379 research outputs found
Arcsecond resolution images of the chemical structure of the low-mass protostar IRAS 16293-2422
It remains a key challenge to establish the molecular content of different
components of low-mass protostars, like their envelopes and disks, and how this
depends on the evolutionary stage and/or environment of the young stars.
Observations at submillimeter wavelengths provide a direct possibility to study
the chemical composition of low-mass protostars through transitions probing
temperatures up to a few hundred K in the gas surrounding these sources. This
paper presents a large molecular line survey of the deeply embedded
protostellar binary IRAS 16293-2422 from the Submillimeter Array (SMA) -
including images of individual lines down to approximately 1.5-3" (190-380 AU)
resolution. More than 500 individual transitions are identified related to 54
molecular species (including isotopologues) probing temperatures up to about
550 K. Strong chemical differences are found between the two components in the
protostellar system with a separation between, in particular, the sulfur- and
nitrogen-bearing species and oxygen-bearing complex organics. The action of
protostellar outflow on the ambient envelope material is seen in images of CO
and SiO and appear to influence a number of other species, including
(deuterated) water, HDO. The effects of cold gas-phase chemistry is directly
imaged through maps of CO, N2D+ and DCO+, showing enhancements of first DCO+
and subsequently N2D+ in the outer envelope where CO freezes-out on dust
grains.Comment: Accepted for publication in A&A, 30 pages, 22 figure
Cold Water Vapor in the Barnard 5 Molecular Cloud
After more than 30 yr of investigations, the nature of gas-grain interactions at low temperatures remains an unresolved issue in astrochemistry. Water ice is the dominant ice found in cold molecular clouds; however, there is only one region where cold ((is) approximately 10 K) water vapor has been detected-L1544. This study aims to shed light on ice desorption mechanisms under cold cloud conditions by expanding the sample. The clumpy distribution of methanol in dark clouds testifies to transient desorption processes at work-likely to also disrupt water ice mantles. Therefore, the Herschel HIFI instrument was used to search for cold water in a small sample of prominent methanol emission peaks. We report detections of the ground-state transition of o-H2O (J = 110-101) at 556.9360 GHz toward two positions in the cold molecular cloud, Barnard 5. The relative abundances of methanol and water gas support a desorption mechanism which disrupts the outer ice mantle layers, rather than causing complete mantle removal
Imaging Simulations of the Sunyaev-Zel'dovich Effect for ALMA
We present imaging simulations of the Sunyaev-Zel'dovich effect of galaxy
clusters for the Atacama Large Millimeter/submillimeter Array (ALMA) including
the Atacama Compact Array (ACA). In its most compact configuration at 90GHz,
ALMA will resolve the intracluster medium with an effective angular resolution
of 5 arcsec. It will provide a unique probe of shock fronts and relativistic
electrons produced during cluster mergers at high redshifts, that are hard to
spatially resolve by current and near-future X-ray detectors. Quality of image
reconstruction is poor with the 12m array alone but improved significantly by
adding ACA; expected sensitivity of the 12m array based on the thermal noise is
not valid for the Sunyaev-Zel'dovich effect mapping unless accompanied by an
ACA observation of at least equal duration. The observations above 100 GHz will
become excessively time-consuming owing to the narrower beam size and the
higher system temperature. On the other hand, significant improvement of the
observing efficiency is expected once Band 1 is implemented in the future.Comment: 16 pages, 12 figures. Accepted for publication in PASJ. Note added in
proof is include
The Sunyaev-Zel'dovich Effect at Five Arc-seconds: RXJ1347.5-1145 Imaged by ALMA
We present the first image of the thermal Sunyaev-Zel'dovich effect (SZE)
obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Combining
7-m and 12-m arrays in Band 3, we create an SZE map toward a galaxy cluster
RXJ1347.5-1145 with 5 arc-second resolution (corresponding to the physical size
of 20 kpc/h), the highest angular and physical spatial resolutions achieved to
date for imaging the SZE, while retaining extended signals out to 40
arc-seconds. The 1-sigma statistical sensitivity of the image is 0.017 mJy/beam
or 0.12 mK_CMB at the 5 arc-second full width at half maximum. The SZE image
shows a good agreement with an electron pressure map reconstructed
independently from the X-ray data and offers a new probe of the small-scale
structure of the intracluster medium. Our results demonstrate that ALMA is a
powerful instrument for imaging the SZE in compact galaxy clusters with
unprecedented angular resolution and sensitivity. As the first report on the
detection of the SZE by ALMA, we present detailed analysis procedures including
corrections for the missing flux, to provide guiding methods for analyzing and
interpreting future SZE images by ALMA.Comment: 20 pages, 13 figures. Accepted for publication in PAS
Myopericarditis diagnosed by a 64-slice coronary CT angiography "triple rule out" protocol
We report a case of myopericarditis in a 30-year-old male complaining of shortness of breath. In an emergency department (ED) setting, the symptoms of myopericarditis may overlap with many disease entities and can be a challenging diagnosis to make. However, with the use of a 64-section coronary CT angiography in a “triple rule out” (TRO) protocol, we were able to detect a large pericardial effusion surrounding the heart and moderate global hypokinesis in the setting of normal-sized heart chambers and normal coronary arteries. We were further able to exclude pulmonary embolism and thoracic dissection. This is the first reported case of diagnosing myopericarditis using a TRO protocol. It demonstrates the usefulness of TRO in making an emergent diagnosis of myopericarditis while excluding other life-threatening diseases that can lead to earlier appropriate ED disposition and care
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