scholarly journals Emission Nebulae as Radio Sources

1956 ◽  
Vol 9 (2) ◽  
pp. 218 ◽  
Author(s):  
BY Mills ◽  
AG Little ◽  
KV Sheridan
Keyword(s):  
Electron Temperature ◽  
Electron Density ◽  
Radio Telescope ◽  
Optical Data ◽  
Radio Sources ◽  
Pencil Beam ◽  
Orion Nebula ◽  
Average Electron Density ◽  
Average Electron ◽  
Bright Emission

Attempts have been made to detect 14 bright emission nebulae at a wavelength of 3?5 m using a pencil-beam radio telescope with a beamwidth of 50 min of arc. Of these nebulae, six were probably observed in emission, seven were undetectable, and one, NGC 6357, was observed in absorption; radio isophotes were obtained for NGC 2237 and NGC 3372. Radio and optical data have been combined to estimate electron densities, masses, and sometimes the electron temperature of many of the nebulae. Values range from an electron density of 3 cm?3 and a mass of 3�10. solar masses for the outer regions of the 30 Doradus complex to an average electron density of 500 cm?3 and a mass of 20 solar masses for the Orion Nebula. Temperatures generally appear to be in the neighbourhood of 10,000 �K, except in the case of NGC 6357, for which 6500 �K is estimated.

A radio method of searching for fine structure in H 11 regions

1967 ◽  
Vol 31 ◽  
pp. 237
Author(s):  
O. B. Slee
Keyword(s):  
Fine Structure ◽  
Radio Emission ◽  
Electron Density ◽  
Path Length ◽  
Low Frequency ◽  
Radio Sources ◽  
Average Electron Density ◽  
Scale Size ◽  
Average Electron ◽  
Radio Method

Fine structure with a scale size of about 10-3pc in the galactic ionized hydrogen may scatter the low-frequency radio emission of extragalactic sources with intrinsically small angular diameters, thus making them apparently large. For example, application of the Chandrasekhar scattering formula to a path length of 100 pc through an H 11 region with an average electron density of 0·1 cm-3, and structure of scale size 10-3pc filling 1% of the volume, results in a scattering to half-brightness points of 8″ (arc) at 38 MHz. Radio sources with apparent angular sizes of this amount should be partially resolved by an interferometer with an effective baseline of about 10 000 wavelengths.

Early free-fall afterglow of a cylindrical mercury vapor plasma

1970 ◽  
Vol 48 (13) ◽  
pp. 1528-1538
Author(s):  
B. C. Gregory
Keyword(s):  
Charge Transfer ◽  
Electron Temperature ◽  
Electron Density ◽  
Free Fall ◽  
Mercury Vapor ◽  
Moment Equation ◽  
Average Electron Density ◽  
Pressure Term ◽  
Complete Series ◽  
Average Electron

The free-fall theory for the decay of average electron density and electron temperature in a mercury vapor discharge afterglow presented recently in a letter (Gregory) is improved by the addition of a pressure term for the ions in the second moment equation. The neglect of charge-transfer collisions is justified. The development of the theory is reviewed in detail and a complete series of comparison curves for the measured and calculated electron density decay is presented for four tubes of different diameter.

scholarly journals X-ray phase determination by the principle of minimum charge

1999 ◽  
Vol 55 (3) ◽  
pp. 489-499 ◽  
Author(s):  
Veit Elser
Keyword(s):  
Electron Density ◽  
Diffraction Data ◽  
Global Minimum ◽  
Unit Cell ◽  
Electronic Charge ◽  
Total Charge ◽  
Phase Determination ◽  
X Ray ◽  
Average Electron Density ◽  
Average Electron

When the electron density in a crystal or a quasicrystal is reconstructed from its Fourier modes, the global minimum value of the density is sensitively dependent on the relative phases of the modes. The set of phases that maximizes the value of the global minimum corresponds, by positivity of the density, to the density having the minimum total charge that is consistent with the measured Fourier amplitudes. Phases that minimize the total electronic charge (i.e. the average electron density) have the additional property that the lowest minima of the electron density become exactly degenerate and proliferate within the unit cell. The large number of degenerate minima have the effect that density maxima are forced to occupy ever smaller regions of the unit cell. Thus, by minimization of the electronic charge, the atomicity of the electron density is enhanced as well. Charge minimization applied to simulated crystalline and quasicrystalline diffraction data successfully reproduces the correct phases starting from random initial phases.

