2,657 research outputs found
Isolation and characterisation of microsatellite loci from Galapagos lava lizards (Microlophus spp.)
CO Abundance Variations in the Orion Molecular Cloud
Infrared stellar photometry from 2MASS and spectral line imaging observations
of 12CO and 13CO J = 1-0 line emission from the FCRAO 14m telescope are
analysed to assess the variation of the CO abundance with physical conditions
throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes
are identified in which the ratio between the 13CO column density and visual
extinction changes corresponding to the photon dominated envelope, the strongly
self-shielded interior, and the cold, dense volumes of the clouds. Within the
strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies
by 100% with a peak value located near regions of enhanced star formation
activity. The effect of CO depletion onto the ice mantles of dust grains is
limited to regions with AV > 10 mag and gas temperatures less than 20 K as
predicted by chemical models that consider thermal-evaporation to desorb
molecules from grain surfaces.
Values of the molecular mass of each cloud are independently derived from the
distributions of Av and 13CO column densities with a constant 13CO-to-H2
abundance over various extinction ranges. Within the strongly self-shielded
interior of the cloud (Av > 3 mag), 13CO provides a reliable tracer of H2 mass
with the exception of the cold, dense volumes where depletion is important.
However, owing to its reduced abundance, 13CO does not trace the H2 mass that
resides in the extended cloud envelope, which comprises 40-50% of the molecular
mass of each cloud. The implied CO luminosity to mass ratios, M/L_{CO}, are 3.2
and 2.9 for Orion A and Orion B respectively, which are comparable to the value
(2.9), derived from gamma-ray observations of the Orion region. Our results
emphasize the need to consider local conditions when applying CO observations
to derive H2 column densities.Comment: Accepted for publication in MNRAS. 21 pages, 14 figure
Refractive errors found in patient at ages 24, 25, and 26 years at the Pacific University Optometry Clinic
The purpose of this paper was to find the refractive error of patients of the clinic of Optometry, Pacific University, whose ages were 24, 25 or 26 years. The total number of patients was 510, of which 231 were females and 279 were males. There were six monocular patients, three males and three females. The total number of seeing eyes was 1014 of which 459 were females and 555 were males
Identification of Ambient Molecular Clouds Associated with Galactic Supernova Remnant IC443
The Galactic supernova remnant (SNR) IC443 is one of the most studied
core-collapse SNRs for its interaction with molecular clouds. However, the
ambient molecular clouds with which IC443 is interacting have not been
thoroughly studied and remain poorly understood. Using Five College Radio
Astronomy Observatory 14m telescope, we obtained fully sampled maps of ~
1{\deg} \times 1{\deg} region toward IC443 in the 12CO J=1-0 and HCO+ J=1-0
lines. In addition to the previously known molecular clouds in the velocity
range v_lsr = -6 to -1 km/s (-3 km/s clouds), our observations reveal two new
ambient molecular cloud components: small (~ 1') bright clouds in v_lsr = -8 to
-3 km/s (SCs), and diffuse clouds in v_lsr = +3 to +10 km/s (+5 km/s clouds).
Our data also reveal the detailed kinematics of the shocked molecular gas in
IC443, however the focus of this paper is the physical relationship between the
shocked clumps and the ambient cloud components. We find strong evidence that
the SCs are associated with the shocked clumps. This is supported by the
positional coincidence of the SCs with shocked clumps and other tracers of
shocks. Furthermore, the kinematic features of some shocked clumps suggest that
these are the ablated material from the SCs upon the impact of the SNR shock.
The SCs are interpreted as dense cores of parental molecular clouds that
survived the destruction by the pre-supernova evolution of the progenitor star
or its nearby stars. We propose that the expanding SNR shock is now impacting
some of the remaining cores and the gas is being ablated and accelerated
producing the shocked molecular gas. The morphology of the +5 km/s clouds
suggests an association with IC443. On the other hand, the -3 km/s clouds show
no evidence for interaction.Comment: Accepted for publication in ApJ. 15 pages (with emulateapj.cls), 17
figures, and 2 table
Spectra of Nearby Galaxies Measured with a New Very Broadband Receiver
Three-millimeter-wavelength spectra of a number of nearby galaxies have been
obtained at the Five College Radio Astronomy Observatory (FCRAO) using a new,
very broadband receiver. This instrument, which we call the Redshift Search
Receiver, has an instantaneous bandwidth of 36 GHz and operates from 74 to
110.5 GHz. The receiver has been built at UMass/FCRAO to be part of the initial
instrumentation for the Large Millimeter Telescope (LMT) and is intended
primarily for determination of the redshift of distant, dust-obscured galaxies.
