Evidence for Evolution of the Outflow Collimation in Very Young Stellar Objects

Torrelles, J. M.; Patel, Nimesh; Anglada, Guillem; Gómez, José F.; Ho, Paul T. P.; Lara, L. M.; Alberdi, A.; Cantó, J.; Curiel, S.; Garay, Guido; Rodrı́guez, Luis F.

doi:10.1086/380750

Cited by 107 publications

(129 citation statements)

References 27 publications

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“…Statistical properties of the spatial distribution of water masers Using VLBA data of three epochs of water maser observations toward the SFRs Cepheus A and W75 N (Torrelles et al 2001b(Torrelles et al , 2003, we compute two-point spatial correlation functions of maser spots in the following subregions: R5 in Cepheus A, and VLA 1 and VLA 2 in W75 N. In each of these subregions, a few hundred maser spots were detected with an S/N ≥ 10 in each one of the three epochs (see Table 1). The uncertainties in the values of these functions are mainly due to position uncertainty of maser spots, which is more significant toward small separations (represented by the error bar sizes shown in Figures 1-3).…”

Section: Resultsmentioning

confidence: 99%

Statistical Analysis of Water Masers in Star-Forming Regions: Cepheus a and W75 N

Uscanga

Cantó

Gómez

et al. 2010

ApJ

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We have done a statistical analysis of Very Long Baseline Array (VLBA) data of water masers in the star-forming regions (SFRs) Cepheus A and W75 N, using correlation functions to study the spatial clustering and Doppler-velocity distribution of these masers. Two-point spatial correlation functions show a characteristic scale size for clusters of water maser spots 1 AU, similar to the values found in other SFRs. This suggests that the scale for water maser excitation tends to be 1 AU. Velocity correlation functions show power-law dependences with indices that can be explained by regular velocity fields, such as expansion and/or rotation. These velocity fields are similar to those indicated by the water maser proper-motion measurements; therefore, the velocity correlation functions appear to reveal the organized motion of water maser spots on scales larger than 1 AU. Subject headings: ISM : individual (Cepheus A) -ISM : individual (W75 N) -ISM : jets and outflows -masers -methods : statistical

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Section: Resultsmentioning

confidence: 99%

Statistical Analysis of Water Masers in Star-Forming Regions: Cepheus a and W75 N

Uscanga

Cantó

Gómez

et al. 2010

ApJ

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“…Although the scaling of the magnetic field in water maser is due to shocks, Vlemmings (2006Vlemmings ( , 2008 empirically showed that even water masers with number densities up to 10 11 cm −3 follow this relation, even if in non-masing gas of similar densities the magnetic field strengths are likely lower due to ambipolar diffusion. Hence, from the magnetic field strengths, we can determine the number density of the cloud where the H 2 O masers arise by the relation B ∝ n 0.47 .…”

Section: |mentioning

confidence: 99%

The structure of the magnetic field in the massive star-forming region W75N

Surcis

Vlemmings

Curiel

et al. 2011

A&A

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Context. A debated topic in star formation theory is the role of magnetic fields during the protostellar phase of high-mass stars. It is still unclear how magnetic fields influence the formation and dynamics of massive disks and outflows. Most current information on magnetic fields close to high-mass protostars comes from polarized maser emissions, which allows us to investigate the magnetic field on small scales by using very long-baseline interferometry. Aims. The massive star-forming region W75N contains three radio continuum sources (VLA 1, VLA 2, and VLA 3), at three different evolutionary stages, and associated masers, while a large-scale molecular bipolar outflow is also present. Very recently, polarization observations of the 6.7 GHz methanol masers at milliarsecond resolution have been able to probe the strength and structure of the magnetic field over more than 2000 AU around VLA 1. The magnetic field is parallel to the outflow, suggesting that VLA 1 is its powering source. The observations of H 2 O masers at 22 GHz can give more information about the gas dynamics and the magnetic fields around VLA 1 and VLA 2. Methods. The NRAO Very Long Baseline Array was used to measure the linear polarization and the Zeeman-splitting of the 22 GHz water masers in the star-forming region W75N. Results. We detected 124 water masers, 36 around VLA 1 and 88 around VLA 2 of W75N, which indicate two different physical environments around the two sources, where VLA 1 is in a more evolved state. The linear polarization of the masers confirms the tightly ordered magnetic field around VLA 1, which is aligned with the large-scale molecular outflow, and also reveals an ordered magnetic field around VLA 2, which is not parallel to the outflow. The Zeeman-splitting measured on 20 of the masers indicates strong magnetic fields around both sources (the averaged values are |B VLA1 | ∼ 700 mG and |B VLA2 | ∼ 1700 mG). The high values of the magnetic field strengths, which come from the shock compression of the gas, are consistent with the methanol and OH magnetic field strengths. Moreover, by studying the maser properties we were also able to determine that the water masers are pumped in C-shocks in both sources.

