Spherical Infall in G10.6-0.4: Accretion through an Ultracompact H
                    <scp>ii</scp>
                    Region

Sollins, P. K.; Zhang, Qizhou; Keto, Eric; Ho, P. T. P.

doi:10.1086/430270

Cited by 71 publications

(83 citation statements)

References 26 publications

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“…Of the three observed sources, we find indications of large scale molecular outflows in two sources (NGC 7538 and G28.2), as well as molecular infall signatures in two sources (NGC 7538 and G10.6). We note that while there is no large scale molecular outflow signature coming from G10.6, an ionized outflow has been previously detected in this region (Keto & Wood 2006) and despite our non-detection of infall in G28.2, an infall signature has been seen in the dense gas (NH 3 , Sollins et al 2005b) surrounding this region.…”

Section: Resultscontrasting

confidence: 59%

“…That these two species show this absorption feature slightly redshifted from the source velocity suggests that perhaps the molecular gas is doing something different than the ionized gas. It should be noted that the NH 3 observations of (Sollins et al 2005b) for this source also show a similar velocity shift at high resolution for the molecular gas. The first moment map they present in Fig.…”

Section: G2820-005supporting

confidence: 62%

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High resolution CO observation of massive star forming regions

Klaassen

Wilson

Keto

et al. 2011

A&A

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Context. To further understand the processes involved in the formation of massive stars, we have undertaken a study of the gas dynamics surrounding three massive star forming regions. By observing the large scale structures at high resolution, we are able to determine properties such as driving source, and spatially resolve the bulk dynamical properties of the gas such as infall and outflow. Aims. With high resolution observations, we are able to determine which of the cores in a cluster forming massive stars is responsible for the large scale structures. Methods. We present CO observations of three massive star forming regions with known HII regions and show how the CO traces both infall and outflow. By combining data taken in two SMA configurations with JCMT observations, we are able to see large scale structures at high resolution. Results. We find large (0.26-0.40 pc), massive (2-3 M ) and energetic (13-17 × 10 44 erg) outflows emanating from the edges of two HII regions suggesting they are being powered by the protostar(s) within. We find infall signatures in two of our sources with mass infall rates of order 10 −4 M yr −1 . Conclusions. We suggest that star formation is ongoing in these sources despite the presence of HII regions. We further conclude that the source(s) within a single HII region are responsible for the observed large scale structures; that these large structures are not the net effect of multiple outflows from multiple HII regions and hot cores.

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Section: Resultscontrasting

confidence: 59%

Section: G2820-005supporting

confidence: 62%

High resolution CO observation of massive star forming regions

Klaassen

Wilson

Keto

et al. 2011

A&A

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“…Is this scenario plausible? Indeed, in the case of G10.62-0.38, a massive star forming region with a luminosity of 9.2 × 10 5 L , Sollins et al (2005) suggest that within a radius of 0.03 pc, several O stars with a total mass of 175 M have formed at the center of a flattened disk. In our case, the existence of (at least) two high-mass YSOs close to the HMC center and separated (in projection) by only 0.…”

Section: Rotating Toroidmentioning

confidence: 99%

“…disk solid angle. It also appears that the powerful ionizing fluxes from these OB-type stars are not sufficient to destroy the disk, which eventually turns into an ionized, rotating accretion flow close to the star (Sollins et al 2005;Keto 2007). …”

Section: Introductionmentioning

confidence: 99%

Dissecting a hot molecular core: the case of G31.41+0.31

Cesaroni

Beltrán

Zhang

et al. 2011

A&A

118

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Context. The role of disks in the formation of high-mass stars is still a matter of debate but the detection of circumstellar disks around O-type stars would have a profound impact on high-mass star formation theories. Aims. We made a detailed observational analysis of a well known hot molecular core lying in the high-mass star-forming region G31.41+0.31. This core is believed to contain deeply embedded massive stars and presents a velocity gradient that has been interpreted either as rotation or as expansion, depending on the authors. Our aim was to shed light on this question and possibly prepare the ground for higher resolution ALMA observations, which could directly detect circumstellar disks around the embedded massive stars. Methods. Observations at sub-arcsecond resolution were performed with the Submillimeter Array in methyl cyanide, a typical hot molecular core tracer, and 12 CO and 13 CO, well known outflow tracers. We also obtained sensitive continuum maps at 1.3 mm. Results. Our findings confirm the existence of a sharp velocity gradient across the core, but cannot confirm the existence of a bipolar outflow perpendicular to it. The improved angular resolution and sampling of the uv plane allow us to attain higher quality channel maps of the CH 3 CN lines with respect to previous studies and thus significantly improve our knowledge of the structure and kinematics of the hot molecular core. Conclusions. While no conclusive argument can rule out any of the two interpretations (rotation or expansion) proposed to explain the velocity gradient observed in the core, in our opinion the observational evidence collected so far indicates the rotating toroid as the most likely scenario. The outflow hypothesis appears less plausible, because the dynamical time scale is too short compared to that needed to form species such as CH 3 CN, and the mass loss and momentum rates estimated from our measurements appear too high.

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“…Hence, spatially disentangling such structures is a difficult task. While several disk candidates exist around early B-stars (e.g., Cesaroni et al 1997Cesaroni et al , 2005Schreyer et al 2002;Shepherd et al 2001;Zhang et al 2002;Chini et al 2004;Kraus et al 2010;Keto & Zhang 2010;Fallscheer et al 2011), more massive O-star like systems rather show larger-scale toroid-like structures not consistent with classical Keplerian accretion disks (e.g., Beltrán et al 2004;Beltrán et al 2011;Beuther et al 2005;Beuther & Walsh 2008;Sollins et al 2005;Keto & Wood 2006;Cesaroni et al 2007;Fallscheer et al 2009). However, the nondetection of Keplerian structures around O-stars does not imply that they do not exist, it rather indicates that they are likely on smaller spatial scales hidden by the toroids.…”

Section: Introductionmentioning

confidence: 99%

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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Spherical Infall in G10.6-0.4: Accretion through an Ultracompact H ii Region

Cited by 71 publications

References 26 publications

High resolution CO observation of massive star forming regions

High resolution CO observation of massive star forming regions

Dissecting a hot molecular core: the case of G31.41+0.31

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

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