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At least 433 records · Page 24
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NASA NTRS1978

Low surface pressure models for Titan's atmosphere

The inversion model for the atmosphere of Titan is reviewed. The basic features of the model are: a cold surface (80 K), a warm stratosphere (160 K) and a low surface pressure (20 mbar). The model is consistent with all existing thermal infrared spectrophotometry, but it cannot preclude the existence of an opaque, cloud, thick atmosphere. The model excludes other gases than methane as bulk constituents. Radio wavelengths observations, including recent data from the very large array, are discussed. These long wavelength observations may be the only direct means of sampling the surface environment before an entry probe or flyby.

Caldwell, J.↗
NASA NTRS1978

Taxonomy of asteroids

A taxonomic system for asteroids is discussed which is based on seven directly observable parameters from polarimetry, spectrophotometry, radiometry, and UBV photometry. The classification scheme is entirely empirical and independent of specific mineralogical interpretations. Five broad classes (designated C, S, M, E, and R), as well as an 'unclassifiable' designation, are defined on the basis of observational data for 523 asteroids. Computer-generated type classifications and derived diameters are given for the 523 asteroids, and the application of the classification procedure is illustrated. Of the 523 asteroids classified, 190 are identified as C objects, 141 as S type, 13 as type M, three as type E, three as type R, 55 as unclassifiable, and 118 as ambiguous. The present taxonomic system is compared with several other asteroid classification systems.

Bowell, E.↗
NASA NTRS1978

The asteroids

The asteroids are small rocky bodies that orbit in modestly eccentric and inclined orbits, mainly between the orbits of Mars and Jupiter. With the comets, they are the only known population of residual planetesimals from the earliest epochs of solar system history. The observational characteristics of asteroids are discussed, taking into account aspects of photometry, rotations, masses and densities, spectrophotometry and surface compositions, surface textures and regoliths, size distribution, and erosion and fragmentation occurring as a result of interasteroidal collisions. Questions of dynamics and orbital evolution are investigated and ramifications for planetary evolution are explored. Attention is given to asteroids as planetesimals, aspects of early orbital evolution, the geochemical evolution of asteroids, commensurabilities and Kirkwood gaps, secular resonances, the material transport from the asteroid belt, Poisson's theorem, planetary masses, catalogs and selection effects, families, and Apollo, Amor, and Mars-crossing asteroids.

Chapman, C. R.↗
NASA NTRS1978

Near-infrared energy distributions of M31

Spectrophotometric data obtained by comparing Spinrad-Taylor (1969) standards with Alpha Lyr are presented, along with a calibration of these data for wavelengths longward of 6000 A. M31 sky measurements made 1 deg south of the nucleus at five wavelengths between 6040 and 10,360 A, inclusive, are compared with near-IR spectrophotometry performed by Spinrad and Taylor (1971), Oke and Schwarzschild (1975), and O'Connell (1976). Agreement and discrepancies among the different data sets are discussed. Some possible explanations of the differences are discounted, and tests are performed which reveal no effects of error in mean extinction and brightness-dependent wavelength response.

Taylor, B. J.↗
NASA NTRS1979

Infrared observations of the X-ray quasars 0241+622 and MR2251-178

Infrared observations of the recently discovered X-ray quasars 0241+622 and MR2251-178 are reported. Broadband photometry of both quasars was conducted in the 1.25 to 20 micron range and spectrophotometry of 0241+622 was carried out from 1.5 to 2.5 microns. The IR energy distributions of 0241+622, MR2251-178 and the X-ray quasar 3C273 are presented, noting that for wavelengths less than 10 microns, the energy distributions of all three quasars are similar and cannot be distinguished from those of other low redshift quasars. The observed IR, visual and X-ray luminosities of the three quasars are compared and are found not to be strongly correlated. It is remarked, however, that the three X-ray quasars are the brightest known quasars at IR and visual wavelengths, which supports the suggestion that all quasars are bright X-ray emitters.

Soifer, B. T.↗
NASA NTRS1979

The ultraviolet flux distribution of Alpha-2 Canum Venaticorum

Intermediate- and narrow-band UV spectrophotometry from Copernicus, OAO 2, the S2-68 experiment on TD 1, and a sounding-rocket experiment are combined with ground-based observations to define the absolute flux distribution of the bright magnetic Ap star Alpha-2 CVn over the wavelength range from 1030 to 7580 A. Two flux distributions are presented which coincide more or less with the rare-earth maximum and minimum in the star's cycle. The results are compared with those for two normal stars, the UV variability of Alpha-2 CVn is characterized as a function of wavelength, and non-LTE effects on the UV continua of C I and Si I are analyzed. Some physical properties of Alpha-2 CVn are estimated, and the evolutionary age of the star is estimated to be between 220 million and 300 million years. It is concluded that Alpha-2 CVn is old enough to have been magnetically braked to its current rotational velocity by either the centrifugal-wind or the accretion mechanism and to have developed its chemical peculiarities by either mechanism.

