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 Oh Observations in the Directions of Galactic Thermal Sources

1967 ◽  
Vol 20 (4) ◽  
pp. 407 ◽  
Author(s):  
RX McGee ◽  
FF Gardner ◽  
BJ Robinson
Keyword(s):  
Linear Polarization ◽  
The Other ◽  
Radio Sources ◽  
Line Radiation ◽  
Thermal Sources ◽  
Made In

A survey for the hydroxyl line radiation has been made in the directions of 30 radio sources (most of them thermal) with the 210 ft telescope of beamwidth 12'� 2 and the multichannel line receiver of bandwidths 10 and 37 kHz. The line at frequency 1665�401 MHz was observed for all sources and the other three lines at 1612, 1667, and 1720 MHz were observed for 10 of the more important sources. The latter were investigated for circular and linear polarization.

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.

Observations of the 126α Line of Excited Hydrogen in Southern HII Regions

1967 ◽  
Vol 1 (1) ◽  
pp. 19-19
Author(s):  
F. F. Gardner ◽  
R. X. McGee
Keyword(s):  
Radial Velocity ◽  
Hii Regions ◽  
Frequency Resolution ◽  
Recombination Line ◽  
Hydrogen Recombination ◽  
Local Standard ◽  
The Mean ◽  
Local Standard Of Rest ◽  
Made In ◽  
The Continuum

A search for the 126a hydrogen recombination line, with a rest frequency of 3248.713 MHz, has been made in the 19 sources listed in Table I using the Parkes telescope. The beamwidth was 6′ are and the frequency resolution 37 kHz. In the Table RCW refers to the Rodgers, Campbell and Whiteoak Atlas, W to the Westerhout catalogue, and the co-ordinate numbers to the Parkes Catalogue of Sources. In each case the ratio of the peak of the line to the continuum TL/TC, the half-intensity width Δv and the mean radial velocity to the local standard of rest, were determined. The related velocities observed in OH emission and absorption are also shown.

The Normal Elliptical Galaxies

1970 ◽  
Vol 1 (7) ◽  
pp. 302-303
Author(s):  
K. C. Freeman
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Hii Regions ◽  
Elliptical Galaxies ◽  
Radio Sources ◽  
Bright Blue

About 13% of bright galaxies are ellipticals (21% SO, 64% Spiral and Im, 2% IO and peculiar). Their obvious features are the smooth luminosity distribution and the near absence of the bright blue stars, HII regions and dust that appear in spiral systems; there is probably very little star formation going on at present in E galaxies. I plan to discuss some of the dynamical and physical properties of these systems; although many of them are known radio sources, I will not be able to discuss their radio properties.

scholarly journals Searching for HI Absorbing Gas in AGN

2001 ◽  
Vol 205 ◽  
pp. 190-191
Author(s):  
Y.M. Pihlström ◽  
J.E. Conway ◽  
R.C. Vermeulen
Keyword(s):  
Atomic Hydrogen ◽  
Host Galaxy ◽  
Radio Sources ◽  
Hydrogen Line

With the aim of probing HI gas in AGN we have searched different samples of radio sources for the 21cm atomic hydrogen line in absorption. Depending on the source morphology, we are able to probe gas that either belongs to the host galaxy ISM, or gas that is situated on scales < 1kpc which then may be connected with the AGN fueling. For the HI absorption detected in 3C216, we argue that such sub-kpc scale gas instead might be due to a jet-cloud interaction.

scholarly journals The Radio Properties of SNRs in the Magellanic Clouds

1983 ◽  
Vol 101 ◽  
pp. 551-558 ◽  
Author(s):  
B. Y. Mills
Keyword(s):  
Supernova Remnants ◽  
Average Distance ◽  
Hii Regions ◽  
Magellanic Clouds ◽  
Selection Effects ◽  
Absolute Distance ◽  
Major Difficulty ◽  
Order Of Magnitude ◽  
Thermal Sources ◽  
Better Than

An understanding of the radio properties and evolution of Galactic supernova remnants has always been hampered by the difficulty of measuring distances. A conventional wisdom has developed around a set of ‘good’ calibrators but most workers involved have drawn attention to the uncertainties and the possibility of selection effects distorting results. This major difficulty is completely overcome by studying SNRs in the Magellanic Clouds. Although there is uncertainty in the absolute distance scale, relative distances can be determined to better than 10% and differences of this magnitude are not significant when intercomparing SNRs. There is, however, another set of problems associated with sensitivity and resolution. The Clouds are an order of magnitude more distant than the average distance of Galactic SNRs, thus many of the SNRs are close to or below the sensitivity limits of most of the southern radiotelescopes and, until recently, the resolution available has often been inadequate to separate non-thermal sources from thermal HII regions, so that both flux densities and spectra have been subject to error. Also there are ∼ 1000 extragalactic background sources which can mimic the flux density and spectra of SNRs in the Clouds, particularly when close to or behind HII regions; as a result numerous incorrect or doubtful SNR identifications have been suggested.

