The Formation of Massive Stars by Accretion through Trapped Hypercompact H<scp>ii</scp>Regions

Keto, Eric

doi:10.1086/379545

Cited by 197 publications

(204 citation statements)

References 41 publications

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“…It appears that in that region the most massive star forms last compared to the lower-mass population, similar to other studies like, e.g., Kumar et al (2006) or Wang et al (2011). Furthermore, the strong concentration of mass within a single object without much further fragmentation (except those on larger scales as reported by Qiu et al 2011; see also Bontemps et al 2010) is consistent with a scaled-up low-mass star formation scenario for the formation of high-mass stars (e.g., McKee & Tan 2002, 2003Krumholz et al 2007Krumholz et al , 2009Kuiper et al 2010). …”

Section: Ngc 7538ssupporting

confidence: 88%

“…This results in disk infall rates oḟ M disk,in ∼ 3.5 × 10 −2 M yr −1 , still very high and in the regime of accretion rates required to form high-mass stars (e.g., Wolfire & Cassinelli 1987;McKee & Tan 2003). Although we cannot prove that the gas falls in that far that it can be accreted onto the star (and does not get reverted by the innermost radiation and outflow pressure), such high infall rates should be a pre-requisite to allow accretion even when the central high-mass star has ignited already (e.g., Keto 2003;Kuiper et al 2010Kuiper et al , 2011. An additional caveat arises from the potential contribution of the accretion luminosity to the total luminosity of the region.…”

Section: Ngc 7538irs1mentioning

confidence: 89%

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The high-mass disk candidates NGC 7538IRS1 and NGC 7538S

Beuther

Linz

Henning

2012

A&A

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Context. The nature of embedded accretion disks around forming high-mass stars is one of the missing puzzle pieces for a general understanding of the formation of the most massive and luminous stars. Aims. We want to dissect the small-scale structure of the dust continuum and kinematic gas emission toward two of the most prominent high-mass disk candidates. Methods. Using the Plateau de Bure Interferometer at ∼1.36 mm wavelengths in its most extended configuration we probe the dust and gas emission at ∼0.3 , corresponding to linear resolution elements of ∼800 AU.Results. Even at that high spatial resolution NGC 7538IRS1 remains a single compact and massive gas core with extraordinarily high column densities, corresponding to visual extinctions on the order of 10 5 mag, and average densities within the central 2000 AU of ∼2.1 × 10 9 cm −3 that have not been measured before. We identify a velocity gradient across in northeast-southwest direction that is consistent with the mid-infrared emission, but we do not find a gradient that corresponds to the proposed CH 3 OH maser disk. The spectral line data toward NGC 7538IRS1 reveal strong blue-and red-shifted absorption toward the mm continuum peak position. While the blue-shifted absorption is consistent with an outflow along the line of sight, the red-shifted absorption allows us to estimate high infall rates on the order of 10 −2 M yr −1 . Although we cannot prove that the gas will be accreted in the end, the data are consistent with ongoing star formation activity in a scaled-up low-mass star formation scenario. Compared to that, NGC 7538S fragments in a hierarchical fashion into several sub-sources. While the kinematics of the main mm peak are dominated by the accompanying jet, we find rotational signatures from a secondary peak. Furthermore, strong spectral line differences exist between the sub-sources which is indicative of different evolutionary stages within the same large-scale gas clump. Conclusions. NGC 7538IRS1 is one of the most extreme high-mass disk candidates known today. The large concentration of mass into a small area combined with the high infall rates are unusual and likely allow continued accretion. While the absorption is interesting for the infall studies, higher-excited lines that do not suffer from the absorption are needed to better study the disk kinematics. In contrast to that, NGC 7538S appears as a more typical high-mass star formation region that fragments into several sources. Many of them will form low-to intermediate-mass stars. The strongest mm continuum peak is likely capable to form a high-mass star, however, likely of lower mass than NGC 7538IRS1.

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Section: Ngc 7538ssupporting

confidence: 88%

Section: Ngc 7538irs1mentioning

confidence: 89%

The high-mass disk candidates NGC 7538IRS1 and NGC 7538S

Beuther

Linz

Henning

2012

A&A

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“…The upper limits for the latter follow from the upper limit on the embedded stellar masses of 8 M . The accretion rates are consistent with those expected for the formation of massive stars (Keto 2003). The combination of small core masses and high accretion rates imply very short time scales of a few thousand years.…”

Section: Accretion Ratessupporting

confidence: 84%

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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“…They are believed to form by accretion in dense cores within molecular cloud complexes (Yorke & Sonnhalter 2002;McKee & Tan 2003;Keto 2003Keto , 2005 and/or coalescence (e.g.…”

Section: Introductionmentioning

confidence: 99%

The molecular environment of the Galactic star forming region G19.61–0.23

Santangelo

Testi

Leurini

et al. 2010

A&A

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Context. Although current facilities allow the study of Galactic star formation at high angular resolution, our current understanding of the high-mass star-formation process is still very poor. In particular, we still need to characterize the properties of clouds giving birth to high-mass stars in our own Galaxy and use them as templates for our understanding of extragalactic star formation. Aims. We present single-dish (sub)millimeter observations of gas and dust in the Galactic high-mass star-forming region G19.61-0.23, with the aim of studying the large-scale properties and physical conditions of the molecular gas across the region. The final aim is to compare the large-scale (about 100 pc) properties with the small-scale (about 3 pc) properties and to consider possible implications for extragalactic studies. Methods. We have mapped CO isotopologues in the J = 1−0 transition using the FCRAO-14m telescope and the J = 2−1 transition using the IRAM-30m telescope. We have also used APEX 870 μm continuum data from the ATLASGAL survey and FCRAO supplementary observations of the 13 CO J = 1−0 line from the BU-FCRAO Galactic Ring Survey, as well as the Spitzer infrared Galactic plane surveys GLIMPSE and MIPSGAL to characterize the star-formation activity within the molecular clouds. Results. We reveal a population of molecular clumps in the 13 CO(1-0) emission, for which we derived the physical parameters, including sizes and masses. Our analysis of the 13 CO suggests that the virial parameter (ratio of kinetic to gravitational energy) varies over an order of magnitude between clumps that are unbound and some that are apparently "unstable". This conclusion is independent of whether they show evidence of ongoing star formation. We find that the majority of ATLASGAL sources have MIPSGAL counterparts with luminosities in the range 10 4 -5 × 10 4 L and are presumably forming relatively massive stars. We compare our results with previous extragalactic studies of the nearby spiral galaxies M 31 and M 33; and the blue compact dwarf galaxy Henize 2-10. We find that the main giant molecular cloud surrounding G19.61-0.23 has physical properties typical for Galactic GMCs and which are comparable to the GMCs in M 31 and M 33. However, the GMC studied here shows smaller surface densities and masses than the clouds identified in Henize 2-10 and associated with super star cluster formation.

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The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

Cited by 197 publications

References 41 publications

The high-mass disk candidates NGC 7538IRS1 and NGC 7538S

The high-mass disk candidates NGC 7538IRS1 and NGC 7538S

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

The molecular environment of the Galactic star forming region G19.61–0.23

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