OH masers and magnetic fields in the bipolar outflow source W75N

Hutawarakorn, B.; Cohen, R. J.; Brebner, G. C.

doi:10.1046/j.1365-8711.2002.05068.x

Cited by 69 publications

(102 citation statements)

References 38 publications

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“…The magnetic field strength obtained from the OH maser polarization observations was ∼7 mG (e.g., Hutawarakorn et al 2002;Slysh et al 2002). During the OH maser flare near VLA 2, Slysh & Migenes (2006) detected a strong magnetic field of more than 40 mG in several maser spots, which increased in the next observations up to 70 mG (Slysh et al 2010).…”

Section: Introductionmentioning

confidence: 98%

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

Surcis

Vlemmings

Curiel

et al. 2011

A&A

106

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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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Section: Introductionmentioning

confidence: 98%

“…In order to determine and investigate the magnetic field of W75N(B), polarization observations of OH and CH 3 OH maser emissions have been made (e.g., Hutawarakorn et al 2002;Fish & Reid 2007;S09). The magnetic field strength obtained from the OH maser polarization observations was ∼7 mG (e.g., Hutawarakorn et al 2002;Slysh et al 2002).…”

Section: Introductionmentioning

confidence: 99%

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

Surcis

Vlemmings

Curiel

et al. 2011

A&A

106

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“…For example the polarization of the OH masers of W75N matches a toroidal field in a massive torus or disk (e.g. Hutawarakorn et al 2002;Gray et al 2003). The H 2 O masers Table 2 and Figs.…”

Section: Introductionmentioning

confidence: 99%

Zeeman splitting of 6.7 GHz methanol masers

Vlemmings

Torres

Dodson

2011

A&A

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Context. To properly determine the role of magnetic fields during massive star formation, a statistically significant sample of field measurements probing different densities and regions around massive protostars needs to be established. However, relating Zeeman splitting measurements to magnetic field strengths needs a carefully determined splitting coefficient. Aims. Polarization observations of, in particular, the very abundant 6.7 GHz methanol maser, indicate that these masers appear to be good probes of the large scale magnetic field around massive protostars at number densities up to n H 2 ≈ 10 9 cm −3 . We thus investigate the Zeeman splitting of the 6.7 GHz methanol maser transition. Methods. We have observed of a sample of 46 bright northern hemisphere maser sources with the Effelsberg 100-m telescope and an additional 34 bright southern masers with the Parkes 64-m telescope in an attempt to measure their Zeeman splitting. We also revisit the previous calculation of the methanol Zeeman splitting coefficients and show that these were severely overestimated making the determination of magnetic field strengths highly uncertain. Results. In total 44 of the northern masers were detected and significant splitting between the right-and left-circular polarization spectra is determined in >75% of the sources with a flux density >20 Jy beam −1 . Assuming the splitting is due to a magnetic field according to the regular Zeeman effect, the average detected Zeeman splitting corrected for field geometry is ∼0.6 m s −1 . Using an estimate of the 6.7 GHz A-type methanol maser Zeeman splitting coefficient based on old laboratory measurements of 25 GHz E-type methanol transitions this corresponds to a magnetic field of ∼120 mG in the methanol maser region. This is significantly higher than expected using the typically assumed relation between magnetic field and density (B ∝ n 0.47 H 2 ) and potentially indicates the extrapolation of the available laboratory measurements is invalid. The stability of the right-and left-circular calibration of the Parkes observations was insufficient to determine the Zeeman splitting of the Southern sample. Spectra are presented for all sources in both samples.Conclusions. There is no strong indication that the measured splitting between right-and left-circular polarization is due to nonZeeman effects, although this cannot be ruled out until the Zeeman coefficient is properly determined. However, although the 6.7 GHz methanol masers are still excellent magnetic field morphology probes through linear polarization observations, previous derivations of magnetic fields strength turn out to be highly uncertain. A solution to this problem will require new laboratory measurements of the methanol Landé-factors.

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“…Several mid-to-early B stars are being formed in this region. It contains a subregion, W75 N (B), which comprises a cluster of ultracompact H ii regions and millimeter wavelength sources powering multiple outflows (Haschick et al 1981;Hunter et al 1994;Shepherd 2001;Hutawarakorn, Cohen, & Brebner 2002;Slysh et al 2002;Shepherd, Kurtz, & Testi 2003a;Shepherd, Testi, & Stark 2003b). Using the Very Large Array (VLA) in 1996, we simultaneously imaged, with 0Љ .1 resolution, the water vapor maser and continuum emission at 1.3 cm from MM1, the most massive of the millimeter cores in W75 N (B).…”

Section: Introductionmentioning

confidence: 99%

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

Torrelles

Patel

Anglada

et al. 2003

ApJ

107

119

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We present Very Long Baseline Array proper-motion measurements of water masers toward two young stellar objects (YSOs) of the W75 N star-forming region. We find that these two objects are remarkable for having a similar spectral type, being separated by 0Љ .7 (corresponding to 1400 AU), and sharing the same environment, but with a strikingly different outflow ejection geometry. One source has a collimated, jetlike outflow at a 2000 AU scale, while the other has a shell outflow at a 160 AU scale expanding in multiple directions with respect to a central compact radio continuum source. This result reveals that outflow collimation is not only a consequence of ambient conditions but is something intrinsic to the individual evolution of stars and brings to light the possibility of noncollimated outflows in the earliest stages of YSOs.

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OH masers and magnetic fields in the bipolar outflow source W75N

Cited by 69 publications

References 38 publications

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

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

Zeeman splitting of 6.7 GHz methanol masers

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

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