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At least 523 records · Page 29
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NASA NTRS1980

The photometric properties of brightest cluster galaxies. I - Absolute magnitudes in 116 nearby Abell clusters

Two-color aperture photometry of the brightest galaxies in a complete sample of nearby Abell clusters is presented. The results are used to anchor the bright end of the Hubble diagram; essentially the entire formal error for this method is then due to the sample of distant clusters used. New determinations of the systematic trend of galaxy absolute magnitude with the cluster properties of richness and Bautz-Morgan type are derived. When these new results are combined with the Gunn and Oke (1975) data on high-redshift clusters, a formal value (without accounting for any evolution) of q sub 0 = -0.55 + or - 0.45 (1 standard deviations) is found.

Hoessel, J. G.↗
NASA NTRS1980

The photometric properties of brightest cluster galaxies. II - SIT and CCD surface photometry

Surface photometry of the first-ranked galaxy in 108 Abell clusters is presented. Galaxy structure, as parameterized by simple Hubble law models, is found to correlate with galaxy absolute magnitude and cluster structure. All the structure data support the dynamical friction evolution model. Twenty-eight percent of the galaxies have multiple component nuclei; the short lifetimes of such systems provide the best available evidence that ongoing evolution actually occurs. Average magnitude and structure evolution rates are derived from the data.

Hoessel, J. G.↗
NASA NTRS1980

Vector space methods of photometric analysis. II - Refinement of the MK grid for B stars. III - The two components of ultraviolet reddening

This paper discusses systematic errors which arise from exclusive use of the MK system to determine reddening. It is found that implementation of uvby, beta photometry to refine the qualitative MK grid substantially reduces stellar mismatch error. A working definition of 'identical' ubvy, beta types is investigated and the relationship of uvby to B-V color excesses is determined. A comparison is also made of the hydrogen based uvby, beta types with the MK system based on He and metal lines. A small core correlated effective temperature luminosity error in the MK system for the early B stars is observed along with a breakdown of the MK luminosity criteria for the late B stars. The second part investigates the wavelength dependence of interstellar extinction in the ultraviolet wavelength range observed with the TD-1 satellite. In this study the sets of identical stars employed to find reddening are determined more precisely than in previous studies and consist only of normal, nonsupergiant stars. A multivariate analysis of variance techniques in an unbiased coordinate system is used for determining the wavelength dependence of reddening.

Massa, D.↗
NASA NTRS1980

Photometric properties of outer planetary satellites

Optical broadband photometry for the satellites J6, J7, J8, S7, S9, U3, U4, and N1 and polarimetry for J6, obtained between 1970 and 1979, are presented. The outer Jovian satellites resemble C-type asteroids; J6 has a rotational lightcurve with a period of approximately 9.5 hr. The satellites beyond Jupiter also show C-like colors with the exception of S7 Hyperion. S9 Phoebe has a rotational lightcurve with period near either 11.25 or 21.1 hr. For U4 and N1 there is evidence for a lightcurve synchronous with the orbital revolution. The seven brighter Saturnian satellites show a regular relation between the ultraviolet dropoff and distance to the planet, probably related with differences in the rock component on their surfaces.

Degewij, J.↗
NASA NTRS1981

Theoretical interpretation of photometric properties of the Martian surface and atmosphere

Earth-based UBV photometry, photographs from the Lowell Observatory, and Mariner 9 data are combined with a new radiative transfer theory to derive physical parameters for the Martian surface and atmosphere, both before and during the 1971 dust storm. Storm dust particles had a single scattering albedo of 0.84 plus or minus 0.02 and an asymmetry factor of 0.35 plus or minus 0.10 in green (V) light. The geometric albedo of Mars was 0.15 and the phase integral 1.83, yielding 0.27 for the Bond albedo. The mean optical thickness of the 'clear' atmosphere averaged over the whole planet was 0.15 plus or minus 0.05 and was not dependent on wavelength. Geometric albedos for the surface are 0.25 (light areas) and 0.17 (dark areas) in V, 0.095 in B, and 0.060 in U. The soil particles are moderately backward scattering with an asymmetry factor of minus 0.20, and therefore rather opaque. The mean surface roughness is 0.57, representing the depth/radius ratio of an average hole, and being only one-half as large as values typical for the moon and asteroids.

