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 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 Episodic accretion constrained by a rich cluster of outflows

2020 ◽  
Vol 636 ◽  
pp. A38 ◽  
Author(s):  
T. Nony ◽  
F. Motte ◽  
F. Louvet ◽  
A. Plunkett ◽  
A. Gusdorf ◽  
...  
Keyword(s):  
High Mass ◽  
Time Variability ◽  
Mass Star ◽  
Rich Cluster ◽  
Star Forming ◽  
Molecular Outflows ◽  
Star Forming Regions ◽  
History Of ◽  
High Dynamics ◽  
Protostellar Collapse

Context. The accretion history of protostars remains widely mysterious, even though it represents one of the best ways to understand the protostellar collapse that leads to the formation of stars. Aims. Molecular outflows, which are easier to detect than the direct accretion onto the prostellar embryo, are here used to characterize the protostellar accretion phase in W43-MM1. Methods. The W43-MM1 protocluster hosts a sufficient number of protostars to statistically investigate molecular outflows in a single, homogeneous region. We used the CO(2–1) and SiO(5–4) line datacubes, taken as part of an ALMA mosaic with a 2000 AU resolution, to search for protostellar outflows, evaluate the influence that the environment has on these outflows’ characteristics and put constraints on outflow variability in W43-MM1. Results. We discovered a rich cluster of 46 outflow lobes, driven by 27 protostars with masses of 1−100 M⊙. The complex environment inside which these outflow lobes develop has a definite influence on their length, limiting the validity of using outflows’ dynamical timescale as a proxy of the ejection timescale in clouds with high dynamics and varying conditions. We performed a detailed study of Position–Velocity diagrams of outflows that revealed clear events of episodic ejection. The time variability of W43-MM1 outflows is a general trend and is more generally observed than in nearby, low- to intermediate-mass star-forming regions. The typical timescale found between two ejecta, ~500 yr, is consistent with that found in nearby protostars. Conclusions. If ejection episodicity reflects variability in the accretion process, either protostellar accretion is more variable, or episodicity is easier to detect in high-mass star-forming regions than in nearby clouds. The timescale found between accretion events could result from instabilities associated with bursts of inflowing gas arising from the close dynamical environment of high-mass star-forming cores.

scholarly journals Chemistry in the Envelopes around Massive Young Stars

2000 ◽  
Vol 197 ◽  
pp. 97-112 ◽  
Author(s):  
Ewine F. van Dishoeck ◽  
Floris F. S. van der Tak
Keyword(s):  
Young Stars ◽  
Physical Models ◽  
Young Stellar Objects ◽  
High Mass ◽  
Mass Star ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Chemical Models ◽  
Low Mass

Recent observational studies of intermediate- and high-mass star-forming regions at submillimeter and infrared wavelengths are reviewed, and chemical diagnostics of the different physical components associated with young stellar objects are summarized. Procedures for determining the temperature, density and abundance profiles in the envelopes are outlined. A detailed study of a set of infrared-bright massive young stars reveals systematic increases in the gas/solid ratios, the abundances of evaporated molecules, and the fraction of heated ices with increasing temperature. Since these diverse phenomena involve a range of temperatures from < 100 K to 1000 K, the enhanced temperatures must be communicated to both the inner and outer parts of the envelopes. This ‘global heating’ plausibly results from the gradual dispersion of the envelopes with time. Similarities and differences with low-mass YSOs are discussed. The availability of accurate physical models will allow chemical models of ice evaporation followed by ‘hot core’ chemistry to be tested in detail.

scholarly journals VERA status and results

2012 ◽  
Vol 8 (S289) ◽  
pp. 194-194
Author(s):  
H. Kobayashi ◽  
Keyword(s):  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Long Baseline ◽  
Beam System ◽  
The Galaxy ◽  
The Status ◽  
Trigonometric Parallaxes ◽  
Turbulence Effects

AbstractVERA is a Very Long Baseline Interferometry (VLBI) array for astrometry, composed of four 20 m radio telescopes. They are located over a range of around 2300 km in Japan. VERA consists of a two-beam system equipped with 2, 6.7, 8, 22, and 43 GHz receivers. The two-beam system is used for phase referencing of the VLBI observations, to compensate for atmospheric-turbulence effects between two nearby objects. It has achieved measurements of annual parallaxes within 5 kpc with 10% accuracy. Observed sources are water, SiO, and methanol masers, which are found in molecular gas around star-forming regions and evolved stars. We have carried out a large program of astrometry to reveal the Galaxy's structure and velocity field. VERA has already measured trigonometric parallaxes of more than 30 sources and observed around a hundred sources using the two-beam astrometry technique. Maser sources are associated with high-mass star-forming regions, which are thought to trace the arm structure of the Galaxy. Using annual parallax and proper-motion measurements, their structure will be shown without kinematic distance assumptions. Some sources exhibit large differences between trigonometric-parallax measurements and kinematic distances. We present the status of the VERA project as well as recent results.

scholarly journals First detection of 13CH in the interstellar medium

2020 ◽  
Vol 640 ◽  
pp. A125 ◽  
Author(s):  
Arshia M. Jacob ◽  
Karl M. Menten ◽  
Helmut Wiesemeyer ◽  
Rolf Güsten ◽  
Friedrich Wyrowski ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Isotopic Ratio ◽  
Far Infrared ◽  
High Spectral Resolution ◽  
High Mass ◽  
Chemical Fractionation ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Star Forming Regions

