scholarly journals Methanol masers and millimetre lines: a common origin in protostellar envelopes

2012 ◽  
Vol 8 (S287) ◽  
pp. 146-150
Author(s):  
Karl J. E. Torstensson ◽  
Huib Jan van Langevelde ◽  
Floris F. S. van der Tak ◽  
Wouter H. T. Vlemmings ◽  
Lars E. Kristensen ◽  
...  
Keyword(s):  
Large Scale ◽  
Major Axis ◽  
Central Peak ◽  
Small Region ◽  
High Mass ◽  
Mass Star ◽  
Semi Major Axis ◽  
High Detection Rate ◽  
Maser Emission ◽  
Compact Sources

AbstractTo understand the origin of the CH3OH maser emission, we map the distribution and excitation of the thermal CH3OH emission in a sample of 14 relatively nearby (<6 kpc) high-mass star forming regions that are identified through 6.7 GHz maser emission. The images are velocity-resolved and allow us to study the kinematics of the regions. Further, rotation diagrams are created to derive rotation temperatures and column densities of the large scale molecular gas. The effects of optical depth and subthermal excitation are studied with population diagrams. For eight of the sources in our sample the thermal CH3OH emission is compact and confined to a region <0.4 pc and with a central peak close (<0.03 pc) to the position of the CH3OH maser emission. Four sources have more extended thermal CH3OH emission without a clear peak, and for the remaining two sources, the emission is too weak to map. The compact sources have linear velocity gradients along the semi-major axis of the emission of 0.3 – 13 kms−1 pc−1. The rotation diagram analysis shows that in general the highest rotation temperature is found close to the maser position. The confined and centrally peaked CH3OH emission in the compact sources indicates a single source for the CH3OH gas and the velocity fields show signs of outflow in all but one of the sources. The high detection rate of the torsionally excited vt = 1 line and signs of high-K lines at the maser position indicate radiative pumping, though the general lack of measurable beam dilution effects may mean that the masing gas is not sampled well and originates in a very small region.

scholarly journals MAGMO: Mapping the Galactic Magnetic field through OH masers

2012 ◽  
Vol 10 (H16) ◽  
pp. 402-402 ◽  
Author(s):  
James A. Green ◽  
Naomi M. McClure-Griffiths ◽  
James L. Caswell ◽  
Tim Robishaw ◽  
Lisa Harvey-Smith ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Ground State ◽  
Large Scale ◽  
Zeeman Splitting ◽  
High Mass ◽  
Mass Star ◽  
Galactic Magnetic Field ◽  
Maser Emission

AbstractWe are undertaking a project (MAGMO) to examine large-scale magnetic fields pervading regions of high-mass star formation. The project will test if the orientations of weak large-scale magnetic fields can be maintained in the contraction (and field amplification) to the high densities encountered in high-mass star forming regions. This will be achieved through correlating targeted observations of ground-state hydroxyl (OH) maser emission towards hundreds of sites of high-mass star formation spread throughout the spiral arms of the Milky Way. Through the Zeeman splitting of the OH maser emission these observations will determine the strength and orientation of the in-situ magnetic field. The completion of the southern hemisphere Methanol Multibeam survey has provided an abundance of targets for ground-state OH maser observations, approximately 1000 sites of high-mass star formation. With this sample, much larger and more homogeneous than previously available, we will have the statistics necessary to outweigh random fluctuations and observe an underlying Galactic magnetic field if it exists. We presented details of the overall progress of the project illustrated by the results of a pilot sample of sources towards the Carina-Sagittarius spiral arm tangent, where a coherent field is implied.

scholarly journals GASTON: Galactic Star Formation with NIKA2. Evidence for the mass growth of star-forming clumps

2021 ◽  
Author(s):  
A J Rigby ◽  
N Peretto ◽  
R Adam ◽  
P Ade ◽  
M Anderson ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Galactic Plane ◽  
High Sensitivity ◽  
High Mass ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Mass Growth ◽  
Star Forming ◽  
Compact Source

