63 research outputs found
A Census of Large-Scale ( 10 pc), Velocity-Coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree
Large-scale gaseous filaments with length up to the order of 100 pc are on
the upper end of the filamentary hierarchy of the Galactic interstellar medium.
Their association with respect to the Galactic structure and their role in
Galactic star formation are of great interest from both observational and
theoretical point of view. Previous "by-eye" searches, combined together, have
started to uncover the Galactic distribution of large filaments, yet inherent
bias and small sample size limit conclusive statistical results to be drawn.
Here, we present (1) a new, automated method to identify large-scale
velocity-coherent dense filaments, and (2) the first statistics and the
Galactic distribution of these filaments. We use a customized minimum spanning
tree algorithm to identify filaments by connecting voxels in the
position-position-velocity space, using the Bolocam Galactic Plane Survey
spectroscopic catalog. In the range of , we
have identified 54 large-scale filaments and derived mass (), length (10-276 pc), linear mass density (54-8625 ), aspect ratio, linearity, velocity gradient, temperature,
fragmentation, Galactic location and orientation angle. The filaments
concentrate along major spiral arms. They are widely distributed across the
Galactic disk, with 50% located within 20 pc from the Galactic mid-plane
and 27% run in the center of spiral arms (aka "bones"). An order of 1% of the
molecular ISM is confined in large filaments. Massive star formation is more
favorable in large filaments compared to elsewhere. This is the first
comprehensive catalog of large filaments useful for a quantitative comparison
with spiral structures and numerical simulations.Comment: Accepted to ApJS. 20 pages (in aastex6 compact format), 6 figures, 1
table. See http://www.eso.org/~kwang/MSTpaper for (1) a preprint with full
resolution Fig 6, (2) filaments catalog (Table 1) in ASCII format, and (3) a
DS9 region file for the coordinates of the filament
Physical characteristics of G331.5-0.1: The luminous central region of a Giant Molecular Cloud
We report molecular line and dust continuum observations toward the high-mass
star forming region G331.5-0.1, one of the most luminous regions of massive
star-formation in the Milky Way, located at the tangent region of the Norma
spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the
G331.5-0.1 GMC in the CO (J=1-0) and C18O (J=1-0) lines with NANTEN, while its
central region was mapped in CS (J=2-1 and J=5-4) with SEST, and in CS (J=7-6)
and 13CO (J=3-2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and
at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust
clumps, making this source one of the most densely populated central regions of
a GMC in the Galaxy. The dust clumps are associated with molecular gas and they
have the following average properties: size of 1.6 pc, mass of 3.2x10^3 Msun,
molecular hydrogen density of 3.7x10^4 cm^{-3}, dust temperature of 32 K, and
integrated luminosity of 5.7x10^5 Lsun, consistent with values found toward
other massive star forming dust clumps. The CS and 13CO spectra show the
presence of two velocity components: a high-velocity component at ~ -89 km
s^{-1}, seen toward four of the clumps, and a low-velocity component at ~ -101
km s^{-1} seen toward the other two clumps. Radio continuum emission is present
toward four of the molecular clumps, with spectral index estimated for two of
them of 0.8+-0.2 and 1.2+-0.2. A high-velocity molecular outflow is found at
the center of the brightest clump, with a line width of 26 km s^{-1} (FWHM) in
CS (J=7-6). Observations of SiO (J=7-6 and J=8-7), and SO (J_K=8_8-7_7 and
J_K=8_7-7_6) lines provide estimates of the gas rotational temperature toward
this outflow >120 K and >75 K, respectively.Comment: 34 pages, 20 figures, 11 tables, Accepted for Publication in The
Astrophysical Journa
The depletion of NO in pre-protostellar cores
Understanding the depletion of heavy elements is a fundamental step towards determining the structure of pre-protostellar cores just prior to collapse. We study the dependence of the NO abundance on position in the pre-protostellar cores L1544 and L183. We observed the 150 GHz and 250~GHz transitions of NO and the 93 GHz transitions of \NTHP \ towards L1544 and L183 using the IRAM 30 m telescope. We compare the variation of the NO column density with position in these objects with the H column density derived from dust emission measurements. We find that NO behaves differently from \NTHP \ and appears to be partially depleted in the high density core of L1544. Other oxygen-containing compounds are also likely to be partially depleted in dense-core nuclei. The principal conclusions are that: the prestellar core L1544 is likely to be 'carbon-rich'; the nitrogen chemistry did not reach equilibrium prior to gravitational collapse, and nitrogen is initially (at densities of the order of ~cm) mainly in atomic form; the grain sticking probabilities of atomic C, N and, probably, O are significantly smaller than unity
Hot gas and dust in a protostellar cluster near W3(OH
We used the IRAM Interferometer to obtain sub-arcsecond resolution
observations of the high-mass star-forming region W3(OH) and its surroundings
at a frequency of 220 GHz. With the improved angular resolution, we distinguish
3 peaks in the thermal dust continuum emission originating from the hot core
region about 6 arcsec (0.06 pc) east of W3(OH). The dust emission peaks are
coincident with known radio continuum sources, one of which is of non-thermal
nature. The latter source is also at the center of expansion of a powerful
bipolar outflow observed in water maser emission. We determine the hot core
mass to be 15 solar masses based on the integrated dust continuum emission.
