1,656 research outputs found
Molecular Line Observations of Infrared Dark Clouds: Seeking the Precursors to Intermediate and Massive Star Formation
We have identified 41 infrared dark clouds from the 8 micron maps of the
Midcourse Space Experiment (MSX), selected to be found within one square degree
areas centered on known ultracompact HII regions. We have mapped these infrared
dark clouds in N2H+(1-0), CS(2-1) and C18O(1-0) emission using the Five College
Radio Astronomy Observatory. The maps of the different species often show
striking differences in morphologies, indicating differences in evolutionary
state and/or the presence of undetected, deeply embedded protostars. We derive
an average mass for these clouds using N2H+ column densities of ~2500 solar
masses, a value comparable to that found in previous studies of high mass star
forming cores using other mass tracers. The linewidths of these clouds are
typically ~2.0 - 2.9 km/s. Based on the fact that they are dark at 8 micron,
compact, massive, and have large velocity dispersions, we suggest that these
clouds may be the precursor sites of intermediate and high mass star formation.Comment: Accepted to ApJS, 22 pages, 10 pages of figures. For full-resolution
images, see http://www.astro.lsa.umich.edu/~seragan/pubs/fcrao/figures.tar.g
Building Telehealth Teams of the Future Through Interprofessional Curriculum Development: A Five-Year Mixed Methodology Study
Building the next generation of telehealth enabled professionals requires a mixture of team-based, interprofessional practice with novel technologies that connect providers and patients. Effective telehealth education is critical for the development of multidisciplinary training curricula to ensure workforce preparedness. In this study, we evaluated the impact of a formal telehealth education curriculum for interprofessional students through an online elective. Over 12 semesters, 170 students self-selected to enroll in the 3-credit hour interprofessional elective and took part in structured didactic, experiential and interprofessional learning opportunities. Mixed-method assessments show significant knowledge and confidence gains with students reflecting on their roles as future healthcare providers. The results from five years’ worth of course data shows not only an opportunity to advance the individual knowledge of trainees, but a larger movement to facilitate changes in practice toward population health goals. Recent global health events have further highlighted the need for a rapid response to public health emergencies by highly trained provider teams who are able to utilize technology as the cornerstone for the continuity of care
Non-Equilibrium Abundances Treated Holistically (NEATH): the molecular composition of star-forming clouds
Much of what we know about molecular clouds, and by extension star formation,
comes from molecular line observations. Interpreting these correctly requires
knowledge of the underlying molecular abundances. Simulations of molecular
clouds typically only model species that are important for the gas
thermodynamics, which tend to be poor tracers of the denser material where
stars form. We construct a framework for post-processing these simulations with
a full time-dependent chemical network, allowing us to model the behaviour of
observationally-important species not present in the reduced network used for
the thermodynamics. We use this to investigate the chemical evolution of
molecular gas under realistic physical conditions. We find that molecules can
be divided into those which reach peak abundances at moderate densities () and decline sharply thereafter (such as CO and HCN), and
those which peak at higher densities and then remain roughly constant (e.g.
NH, NH). Evolving the chemistry with physical properties held
constant at their final values results in a significant overestimation of
gas-phase abundances for all molecules, and does not capture the drastic
variations in abundance caused by different evolutionary histories. The
dynamical evolution of molecular gas cannot be neglected when modelling its
chemistry.Comment: 14 pages, 13 figures. MNRAS accepte
NEATH II: NH as a tracer of imminent star formation in quiescent high-density gas
Star formation activity in molecular clouds is often found to be correlated
with the amount of material above a column density threshold of . Attempts to connect this column density threshold to a density above which star formation can occur are limited by the fact
that the volume density of gas is difficult to reliably measure from
observations. We post-process hydrodynamical simulations of molecular clouds
with a time-dependent chemical network, and investigate the connection between
commonly-observed molecular species and star formation activity. We find that
many molecules widely assumed to specifically trace the dense, star-forming
component of molecular clouds (e.g. HCN, HCO, CS) actually also exist in
substantial quantities in material only transiently enhanced in density, which
will eventually return to a more diffuse state without forming any stars. By
contrast, NH only exists in detectable quantities above a volume
density of , the point at which CO, which reacts
destructively with NH, begins to deplete out of the gas phase onto
grain surfaces. This density threshold for detectable quantities of NH
corresponds very closely to the volume density at which gas becomes
irreversibly gravitationally bound in the simulations: the material traced by
NH never reverts to lower densities, and quiescent regions of molecular
clouds with visible NH emission are destined to eventually form stars.
