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NASA NTRS1981

Near-infrared spectrophotometry of the satellites and rings of Uranus

New spectrophotometry from 1.5 to 2.5 microns is reported for the Uranian satellites Titania, Oberon, and Umbriel. A spectrum of the rings of Uranus from 2.0 to 2.4 microns is also reported. No evidence is found for frost covering the surface of the ring material, consistent with the low albedo of the rings previously reported by Nicholson and Jones (1980). The surfaces of the satellites are found to be covered by dirty water frost. Assuming albedos of the frost and gray components covering the Uranian satellites to be the same as the light and dark faces of Iapetus, radii are derived that are roughly twice those inferred from the assumption of a visual albedo of 0.5.

Soifer, B. T.↗
NASA NTRS1982

Documentation for the machine-readable version of the Absolute Calibration of Stellar Spectrophotometry

The machine-readable data file of The Absolute Calibration of Stellar Spectrophotometry as distributed by the Astronomical Data Center is described. The data file contains the absolute fluxes for 16 stars published in Tables 1 and 2 of Johnson (1980). The absolute calibrations were accomplished by combining the 13-color photometry calibrations of Johnson and Mitchell (1975) with spectra obtained with a Michelson spectrophotometer and covering the wavelength range 4000 to 10300 A (Johnson 1977). The agreement between this absolute calibration and another recent one based upon data for a Lyr and 109 Vir by Tug, White and Lockwood (1977) is shown by Johnson (1980) to be quite good.

Warren, W. H., Jr.↗
NASA NTRS1982

Low resolution ultraviolet and optical spectrophotometry of symbiotic stars

Low resolution International Ultraviolet Explorer spectra combined with optical spectrophotometry provide absolute flux distributions for seven symbiotic variables from 1200 to 6450 A. For five stars (EG And, BF Cyg, CI Cyg, AG Peg, and Z And) the data are representative of the quiescent/out-of-eclipse energy distributions; for CH Cyg and AX Per, the observations were obtained following their atest outburst in 1977 and 1978, respectively. The de-reddened distributions reveal a remarkable diversity of both line spectra and continua. While the optical and near infrared regions lambda = 5500 A) are well represented by single component stellar models, multicomponent flux distributions are required to reproduce the ultraviolet continua.

Slovak, M. H.↗
NASA NTRS1981

4-8 micron spectrophotometry of OH 0739-14

Spectrophotometry of the dust-embedded late-type star OH 0739-14 shows an absorption feature at 6.0 microns characteristic of H2O ice at temperatures significantly lower than 150 K, confirming the identification of H2O ice in the circumstellar shell in this source. The differences in the infrared spectra of HO 0739-14 and embedded molecular cloud sources are attributed to the different cloud lifetimes and temperature regimes in which the molecules are formed. A lower limit to the mass loss rate of 0.0001 solar mass per year is derived, based on the column density of ice and the size and the expansion velocity of the circumstellar cloud.

Soifer, B. T.↗
NASA NTRS1982

Near-infrared spectrophotometry of four Seyfert 1 galaxies and NGC 1275

Low-resolution spectrophotometry from 2 to 4 microns is reported for the four Seyfert 1 galaxies Mrk 335, 3C 120, Mrk 509, NGC 7469, and the peculiar emission-line galaxy NGC 1275. The spectrum of NGC 7469 exhibits a strong 3.3-micron dust feature, indicating a thermal origin for the bulk of its considerable nonstellar infrared emission. NGC 1275 has a large stellar contribution to its infrared flux at wavelengths shortward of 3 microns. The spectrum from 3 to 4 microns fits a power law which fits the 10-micron and 20-micron broad bands, as well. A thermal model which can explain the spectrum of NGC 1275 is discussed. Mrk 335 displays a complex spectrum suggestive of thermal dust emission. 3C 120 and Mrk 509 have nonstellar infrared emission shortward of 2 microns, but the data are ambiguous as to whether this emission is thermal or nonthermal in origin.

