302 research outputs found
High mass star formation in the infrared dark cloud G11.11-0.12
We report detection of moderate to high-mass star formation in an infrared
dark cloud (G11.11-0.12) where we discovered class II methanol and water maser
emissions at 6.7 GHz and 22.2 GHz, respectively. We also observed the object in
ammonia inversion transitions. Strong emission from the (3,3) line indicates a
hot (~60 K) compact component associated with the maser emission. The line
width of the hot component (4 km/s), as well as the methanol maser detection,
are indicative of high mass star formation. To further constrain the physical
parameters of the source, we derived the spectral energy distribution (SED) of
the dust continuum by analysing data from the 2MASS survey, HIRAS, MSX, the
Spitzer Space Telescope, and interferometric 3mm observations. The SED was
modelled in a radiative transfer program: a) the stellar luminosity equals 1200
L_sun corresponding to a ZAMS star of 8 M_sun; b) the bulk of the envelope has
a temperature of 19 K; c) the mass of the remnant protostellar cloud in an area
8x10^17 cm or 15 arcsec across amounts to 500M_sun, if assuming standard dust
of the diffuse medium, and to about 60 M_sun, should the grains be fluffy and
have ice mantles; d) the corresponding visual extinction towards the star is a
few hundred magnitudes. The near IR data can be explained by scattering from
tenuous material above a hypothetical disk. The class II methanol maser lines
are spread out in velocity over 11 km/s. To explain the kinematics of the
masing spots, we propose that they are located in a Kepler disk at a distance
of about 250 AU. The dust temperatures there are around 150 K, high enough to
evaporate methanol--containing ice mantles.Comment: 10 pages, 6 figures, Accepted for publication in Astronomy &
Astrophysics Journa
Spectral Energy Distributions of 6.7 GHz methanol masers
The 6.7 GHz maser transition of methanol has been found exclusively towards
massive star forming regions. A majority of the masers have been found to lack
the presence of any associated radio continuum. This could be due to the maser
emission originating prior to the formation of an HII region around the central
star, or from the central object being too cool to produce a HII region. One
way to distinguish between the two scenarios is to determine and model the
spectral energy distributions (SEDs) of the masers. We observed a sample of 20
6.7 GHz methanol masers selected from the blind Arecibo survey, from centimeter
to submillimeter wavelengths. We combined our observations with existing data
from various Galactic plane surveys to determine SEDs from centimeter to
near-infrared wavelengths. We find that 70% of the masers do not have any
associated radio continuum, with the rest of the sources being associated with
hypercompact and ultracompact HII regions. Modeling the SEDs shows them to be
consistent with rapidly accreting massive stars, with accretion rates well
above 10^{-3} M_sun/yr. The upper limits on the radio continuum are also
consistent with any ionized region being confined close to the stellar surface.
This confirms the paradigm of 6.7 GHz methanol masers being signposts of early
phases of massive star formation, mostly prior to the formation of a
hypercompact HII region.Comment: 15 pages, 4 figures; Accepted by A&
Dynamics of the 6.7 and 12.2 GHz methanol masers around Cepheus A HW2
The 6.7 GHz methanol maser is exclusively associated with high-mass star
formation. However, it remains unclear what structures harbour the methanol
masers. Cepheus A is one of the closest regions of massive star formation,
making it an excellent candidate for detailed studies. We determine the
dynamics of maser spots in the high-mass star-forming region Cepheus A in order
to infer where and when the maser emission occurs. Very long baseline
interferometry (VLBI) observations of the 6.7 and 12.2 GHz methanol masers
allows for mapping their spatial and velocity distribution. Phase-referencing
is used to determine the astrometric positions of the maser emission, and
multi-epoch observations can reveal 3D motions. The 6.7 GHz methanol masers are
found in a filamentary structure over ~1350 AU, straddling the waist of the
radio jet HW2. The positions agree well with previous observations of both the
6.7 and 12.2 GHz methanol masers. The velocity field of the maser spots does
not show any sign of rotation, but is instead consistent with an infall
signature. The 12.2 GHz methanol masers are closely associated with the 6.7 GHz
methanol masers, and the parallax that we derive confirms previous
measurements. We show that the methanol maser emission very likely arises in a
shock interface in the equatorial region of Cepheus A HW2 and presents a model
in which the maser emission occurs between the infalling gas and the accretion
disk/process.Comment: 9 pages, 5 figures; accepted for publication in Astronomy and
Astrophysic
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
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
Absolute positions of 6.7-GHz methanol masers
The ATCA, MERLIN and VLA interferometers were used to measure the absolute
positions of 35 6.7 GHz methanol masers to subarcsecond or higher accuracy. Our
measurements represent essential preparatory data for Very Long Baseline
Interferometry, which can provide accurate parallax and proper motion
determinations of the star-forming regions harboring the masers. Our data also
allow associations to be established with infrared sources at different
wavelengths. Our findings support the view that the 6.7 GHz masers are
associated with the earliest phases of high-mass star formation.Comment: A&A accepted 29 pages, 6 figures, 5 table
Intersex in the clam Scrobicularia plana (Da Costa): Widespread occurrence in English Channel estuaries and surrounding areas
Estuarine clams Scrobicularia plana were sampled from 108 intertidal locations around the English Channel and adjacent areas. Although S. plana is believed to be a strict gonochorist, 58% of the populations sampled included intersexed individuals (described as male clams exhibiting ovotestis). Over the entire region, on average, 8.6% of male clams exhibited intersex, although proportions of affected males ranged from 0% to 53% depending on location. The severity of intersex was assessed using a simple classification scale, with the majority of individuals showing low levels of impact. Sex ratios were significantly skewed at some sites. There were no significant relationships between the incidence and severity of intersex; or of associations with size or parasitism of individual clams. Intersex in S. plana is a useful tool to assess endocrine disruptive effects in estuaries, although mechanisms of impact and causative agents remain uncertain
CH3OH and H2O masers in high-mass star-forming regions
We present a comparison of ClassII CH3OH and H2O masers at high spatial
resolution in a sample of 29 massive star-forming regions. Absolute positions
of both maser types are compared with mm dust continuum, cm continuum and
mid-infrared sources. Spatial correlations of the different tracers and
kinematic signatures are discussed.Comment: 12 pages, 5 figures, accepted by Astronomy and Astrophysic
OH main line masers in the M82 starburst
A study of the distribution of OH gas in the central region of the nearby
active starburst galaxy M82 has confirmed two previously known bright masers
and revealed several new main line masers. Three of these are seen only at 1665
MHz, one is detected only at 1667 MHz, while the rest are detected in both
lines. Observations covering both the 1665 and 1667 MHz lines, conducted with
both the Very Large Array (VLA) and the Multi-Element Radio Linked
Interferometer Network (MERLIN), have been used to accurately measure the
positions and velocities of these features. This has allowed a comparison with
catalogued continuum features in the starburst such as HII regions and
supernova remnants, as well as known water and satellite line OH masers. Most
of the main line masers appear to be associated with known HII regions although
the two detected only at 1665 MHz are seen along the same line of sight as
known supernova remnants.Comment: MNRAS accepted. 16 pages, 13 figure
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
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