477 research outputs found
Continuum Observations at 350 Microns of High-Redshift Molecular Emission Line Galaxies
We report observations of 15 high redshift (z = 1-5) galaxies at 350 microns
using the Caltech Submillimeter Observatory and SHARC-II array detector.
Emission was detected from eight galaxies, for which far-infrared luminosities,
star formation rates, total dust masses, and minimum source size estimates are
derived. These galaxies have star formation rates and star formation
efficiencies comparable to other high redshift molecular emission line
galaxies. The results are used to test the idea that star formation in these
galaxies occurs in a large number of basic units, the units being similar to
star-forming clumps in the Milky Way. The luminosity of these extreme galaxies
can be reproduced in a simple model with (0.9-30) *10^6 dense clumps, each with
a luminosity of 5 *10^5 Lsun, the mean value for such clumps in the Milky Way.
Radiative transfer models of such clumps can provide reasonable matches to the
overall SEDs of the galaxies. They indicate that the individual clumps are
quite opaque in the far-infrared. Luminosity to mass ratios vary over two
orders of magnitude, correlating strongly with the dust temperature derived
from simple fits to the SED. The gas masses derived from the dust modeling are
in remarkable agreement with those from CO luminosities, suggesting that the
assumptions going into both calculations are reasonable.Comment: 17 pages, 8 figures. Accepted by Ap
A study on the effects of situated cognition on the study of foreign language.
This study examined situated cognition and anchored instruction in the context of foreign language learning. Based upon situated learning models proposed by McLellan (1996) and Thurman (1993), a situated lesson was adapted for foreign language learning and tested.This quantitative study examined situated learning in a class of international freshmen composition students enrolled at a private American university. The experimental group was taught to write a composition in a situated class. Activities included: problem solving, working in groups, interviewing and collaborative writing. The ANCOVA was applied with the Nelson Reading Test as the covariate. A Recall-protocol scoring template graded by a panel of instructors was used as the instrument. No significant differences were reported. Possibilities outlined for failure to reject the hypothesis included necessity for increase of sample size and length of study. However, both the covariate and the Test of English as Second Language (TOEFL) were found to have a significant relationship with the instrument. These facts and others lead to a discussion and suggestions on how this model could be applied to future studies
James Dunham, Pei-Shan Lee, Paul Katz with the Fry Street Quartet
The performance with the Fry Street Quartet is part of the Visiting Artists and Scholars Series.https://digitalcommons.usu.edu/music_programs/1227/thumbnail.jp
The Spitzer Gould Belt Survey of Large Nearby Interstellar Clouds: Discovery of A Dense Embedded Cluster in the Serpens-Aquila Rift
We report the discovery of a nearby, embedded cluster of young stellar objects, associated filamentary infrared dark cloud, and 4.5 mu m shock emission knots from outflows detected in Spitzer IRAC mid-infrared imaging of the Serpens-Aquila Rift obtained as part of the Spitzer Gould Belt Legacy Survey. We also present radial velocity measurements of the region from molecular line observations obtained with the Submillimeter Array (SMA) that suggest the cluster is comoving with the Serpens Main embedded cluster to the north. We therefore assign it 3 degrees the same distance, 260 pc. The core of the new cluster, which we call Serpens South, is composed of an unusually large fraction of protostars (77%) at high mean surface density (> 430 pc(-2)) and short median nearest neighbor spacing (3700 AU). We perform basic cluster structure characterization using nearest neighbor surface density mapping of the YSOs and compare our findings to other known clusters with equivalent analyses available in the literature.Astronom
The Bolocam Galactic Plane Survey: Survey Description and Data Reduction
We present the Bolocam Galactic Plane Survey (BGPS), a 1.1 mm continuum
survey at 33" effective resolution of 170 square degrees of the Galactic Plane
visible from the northern hemisphere. The survey is contiguous over the range
-10.5 < l < 90.5, |b| < 0.5 and encompasses 133 square degrees, including some
extended regions |b| < 1.5. In addition to the contiguous region, four targeted
regions in the outer Galaxy were observed: IC1396, a region towards the Perseus
Arm, W3/4/5, and Gem OB1. The BGPS has detected approximately 8400 clumps over
the entire area to a limiting non-uniform 1-sigma noise level in the range 11
to 53 mJy/beam in the inner Galaxy. The BGPS source catalog is presented in a
companion paper (Rosolowsky et al. 2010). This paper details the survey
observations and data reduction methods for the images. We discuss in detail
the determination of astrometric and flux density calibration uncertainties and
compare our results to the literature. Data processing algorithms that separate
astronomical signals from time-variable atmospheric fluctuations in the data
time-stream are presented. These algorithms reproduce the structure of the
astronomical sky over a limited range of angular scales and produce artifacts
in the vicinity of bright sources. Based on simulations, we find that extended
emission on scales larger than about 5.9' is nearly completely attenuated (>
90%) and the linear scale at which the attenuation reaches 50% is 3.8'.
