Physical and chemical variations within the W3 star-forming region

Helmich, Frank; Jansen, D. J.; Graauw, Th. de; Groesbeck, T. D.; Dishoeck, E. F. van

doi:10.1007/bfb0102150

Cited by 42 publications

(67 citation statements)

References 58 publications

(108 reference statements)

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“…Helmich et al (1994) also reported that the CH 3 OH abundance is remarkably low, even compared to typical dark clouds. From our SMA data, and the results from Wang et al (2012), we find that sulfur-bearing molecules such as SO, SO 2 and their isotopologues, strongly peak toward the submillimeter sources SMM1 and SMM2 (zone A) with extended emission toward SMM3, SMM4 and SMM5 (Fig.…”

Section: Distinct Molecular Zonesmentioning

confidence: 94%

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Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation

Wang

Bourke

Hogerheijde

et al. 2013

A&A

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Context. Two competing models describe the formation of massive stars in objects like the Orion Trapezium. In the turbulent core accretion model, the resulting stellar masses are directly related to the mass distribution of the cloud condensations. In the competitive accretion model, the gravitational potential of the protocluster captures gas from the surrounding cloud for which the individual cluster members compete. Aims. With high resolution submillimeter observations of the structure, kinematics, and chemistry of the proto-Trapezium cluster W3 IRS5, we aim to determine which mode of star formation dominates. Methods. We present 354 GHz Submillimeter Array observations at resolutions of 1 -3 (1800-5400 AU) of W3 IRS5. The dust continuum traces the compact source structure and masses of the individual cores, while molecular lines of CS, SO, SO 2 , HCN, H 2 CS, HNCO, and CH 3 OH (and isotopologues) reveal the gas kinematics, density, and temperature. Results. The observations show five emission peaks (SMM1-5). SMM1 and SMM2 contain massive embedded stars (∼20 M ); SMM3-5 are starless or contain low-mass stars (<8 M ). The inferred densities are high, ≥10 7 cm −3 , but the core masses are small, 0.2−0.6 M . The detected molecular emission reveals four different chemical zones. Abundant (X ∼ few 10 −7 to 10 −6 ) SO and SO 2 are associated with SMM1 and SMM2, indicating active sulfur chemistry. A low abundance (5 × 10 −8 ) of CH 3 OH concentrated on SMM3/4 suggest the presence of a hot core that is only just turning on, possibly by external feedback from SMM1/2. The gas kinematics are complex with contributions from a near pole-on outflow traced by CS, SO, and HCN; rotation in SO 2 , and a jet in vibrationally excited HCN. Conclusions. The proto-Trapezium cluster W3 IRS5 is an ideal test case to discriminate between models of massive star formation. Either the massive stars accrete locally from their local cores; in this case the small core masses imply that W3 IRS5 is at the very end stages (1000 yr) of infall and accretion, or the stars are accreting from the global collapse of a massive, cluster forming core. We find that the observed masses, densities and line widths observed toward W3 IRS 5 and the surrounding cluster forming core are consistent with the competitive accretion of gas at rates ofṀ ∼10 −4 M yr −1 by the massive young forming stars. Future mapping of the gas kinematics from large to small scales will determine whether large-scale gas inflow occurs and how the cluster members compete to accrete this material.

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Section: Distinct Molecular Zonesmentioning

confidence: 94%

“…A JCMT spectral line survey characterized W3 IRS5 as a remarkable massive star-forming region with rich spectral features from sulfur-bearing molecules (Helmich et al 1994;Helmich & van Dishoeck 1997). Helmich et al (1994) also reported that the CH 3 OH abundance is remarkably low, even compared to typical dark clouds.…”

Section: Distinct Molecular Zonesmentioning

confidence: 99%

Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation

Wang

Bourke

Hogerheijde

et al. 2013

A&A

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“…Helmich et al (1994). The estimated error on the line fluxes is a factor of two, due to the uncertain contribution from high-velocity gas.…”

Section: Molecular Abundancesmentioning

confidence: 98%

Sulphur chemistry in the envelopes of massive young stars

Tak

Boonman²,

Braakman³

et al. 2003

A&A

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139

150

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Abstract. The sulphur chemistry in nine regions in the earliest stages of high-mass star formation is studied through singledish submillimeter spectroscopy. The line profiles indicate that 10-50% of the SO and SO 2 emission arises in high-velocity gas, either infalling or outflowing. For the low-velocity gas, excitation temperatures are 25 K for H 2 S, 50 K for SO, H 2 CS, NS and HCS + , and 100 K for OCS and SO 2 , indicating that most observed emission traces the outer parts (T < 100 K) of the molecular envelopes, except high-excitation OCS and SO 2 lines. Abundances in the outer envelopes, calculated with a Monte Carlo program, using the physical structures of the sources derived from previous submillimeter continuum and CS line data, are ∼10 −8 for OCS, ∼10 −9 for H 2 S, H 2 CS, SO and SO 2 , and ∼10 −10 for HCS + and NS. In the inner envelopes (T > 100 K) of six sources, the SO 2 abundance is enhanced by a factor of ∼100-1000. This region of hot, abundant SO 2 has been seen before in infrared absorption, and must be small, < ∼ 0. 2 (180 AU radius). The derived abundance profiles are consistent with models of envelope chemistry which invoke ice evaporation at T ∼ 100 K. Shock chemistry is unlikely to contribute. A major sulphur carrier in the ices is probably OCS, not H 2 S as most models assume. The source-to-source abundance variations of most molecules by factors of ∼10 do not correlate with previous systematic tracers of envelope heating. Without observations of H 2 S and SO lines probing warm ( > ∼ 100 K) gas, sulphur-bearing molecules cannot be used as evolutionary tracers during star formation.

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“…NGC7538 IRS9 and NGC7538 IRS1 are located in Perseus, and NGC7538 IRS1 is known to house a bright hot core 19 and is situated in the middle of a cluster of continuum peaks and molecular outflows. W3 IRS5 is associated with at least five young stellar objects, two of which are massive [20][21][22][23][24] , and is known to present strong S-bearing molecular lines 25 . In summary all three sources are known to have complicated structures with many different potential origins of complex molecular emission.…”

Section: Observations and Source Characteristicsmentioning

confidence: 99%

Complex molecule formation around massive young stellar objects

et al. 2014

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Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. Individually these observations provide limited constraints, however, on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Toward the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH 3 CCH and CH 3 CN seem to always trace a luke-warm (T∼60 K) and a hot (T>100 K) complex chemistry, respectively. These spatial trends are consistent with abundance-temperature correlations of four representative complex organics -CH 3 CCH, CH 3 CN, CH 3 OCH 3 and CH 3 CHO -in a large sample of complex molecule hosts mined from the literature. Together these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, as well as provide information about its formation history.

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Physical and chemical variations within the W3 star-forming region

Cited by 42 publications

References 58 publications

Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation

Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation

Sulphur chemistry in the envelopes of massive young stars

Complex molecule formation around massive young stellar objects

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