Disks around O-type young stellar objects

Accretion disks are one of the key ingredients of the star formation process. They redistribute angular momentum and, in the case of high-mass stars (M > 8Msun), disks would relieve the radiation pressure on the accreting material, in particular in the equatorial direction, by beaming the radiation through the poles of the system and this would allow the accretion to proceed onto the central protostar (e.g., Tan et al. 2014 for a review on massive star formation). In fact, in recent years, all high-mass star-forming theories appear to converge to a disk-mediated accretion scenario (e.g., Krumholz et al. 2007; Kuiper et al. 2011; Bonnell & Bate 2006; Keto 2007) but do the observations of high-mass young stellar objects (YSOs) confirm the theory predictions? Or in other words, do true accretion disks around massive stars really exist

Accretion disks in luminous young stellar objects

An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and, therefore, predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates

Massive star-formation in G24.78+0.08 studied by means of maser VLBI and thermal interferometric observations

This work presents the results of VLBI observations of 6.7 GHz methanol and 22.2 GHz water masers towards the mm core A in the massive star-forming region G24.78+0.08. Comparing the maser with previous millimeter interferometric and recent continuum VLA observations, the physical properties and the gas kinematics of the G24 A core on linear scales from ~100 AU to ~0.1 pc are determined

Development Plan Study for Optimization and Production Engineering of Band 2+3 Prototype Components for ALMA Receivers INAF Mid Term Report

Scope of this document is to report the activity @ INAF in relation to the work of the collaboration agreement No.74288/16/8223/OSZ entitled ‘Band 2+3 Prototype Passive Components for ALMA Receiver’ for the Development Advanced Study for upgrades of the Atacama Large Millimeter / Submillimeter Array(ALMA). Specifically, this release covers the activities performed in agreement with the Statement of Work [AD2] from Kick-off to up to now and serve as activity report for the Mid Term Revie

In-depth study of the hypercompact H II region G24.78+0.08 A1

Context. The earliest phases of the evolution of a massive star are closely related to the developement of an H II region. Hypercompact H II regions are the most interesting in this respect because they are very young, and hence best suited to study the beginning of the expansion of the ionised gas inside the parental core. Aims: We have analysed the geometrical and physical structure of the hypercompact H II region G24.78+0.08 A1, making use of new continuum and hydrogen recombination line data (H41α, H63α, H66α, H68α) and data from the literature (H30α, H35α). Methods: We fit the continuum spectrum with a homogenous, isothermal shell of ionised gas at 104 K and derive the size of the H II region and the Lyman continuum luminosity of the ionising star. We also fit the recombination line spectra emitted from the same shell with a model taking into account expansion at constant speed. Results: The best fits to the continuum and line spectra allow the derivation of the Lyman continuum luminosity of the ionising star, H II region size, geometrical thickness of the shell, and expansion velocity. Comparison between the 5 cm and 7 mm brightness temperature distributions demonstrates that a thin layer of ionised gas of a few 1000 K at the surface of the H II region is necessary to reproduce the morphology of the continuum emission at both wavelengths. Conclusions: We confirm that the G24 A1 hypercompact H II region consists of a thin shell ionised by an O9.5 star. The shell is expanding at a speed comparable to the sound speed in the ionised gas. The radius of the H II region exceeds the critical value needed to trap the ionised gas by the gravitational field of the star, consistent with the observed expansion

Infall and the Formation of a Massive Star

We present evidence of infall in a circumstellar rotating toroid enshrouding a luminous star in the massive star-forming region G24.78+0.08. Besides being one of the rare direct detections of infall in a young high-mass star, our finding stands unique for the simultaneous presence of three elements in the same massive object: a rotating, collapsing toroid, a bipolar outflow, ejected along the rotation axis, and a hypercompact ionized H II region. The large accretion rate and the existence of a hypercompact H II region confirm that the accretion cannot be spherically symmetric and must occur in a circumstellar disk

The Forgotten Quadrant Survey

The Forgotten Quadrant Survey (FQS) is an ESO large project at the 12-m Kitt Peak antenna of the Arizona Radio Observatory with the aim to map the Galactic Plane in the range 220\degr12CO (1-0), and 13CO (1-0). FQS will produce a dataset of great legacy value, largely improving the data quality both in terms of sensitivity and spatial resolution over existing datasets, in this poorly studied portion of the outer Galaxy. FQS contributes to the general effort to produce a new generation of high-quality spectroscopic data for the Galactic Plane. Such data, in conjunction with the latest generation continuum surveys, will produce a new and more detailed picture of the plane of the Milky Way

Observational perspective of the youngest phases of intermediate-mass stars

Intermediate-mass protostars are the long-forgotten actors in the star-formation scenario. Historically, intermediate-mass stars have been associated to the low-mass regime and not too much attention has been drawn to them as a separate group. However, although their pre-main sequence evolution should be similar to that of low-mass protostars, intermediate-mass young stellar objects share many characteristics with their higher mass counterparts. This suggests that the star-formation mechanism could be similar for all luminosities

VizieR Online Data Catalog: G35.20-0.74N VLA continuum images (Beltran+, 2016)

The files are the VLA data used to produce the maps in Figs. 1, 2, 3, 6, 7, and 8. Units are Jy/beam. Coordinate system is equatorial (J2000.0)