113 research outputs found
Kinematic structure of massive star-forming regions - I. Accretion along filaments
The mid- and far-infrared view on high-mass star formation, in particular
with the results from the Herschel space observatory, has shed light on many
aspects of massive star formation. However, these continuum studies lack
kinematic information.
We study the kinematics of the molecular gas in high-mass star-forming
regions.
We complemented the PACS and SPIRE far-infrared data of 16 high-mass
star-forming regions from the Herschel key project EPoS with N2H+ molecular
line data from the MOPRA and Nobeyama 45m telescope. Using the full N2H+
hyperfine structure, we produced column density, velocity, and linewidth maps.
These were correlated with PACS 70micron images and PACS point sources. In
addition, we searched for velocity gradients.
For several regions, the data suggest that the linewidth on the scale of
clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and
G11.11 show two velocity components along several lines of sight. We find that
all regions with a diameter larger than 1pc show either velocity gradients or
fragment into independent structures with distinct velocities. The velocity
profiles of three regions with a smooth gradient are consistent with gas flows
along the filament, suggesting accretion flows onto the densest regions.
We show that the kinematics of several regions have a significant and complex
velocity structure. For three filaments, we suggest that gas flows toward the
more massive clumps are present.Comment: accepted by A&
A protostellar system fed by a streamer of 10,500 au length
Binary formation is an important aspect of star formation. One possible route
for close-in binary formation is disk fragmentation. Recent
observations show small scale asymmetries (<300 au) around young
protostars, although not always resolving the circumbinary disk, are
linked to disk phenomena. In later stages, resolved circumbinary disk
observations (<200 au) show similar asymmetries, suggesting the origin
of the asymmetries arises from binary-disk interactions. We
observed one of the youngest systems to study the connection between disk and
dense core. We find for the first time a bright and clear streamer in
chemically fresh material (Carbon-chain species) that originates from outside
the dense core (>10,500 au). This material connects the outer dense core with
the region where asymmetries arise near disk scales. This new structure type,
10x larger than those seen near disk scales, suggests a different
interpretation of previous observations: large-scale accretion flows funnel
material down to disk scales. These results reveal the under-appreciated
importance of the local environment on the formation and evolution of disks in
early systems and a possible initial condition for the formation of
annular features in young disks.Comment: Published in Nature Astronomy on July 27th 2020. This is the authors'
version before final edits, including methods section. Link to the NatAstro
publication: https://www.nature.com/articles/s41550-020-1150-
Initial conditions of star formation at 2000 au: physical structure and NH depletion of three early-stage cores
Pre-stellar cores represent a critical evolutionary phase in low-mass star
formation. We aim to unveil the detailed thermal structure and density
distribution of three early-stage cores, starless core L1517B, and prestellar
core L694-2 and L429, with the high angular resolution observations of the
NH (1,1) and (2,2) inversion transitions obtained with VLA and GBT. In
addition, we explore where/if NH depletes in the central regions.
Applying the mid-infrared extinction method to the 8m
map we obtain a high angular resolution hydrogen column density map, and derive
the gas density profile to assess the variation of NH abundance as a
function of gas volume density. The measured temperature profiles of L429 and
L1517B show a minor decrease towards the core center, dropping from 9\~K
to below 8\~K, and 11 K to 10 K, while L694-2 has a rather uniform
temperature distribution around 9 K. Among the three cores, L429 has the
highest central gas density, close to sonic velocity line-width, and largest
localised velocity gradient, all indicative of an advanced evolutionary stage.
