262 research outputs found
Molecular line contamination in the SCUBA-2 450 {\mu}m and 850 {\mu}m continuum data
Observations of the dust emission using millimetre/submillimetre bolometer
arrays can be contaminated by molecular line flux, such as flux from 12CO. As
the brightest molecular line in the submillimetre, it is important to quantify
the contribution of CO flux to the dust continuum bands. Conversion factors
were used to convert molecular line integrated intensities to flux detected by
bolometer arrays in mJy per beam. These factors were calculated for 12CO line
integrated intensities to the SCUBA-2 850 {\mu}m and 450 {\mu}m bands. The
conversion factors were then applied to HARP 12CO 3-2 maps of NGC 1333 in the
Perseus complex and NGC 2071 and NGC 2024 in the Orion B molecular cloud
complex to quantify the respective 12CO flux contribution to the 850 {\mu}m
dust continuum emission. Sources with high molecular line contamination were
analysed in further detail for molecular outflows and heating by nearby stars
to determine the cause of the 12CO contribution. The majority of sources had a
12CO 3-2 flux contribution under 20 per cent. However, in regions of molecular
outflows, the 12CO can dominate the source dust continuum (up to 79 per cent
contamination) with 12CO fluxes reaching \sim 68 mJy per beam.Comment: Accepted 2012 April 19 for publication in MNRAS. 21 pages, 13
figures, 3 table
The JCMT dense gas survey of the Perseus Molecular Cloud
We present the results of a large-scale survey of the very dense gas in the
Perseus molecular cloud using HCO+ and HCN (J = 4 - 3) transitions. We have
used this emission to trace the structure and kinematics of gas found in pre-
and protostellar cores, as well as in outflows. We compare the HCO+/HCN data,
highlighting regions where there is a marked discrepancy in the spectra of the
two emission lines. We use the HCO+ to identify positively protostellar
outflows and their driving sources, and present a statistical analysis of the
outflow properties that we derive from this tracer. We find that the relations
we calculate between the HCO+ outflow driving force and the Menv and Lbol of
the driving source are comparable to those obtained from similar outflow
analyses using 12CO, indicating that the two molecules give reliable estimates
of outflow properties. We also compare the HCO+ and the HCN in the outflows,
and find that the HCN traces only the most energetic outflows, the majority of
which are driven by young Class 0 sources. We analyse the abundances of HCN and
HCO+ in the particular case of the IRAS 2A outflows, and find that the HCN is
much more enhanced than the HCO+ in the outflow lobes. We suggest that this is
indicative of shock-enhancement of HCN along the length of the outflow; this
process is not so evident for HCO+, which is largely confined to the outflow
base.Comment: 25 pages, 14 figures, 9 table
CS Lines Profiles in Hot Cores
We present a theoretical study of CS line profiles in archetypal hot cores.
We provide estimates of line fluxes from the CS(1-0) to the CS(15-14)
transitions and present the temporal variation of these fluxes. We find that
\textit{i)} the CS(1-0) transition is a better tracer of the Envelope of the
hot core whereas the higher-J CS lines trace the ultra-compact core;
\textit{ii)} the peak temperature of the CS transitions is a good indicator of
the temperature inside the hot core; \textit{iii)} in the Envelope, the older
the hot core the stronger the self-absorption of CS; \textit{iv)} the
fractional abundance of CS is highest in the innermost parts of the
ultra-compact core, confirming the CS molecule as one of the best tracers of
very dense gas.Comment: 17 pages, 5 figures, 1 table, In press in Ap
3-D Models of Embedded High-Mass Stars: Effects of a Clumpy Circumstellar Medium
We use 3-D radiative transfer models to show the effects of clumpy
circumstellar material on the observed infrared colors of high mass stars
embedded in molecular clouds. We highlight differences between 3-D clumpy and
1-D smooth models which can affect the interpretation of data. We discuss
several important properties of the emergent spectral energy distribution
(SED): More near-infrared light (scattered and direct from the central source)
can escape than in smooth 1-D models. The near- and mid-infrared SED of the
same object can vary significantly with viewing angle, depending on the clump
geometry along the sightline. Even the wavelength-integrated flux can vary with
angle by more than a factor of two. Objects with the same average circumstellar
dust distribution can have very different near-and mid-IR SEDs depending on the
clump geometry and the proximity of the most massive clump to the central
source.