Comparison with other millimeter-wave data sets implies a possible systematic
offset in flux calibration, for which no cause has been discovered. This
presentation serves as a companion and guide to the public data release through
NASA's Infrared Processing and Analysis Center (IPAC) Infrared Science Archive
(IRSA). New data releases will be provided through IPAC IRSA with any future
improvements in the reduction.Comment: Accepted for publication in Astrophysical Journal Supplemen
Testing for SARS-CoV-2 infection in care home residents and staff in English care homes: A service evaluation
Context COVID-19 is especially dangerous to older adults living in residential care. Objective To evaluate the usefulness of a nurse-led Enhanced Care Home Team (ECHT) SARS-CoV-2 testing strategy to identify resident cases early, identify typical illness presentation residents, and correctly attribute cause of death in care home settings in Norfolk, UK. Method Residents and staff received nose and throat swab tests (7 April to 29 June 2020). Resident test results were linked with symptoms on days 0-14 after test and mortality to 13 July 2020. The data collected were used to evaluate service performance. Findings Residents (n=521) and staff (estimated n=340) in 44 care homes were tested in the ECHT service. SARS-CoV-2 positivity was identified in 103 residents in 14 homes and 49 staff in seven homes. Of 103 SARS-CoV-2+ residents, just 37 had what were understood to be typical COVID-19 symptom(s). Among 51 residents without symptoms when initially tested, 13 (25%) developed symptoms within 14 days. Many SARS-CoV-2+ residents lacked typical symptoms but presented rather as ‘generally unwell’ (n=16). Of 39 resident deaths during the monitoring period, 20 (51%) were initially attributed to SARS-CoV-2, all of whom tested SARS-CoV-2+. One deceased person not initially attributed to SARS-CoV-2 tested positive through a different monitoring programme. 9% of all staff tests were positive. Implications A locally designed and integrated joint nursing and social care team approach successfully identified asymptomatic and pre-symptomatic SARS-CoV-2+ residents and staff. Being ‘generally unwell’ was common amongst symptomatic residents and indicated SARS-CoV-2 infection in older people in the absence of more ‘typical’ symptoms. The service supported correct attribution of cause of death
Externally Fed Accretion onto Protostars
The asymmetric molecular emission lines from dense cores reveal slow, inward
motion in the clouds' outer regions. This motion is present both before and
after the formation of a central star. Motivated by these observations, we
revisit the classic problem of steady, spherical accretion of gas onto a
gravitating point mass, but now include self-gravity of the gas and impose a
finite, subsonic velocity as the outer boundary condition. We find that the
accretion rate onto the protostar is lower than values obtained for isolated,
collapsing clouds, by a factor that is the Mach number of the outer flow.
Moreover, the region of infall surrounding the protostar spreads out more
slowly, at a speed close to the subsonic, incoming velocity. Our calculation,
while highly idealized, provides insight into two longstanding problems -- the
surprisingly low accretion luminosities of even the most deeply embedded
stellar sources, and the failure so far to detect spatially extended,
supersonic infall within their parent dense cores. Indeed, the observed
subsonic contraction in the outer regions of dense cores following star
formation appears to rule out a purely hydrodynamic origin for these clouds.Comment: accepted by MNRA
The Luminosities of Protostars in the Spitzer c2d and Gould Belt Legacy Clouds
Motivated by the long-standing "luminosity problem" in low-mass star
formation whereby protostars are underluminous compared to theoretical
expectations, we identify 230 protostars in 18 molecular clouds observed by two
Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We
compile complete spectral energy distributions, calculate Lbol for each source,
and study the protostellar luminosity distribution. This distribution extends
over three orders of magnitude, from 0.01 Lsun - 69 Lsun, and has a mean and
median of 4.3 Lsun and 1.3 Lsun, respectively. The distributions are very
similar for Class 0 and Class I sources except for an excess of low luminosity
(Lbol < 0.5 Lsun) Class I sources compared to Class 0. 100 out of the 230
protostars (43%) lack any available data in the far-infrared and submillimeter
(70 um < wavelength < 850 um) and have Lbol underestimated by factors of 2.5 on
average, and up to factors of 8-10 in extreme cases. Correcting these
underestimates for each source individually once additional data becomes
available will likely increase both the mean and median of the sample by 35% -
40%. We discuss and compare our results to several recent theoretical studies
of protostellar luminosities and show that our new results do not invalidate
the conclusions of any of these studies. As these studies demonstrate that
there is more than one plausible accretion scenario that can match
observations, future attention is clearly needed. The better statistics
provided by our increased dataset should aid such future work.Comment: Accepted for publication in AJ. 21 pages, 10 figures, 4 table
Young Stellar Objects in the Gould Belt
We present the full catalog of Young Stellar Objects (YSOs) identified in the
18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks"
(c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed
by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of
which survive visual inspection and form our final catalog of YSOs in the Gould
Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and
tabulate the infrared spectral index, bolometric luminosity, and bolometric
temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and
1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III,
respectively, and show that the Class III sample suffers from an overall
contamination rate by background AGB stars between 25% and 90%. Adopting
standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0+I YSOs
and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass
uncertainties in the adopted assumptions. Including information from
(sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as
Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr
(Class I). We revisit infrared color-color diagrams used in the literature to
classify YSOs and propose minor revisions to classification boundaries in these
diagrams. Finally, we show that the bolometric temperature is a poor
discriminator between Class II and Class III YSOs.Comment: Accepted for publication in ApJS. 29 pages, 11 figures, 14 tables, 4
appendices. Full versions of data tables (to be published in machine-readable
format by ApJS) available at the end of the latex source cod
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