SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Using an integrating-television method, photometric studies were made of the Crab Nebula in the light of the H beta, forbidden O III, and forbidden O I emission lines. The H beta and forbidden O III fluxes from the whole nebula may be larger than previously estimated. In view of these results, the very difficult problem of finding the mass of the Crab Nebula is discussed.
The stellar Lyman-alpha line at 1216 A was observed in 29 lightly reddened stars of spectral type B2.5 to B9 by a far-UV spectrophotometer on OAO-2. The equivalent widths obtained range from 15 A at type B2.5 to 65 A at type B8; in the late-B stars, the L-alpha line removes 2 to 3% of the total stellar flux. In this sampling, the strength of the L-alpha line correlates well with measures of the Balmer discontinuity and Balmer line strengths; luminosity classification does not seem to affect the line strength. The observed line widths also agree with the predictions of Mihala's grid of non-LTE model atmospheres. In some cases, the L-alpha line influences the interstellar column densities reported in the interstellar OAO-2 L-alpha survey. Hence, these data toward lightly reddened B2 and B1.5 stars should be regarded as upper limits only.
Medium- and broad-bandwidth photometric measurements have been made of seven compact H II regions at wavelengths between 30 and 650 microns. The results are consistent with the hypothesis that the far-infrared flux is continuum radiation from dust grains. Color temperatures range from 33 to 85 K. For most of the sources, the infrared flux is low enough so that the dust could conceivably be mixed with the ionized gas. In at least one case, however, the far-infrared spectrum and luminosity of the source cannot be reconciled with reasonable grain models unless the far-infrared flux comes from a shell surrounding the H II region. M42 (Orion) and NGC 2024 (Orion B) have been mapped at 90 microns with a resolution (half-power beam diameter) of 2.2 min. Although the peak far-infrared brightness in M42 occurs at the position of the Kleinmann-Low infrared nebula, most of the flux originates in a more extended (about 6 x 8 min) source. The energy for the diffuse component could be supplied by the stars in the Trapezium cluster. However, the single early-type star visible in NGC 2024 is not luminous enough to account for either the infrared flux or the observed free-free flux.
Results are presented of far infrared photometric measurements of H2 regions in the galactic plane between longitudes 350 and 40 degrees. The results are combined from balloon flights in 1972 and 1973 carried out in cooperation with CNES in the south of France.
UBV observations of asteroid 433 Eros were conducted on 17 nights during the winter of 1974/75. The peak-to-peak amplitude of the light curve varied from about 0.3 mag to nearly 1.4 mag. The absolute V magnitude, extrapolated to zero phase, is 10.85. Phase coefficients of 0.0245 mag/degree, 0.0009 mag/degree, and 0.0004 mag/degree were derived for V, B-V, and U-B, respectively. The zero-phase color of Eros (B-V = 0.88, U-B = 0.50) is representative of an S (silicaceous) compositional type asteroid. The color does not vary with rotation. The photometric behavior of Eros can be modeled by a cylinder with rounded ends having an axial ratio of about 2.3:1.
Six-color photometric observations made during Saturn's 1972/73 opposition enable us to separate the solar phase and orbital phase contributions to the observed light variations of Iapetus, Titan, Rhea, Dione and Tethys. Titan shows no orbital variations, but has phase coefficients which range from negligible values in the infrared to 0.014 mag/deg in the ultraviolet. Rhea has a bright leading side, a light curve amplitude of about 0.2 mag, and surprisingly large phase coefficients. Combined with other available information, the observations suggest a very porous, texturally complex surface layer. Dione has a leading side which is a few tenths of a magnitude brighter than the trailing side, but the light curve amplitude has little wavelength dependence and the phase coefficients are significantly smaller than those of Rhea, suggesting a less intricate surface texture. The leading side of Tethys is probably a few tenths of a magnitude brighter than the trailing side. Our Iapetus observations generally supplement the earlier work by Millis.
Surface brightness and color data are derived for two points in the bridge and tail structure of Arp 295. The best observed point has a surface brightness in V of 25.9 magnitudes per square arc second and (B-V) = +1.00 m. A point on the tail is brighter with the same color.