A Rediscussion of the Radio Spectrum of the Orion Nebula

1969 ◽  
Vol 1 (5) ◽  
pp. 217-218
Author(s):  
P. A. Shaver ◽  
B. Y. Mills
Keyword(s):  
Electron Temperature ◽  
Radio Spectrum ◽  
Radio Continuum ◽  
Orion Nebula ◽  
Low Frequencies ◽  
Continuum Spectrum ◽  
The Subject ◽  
Bright Emission

The Orion Nebula is the best known and most often observed of the bright emission nebulae. However, the radio continuum spectrum of the nebula has been the subject of some misconception, particularly at low frequencies. A rediscussion is worthwhile as the spectrum has been used to derive an electron temperature for the nebula which is at variance with other determinations and carries important implications. Also some of the difficulties of measurement and problems of interpretation are relevant to similar investigations of other emission nebulae.

scholarly journals 21. The low-frequency spectrum of Cygnus A and Cassiopeia A

1957 ◽  
Vol 4 ◽  
pp. 145-147
Author(s):  
R. J. Lamden ◽  
A. C. B. Lovell
Keyword(s):  
Lower Limit ◽  
Radio Telescope ◽  
Low Frequency ◽  
Radio Sources ◽  
Pencil Beam ◽  
Frequency Range ◽  
Present Communication ◽  
Cassiopeia A ◽  
Cygnus A ◽  
Radio Transmitters

The published measurements of the intensity of the radio sources cover a frequency range down to a lower limit of 22·6 Mc./s., at which measurements have been made on Cygnus and Cassiopeia by Hey and Hughes (1954)[1]. Information about the spectrum at still lower frequencies is difficult to obtain because of interference arising from ionospheric reflexion of distant radio transmitters. Some of this trouble can be alleviated by using a narrow pencil-beam radio telescope for reception and the present communication describes measurements made on frequencies of 16·5, 19·0, 22·6 and 30·0 Mc./s. using the 218 ft. transit radio telescope at Jodrell Bank.

scholarly journals Pulsar distances, spiral structure and the interstellar medium

1970 ◽  
Vol 38 ◽  
pp. 178-181 ◽  
Author(s):  
B. Y. Mills
Keyword(s):  
Interstellar Medium ◽  
Electron Density ◽  
Supernova Remnants ◽  
Spiral Structure ◽  
Radio Continuum ◽  
Average Electron Density ◽  
Uniform Medium ◽  
The Mean ◽  
Average Electron

The distances of all pulsars are calculated on the assumption that they are immersed in a uniform medium of average electron density 0.06 cm−3. It then appears that the pulsars are concentrated towards the local and Sagittarius spiral features and that their mean height above the plane is consistent with that of known supernova remnants. The mean distances appear to be approximately correct, but individual distances are uncertain by about a factor of two. Evidence from radio continuum results supports this model of the ionized interstellar medium.

scholarly journals High Resolution Observations of the Orion Nebula at 408 MHz

1968 ◽  
Vol 21 (1) ◽  
pp. 95 ◽  
Author(s):  
BY Mills ◽  
PA Shaver
Keyword(s):  
High Resolution ◽  
Electron Temperature ◽  
Radio Telescope ◽  
Central Region ◽  
High Frequency ◽  
Orion Nebula ◽  
Radio Observatory

The Orion Nebula has been observed at 408 MHz with the 1 mile Cross radio telescope at the Molonglo Radio Observatory. NGC 1976 and NGC 1982 were observed separately and the former was well resolved.. Comparison with high frequency results shows that the central region is opti('ally thick; the electron temperature was measured directly at 7 6000K � 800 degK. Both nebulae are strongly concentrated towards their exciting stars..

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