Up in the air? The matter of radio studies

Several regional surveys of southern HI made with the Argentine 100-m telescope were published (30.155.031). HI and other data were used by Dolidze (30.155. 044) to study the local distribution of gas and star forming regions. The Perseus arm region was the subject of an analogous study by Gerasimenko (34.155.139). Vallée (34.155.005) used rotation measure data from extragalactic sources in the direction of the Perseus arm to determine the magnetic field structure there and to constrain gravitational collapse theories of magnetic compression. HI in the direction of the Puppis window was surveyed by Stacy and Jackson (32.131.277) and used to study the turbulent characteristics of the interstellar medium. HI related to Gould“s Belt was studied by Pöppel and Olano (32.155.024, 33.155.030). Salter (34. 131.014) reviewed radio and other observations pertaining tc Loop I, the North Polar Spur, and considered the influence which this structure might have on the local medium.

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The Influence of the Atmosphere on Radar Meteor Rates

Symposium - International Astronomical Union ◽

10.1017/s0074180900066547 ◽

1980 ◽

Vol 90 ◽

pp. 101-104

Author(s):

W.G. Elford.

Keyword(s):

Initial Diameter ◽

Meteor Trail ◽

Radio Studies ◽

The Difference ◽

Sporadic Meteors ◽

Radar Meteor ◽

Sharp Cutoff ◽

Selection Of

The majority of radio studies of meteors have been carried out at frequencies higher than 17MHz and most of the rate observation at frequencies above 30MHz. At these frequencies a severe height selection of meteors occurs. In Figure 1(a) are shown the normalized height distributions of sporadic meteors observed at Adelaide on frequencies of 27MHz and 2MHz (Brown, 1976). The sharp cutoff of the latter distribution below 87 km is instrumental. The difference in the height distributions is due to the effect of the finite diameter of a meteor trail on its radar detectability. If the trail diameter is ≪ λ signals from the near and far edges reinforce but as the trail expands due to diffusion and the diameter becomes ≃ λ/4, interference reduces the amplitude. A meteor trail, produced by a particle with a velocity of 30 km s−1, has an initial diameter of 0.4m at 80 km, 2.0m at 104 km and 4.0m at 116 km.

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Radio studies of HII regions and galactic structure

Symposium - International Astronomical Union ◽

10.1017/s0074180900052396 ◽

1964 ◽

Vol 20 ◽

pp. 116-122

Author(s):

M. M. Komesaroff ◽

G. Westerhout

Keyword(s):

Thermal Emission ◽

Hii Regions ◽

Radio Spectrum ◽

Line Of Sight ◽

Radio Waves ◽

Low Frequencies ◽

High Frequencies ◽

The Galaxy ◽

Radio Studies ◽

Considerable Detail

Radio studies of galactic HII regions are best carried out at the two ends of the radio spectrum. At high frequencies, of hundreds or thousands of megacycles per second, HII regions are seen by virtue of their thermal emission against a weak nonthermal background. Since radio waves are unaffected by the obscuration along the plane, it is possible in principle to see right through the Galaxy, and the high resolution which can be achieved in the thousands of megacycles range enables us to study at least the nearer regions in considerable detail. At low frequencies, below about 20 Mc/s, ionized hydrogen is seen in absorption against a bright nonthermal background. Since quite tenuous regions may be almost opaque at the lower frequencies, the technique provides quite a sensitive method of detecting them. The absorption increases with decreasing frequency so that studies at different frequencies enable us to see to varying depths along the line of sight and could permit the derivation of rough distance estimates.

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