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The role of massive (≥ 8 |$\, {\rm M}_{\odot }$|⁠) stars in defining the energy budget and chemical enrichment of the interstellar medium in their host galaxy is significant. In this first paper from the Tracing Evolution in Massive Protostellar Objects (TEMPO) project we introduce a colour-luminosity selected (L* ∼ 3 × 103 to 1 × 105 L⊙) sample of 38 massive star-forming regions observed with ALMA at 1.3 mm and explore the fragmentation, clustering, and flux density properties of the sample. The TEMPO sample fields are each found to contain multiple fragments (between 2 and 15 per field). The flux density budget is split evenly (53 per cent–47 per cent) between fields where emission is dominated by a single high flux density fragment and those in which the combined flux density of fainter objects dominates. The fragmentation scales observed in most fields are not comparable with the thermal Jeans length, λ J , being larger in the majority of cases, suggestive of some non-thermal mechanism. A tentative evolutionary trend is seen between luminosity of the clump and the 'spectral line richness' of the TEMPO fields; with 6.7 GHz maser associated fields found to be lower luminosity and more line rich. This work also describes a method of line-free continuum channel selection within ALMA data and a generalized approach used to distinguishing sources which are potentially star-forming from those which are not, utilizing interferometric visibility properties. [ABSTRACT FROM AUTHOR]

We present high-angular resolution observations of OH maser emission towards the high-mass star-forming region IRAS 06056+2131. The observations were carried out using the UK radio interferometer array, Multi-Element Radio Linked Interferometer Network (MERLIN) in the OH main lines at 1665 and 1667 MHz, in addition to the OH satellite line at 1720 MHz. The results of this study reveal the small upper limit to the size of emission in the 1665-MHz line with an estimated total intensity of ∼4 Jy. We did not detect any emission from the 1667 and 1720-MHz lines. The full polarization mode of MERLIN enables us to investigate the magnetic field in the OH maser region. In this transition, a Zeeman pair is identified from which a magnetic strength of ∼−1.5 mG is inferred. Our results show that IRAS 06056+2131 is highly polarized, with ∼ 96 |${{\ \rm per\ cent}}$| circular polarization and ∼6 |${{\ \rm per\ cent}}$| linear polarization. The linear polarization angle is ∼29°, implying a magnetic field which could be aligned with the outflow direction detected towards this region, but the actual magnetic field direction has an uncertainty of up to 110° due to the possible effects of Faraday rotation. The star-forming evolutionary status of the embedded protostellar object is discussed. [ABSTRACT FROM AUTHOR]

We investigate the kinematics of high-mass protostellar objects within the high-mass star-forming region IRAS 19410+2336. We performed high angular resolution observations of 6.7-GHz methanol and 22 GHz water masers using the Multi-Element Radio Linked Interferometer Network (MERLIN) and e-MERLIN interferometers. The 6.7-GHz methanol maser emission line was detected within the ∼16–27 km s−1 velocity range with a peak flux density ∼50 Jy. The maser spots are spread over ∼1.3 arcsec on the sky, corresponding to ∼2800 au at a distance of 2.16 kpc. These are the first astrometric measurements at 6.7 GHz in IRAS 19410+2336. The 22-GHz water maser line was imaged in 2005 and 2019 (the latter with good astrometry). Its velocities range from 13 to ∼29 km s−1. The peak flux density was found to be 18.7 and 13.487 Jy in 2005 and 2019, respectively. The distribution of the water maser components is up to 165 mas, ∼350 au at 2.16 kpc. We find that the Eastern methanol masers most probably trace outflows from the region of millimetre source mm1. The water masers to the West lie in a disc (flared or interacting with outflow/infall) around another more evolved millimetre source (13-s). The maser distribution suggests that the disc lies at an angle of 60° or more to the plane of the sky and the observed line-of-sight velocities then suggest an enclosed mass between 44 M⊙ and as little as 11 M⊙ if the disc is edge-on. The Western methanol masers may be infalling. [ABSTRACT FROM AUTHOR]

