339 research outputs found
New class I methanol masers
We review properties of all known collisionally pumped (class I) methanol
maser series based on observations with the Australia Telescope Compact Array
(ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most
widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the
most energetic shocks. A survey of many southern masers at 36 and 44 GHz
suggests that these two transitions are highly complementary. The 23.4 GHz
maser is a new type of rare class I methanol maser, detected only in two
high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a
behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions
suggest that shocks responsible for class I masers could arise from a range of
phenomena, not merely an outflow scenario. For example, some masers might be
caused by interaction of an expanding HII region with its surrounding molecular
cloud. This has implications for evolutionary sequences incorporating class I
methanol masers if they appear more than once during the evolution of the
star-forming region. We also make predictions for candidate maser transitions
at the ALMA frequency range.Comment: 8 pages, 2 figures, to appear in proceedings for IAUS 287: Cosmic
Masers - from OH to H
Trigonometric Parallaxes of Massive Star Forming Regions: II. Cep A & NGC 7538
We report trigonometric parallaxes for the sources NGC 7538 and Cep A,
corresponding to distances of 2.65 [+0.12/-0.11] kpc and 0.70 [+0.04/-0.04]
kpc, respectively. The distance to NGC 7538 is considerably smaller than its
kinematic distance and places it in the Perseus spiral arm. The distance to Cep
A is also smaller than its kinematic distance and places it in the Local arm or
spur. Combining the distance and proper motions with observed radial velocities
gives the location and full space motion of the star forming regions. We find
significant deviations from circular Galactic orbits for these sources: both
sources show large peculiar motions (> 10 km/s) counter to Galactic rotation
and NGC 7538 has a comparable peculiar motion toward the Galactic center.Comment: 21 pages, 8 figures; to appear in the Astrophysical Journa
The Formaldehyde Masers in NGC 7538 and G29.96-0.02: VLBA, MERLIN, and VLA Observations
The 6 cm formaldehyde (H2CO) maser sources in the compact HII regions NGC
7538-IRS1 and G29.96-0.02 have been imaged at high resolution (beams < 50 mas).
Using the VLBA and MERLIN, we find the angular sizes of the NGC 7538 masers to
be ~10 mas (30 AU) corresponding to brightness temperatures ~10^8 K. The
angular sizes of the G29.96-0.02 masers are ~20 mas (130 AU) corresponding to
brightness temperatures ~10^7 K. Using the VLA, we detect 2 cm formaldehyde
absorption from the maser regions. We detect no emission in the 2 cm line,
indicating the lack of a 2 cm maser and placing limits on the 6 cm excitation
process. We find that both NGC 7538 maser components show an increase in
intensity on 5-10 year timescales while the G29.96-0.02 masers show no
variability over 2 years. A search for polarization provides 3-sigma upper
limits of 1% circularly polarized and 10% linearly polarized emission in NGC
7538 and of 15% circularly polarized emission in G29.96-0.02. A pronounced
velocity gradient of 28 km/s/arcsecond (1900 km/s/pc) is detected in the NGC
7538 maser gas.Comment: accepted to ApJ, 15 figures, 11 table
Semi-supervised prediction of protein interaction sentences exploiting semantically encoded metrics
Protein-protein interaction (PPI) identification is an integral component of many biomedical research and database curation tools. Automation of this task through classification is one of the key goals of text mining (TM). However, labelled PPI corpora required to train classifiers are generally small. In order to overcome this sparsity in the training data, we propose a novel method of integrating corpora that do not contain relevance judgements. Our approach uses a semantic language model to gather word similarity from a large unlabelled corpus. This additional information is integrated into the sentence classification process using kernel transformations and has a re-weighting effect on the training features that leads to an 8% improvement in F-score over the baseline results. Furthermore, we discover that some words which are generally considered indicative of interactions are actually neutralised by this process
The brightest OH maser in the sky: a flare of emission in W75 N
A flare of maser radio emission in the OH-line 1665 MHz has been discovered
in the star forming region W75 N in 2003, with the flux density of about 1000
