scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

scholarly journals The Star-formation Law in Galactic High-mass Star-forming Molecular Clouds

2017 ◽  
Vol 839 (2) ◽  
pp. 113 ◽  
Author(s):  
R. Retes-Romero ◽  
Y. D. Mayya ◽  
A. Luna ◽  
L. Carrasco
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
High Mass ◽  
Mass Star ◽  
Star Forming

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.

scholarly journals Constraining How Star Formation Proceeds: Surveys in the Sub-mm and FIR

2009 ◽  
Vol 5 (H15) ◽  
pp. 406-407
Author(s):  
Doug Johnstone
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Mass Star ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Multi Wavelength ◽  
Low Mass ◽  
High Column

AbstractCoordinated multi-wavelength surveys of molecular clouds are providing strong constraints on the physical conditions within low-mass star-forming regions. In this manner, Perseus and Ophiuchus have been exceptional laboratories for testing the earliest phases of star formation. Highlights of these results are: (1) dense cores form only in high column density regions, (2) dense cores contain only a few percent of the cloud mass, (3) the mass distribution of the dense cores is similar to the IMF, (4) the more massive cores are most likely to contain embedded protostars, and (5) the kinematics of the dense cores and the bulk gas show significant coupling.

scholarly journals Observational constraints on the likelihood of 26Al in planet-forming environments

2020 ◽  
Vol 644 ◽  
pp. L1
Author(s):  
Megan Reiter
Keyword(s):  
Solar System ◽  
Planet Formation ◽  
Radioactive Decay ◽  
High Mass ◽  
Mass Star ◽  
Early Solar System ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Order Of Magnitude

Recent work suggests that 26Al may determine the water budget in terrestrial exoplanets as its radioactive decay dehydrates planetesimals leading to rockier compositions. Here I consider the observed distribution of 26Al in the Galaxy and typical star-forming environments to estimate the likelihood of 26Al enrichment during planet formation. I do not assume Solar-System-specific constraints as I am interested in enrichment for exoplanets generally. Observations indicate that high-mass stars dominate the production of 26Al with nearly equal contributions from their winds and supernovae. Observed 26Al abundances are comparable to those in the early Solar System in the high-mass star-forming regions where most stars (and thereby most planets) form. These high abundances appear to be maintained for a few million years, which is much longer than the 0.7 Myr half-life. Observed bulk 26Al velocities are an order of magnitude slower than expected from winds and supernovae. These observations are at odds with typical model assumptions that 26Al is provided instantaneously by high velocity mass loss from supernovae and winds. The regular replenishment of 26Al, especially when coupled with the small age differences that are common in high-mass star-forming complexes, may significantly increase the number of star- and planet-forming systems exposed to 26Al. Exposure does not imply enrichment, but the order of magnitude slower velocity of 26Al may alter the fraction that is incorporated into planet-forming material. Together, this suggests that the conditions for rocky planet formation are not rare, nor are they ubiquitous, as small regions such as Taurus, that lack high-mass stars to produce 26Al may be less likely to form rocky planets. I conclude with suggested directions for future studies.

scholarly journals Filamentary Fragmentation and Accretion in High-mass Star-forming Molecular Clouds

2018 ◽  
Vol 855 (1) ◽  
pp. 9 ◽  
Author(s):  
Xing Lu ◽  
Qizhou Zhang ◽  
Hauyu Baobab Liu ◽  
Patricio Sanhueza ◽  
Ken’ichi Tatematsu ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
High Mass ◽  
Mass Star ◽  
Star Forming

Nitrogen isotopic ratio across the Galaxy through observations of high-mass star-forming cores

2018 ◽  
Vol 14 (A30) ◽  
pp. 277-277
Author(s):  
L. Colzi ◽  
F. Fontani ◽  
V. M. Rivilla ◽  
A. Sánchez-Monge ◽  
L. Testi ◽  
...  
Keyword(s):  
Isotopic Ratio ◽  
High Mass ◽  
Mass Star ◽  
Rich Cluster ◽  
Star Forming ◽  
Star Forming Regions ◽  
Stellar Nucleosynthesis ◽  
Chemical Models ◽  
The Galaxy ◽  
Solar System Bodies

