Engineering topics

Colgan, Sean W. J.

Publications and source records attributed to Colgan, Sean W. J..

40 records · Page 3

NASA NTRS1989

Arecibo emission-absorption observations of Galactic OH

Observations of OH emission/absorption toward 19 low-Galactic-latitude background-continuum sources are reported. Data obtained at 1.665 and 1.667 GHz using the 12-m radio telescope at Arecibo Observatory during February-March 1984, are presented in extensive tables and graphs and characterized in detail, with reference to theoretical models. A total of 11 OH absorption features were detected toward nine of the sources, with an average of one feature of optical depth 0.02 or greater per 5 kpc of path length and an average column density of 1.6 x 10 to the 12th/sq cm (corrected to b = 90 deg).

Colgan, Sean W. J.↗

NASA NTRS1988

Observation of Fe II (26.0 microns) in SN 1987A

The first observation of the 26-micron line from singly ionized iron in SN 1987A is reported. The total flux is 4.5 + or - 0.9 x 20 to the -18th W/sq cm. The line width (FWHM) is 4000 + or - 600 km/s. The minimum iron mass is found to be about 0.02 solar, indicating that the emission originates in the heavy element mantle and not in the hydrogen-rich envelope. Since this mass is less than estimates based on near-infrared measurements or the optical light curve, the emission is probably optically thick. In this case, the flux measurement together with the observed line width suggest a temperature of 3500 + or - 1500 K for the mantle. The broad line width suggests that mixing of the ejected iron with lighter elements in overlying layers has occurred.

Erickson, Edwin F.↗

NASA NTRS1988

Theoretical infrared spectra of SN 1987A

A simple model for the ejecta of SN 1987A is used to show that the expected fluxes in infared fine structure lines from nickel, cobalt, iron, argon, sulfur, silicon, and neon are likely to be detectable for several years following the supernova explosion. Energy sources due to radioactive decay and a central pulsar are considered separately. Most of the mass of heavy elements resides in the inner, pure metal shells of the ejecta, so that the infrared lines will probe the temperature, ejecta masses, and dynamics of this region and not the overlying, hydrogen-rich envelope.

Colgan, Sean W. J.↗

NASA NTRS1988

H I emission-absorption studies with high-velocity resolution

The properties of interstellar H I are investigated using high-velocity resolution, Arecibo emission-absorption spectra in the direction of 40 radio continuum sources, including 21 at low Galactic latitude. Comparison of the data with the results of previous studies confirms the earlier suggestion that the H I density in the nearest 100 pc is lower than the disk average by about a factor of two and the separation of H I emission into material associated with absorbing 'clouds' and physically independent, not strongly absorbing material. A comparison of lines of sight with different geometries supports the suggestion that spin temperatures are higher far above the Galactic disk. There is little correlation between the properties of the H I emission fluctuations on 3.8 arcmin separations and the properties of either the emission or absorption profiles.

Colgan, Sean W. J.↗