Simultaneously many molecular lines are detected allowing the analysis of the
temperature structure and the distribution of complex organic molecules in the
hot core. From HNCO lines, spanning a wide range of excitation, two 200 K
temperature peaks are found coincident with dust continuum emission peaks
suggesting embedded heating sources within them.Comment: 12 pages, 3 figure
First detection of water vapor in a pre-stellar core
Water is a crucial molecule in molecular astrophysics as it controls much of
the gas/grain chemistry, including the formation and evolution of more complex
organic molecules in ices. Pre-stellar cores provide the original reservoir of
material from which future planetary systems are built, but few observational
constraints exist on the formation of water and its partitioning between gas
and ice in the densest cores. Thanks to the high sensitivity of the Herschel
Space Observatory, we report on the first detection of water vapor at high
spectral resolution toward a dense cloud on the verge of star formation, the
pre-stellar core L1544. The line shows an inverse P-Cygni profile,
characteristic of gravitational contraction. To reproduce the observations,
water vapor has to be present in the cold and dense central few thousand AU of
L1544, where species heavier than Helium are expected to freeze-out onto dust
grains, and the ortho:para H2 ratio has to be around 1:1 or larger. The
observed amount of water vapor within the core (about 1.5x10^{-6} Msun) can be
maintained by Far-UV photons locally produced by the impact of galactic cosmic
rays with H2 molecules. Such FUV photons irradiate the icy mantles, liberating
water wapor in the core center. Our Herschel data, combined with radiative
transfer and chemical/dynamical models, shed light on the interplay between gas
and solids in dense interstellar clouds and provide the first measurement of
the water vapor abundance profile across the parent cloud of a future
solar-type star and its potential planetary system.Comment: The Astrophysical Journal Letters, in pres
The central 1000 AU of a pre-stellar core revealed with ALMA. I. 1.3 mm continuum observations
Stars like our Sun form in self-gravitating dense and cold structures within
interstellar clouds, called pre-stellar cores. Although much is known about the
physical structure of dense clouds just before and soon after the switch-on of
a protostar, the central few thousand astronomical units (au) of pre-stellar
cores are unexplored. It is within these central regions that stellar systems
assemble and fragmentation may take place, with the consequent formation of
binaries and multiple systems. We present ALMA Band 6 observations (ACA and 12m
array) of the dust continuum emission of the 8 Msun pre-stellar core L1544,
with angular resolution of 2'' x 1.6'' (linear resolution 270 au x 216 au).
