scholarly journals Molecular complexity on disc scales uncovered by ALMA

2019 ◽  
Vol 628 ◽  
pp. A2 ◽  
Author(s):  
Eva G. Bøgelund ◽  
Andrew G. Barr ◽  
Vianney Taquet ◽  
Niels F. W. Ligterink ◽  
Magnus V. Persson ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Star Formation ◽  
Chemical Composition ◽  
Column Density ◽  
Angular Resolution ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
Complex Species ◽  
Low Mass

Context. The chemical composition of high-mass protostars reflects the physical evolution associated with different stages of star formation. In addition, the spatial distribution and velocity structure of different molecular species provide valuable information on the physical structure of these embedded objects. Despite an increasing number of interferometric studies, there is still a high demand for high angular resolution data to study chemical compositions and velocity structures for these objects. Aims. The molecular inventory of the forming high-mass star AFGL 4176, located at a distance of ~3.7 kpc, is studied in detail at a high angular resolution of ~0.35′′, equivalent to ~1285 au at the distance of AFGL 4176. This high resolution makes it possible to separate the emission associated with the inner hot envelope and disc around the forming star from that of its cool outer envelope. The composition of AFGL 4176 is compared with other high- and low-mass sources, and placed in the broader context of star formation. Methods. Using the Atacama Large Millimeter/submillimeter Array (ALMA) the chemical inventory of AFGL 4176 has been characterised. The high sensitivity of ALMA made it possible to identify weak and optically thin lines and allowed for many isotopologues to be detected, providing a more complete and accurate inventory of the source. For the detected species, excitation temperatures in the range 120–320 K were determined and column densities were derived assuming local thermodynamic equilibrium and using optically thin lines. The spatial distribution of a number of species was studied. Results. A total of 23 different molecular species and their isotopologues are detected in the spectrum towards AFGL 4176. The most abundant species is methanol (CH3OH) with a column density of 5.5 × 1018 cm−2 in a beam of ~0.3′′, derived from its 13C-isotopologue. The remaining species are present at levels between 0.003 and 15% with respect to methanol. Hints that N-bearing species peak slightly closer to the location of the peak continuum emission than the O-bearing species are seen. A single species, propyne (CH3C2H), displays a double-peaked distribution. Conclusions. AFGL 4176 comprises a rich chemical inventory including many complex species present on disc scales. On average, the derived column density ratios, with respect to methanol, of O-bearing species are higher than those derived for N-bearing species by a factor of three. This may indicate that AFGL 4176 is a relatively young source since nitrogen chemistry generally takes longer to evolve in the gas phase. Taking methanol as a reference, the composition of AFGL 4176 more closely resembles that of the low-mass protostar IRAS 16293–2422B than that of high-mass, star-forming regions located near the Galactic centre. This similarity hints that the chemical composition of complex species is already set in the cold cloud stage and implies that AFGL 4176 is a young source whose chemical composition has not yet been strongly processed by the central protostar.

scholarly journals Nobeyama 45 m mapping observations toward the nearby molecular clouds Orion A, Aquila Rift, and M17: Project overview

2019 ◽  
Vol 71 (Supplement_1) ◽  
Author(s):  
Fumitaka Nakamura ◽  
Shun Ishii ◽  
Kazuhito Dobashi ◽  
Tomomi Shimoikura ◽  
Yoshito Shimajiri ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Column Density ◽  
Angular Resolution ◽  
High Mass ◽  
Mass Star ◽  
Calibration Data ◽  
Star Forming ◽  
Star Formation Activity ◽  
Scientific Results

Abstract We carried out mapping observations toward three nearby molecular clouds, Orion A, Aquila Rift, and M 17, using a new 100 GHz receiver, FOREST, on the Nobeyama 45 m telescope. We describe the details of the data obtained such as intensity calibration, data sensitivity, angular resolution, and velocity resolution. Each target contains at least one high-mass star-forming region. The target molecular lines were 12CO (J = 1–0), 13CO (J = 1–0), C18O (J = 1–0), N2H+ (J = 1–0), and CCS (JN = 87–76), with which we covered the density range of 102 cm−3 to 106 cm−3 with an angular resolution of ∼20″ and a velocity resolution of ∼0.1 km s−1. Assuming the representative distances of 414 pc, 436 pc, and 2.1 kpc, the maps of Orion A, Aquila Rift, and M17 cover most of the densest parts with areas of about 7 pc × 15 pc, 7 pc × 7 pc, and 36 pc × 18 pc, respectively. On the basis of the 13CO column density distribution, the total molecular masses are derived to be $3.86 \times 10^{4}\, M_\odot$, $2.67 \times 10^{4}\, M_{\odot }$, and $8.1\times 10^{5}\, M_{\odot }$ for Orion A, Aquila Rift, and M17, respectively. For all the clouds, the H2 column density exceeds the theoretical threshold for high-mass star formation of ≳ 1 g cm−2 only toward the regions which contain current high-mass star-forming sites. For other areas, further mass accretion or dynamical compression would be necessary for future high-mass star formation. This is consistent with the current star formation activity. Using the 12CO data, we demonstrate that our data have enough capability to identify molecular outflows, and for the Aquila Rift we identify four new outflow candidates. The scientific results will be discussed in detail in separate papers.