Jy. At the time it was the strongest OH maser detected during the whole history
of observations since the discovery of cosmic masers in 1965. The flare
emission is linearly polarized with a degree of polarization near 100%. A
weaker flare with a flux of 145 Jy was observed in this source in 2000 - 2001,
which was probably a precursor of the powerful flare. Intensity of two other
spectral features has decreased after beginning of the flare. Such variation of
the intensity of maser condensation emission (increasing of one and decreasing
of the other) can be explained by passing of the magneto hydrodynamic shock
across regions of enhanced gas concentration.Comment: 9 pages with 2 figures, accepted for publication in Astronomy Letter
The Herschel view of the on-going star formation in the Vela-C molecular cloud
As part of the Herschel guaranteed time key program 'HOBYS', we present the
photometric survey of the star forming region Vela-C, one of the nearest sites
of low-to-high-mass star formation in the Galactic plane. Vela-C has been
observed with PACS and SPIRE in parallel mode between 70 um and 500 um over an
area of about 3 square degrees. A photometric catalogue has been extracted from
the detections in each band, using a threshold of 5 sigma over the local
background. Out of this catalogue we have selected a robust sub-sample of 268
sources, of which 75% are cloud clumps and 25% are cores. Their Spectral Energy
Distributions (SEDs) have been fitted with a modified black body function. We
classify 48 sources as protostellar and 218 as starless. For two further
sources, we do not provide a secure classification, but suggest they are Class
0 protostars.
From SED fitting we have derived key physical parameters. Protostellar
sources are in general warmer and more compact than starless sources. Both
these evidences can be ascribed to the presence of an internal source(s) of
moderate heating, which also causes a temperature gradient and hence a more
peaked intensity distribution. Moreover, the reduced dimensions of protostellar
sources may indicate that they will not fragment further. A virial analysis of
the starless sources gives an upper limit of 90% for the sources
gravitationally bound and therefore prestellar. We fit a power law N(logM) prop
M^-1.1 to the linear portion of the mass distribution of prestellar sources.
This is in between that typical of CO clumps and those of cores in nearby
star-forming regions. We interpret this as a result of the inhomogeneity of our
sample, which is composed of comparable fractions of clumps and cores.Comment: 9 pages, 7 figures, accepted by A&
A Search for Propylene Oxide and Glycine in Sagittarius B2 (LMH) and Orion
We have used the Mopra Telescope to search for glycine and the simple chiral
molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We
have not detected either species, but have been able to put sensitive upper
limits on the abundances of both molecules. The 3-sigma upper limits derived
for glycine conformer I are 3.7 x 10^{14} cm^{-2} in both Orion-KL and Sgr B2
(LMH), comparable to the reported detections of conformer I by Kuan et al.
However, as our values are 3-sigma upper limits rather than detections we
conclude that this weighs against confirming the detection of Kuan et al. We
find upper limits for the glycine II column density of 7.7 x 10^{12} cm^{-2} in
both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al.
The results presented here show that glycine conformer II is not present in the
extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA
results (Jones et al.) have ruled out the detection of glycine (both conformers
I and II) in the compact hot core of the LMH at the levels reported, so we
conclude that it is unlikely that Kuan et al. have detected glycine in either
Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of 3.0 x
10^{14} cm^{-2} in Orion-KL and 6.7 x 10^{14} cm^{-2} in Sgr B2 (LMH). We have
detected fourteen features in Sgr B2 and four features in Orion-KL which have
not previously been reported in the ISM, but have not be able to plausibly
assign these transitions to any carrier.Comment: 12 pages, 3 figures. Accepted by MNRAS 12th January 200
Clustered Star Formation in W75 N
We present 2" to 7" resolution 3 mm continuum and CO(J=1-0) line emission and
near infrared Ks, H2, and [FeII] images toward the massive star forming region
W75 N. The CO emission uncovers a complex morphology of multiple, overlapping
outflows. A total flow mass of greater than 255 Msun extends 3 pc from
end-to-end and is being driven by at least four late to early-B protostars.