Within the primary beam, a compact region of 0.1 Msun, which we call a
"kernel", has been unveiled. The kernel is elongated, with a central flat zone
with radius Rker ~ 10'' (~ 1400 au). The average number density within Rker is
~1 x 10^6 cm^{-3}, with possible local density enhancements. The region within
Rker appears to have fragmented, but detailed analysis shows that similar
substructure can be reproduced by synthetic interferometric observations of a
smooth centrally concentrated dense core with a similar central flat zone. The
presence of a smooth kernel within a dense core is in agreement with non-ideal
magneto-hydro-dynamical simulations of a contracting cloud core with a peak
number density of 1 x 10^7 cm^{-3}. Dense cores with lower central densities
are completely filtered out when simulated 12m-array observations are carried
out. These observations demonstrate that the kernel of dynamically evolved
dense cores can be investigated at high angular resolution with ALMA.Comment: accepted for publication in The Astrophysical Journa
Large-scale filaments associated with Milky Way spiral arms
The ubiquity of filamentary structure at various scales through out the
Galaxy has triggered a renewed interest in their formation, evolution, and role
in star formation. The largest filaments can reach up to Galactic scale as part
of the spiral arm structure. However, such large scale filaments are hard to
identify systematically due to limitations in identifying methodology (i.e., as
extinction features). We present a new approach to directly search for the
largest, coldest, and densest filaments in the Galaxy, making use of sensitive
Herschel Hi-GAL data complemented by spectral line cubes. We present a sample
of the 9 most prominent Herschel filaments, including 6 identified from a pilot
search field plus 3 from outside the field. These filaments measure 37-99 pc
long and 0.6-3.0 pc wide with masses (0.5-8.3), and
beam-averaged (, or 0.4-0.7 pc) peak H column densities of
(1.7-9.3). The bulk of the filaments are
relatively cold (17-21 K), while some local clumps have a dust temperature up
to 25-47 K. All the filaments are located within <~60 pc from the Galactic
mid-plane. Comparing the filaments to a recent spiral arm model incorporating
the latest parallax measurements, we find that 7/9 of them reside within arms,
but most are close to arm edges. These filaments are comparable in length to
the Galactic scale height and therefore are not simply part of a grander
turbulent cascade.Comment: Published 2015MNRAS.450.4043W; this version contains minor proof
corrections. FT-based background removal code at
https://github.com/esoPanda/FTbg SED fitting code at
http://hi-gal-sed-fitter.readthedocs.org 3D interactive visualization at
http://www.eso.org/~kwan
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A national-scale assessment of climate change impacts on species: assessing the balance of risks and opportunities for multiple taxa
It is important for conservationists to be able to assess the risks that climate change poses to species, in order to inform decision making. Using standardised and repeatable methods, we present a national-scale assessment of the risks of range loss and opportunities for range expansion, that climate change could pose for over 3,000 plants and animals that occur in England. A basic risk assessment that compared projected future changes in potential range with recently observed changes classified 21% of species as being at high risk and 6% at medium risk of range loss under a B1 climate change scenario. A greater number of species were classified as having a medium (16%) or high (38%) opportunity to potentially expand their distribution. A more comprehensive assessment, incorporating additional ecological information, including potentially confounding and exacerbating factors, was applied to 402 species, of which 35 % were at risk of range loss and 42 % may expand their range extent. This study covers a temperate region with a significant proportion of species at their poleward range limit. The balance of risks and opportunities from climate change may be different elsewhere. The outcome of both risk assessments varied between taxonomic groups, with bryophytes and vascular plants containing the greatest proportion of species at risk from climate change. Upland habitats contained more species at risk than other habitats. Whilst the overall pattern was clear, confidence was generally low for individual assessments, with the exception of well-studied taxa such as birds. In response to climate change, nature conservation needs to plan for changing species distributions and increasing uncertainty of the future
Minithoracotomy vs Conventional Sternotomy for Mitral Valve Repair: A Randomized Clinical Trial