Context. Circumstellar discs around massive stars could mediate the accretion onto the star from the infalling envelope, and could minimize the effects of radiation pressure. Despite such a crucial role, only a few convincing candidates have been provided for discs around deeply embedded O-type (proto)stars. Aims. In order to establish whether disc-mediated accretion is the formation mechanism for the most massive stars, we have searched for circumstellar, rotating discs around a limited sample of six luminous (>105 L⊙) young stellar objects. These objects were selected on the basis of their IR and radio properties in order to maximize the likelihood of association with disc+jet systems. Methods. We used ALMA with ~0".2 resolution to observe a large number of molecular lines typical of hot molecular cores. In this paper we limit our analysis to two disc tracers (methyl cyanide, CH3CN, and its isotopologue, 13CH3CN), and an outflow tracer (silicon monoxide, SiO). Results. We reveal many cores, although their number depends dramatically on the target. We focus on the cores that present prominent molecular line emission. In six of these a velocity gradient is seen across the core, three of which show evidence of Keplerian-like rotation. The SiO data reveal clear but poorly collimated bipolar outflow signatures towards two objects only. This can be explained if real jets are rare (perhaps short-lived) in very massive objects and/or if stellar multiplicity significantly affects the outflow structure. For all cores with velocity gradients, the velocity field is analysed through position-velocity plots to establish whether the gas is undergoing rotation with 3rot ∝ R-α, as expected for Keplerian-like discs. Conclusions. Our results suggest that in three objects we are observing rotation in circumstellar discs, with three more tentative cases, and one core where no evidence for rotation is found. In all cases but one, we find that the gas mass is less than the mass of any embedded O-type star, consistent with the (putative) discs undergoing Keplerian-like rotation. With the caveat of low number statistics, we conclude that the disc detection rate could be sensitive to the evolutionary stage of the young stellar object. In young, deeply embedded sources, the evidence for discs could be weak because of confusion with the surrounding envelope, while in the most evolved sources the molecular component of the disc could have already been dispersed. Only in those objects that are at an intermediate stage of the evolution would the molecular disc be sufficiently prominent and relatively less embedded to be detectable by mm/submm observations. [ABSTRACT FROM AUTHOR]

Context. Theoretical scenarios propose that high-mass stars are formed by disk-mediated accretion. Aims. To test the theoretical predictions on the formation of massive stars, we wish to make a thorough study at high-angular resolution of the structure and kinematics of the dust and gas emission toward the high-mass star-forming region G35.03+0.35, which harbors a disk candidate around a B-type (proto)star. Methods. We carried out ALMA Cycle 0 observations at 870 μm of dust of typical high-density, molecular outflow, and cloud tracers with resolutions of <0.''5. Complementary Subaru COMICS 25 μm observations were carried out to trace the mid-infrared emission toward this star-forming region. Results. The submillimeter continuum emission has revealed a filamentary structure fragmented into six cores, called A-F. The filament could be in quasi-equilibrium taking into account that the mass per unit length of the filament, 200-375 M☉/pc, is similar to the critical mass of a thermally and turbulently supported infinite cylinder, ∼335 M☉/pc. The cores, which are on average separated by ∼0.02 pc, have deconvolved sizes of 1300-3400 AU, temperatures of 35-240 K, H2 densities >107 cm -3, and masses in the range 1-5 M☉, and they are subcritical. Core A, which is associated with a hypercompact Hii region and could be the driving source of the molecular outflow observed in the region, is the most chemically rich source in G35.03+0.35 with strong emission of typical hot core tracers such as CH3CN. Tracers of high density and excitation show a clear velocity gradient along the major axis of the core, which is consistent with a disk rotating about the axis of the associated outflow. The PV plots along the SE-NW direction of the velocity gradient show clear signatures of Keplerian rotation, although infall could also be present, and they are consistent with the pattern of an edge-on Keplerian disk rotating about a star with a mass in the range 5-13 M☉. The high tff/trot ratio for core A suggests that the structure rotates fast and that the accreting material has time to settle into a centrifugally supported disk. Conclusions. G35.03+0.35 is one of the most convincing examples of Keplerian disks rotating about high-mass (proto)stars. This supports theoretical scenarios according to which high-mass stars, at least B-type stars, would form through disk-mediated accretion. [ABSTRACT FROM AUTHOR]