Although clumpiness can cause similar objects to have very different SEDs,
there are some observable trends. Near- and mid-infrared colors are sensitive
to the weighted average distance of clumps from the central source and to the
magnitude of clumpy density variations (smooth-to-clumpy ratio). Far-infrared
emission remains a robust measure of the total dust mass. We present simulated
SEDs, colors, and images for 2MASS and Spitzer filters. We compare to
observations of some UCHII regions and find that 3-D clumpy models fit better
than smooth models. In particular, clumpy models with fractal dimensions in the
range 2.3-2.8, smooth to clumpy ratios of <50%, and density distributions with
shallow average radial density profiles fit the SEDs best.Comment: accepted to ApJ; version with full-res figures:
http://www.astro.virginia.edu/~ri3e/clumpy3d.pd
The Effect of Molecular Contamination on the Emissivity Spectral Index in Orion A
The emissivity spectral index is a critical component in the study of the physical properties of dust grains in cold and optically thin interstellar star forming regions. Since submillimeter astronomy is an ideal tool to measure the thermal emission of those dust grains, it can be used to characterize this important parameter. We present the SCUBA-2 shared risks observations at 450 ÎĽm and 850 ÎĽm of the Orion A molecular cloud obtained at the James-Clerk-Maxwell telescope. Previous studies showed that molecular emission lines can also contribute significantly to the measured fluxes in those continuum bands. We use HARP 12CO 3-2 maps to evaluate the total molecular line contamination in the SCUBA-2 maps and its effect on the determination of the spectral index in highly contaminated areas. With the corrected fluxes, we have obtained new spectral index maps for different regions of the well-known integral-shaped filament. This work is part of an ongoing effort to characterize the properties of star forming regions in the Gould belt with the new instruments available at the JCMT
The James Clerk Maxwell telescope dense gas survey of the Perseus molecular cloud
This is the final version of the article. Available from the publisher via the DOI in this record.We present the results of a large-scale survey of the very dense (n > 106 cm-3) gas in the Perseus molecular cloud using HCO+ and HCN (J = 4 → 3) transitions. We have used this emission to trace the structure and kinematics of gas found in pre- and protostellar cores, as well as in outflows. We compare the HCO+/HCN data, highlighting regions where there is a marked discrepancy in the spectra of the two emission lines. We use the HCO+ to identify positively protostellar outflows and their driving sources, and present a statistical analysis of the outflow properties that we derive from this tracer. We find that the relations we calculate between the HCO+ outflow driving force and the Menv and Lbol of the driving source are comparable to those obtained from similar outflow analyses using 12CO, indicating that the two molecules give reliable estimates of outflow properties. We also compare the HCO+ and the HCN in the outflows, and find that the HCN traces only the most energetic outflows, the majority of which are driven by young Class 0 sources. We analyse the abundances of HCN and HCO+ in the particular case of the IRAS 2A outflows, and find that the HCN is much more enhanced than the HCO+ in the outflow lobes. We suggest that this is indicative of shock enhancement of HCN along the length of the outflow; this process is not so evident for HCO+, which is largely confined to the outflow base. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.SLW-S and JH are funded by the Science and Technology Facilities
Council of the UK. The James Clerk Maxwell Telescope is
operated by the Joint Astronomy Centre on behalf of the Science
and Technology Facilities Council of the United Kingdom, the National
Research Council of Canada and (until 2013 March 31) the
Netherlands Organisation for Scientific Researc
AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Perseus region
We present deep radio continuum observations of the cores identified as
deeply embedded young stellar objects in the Perseus molecular cloud by the
Spitzer c2d programme at a wavelength of 1.8 cm with the Arcminute Microkelvin
Imager Large Array (AMI-LA). We detect 72% of Class 0 objects from this sample
and 31% of Class I objects. No starless cores are detected. We use the flux
