1,033 research outputs found
A Neutral Hydrogen Self-Absorption Cloud in the SGPS
Using data from the Southern Galactic Plane Survey (SGPS) we analyze an HI
self-absorption cloud centered on l = 318.0 deg, b = -0.5 deg, and velocity, v
= -1.1 km/s. The cloud was observed with the Australia Telescope Compact Array
(ATCA) and the Parkes Radio Telescope, and is at a near kinematic distance of
less than 400 pc with derived dimensions of less than 5 x 11 pc. We apply two
different methods to find the optical depth and spin temperature. In both
methods we find upper limit spin temperatures ranging from 20 K to 25 K and
lower limit optical depths ~ 1. We look into the nature of the HI emission and
find that 60-70% originates behind the cloud. We analyze a second cloud at the
same velocity centered on l = 319 deg and b = 0.4 deg with an upper limit spin
temperature of 20 K and a lower limit optical depth of 1.6. The similarities in
spin temperature, optical depth, velocity, and spatial location are evidence
the clouds are associated, possibly as one large cloud consisting of smaller
clumps of gas. We compare HI emission data with 12CO emission and find a
physical association of the HI self-absorption cloud with molecular gas.Comment: 33 pages, 17 figures, 5 tables; Accepted for publication in ApJ. A
version with higher quality images availabe at
http://www.astro.umn.edu/~dkavars/ms.p
G28.17+0.05: An unusual giant HI cloud in the inner Galaxy
New 21 cm HI observations have revealed a giant HI cloud in the Galactic
plane that has unusual properties. It is quite well defined, about 150 pc in
diameter at a distance of 5 kpc, and contains as much as 100,000 Solar Masses
of atomic hydrogen. The outer parts of the cloud appear in HI emission above
the HI background, while the central regions show HI self-absorption. Models
which reproduce the observations have a core with a temperature <40 K and an
outer envelope as much as an order of magnitude hotter. The cold core is
elongated along the Galactic plane, whereas the overall outline of the cloud is
approximately spherical. The warm and cold parts of the HI cloud have a
similar, and relatively large, line width of approximately 7 km/s. The cloud
core is a source of weak, anomalously-excited 1720 MHz OH emission, also with a
relatively large line width, which delineates the region of HI self-absorption
but is slightly blue-shifted in velocity. The intensity of the 1720 MHz OH
emission is correlated with N(H) derived from models of the cold core. There is
12CO emission associated with the cloud core. Most of the cloud mass is in
molecules, and the total mass is > 200,000 Solar Masses. In the cold core the
HI mass fraction may be 10 percent. The cloud has only a few sites of current
star formation. There may be about 100 more objects like this in the inner
Galaxy; every line of sight through the Galactic plane within 50 degrees of the
Galactic center probably intersects at least one. We suggest that G28.17+0.05
is a cloud being observed as it enters a spiral arm and that it is in the
transition from the atomic to the molecular state.Comment: 35 pages, inludes 12 figure
The VLT/NaCo Large program to probe the occurrence of exoplanets and brown dwarfs in wide orbits: I- Sample definition and characterization
Young, nearby stars are ideal targets to search for planets using the direct
imaging technique. The determination of stellar parameters is crucial for the
interpretation of imaging survey results particularly since the luminosity of
substellar objects has a strong dependence on system age. We have conducted a
large program with NaCo at the VLT in order to search for planets and brown
dwarfs in wide orbits around 86 stars. A large fraction of the targets observed
with NaCo were poorly investigated in the literature. We performed a study to
characterize the fundamental properties (age, distance, mass) of the stars in
our sample. To improve target age determinations, we compiled and analyzed a
complete set of age diagnostics. We measured spectroscopic parameters and age
diagnostics using dedicated observations acquired with FEROS and CORALIE
spectrographs at La Silla Observatory. We also made extensive use of archival
spectroscopic data and results available in the literature. Additionally, we
exploited photometric time-series, available in ASAS and Super-WASP archives,
to derive rotation period for a large fraction of our program stars. We
provided updated characterization of all the targets observed in the VLT NaCo
Large program, a survey designed to probe the occurrence of exoplanets and
brown dwarfs in wide orbits. The median distance and age of our program stars
are 64 pc and 100 Myr, respectively. Nearly all the stars have masses between
0.70 and 1.50sun, with a median value of 1.01 Msun. The typical metallicity is
close to solar, with a dispersion that is smaller than that of samples usually
observed in radial velocity surveys. Several stars are confirmed or proposed
here to be members of nearby young moving groups. Eight spectroscopic binaries
are identified.Comment: 64 pages with Appendix, 15 figures, accepted to A&
Probing the Early Evolution of Young High-Mass Stars
Near-infrared imaging surveys of high-mass star-forming regions reveal an
amazingly complex interplay between star formation and the environment
(Churchwell et al. 2006; Alvarez et al. 2004). By means of near-IR spectroscopy
the embedded massive young stars can be characterized and placed in the context
of their birth site. However, so far spectroscopic surveys have been hopelessly
incomplete, hampering any systematic study of these very young massive stars.
