Methanol and water masers in IRAS 20126+4104: the distance, the disk, and the jet

Abstract

Context. Knowledge of the distance to high-mass star forming regions is crucial to obtain accurate luminosity and mass estimates of young OB-type (proto)stars and thus better constrain their nature and age. IRAS 20126+4104 is a special case, being the best candidate of a high-mass (proto)star surrounded by an accretion disk. Such a fact may be used to set constraints on theories of highmass star formation, but requires confirmation that the mass and luminosity of IRAS 20126+4104 are indeed typical of a B0.5 star, which in turn requires an accurate estimate of the distance. Aims. The goal of our study is twofold: to determine the distance to IRAS 20126+4104, using the parallax of H 2 O masers associated with the source, and unveil the 3D velocity field of the disk, through proper motion measurements of the 6.7 GHz CH 3 OH masers. At the same time, we can also obtain an estimate of the systemic velocity in the plane of the sky of the disk+star system. Methods. We used the Very Long Baseline Array and the European VLBI Network to observe the 22.2 GHz H 2 O and 6.7 GHz CH 3 OH masers in IRAS 20126+4104 at a number of epochs suitably distributed in time. The absolute positions of the maser features were established with respect to reference quasars, which allowed us to derive absolute proper motions. Results. From the parallax of the H 2 O masers we obtain a distance of 1.64 ± 0.05 kpc, which is very similar to the value adopted so far in the literature (1.7 kpc) and confirms that IRAS 20126+4104 is a high-mass (proto)star. From the CH 3 OH masers we derive the component in the plane of the sky of the systemic velocity of the disk+star system (−16 km s −1 in right-ascension and +7.6 km s −1 in declination). Accurate knowledge of the distance and systemic velocity allows us to improve on the model fit to the H 2 O maser jet presented in a previous study. Finally, we identify two groups of CH 3 OH maser features, one undergoing rotation in the disk and possibly distributed along a narrow ring centered on the star, the other characterised by relative proper motions indicating that the features are moving away from the disk, perpendicular to it. We speculate that the latter group might be tracing the disk material marginally entrained by the jet. Conclusions. VLBI multi-epoch observations with phase referencing are confirmed to be an excellent tool for distance determinations and for the investigation of the structure and 3D velocity field within a few 100 AU from newly born high-mass stars.

Chemistry of massive young stellar objects with a disk-like structure

“…The G31 hot molecular core (HMC) is part of a complex region in which multiple stellar sources are detected (Benjamin et al 2003); indeed, it is separated from an ultracompact (UC) HII region by only ∼5 and overlaps with a diffuse halo of freefree emission, possibly associated with the UC HII region itself (Cesaroni et al 1998). More recent interferometric observations confirm the velocity gradient in the NH 3 (4,4) inversion transition and in CH 3 CN data (Cesaroni et al 2010(Cesaroni et al , 2011. Line profiles look like a rotating toroid with infall motion.…”

“…Observations of CH 3 CN transitions show a References. (a) Cesaroni et al (1997), (b) Moscadelli et al (2011), (c) Leurini et al (2007), (d) Sridharan et al (2002), (e) Xu et al (2011), ( f ) Cesaroni et al (1994b), (g) Churchwell et al (1990), (h) Fontani et al (2007).…”

A double-jet system in the G31.41 + 0.31 hot molecular core

“…Assuming that in G31.41+0.31 (as verified in several sources, Moscadelli et al 2010Moscadelli et al , 2011Sanna et al 2010a,b) methanol masers move (with respect to the star) significantly slower than the water masers, we can use the absolute proper motion of the methanol masers to correct the absolute proper motion of the water masers. The result should be a good approximation of the water maser velocities with respect to the reference system comoving with the star.…”

Probing the envelopes of massive young stellar objects with diffraction limited mid-infrared imaging

“…These findings associate the MIR emission of massive YSOs with outflow cavities, rather than circumstellar discs. Nevertheless, the kinematic diversity of methanol masers in a large sample of massive outflow sources does not support a uniquely identifiable source within the close MYSO environment (Cyganowski et al 2009;Moscadelli et al 2011). Therefore, the source of the MIR emission of MYSOs has yet to be conclusively established.…”