Engineering topics

Shaya, E. J.

Publications and source records attributed to Shaya, E. J..

5 records

NASA NTRS1987

The H I distribution in clouds within galaxies

An interpretation is given for the relatively flat distribution of atomic hydrogen as a function of radius within the visible disks of spiral galaxies and the existence of a correlation between H I surface density and morphological class of spiral galaxy. The H I is mostly contained in constant column density envelopes of molecular clouds. The clouds have a two-dimensional filling factor of unity when a galaxy is viewed face on. The column density of the cloud envelopes depends on the ratio of flux of H2 dissociating radiation in the ambient medium to envelope gas density. The flat H I profiles imply the gas density and pressure follow the ultraviolet ambient flux on kiloparsec scales throughout a given galaxy. Later-type galaxies have larger ultraviolet surface brightnesses, as deduced from the H-alpha surface brightnesses. Therefore, thicker protective H I envelopes develop in late-type spirals.

Shaya, E. J.↗

NASA NTRS1985

Polar Cap Formation on Ganymede

Since thermal migration is not an effective mechanism for water transport in the polar regions at the Galilean satellites, some other process must be responsible for the formation of Ganymede's polar caps. It is proposed that Ganymede's polar caps are the optical manifestation of a process that began with the distribution of an ice sheet over the surface of Ganymede. The combined processes of impact gardening and thermal migration led, in regions at latitudes less than 40 to 45 deg., to the burial of some fraction of this ice, the migration of some to the polar caps margins, and a depletion of free ice in the optical surface. At higher latitudes, no process was effective in removing ice from the optical surface, so the remanants of the sheet are visible today.

Pilcher, C. B.↗

NASA NTRS1984

Polar cap formation on Ganymede

It is argued that Ganymede's polar caps are the remnants of a more extensive covering of water ice that formed during a period in which the satellite was geologically active. It is inferred that the initial thickness of this covering was a significant fraction of the gardening depth since the covering formed. This suggests an initial thickness of at least a few meters over heavily cratered regions such as the south polar grooved terrain. The absence of similar polar caps on Callisto apparently reflects the absence of comparable geologic activity in the history of this satellite.

Shaya, E. J.↗

NASA NTRS1980

The abundance of CO in diffuse interstellar clouds - An ultraviolet survey

CO was detected in 17 directions and its upper limits were estimated in 21 directions by a UV survey carried out with the Copernicus satellite in the C-X 1088 A and E-X 1076 A lines toward 48 bright stars. The CO column densities range from 10 to the 12th to 10 to the 17th/sq cm and correlate with C I and H2. The tendency of the C I/CO ratio to be about 10 follows the ratio of particular atomic and molecular cross-sections and the physical parameters of interstellar clouds. Finally, the connection between UV observations in diffuse clouds and radio observations of (C-13)O in dark clouds is discussed.

Federman, S. R.↗

NASA NTRS1979

A survey of interstellar C I - Insights on carbon abundances, UV grain albedos, and pressures in the interstellar medium

Interstellar atomic carbon has been sampled over 33 different paths with visual extinctions ranging from about 0.15 to 1.5 mag. The trend of C I vs different forms of hydrogen is found to be steep and somewhat erratic. It is concluded that the observed behavior can be explained by strong differences in the responses of C I, H I, and H2 equilibria to physical conditions, together with marked variations of these conditions within different interstellar clouds.

Jenkins, E. B.↗