Search NASA⌕ Search

Engineering topics

Shaffer, D. B.

Publications and source records attributed to Shaffer, D. B..

28 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The compact radio sources in 4C 39.25 and 3C 345

Long-baseline interferometry of the quasars 4C 39.25 and 3C 345 at 10.65 and 14.77 GHz shows that the centimeter radio source in each object is double, with component separations of 0.0020 arcsec (4C 39.25) and 0.0013 arcsec (3C 345 at 1974.5). For each source, the separation is the same at both frequencies, as well as similar to the structure observed at 7.85 GHz (and 5.0 GHz for 4C 39.25). The spectra of the individual components are derived and shown to vary with time approximately as expected for expanding self-absorbed synchrotron sources. The magnetic fields in the components are estimated to be as high as 0.1 gauss, but the structure of the sources appears to be unrelated to the magnetic-field orientation derived from low-resolution polarization measurements. The component separation in 4C 39.25 has not changed for several years, whereas 3C 345 shows rapid expansion.

Shaffer, D. B.↗
NASA NTRS1977

A compact radio source in the nucleus of M82

The brightest compact radio source in the nucleus of M82 has a linear diameter of about 0.02 parsecs (25 light-days). On the basis of this small size and energy considerations, it seems that this source is probably not a supernova remnant, but is similar in nature to the compact radio sources found in the nuclei of spiral and elliptical galaxies, Seyfert galaxies, radio galaxies, and in quasi-stellar objects.

Geldzahler, B. J.↗
NASA NTRS1977

The small radio source at the galactic center

Very-long-baseline interferometer observations show that the compact radio source at the Galactic Center has dimensions of approximately 200 AU and that about 25% of the emission comes from a region only 10 AU across. There is no evidence for any expansion or contraction of this compact source, with a velocity of at least a few tens of kilometers per second.

Kellermann, K. I.↗
NASA NTRS1971

The small-scale structure of radio galaxies and quasi-stellar sources at 3.8 centimeters.

Observation of fringes from 31 compact radio sources, including eight known or suspected galaxies and 20 known or suspected QSSs, by using the Goldstack interferometer at lambda = 3.8 cm (d/lambda = 10 to the 8th power). Fringe visibility curves were obtained for nine sources showing structure on a scale of .001 sec of arc, and simple models are fitted to the data. Results for 3C 273 and 3C 279 are compared with data taken by Knight et al. (1971) at an earlier epoch. The apparent changes in brightness distribution of 3C 273 and 3C 279 are difficult to explain.

Cohen, M. H.↗