Context. The formation process of high-mass stars (with masses >8 M☉) is still poorly understood, and represents a challenge from both the theoretical and observational points of view. The advent of the Atacama Large Millimeter Array (ALMA) is expected to provide observational evidence to better constrain the theoretical scenarios. Aims. The present study aims at characterizing the high-mass star forming region G35.20-0.74 N, which is found associated with at least one massive outflow and contains multiple dense cores, one of them recently found associated with a Keplerian rotating disk. Methods. We used the radio-interferometer ALMA to observe the G35.20-0.74 N region in the submillimeter continuum and line emission at 350 GHz. The observed frequency range covers tracers of dense gas (e.g., H13CO+, C17O), molecular outflows (e.g., SiO), and hot cores (e.g., CH3CN, CH3OH). These observations were complemented with infrared and centimeter data. Results. The ALMA 870 μm continuum emission map reveals an elongated dust structure (∼0.15 pc long and ∼0.013 pc wide; full width at half maximum) perpendicular to the large-scale molecular outflow detected in the region, and fragmented into a number of cores with masses ∼1-10 M☉ and sizes ∼1600 AU (spatial resolution ∼960 AU). The cores appear regularly spaced with a separation of ∼0.023 pc. The emission of dense gas tracers such as H13CO+, C17O is extended and coincident with the dust elongated structure. The three strongest dust cores show emission of complex organic molecules characteristic of hot cores, with temperatures around 200 K, and relative abundances 0.2-2 × 10-8 for CH3CN and 0.6-5 × 10-6 for CH3OH. The two cores with highest mass (cores A and B) show coherent velocity fields, with gradients almost aligned with the dust elongated structure. Those velocity gradients are consistent with Keplerian disks rotating about central masses of 4-18 M☉. Perpendicular to the velocity gradients we have identified a large-scale precessing jet/outflow associated with core B, and hints of an east-west jet/outflow associated with core A. Conclusions. The elongated dust structure in G35.20-0.74 N is fragmented into a number of dense cores that may form high-mass stars. Based on the velocity field of the dense gas, the orientation of the magnetic field, and the regularly spaced fragmentation, we interpret this elongated structure as the densest part of a 1D filament fragmenting and forming high-mass stars. [ABSTRACT FROM AUTHOR]

We report on ALMA observations of continuum and molecular line emission with 0."4 resolution towards the high-mass star-forming region G35.20-0.74 N. Two dense cores are detected in typical hot-core tracers (e.g., CH3CN) that reveal velocity gradients. In one of these cores, the velocity field can be fitted with an almost edge-on Keplerian disk rotating about a central mass of ~18 M⊙. This finding is consistent with the results of a recent study of the CO first overtone bandhead emission at 2.3 μm towards G35.20-0.74 N. The disk radius and mass are ≳2500 au and ~3 M⊙. To reconcile the observed bolometric luminosity (~3 × 104 L⊙) with the estimated stellar mass of 18 M⊙, we propose that the latter is the total mass of a binary system. [ABSTRACT FROM AUTHOR]

We report on ALMA observations of continuum and molecular line emission with 0". 4 resolution towards the high-mass star-forming region G35.20-0.74 N. Two dense cores are detected in typical hot-core tracers (e.g., CH3CN) that reveal velocity gradients. In one of these cores, the velocity field can be fitted with an almost edge-on Keplerian disk rotating about a central mass of ~18 M☉. This finding is consistent with the results of a recent study of the CO first overtone bandhead emission at 2.3 μm towards G35.20-0.74 N. The disk radius and mass are ≳2500 au and ~3 M☉. To reconcile the observed bolometric luminosity (~3×104 L☉) with the estimated stellar mass of 18 M☉, we propose that the latter is the total mass of a binary system. [ABSTRACT FROM AUTHOR]

ABSTRACT MERLIN phase-referenced polarimetric observations towards the W51 complex were carried out in 2006 March in the Class II methanol maser transition at 6.668 GHz and three of the four excited OH maser hyperfine transitions at 6 GHz. Methanol maser emission is found towards both W51 Main and South. We did not detect any emission in the excited OH maser lines at 6.030 and 6.049 GHz down to a 3σ limit of ∼20 mJy beam−1. Excited OH maser emission at 6.035 GHz is only found towards W51 Main. This emission is highly circularly polarized (typically ≥45 per cent and up to 87 per cent). Seven Zeeman pairs were identified in this transition, one of which contains detectable linear polarization. The magnetic field strength derived from these Zeeman pairs ranges from +1.6 to +6.8 mG, consistent with the previously published magnetic field strengths inferred from the OH ground-state lines. The bulk of the methanol maser emission is associated with W51 Main, sampling a total area of ∼3 × 2.2 arcsec2 (i.e. ∼16 200 × 11 900 au), while only two maser components, separated by ∼2.5 arcsec, are found in the W51 South region. The astrometric distributions of both 6.668-GHz methanol and 6.035-GHz excited-OH maser emission in the W51 Main/South region are presented here. The methanol masers in W51 Main show a clear coherent velocity and spatial structure with the bulk of the maser components distributed into two regions showing a similar conical opening angle with a central velocity of ∼+55.5 km s−1 and an expansion velocity of ≤5 km s−1. The mass contained in this structure is estimated to be at least 22 M⊙. The location of maser emission in the two aforementioned lines is compared with that of previously published OH ground-state emission. The association with the ultra-compact H ii regions in the W51 Main/South complex and the relationship of the masers to infall or outflow in the region are discussed. [ABSTRACT FROM AUTHOR]