Abstract Determining the mechanism by which high-mass stars are formed is essential for our understanding of the energy budget and chemical evolution of galaxies. By using the New IRAM KIDs Array 2 (NIKA2) camera on the Institut de Radio Astronomie Millimétrique (IRAM) 30-m telescope, we have conducted high-sensitivity and large-scale mapping of a fraction of the Galactic plane in order to search for signatures of the transition between the high- and low-mass star-forming modes. Here, we present the first results from the Galactic Star Formation with NIKA2 (GASTON) project, a Large Programme at the IRAM 30-m telescope which is mapping ≈2 deg2 of the inner Galactic plane (GP), centred on ℓ = 23${_{.}^{\circ}}$9, b = 0${_{.}^{\circ}}$05, as well as targets in Taurus and Ophiuchus in 1.15 and 2.00 mm continuum wavebands. In this paper we present the first of the GASTON GP data taken, and present initial science results. We conduct an extraction of structures from the 1.15 mm maps using a dendrogram analysis and, by comparison to the compact source catalogues from Herschel survey data, we identify a population of 321 previously-undetected clumps. Approximately 80 per cent of these new clumps are 70 μm-quiet, and may be considered as starless candidates. We find that this new population of clumps are less massive and cooler, on average, than clumps that have already been identified. Further, by classifying the full sample of clumps based upon their infrared-bright fraction – an indicator of evolutionary stage – we find evidence for clump mass growth, supporting models of clump-fed high-mass star formation.

scholarly journals Modelling decretion discs in Be/X-ray binaries

2019 ◽  
Author(s):  
R O Brown ◽  
M J Coe ◽  
W C G Ho ◽  
A T Okazaki
Keyword(s):  
Neutron Star ◽  
Orbital Period ◽  
Major Axis ◽  
High Mass ◽  
Model Parameters ◽  
Be Stars ◽  
Semi Major Axis ◽  
X Ray ◽  
Smoothed Particle ◽  
X Ray Binaries

Abstract As the largest population of high mass X-ray binaries, Be/X-ray binaries provide an excellent laboratory to investigate the extreme physics of neutron stars. It is generally accepted that Be stars possess a circumstellar disc, providing an additional source of accretion to the stellar winds present around young hot stars. Interaction between the neutron star and the disc is often the dominant accretion mechanism. A large amount of work has gone into modelling the properties of these circumstellar discs, allowing for the explanation of a number of observable phenomena. In this paper, smoothed particle hydroynamics simulations are performed whilst varying the model parameters (orbital period, eccentricity, the mass ejection rate of the Be star and the viscosity and orientation of the disc). The relationships between the model parameters and the disc’s characteristics (base gas density, the accretion rate of the neutron star and the disc’s size) are presented. The observational evidence for a dependency of the size of the Be star’s circumstellar disc on the orbital period (and semi-major axis) is supported by the simulations.

scholarly journals Deciphering the Lyman α blob 1 with deep MUSE observations

2020 ◽  
Vol 642 ◽  
pp. A55 ◽  
Author(s):  
Edmund Christian Herenz ◽  
Matthew Hayes ◽  
Claudia Scarlata
Keyword(s):  
Line Profile ◽  
Galaxy Formation ◽  
Large Scale ◽  
Major Axis ◽  
High Mass ◽  
Electromagnetic Spectrum ◽  
Line Profile Analysis ◽  
Angular Momentum Vector ◽  
Upper Limits ◽  
Integral Field Spectrograph

