The Second VLBA Calibrator Survey: VCS2

Fomalont, Ed; Petrov, Leonid; MacMillan, D. S.; Gordon, D.; Ma, C.

doi:10.1086/378712

Cited by 164 publications

(154 citation statements)

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“…Its absolute position is known to better than ±2 mas, and its flux measured with the VLBA at S and X bands is 68 and 151 mJy beam −1 , respectively (Fomalont et al 2003). Five fringe finders (J1642+3948; J1751+0939; J1800+3848; J2101+0341; J2253+1608) were observed for bandpass, single-band delay, and instrumental phase-offset calibration.…”

Section: Maser Vlbimentioning

confidence: 96%

VLBI study of maser kinematics in high-mass star-forming regions

Sanna

Moscadelli

Cesaroni

et al. 2010

A&A

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Aims. We performed a detailed study of maser and radio continuum emission toward the high-mass star-forming region G23.01−0.41. This study aims at improving our knowledge of the high-mass star-forming process by comparing the gas kinematics near a newly born young stellar object (YSO), analyzed through high spatial resolution maser data, with the large-scale environment of its native hot molecular core (HMC), identified in previous interferometric observations of thermal continuum and molecular lines. Methods. Using the VLBA and the EVN arrays, we conducted phase-referenced observations of the three most powerful maser species in G23.01−0.41: H 2 O at 22.2 GHz (4 epochs), CH 3 OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1 epoch). In addition, we performed high-resolution (≥0. 1), high-sensitivity (<0.1 mJy) VLA observations of the radio continuum emission from the HMC at 1.3 and 3.6 cm. Results. We have detected H 2 O, CH 3 OH, and OH maser emission clustered within 2000 AU from the center of a flattened HMC, oriented SE-NW, from which emerges a massive 12 CO outflow, elongated NE-SW, extended up to the pc-scale. Although the three maser species show a clearly different spatial and velocity distribution and sample distinct environments around the massive YSO, the spatial symmetry and velocity field of each maser specie can be explained in terms of expansion from a common center, which possibly denotes the position of the YSO driving the maser motion. Water masers trace both a fast shock (up to 50 km s −1 ) closer to the YSO, powered by a wide-angle wind, and a slower (20 km s −1 ) bipolar jet, at the base of the large-scale outflow. Because the compact free-free emission is found offset from the putative location of the YSO along a direction consistent with that of the maser jet axis, we interpret the radio continuum in terms of a thermal jet. The velocity field of methanol masers can be explained in terms of a composition of slow (4 km s −1 in amplitude) motions of radial expansion and rotation about an axis approximately parallel to the maser jet. Finally, the distribution of line-of-sight velocities of the hydroxyl masers suggests that they can trace gas less dense (n H 2 ≤ 10 6 cm −3 ) and more distant from the YSO than that traced by the water and methanol masers, which is expanding toward the observer. A few pairs of OH masers, with different circular polarization, are well aligned in position on the sky and we interpret them as Zeeman pairs. From Zeeman splitting, the derived typical values of the magnetic field are of a few mG.

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Section: Maser Vlbimentioning

confidence: 96%

VLBI study of maser kinematics in high-mass star-forming regions

Sanna

Moscadelli

Cesaroni

et al. 2010

A&A

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“…For the best candidates, we determined their position to a sub-arcsecond accuracy to use them as a position reference in the EVN observations. Additionally, several known VLBA calibrators were used, namely: J2003+3034 and J0613+1708 (Fomalont et al 2003), J0603+215S(9) and J0613+1306 (Ma et al 1998), J0047+5657 (Beasley et al 2002), J2223+6249 (Petrov et al 2005), J0035+6130 (Petrov et al 2006), and J0606-0724 (Kovalev et al 2007). Table 2 lists the positions of the masers and their background sources.…”

Section: Observations and Data Analysismentioning

confidence: 99%

Trigonometric parallaxes of 6.7 GHz methanol masers

Rygl

Brunthaler

Reid³

et al. 2010

A&A

153

131

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Aims. Emission from the 6.7 GHz methanol maser transition is very strong, is relatively stable, has small internal motions, and is observed toward numerous massive star-forming regions in the Galaxy. Our goal is to perform high-precision astrometry using this maser transition to obtain accurate distances to their host regions. −0.06 kpc for S 255. The distances and proper motions yield the full space motions of the star-forming regions hosting the masers, and we find that these regions lag circular rotation on average by ∼17 km s −1 , a value comparable to those found recently by similar studies.

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“…Its absolute position is known to better than ±2 mas, and its flux measured with the Very Long Baseline Array (VLBA) at S and X bands is 48 and 112 mJy beam −1 , respectively (Fomalont et al 2003). Five fringe finders (J1642+3948; J1751+0939; J1800+3848; J2101+0341; J2253+1608) were observed for bandpass, singleband delay, and instrumental phase-offset calibration.…”

Section: Maser Vlbimentioning

confidence: 99%

VLBI study of maser kinematics in high-mass star-forming regions

Sanna

Moscadelli

Cesaroni

et al. 2010

A&A

View full text Add to dashboard Cite

Aims. To study the high-mass star-forming process, we started a large project to unveil the gas kinematics close to young stellar objects (YSOs) through the Very Long Baseline Interferometry (VLBI) of maser associations. By comparing the high spatial resolution maser data that traces the inner kinematics of the (proto)stellar cocoon with interferometric thermal data that traces the large-scale environment of the hot molecular core (HMC) harboring the (proto)stars, we can investigate the nature and identify the sources of large-scale motions. The present paper focuses on the high-mass star-forming region G16.59-0.05. Methods. Using the VLBA and the EVN arrays, we conducted phase-referenced observations of the three most powerful maser species in G16.59-0.05: H 2 O at 22.2 GHz (4 epochs), CH 3 OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1 epoch). In addition, we performed high-resolution (≥0. 1), high-sensitivity (<0.1 mJy) VLA observations of the radio continuum emission from the starforming region at 1.3 and 3.6 cm.Results. This is the first work to report accurate measurements of the relative proper motions of the 6.7 GHz CH 3 OH masers. The different spatial and 3-D velocity distributions clearly indicate that the 22 GHz water and 6.7 GHz methanol masers trace different kinematic environments. The bipolar distribution of 6.7 GHz maser line-of-sight velocities and the regular pattern of observed proper motions suggest that these masers are tracing rotation around a central mass of about 35 M . The flattened spatial distribution of the 6.7 GHz masers, oriented NW−SE, suggests that they can originate in a disk/toroid rotating around the massive YSO that drives the 12 CO (2−1) outflow, oriented NE−SW, observed on an arcsec scale. The extended, radio continuum source observed close to the 6.7 GHz masers could be excited by a wide-angle wind emitted from the YSO associated with the methanol masers, and such a wind has proven to be energetic enough to drive the NE−SW 12 CO (2−1) outflow. The H 2 O masers are distributed across a region offset about 0. 5 to the NW of the CH 3 OH masers, in the same area as where the emission of high-density molecular tracers, typical of HMCs, was detected. We postulate that a distinct YSO, possibly in an earlier evolutionary phase than what excites the methanol masers, is responsible for the excitation of the water masers and the HMC molecular lines.

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The Second VLBA Calibrator Survey: VCS2

Cited by 164 publications

References 5 publications

VLBI study of maser kinematics in high-mass star-forming regions

VLBI study of maser kinematics in high-mass star-forming regions

Trigonometric parallaxes of 6.7 GHz methanol masers

VLBI study of maser kinematics in high-mass star-forming regions

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