scholarly journals EXPLORING THE NATURE OF COMPACT RADIO SOURCES ASSOCIATED TO UCHII REGIONS

2021 ◽  
Vol 57 (1) ◽  
pp. 81-89
Author(s):  
J. M. Masqué ◽  
L. F. Rodríguez ◽  
S. A. Dzib ◽  
S. N. Medina ◽  
L. Loinard ◽  
...  
Keyword(s):  
Massive Star ◽  
Thermal Emission ◽  
Hii Regions ◽  
Radio Sources ◽  
Large Array ◽  
Gravitational Radius ◽  
Very Large Array ◽  
Thermal Sources

We present Very Large Array 7 mm continuum observations of four ultracompact (UC) HII regions, observed previously at 1.3 cm, in order to investigate the nature of the compact radio sources associated with these regions. We detect a total of seven compact radio sources, four of them with thermal emission, and two compact radio sources with clear non- thermal emission. The thermal emission is consistent with the presence of an ionized envelope, either static (i.e., trapped in the gravitational radius of an associated massive star) or flowing away (i.e., a photo-evaporative flow). The nature of the non-thermal sources remains unclear and several possibilities are proposed. The possibility that most of these compact radio sources are photo-evaporating objects, and the remaining ones more evolved objects, is consistent with previous studies on UCHII regions.

scholarly journals Early results from a diagnostic 1.3 cm survey of massive young protostars

2012 ◽  
Vol 8 (S287) ◽  
pp. 497-501
Author(s):  
Crystal L. Brogan ◽  
Todd R. Hunter ◽  
Claudia J. Cyganowski ◽  
Remy Indebetouw ◽  
Rachel Friesen ◽  
...  
Keyword(s):  
Massive Star ◽  
Thermal Emission ◽  
Young Stellar Objects ◽  
Large Array ◽  
Stellar Objects ◽  
Very Large Array ◽  
Early Results ◽  
Wide Range ◽  
First Time ◽  
24 Ghz

AbstractWe have used the recently-upgraded Karl G. Jansky Very Large Array (JVLA) to conduct a K-band (~24 GHz) study of 22 massive young stellar objects in 1.3 cm continuum and a comprehensive set of diagnostic lines. This survey is unique in that it samples a wide range of massive star formation signposts simultaneously for the first time. In this proceeding we present preliminary results for the 11 sources in the 2-4 kpc distance bin. We detect compact NH3 cores in all of the fields, with many showing emission up through the (6,6) transition. Maser emission in the 25 GHz CH3OH ladder is present in 7 of 11 sources. We also detect non-thermal emission in the NH3 (3,3) transition in 7 of 11 sources.

scholarly journals Interferometric and single-dish observations of 44, 84 and 95 GHz Class I methanol masers

2017 ◽  
Vol 13 (S336) ◽  
pp. 239-242
Author(s):  
Carolina B. Rodríguez-Garza ◽  
Stanley E. Kurtz ◽  
Arturo I. Gómez-Ruiz ◽  
Peter Hofner ◽  
Esteban D. Araya ◽  
...  
Keyword(s):  
Massive Star ◽  
Wide Band ◽  
Hii Regions ◽  
Spectral Lines ◽  
Class I ◽  
Detection Rates ◽  
Very Large Array ◽  
Star Forming ◽  
Star Forming Regions ◽  
Methanol Masers

AbstractWe present observations of massive star-forming regions selected from the IRAS Point Source Catalog. The observations were made with the Very Large Array and the Large Millimeter Telescope to search for Class I methanol masers. We made interferometric observations of 125 massive star-forming regions in the 44 GHz methanol maser transition; 53 of the 125 fields showed emission. The data allow us to demonstrate associations, at arcsecond precision, of the Class I maser emission with outflows, HII regions and shocks traced by 4.5 μm emission. We made single-dish observations toward 38 of the 53 regions with 44 GHz masers detected to search for the methanol transitions at 84.5, 95.1, 96.7, 107.0, and 108.8 GHz. We find detection rates of 74, 55, 100, 3, and 45%, respectively. We used a wide-band receiver which revealed many other spectral lines that are common in star-forming regions.

Subarcminute resolution imaging of radio sources at 74 MHz with the Very Large Array

1993 ◽  
Vol 106 ◽  
pp. 2218 ◽  
Author(s):  
N. E. Kassim ◽  
R. A. Perley ◽  
W. C. Erickson ◽  
K. S. Dwarakanath
Keyword(s):  
Radio Sources ◽  
Large Array ◽  
Very Large Array ◽  
Resolution Imaging

scholarly journals A review of H2CO 6cm masers in the Galaxy

2007 ◽  
Vol 3 (S242) ◽  
pp. 110-119 ◽  
Author(s):  
E. Araya ◽  
P. Hofner ◽  
W. M. Goss
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Large Array ◽  
Massive Star Formation ◽  
Very Large Array ◽  
Ongoing Work ◽  
The Galaxy ◽  
Green Bank Telescope

AbstractWe present a review of the field of formaldehyde (H2CO) 6cm masers in the Galaxy. Previous to our ongoing work, H2CO 6cm masers had been detected in the Galaxy only toward three regions: NGC7538 IRS1, Sgr B2, and G29.96–0.02. Current efforts by our group using the Very Large Array, Arecibo, and the Green Bank Telescope have resulted in the detection of four new H2CO 6cm maser regions. We discuss the characteristics of the known H2CO masers and the association of H2CO 6cm masers with very young regions of massive star formation. We also review the current ideas on the pumping mechanism for H2CO 6cm masers.

scholarly journals Formaldehyde Abundances in the Dense Molecular Cores DR 21 and W 3(OH)