Rudy, R. J.↗
NASA NTRS1982

Voyager absolute far-ultraviolet spectrophotometry of hot stars

Voyager observations in the 912-1200 A spectral region are used to indirectly intercompare absolute stellar spectrophotometry from previous experiments. Measurements of hot stars obtained by the Voyager 1 and 2 ultraviolet spectrometers show considerably higher 912-1200 A continuum fluxes than the recent observations of Brune et al. (1979) and Carruthers et al. (1981). The intercomparisons show all observations in basic agreement near 1200 A. The Carruthers et al. flux measurements are preferred down to 1050 A at which point the Voyager and Brune et al. values are respectively 60% higher and 60% lower. Below 1050 A the diasgreement among the observations becomes very large and the fluxes predicted by model atmospheres have been adopted. The pure hydrogen line-blanketed model atmosphere calculations of Wesemael et al. 1980) in comparison with Voyager observations of HZ 43 are used to adjust the Voyager calibration below 1050 A. This adjusted Voyager calibration, which is in good agreement with current model atmosphere fluxes for both early-type stars and DA white dwarfs, will be used for Voyager astronomical observations.

Holberg, J. B.↗
NASA NTRS1982

Spectrophotometry of the Cygnus Loop

New spectrophotometry for 17 filaments in the Cygnus Loop are presented. A wide variety of spectral properties is observed within the remnant. Comparisons with published shock models indicate significant differences between the models and observations with the range of observed line intensities not well described by models with varying shock velocity. Interference-filter photographs of the remnant's northeastern, northwestern, and western nebulae in H-alpha + N II, S II, O III, and O I show radial variations of line emission intensity with a scale much larger than that expected from a shock moving through a uniform medium. It is suggested that the emission variations and apparent ionization structure are the result of the shock front encountering an inhomogeneous interstellar medium.

Fesen, R. A.↗
NASA NTRS1983

Secondary standard stars for absolute spectrophotometry

Based on an adopted absolute spectral energy distribution for the primary standard star Alpha Lyrae, absolute fluxes are given for the four very metal-deficient F type subdwarfs HD 19445, HD 84937, BD + 26.2606 deg, and BD + 17.4703 deg. Somewhat inferior data are also given for HD 140283. The data are given for 40-A bands and cover the wavelength range from 3080 A to 12,000 A. The four stars, all near magnitude 9 and distributed around the sky, are intended as secondary standards for absolute spectrophotometry.

Oke, J. B.↗
NASA NTRS1983

Absolute spectrophotometry of Neptune - 3390 to 7800 A

Comparisons are undertaken of the results of Neptune absolute spectrophotometry from 3390 to 7800 A (having 10-A resolution over 3390-6055 A and 20-A resolution over 6055-7800 A) with both filter photometry and synthetic spectra computed on the basis of a parameterization proposed by Podolak and Danielson (1977) for aerosol scattering and absorption. A CH4/O2 ratio of between 0.01 and 0.1 is derived for the convectively mixed portion of the Neptune atmosphere, which constrains the optical properties of hypothetical aerosol layers.

Bergstralh, J. T.↗
NASA NTRS1983

Spectrophotometry of 2 complete samples of flat radio spectrum quasars

Spectrophotometry of two complete samples of flat-spectrum radio quasars show that for these objects there is a strong correlation between the equivalent width of the CIV wavelength 1550 emission line and the luminosity of the underlying continuum. Assuming Friedmann cosmologies, the scatter in this correlation is a minimum for q (sub o) is approximately 1. Alternatively, luminosity evolution can be invoked to give compact distributions for q (sub o) is approximately 0 models. A sample of Seyfert galaxies observed with IUE shows that despite some dispersion the average equivalent width of CIV wavelength 1550 in Seyfert galaxies is independent of the underlying continuum luminosity. New redshifts for 4 quasars are given.

Wampler, E. J.↗
NASA NTRS1984

Spectrophotometry of two complete samples of flat radio spectrum quasars

Spectrophotometry of two complete samples of flat-spectrum radio quasars show that for these objects there is a strong correlation between the equivalent width of the C IV 1550 A emission line and the luminosity of the underlying continuum. Assuming Friedmann cosmologies, the scatter in this correlation is a minimum for Q(O) approximately unity. Alternatively, luminosity evolution can be invoked to give compact distributions for Q(O) approximately zero models. A sample of Seyfert galaxies observed with IUE shows that despite some dispersion the average equivalent width of C IV 1550 A in Seyfert galaxies is independent of the underlying continuum luminosity. New redshifts are given for four quasars.

Gaskell, C. M.↗
NASA NTRS1984

Absolute spectrophotometry of Wolf-Rayet stars from 1200 to 7000 A - A cautionary tale

It is demonstrated that absolute spectrophotometry of the continua of Wolf-Rayet stars may be obtained over the wavelength range 1200-7000 A using IUE and optical measurements. It is shown that the application of a 'standard' reddening law to the observed data gives spurious results in many cases. Additional UV extinction is apparently necessary and may well be circumstellar in origin. In such hot stars, the long-wavelength 'tail' of the emergent stellar continuum are measured. The inadequacy of previous attempts to determine intrinsic continua and effective temperatures of Wolf-Rayet stars is pointed out.