AbstractThere is a growing evidence that our Sun was born in a rich cluster that also contained massive stars. Therefore, the study of high-mass star-forming regions is key to understand our chemical heritage. In fact, molecules found in comets, in other pristine Solar System bodies and in protoplanetary disks, are enriched in 15N, because they show a lower 14N/15N ratio (100-150) with respect to the value representative of the Proto-Solar Nebula (PSN, 441 ± 6), but the reasons of this enrichment cannot be explained by current chemical models. Moreover, the 14N/15N ratio is important because from it we can learn more about the stellar nucleosynthesis processes that produces both the elements. In this sense observations of star-forming regions are useful to constrain Galactic chemical evolution (GCE) models.

scholarly journals ALMA CO observations of a giant molecular cloud in M 33: Evidence for high-mass star formation triggered by cloud–cloud collisions

2020 ◽  
Author(s):  
Hidetoshi Sano ◽  
Kisetsu Tsuge ◽  
Kazuki Tokuda ◽  
Kazuyuki Muraoka ◽  
Kengo Tachihara ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Line Emission ◽  
High Mass ◽  
H Ii Regions ◽  
Mass Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Giant Molecular Cloud

Abstract We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J = 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position–velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud–cloud collisions in the Galactic and Magellanic Cloud H ii regions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.

scholarly journals Multi-line Herschel/HIFI observations of water reveal infall motions and chemical segregation around high-mass protostars

2019 ◽  
Vol 625 ◽  
pp. A103 ◽  
Author(s):  
F. F. S. van der Tak ◽  
R. F. Shipman ◽  
T. Jacq ◽  
F. Herpin ◽  
J. Braine ◽  
...  
Keyword(s):  
Spherical Shape ◽  
High Mass ◽  
Small Scale ◽  
Chemical Information ◽  
Mass Star ◽  
Chemical Homogeneity ◽  
Water Abundance ◽  
Physical Conditions ◽  
Warm Core ◽  
Molecular Abundances

Context. The physical conditions during high-mass star formation are poorly understood. Outflow and infall motions have been detected around massive protostellar objects, but their dependence on mass, luminosity, and age is unclear. In addition, physical conditions and molecular abundances are often estimated using simple assumptions such as spherical shape and chemical homogeneity, which may limit the accuracy of the results. Aims. We aim to characterize the dust and gas distribution and kinematics of the envelopes of high-mass protostars. In particular, we search for infall motions, abundance variations, and deviations from spherical symmetry, using Herschel data from the WISH program. Methods. We used HIFI maps of the 987 GHz H2O 202–111 emission to measure the sizes and shapes of 19 high-mass protostellar envelopes. To identify infall, we used HIFI spectra of the optically thin C18O 9–8 and H218O 111–000 lines. The high-J C18O line traces the warm central material and redshifted H218O 111–000 absorption indicates material falling onto the warm core. We probe small-scale chemical differentiation by comparing H2O 752 and 987 GHz spectra with those of H218O. Results. Our measured radii of the central part of the H2O 202–111 emission are 30–40% larger than the predictions from spherical envelope models, and axis ratios are <2, which we consider good agreement. For 11 of the 19 sources, we find a significant redshift of the H218O 111–000 line relative to C18O 9–8. The inferred infall velocities are 0.6–3.2 km s−1, and estimated mass inflow rates range from 7 × 10−5 to 2 × 10−2 M⊙ yr−1. The highest mass inflow rates seem to occur toward the sources with the highest masses, and possibly the youngest ages. The other sources show either expanding motions or H218O lines in emission. The H218O 111–000 line profiles are remarkably similar to the differences between the H2O 202–111 and 211–202 profiles, suggesting that the H218O line and the H2O 202–111 absorption originate just inside the radius where water evaporates from grains, typically 1000–5000 au from the center. In some sources, the H218O line is detectable in the outflow, where no C18O emission is seen. Conclusions. Together, the H218O absorption and C18O emission profiles show that the water abundance around high-mass protostars has at least three levels: low in the cool outer envelope, high within the 100 K radius, and very high in the outflowing gas. Thus, despite the small regions, the combination of lines presented in this work reveals systematic inflows and chemical information about the outflows.

scholarly journals Evolutionary study of complex organic molecules in high-mass star-forming regions

