Engineering topics

Backman, Dana E.

Publications and source records attributed to Backman, Dana E..

7 records

NASA NTRS1995

Rotation periods of open-cluster stars, 3

We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several show rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using all available Pleiades stars with photometric periods together with current X-ray flux measurements, we illustrate the X-ray activity/rotation relation among Pleiades late-G/K dwarfs. The data show a clear break in the rotation-activity relation around P approximately 6-7 days -- in general accordance with previous results using more heterogeneous samples of G/K stars.

Prosser, Charles F.↗

NASA NTRS1994

Planetary system evolution and the Vega stars: The potential for ESA's Infrared Space Observatory

ESA's Infrared Space Observatory (ISO), scheduled for launch within the next 2-3 years, will place a complement of powerful infrared imagers and spectrometers into high orbit, with an operational life anticipated to be about 18 months. During this time, numerous scientific investigations of every conceivable astrophysical target will be made. The purpose of this paper is to consider the instrumental complement in terms of specific observations of Vega-like systems with cold, infrared excesses, in order to investigate problems relating to the evolution of planetary systems, and to optimize the scientific results possible with ISO on such topics.

Stencel, Robert E.↗

NASA NTRS1994

4.8 - 20 micrometer imaging of Orion BN/KL: 2: A new look at luminosity at sources and the role of IRc2

We have reconsidered the energetics of the BN/KL infrared complex, using array images at nine wavelengths between 4.8 and 20 micrometer, and find a much lower luminosity for IRc2 than the generally accepted value. The new observations resolve 1arcsec structure throughout the region, including several new compact sources within a few arcsec of IRc2 and significant details imaged in the 9.7 micrometer silicate feature. Together with other recent work, the results suggest that luminous stars associated with three compact HII regions found within BN/KL, rather than IRc2, may be the more significant luminosity sources for the complex.

Gezari, Daniel Y.↗

NASA NTRS1993

Rotation periods of open-cluster stars, 2

We present the results from a photometric monitoring program of 21 stars observed during 1992 in the Pleiades and Alpha Persei open clusters. Period determinations for 16 stars are given, 13 of which are the first periods reported for these stars. Brightness variations for an additional five cluster stars are also given. One K dwarf member of the alpha Per cluster is observed to have a period of rotation of only 4.39 hr. perhaps the shortest period currently known among BY Draconis variables. The individual photometric measurements have been deposited with the NSSDC. Combining current X-ray flux determinations with known photometric periods, we illustrate the X-ray activity/rotation relation among Pleiades K dwarfs based on available data.

Prosser, Charles F.↗

NASA NTRS1993

Main-sequence stars with circumstellar solid material - The Vega phenomenon

The detection of solid grains with temperatures of 50 to 125 K and fractional bolometric luminosities in the range 10 exp -5 to 10 exp -3 early in the IRAS mission around three nearby A main-sequence stars, Alpha Lyrae (Vega), Alpha Piscis Austrinus (Fomalhaut), and Beta Pictoris, is discussed. Spatial resolution of the emission indicates that: the grains are larger than interstellar grains, the material probably lies in disks in the stellar equatorial planes, the disks extend to distances of 100 to 1000 AU from the stars, and zones a few tens of AU in radius around the central stars are relatively empty. Subsequent surveys of IRAS data reveal more than 100 main-sequence stars of all spectral classes having unresolved excesses with similar temperatures and fractional luminosities to the three prototypes. Some stars with excesses have estimated ages of 1 to 5 Gyr. Thus, main-sequence FIR excesses appear to be widespread and are present in systems old enough to be probably past the stage of active planet formation.

Backman, Dana E.↗

NASA NTRS1991

A survey for infrared excesses among high galactic latitude SAO stars

This project involves extending the previous analysis of infrared excesses among a volume-limited sample of 134 nearby A-K main-sequence stars to a magnitude-limited sample of stars, culled from the SAO Catalog, with excesses determined from the IRAS Point Source Catalog flux density ratios. This new sample includes 5706 B-M type stars, 379 of which have infrared excesses. The objective involved use of a statistically complete survey of objects in a standard catalog in order to assess the frequency with which different physical processes can affect the infrared output of stars. These processes include, but are not limited to, orbiting cold particle clouds and the onset of rapid mass loss. It is concluded that cold disks are consistent with the infrared excesses found among A-G dwarfs and G-K giants in the sample.

Stencel, Robert E.↗

NASA NTRS1991

Nearby main sequence stars with cool circumstellar material

The discovery of the so-called Vega phenomenon was one of the most important and unexpected results of the IRAS mission. Several nearby main sequence stars were found to possess clouds of solid grains emitting strongly in the far-IR. Three of these objects were marginally resolved by IRAS. This phenomenon appears to be widespread and not limited to proto-planetary epochs. Possible connection of this phenomenon to the existing of planets is discussed.

Backman, Dana E.↗