densities measured from these data to improve constraints on the correlations
between radio luminosity and bolometric luminosity, infrared luminosity and,
where measured, outflow force. We discuss the differing behaviour of these
objects as a function of protostellar class and investigate the differences in
radio emission as a function of core mass. Two of four possible very low
luminosity objects (VeLLOs) are detected at 1.8 cm.Comment: 18 pages, 9 figures, accepted MNRA
APECS - The Atacama Pathfinder Experiment Control System
APECS is the distributed control system of the new Atacama Pathfinder
EXperiment (APEX) telescope located on the Llano de Chajnantor at an altitude
of 5107 m in the Atacama desert in northern Chile. APECS is based on Atacama
Large Millimeter Array (ALMA) software and employs a modern, object-oriented
design using the Common Object Request Broker Architecture (CORBA) as the
middleware. New generic device interfaces simplify adding instruments to the
control system. The Python based observer command scripting language allows
using many existing software libraries and facilitates creating more complex
observing modes. A new self-descriptive raw data format (Multi-Beam FITS or
MBFITS) has been defined to store the multi-beam, multi-frequency data. APECS
provides an online pipeline for initial calibration, observer feedback and a
quick-look display. APECS is being used for regular science observations in
local and remote mode since August 2005.Comment: 4 pages, A&A, accepte
Star formation in Perseus
We present a complete survey of current star formation in the Perseus
molecular cloud, made at 850 and 450 micron with SCUBA at the JCMT. Covering 3
deg^2, this submillimetre continuum survey for protostellar activity is second
in size only to that of rho Ophiuchus (Johnstone et al. 2004). Complete above
0.4 msun (5 sigma detection in a 14'' beam), we detect a total of 91 protostars
and prestellar cores. Of these, 80% lie in clusters, representative of star
formation across the Galaxy. Two of the groups of cores are associated with the
young stellar clusters IC348 and NGC1333, and are consistent with a steady or
reduced star formation rate in the last 0.5 Myr, but not an increasing one. In
Perseus, 40--60% of cores are in small clusters (< 50 msun) and isolated
objects, much more than the 10% suggested from infrared studies. Complementing
the dust continuum, we present a C^18O map of the whole cloud at 1' resolution.
The gas and dust show filamentary structure of the dense gas on large and small
scales, with the high column density filaments breaking up into clusters of
cores. The filament mass per unit length is 5--11 msun per 0.1 pc. Given these
filament masses, there is no requirement for substantial large scale flows
along or onto the filaments in order to gather sufficient material for star
formation. We find that the probability of finding a submillimetre core is a
strongly increasing function of column density, as measured by C^18O integrated
intensity, prob(core) proportional to I^3.0. This power law relation holds down
to low column density, suggesting that there is no A_v threshold for star
formation in Perseus, unless all the low-A_v submm cores can be demonstrated to
be older protostars which have begun to lose their natal molecular cloud.Comment: 15 pages, 5 figures, bibtex file scubasf_astroph.bbl, included tex
files SSA-clusters-sorted-tidy.te
Detection of abundant solid methanol toward young low mass stars
We present detections of the absorption band at 3.53 micron due to solid
methanol toward three low-mass young stellar objects located in the Serpens and
Chameleon molecular cloud complexes. The sources were observed as part of a
large spectroscopic survey of ~40 protostars. This is the first detection of
solid methanol in the vicinity of low mass (M <1 Msol) young stars and shows
that the formation of methanol does not depend on the proximity of massive
young stars. The abundances of solid methanol compared to water ice for the
three sources are in the range 15-25% which is comparable to those for the most
methanol-rich massive sources known. The presence of abundant methanol in the
circumstellar environment of some low mass young stars has important
consequences for the formation scenarios of methanol and more complex organic
species near young solar-type stars.Comment: Accepted for publication in A&A letter
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