Search for Very Young Massive Stars

Henning, Thomas; Klein, Randolf; Launhardt, R.; Schreyer, K.; Stecklum, B.

doi:10.1007/3-540-45553-1_42

Cited by 64 publications

(107 citation statements)

References 17 publications

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“…This hot core is associated with a massive molecular outflow and various infrared and radio sources (Henning et al 2000). Figure 7 shows the observed lines and the best-fit model (Table 8).…”

Section: Iras 12326-6245mentioning

confidence: 96%

Structure of evolved cluster-forming regions

Rolffs

Schilke

Wyrowski

et al. 2011

A&A

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Context. An approach towards understanding the formation of massive stars and star clusters is to study the structure of their hot core phase, an evolutionary stage where dust has been heated, but molecules have not yet been destroyed by ultraviolet radiation. These hot molecular cores are very line-rich, but the interpretation of line surveys is also hampered by poor knowledge of the physical and chemical structure. Aims. To constrain the radial structure of high-mass star-forming regions containing hot cores, we attempt to reproduce by radiative transfer modeling both the intensity and shape of a variety of molecular lines. Methods. We observed 12 hot cores with the Atacama Pathfinder EXperiment (APEX) in lines of HCN, HCO + , CO, and their isotopologues, including high-J lines and vibrationally excited HCN. We investigate how well the sources can be modeled as centrally heated spheres with a power-law density gradient, making use of the radiative transfer code RATRAN and the radial profile of the submm continuum emission, taken from the APEX Telescope Large Area Survey of the GALaxy (ATLASGAL). Results. Most of the observed lines have complicated shapes that incorporate self-absorption, asymmetries, and line wings. Vibrationally excited HCN is detected in all sources, and vibrationally excited H 13 CN in half of the sources. We are able to successfully model most features seen in the APEX data, such as the ratio of the isotopologue lines (very high optical depths), self-absorption (temperature gradient), blue asymmetries (moderate infall), vibrationally excited HCN (high inner temperatures), and H 13 CN (high HCN abundance under dense and hot conditions). Other features could not be reproduced, such as an occasional lack of self-absorption, the emission from high-J lines in the outer pixels of the CHAMP+ receiver (15 −20 from the center), the outflow wings, and the red asymmetric profiles. Conclusions. The amount of molecular gas, in particular of HCN, at very high temperatures is larger than previously thought. A complex interplay between infall and outflow motions is present. Our basic model assumptions of pure central heating and a power-law radial density distribution can serve as approximations for most sources, but are too simple to explain all observed lines. In particular, taking into account clumpiness, multiplicity of heating sources and a more complex velocity field seems to be necessary to more closely match model calculations to observations. This would require three-dimensional radiative transfer modeling of high-resolution interferometric data.

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Section: Iras 12326-6245mentioning

confidence: 96%

Structure of evolved cluster-forming regions

Rolffs

Schilke

Wyrowski

et al. 2011

A&A

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“…Let us recall a few points about this accretion law. Firstly, it is based on an empirical relation, which was established by Churchwell (1998) and confirmed by Henning et al (2000), between the mass outflow rate,Ṁ out , and the bolometric luminosity, L, of the accreting object in ultra-compact HII regions:…”

Section: Mass Accretion Ratementioning

confidence: 99%

Star formation with disc accretion and rotation

Haemmerlé¹,

Eggenberger²,

Meynet³

et al. 2013

A&A

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Context. The way angular momentum is built up in stars during their formation process may have an impact on their further evolution. Aims. In the framework of the cold disc accretion scenario, we study how angular momentum builds up inside the star during its formation for the first time and what the consequences are for its evolution on the main sequence (MS). Methods. Computation begins from a hydrostatic core on the Hayashi line of 0.7 M at solar metallicity (Z = 0.014) rotating as a solid body. Accretion rates depending on the luminosity of the accreting object are considered, which vary between 1.5 × 10 −5 and 1.7 × 10 −3 M yr −1 . The accreted matter is assumed to have an angular velocity equal to that of the outer layer of the accreting star. Models are computed for a mass-range on the zero-age main sequence (ZAMS) between 2 and 22 M . Results. We study how the internal and surface velocities vary as a function of time during the accretion phase and the evolution towards the ZAMS. Stellar models, whose evolution has been followed along the pre-MS phase, are found to exhibit a shallow gradient of angular velocity on the ZAMS. Typically, the 6 M model has a core that rotates 50% faster than the surface on the ZAMS. The degree of differential rotation on the ZAMS decreases when the mass increases (for a fixed value of v ZAMS /v crit ). The MS evolution of our models with a pre-MS accreting phase show no significant differences with respect to those of corresponding models computed from the ZAMS with an initial solid-body rotation. Interestingly, there exists a maximum surface velocity that can be reached through the present scenario of formation for masses on the ZAMS larger than 8 M . Typically, only stars with surface velocities on the ZAMS lower than about 45% of the critical velocity can be formed for 14 M models. Reaching higher velocities would require starting from cores that rotate above the critical limit. We find that this upper velocity limit is smaller for higher masses. In contrast, there is no restriction below 8 M , and the whole domain of velocities to the critical point can be reached.

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“…The main argument stems from massive molecular outflow observations that identify collimated and energetic outflows from high-mass protostars, resembling the properties of known low-mass star formation sites (e.g., Henning et al 2000;Beuther et al 2002;Wu et al 2004;Zhang et al 2005;Arce et al 2007;López-Sepulcre et al 2009). Such collimated jet-like outflow structures are only explainable with an underlying massive accretion disk driving the outflows via magneto-centrifugal acceleration.…”

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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Search for Very Young Massive Stars

Cited by 64 publications

References 17 publications

Structure of evolved cluster-forming regions

Structure of evolved cluster-forming regions

Star formation with disc accretion and rotation

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

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