It is being tested on the FCRAO 14m by measuring the 3mm spectra of a number of
nearby galaxies. There are interesting differences in the chemistry of these
galaxies.Comment: published in the Proceedings of the International Astronomical Union
(2008), 4. Vol 251, pp 251-256 Cambridge University Pres
Embedded Stellar Clusters in the W3/W4/W5 Molecular Cloud Complex
We analyze the embedded stellar content in the vicinity of the W3/W4/W5 HII
regions using the FCRAO Outer Galaxy 12CO(J=1-0) Survey, the IRAS Point Source
Catalog, published radio continuum surveys, and new near-infrared and molecular
line observations. Thirty-four IRAS Point Sources are identified that have
far-infrared colors characteristic of embedded star forming regions, and we
have obtained K' mosaics and 13CO(J=1-0) maps for 32 of them. Ten of the IRAS
sources are associated with an OB star and 19 with a stellar cluster, although
three OB stars are not identified with a cluster. Half of the embedded stellar
population identified in the K' images is found in just the 5 richest clusters,
and 61% is contained in IRAS sources associated with an embedded OB star. Thus
rich clusters around OB stars contribute substantially to the stellar
population currently forming in the W3/W4/W5 region. Approximately 39% of the
cluster population is embedded in small clouds with an average mass of ~130 Mo
that are located as far as 100 pc from the W3/W4/W5 cloud complex. We speculate
that these small clouds are fragments of a cloud complex dispersed by previous
episodes of massive star formation. Finally, we find that 4 of the 5 known
embedded massive star forming sites in the W3 molecular cloud are found along
the interface with the W4 HII region despite the fact that most of the
molecular mass is contained in the interior regions of the cloud. These
observations are consistent with the classical notion that the W4 HII region
has triggered massive star formation along the eastern edge of the W3 molecular
cloud.Comment: to appear in ApJS, see http://astro.caltech.edu/~jmc/papers/w
Star Formation in Bright Rimmed Clouds. I. Millimeter and Submillimeter Molecular Line Surveys
We present the results of the first detailed millimeter and submillimeter
molecular line survey of bright rimmed clouds, observed at FCRAO in the CO
(J=1-0), C18O (J=1-0), HCO+ (J=1-0), H13CO+ (J=1-0), and N2H+ (J=1-0)
transitions, and at the HHT in the CO (J=2-1), HCO+ (J=3-2), HCO+ (J=4-3),
H13CO+ (J=3-2), and H13CO+ (J=4-3) molecular line transitions. The source list
is composed of a selection of bright rimmed clouds from the catalog of such
objects compiled by Sugitani et al. (1991). We also present observations of
three Bok globules done for comparison with the bright rimmed clouds. We find
that the appearance of the millimeter CO and HCO+ emission is dominated by the
morphology of the shock front in the bright rimmed clouds. The HCO+ (J=1-0)
emission tends to trace the swept up gas ridge and overdense regions which may
be triggered to collapse as a result of sequential star formation. Five of the
seven bright rimmed clouds we observe seem to have an outflow, however only one
shows the spectral line blue-asymmetric signature that is indicative of infall,
in the optically thick HCO+ emission. We also present evidence that in bright
rimmed clouds the nearby shock front may heat the core from outside-in thereby
washing out the normally observed line infall signatures seen in isolated star
forming regions. We find that the derived core masses of these bright rimmed
clouds are similar to other low and intermediate mass star forming regions.Comment: 67 pages, including 35 figures and 6 tables. Accepted for publication
in ApJ. Version with embedded full-resolution figures available at
http://www.astro.umass.edu/~devries/brc1
First Passage Properties of the Erdos-Renyi Random Graph
We study the mean time for a random walk to traverse between two arbitrary
sites of the Erdos-Renyi random graph. We develop an effective medium
approximation that predicts that the mean first-passage time between pairs of
nodes, as well as all moments of this first-passage time, are insensitive to
the fraction p of occupied links. This prediction qualitatively agrees with
numerical simulations away from the percolation threshold. Near the percolation
threshold, the statistically meaningful quantity is the mean transit rate,
namely, the inverse of the first-passage time. This rate varies
non-monotonically with p near the percolation transition. Much of this behavior
can be understood by simple heuristic arguments.Comment: 10 pages, 9 figures, 2-column revtex4 forma
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