Leckrone, D. S.↗
NASA NTRS1979

Infrared and optical measurements of the ionized gas in K3-50

Results are reported for optical, near-IR, and mid-IR spectrophotometry of the compact H II region K3-50A. The emission-line observations imply an electron density of about 100,000 per cu cm; the consistency of density measurements in the optical, IR, and radio sources suggests that the optical counterpart of K3-50A is a reflection nebula. Previous measurements of the anomalous extinction law in K3-50A are confirmed, this law is extended out to B-alpha at 4 microns, and a 9-micron optical depth of about 2.5 is obtained. Elemental abundances are derived from measurements of emission lines of several dominant ions of the same element and found to be in close agreement (50%) with mean cosmic abundances. Individual ionic ratios are compared with model H II region calculations to determine the nature of the ionizing radiation. It is concluded that if nongray UV dust absorption does not modify the spectrum appreciably, the radiation temperature can be associated with a stellar surface temperature of about 37,000 K, corresponding to an O6 supergiant.

Lester, D. F.↗
NASA NTRS1979

Infrared observations of NGC 2071/IRS/ and AFGL 490 - Two low-luminosity young stars

Infrared observations are presented of two compact sources associated with molecular clouds. Photometry from 2 to 200 microns of the source associated with an OH maser in NGC 2071, OH 205.1-14.1, shows a steep increase in flux from 2 to 50 microns. Scans at several wavelengths fail to resolve the source. Photometry at 50-200 microns of the other object, GL 490, when combined with earlier 2-20-micron spectrophotometry, shows an infrared energy distribution that is much broader than that of the NGC 2071 source. Both sources are interpreted as young, possibly pre-main-sequence objects with differences in energy distributions due principally to differences in the distribution of circumstellar matter.

Harvey, P. M.↗
NASA NTRS1979

Absolute calibration in the 1750 A-3350 A region

The absolute flux measurements in the rocket ultraviolet made by Bohlin, Frimout, and Lillie (BFL) are revised using a more correct treatment of the air extinction that enters the air calibration of their instrument. The absorption by molecular oxygen and ozone, Rayleigh scattering, and extinction by aerosols is tabulated for general use in ultraviolet calibrations performed in air. The revised absolute flux of Eta UMa and final fluxes for Alpha Lyr and Zeta Oph are presented in the 1750 A-3350 A region. The absolute flux of the star Eta UMa (B3 V) is compared to four other independent determinations in the 1200 A-3400 A region and a maximum difference of 35% is found near 1500 A between the OAO-2 and Apollo 17 fluxes. Longward of 1700 A the typical scatter in the different determinations is only plus or minus 5%. The rocket measurements of BFL, the ANS and TD-1 satellite data, and the Apollo 17 data are compared to the ultraviolet fluxes from the OAO-2, demonstrating a photometric reproducibility of about plus or minus 3%. Therefore, all four sets of spectrophotometry can be reduced to a common absolute scale.

Strongylis, G. J.↗
NASA NTRS1979

IUE spectra of the nuclei of M31 and M32

Observed spectra are reproduced in the 1000-3400 wavelength range; line identifications are tabulated, and spectrophotometry of parts of the continua is given. The flux density of a few line emissions can be estimated from their equivalent widths. The strongest line emissions differ in the two nuclei, and they do not fit spectral patterns that are observed in the sun, hot stars, gaseous nebulae, or quasi-stellar objects. However, the absorption-line features are rather similar to those of the sun.

Johnson, H. M.↗
NASA NTRS1979

The 4-8 micron spectrum of the infrared source W33 A

The spectrum of the highly obscured infrared source W33 A from 4.5 to 8 microns is measured in order to investigate the intervening cold, dense interstellar material. Spectrophotometry at a relative spectral resolution of about 0.015 by an airborne filter-wheel infrared spectrometer reveals strong absorption features at 4.61, 5.99 and 6.78 microns. The absorption at 4.61 microns is attributed primarily to the fundamental vibration-rotation band of CO at a column density (at least 10 to the 19th/sq cm) which is 10% of the carbon inferred from silicate abundances. The strengths and line widths of the absorption agt 5.99 and 6.78 microns are interpreted as evidence of absorption in the resonance bands of carbonyl, carbon-carbon double, methyl and methylene bonds of hydrocarbons associated with interstellar dust.

Soifer, B. T.↗
NASA NTRS1979

Determination of physical and chemical states of lubricants in concentrated contacts, part 1

A Fourier emission infrared microspectrometer, set up on a vibration-proof optical table and interfaced to a dedicated minicomputer, was used to record infrared emission spectra from elastohydrodynamic bearing contacts. Its range was extended to cover the entire mid-infrared from 2 to 15 micron. A series of experiments with 5P4E polyphenyl ether showed the existence of a temperature gradient through the lubricant in an ehd contact, which is perpendicular to the flow direction. The experiments also show marked polarization of some of the spectral bands, indicating a molecular alignment. Alignment is less evident at high pressure than at low pressure. To account for this behavior, a model is suggested along the lines developed for the conformational changes observed in long-chain polymers when subjected to increased pressure--to accommodate closer packing, molecules become kinked and curl up. Experiments with a traction fluid showed periodic changes of flow pattern associated with certain spectral changes. These observations will be studied further. A study by infrared attenuated total reflection spectrophotometry was undertaken to determine whether gamma irradiation would change polyethylene wear specimens. The results were negative.