2020 ◽  
Vol 641 ◽  
pp. A54 ◽  
Author(s):  
A. Coletta ◽  
F. Fontani ◽  
V. M. Rivilla ◽  
C. Mininni ◽  
L. Colzi ◽  
...  
Keyword(s):  
Star Formation ◽  
Organic Molecules ◽  
High Mass ◽  
Physical Parameters ◽  
Mass Star ◽  
Evolutionary Trend ◽  
Star Forming ◽  
Star Forming Regions ◽  
Molecular Abundances ◽  
Complex Organic

We have studied four complex organic molecules (COMs), the oxygen-bearing methyl formate (CH3OCHO) and dimethyl ether (CH3OCH3) as well as the nitrogen-bearing formamide (NH2CHO) and ethyl cyanide (C2H5CN), towards a large sample of 39 high-mass star-forming regions representing different evolutionary stages, from early to evolved phases. We aim to identify potential correlations and chemical links between the molecules and to trace their evolutionary sequence through the star formation process. We analysed spectra obtained at 3, 2, and 0.9 mm with the IRAM-30m telescope. We derived the main physical parameters for each species by fitting the molecular lines. We compared them and evaluated their evolution while also taking several other interstellar environments into account. We report detections in 20 sources, revealing a clear dust absorption effect on column densities. Derived abundances range between ~ 10−10−10−7 for CH3OCHO and CH3OCH3, ~ 10−12−10−10 for NH2CHO, and ~ 10−11−10−9 for C2H5CN. The abundances of CH3OCHO, CH3OCH3, and C2H5CN are very strongly correlated (r ≥ 0.92) across ~ 4 orders of magnitude. We note that CH3OCHO and CH3OCH3 show the strongest correlations in most parameters, and a nearly constant ratio (~ 1) over a remarkable ~ 9 orders of magnitude in luminosity for the following wide variety of sources: pre-stellar to evolved cores, low- to high-mass objects, shocks, Galactic clouds, and comets. This indicates that COMs chemistry is likely early developed and then preserved through evolved phases. Moreover, the molecular abundances clearly increase with evolution, covering ~ 6 orders of magnitude in the luminosity/mass ratio. We consider CH3OCHO and CH3OCH3 to be most likely chemically linked. They could, for example, share a common precursor, or be formed one from the other. Based on correlations, ratios, and the evolutionary trend, we propose a general scenario for all COMs, involving a formation in the cold, earliest phases of star formation and a following increasing desorption with the progressive thermal and shock-induced heating of the evolving core.

scholarly journals On the size of the CO-depletion radius in the IRDC G351.77−0.51

2019 ◽  
Vol 490 (4) ◽  
pp. 4489-4501 ◽  
Author(s):  
G Sabatini ◽  
A Giannetti ◽  
S Bovino ◽  
J Brand ◽  
S Leurini ◽  
...  
Keyword(s):  
Large Scale ◽  
Spatial Scales ◽  
High Mass ◽  
Mass Star ◽  
Number Density ◽  
Dark Cloud ◽  
Star Forming ◽  
Dark Clouds ◽  
Physical Conditions ◽  
Star Forming Regions

ABSTRACT An estimate of the degree of CO-depletion (fD) provides information on the physical conditions occurring in the innermost and densest regions of molecular clouds. A key parameter in these studies is the size of the depletion radius, i.e. the radius within which the C-bearing species, and in particular CO, are largely frozen on to dust grains. A strong depletion state (i.e. fD &gt; 10, as assumed in our models) is highly favoured in the innermost regions of dark clouds, where the temperature is &lt;20 K and the number density of molecular hydrogen exceeds a few × 104 cm−3. In this work, we estimate the size of the depleted region by studying the Infrared Dark Cloud (IRDC) G351.77−0.51. Continuum observations performed with the Herschel Space Observatory and the LArge APEX BOlometer CAmera, together with APEX C18O and C17O J = 2→1 line observations, allowed us to recover the large-scale beam- and line-of-sight-averaged depletion map of the cloud. We built a simple model to investigate the depletion in the inner regions of the clumps in the filament and the filament itself. The model suggests that the depletion radius ranges from 0.02 to 0.15 pc, comparable with the typical filament width (i.e. ∼0.1 pc). At these radii, the number density of H2 reaches values between 0.2 and 5.5 × 105 cm−3. These results provide information on the approximate spatial scales on which different chemical processes operate in high-mass star-forming regions and also suggest caution when using CO for kinematical studies in IRDCs.

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