Statistical analysis of the physical properties of the 6.7 GHz methanol maser features based on VLBI data

2017 ◽  
Vol 13 (S336) ◽  
pp. 321-322 ◽  
Author(s):  
R. Sarniak ◽  
M. Szymczak ◽  
A. Bartkiewicz
Keyword(s):  
Statistical Analysis ◽  
Star Formation ◽  
Physical Properties ◽  
Angular Resolution ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
Methanol Maser ◽  
Vlbi Data ◽  
Methanol Masers

AbstractMethanol masers observed at high angular resolution are useful tool to investigate the processes of high-mass star formation. Here, we present the results of statistical analysis of the 6.7 GHz methanol maser structures in 60 sources observed with the EVN. The parameters of the maser clouds and exciting stars were derived. There is evidence that the emission structures composed of larger number of maser clouds are formed in the vicinity of more luminous exciting stars.

scholarly journals High Resolution Radio Continuum Observations of High Mass Star Formation Regions

2001 ◽  
Vol 205 ◽  
pp. 280-281
Author(s):  
S. Kurtz ◽  
P. Hofner ◽  
C. Vargas ◽  
W. Díaz-Merced
Keyword(s):  
Star Formation ◽  
Radio Continuum ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
High Quality ◽  
Very Large Array ◽  
Adverse Conditions ◽  
Star Formation Regions ◽  
Calibration Techniques

We present high angular resolution centimeter and millimeter continuum observations of several galactic massive star formation regions. Using calibration techniques pioneered at the Very Large Array, we are able to obtain high quality images even under adverse conditions of phase stability. Techniques such as these will be essential if future millimeter arrays are to obtain high quality and high precision images. We provide a current summary of our on-going survey, and present images and a brief discussion of several of the more intriguing sources.

scholarly journals Massive and low-mass protostars in massive “starless” cores

2019 ◽  
Vol 622 ◽  
pp. A54 ◽  
Author(s):  
Thushara Pillai ◽  
Jens Kauffmann ◽  
Qizhou Zhang ◽  
Patricio Sanhueza ◽  
Silvia Leurini ◽  
...  
Keyword(s):  
Star Formation ◽  
Detection Limit ◽  
High Mass ◽  
Mass Star ◽  
Core Mass ◽  
Filamentary Structure ◽  
Dark Clouds ◽  
Low Mass ◽  
Infrared Dark Clouds ◽  
Dense Clump

The infrared dark clouds (IRDCs) G11.11−0.12 and G28.34+0.06 are two of the best-studied IRDCs in our Galaxy. These two clouds host clumps at different stages of evolution, including a massive dense clump in both clouds that is dark even at 70 and 100 μm. Such seemingly quiescent massive dense clumps have been speculated to harbor cores that are precursors of high-mass stars and clusters. We observed these two “prestellar” regions at 1 mm with the Submillimeter Array (SMA) with the aim of characterizing the nature of such cores. We show that the clumps fragment into several low- to high-mass cores within the filamentary structure of the enveloping cloud. However, while the overall physical properties of the clump may indicate a starless phase, we find that both regions host multiple outflows. The most massive core though 70 μm dark in both clumps is clearly associated with compact outflows. Such low-luminosity, massive cores are potentially the earliest stage in the evolution of a massive protostar. We also identify several outflow features distributed in the large environment around the most massive core. We infer that these outflows are being powered by young, low-mass protostars whose core mass is below our detection limit. These findings suggest that low-mass protostars have already formed or are coevally formed at the earliest phase of high-mass star formation.

scholarly journals Fragmentation of a Protostellar Core: The Case of CB 230

2001 ◽  
Vol 200 ◽  
pp. 117-121 ◽  
Author(s):  
Ralf Launhardt
Keyword(s):  
Main Sequence ◽  
Angular Resolution ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
Binary Separation ◽  
Molecular Outflow ◽  
Low Mass ◽  
Core Fragmentation

The Bok globule CB230 (L1177) contains an active, low-mass star-forming core which is associated with a double NIR reflection nebula, a collimated bipolar molecular outflow, and strong mm continuum emission. The morphology of the NIR nebula suggests the presence of a deeply embedded, wide binary protostellar system. High-angular resolution observations now reveal the presence of two sub-cores, two distinct outflow centers, and an embedded accretion disk associated with the western bipolar NIR nebula. Judging from the separation and specific angular momentum, the CB230 double protostar system probably results from core fragmentation and will end up at the upper end of the pre-main sequence binary separation distribution.