More than 10% of the molecular cloud has been accelerated to high velocities by
the molecular flows (> 5.2 km/s relative to v{LSR}) and the mechanical energy
in the outflowing gas is roughly half the gravitational binding energy of the
cloud. The W75 N cluster members represent a range of evolutionary stages, from
stars with no apparent circumstellar material to deeply embedded protostars
that are actively powering massive outflows. Nine cores of
millimeter-wavelength emission highlight the locations of embedded protostars
in W75 N. The total mass of gas & dust associated with the millimeter cores
ranges from 340 Msun to 11 Msun. The infrared reflection nebula and shocked H2
emission have multiple peaks and extensions which, again, suggests the presence
of several outflows. Diffuse H2 emission extends about 0.6 parsecs beyond the
outer boundaries of the CO emission while the [FeII] emission is only detected
close to the protostars. The infrared line emission morphology suggests that
only slow, non-dissociative J-type shocks exist throughout the pc-scale
outflows. Fast, dissociative shocks, common in jet-driven low-mass outflows,
are absent in W75 N. Thus, the energetics of the outflows from the late to
early B protostars in W75 N differ from their low-mass counterparts -- they do
not appear to be simply scaled-up versions of low-mass outflows.Comment: Astrophysical Journal, in press. 23 pages plus 10 figures (jpg
format). See http://www.aoc.nrao.edu/~dshepher/science.shtml for reprint with
full resolution figure
Millimeter and sub-millimeter atmospheric performance at Dome C combining radiosoundings and ATM synthetic spectra
The reliability of astronomical observations at millimeter and sub-millimeter
wavelengths closely depends on a low vertical content of water vapor as well as
on high atmospheric emission stability. Although Concordia station at Dome C
(Antarctica) enjoys good observing conditions in this atmospheric spectral
windows, as shown by preliminary site-testing campaigns at different bands and
in, not always, time overlapped periods, a dedicated instrument able to
continuously determine atmospheric performance for a wide spectral range is not
yet planned. In the absence of such measurements, in this paper we suggest a
semi-empirical approach to perform an analysis of atmospheric transmission and
emission at Dome C to compare the performance for 7 photometric bands ranging
from 100 GHz to 2 THz. Radiosoundings data provided by the Routine
Meteorological Observations (RMO) Research Project at Concordia station are
corrected by temperature and humidity errors and dry biases and then employed
to feed ATM (Atmospheric Transmission at Microwaves) code to generate synthetic
spectra in the wide spectral range from 100 GHz to 2 THz. To quantify the
atmospheric contribution in millimeter and sub-millimeter observations we are
considering several photometric bands in which atmospheric quantities are
integrated. The observational capabilities of this site at all the selected
spectral bands are analyzed considering monthly averaged transmissions joined
to the corresponding fluctuations. Transmission and pwv statistics at Dome C
derived by our semi-empirical approach are consistent with previous works. It
is evident the decreasing of the performance at high frequencies. We propose to
introduce a new parameter to compare the quality of a site at different
spectral bands, in terms of high transmission and emission stability, the Site
Photometric Quality Factor.Comment: accepted to MNRAS with minor revision
12.2-GHz methanol maser MMB follow-up catalogue - I. Longitude range 330 to 10 degrees
We present a catalogue of 12.2-GHz methanol masers detected towards 6.7-GHz
methanol masers observed in the unbiased Methanol Multibeam (MMB) survey in the
longitude range 330\circ (through 360\circ) to 10\circ. This is the first
portion of the catalogue which, when complete, will encompass all of the MMB
detections. We report the detection of 184 12.2-GHz sources towards 400 6.7-GHz
methanol maser targets, equating to a detection rate of 46 per cent. Of the 184
12.2-GHz detections, 117 are reported here for the first time. We draw
attention to a number of 'special' sources, particularly those with emission at
12.2-GHz stronger than their 6.7-GHz counterpart and conclude that these
unusual sources are not associated with a specific evolutionary stage.Comment: accepted to MNRAS 21 Dec 201
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