Context. Lyman α blobs (LABs) are large-scale radio-quiet Lyman α (Lyα) nebula at high-z that occur predominantly in overdense proto-cluster regions. In particular, there is the prototypical SSA22a-LAB1 at z = 3.1, which has become an observational reference for LABs across the electromagnetic spectrum. Aims. We want to understand the powering mechanisms that drive the LAB so that we may gain empirical insights into the galaxy-formation processes within a rare dense environment at high-z. Thus, we need to infer the distribution, the dynamics, and the ionisation state of LAB 1’s Lyα emitting gas. Methods. LAB 1 was observed for 17.2 h with the VLT/MUSE integral-field spectrograph. We produced optimally extracted narrow band images, in Lyαλ1216, He IIλ1640, and we tried to detect C IVλ1549 emission. By utilising a moment-based analysis, we mapped the kinematics and the line profile characteristics of the blob. We also linked the inferences from the line profile analysis to previous results from imaging polarimetry. Results. We map Lyα emission from the blob down to surface-brightness limits of ≈6 × 10−19 erg s−1 cm−2 arcsec−2. At this depth, we reveal a bridge between LAB 1 and its northern neighbour LAB 8, as well as a shell-like filament towards the south of LAB 1. The complexity and morphology of the Lyα profile vary strongly throughout the blob. Despite the complexity, we find a coherent large-scale east-west velocity gradient of ∼1000 km s−1 that is aligned perpendicular to the major axis of the blob. Moreover, we observe a negative correlation of Lyα polarisation fraction with Lyα line width and a positive correlation with absolute line-of-sight velocity. Finally, we reveal He II emission in three distinct regions within the blob, however, we can only provide upper limits for C IV. Conclusions. Various gas excitation mechanisms are at play in LAB 1: ionising radiation and feedback effects dominate near the embedded galaxies, while Lyα scattering contributes at larger distances. However, He II/Lyα ratios combined with upper limits on C IV/Lyα are not able to discriminate between active galactic nucleus ionisation and feedback- driven shocks. The alignment of the angular momentum vector parallel to the morphological principal axis appears to be at odds with the predicted norm for high-mass halos, but this most likely reflects that LAB 1 resides at a node of multiple intersecting filaments of the cosmic web. LAB 1 can thus be thought of as a progenitor of a present-day massive elliptical within a galaxy cluster.

scholarly journals Characterising the high-mass star forming filament G351.776–0.527 with Herschel and APEX dust continuum and gas observations

2019 ◽  
Vol 621 ◽  
pp. A130 ◽  
Author(s):  
S. Leurini ◽  
E. Schisano ◽  
T. Pillai ◽  
A. Giannetti ◽  
J. Urquhart ◽  
...  
Keyword(s):  
Large Scale ◽  
Galactic Plane ◽  
Constant Width ◽  
Stable State ◽  
Far Infrared ◽  
High Mass ◽  
Mass Star ◽  
Large Reservoir ◽  
Main Structure ◽  
Main Filament

G351.776-0.527 is among the most massive, closest, and youngest filaments in the inner Galactic plane and therefore it is an ideal laboratory to study the kinematics of dense gas and mass replenishment on a large scale. In this paper, we present far-infrared and submillimetre wavelength continuum observations combined with spectroscopic C18O (2–1) data of the entire region to study its temperature, mass distribution, and kinematics. The structure is composed of a main elongated region with an aspect ratio of ~23, which is associated with a network of filamentary structures. The main filament has a remarkably constant width of 0.2 pc. The total mass of the network (including the main filament) is ≥2600M⊙, while we estimate a mass of ~2000M⊙ for the main structure. Therefore, the network harbours a large reservoir of gas and dust that could still be accreted onto the main structure. From the analysis of the gas kinematics, we detect two velocity components in the northern part of the main filament. The data also reveal velocity oscillations in C18O along the spine in the main filament and in at least one of the branches. Considering the region as a single structure, we find that it is globally close to virial equilibrium indicating that the entire structure is approximately in a stable state.

scholarly journals High-sensitivity observations of molecular lines with the Arecibo Telescope

2020 ◽  
Vol 497 (2) ◽  
pp. 1348-1364
Author(s):  
W S Tan ◽  
E D Araya ◽  
L E Lee ◽  
P Hofner ◽  
S Kurtz ◽  
...  
Keyword(s):  
Large Scale ◽  
High Sensitivity ◽  
Radio Continuum ◽  
High Mass ◽  
Absorption Feature ◽  
Lower Sensitivity ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Molecular Lines

