Context. Theory predicts, and observations confirm, that the column density ratio of a molecule containing D to its counterpart containing H can be used as an evolutionary tracer in the low-mass star formation process. Aims. Since it remains unclear if the high-mass star formation process is a scaled-up version of the low-mass one, we investigated whether the relation between deuteration and evolution can be applied to the high-mass regime. Methods. With the IRAM-30 m telescope, we observed rotational transitions of N 2 D + and N 2 H + and derived the deuterated fraction in 27 cores within massive star-forming regions understood to represent different evolutionary stages of the massive-star formation process.Results. The abundance of N 2 D + is higher at the pre-stellar/cluster stage, then drops during the formation of the protostellar object(s) as in the low-mass regime, remaining relatively constant during the ultra-compact HII region phase. The objects with the highest fractional abundance of N 2 D + are starless cores with properties very similar to typical pre-stellar cores of lower mass. The abundance of N 2 D + is lower in objects with higher gas temperatures as in the low-mass case but does not seem to depend on gas turbulence. Conclusions. Our results indicate that the N 2 D + -to-N 2 H + column density ratio can be used as an evolutionary indicator in both lowand high-mass star formation, and that the physical conditions influencing the abundance of deuterated species likely evolve similarly during the processes that lead to the formation of both low-and high-mass stars.

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

Context High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2 (hereafter Mon R2), at a distance of 830 pc, harbors one of the closest such systems, making it an excellent target for case studies. Aims We investigate the morphology, stability and dynamical properties of the Mon R2 hub-filament system. Methods We employ observations of the 13CO and C18O 1→0 and 2→1 lines obtained with the IRAM-30m telescope. We also use H2 column density maps derived from Herschel dust emission observations. Results We identified the filamentary network in Mon R2 with the DisPerSE algorithm and characterized the individual filaments as either main (converging into the hub) or secondary (converging to a main filament) filaments. The main filaments have line masses of 30–100 M⊙ pc−1 and show signs of fragmentation, while the secondary filaments have line masses of 12–60 M⊙ pc−1 and show fragmentation only sporadically. In the context of Ostriker’s hydrostatic filament model, the main filaments are thermally supercritical. If non-thermal motions are included, most of them are trans-critical. Most of the secondary filaments are roughly transcritical regardless of whether non-thermal motions are included or not. From the morphology and kinematics of the main filaments, we estimate a mass accretion rate of 10−4–10−3 M⊙ yr−1 into the central hub. The secondary filaments accrete into the main filaments with a rate of 0.1–0.4×10−4 M⊙ yr−1. The main filaments extend into the central hub. Their velocity gradients increase towards the hub, suggesting acceleration of the gas.We estimate that with the observed infall velocity, the mass-doubling time of the hub is ~ 2:5 Myr, ten times larger than the free-fall time, suggesting a dynamically old region. These timescales are comparable with the chemical age of the Hii region. Inside the hub, the main filaments show a ring- or a spiral-like morphology that exhibits rotation and infall motions. One possible explanation for the morphology is that gas is falling into the central cluster following a spiral-like pattern.

Context. We present an initial overview of the filamentary structure in the Orion A molecular cloud utilizing a high angular and velocity resolution C18O(1–0) emission map that was recently produced as part of the CARMA-NRO Orion Survey. Aims. The main goal of this study is to build a credible method to study varying widths of filaments which has previously been linked to star formation in molecular clouds. Due to the diverse star forming activities taking place throughout its ~20 pc length, together with its proximity of 388 pc, the Orion A molecular cloud provides an excellent laboratory for such an experiment to be carried out with high resolution and high sensitivity. Methods. Using the widely-known structure identification algorithm, DisPerSE, on a three-dimensional (PPV) C18O cube, we identify 625 relatively short (the longest being 1.74 pc) filaments over the entire cloud. We studied the distribution of filament widths using FilChaP, a python package that we have developed and made publicly available. Results. We find that the filaments identified in a two square-degree PPV cube do not overlap spatially, except for the complex OMC-4 region that shows distinct velocity components along the line of sight. The filament widths vary between 0.02 and 0.3 pc depending on the amount of substructure that a filament possesses. The more substructure a filament has, the larger is its width. We also find that despite this variation, the filament width shows no anticorrelation with the central column density which is in agreement with previous Herschel observations.

Context. Atacama Large Millimeter/submillimeter Array (ALMA) observations of the high-mass star-forming region G35.20−0.74N have revealed the presence of a Keplerian disk in core B rotating about a massive object of 18 M⊙, as computed from the velocity field. The luminosity of such a massive star would be comparable to (or higher than) the luminosity of the whole star-forming region. To solve this problem it has been proposed that core B could harbor a binary system. This could also explain the possible precession of the radio jet associated with this core, which has been suggested by its S-shaped morphology. Aims. We establish the origin of the free-free emission from core B and investigate the existence of a binary system at the center of this massive core and the possible precession of the radio jet. Methods. We carried out VLA continuum observations of G35.20−0.74N at 2 cm in the B configuration and at 1.3 cm and 7 mm in the A and B configurations. The bandwidth at 7 mm covers the CH3OH maser line at 44.069 GHz. Continuum images at 6 and 3.6 cm in the A configuration were obtained from the VLA archive. We also carried out VERA observations of the H2O maser line at 22.235 GHz.Results. The observations have revealed the presence of a binary system of UC/HC Hii regions at the geometrical center of the radio jet in G35.20−0.74N. This binary system, which is associated with a Keplerian rotating disk, consists of two B-type stars of 11 and 6 M⊙. The S-shaped morphology of the radio jet has been successfully explained as being due to precession produced by the binary system. The analysis of the precession of the radio jet has allowed us to better interpret the IR emission in the region, which would be not tracing a wide-angle cavity open by a single outflow with a position angle of ∼55 • , but two different flows: a precessing one in the NE-SW direction associated with the radio jet, and a second one in an almost E-W direction. Comparison of the radio jet images obtained at different epochs suggests that the jet is expanding at a maximum speed on the plane of the sky of 300 km s −1 . The proper motions of the H2O maser spots measured in the region also indicate expansion in a direction similar to that of the radio jet. Conclusions. We have revealed a binary system of high-mass young stellar objects embedded in the rotating disk in G35.20−0.74N. The presence of a massive binary system is in agreement with the theoretical predictions of high-mass star formation, according to which the gravitational instabilities during the collapse would produce the fragmentation of the disk and the formation of such a system. For the first time, we have detected a high-mass young star associated with an UC/HC Hii region and at the same time powering a radio jet.