scholarly journals Fragmentation and dynamics in Massive Dense Cores in Cygnus-X

2010 ◽  
Vol 6 (S270) ◽  
pp. 53-56 ◽  
Author(s):  
T. Csengeri ◽  
S. Bontemps ◽  
N. Schneider ◽  
F. Motte
Keyword(s):  
Angular Resolution ◽  
High Density ◽  
High Mass ◽  
High Angular Resolution ◽  
Low Mass Stars ◽  
Dense Cores ◽  
Evolutionary Scenario ◽  
Low Mass ◽  
Molecular Tracers ◽  
Resolution Study

AbstractA systematic, high angular-resolution study of IR-quiet Massive Dense Cores (MDCs) of Cygnus-X in continuum and high-density molecular tracers is presented. The results are compared with the quasi-static and the dynamical evolutionary scenario. We find that the fragmentation properties are not compatible with the quasi-static, monolithic collapse scenario, nor are they entirely compatible with the formation of a cluster of mostly low-mass stars. The kinematics of MDCs shows individual velocity components appearing as coherent flows, which indicate important dynamical processes at the scale of the mass reservoir around high-mass protostars.

scholarly journals High-Mass Star and Massive Cluster Formation in the Milky Way

2018 ◽  
Vol 56 (1) ◽  
pp. 41-82 ◽  
Author(s):  
Frédérique Motte ◽  
Sylvain Bontemps ◽  
Fabien Louvet
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Plane ◽  
Cluster Formation ◽  
Theoretical Models ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
Massive Cluster

This review examines the state-of-the-art knowledge of high-mass star and massive cluster formation, gained from ambitious observational surveys, which acknowledges the multiscale characteristics of these processes. After a brief overview of theoretical models and main open issues, we present observational searches for the evolutionary phases of high-mass star formation, first among high-luminosity sources and more recently among young massive protostars and the elusive high-mass prestellar cores. We then introduce the most likely evolutionary scenario for high-mass star formation, which emphasizes the link of high-mass star formation to massive cloud and cluster formation. Finally, we introduce the first attempts to search for variations of the star-formation activity and cluster formation in molecular cloud complexes in the most extreme star-forming sites and across the Milky Way. The combination of Galactic plane surveys and high–angular resolution images with submillimeter facilities such as Atacama Large Millimeter Array (ALMA) are prerequisites to make significant progress in the forthcoming decade.

scholarly journals Probing the initial conditions of high-mass star formation

2019 ◽  
Vol 627 ◽  
pp. A85 ◽  
Author(s):  
Chuan-Peng Zhang ◽  
Timea Csengeri ◽  
Friedrich Wyrowski ◽  
Guang-Xing Li ◽  
Thushara Pillai ◽  
...  
Keyword(s):  
Star Formation ◽  
Multiple Scales ◽  
Initial Conditions ◽  
Dust Emission ◽  
Radio Continuum ◽  
High Mass ◽  
Small Scale ◽  
High Angular Resolution ◽  
H Ii Regions ◽  
Mass Star

Context. Fragmentation and feedback are two important processes during the early phases of star formation. Aims. Massive clumps tend to fragment into clusters of cores and condensations, some of which form high-mass stars. In this work, we study the structure of massive clumps at different scales, analyze the fragmentation process, and investigate the possibility that star formation is triggered by nearby H ii regions. Methods. We present a high angular resolution study of a sample of massive proto-cluster clumps G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71. Combining infrared data at 4.5, 8.0, 24, and 70 μm, we use a few arcsecond resolution, radiometer and millimeter inteferometric data taken at 1.3 cm, 3.5 mm, 1.3 mm, and 870 μm to study their fragmentation and evolution. Our sample is unique in the sense that all the clumps have neighboring H ii regions. Taking advantage of that, we tested triggered star formation using a novel method where we study the alignment of the center of mass traced by dust emission at multiple scales. Results. The eight massive clumps, identified based on single-dish observations, have masses ranging from 228 to 2279 M⊙ within an effective radius of Reff ~ 0.5 pc. We detect compact structures towards six out of the eight clumps. The brightest compact structures within infrared bright clumps are typically associated with embedded compact radio continuum sources. The smaller scale structures of Reff ~ 0.02 pc observed within each clump are mostly gravitationally bound and massive enough to form at least a B3-B0 type star. Many condensations have masses larger than 8 M⊙ at a small scale of Reff ~ 0.02 pc. We find that the two infrared quiet clumps with the lowest mass and lowest surface density with <300 M⊙ do not host any compact sources, calling into question their ability to form high-mass stars. Although the clumps are mostly infrared quiet, the dynamical movements are active at clump scale (~1 pc). Conclusions. We studied the spatial distribution of the gas conditions detected at different scales. For some sources we find hints of external triggering, whereas for others we find no significant pattern that indicates triggering is dynamically unimportant. This probably indicates that the different clumps go through different evolutionary paths. In this respect, studies with larger samples are highly desired.

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