The NH line intensity is likely to directly correlate with the star
formation rate averaged over timescales of around a Myr.Comment: 10 pages, 10 figures. MNRAS accepte
Recommended from our members
Assessment of cleaning to control lead dust in homes of children with moderate lead poisoning: treatment of lead-exposed children trial
In this article we describe the assessment and control of lead dust exposure in the Treatment of Lead-exposed Children (TLC) Trial, a clinical trial of the effects of oral chelation on developmental end points in urban children with moderately elevated blood lead levels. To reduce potential lead exposure from settled dust or deteriorated paint during the drug treatment phase of the trial, the homes of 765 (98%) of the randomized children (both active and placebo drug treatment groups) were professionally cleaned. Lead dust measurements were made in a sample of 213 homes before and after cleaning. Geometric mean dust lead loadings before cleaning were 43, 29, 308, and 707 micro g/ft2 in the kitchen floor, playroom floor, playroom windowsill, and playroom window well samples respectively. Following cleaning, floor dust lead loadings were reduced on average 32% for paired floor samples (p < 0.0001), 66% for windowsills (p < 0.0001), and 93% for window wells (p < 0.0001). Cleaning was most effective for 146 homes with precleaning dust lead levels above the recommended clearance levels, with average reductions of 44%, 74%, and 93% for floors (p < 0.0001), windowsills (p < 0.0001), and window wells (p < 0.0001), respectively. Despite these substantial reductions in dust lead loadings, a single professional cleaning did not reduce the lead loadings of all dust samples to levels below current federal standards for lead in residential dust. Attainment of dust levels below current standards will require more intensive cleaning and lead hazard reduction strategies
Observations of the BL Lac Object 3C 66A with STACEE
We present the analysis and results of recent high-energy gamma-ray
observations of the BL Lac object 3C 66A conducted with the Solar Tower
Atmospheric Cherenkov Effect Experiment (STACEE). During the 2003-2004
observing season, STACEE extensively observed 3C 66A as part of a
multiwavelength campaign on the source. A total of 33.7 hours of data was taken
on the source, plus an equivalent-duration background observation. After
cleaning the data set a total of 16.3 hours of live time remained, and a net
on-source excess of 1134 events was seen against a background of 231742 events.
At a significance of 2.2 standard deviations this excess is insufficient to
claim a detection of 3C 66A, but is used to establish flux upper limits for the
source.Comment: Accepted for publication in the Astrophysical Journa
'The Brick' is not a brick : A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.In this paper we provide a comprehensive description of the internal dynamics of G0.253+0.016 (a.k.a. 'the Brick'); one of the most massive and dense molecular clouds in the Galaxy to lack signatures of widespread star formation. As a potential host to a future generation of high-mass stars, understanding largely quiescent molecular clouds like G0.253+0.016 is of critical importance. In this paper, we reanalyse Atacama Large Millimeter Array cycle 0 HNCO data at 3 mm, using two new pieces of software which we make available to the community. First, scousepy, a Python implementation of the spectral line fitting algorithm scouse. Secondly, acorns (Agglomerative Clustering for ORganising Nested Structures), a hierarchical n-dimensional clustering algorithm designed for use with discrete spectroscopic data. Together, these tools provide an unbiased measurement of the line of sight velocity dispersion in this cloud, kms, which is somewhat larger than predicted by velocity dispersion-size relations for the Central Molecular Zone (CMZ). The dispersion of centroid velocities in the plane of the sky are comparable, yielding . This isotropy may indicate that the line-of-sight extent of the cloud is approximately equivalent to that in the plane of the sky. Combining our kinematic decomposition with radiative transfer modelling we conclude that G0.253+0.016 is not a single, coherent, and centrally-condensed molecular cloud; 'the Brick' is not a \emph{brick}. Instead, G0.253+0.016 is a dynamically complex and hierarchically-structured molecular cloud whose morphology is consistent with the influence of the orbital dynamics and shear in the CMZ.Peer reviewedFinal Accepted Versio
- …