We resolve that the abundance of NH becomes two times lower in the
central region of L429, occurring around a gas density of
4.410. Compared to Ophiuchus/H-MM1 which shows an even
stronger drop of the NH abundance at 210, the
abundance variations of the three cores plus Ophiuchus/H-MM1 suggest a
progressive NH depletion with increasing central density of the core.Comment: 23 pages, 23 figures incl. appendix; A&A accepte
Herschel observations of extraordinary sources: Full Herschel/HIFI molecular line survey of Sagittarius B2(M)
We present a full analysis of a broadband spectral line survey of Sagittarius
B2 (Main), one of the most chemically rich regions in the Galaxy located within
the giant molecular cloud complex Sgr B2 in the Central Molecular Zone. Our
goal is to derive the molecular abundances and temperatures of the high-mass
star-forming region Sgr B2(M) and thus its physical and astrochemical
conditions. Sgr B2(M) was observed using the Heterodyne Instrument for the
Far-Infrared (HIFI) on board the Herschel Space Observatory in a spectral line
survey from 480 to 1907 GHz at a spectral resolution of 1.1 MHz, which provides
one of the largest spectral coverages ever obtained toward this high-mass
star-forming region in the submillimeter with high spectral resolution and
includes frequencies > 1 THz unobservable from the ground. We model the
molecular emission from the submillimeter to the far-IR using the XCLASS
program. For each molecule, a quantitative description was determined taking
all emission and absorption features of that species across the entire spectral
range into account. Additionally, we derive velocity resolved ortho / para
ratios for those molecules for which ortho and para resolved molecular
parameters are available. Finally, the temperature and velocity distributions
are analyzed and the derived abundances are compared with those obtained for
Sgr B2(N) from a similar HIFI survey. A total of 92 isotopologues were
identified, arising from 49 different molecules, ranging from free ions to
complex organic compounds and originating from a variety of environments from
the cold envelope to hot and dense gas within the cores. Sulfur dioxide,
methanol, and water are the dominant contributors. For the ortho / para ratios
we find deviations from the high temperature values between 13 and 27 %. In
total 14 % of all lines remain unidentified.Comment: 67 pages, 102 figures, submitted to A&
Kinematic structure of massive star-forming regions - I. Accretion along filaments
The mid- and far-infrared view on high-mass star formation, in particular
with the results from the Herschel space observatory, has shed light on many
aspects of massive star formation. However, these continuum studies lack
kinematic information.
We study the kinematics of the molecular gas in high-mass star-forming
regions.
We complemented the PACS and SPIRE far-infrared data of 16 high-mass
star-forming regions from the Herschel key project EPoS with N2H+ molecular
line data from the MOPRA and Nobeyama 45m telescope. Using the full N2H+
hyperfine structure, we produced column density, velocity, and linewidth maps.
These were correlated with PACS 70micron images and PACS point sources. In
addition, we searched for velocity gradients.
For several regions, the data suggest that the linewidth on the scale of
clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and
G11.11 show two velocity components along several lines of sight. We find that
all regions with a diameter larger than 1pc show either velocity gradients or
fragment into independent structures with distinct velocities. The velocity
profiles of three regions with a smooth gradient are consistent with gas flows
along the filament, suggesting accretion flows onto the densest regions.
We show that the kinematics of several regions have a significant and complex
velocity structure. For three filaments, we suggest that gas flows toward the
more massive clumps are present.Comment: accepted by A&
Continuum radiative transfer Modeling of Sagittarius B2
We present results from radiative transfer modeling of the continuum emission towards Sagittarius B2 (hereafter Sgr B2). We have developed a radiative transfer framework – Pandora – that employs RADMC-3D (Dullemond 2012) for a self-consistent determination of the dust temperature. With this pipeline, we have set-up a single model that consistently reproduces the thermal dust and free-free continuum emission of Sgr B2 spanning four orders of magnitude in spatial scales (0.02–45 pc) and two orders of magnitude in frequency (20–4000 GHz)
European consensus meeting of ARM-Net members concerning diagnosis and early management of newborns with anorectal malformations.
The ARM-Net (anorectal malformation network) consortium held a consensus meeting in which the classification of ARM and preoperative workup were evaluated with the aim of improving monitoring of treatment and outcome. The Krickenbeck classification of ARM and preoperative workup suggested by Levitt and Peña, used as a template, were discussed, and a collaborative consensus was achieved. The Krickenbeck classification is appropriate in describing ARM for clinical use. The preoperative workup was slightly modified. In males with a visible fistula, no cross-table lateral X-ray is needed and an anoplasty or (mini-) posterior sagittal anorectoplasty can directly be performed. In females with a small vestibular fistula (Hegar size 5 mm, and in the meantime, gentle painless dilatations can be performed. In both male and female perineal fistula and either a low birth weight (<2,000 g) or severe associated congenital anomalies, prolonged preoperative painless dilatations might be indicated to decrease perioperative morbidity caused by general anesthesia. The Krickenbeck classification is appropriate in describing ARM for clinical use. Some minor modifications to the preoperative workup by Levitt and Peña have been introduced in order to refine terminology and establish a comprehensive preoperative workup
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