Lumme, K.↗
NASA NTRS1981

Atmospheric emission photometric imaging

A dual-channel video system mounted on a stabilized two-axis gimbal system (mounted on the pallet) with associated optics and data handling electronics described the low light flux observations are required for: (1) investigating ionospheric transport processes by observing Mg+ ions; (2) supporting magnetospheric electron bounce experiments; (3) measuring electron cross sections for selected atmospheric species; (4) detecting small particle contamination; and (5) studying natural auroras.

Mende, S. B.↗
NASA NTRS1982

The photometric performance of the IUE

The scientific objectives and performance characteristics of a new astronomy mission referred to as the far ultraviolet spectroscopic explorer, or FUSE are being defined by team involving people experienced in instrumentation, observations, and theory in order to develop. mission and instrumental requirements that best meet the scientific needs. The team is intended to have a lifetime of about one year, ending with the submission of a report to NASA which could be used as the basis for an engineering design study. The principal objective of FUSE is to obtain astronomical spectra at wavelengths shorter than is possible with the Space Telescope.

Holm, A. V.↗
NASA NTRS1981

Image tube spectroscopic studies of rapid variables. IV - Spectroscopic and photometric observations of AE Aquarii

Photoelectric and time-resolved spectroscopic observations of the short-period eruptive binary AE Aqr are presented. The system has a period of 0.4116537 days, and emission and absorption-line components equal to 135 km/sec and 159 km/sec, respectively. The spectral type of the absorption-line component is found to be K5V, from which M1 = 0.82 solar mass, M2 = 0.69 solar mass, and i = 64 deg. A predominantly Ca II emission region occurs on the hemisphere of the K5V star facing the broad emission-line component, whose center of light is located 0.64 of the way from the inner Lagrangian point to the center of mass of the K star. This emission appears to be associated with the transfer of mass from the K5V star to the accretion disk surrounding the primary. In the absence of flare activity, the light of the system is variable in the orbital period with a range in V of about 0.16 mag; maxima occurs near the times of maximum recession velocity and during the approach of each of the two components of the system (0.25 P and 0.80 P).

Chincarini, G.↗
NASA NTRS1982

Further photometric observations of 2A 0311-227

Simultaneous V, B, and U photometry is presented for the AM Herculis type system 2A 0311-227. A Fourier analysis has failed to detect the 6 minute quasi-periodic oscillation reported earlier. It has, however, revealed the presence of oscillations at 20.2 and 13.7 minutes. These are interpreted in terms of a nonsinusoidal light curve. U, B, and V light curves are given and discussed in terms of current models for AM Her systems. B-V and U-B color curves are also presented, as is the behavior of the system in the color-color plane.

Williams, G.↗
NASA NTRS1981

Predicted star counts in selected fields and photometric bands Applications to galactic structure, the disk luminosity function, and the detection of a massive halo

Tables are presented of predicted star counts in 17 selected directions on the sky as a function of apparent B, V, R, and I magnitudes and absolute visual magnitudes calculated from the Bahcall-Soneira Galaxy model. It is noted that eight of the fields were selected ab initio for their usefulness in determining from star counts either parameters of galactic structure, the faint end of the disk luminosity function, or the detection of a massive stellar halo. Star counts in specified fields to m sub I = 19 mag are able to reveal the faint end of the disk luminosity function down to the end of the hydrogen-burning main sequence. It is thought that star counts at high galactic latitudes to m sub I = 22 mag should reveal the stellar constituents of a massive halo if they are massive enough to be on the hydrogen-burning main sequence.

Bahcall, J. N.↗
NASA NTRS1982

A rocket-borne photometric measurement of O3 and NO2 in the equatorial stratosphere

A determination of the NO2 and O3 mixing ratios has been made by measuring the attenuation of sunlight at 409 nm and 254, 288, 316 nm from an ascending rocket launched from Kourou, French Guiana (5 N) during the morning twilight of March 21, 1974. A peak NO2 volume mixing ratio of 4.4 x 10 to the -9th + 40%, -50% was measured at 30 km altitude.

Schlyter, P.↗
NASA NTRS1982

Analysis of photometric spectra of 17 meteors

The initial phase of the photometry which involved 17 meteor spectra consisting of eight Geminid spectra, six Orionid spectra and three Eta Aquarid spectra is discussed. Among these 17 spectra it is found that the Geminid spectra are of the best quality and are used for the identification of the atomic lines and molecular bands that normally appear on video tape spectra. The data from the Geminid records are used for developing calibration techniques in photometry. The Orionid and Eta Aquarid spectra are chosen for early analysis because of the current interest in all physical and chemical data relating to Comet Halley.

