2,518 research outputs found
The 51.8 micron (0 3) line emission observed in four galactic H 2 regions
The (0 III) 51.8 microns line from four H II regions, M42, M17, W51 and NGC 6375A was detected. Respective line strengths are 7 x 10 to the minus 15 power, 1.0 x 10 to the minus 14 power, 2.1 x 10 to the minus 15 power and 2.6 x 10 to the minus 15 power watt cm/2. Observations are consistent with previously reported line position and place the line at 51.80 + or 0.05 micron. When combined with the 88.35 microns (0 III) reported earlier, clumping seems to be an important factor in NGC 6375A and M42 and to a lesser extent in W51 and M17. The combined data also suggest an (0 III) abundance of approximately 3 x 0.0001 sub n e' a factor of 2 greater than previously assumed
Integrative Model-based clustering of microarray methylation and expression data
In many fields, researchers are interested in large and complex biological
processes. Two important examples are gene expression and DNA methylation in
genetics. One key problem is to identify aberrant patterns of these processes
and discover biologically distinct groups. In this article we develop a
model-based method for clustering such data. The basis of our method involves
the construction of a likelihood for any given partition of the subjects. We
introduce cluster specific latent indicators that, along with some standard
assumptions, impose a specific mixture distribution on each cluster. Estimation
is carried out using the EM algorithm. The methods extend naturally to multiple
data types of a similar nature, which leads to an integrated analysis over
multiple data platforms, resulting in higher discriminating power.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS533 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Observations of the 51.8 micron (O III) emission line in Orion
The 51.8 micron fine structure transition P2:3P2 3P1 for doubly ionized oxygen was observed in the Orion nebula. The observed line strength is of 5 plus or minus 3 times 10 to the minus 15th power watt/sq cm is in good agreement with theoretical predictions. Observations are consistent with the newly predicted 51.8 micron line position. The line lies close to an atmospheric water vapor feature at 51.7 micron, but is sufficiently distant so that corrections for this feature are straightforward. Observations of the 51.8 (O III) line are particularly important since the previously discovered 88 micron line from the same ion also is strong. This pair of lines should, therefore, yield new data about densities in observed H II regions; or else, if density data already are available from radio or other observations, the lines can be used to determine the differential dust absorption between 52 and 88 micron in front of heavily obscured regions
Preparation of microscopic cross sections of U235 for reactor calculations
Preparation of microscopic cross section of uranium 235 for high temperature reactor calculation
Physical properties of outflows: Comparing CO and H2O based parameters in Class 0 sources
Context. The observed physical properties of outflows from low-mass sources
put constraints on possible ejection mechanisms. Historically, these quantities
have been derived from CO using ground-based observations. It is thus important
to investigate whether parameters such as momentum rate (thrust) and mechanical
luminosity (power) are the same when different molecular tracers are used.
Aims. We aim at determining the outflow momentum, dynamical time-scale, thrust,
energy and power using CO and H2O as tracers of outflow activity. Methods.
Within the framework of the WISH key program, three molecular outflows from
Class 0 sources have been mapped using the HIFI instrument aboard Herschel. We
use these observations together with previously published H2 data to infer the
physical properties of the outflows. We compare the physical properties derived
here with previous estimates based on CO observations. Results. Inspection of
the spatial distribution of H2O and H2 confirms that these molecules are
co-spatial. The most prominent emission peaks in H2 coincide with strong H2O
emission peaks and the estimated widths of the flows when using the two tracers
are comparable. Conclusions. For the momentum rate and the mechanical
luminosity, inferred values are independent of which tracer that is used, i.e.,
the values agree to within a factor of 4 and 3 respectively.Comment: Accepted for publication in A&A, 5 pages, 2 figure
SBS 0335-052W: The Lowest-Metallicity Star-Forming Galaxy Known
We present 4-meter Kitt Peak telescope and 6.5-meter MMT spectrophotometry of
the extremely low-metallicity galaxy SBS 0335-052W, the western companion of
the blue compact dwarf galaxy SBS 0335-052E. These observations have been
combined with published 10-meter Keck data to derive for the brightest region
of SBS 0335-052W an oxygen abundance 12+logO/H=7.12+/-0.03. This makes SBS
0335-052W the lowest metallicity star-forming galaxy known in the local
universe. Using a Monte Carlo technique, we fit the spectral energy
distribution of SBS 0335-052W to derive the age of the oldest stars
contributing to its optical light. We find that star formation in SBS 0335-052W
began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical
Journa
The Exceptionally Soft X-ray Spectrum of the Low-mass Starburst Galaxy NGC 1705
NGC 1705 is one of the optically brightest and best studied dwarf galaxies.