Multi-Element Radio-Linked Interferometer Network polarization measurements of the OH 1.7- and 6.0-GHz, and the H2O 22-GHz masers in the massive star-forming region S140-IRS1 are presented. The observations were taken with astrometric accuracy of 15–30 mas. OH maser emission has been detected only in the ground-state 1665-MHz line. The OH masers are located approximately 2.5 arcsec north-west of IRS1. They lie in two distinct regions separated by approximately 1 arcsec along a north-east/south-west axis. Analysis of the OH maser polarization yields a magnetic field of mG, directed towards us. The polarization position angles attest to a magnetic field which is preferentially orientated along the direction of the CO outflow associated with IRS1. The brightest H2O masers coincide in position with IRS1 and show a gradient of increasing Doppler velocity from north-west to south-east. These water masers also have proper motions of ∼18 km s−1 in a similar direction. The closest OH and H2O masers are separated by more than 2 arcsec. H2O masers have also been detected at several locations up to ≈0.5 arcmin distance, where masers have not previously been reported. The relationships between our maser observations, the central engine/object of IRS1 and the multiple outflows detected by observations at other wavelengths are also discussed. [ABSTRACT FROM AUTHOR]

We present single-baseline Multi-Element Radio-Linked Interferometer Network (MERLIN) measurements of excited OH 6.0-GHz masers and methanol 6.7-GHz masers for the source W3(OH). These allow us to compare the positions of individual maser spots of these two species to∼15 mas accuracy for the first time, and to compare these with previously published positions of ground-state OH masers near 1.7 GHz and excited-state OH masers near 4.7 GHz. There is a strong association between OH 6035-MHz and 1665-MHz masers. OH and methanol have very similar distributions, but associations of individual masers are relatively rare: most methanol 6.7-GHz masers are within 100 mas of OH 6.0-GHz masers, but only four methanol masers are within 15 mas of an OH 6.0-GHz maser. There are no correspondences of either species with excited OH 4.7-GHz masers. Zeeman splitting of the 6.0-GHz OH lines indicates an ordered magnetic field ranging from 3.2 to 14.4 mG. The magnetic fields estimated from co-propagating masers such as 6035 and 1665 MHz are generally in good agreement with each other. [ABSTRACT FROM AUTHOR]

W49 A is a star-forming region (SFR) found in the constellation of Aquila. It contains 3 active regions: W49 North (W49 N), W49 South West (W49 SW) and W49 South (W49 S). We present preliminary results from two epochs (e-)MERLIN observations of all ground-state OH masers towards the star-forming region (SFR) complex W49 A. The first epoch of observations was done in full-polarization mode with MERLIN in 2005 while the second epoch was obtained only in dual circular polarization during the test observations of the upgraded e-MERLIN in 2013. The overall maser spatial distributions in both epochs are in good agreement. We found several new high velocity maser features up to +34 km s−1 and −28 km s−1. The magnetic field strengths are between 1.1 to 10.8 mG. All three sources show evidence of magnetic field reversal. [ABSTRACT FROM AUTHOR]

High angular resolution observations are essential for understanding the nature of maser emission and the sources which excite it. Here we present preliminary results from MERLIN observations of three methanol masers from the Toruń survey. These MERLIN observations are being analysed as part of the interferometric component of the Methanol Multibeam (MMB) Survey which is surveying the Galactic plane at |b|≤2° for 6.67 GHz methanol maser sources. [ABSTRACT FROM PUBLISHER]