Millman, P. M.↗
NASA NTRS1983

A large-amplitude photometric periodicity on a T Tauri star

B, V, and R light curvea are presented for the years 1970-1972, during whith the T Tauri star SY Chamaeleontis was observed to undergo precisely periodic brightness oscillations with a 1.6 mag B amplitude and a 6.129-day period. While SY Cha has shown small amplitude irregular variability since 1901, and in 1971 exhibited a sinusoidal light curve in the 13.4-14.2 mag range, this range was found to increase during 1971-1972 to 12.76-14.34 mag. Between 1973 and 1978, the odd behavior pattern was resumed. It is suggested that a localized bright spot formed on, or near, the surface of SY Cha, and that stellar rotation has caused the spot to appear and disapear from the vantage point of the earth.

Schaefer, B. E.↗
NASA NTRS1984

Photometric Studies of Heat Flow at the Photosphere

Continuum photometry is carried out and the results of comparing these observations with models of photospheric heat flow are described. The main results are: (1) a possible detection of weak bright rings around some spot penumbrae; (2) no evidence is found for large scale photospheric brightness inhomogeneities exceeding 2-3 K which places tighter constraints on models of global scale convection; (3) supergranular scale continuum structures observed across the photosphere appear mainly due to random clumping of granules; (4) the one case observed of a sunspot emergence shows no thermal shadow exceeding 1.5 K rms one day prior to umbra appearance; (5) network and faculae are found to show a small excess brightness even at mu = 1, so detection of faculae at mu = 1 by differential photometry indicates a gentler temperature gradient near tau = 1 in the facular (relative to cell) atmosphere; (6) the limb darkening study shows no significant global variations to within 0.1% rms.

Foukal, P.↗
NASA NTRS1983

Ultraviolet response of film candidates for the solar optical telescope photometric filtergraph

Measurements of UV response between 2000 and 3000 A of Kodak films 2415, Aerocon II 3412, and SO-415 are reported. The short wavelength cutoff of the response of all films studied lies near 2100 A, occurring as a gentle falloff starting near 2500 A. The sensitivity of the films appears to remain roughly constant from 2500 to 3000 A. Estimates of UV Gamma for 2415 and the effect of hard UV on the optics in the experiment are also discussed.

Morgan, J. A.↗
NASA NTRS1984

Photometric properties of powdered sulfur

Particle size, temperature, thermal history, and scattering geometry are shown by the present laboratory investigation of the spectrophotometric properties of three particle-size fractions of sulfur to influence the spectral reflectance of both normal and quenched molten samples of sulfur. A scattering law that consists of a linear combination of lunar-like and Lambertian terms adequately describes the data for all particle sizes. Near opposition, sulfur particles closely follow a Minnaert limb darkening law except where the reflectance is low, as in the strong UV absorption band of the larger particle size fractions. The present data indicate that quantitative comparisons between disk-integrated observations of Io and laboratory measurements of flat sulfur samples are inadequate unless temperature effects and scattering geometry changes are included.

Gradie, J.↗
NASA NTRS1984

Photometric study of NGC 2023 in the 3500 A to 10000 A region - Confirmation of a near-IR emission process in reflection nebulae

A surface brightness study of the reflection nebula NGC 2023 covering the 3500-10,000 A wavelength region performed with uvby photoelectric photometry and BVRI imaging with a CCD detector is reported along with VRI photometry of a cluster of embedded red stars. The nebular radiation in the 3500-5500 A region is dust-scattered starlight originating in the star HD 37903. The embedded red stars are probably pre-main sequence stars. The nebular surface brightness in R and I exceeds that expected on the basis of a reasonable radiative transfer model by factors of two and more than three, respectively. The excess radiation is extended across the nebula in a manner similar to the scattered light. The extended red emission may be interpreted as the high-frequency extension of extended emission discovered by Sellgren, Werner, and Dinerstein (1983) in the 2-5 micron region in NGC 2023 and two other reflection nebulae.

Schild, R. E.↗
NASA NTRS1984

Photometric standard stars for L' and M filter bands

L' (3.8 microns) and M (4.9 microns) photometry of 20 primary and 21 secondary standard stars that are sufficiently faint for large telescope observation is presented. The estimated uncertainties in the magnitudes of the primary standards are 0.01 at L', 0.02 at M, and 0.015 for the L'-M color. A color transformation between the present L' magnitudes and the L magnitudes of Elias et al. (1982) is obtained and found to be near agreement with that predicted for black-bodies.

Sinton, W. M.↗