Infrared (0.9- to 18-micron) photometric magnitudes are tabulated for all 14 CIT objects as a group. NML Cyg, NML Tau, and IRC + 10216 are also included. Comparisons between the CIT sources and other infrared objects are briefly discussed.
Asteroids (6), (14), (39), and (51) were observed at the Leiden Southern Station. Only (39) Laetitia seems to show some variation in color (3% in visual-ultraviolet) correlated to the light curve. If a similar effect is present for (6) Hebe, it should only be present at small phase angles. The light curves of (14) Irene and (39) Laetitia show light variations of a few percent of the rotational period indicating probable surface macrostructure.
Observations of Comets Kohoutek (1973f), Bradfield (1974b), and P/Encke have been made at a number of wavelengths between 0.55 and 18 microns. The silicate feature first observed in Comet Bennett (1969i) seems to be a common characteristic of cometary material. The comas of these comets radiate infrared with an effective temperature higher than the black-body temperature at the given distance from the sun. The albedo of the dust particles is between 0.10 and 0.20. The particles in the coma and tail are small, but the particles in the anti-tail of Comet Kohoutek must be larger than about 10 microns diameter. The observations give an absolute upper limit to the diameter of Comet Kohoutek of 30 km. A consistent interpretation would indicate that Comets Kohoutek and Bradfield have nuclear diameters of 5 to 10 km, that Bennett was several times larger, and that P/Encke is 10 times smaller. The peculiar behavior of Bradfield showed that the coma of a single comet can abruptly change its dust composition.
Explore the source record for details and available documents.
A critical analysis of selected high-quality photometric observations of Mars indicates that: (1) the phase function is concave upward out to at least 40-deg phase. No sudden brightening occurs at opposition, but the curvature increases at small phase; (2) large systematic differences (0.1-0.2 mag.) exist between different observers' data. However, the small random scatter attributable to Mars (0.01-0.02 mag.) in the better series suggests that these differences represent systematic errors in data reduction, not variations in the planet's brightness; (3) the disentangling of seasonal, diurnal, and phase effects leaves considerable ambiguity; more observations are needed, over a long time, with a stable instrumental system. However, even the present data are sufficient to expose substantial errors in published phase curves of Mars (and consequently, in interpretations based on them).
Narrowband photoelectric measurements of CN (3870), CO(+) (4250), C2 (4700), and C2 (5120) were made on twelve nights in December and January of Comet Kohoutek. CN and C2 appear to be stronger after perihelion, and CO(+) showed a strong post perihelion increase coincident with the first appearance of a strong gas tail and then decreased to a fairly constant level.
Explore the source record for details and available documents.
Attention is given to the reduction of electronographic camera images obtained with the aid of the Kron camera. A description is given of the equipment used to digitize the plate material. The response of the camera-emulsion-microdensitometer system is discussed along with present system performance figures. An outline is presented of existing and future computer reduction techniques.
Explore the source record for details and available documents.
The spectrum of a bright filament in the outer portion of the Orion nebula, 14 min from the Trapezium, was studied. The temperature of the filament, derived from /N II/ lambda 5755/6583 ratio, is 9560 K. The electron density (from /S II/ lambda 6717, 6731) is low: 360 plus or minus 150 per cu cm. The ionic abundances of He(+), N(+), O(++), and S(-) are about the same as Peimbert and Costero (1969) found in regions in Orion closer to the Trapezium. It is concluded that the filament is photoionized, presumably by the Trapezium, rather than a shock front, as had originally been suspected.
UBV measurements of Dione, Tethys, and Enceladus were made with an area-scanning photometer on several nights during the 1972/73 and 1973/74 apparitions of Saturn. The observed brightness variations have been separated into two components - one a function of orbital position, the other a function of solar phase angle. Dione and Tethys are brightest near greatest eastern elongation and faintest near greatest western elongation. The reverse is true of Enceladus. Opposition surges are observed for Dione and Tethys.