It appears to be in the late stage of a major starburst and contains a young
super star cluster. Type II supernovae are therefore likely to have been a
major effect in the recent evolution of this galaxy and are likely to have
produced a superbubble whose affects on the low-density ambient interstellar
medium can be ideally studied. ROSAT PSPC observations of this galaxy reveal
two striking blobs of X-ray emission embedded in \Ha loops which can be
interpreted as both sides of the upper plumes of the same superbubble. These
sources are a surprise. They are much softer than those observed from other
starburst dwarf galaxies, and are so soft that they should have been blocked if
the observed Galactic HI column density were uniformly distributed across NGC
1705 or if the sources were embedded in the HI disk of NGC 1705. In addition,
the total X-ray luminosity in the ROSAT energy band of 1.2x10^{38} erg s^{-1}
is low in comparison to similar objects. We discuss possible models for the two
X-ray peaks in NGC 1705 and find that the sources most likely originate from
relatively cool gas of one single superbubble in NGC 1705. The implications of
the exceptional softness of these sources are addressed in terms of intrinsic
properties of NGC 1705 and the nature of the foreground Galactic absorption.Comment: 7 pages, 2 ps-figures, LATEX-file; accepted for publication in
ApJ.Letter
The Initial Mass Functions in the Super-Star-Clusters NGC 1569A and NGC 1705-1
I use recent photometric and stellar velocity dispersion measurements of the
super-star-clusters (SSCs) NGC 1569A and NGC 1705-1 to determine their
present-day luminosity/mass (L_V/M) ratios. I then use the inferred L_V/M
ratios, together with population synthesis models of evolving star-clusters, to
constrain the initial-mass-functions (IMFs) in these objects.
I find that (L_V/M)_solar=28.9 in 1569A, and (L_V/M)_solar=126 in 1705-1. It
follows that in 1569A the IMF is steep with alpha~2.5 for m**(-alpha)dm IMFs
which extend to 0.1 M_sun. This implies that most of the stellar mass in 1569A
is contained in low-mass (< 1 M_sun) stars. However, in 1705-1 the IMF is
either flat, with alpha<2$, or it is truncated at a lower mass-limit between 1
and 3 M_sun.
I compare the inferred IMFs with the mass functions (MFs) of Galactic
globular clusters. It appears that 1569A has a sufficient reservoir of low-mass
stars for it to plausibly evolve into an object similar to Galactic globular
clusters. However, the apparent deficiency of low-mass stars in 1705-1 may make
it difficult for this SSC to become a globular cluster. If low-mass stars do
dominate the cluster mass in 1705-1, the large L_V/M ratio in this SSC may be
evidence that the most massive stars have formed close to the cluster cores.Comment: ApJ, in press. 19 Pages, Latex; [email protected]
Metabolism of Nonessential N15-Labeled Amino Acids and the Measurement of Human Whole-Body Protein Synthesis Rates
Eight N-15 labeled nonessential amino acids plus (15)NH4Cl were administered over a 10 h period to four healthy adult males using a primed-constant dosage regimen. The amount of N-15 excreted in the urine and the urinary ammonia, hippuric acid, and plasma alanine N-15 enrichments were measured. There was a high degree of consistency across subjects in the ordering of the nine compounds based on the fraction of N-15 excreted (Kendall coefficient of concordance W = 0.83, P is less than 0.01). Protein synthesis rates were calculated from the urinary ammonia plateau enrichment and the cumulative excretion of N-15. Glycine was one of the few amino acids that gave similar values by both methods
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