On the accretion process in a high-mass star forming region

Hajigholi, M.; Persson, C. M.; Wirström, E. S.; Black, J. H.; Bergman, P.; Olofsson, A. O. H.; Olberg, M.; Wyrowski, F.; Coutens, A.; Menten, K. M.

doi:10.1051/0004-6361/201526451

Cited by 15 publications

(17 citation statements)

References 73 publications

(113 reference statements)

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“…Thus, our results show that while the infall velocity toward l59-444 is comparable to the values found by Di Francesco et al (2001) and Kristensen et al (2012, who analyze low-mass protostars), the values of σ (and the value of V in toward l30-304) are somewhat higher, since these authors find V in , σ < ∼ 1 km s −1 . Our estimated values of σ are consistent with those found by Hajigholi et al (2015) toward G34.3+0.15. Some of the high-mass protostars studied by van der Tak et al (2013) also show regular and inverse P-Cygni profiles, but they do not analyze the line profiles and thus we cannot directly compare our results.…”

Section: Sourcesupporting

confidence: 91%

“…3.4.2). A recent example of multiple ammonia lines, observed with Herschel toward the massive star-forming region G34.3+0.15 and showing inverse P-Cygni profiles, can be found in Hajigholi et al (2015). The only regular P-Cygni profile we have detected, toward source l30-512, is also superposed on what looks like an outflow/shock component.…”

Section: Regular and Inverse P-cygni Profilesmentioning

confidence: 63%

“…1. In comparison, Hajigholi et al (2015) find an excitation temperature of 7−8 K in the absorbing envelope of source G34.3+0.15.…”

Section: Sourcementioning

confidence: 87%

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Herschel-HIFI observations of H₂O, NH₃, and N₂H⁺toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

Olmi

Persson

Codella

2015

A&A

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Context. Our present understanding of high-mass star formation still remains very schematic. In particular, it is not yet clear how much of the difference between low-mass and high-mass star formation occurs during the earliest star formation phases. Aims. The chemical characteristics of massive cold clumps, and the comparison with those of their low-mass counterparts, could provide crucial clues about the exact role that chemistry plays in differentiating the early phases of low-mass and high-mass star formation. Water, in particular, is a unique probe of physical and chemical conditions in star-forming regions. Methods. Using the HIFI instrument of Herschel, we have observed the ortho−NH 3 (1 0 −0 0 ) (572 GHz), ortho−H 2 O (1 10 −1 01 ) (557 GHz), and N 2 H + (6−5) (559 GHz) lines toward a sample of high-mass starless and protostellar clumps selected from the Herschel Infrared Galactic Plane Survey (Hi-GAL). We compare our results to previous studies of low-mass and high-mass protostellar objects. Results. At least one of the three molecular lines was detected in 4 (out of 35) and 7 (out of 17) objects in the = 59 • and = 30 • galactic regions, respectively. All detected sources are protostellar. The water spectra are complex and consist of several kinematic components, identified through a Gaussian decomposition, and we detected inverse and regular P-Cygni profiles in a few sources. All water line profiles of the = 59 • region are dominated by a broad Gaussian emission feature, indicating that the bulk of the water emission arises in outflows. No such broad emission is detected toward the = 30 • objects. The ammonia line in some cases also shows line wings and an inverse P-Cygni profile, thus confirming that NH 3 rotational transitions can be used to probe the dynamics of high-mass, star-forming regions. Both bolometric and water line luminosity increase with the continuum temperature. Conclusions. The higher water abundance toward the = 59 • sources, characterized by the presence of outflows and shocks, supports a scenario in which the abundance of this molecule is linked to the shocked gas. Various indicators suggest that the detected sources toward the = 30 • region are in a somewhat later evolutionary phase compared to the = 59 • field, although a firm conclusion is limited by the small number of observed sources. We find many similarities with studies carried out toward low-mass protostellar objects, but there are indications that the level of infall and turbulence in the high-mass protostars studied here could be significantly higher.

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Section: Sourcesupporting

confidence: 91%

Section: Regular and Inverse P-cygni Profilesmentioning

confidence: 63%

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Herschel-HIFI observations of H₂O, NH₃, and N₂H⁺toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

Olmi

Persson

Codella

2015

A&A

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“…Assuming a typical 10% of the free-fall velocity, we obtain an infall velocity of ≈ 0.3 km s −1 for the clumps in the TOP100, which has a negligible effect in terms of broadening. Hajigholi et al (2016), however, show that in the inner regions of the envelope the infall proceeds with a velocity 0.4 − 0.7 of the free-fall value, which is also in line with a progressive broadening of the linewidth on smaller scales. Figure 17 illustrates that a relation exists between the temperature in the inner part of the envelope and the volume density of molecular hydrogen, calculated at the peak of continuum emission as n H 2 = N H 2 /2R, where R is the source radius, as measured from dust.…”

