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NASA NTRS1982

Documentation for the machine-readable version of OAO 2 filter photometry of 531 stars of diverse types

A magnetic tape version of the ultraviolet photometry of 531 stars observed with the Wisconsin Experiment Package aboard the Orbiting Astronomical Observatory (OAO 2) is described. The data were obtained with medium band interference filters and were reduced to a uniform magnitude system. They represent a subset of partially reduced data currently on file at the National Space Science Data Center. The document is intended to enable users of the tape file to read and process data without problems or guesswork. For technical details concerning the observations, instrumentation limitations, and interpretation of the data the reference publication should be consulted. This document was designed for distribution with any machine-readable version of the OAO 2 photometric data.

Warren, W. H., Jr.↗
DOE OSTI2020

The ALFALFA-SDSS Galaxy Catalog

We present a H i optical catalog of ~30,000 galaxies based on the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey combined with data from the Sloan Digital Sky Survey (SDSS). Our goal is to facilitate the public use of the completed ALFALFA catalog by providing carefully determined matches to SDSS counterparts, including matches for ~10,000 galaxies that do not have SDSS spectra. These identifications can provide a basis for further crossmatching with other surveys using SDSS photometric IDs as a reference point. We derive absolute magnitudes and stellar masses for each galaxy using optical colors combined with an internal reddening correction designed for small- and intermediate-mass galaxies with active star formation. We also provide measures of stellar masses and star formation rates based on infrared and/or ultraviolet photometry for galaxies that are detected by the Wide-field Infrared Survey Explorer and/or the Galaxy Evolution Explorer. Finally, we compare the galaxy population in the ALFALFA-SDSS sample with the populations in several other publicly available galaxy catalogs and confirm that ALFALFA galaxies typically have lower masses and bluer colors.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2007

White Dwarfs in the GALEX Survey

We have cross-correlated the 2dF QSO Redshift Survey (2QZ) white dwarf catalog with the GALEX 2nd Data Release and the Sloan Digital Sky Survey (SDSS) data release 5 to obtain ultraviolet photometry (FUV, NUV) for approximately 700 objects and optical photometry (ugriz) for approximately 800 objects. We have compared the optical-ultraviolet colors to synthetic white dwarf colors to obtain temperature estimates for approximately 250 of these objects. These white dwarfs have effective temperatures ranging from 10 000 K (cooling age of about 1Gyr) up to about 40000 K (cooling age of about 3 Myrs), with a few that have even higher temperatures. We found that to distinguish white dwarfs from other stellar luminosity classes both optical and ultraviolet colors are necessary, in particular for the hotter objects where there is contamination from B and 0 main-sequence stars. Using this sample we build a luminosity function for the DA white dwarfs with Mv < 12 mag.

Kawka, Adela↗
DOE OSTI2020

Clues on the history of early-type galaxies from SDSS spectra and GALEX photometry

ABSTRACT Stellar population studies of early-type galaxies (ETGs) based on their optical stellar continuum suggest that these are quiescent systems. However, emission lines and ultraviolet photometry reveal a diverse population. We use a new version of the starlight spectral synthesis code and state-of-the-art stellar population models to simultaneously fit Sloan Digital Sky Survey spectra and Galaxy Evolution Explorer photometry for a sample of 3453 galaxies at z < 0.1 with near ultraviolet (NUV) − r > 5 that are classified as elliptical by Galaxy Zoo. We reproduce far ultraviolet (FUV) magnitudes for 80 per cent of UV upturn galaxies selected using criteria from the literature, suggesting that additional stellar population ingredients such as binaries and extreme horizontal branch stars may have a limited contribution to the UV upturn. The addition of ultraviolet data leads to a broadening of the distributions of mean stellar ages, metallicities, and attenuation. Stellar populations younger than $1\,$ Gyr are required to reproduce the ultraviolet emission in 17 per cent of our sample. These systems represent 43 per cent of the sample at 5 < NUV − r < 5.5 and span the same stellar mass range as other ETGs in our sample. ETGs with young stellar components have larger H α equivalent widths (WH α) and larger dust attenuation. Emission line ratios and WH α indicate that the ionizing source in these systems is a mixture of young and old stellar populations. Their young stellar populations are metal-poor, especially for high-mass galaxies, indicating recent star formation associated with rejuvenation events triggered by external processes, such as minor mergers.