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“…Therefore, observational signatures of rotating disks around O-type forming stars are essential to progressing in our understanding of the mass-accretion process and to constraining theoretical models of high-mass star formation. In this context, one excellent diagnostic tool of gas kinematics within 10-1000 AU from YSOs is provided by multiepoch very long baseline interferometric (VLBI) observations of interstellar masers Goddi et al , 2011Matthews et al 2010;Moscadelli et al 2007Moscadelli et al , 2011Moscadelli et al , 2013Sanna et al 2010a,b;Torrelles et al 2003Torrelles et al , 2011. Among different molecular masers, CH 3 OH is particularly interesting, because it is exclusively associated with high-mass star formation and provides an excellent probe of accretion.…”

Section: Introductionmentioning

confidence: 99%

A multiple system of high-mass YSOs surrounded by disks in NGC 7538 IRS1

Moscadelli

Goddi

2014

A&A

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Context. It has been claimed that NGC 7538 IRS1 is a high-mass young stellar object (YSO) with 30 M , surrounded by a rotating Keplerian disk, probed by a linear distribution of methanol masers. The YSO is also powering a strong compact Hii region or ionized wind, and is driving at least one molecular outflow. The axis orientations of the different structures (ionized gas, outflow, and disk) are, however, misaligned, which has led to the different competing models proposed to explain individual structures. Aims. We investigate the 3D kinematics and dynamics of circumstellar gas with very high linear resolution, from tens to 1500 AU, with the ultimate goal of building a comprehensive dynamical model for what is considered the best high-mass accretion disk candidate around an O-type young star in the northern hemisphere. Methods. We used high-angular resolution observations of 6.7 GHz CH 3 OH masers with the EVN, NH 3 inversion lines with the JVLA B-Array, and radio continuum with the VLA A-Array. In particular, we employed four different observing epochs of EVN data at 6.7 GHz, spanning almost eight years, which enabled us to measure line-of-sight (l.o.s.) accelerations and proper motions of CH 3 OH masers, besides l.o.s. velocities and positions (as done in previous works). In addition, we imaged highly excited NH 3 inversion lines, from (6,6) to (13,13), which enabled us to probe the hottest molecular gas very close to the exciting source(s). Results. We confirm previous results that five 6.7 GHz maser clusters (labeled from "A" to "E") are distributed over a region extended N-S across ≈1500 AU, and are associated with three components of the radio continuum emission. We propose that these maser clusters identify three individual high-mass YSOs in NGC 7538 IRS1, named IRS1a (associated with clusters "B" and "C"), IRS1b (associated with cluster "A"), and IRS1c (associated with cluster "E"). We find that the 6.7 GHz masers distribute along a line, with a regular variation in V LSR with position, along the major axis of the distribution of maser cluster "A" and the combined clusters "B" + "C". A similar V LSR gradient (although shallower) is also detected in the NH 3 inversion lines. Interestingly, the variation in V LSR with projected position is not linear but quadratic for both maser clusters. We measure proper motions for 33 maser features, which have an average amplitude (4.8 ± 0.6 km s −1 ) similar to the variation in V LSR across the maser cluster, and are approximately parallel to the clusters' elongation axes. By studying the time variation in the maser spectrum, we also derive l.o.s. accelerations for 30 features, with typical amplitude of ∼10 −3 −10 −2 km s −1 yr −1 . We modeled the masers in both clusters "A" and "B" + "C" in terms of an edge-on disk in centrifugal equilibrium. Based on our modeling, masers of clusters "B" + "C" may trace a quasi-Keplerian ∼1 M , thin disk, orbiting around a high-mass YSO, IRS1a, of up to ≈25 M . This YSO dominates the bolometric luminosity of the region. The d...

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Evidence for Evolution of the Outflow Collimation in Very Young Stellar Objects

Cited by 107 publications

References 27 publications

Statistical Analysis of Water Masers in Star-Forming Regions: Cepheus a and W75 N

Statistical Analysis of Water Masers in Star-Forming Regions: Cepheus a and W75 N

The structure of the magnetic field in the massive star-forming region W75N

A multiple system of high-mass YSOs surrounded by disks in NGC 7538 IRS1

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