Related papers: Flux Density Variations at 3.6 cm in the Massive S…

We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6~cm and at 7~mm at resolutions of 0\farcs15 (1650 au) and 0\farcs04 (440 au), respectively. The 3.6~cm data reveal new…

Over a timescale of a few years, an observed change in the optically thick radio continuum flux can indicate whether an unresolved H II region around a newly formed massive star is changing in size. In this Letter we report on a study of…

We have recently published observations of significant flux density variations at 1.3 cm in HII regions in the star forming regions Sgr B2 Main and North (De Pree et al. 2014). To further study these variations, we have made new 7 mm…

Accretion flows onto massive stars must transfer mass so quickly that they are themselves gravitationally unstable, forming dense clumps and filaments. These density perturbations interact with young massive stars, emitting ionizing…

We have compared the star-formation properties of the W49A and W51 regions by using far-infrared data from the Herschel infrared Galactic Plane Survey (Hi-GAL) and 850-um observations from the James Clerk Maxwell Telescope (JCMT) to obtain…

We present high angular resolution ($\sim0\rlap.{''}1$-$0\rlap.{''}4$) VLA observations at 2 and 6 cm made in 1983, 1986, and 1995 toward the ultracompact bipolar H II region NGC 7538 IRS1. We find, at both wavelengths, clear evidence of a…

This paper reports 43 GHz imaging of the high-mass protostars W33A, AFGL 2591 and NGC 7538 IRS9 at 0.04'' and 0.6'' resolution. In each case, weak (~mJy), compact (~100 AU) emission is detected, which has an elongated shape (axis ratio ~3).…

We report the Chandra detection of hard X-ray emission from the Welch ring in W49A, an organized structure of ultra-compact (UC) HII regions containing a dozen nascent early-type stars. Two UC HII regions are associated with hard X-ray…

We report multi-frequency Very Large Array observations of three massive star formation regions (MSFRs) containing radio continuum components that were identified as broad radio recombination line (RRL) sources and hypercompact (HC) H II…

The W49A star-forming region is embedded in a 10^6 solar mass molecular cloud, one of the most massive in our Galaxy. It has been long known as one of the most luminous radio HII regions, containing 30-40 compact and ultracompact HII…

We present the results of a 3.3-year project to monitor the flux density of Sagittarius A* at 2.0, 1.3, and 0.7 cm with the VLA. The fully calibrated light curves for Sgr A* at all three wavelengths are presented. Typical errors in the flux…

We report the detection of a variable point source, imaged at L'(3.8 microns) with the W. M. Keck II 10-meter telescope's adaptive optics system, that is coincident to within 18 mas of the Galaxy's central supermassive black hole and the…

High-resolution images of the hypercompact HII regions (HCHII) in W3 IRS 5 taken with the Very Large Array (VLA) at 1.3 and 0.7 cm are presented. Four HCHII regions were detected with sufficient signal-to-noise ratios to allow the…

W49A is one of the most luminous giant H II (GH II) regions in our Galaxy. This star forming complex contains numerous compact and ultra-compact (UC) H II regions, extending over an area of 15 pc. It emits about 10^{51} Lyman continuum…

We present results of high-resolution radio continuum observations towards the binary star WR 21a (Wack 2134) obtained with the Australia Telescope Compact Array (ATCA) at 4.8 and 8.64 GHz. We detected the system at 4.8 GHz (6 cm) with a…

Ultracompact and hypercompact HII regions appear when a star with a mass larger than about 15 solar masses starts to ionize its own environment. Recent observations of time variability in these objects are one of the pieces of evidence that…

Context: Theoretical models of early accretion during the formation process of massive stars have predicted that HII regions exhibit radio variability on timescales of decades. However, large-scale searches for such temporal variations with…

High resolution (0.15") Very Large Array observations of 7 mm continuum and H53a line emission toward the hypercompact H II region G28.20-0.04N reveal the presence of large-scale ordered motions. We find a velocity gradient of 1000 km/s/pc…

The massive and luminous star-forming region W49A is a well known Galactic candidate to probe the physical conditions and chemistry similar to those expected in external starburst galaxies. We aim to probe the physical and chemical…

We present Very Large Array (VLA) observations at 1.4 GHz and 5 GHz of a sample of 12 Quasi-stellar Objects (QSOs) at z = 3.99 to 4.46. The sources were selected as the brightest sources at 250 GHz from the recent survey of Omont et al.…