High resolution CO observation of massive star forming regions

Klaassen, Pamela; Wilson, C. D.; Keto, Eric; Zhang, Qizhou; Galván-Madrid, Roberto; Liu, Hauyu Baobab

doi:10.1051/0004-6361/201016371

Cited by 22 publications

(33 citation statements)

References 54 publications

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“…Compared to the blue-shifted absorption observed by Keto (1991) and Zheng et al (2001) in the lowexcitation NH 3 lines that is indicative of outflowing gas motions, Qiu et al (2011) detected first red-shifted absorption toward the main mm core which they interprete as signature of ongoing infall. Furthermore, the general structure of their proposed multiple outflows is consistent with the northwest-southeast outflow previously reported by, e.g., Keto (1991); Davis et al (1998); Klaassen et al (2011). Our data now resolve the region at again an order of magnitude higher spatial resolution, allowing us to study the central core in unprecedented detail.…”

Section: Introductionsupporting

confidence: 67%

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: Introductionsupporting

confidence: 67%

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

Beuther

Linz

Henning

2012

A&A

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“…From this respect, we found that the outflow parameters derived from CO observations of BHR71 are obviously systematically less than the values inferred in more massive environments (e.g. Duarte-Cabral et al 2013;Klaassen et al 2011), let alone in the outflows associated with O-type stars (López-Sepulcre et al 2009). This is also true for SiOrelated energetic parameters: BHR71 is less energetic from this point of view than its massive counterparts (Sánchez-Monge et al 2013).…”

Section: Employing Shock Models: Energeticsmentioning

confidence: 83%

Impacts of pure shocks in the BHR71 bipolar outflow

Gusdorf

Riquelme

Anderl

et al. 2015

A&A

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Context. During the formation of a star, material is ejected along powerful jets that impact the ambient material. This outflow regulates star formation by e.g. inducing turbulence and heating the surrounding gas. Understanding the associated shocks is therefore essential to the study of star formation. Aims. We present comparisons of shock models with CO, H 2 , and SiO observations in a "pure" shock position in the BHR71 bipolar outflow. These comparisons provide an insight into the shock and pre-shock characteristics, and allow us to understand the energetic and chemical feedback of star formation on Galactic scales. Methods. New CO (J up = 16, 11, 7, 6, 4, 3) observations from the shocked regions with the SOFIA and APEX telescopes are presented and combined with earlier H 2 and SiO data (from the Spitzer and APEX telescopes). The integrated intensities are compared to a grid of models that were obtained from a magneto-hydrodynamical shock code, which calculates the dynamical and chemical structure of these regions combined with a radiative transfer module based on the "large velocity gradient" approximation. Results. The CO emission leads us to update the conclusions of our previous shock analysis: pre-shock densities of 10 4 cm −3 and shock velocities around 20−25 km s −1 are still constrained, but older ages are inferred (∼4000 years). Conclusions. We evaluate the contribution of shocks to the excitation of CO around forming stars. The SiO observations are compatible with a scenario where less than 4% of the pre-shock SiO belongs to the grain mantles. We infer outflow parameters: a mass of 1.8 × 10 −2 M was measured in our beam, in which a momentum of 0.4 M km s −1 is dissipated, corresponding to an energy of 4.2 × 10 43 erg. We analyse the energetics of the outflow species by species. Comparing our results with previous studies highlights their dependence on the method: H 2 observations only are not sufficient to evaluate the mass of outflows.

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“…Secondly, the disk temperature is a function of the accretion rate. We consider disks with steady-state accretion at rates ranging fromṀ = 10 −8 − 10 −3 M yr −1 , where the lower end is consistent with accretion rates observed on actively accreting T Tauri stars towards the end of their lives, and the highest rates represent a generous upper limit set by infall from a supersonic core for more massive stars (McKee & Tan 2003;Klaassen et al 2011) . In reality, a disk with a given surface density and temperature profile cannot support an arbitrary accretion rate in steady state.…”

Section: Accretion Ratesmentioning

confidence: 99%

Gravitational Instabilities in Circumstellar Disks

Kratter

Lodato

2016

Annu. Rev. Astron. Astrophys.

454

380

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Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability, and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability, supplemented with a survey of numerical simulations that aim to capture the non-linear evolution. We emphasize the role of thermodynamics and large scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared to their host star, M d /M * ≥ 0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. While instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to (1) the development of a turbulent cascade in thin disks, and (2) the role of mode-mode coupling in setting the maximum angular momentum transport rate in thick disks. We dedicate this article to the memory of Francesco Palla, who has been a source of inspiration for star formation and disk studies throughout the years. Through his support and encouragement of young scientists, his contributions live on.

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High resolution CO observation of massive star forming regions

Cited by 22 publications

References 54 publications

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

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

Impacts of pure shocks in the BHR71 bipolar outflow

Gravitational Instabilities in Circumstellar Disks

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