Werle, A.↗
NASA NTRS1974

OAO-2 observations of the helium spectrum variable a Centauri

Ultraviolet photometry and spectrometer data are presented for a Cen, which exhibits large variations in the strength of its He I lines. The photometry indicates that the star becomes brighter at the helium-weak phase by 0.05 mag throughout the ultraviolet and visual region. A model atmosphere analysis indicates that the photometric variations are not due to flux redistribution from back-warming effects, but can be interpreted as due to the rotation of a distorted stellar disk in the shape of a prolate spheroid.

Molnar, M. R.↗
NASA NTRS1972

Metal line blanketing and opacity in the ultraviolet of alpha 2 Canum Venaticorum

Ultraviolet photometry by OAO-2 was made of alpha 2 CVn covering the entire 5.5d period of this magnetic Ap variable. The light curves ranging from 1330 A to 3320 A indicate the dominant role of rare-earth line-blanketing in redistributing flux. In a broad depression of the continuum covering 2300-2600 A, scanner observations possibly identify strong lines of Eu III as major contributors to this feature. At maximum intensity of the rare-earth lines, the ultraviolet continuum shortward of 2900 A is greatly diminished while the longer wavelength regions into the visual become brighter. In addition, there is evidence that the hydrogen line opacity is variable and the photoionization edge of Si I at 1680 A is identified.

Molnar, M. R.↗
NASA NTRS1976

Feige 24 - A very hot white dwarf

OAO-2 ultraviolet photometry of the composite spectrum white dwarf Feige 24 is compared with model atmospheres to derive an effective temperature of 70,000 (+20,000, -15,000) K. The distance to this star is estimated to be 90 (+55, -31) pc if the cool component is assumed to be a main-sequence star with a red and near-infrared energy distribution that is normal for its spectral type. The derived characteristics of Feige 24 are compatible with its identification as the extreme-ultraviolet source observed by Margon et al.

Holm, A. V.↗
NASA NTRS1986

A survey of chromospherically active stars

Photometric and/or spectroscopic observations have been obtained of 52 late-type stars which are suspected or known to be chromospherically active. Although not all types of observations were obtained for each star, these observations include all-sky BVRI Johnson photometry, ultraviolet spectrograms, low-dispersion blue-wavelength spectrograms, and high-dispersion red-wavelength spectrograms. From the spectroscopic observations v sin i's, radial velocities, and the appearance of the Ca II H and K emission lines have been determined as well as the H-alpha line. The photometric observations indicate that chromospherically active stars have V - R and V - I color excesses. Such excesses will affect the surface fluxes determined with the surface brightness-color relationship. On the other hand all-sky BVRI photometry appears to be an excellent way to identify chromospherically active stars. A small group of moderately rapidly rotating, possibly single G8-K2 giants has been found. These stars have very modest chromospheric activity and so are not FK comae stars. A number of other unusual chromospherically active stars are identified.

Fekel, F. C.↗
NASA NTRS1978

Ultraviolet observations and the extended spectrum of NGC 4151

Five-channel ultraviolet photometry of the Seyfert galaxy NGC 4151 was obtained at three epochs with the ANS. These data are combined with other recent results to illustrate the spectrum of the nucleus of NGC 4151 from 34 microns to 20 MeV, with corrections for galaxy contamination. It is found that no other part of the spectrum has a slope like the best-fitting power law for the X-rays. The C IV emission-line flux is measured; the C IV/H-beta ratio is between 5 and 8, which is similar to the ratio in quasars.

Wu, C.-C.↗
NASA NTRS1978

Limb darkening 1945-3245 A for the quiet sun from Skylab data

Limb-darkening measurements of the quiet sun in the spectral range 1945-3245 A have been made using NRL's SO82B instrument on board Skylab. The spectral intensities have been averaged over 10 A wavelength bands, and coefficients for linear, quadratic, and logarithmic fits to the observed center-to-limb variations have been calculated and tabulated as a function of wavelength. The quadratic fits are found to represent the observations best, the observed and calculated values agreeing to better than plus or minus 15% on the average. Attention is drawn to the value of the results for ultraviolet photometry of eclipsing binaries.

