S255‐2: The Formation of a Stellar Cluster

Howard, Eric M.; Pipher, J. L.; Forrest, W. J.

doi:10.1086/304046

Cited by 33 publications

(55 citation statements)

References 27 publications

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“…The YSO IRS1 is the most prominent of the infrared sources in the core of the S255 molecular cloud, and its emission measure indicates the presence of a compact or ultracompact H II region. High angular resolution observations (unresolved by ISO-SWS) reveal IRS1 to contain at least two pointlike IR sources apart, 2A .6 each probably located behind a dust disk or torus (Howard, Pipher, & Forrest 1997). In the context of this paper, the property that most signiÐcantly distinguishes high-mass from low-mass YSOs is the large amount of Lyman continuum in the former.…”

Section: Description Of the Sourcesmentioning

confidence: 76%

Solid Carbon Dioxide in Regions of Low‐Mass Star Formation

Nummelin

Whittet

Gibb

et al. 2001

ApJ

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We present high-resolution (R D 1500È2000) spectra of the 4.27 km asymmetric stretching feature of solid in eight lines of sight observed with the Short Wavelength Spectrometer of the Infrared Space CO 2 Observatory. Two of the sources are Ðeld stars located behind the Taurus molecular cloud ; the others are young stellar objects (YSOs) of predominantly low-to-intermediate mass. We Ðnd a signiÐcant source-tosource variation in the solid abundance ratio in our sample : two lines of sight, Elias 18 andabundances of D 34%È37%, considerably higher than in other lines of sight CO 2 studied to date. In agreement with a previous study of Elias 16, we conÐrm a substantial (D20%) abundance of solid relative to in the quiescent intracloud medium. We compare the proÐles CO 2 H 2 O C O 2 with laboratory spectra of interstellar ice analogs from the Leiden Observatory Laboratory database. Results show that the 4.27 km proÐles toward Ðeld stars and embedded low-mass objects are remarkably similar to each other and seem to originate mostly in cold ice. In two higher mass YSOs H 2 O-rich (RAFGL 989 and S255 IRS1), the proÐles are clearly di †erent, and at least the latter source shows signs of thermal processing.

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Section: Description Of the Sourcesmentioning

confidence: 76%

Solid Carbon Dioxide in Regions of Low‐Mass Star Formation

Nummelin

Whittet

Gibb

et al. 2001

ApJ

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“…Compressive triggering increases the external pressure, and thus the density of a core, and in doing so speeds up the star formation. The close association of other clusters with adjacent HII regions has also suggested that triggering may have played an important role in the formation of at least some clusters [e.g., S 255 (Howard et al 1997), S 281 (Megeath & Wilson 1997), W3-W4 ]. At some point, when molecular gas is either depleted or expelled from the cluster, star formation ceases and the cluster emerges from its molecular womb.…”

Section: Formation Of Embedded Clustersmentioning

confidence: 99%

Embedded Clusters in Molecular Clouds

Lada

2003

Annu. Rev. Astron. Astrophys.

2,927

179

3,527

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Stellar clusters are born embedded within giant molecular clouds (GMCs) and during their formation and early evolution are often only visible at infrared wavelengths, being heavily obscured by dust. Over the past 15 years advances in infrared detection capabilities have enabled the first systematic studies of embedded clusters in galactic molecular clouds. In this article we review the current state of empirical knowledge concerning these extremely young protocluster systems. From a survey of the literature we compile the first extensive catalog of galactic embedded clusters. We use the catalog to construct the mass function and estimate the birthrate for embedded clusters within ∼2 kpc of the sun. We find that the embedded cluster birthrate exceeds that of visible open clusters by an order of magnitude or more indicating a high infant mortality rate for protocluster systems. Less than 4-7% of embedded clusters survive emergence from molecular clouds to become bound clusters of Pleiades age. The vast majority (90%) of stars that form in embedded clusters form in rich clusters of 100 or more members with masses in excess of 50 M . Moreover, observations of nearby cloud complexes indicate that embedded clusters account for a significant (70-90%) fraction of all stars formed in GMCs. We review the role of embedded clusters in investigating the nature of the initial mass function (IMF) that, in one nearby example, has been measured over the entire range of stellar and substellar mass, from OB stars to substellar objects near the deuterium burning limit. We also review the role embedded clusters play in the investigation of circumstellar disk evolution and the important constraints they provide for understanding the origin of planetary systems. Finally, we discuss current ideas concerning the origin and dynamical evolution of embedded clusters and the implications for the formation of bound open clusters.

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“…Because the H 2 O masers are associated with the inner part of the jet/outflow system (PA jet = 67 • , Howard et al 1997; PA CO out = 75 • , Wang et al 2011), NIR 3 is thought to be the driving source of this jet/outflow system and should not be older than 10 5 yr (Wang et al 2011). The velocities of the blue-shifted and red-shifted lobes of the CO-outflow are −40 km s −1 < V blue S255−IR < 0 km s −1 and +16 km s −1 < V red S255−IR < +56 km s −1 , respectively (Wang et al 2011).…”

Section: S255-irmentioning

confidence: 99%

EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

Surcis

Vlemmings

Langevelde

et al. 2013

A&A

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Context. Magnetic fields have only recently been included in theoretical simulations of high-mass star formation. The simulations show that magnetic fields play an important role in the formation and dynamics of molecular outflows. Masers, in particular 6.7-GHz CH 3 OH masers, are the best probes of the magnetic field morphologies around massive young stellar objects on the smallest scales of 10-100 AU. Aims. Providing new observational measurements of the morphology of magnetic fields around massive young stellar objects by using 6.7-GHz CH 3 OH maser emission is very important for setting constraints on the numerical simulations of massive star formation. Methods. This paper focuses on 4 massive young stellar objects, IRAS 06058+2138-NIRS 1, IRAS 22272+6358A, S255-IR, and S231, which complement our previous 2012 sample (the first EVN group). From all these sources, molecular outflows have been detected in the past. Seven of the European VLBI Network antennas were used to measure the linear polarization and Zeeman-splitting of the 6.7-GHz CH 3 OH masers in the star-forming regions in this second EVN group. Results. We detected a total of 128 CH 3 OH masing cloudlets. Fractional linear polarization (0.8%-11.3%) was detected towards 18% of the CH 3 OH masers in our sample. The linear polarization vectors are well ordered in all the massive young stellar objects. We measured significant Zeeman-splitting in IRAS 06058+2138-NIRS 1 (ΔV Z = 3.8 ± 0.6 m s −1 ) and S255-IR (ΔV Z = 3.2 ± 0.7 m s −1 ). Conclusions. By considering the 20 massive young stellar objects towards which the morphology of magnetic fields was determined by observing 6.7-GHz CH 3 OH masers in both hemispheres, we find no evident correlation between the linear distributions of CH 3 OH masers and the outflows or the linear polarization vectors. On the other hand, we present first statistical evidence that the magnetic field (on scales 10-100 AU) is primarily oriented along the large-scale outflow direction. Moreover, we empirically find that the linear polarization fraction of unsaturated CH 3 OH masers is P l < 4.5%.

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S255‐2: The Formation of a Stellar Cluster

Cited by 33 publications

References 27 publications

Solid Carbon Dioxide in Regions of Low‐Mass Star Formation

Solid Carbon Dioxide in Regions of Low‐Mass Star Formation

Embedded Clusters in Molecular Clouds

EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

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