scholarly journals Absorption of 19.7-Mc/s radiation in HII regions

1959 ◽  
Vol 9 ◽  
pp. 451-459
Author(s):  
C. A. Shain
Keyword(s):  
Detailed Analysis ◽  
Hii Regions ◽  
Brightness Distribution ◽  
Main Program ◽  
General Picture ◽  
Ionospheric Effects ◽  
Ionospheric Absorption ◽  
Made In

The main program of the Sydney 19.7-Mc/s cross is devoted to the observation of the brightness distribution in a strip, extending some 10 degrees on either side of the galactic equator, the particular interest being the detection of absorption in HII regions. This program is well advanced, but since observing time is limited by ionospheric absorption and interference, records are not yet available for a number of galactic crossings. The detailed analysis of the observations has just begun, and will take some time. In the meantime a rough analysis of the data has been made in order to get a general picture of what might be expected, and this paper gives an outline of the results. The application of various instrumental corrections and the detailed analysis of ionospheric effects may subsequently necessitate some changes in the numbers involved in the calculations, but it is expected that the general conclusions will still hold.

Shock-wave observations of rate constants for atomic hydrogen recombination from 2500 to 7000 °K: collisional stabilization by exchange of hydrogen atoms

1969 ◽  
Vol 310 (1501) ◽  
pp. 253-276 ◽  
Keyword(s):  
Shock Waves ◽  
Rate Constant ◽  
Rate Constants ◽  
Atomic Hydrogen ◽  
Functional Form ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Hydrogen Molecules ◽  
Hydrogen Recombination ◽  
Equilibrium Dissociation

Rate constants for the recombination of atomic hydrogen with hydrogen molecules, hydrogen atoms, and argon atoms as the third bodies are presented in functional form for the range of temperatures from about 2500 to 7000 °K and are critically compared with the results of other workers. The rate constants are evaluated from detailed analyses of spectrum-line reversal measurements of the fall in temperature accompanying dissociation behind shock waves in gas mixtures containing 20, 40, 50 and 60% of hydrogen in argon. The rate constants for recombination with hydrogen molecules ( k -1 ) and argon atoms ( k -3 ) fit the equations log 10 k -1 = 15.243 - 1.95 x 10 -4 T cm 6 mole -2 s -1 , log 10 k -3 = 15.787 - 2.75 x 10 -4 T cm 6 mole -2 s -1 , with a standard deviation of 0.193 in log 10 k -1 . The rate constant for recombination with hydrogen atoms is about ten times larger than these at 3000 °K and shows a steep inverse dependence on temperature ( ~ T -6 ) above 4000 °K. Below this temperature the power of this dependence decreases rapidly and there is strong evidence that the value of this rate constant has a maximum around 3000 °K. This behaviour is interpreted on the basis of a process of collisional stabilization by atom exchange, requiring an activation energy around 8 kcal mole -1 and taking place under conditions of vibrational adiabaticity. The over-all results indicate that the assumption of equality between the equilibrium constant and the ratio of the rate constants for dissociation and recombination is valid throughout the region of non-equilibrium dissociation and at all temperatures in the shock waves examined.

scholarly journals Classification of Supernova Remnants and HII Regions from their Recombination Line Emission

1972 ◽  
Vol 25 (5) ◽  
pp. 539 ◽  
Author(s):  
JR Dickel ◽  
DK Milne
Keyword(s):  
Electron Temperature ◽  
Supernova Remnants ◽  
Line Emission ◽  
Hii Regions ◽  
Radio Sources ◽  
Recombination Line ◽  
Line Frequency ◽  
Upper Limits ◽  
Galactic Radio

H109a, recombination line observations are used in an attempt to classify 46 galactic radio sources as either supernova remnants or HII regions. Long integrations at the H109a line frequency on two well-known supernova remnants (IC 443 and 3C 391) provide improved upper limits on the line emission from these objects. From these results the electron temperature in IC 443 is estimated to be in excess of 1�6 � 104 K.

scholarly journals I. Observations Of Small Diameter Sources

1966 ◽  
Vol 19 (3) ◽  
pp. 441 ◽  
Keyword(s):  
Wavelength Range ◽  
Small Diameter ◽  
Short Wave ◽  
Polarization Angle ◽  
Radio Sources ◽  
Slight Variation ◽  
Fine Scale ◽  
Antenna Gain ◽  
System Noise ◽  
Made In

This paper is concerned with the observations of the polarization of small diameter radio sources made in 1963 with the Parkes 210 ft telescope over the wavelength range 11-74 cm. The sources of error in making such measurements with a single dish are discussed. At the short-wave end, the main limitation is system noise, and there is some complication from a slight variation of antenna gain with polarization angle; at long wavelengths, the limitation is the fine-scale structure of the galactic polarization in the direction of the source. The latter varies greatly across the sky.

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