derived from CO J = 1-0 observations
Resolving the Dusty Circumstellar Structure of the Enigmatic Symbiotic Star CH Cygni with the MMT Adaptive Optics System
We imaged the symbiotic star CH Cyg and two PSF calibration stars using the
unique 6.5m MMT deformable secondary adaptive optics system. Our
high-resolution (FWHM=0.3"), very high Strehl (98%+-2%) mid-infrared (9.8 and
11.7 um) images of CH Cyg allow us to probe finer length scales than ever
before for this object. CH Cyg is significantly extended compared to our
unresolved PSF calibration stars (Mu UMa and Alpha Her) at 9.8 and 11.7 um. We
estimated the size of the extension by convolving a number of simple Gaussian
models with the Mu UMa PSF and determining which model provided the best fit to
the data. Adopting the Hipparcos distance for this object of 270 pc, we found a
nearly Gaussian extension with a FWHM at 9.8 um of ~40.5+-2.7 AU (0.15+-0.01")
and a FWHM at 11.7 um of 45.9+-2.7 AU (0.17+-0.01"). After subtracting out the
Gaussian component of the emission (convolved with our PSF), we found a faint
\~0.7" asymmetric extension which peaks in flux ~0.5" north of the stars. This
extension is roughly coincident with the northern knotlike feature seen in HST
WFPC2 images obtained in 1999.Comment: 18 pages, 7 figures, accepted by the Astrophysical Journa
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