Lauer, J. L.↗
NASA NTRS1980

The discovery of optical emission from the SNR G 126.2 + 1.6

Interference filter photographs were used to identify an arc of nebulosity that is coincident with the radio contours of the galactic supernova remnant G 126.2 + 1.6. Spectrophotometry of the filament shows that the emission line spectrum matches the spectra of other galactic supernova remnants. In particular, the arc shows the usual strong SII, and NII emission lines seen in other remnants and unusually strong OII emission as seen in a few remnants. The spectrum can be adequately matched by a shock of velocity near 100 km/s in an interstellar cloud of density 3. If the SNR is at a distance of 4.5 kpc as indicated by the radio signal-D relation, then the observed pressure in the filament requires an initial energy near 4 x 10 to the 51st power (d/4.5 kpc) to the 3rd power ergs.

Blair, W. P.↗
NASA NTRS1979

Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars

This paper discusses effective temperatures, angular diameters, distances, and linear diameters that have been determined for 160 O and B stars on the basis of published UV spectrophotometry, visible and near-IR intermediate-band photometry, and model-atmosphere fluxes. The results are compared with previous measurements and calculations for main-sequence and giant O and B stars. It is found that: (1) the flux effective temperatures of O and B supergiants are systematically lower than those of main-sequence and giant stars of the same subtype; (2) the effective temperatures and radii of Beta Cep stars are the same as those of nonvariable stars of the same spectral type; (3) Be stars that do not have two Balmer jumps have effective temperatures very similar to those of normal B stars of the same subtype; (4) O and B stars increase in size from the main sequence to supergiants; and (5) late B supergiants are approximately twice as large as O9 supergiants.

Underhill, A. B.↗
NASA NTRS1979

Optical studies of the Seyfert 2 X-ray galaxy NGC 2110

Spectrophotometry of the nucleus of the X-ray galaxy NGC2110 shows a typical Seyfert Type 2 spectrum with a strong galactic continuum. The widths of the forbidden lines are about 360 km/s (FWHM), H-beta being somewhat broader. The moderate Balmer decrement implies that the interstellar reddening is approximately 2.1 mag. The average electron density and temperature in the line-emitting region are approximately 300 per cu cm and 35,000 K, respectively. From measurements of the nebulium line, it is found that the extent of the nucleus measured along the major axis of the galaxy is about 10 arcsec (2100 pc) and the full range of gas velocities is about 700 km/s. A direct plate is discussed which shows faint spirallike features in NGC2110, a galaxy currently classified as elliptical. NGC2110 is a member of a new class (about 5 members) of very nearby (cz less than 2500 km/s) X-ray galaxies. Bradt et al. (1978) tentatively concluded that they are Seyfert Type 2 galaxies. This conclusion is supported, and it is shown that this is not inconsistent with the narrowness (less than 500 km/s FWHM) of their emission line.

Mcclintock, J. E.↗
NASA NTRS1979

X-ray and optical variability in 2A1052+606 - A new RS CVn-type system

The paper discusses a star with RS CVn-type characteristics discovered as a result of an accurate X-ray location. The RS CVn binaries have been found to be a new class of soft X-ray sources from the HEAO 1 low energy sky survey. The source was detected at energies below 1 keV and evidence is presented for variability on time scales of approximately 1 day. The strong soft X-ray source was observed at a position consistent with 2A1052+606 and the X-ray light curve shows that the source underwent a strong soft X-ray flare. Subsequent spectrophotometry revealed variable H(alpha) and possibly CaII H,K emission which strongly supports its classification as an RS CVn system.

Charles, P.↗
NASA NTRS1980

Galaxy spectral synthesis. II - M32 and the ages of galaxies

The paper presents a population synthesis performed on absolute spectrophotometry for the central 31 in. of M32. The metallicity of M32 is solar with 0.1 dex, implying that major star formation continued in M32 until 5 Gyr ago, or 10 Gyr after the oldest globular clusters formed. The synthesis models predict that the rate of mass return to the interstellar medium in M32 from evolving stars is about 0.0008 solar mass/yr; however, the upper limit for star formation during the past 1 Gyr is about 0.003/yr, showing that the available optical observations do not exclude complete recycling of gas lost during stellar evolution into new generations of stars.

Oconnell, R. W.↗
NASA NTRS1980

Discovery of optical molecular emission from the bipolar nebula surrounding HD 44179

Spectrophotometry and spectropolarimetry with HD 44179 are presented. These measurements reveal that the very broad bump evident in previous low-resolution spectra possesses a large amount of structure, including groups of narrow emission lines and several diffuse features. A reduction in polarization, but constant position angle, through the bump indicates that this emission originates within the nebula itself and merely dilutes the polarized scattered starlight. A few very weak atomic emission lines are detected, but the overall feature, which strongly resembles the emission spectra of some molecules, remains unidentified. Constraints on the excitation mechanism are discussed.

Schmidt, G. D.↗