1987 ◽  
Vol 120 ◽  
pp. 185-186
Author(s):  
H. R. Dickel ◽  
W. M. Goss ◽  
A. H. Rots
Keyword(s):  
Radiative Transfer ◽  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Hii Regions ◽  
Large Array ◽  
Very Large Array ◽  
Hydrogen Density ◽  
Dense Cores ◽  
Ultracompact Hii

Formaldehyde absorption has been observed with the Very Large Array in both the 6 cm and 2 cm transitions towards a number of ultracompact HII regions which are embedded in the dense cores of molecular clouds. Such data have been compared with the results of radiative transfer calculations to derive the distributions of the molecular hydrogen density and of the abundance of formaldehyde relative to molecular hydrogen. Results are presented for the sources DR 21 and W 3(OH).

scholarly journals Comparison of the Optical and Radio Reference Frames

1986 ◽  
Vol 7 ◽  
pp. 103-108 ◽  
Author(s):  
K. J. Johnston ◽  
Chr. de Vegt
Keyword(s):  
Radio Emission ◽  
Reference Frame ◽  
Radio Telescope ◽  
Reference Frames ◽  
Radio Sources ◽  
Large Array ◽  
Very Large Array ◽  
Extragalactic Radio Sources ◽  
Optical Reference ◽  
Lack Of Knowledge

The Very Large Array (VLA) has made possible the measurement of the precise positions of the radio emission associated with stars. This allows the direct comparison of the optical reference frame (FK4) with the radio reference frame which is defined by the quasi-absolute positions of extragalactic radio sources. This comparison is limited by the small number of bright stars that display detectable radio emission and the lack of knowledge of the precise coincidence of the radio emission with the optical photocenter of the star. Since the VLA is the most sensitive astrometrically capable radio telescope, positions of the largest number of stars north of declination -20 degrees can be measured. The accuracy of the positions on the extragalactic reference frame should approach a milliarcsecond.

scholarly journals Is there a cluster in the massive star forming region IRAS 20126+4104?

2015 ◽  
Vol 12 (S316) ◽  
pp. 157-158
Author(s):  
V. A. Montes ◽  
Peter Hofner ◽  
C. Anderson ◽  
V. Rosero
Keyword(s):  
Surface Density ◽  
Massive Star ◽  
Radio Observation ◽  
Large Array ◽  
Very Large Array ◽  
X Ray ◽  
Star Forming ◽  
Continuum Radio

AbstractA Chandra X-ray Observatory ACIS-I observation and a 6 cm continuum radio observation with the Karl G. Jansky Very Large Array (VLA) together with a multiwavelength study in infrared (2MASS and Spitzer) and optical (USNO-B1.0) shows an increasing surface density of X-ray sources toward the massive protostar. There are at least 43 YSOs within 1.2 pc distance from the massive protostar. This number is consistent with typical B-type stars clusters (Lada & Lada 2003).

scholarly journals The Excited Atomic Hydrogen Lines 126a and 127a in HII Regions

1968 ◽  
Vol 21 (2) ◽  
pp. 149 ◽  
Author(s):  
RX McGee ◽  
FF Gardner
Keyword(s):  
Atomic Hydrogen ◽  
Hii Regions ◽  
Radio Sources ◽  
Hydrogen Recombination ◽  
Hydrogen Lines ◽  
Thermal Sources ◽  
Made In

Forty radio sources have been observed for the presence of the hydrogen recombination lines 126", at 3248�708 MHz and 127", at 3172�864 MHz with a 6' arc aerial beam and a receiver with 48 channels of 37 kHz bandwidth each. Detections were made in 34 sources, all of which were either HI! regions or optically unidentified thermal sources.

scholarly journals VLA Observations of Nine Extended Green Objects in the Milky Way: Ubiquitous Weak, Compact Continuum Emission, and Multi-epoch Emission from Methanol, Water, and Ammonia Masers

2021 ◽  
Vol 923 (2) ◽  
pp. 263
Author(s):  
A. P. M. Towner ◽  
C. L. Brogan ◽  
T. R. Hunter ◽  
C. J. Cyganowski
Keyword(s):  
Milky Way ◽  
Thermal Emission ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Large Array ◽  
Spectral Indices ◽  
Physical Processes ◽  
Stellar Objects ◽  
Maser Emission ◽  
Very Large Array

Abstract We have observed a sample of nine Extended Green Objects (EGOs) at 1.3 and 5 cm with the Very Large Array (VLA) with subarcsecond resolution and ∼7–14 μJy beam−1-sensitivities in order to characterize centimeter continuum emission as it first appears in these massive protoclusters. We find an EGO-associated continu um emission—within 1″ of the extended 4.5 μm emission—in every field, which is typically faint (order 101–102 μJy) and compact (unresolved at 0″.3–0″.5). The derived spectral indices of our 36 total detections are consistent with a wide array of physical processes, including both non-thermal (19% of detections) and thermal free–free processes (e.g., ionized jets and compact H ii regions, 78% of sample) and warm dust (1 source). We also find an EGO-associated 6.7 GHz CH3OH and 22 GHz H2O maser emission in 100% of the sample and a NH3 (3,3) masers in ∼45%; we do not detect any NH3 (6,6) masers at ∼5.6 mJy beam−1 sensitivity. We find statistically-significant correlations between L radio and L bol at two physical scales and three frequencies, consistent with thermal emission from ionized jets, but no correlation between L H 2 O and L radio for our sample. From these data, we conclude that EGOs likely host multiple different centimeter continuum-producing processes simultaneously. Additionally, at our ∼1000 au resolution, we find that all EGOs except G18.89−0.47 contain 1 ∼ 2 massive sources based on the presence of CH3OH maser groups, which is consistent with our previous work suggesting that these are typical massive protoclusters, in which only one to a few of the young stellar objects are massive.

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