ABSTRACT We report on one of the highest sensitivity surveys for molecular lines in the frequency range 6.0–7.4 GHz conducted to date. The observations were done with the 305- m Arecibo Telescope toward a sample of 12 intermediate-/high-mass star-forming regions. We searched for a large number of transitions of different molecules, including CH3OH and OH. The low rms noise of our data ($\sim \!5\,$ mJy for most sources and transitions) allowed detection of spectral features that have not been seen in previous lower sensitivity observations of the sources, such as detection of excited OH and 6.7 GHz CH3OH absorption. A review of 6.7 GHz CH3OH detections indicates an association between absorption and radio continuum sources in high-mass star-forming regions, although selection biases in targeted projects and low sensitivity of blind surveys imply incompleteness. Absorption of excited OH transitions was also detected toward three sources. In particular, we confirm a broad 6.035 GHz OH absorption feature in G34.26+0.15 characterized by an asymmetric blueshifted wing indicative of expansion, perhaps a large-scale outflow in this H ii region.

scholarly journals 10 years of 12.2 GHz methanol maser VLBI observations towards NGC 7538 IRS1 N: proper motions and maser saturation

2012 ◽  
Vol 8 (S287) ◽  
pp. 186-187 ◽  
Author(s):  
Michele Pestalozzi ◽  
Anders Jerkstrand ◽  
John Conway
Keyword(s):  
Proper Motion ◽  
Central Peak ◽  
Time Span ◽  
High Mass ◽  
Mass Star ◽  
Proper Motions ◽  
Motion Signal ◽  
Spatial Features ◽  
Vlbi Observations ◽  
Peak Flux

AbstractWe present the outcomes of the consistent analysis of 6 epochs of VLBA 12.2 GHz data obtained between 1995 and 2005 towards the known high-mass star formation reigon NGC7538 IRS1 N. Our analysis concentrates on the study of the main spectral/spatial feature, which is 20 VLBA synthesized beams in size with a distinct velocity gradient. We looked for proper motion signals relative to the central peak which, in an edge-on disc framework, is expected to be stationary. We also study the peak flux and the spatial brightness profile of the main maser feature searching for maser variability. Our results are twofold: we detect a clear proper motion signal of three spatial features (0.21, 0.1, 0.65 mas yr−1) and conclude that these can be made consistent with previous modelling of a Keplerian disc seen edge-on around a high-mass protostar. We further detect a consistent decrease of the peak flux over the time-span 1995-2005 (~ 5.4 Jy yr−1), confirmed when taking into account earlier data (1986, 1987) as well as by the 6.7 GHz maser emission. Also, the width of the spatial brightness profile of the main feature seems to decrease between 1995 and 2005 by some 50%. We consider these observables as clear signs of partial maser saturation.

scholarly journals Constraints on Bars in the Local Universe from 5000 SDSS Galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 76-76 ◽  
Author(s):  
Fabio D. Barazza ◽  
Shardha Jogee ◽  
Irina Marinova
Keyword(s):  
Large Scale ◽  
Major Axis ◽  
Disk Galaxies ◽  
Semi Major Axis ◽  
Local Universe ◽  
Barred Galaxies ◽  
Sky Survey ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Local Disk