Garmany, C. D.↗
NASA NTRS1984

The Use of Self-scanned Silicon Photodiode Arrays for Astronomical Spectrophotometry

The use of a Reticon self scanned silicon photodiode array for precision spectrophotometry is discussed. It is shown that internal errors are + or - 0.003 mag. Observations obtained with a photodiode array are compared with observations obtained with other types of detectors with agreement, from 3500 A to 10500 A, of 1%. The photometric properties of self scanned photodiode arrays are discussed. Potential pitfalls are given.

Cochran, A. L.↗
NASA NTRS1984

8- to 13-micron spectrophotometry of Comet IRAS-Araki-Alcock

Spectrophotometry between 8.0 and 13.0 microns at 2 percent spectral resolution is presented for areas in and near the nuclear condensation of Comet IRAS-Araki-Alcock (1983d) on May 11 and 12, 1983. All the spectra can be fit very well by blackbody curves, and no 10-micron silicate emissions are seen. The temperature structure of the coma suggests the presence of small (radii less than 5 microns) dust particles within 150 km of the nucleus and larger ones further out. The change in the spatial distribution of the infrared flux between the two nights suggests that an outburst may have occurred sometime on May 11.

Feierberg, M. A.↗
NASA NTRS1985

The nature of C-class asteroids from 3-micron spectrophotometry

Narrowband spectrophotometry between 2.3 and 3.5 micrometers is presented for 14 main-belt C asteroids greater than 100 km in diameter. Absorption features at 3 micrometers due to water of hydration are present in the spectra of nine of the asteroids, with intensities ranging from 6 to 23 percent. The other five asteroids have no such absorption greater than 2 percent in intensity. The present C-asteroid population may be fragments of larger parent bodies with anhydrous C3-like cores and hydrated C1I- or C2M-like mantles.

Feierberg, M. A.↗
NASA NTRS1985

2.7- to 4.1-micron spectrophotometry of icy satellites of Saturn and Jupiter

Spectrophotometry is presented in the 2.7-4.1 micrometer spectral region for icy satellites of Saturn (Tethys, Dione, Rhea, Iapetus and Hyperion) and Jupiter (Europa, Ganymede and Callisto). The 3.6-micrometer reflectance peak characteristic of fine-grained water ice is observed prominently on the satellites of Saturn, faintly on the leading side of Europa, and not at all on Ganymede, Callisto or the dark side of Iapetus. The spectral reflectances of these icy satellites may be affected by their equilibrium surface temperatures and magnetospheric effects.

Lebofsky, L. A.↗
NASA NTRS1985

Spectrophotometry of peculiar B and A stars. XVIII - The helium rich variable stars HR 1890, Sigma Orionis E, and HD 37776

Optical region spectrophotometry at 3300-7850 A has been obtained for three helium rich stars, HR 1890, Sigma Ori E, and HD 37776, of the Orion OB1 Association. New uvby-beta photometry of HR 1890 and HD 37776 as well as published data are also used to investigate the variability of these stars. A new period of 1.53862 days was determined for HD 37776. For all three stars H-beta varies in antiphase with strong He I lines. The spectrophotometric bandpass containing the strong He I line at 4471 A varies in phase with the R index of Pedersen and Thomsen (1977). Evidence is found for weak absorption features which appear to be an extension of the 5200 A feature seen in cooler CP stars.

Adelman, S. J.↗
NASA NTRS1986

Far-ultraviolet and optical spectrophotometry of X-ray selected Seyfert galaxies

Five X-ray selected Seyfert galaxies were examined via near-simultaneous far-ultraviolet and optical spectrophotometry in an effort to test models for excitation of emission lines by X-ray and ultraviolet continuum photoionization. The observed Ly-alpha/H-beta ratio in the present sample averages 22, with an increase found toward the high-velocity wings of the H lines in the spectrum of at least one of the Seyfert I nuclei. It is suggested that Seyfert galaxies with the most high-velocity gas exhibit the highest Ly-alpha/H-beta ratios at all velocities in the line profiles, and that sometimes this ratio may be highest for the highest velocity material in the broad-line clouds. Since broad-lined objects are least affected by Ly-alpha trapping effects, they have Ly-alpha/H-beta ratios much closer to those predicted by early photoionization calculations.

Clarke, J. T.↗