Importance: The safety and effectiveness of mitral valve repair via thoracoscopically-guided minithoracotomy (minithoracotomy) compared with median sternotomy (sternotomy) in patients with degenerative mitral valve regurgitation is uncertain. Objective: To compare the safety and effectiveness of minithoracotomy vs sternotomy mitral valve repair in a randomized trial. Design, Setting, and Participants: A pragmatic, multicenter, superiority, randomized clinical trial in 10 tertiary care institutions in the UK. Participants were adults with degenerative mitral regurgitation undergoing mitral valve repair surgery. Interventions: Participants were randomized 1:1 with concealed allocation to receive either minithoracotomy or sternotomy mitral valve repair performed by an expert surgeon. Main Outcomes and Measures: The primary outcome was physical functioning and associated return to usual activities measured by change from baseline in the 36-Item Short Form Health Survey (SF-36) version 2 physical functioning scale 12 weeks after the index surgery, assessed by an independent researcher masked to the intervention. Secondary outcomes included recurrent mitral regurgitation grade, physical activity, and quality of life. The prespecified safety outcomes included death, repeat mitral valve surgery, or heart failure hospitalization up to 1 year. Results: Between November 2016 and January 2021, 330 participants were randomized (mean age, 67 years, 100 female [30%]); 166 were allocated to minithoracotomy and 164 allocated to sternotomy, of whom 309 underwent surgery and 294 reported the primary outcome. At 12 weeks, the mean between-group difference in the change in the SF-36 physical function T score was 0.68 (95% CI, −1.89 to 3.26). Valve repair rates (≈ 96%) were similar in both groups. Echocardiography demonstrated mitral regurgitation severity as none or mild for 92% of participants at 1 year with no difference between groups. The composite safety outcome occurred in 5.4% (9 of 166) of patients undergoing minithoracotomy and 6.1% (10 of 163) undergoing sternotomy at 1 year. Conclusions and relevance: Minithoracotomy is not superior to sternotomy in recovery of physical function at 12 weeks. Minithoracotomy achieves high rates and quality of valve repair and has similar safety outcomes at 1 year to sternotomy. The results provide evidence to inform shared decision-making and treatment guidelines. Trial Registration: isrctn.org Identifier: ISRCTN1393045
A novel formulation of inhaled sodium cromoglicate (PA101) in idiopathic pulmonary fibrosis and chronic cough: a randomised, double-blind, proof-of-concept, phase 2 trial
Background Cough can be a debilitating symptom of idiopathic pulmonary fibrosis (IPF) and is difficult to treat. PA101 is a novel formulation of sodium cromoglicate delivered via a high-efficiency eFlow nebuliser that achieves significantly higher drug deposition in the lung compared with the existing formulations. We aimed to test the efficacy and safety of inhaled PA101 in patients with IPF and chronic cough and, to explore the antitussive mechanism of PA101, patients with chronic idiopathic cough (CIC) were also studied. Methods This pilot, proof-of-concept study consisted of a randomised, double-blind, placebo-controlled trial in patients with IPF and chronic cough and a parallel study of similar design in patients with CIC. Participants with IPF and chronic cough recruited from seven centres in the UK and the Netherlands were randomly assigned (1:1, using a computer-generated randomisation schedule) by site staff to receive PA101 (40 mg) or matching placebo three times a day via oral inhalation for 2 weeks, followed by a 2 week washout, and then crossed over to the other arm. Study participants, investigators, study staff, and the sponsor were masked to group assignment until all participants had completed the study. The primary efficacy endpoint was change from baseline in objective daytime cough frequency (from 24 h acoustic recording, Leicester Cough Monitor). The primary efficacy analysis included all participants who received at least one dose of study drug and had at least one post-baseline efficacy measurement. Safety analysis included all those who took at least one dose of study drug. In the second cohort, participants with CIC were randomly assigned in a study across four centres with similar design and endpoints. The study was registered with ClinicalTrials.gov (NCT02412020) and the EU Clinical Trials Register (EudraCT Number 2014-004025-40) and both cohorts are closed to new participants. Findings Between Feb 13, 2015, and Feb 2, 2016, 24 participants with IPF were randomly assigned to treatment groups. 28 participants with CIC were enrolled during the same period and 27 received study treatment. In patients with IPF, PA101 reduced daytime cough frequency by 31·1% at day 14 compared with placebo; daytime cough frequency decreased from a mean 55 (SD 55) coughs per h at baseline to 39 (29) coughs per h at day 14 following treatment with PA101, versus 51 (37) coughs per h at baseline to 52 (40) cough per h following placebo treatment (ratio of least-squares [LS] means 0·67, 95% CI 0·48–0·94, p=0·0241). By contrast, no treatment benefit for PA101 was observed in the CIC cohort; mean reduction of daytime cough frequency at day 14 for PA101 adjusted for placebo was 6·2% (ratio of LS means 1·27, 0·78–2·06, p=0·31). PA101 was well tolerated in both cohorts. The incidence of adverse events was similar between PA101 and placebo treatments, most adverse events were mild in severity, and no severe adverse events or serious adverse events were reported. Interpretation This study suggests that the mechanism of cough in IPF might be disease specific. Inhaled PA101 could be a treatment option for chronic cough in patients with IPF and warrants further investigation
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