In recent years, a plethora of observations with high spectral resolution of sub-millimetre and far-infrared transitions of methylidene (CH), conducted with Herschel and SOFIA, have demonstrated this radical to be a valuable proxy for molecular hydrogen that can be used for characterising molecular gas within the interstellar medium on a Galactic scale, including the CO-dark component. We report the discovery of the 13CH isotopologue in the interstellar medium using the upGREAT receiver on board SOFIA. We have detected the three hyperfine structure components of the ≈2 THz frequency transition from its X2Π1∕2 ground-state towards the high-mass star-forming regions Sgr B2(M), G34.26+0.15, W49(N), and W51E and determined 13CH column densities. The ubiquity of molecules containing carbon in the interstellar medium has turned the determination of the ratio between the abundances of the two stable isotopes of carbon, 12C/13C, into a cornerstone for Galactic chemical evolution studies. Whilst displaying a rising gradient with galactocentric distance, this ratio, when measured using observations of different molecules (CO, H2CO, and others), shows systematic variations depending on the tracer used. These observed inconsistencies may arise from optical depth effects, chemical fractionation, or isotope-selective photo-dissociation. Formed from C+ either through UV-driven or turbulence-driven chemistry, CH reflects the fractionation of C+, and does not show any significant fractionation effects, unlike other molecules that were previously used to determine the 12C/13C isotopic ratio. This makes it an ideal tracer for the 12C/13C ratio throughout the Galaxy. By comparing the derived column densities of 13CH with previously obtained SOFIA data of the corresponding transitions of the main isotopologue 12CH, we therefore derive 12C/13C isotopic ratios toward Sgr B2(M), G34.26+0.15, W49(N) and W51E. Adding our values derived from 12∕13CH to previous calculations of the Galactic isotopic gradient, we derive a revised value of 12C/13C = 5.87(0.45)RGC + 13.25(2.94).

scholarly journals Looking for outflow and infall signatures in high-mass star-forming regions

2012 ◽  
Vol 538 ◽  
pp. A140 ◽  
Author(s):  
P. D. Klaassen ◽  
L. Testi ◽  
H. Beuther
Keyword(s):  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions

scholarly journals Nitrogen and hydrogen fractionation in high-mass star-forming cores from observations of HCN and HNC

2018 ◽  
Vol 609 ◽  
pp. A129 ◽  
Author(s):  
L. Colzi ◽  
F. Fontani ◽  
P. Caselli ◽  
C. Ceccarelli ◽  
P. Hily-Blant ◽  
...  
Keyword(s):  
Solar System ◽  
Solar Nebula ◽  
Rotational Transition ◽  
High Mass ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Stellar Cluster ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores

The ratio between the two stable isotopes of nitrogen, 14N and 15N, is well measured in the terrestrial atmosphere (~272), and for the pre-solar nebula (~441, deduced from the solar wind). Interestingly, some pristine solar system materials show enrichments in 15N with respect to the pre-solar nebula value. However, it is not yet clear if and how these enrichments are linked to the past chemical history because we have only a limited number of measurements in dense star-forming regions. In this respect, dense cores, which are believed to be the precursors of clusters and also contain intermediate- and high-mass stars, are important targets because the solar system was probably born within a rich stellar cluster, and such clusters are formed in high-mass star-forming regions. The number of observations in such high-mass dense cores has remained limited so far. In this work, we show the results of IRAM-30 m observations of the J = 1−0 rotational transition of the molecules HCN and HNC and their 15N-bearing counterparts towards 27 intermediate- and high-mass dense cores that are divided almost equally into three evolutionary categories: high-mass starless cores, high-mass protostellar objects, and ultra-compact Hii regions. We have also observed the DNC(2–1) rotational transition in order to search for a relation between the isotopic ratios D/H and 14N/15N. We derive average 14N/15N ratios of 359 ± 16 in HCN and of 438 ± 21 in HNC, with a dispersion of about 150–200. We find no trend of the 14N/15N ratio with evolutionary stage. This result agrees with what has been found for N2H+ and its isotopologues in the same sources, although the 14N/15N ratios from N2H+ show a higher dispersion than in HCN/HNC, and on average, their uncertainties are larger as well. Moreover, we have found no correlation between D/H and 14N/15N in HNC. These findings indicate that (1) the chemical evolution does not seem to play a role in the fractionation of nitrogen, and that (2) the fractionation of hydrogen and nitrogen in these objects is not related.

scholarly journals ATLASGAL – Ammonia observations towards the southern Galactic plane

2018 ◽  
Vol 609 ◽  
pp. A125 ◽  
Author(s):  
M. Wienen ◽  
F. Wyrowski ◽  
K. M. Menten ◽  
J. S. Urquhart ◽  
C. M. Walmsley ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Hyperfine Structure ◽  
Optical Depth ◽  
Line Width ◽  
Rotational Temperature ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass

Context. The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 μm, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims. We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant. Methods. Using the Parkes telescope, we observed the NH3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300° and 359° and a latitude within ± 1.5°. For a subsample of 289 sources, the N2H+ (1–0) line was measured with the Mopra telescope. Results. We measured a median NH3 (1, 1) line width of ~ 2 km s-1, rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH3 abundances from 1.6 × 10-6 to 10-8. For a subsample with detected NH3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of ~ 1 is determined using the broader N2H+ line width than is estimated from the NH3 line width of ~ 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH3 (1, 1)/N2H+ line-width ratio with increasing rotational temperature. Conclusions. A comparison of NH3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 ± 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 ± 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 ± 0.02 and standard deviation of 0.37 are closer to 1.

Magnetic fields in high-mass star-forming regions

2015 ◽  
pp. 199-209
Author(s):  
Antonio Chrysostomou ◽  
Martin Houde ◽  
Brenda C. Matthews
Keyword(s):  
Magnetic Fields ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions
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