New integral field instrumentation available at ESO has opened the possibility
to take a huge step forward by obtaining a full spectral inventory of the
youngest massive stellar populations in star-forming regions currently
accessible. Simultaneously, the analysis of the extended emission allows the
characterization of the environmental conditions. The Formation and Early
Evolution of Massive Stars (FEMS) collaboration aims at setting up a large
observing campaign to obtain a full census of the stellar content, ionized
material, outflows and PDR's over a sample of regions that covers a large
parameter space. Complementary radio, mm and infrared observations will be used
for the characterization of the deeply embedded population. For the first eight
regions we have obtained 40 hours of SINFONI observations. In this
contribution, we present the first results on three regions that illustrate the
potential of this strategy.Comment: To appear in ASP Conf. Proceedings of "Massive Star Formation:
Observations confront Theory", H. Beuther et al. (eds.), held in Heidelberg,
September 200
An Automated Method for the Detection and Extraction of HI Self-Absorption in High-Resolution 21cm Line Surveys
We describe algorithms that detect 21cm line HI self-absorption (HISA) in
large data sets and extract it for analysis. Our search method identifies HISA
as spatially and spectrally confined dark HI features that appear as negative
residuals after removing larger-scale emission components with a modified CLEAN
algorithm. Adjacent HISA volume-pixels (voxels) are grouped into features in
(l,b,v) space, and the HI brightness of voxels outside the 3-D feature
boundaries is smoothly interpolated to estimate the absorption amplitude and
the unabsorbed HI emission brightness. The reliability and completeness of our
HISA detection scheme have been tested extensively with model data. We detect
most features over a wide range of sizes, linewidths, amplitudes, and
background levels, with poor detection only where the absorption brightness
temperature amplitude is weak, the absorption scale approaches that of the
correlated noise, or the background level is too faint for HISA to be
distinguished reliably from emission gaps. False detection rates are very low
in all parts of the parameter space except at sizes and amplitudes approaching
those of noise fluctuations. Absorption measurement biases introduced by the
method are generally small and appear to arise from cases of incomplete HISA
detection. This paper is the third in a series examining HISA at high angular
resolution. A companion paper (Paper II) uses our HISA search and extraction
method to investigate the cold atomic gas distribution in the Canadian Galactic
Plane Survey.Comment: 39 pages, including 14 figure pages; to appear in June 10 ApJ, volume
626; figure quality significantly reduced for astro-ph; for full resolution,
please see http://www.ras.ucalgary.ca/~gibson/hisa/cgps1_survey
Tick species from cattle in the Adama Region of Ethiopia and pathogens detected
Ticks will diminish productivity among farm animals and transmit zoonotic diseases. We conducted a study to identify tick species infesting slaughter bulls from Adama City and to screen them for tick-borne pathogens. In 2016, 291 ticks were collected from 37 bulls in Adama, which were ready for slaughter. Ticks were identified morphologically. Total genomic DNA was extracted from ticks and used to test for Rickettsia spp. with real-time PCR. Species identification was done by phylogenetic analysis using sequencing that targeted the 23S-5S intergenic spacer region and ompA genes. Four tick species from two genera, Amblyomma and Rhipicephalus, were identified. Amblyomma cohaerens was the dominant species (n = 241, 82.8%), followed by Amblyomma variegatum (n = 22, 7.5%), Rhipicephalus pulchellus (n = 19, 6.5%), and Rhipicephalus decoloratus (n = 9, 3.0%). Among all ticks, 32 (11%) were positive for Rickettsia spp. and 15 (5.2%) of these were identified as R. africae comprising at least two genetic clades, occurring in A. variegatum (n = 10) and A. cohaerens (n = 5). The remainder of Rickettsia-positive samples could not be amplified due to low DNA yield. Furthermore, another 15 (5.2%) samples carried other pathogenic bacteria: Ehrlichia ruminantium (n = 9; 3.1%) in A. cohaerens, Ehrlichia sp. (n = 3; 1%) in Rh. pulchellus and A. cohaerens, Anaplasma sp. (n = 1; 0.5%) in A. cohaerens, and Neoehrlichia mikurensis (n = 2; 0.7%) in A. cohaerens. All ticks were negative for Bartonella spp., Babesia spp., Theileria spp., and Hepatozoon spp. We reported for the first time E. ruminatium, N. mikurensis, Ehrlichia sp., and Anaplasma sp. in A. cohaerens. Medically and veterinarily important pathogens were mostly detected from A. variegatum and A. cohaerens. These data are relevant for a One-health approach for monitoring and prevention of tick-borne disease transmission
The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits: II- Survey description, results and performances
In anticipation of the VLT/SPHERE planet imager guaranteed time programs, we
have conducted a preparatory survey of 86 stars between 2009 and 2013 in order
to identify new faint comoving companions to ultimately carry out a
comprehensive analysis of the occurence of giant planets and brown dwarf
companions at wide (10-2000 AU) orbits around young, solar-type stars. We used
NaCo at VLT to explore the occurrence rate of giant planets and brown dwarfs
between typically 0.1 and 8''. Diffraction-limited observations in H-band
combined with angular differential imaging enabled us to reach primary
star-companion brightness ratios as small as 10-6 at 1.5''. 12 systems were
resolved as new binaries, including the discovery of a new white dwarf
companion to the star HD8049. Around 34 stars, at least one companion candidate
was detected in the observed field of view. More than 400 faint sources were
detected, 90% of them in 4 crowded fields. With the exception of HD8049B, we
did not identify any new comoving companions. The survey also led to spatially
resolved images of the thin debris disk around HD\,61005 that have been
published earlier. Finally, considering the survey detection limits, we derive
a preliminary upper limit on the frequency of giant planets for semi-major axes
of [10,2000] AU: typically less than 15% between 100 and 500 AU, and less than
10% between 50 and 500 AU for exoplanets more massive than 5 MJup and 10 MJup
respectively, considering a uniform input distribution and with a confidence
level of 95%.Comment: 19 pages, 8 figures, 12 Tables, accepted to A&
- âŠ