AbstractWe present the first study of bars in the local Universe, based on the Sloan Digitized Sky Survey (SDSS). The large sample of ~5000 local galaxies provides the largest study to date of local bars and minimizes the effect of cosmic variance. The sample galaxies have Mg ≤ −18.5 mag and cover the redshift range 0.01 ≤ z < 0.04. We use a color cut in the color-magnitude diagram and the Sérsic index n to identify disk galaxies. We characterize bars and disks using r-band images and the method of iterative ellipse fits and quantitative criteria developed in Jogee at al. (2004, ApJL, 615, L105). After excluding highly inclined (i>60°) systems our results are: (1) the optical (r-band) fraction of barred galaxies among local disk galaxies is 43% (Figure 1, left panel), which confirms the ubiquity of local bars, in agreement with other optical studies based on smaller samples (e.g. Eskridge et al 2000, AJ, 119, 536, Marinova & Jogee 2006, astro-ph/0608039); (2) the optical bar fraction rises for bluer galaxies, suggesting a relation between bars and star formation (Figure 1, middle panel); (3) preliminary analyzes suggest that the optical bar fraction increases steeply with the galaxy effective radius (reff, Figure 1, right panel); (4) the optical bar fraction at z ~ 0 is ~35% for bright disks (Mg ≤ −19.3 mag) and strong (bar ellipticity >0.4), large-scale (bar semi-major axis >1.5 kpc) bars, which is comparable to the value of ~30 ± 6% reported earlier (Jogee et al 2004) for similar disks and bars at z ~ 0.2 − 1.0.

scholarly journals Star formation in ‘the Brick’: ALMA reveals an active protocluster in the Galactic centre cloud G0.253+0.016

2021 ◽  
Vol 503 (1) ◽  
pp. 77-95
Author(s):  
Daniel L Walker ◽  
Steven N Longmore ◽  
John Bally ◽  
Adam Ginsburg ◽  
J M Diederik Kruijssen ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
High Mass ◽  
Galactic Centre ◽  
Mass Star ◽  
Active Star ◽  
Continuum Source ◽  
Active Star Formation ◽  
The Masses ◽  
Water Maser

ABSTRACT G0.253+0.016, aka ‘the Brick’, is one of the most massive (&gt;105 M⊙) and dense (&gt;104 cm−3) molecular clouds in the Milky Way’s Central Molecular Zone. Previous observations have detected tentative signs of active star formation, most notably a water maser that is associated with a dust continuum source. We present ALMA Band 6 observations with an angular resolution of 0.13 arcsec (1000 AU) towards this ‘maser core’ and report unambiguous evidence of active star formation within G0.253+0.016. We detect a population of eighteen continuum sources (median mass ∼2 M⊙), nine of which are driving bi-polar molecular outflows as seen via SiO (5–4) emission. At the location of the water maser, we find evidence for a protostellar binary/multiple with multidirectional outflow emission. Despite the high density of G0.253+0.016, we find no evidence for high-mass protostars in our ALMA field. The observed sources are instead consistent with a cluster of low-to-intermediate-mass protostars. However, the measured outflow properties are consistent with those expected for intermediate-to-high-mass star formation. We conclude that the sources are young and rapidly accreting, and may potentially form intermediate- and high-mass stars in the future. The masses and projected spatial distribution of the cores are generally consistent with thermal fragmentation, suggesting that the large-scale turbulence and strong magnetic field in the cloud do not dominate on these scales, and that star formation on the scale of individual protostars is similar to that in Galactic disc environments.

scholarly journals Orbital Elements of MACHO Project Eclipsing Binary Stars

2005 ◽  
Vol 13 ◽  
pp. 467-467
Author(s):  
Charles Alcock
Keyword(s):  
Binary Stars ◽  
Large Scale ◽  
Major Axis ◽  
Orbital Elements ◽  
Semi Major Axis ◽  
Eclipsing Binary ◽  
Eclipsing Binary Stars ◽  
Large Numbers ◽  
Short Period ◽  
Velocity Information

Large scale photometric surveys can deliver very large numbers of eclipsing binary stars. It is not presently possible to obtain radial velocity information for more than a small fraction of these. We have made some progress in the estimation of the statistical distributions of orbital elements (including semi-major axis and eccentricity) in the MACHO Project catalog of eclipsing binary stars. We see the well-known tendency to circularization in short period orbits and also detect late tidal circularization during the giant phase. The extension of these techniques to newer surveys will also be discussed.

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