Section: Evolution Of Linewidths and Volume Densitiesmentioning

confidence: 71%

ATLASGAL-selected massive clumps in the inner Galaxy

Giannetti

Leurini

Wyrowski

et al. 2017

A&A

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Context. Observational identification of a solid evolutionary sequence for high-mass star-forming regions is still missing. Spectroscopic observations give the opportunity to test possible schemes and connect the phases identified to physical processes. Aims. We aim to use the progressive heating of the gas caused by the feedback of high-mass young stellar objects to prove the statistical validity of the most common schemes used to observationally define an evolutionary sequence for high-mass clumps, and characterise the sensitivity of different tracers to this process. Methods. From the spectroscopic follow-ups carried out towards submillimeter continuum (dust) emission-selected massive clumps (the ATLASGAL TOP100 sample) with the IRAM 30 m, Mopra, and APEX telescopes between 84 GHz and 365 GHz, we selected several multiplets of CH 3 CN, CH 3 CCH, and CH 3 OH emission lines to derive and compare the physical properties of the gas in the clumps along the evolutionary sequence, fitting simultaneously the large number of lines that these molecules have in the observed band. Our findings are compared with results obtained from optically thin CO isotopologues, dust, and ammonia from previous studies on the same sample. Results. The chemical properties of each species have a major role on the measured physical properties. Low temperatures are traced by ammonia, methanol, and CO (in the early phases), the warm and dense envelope can be probed with CH 3 CN, CH 3 CCH, and, in evolved sources where CO is abundant in the gas phase, via its optically thin isotopologues. CH 3 OH and CH 3 CN are also abundant in the hot cores, and we suggest that their high-excitation transitions are good tools to study the kinematics in the hot gas associated with the inner envelope surrounding the young stellar objects that these clumps are hosting. All tracers show, to different degrees according to their properties, progressive warming with evolution. The relation between gas temperature and the luminosity-to-mass (L/M) ratio is reproduced by a simple toy model of a spherical, internally heated clump. Hii regions become common, showing that dissipation of the parental clump dominates.

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“…ALI has been tested and used, for example by Maercker et al (2008) and Wirström et al (2014). We also used this code in our current modelling of our Herschel-HIFI observations of seven rotational ammonia transitions in G34.3 (Hajigholi et al 2016), and W31C, W49N and W51 (Persson et al, in prep.). Collision rates for neutral impact on NH 2 were estimated based upon an assumed quenching rate coefficient of 5 × 10 −11 cm 3 s −1…”

Section: Ali Modelling: Hot Core Emission and Excitation In The Envelmentioning

confidence: 99%

Ortho-to-para ratio of NH₂

Persson

Olofsson

Gal

et al. 2016

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We have used the Herschel-HIFI instrument to observe the two nuclear spin symmetries of amidogen (NH 2 ) towards the high-mass star-forming regions W31C (G10.6−0.4), W49N (G43.2−0.1), W51 (G49.5−0.4), and G34.3+0.1. The aim is to investigate the ratio of nuclear spin types, the ortho-to-para ratio (OPR) of NH 2 in the translucent interstellar gas, where it is traced by the line-of-sight absorption, and in the envelopes that surround the hot cores. The HIFI instrument allows spectrally resolved observations of NH 2 that show a complicated pattern of hyperfine structure components in all its rotational transitions. The excited NH 2 transitions were used to construct radiative transfer models of the hot cores and surrounding envelopes to investigate the excitation and possible emission of the ground-state rotational transitions of ortho-NH 2 N Ka,Kc J = 1 1,1 3/2-0 0,0 1/2 (953 GHz) and para-NH 2 2 1,2 5/2-1 0,1 3/2 (1444 GHz) used in the OPR calculations. Our best estimate of the average OPR in the envelopes lie above the high-temperature limit of three for W49N, specifically 3.5 with formal errors of ±0.1, but for W31C, W51, and G34.3+0.1 we find lower values of 2.5 ± 0.1, 2.7 ± 0.1, and 2.3 ± 0.1, respectively. Values this low are strictly forbidden in thermodynamical equilibrium since the OPR is expected to increase above three at low temperatures. In the translucent interstellar gas towards W31C, where the excitation effects are low, we find similar values between 2.2 ± 0.2 and 2.9 ± 0.2. In contrast, we find an OPR of 3.4 ± 0.1 in the dense and cold filament connected to W51 and also two lower limits of 4.2 and 5.0 in two other translucent gas components towards W31C and W49N. At low temperatures (T 50 K) the OPR of H 2 is <10 −1 , far lower than the terrestrial laboratory normal value of three. In this para-enriched H 2 gas, our astrochemical models can reproduce the variations of the observed OPR, both below and above the thermodynamical equilibrium value, by considering nuclear-spin gas-phase chemistry. The models suggest that values below three arise in regions with temperatures 20−25 K, depending on time, and values above three at lower temperatures.

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On the accretion process in a high-mass star forming region

Cited by 15 publications

References 73 publications

Herschel-HIFI observations of H₂O, NH₃, and N₂H⁺toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

Herschel-HIFI observations of H₂O, NH₃, and N₂H⁺toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

ATLASGAL-selected massive clumps in the inner Galaxy

Ortho-to-para ratio of NH₂

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On the accretion process in a high-mass star forming region

Cited by 15 publications

References 73 publications

Herschel-HIFI observations of H2O, NH3, and N2H+toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

Herschel-HIFI observations of H2O, NH3, and N2H+toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

ATLASGAL-selected massive clumps in the inner Galaxy

Ortho-to-para ratio of NH2

Contact Info

Product

Resources

About

Herschel-HIFI observations of H₂O, NH₃, and N₂H⁺toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

Herschel-HIFI observations of H₂O, NH₃, and N₂H⁺toward high-mass starless and protostellar clumps identified by the Hi-GAL survey

Ortho-to-para ratio of NH₂