Moe, O. K.↗
NASA NTRS1978

A synthetic light curve solution of the OAO-2 ultraviolet light curves of u Herculis

OAO 2 ultraviolet photometry of the eclipsing binary u Her is reported and interpreted. The light curve of u Her is found to be intrinsically variable, the variable light curve is rectified, and the adjusted light and color curves are plotted. A simultaneous solution to three adjusted OAO 2 light curves (at respective wavelengths of 3320, 1910, and 1550 A) is obtained by using the Roche model. The results indicate that the system is semidetached if the gravity darkening of the secondary is not significantly larger than expected. It is suggested that the primary is responsible for the variable light curve, that the monochromatic albedo of the secondary is very low at short wavelengths, and that the depth of primary eclipse is strongly dependent on the primary's limb darkening.

Eaton, J. A.↗
NASA NTRS1984

Local Interstellar Extinction with an Emphasis on Uvby Beta Results

Some theories concerning the distribution of interstellar dust are surveyed. Average reddening and the distribution of local dust studied by means of ultraviolet photometry are discussed. The existence of local dust in the pole directions, local voids, variations of color excess with distance, and properties of local diffuse dust clouds are among the topics considered.

Knude, J.↗
NASA NTRS1984

The ultraviolet variability of early-type supergiants

Four early-type supergiants - HD 79186 (B5 Ia), HD 96919 (B9 Ia), HD 105056 (ON9.7 Iae), and HD 148379 (B2 Iae) - have been observed with the low-resolution spectrographs of IUE in the large aperture on 14 days. The behavior of the ultraviolet fluxes with time is studied. The light from all four stars seems to vary. Typically the dispersion about the mean magnitude at any wavelength corresponds to + or - 0.085, + or - 0.080, + or - 0.101, and + or - 0.106 mag, respectively. These amplitudes exceed the typical uncertainty in an IUE measurement of flux by about a factor of 3; they are somewhat larger than the variations known in the visible wavelength range. There are insufficient data to investigate periodicity in the observed light changes. The effective temperatures and angular diameters of the stars have been estimated using the present ultraviolet photometry, published UBV and uvby photometry, and the model-atmosphere fluxes reported by Kurucz in 1979. The program stars have dimensions typical for their spectral types. A brief discussion is given of possible causes of the variability of hot supergiants.

Underhill, A. B.↗
NASA NTRS1994

The pre-cataclysmic binary EUVE 2013+400

New optical spectroscopy shows a 0.706 d orbital period for Extreme Ultraviolet Explorer (EUVE) 2013+400 and confirms its membership in a class of close binary systems emerging from common-envelope evolution. This binary, like the prototype Feige 24, consists of an extreme ultraviolet (EUV) emitting hot white dwarf and a late-type dwarf. Bergeron et al.'s (1994) optical spectroscopy and ultraviolet spectrophotometry indicate that the white dwarf is hot (T(sub eff) approximately equals 50 000 K) and therefore very young (t(sub age) less than or equal 5 x 10(exp 6) yr), and extreme ultraviolet photometry places EUVE 2013+400 along a neutral hydrogen column density in the interstellar medium of n(sub H) approximately equal to 10(exp 19)/sq cm. The white dwarf is a DAO type and we obtained two independent estimates of the helium abundance from EUV photometric measurements (log(y) approximately equal to -3.2) and from the He II lambda-4686 line profile (log(y) approximately equal to -2.8). The data possibly indicate a level of heterogeneity expected in the context of on-going chemical separation in the photospheric layers. The Balmer lines show narrow emission that varies with binary phase with the equivalent widths of the emission trailing the radial velocities by 1/4 cycle: this phasing shows that most of the emission arises on the EUV-illuminated face of the red dwarf. A spectrophotometric decomposition shows that the secondary's spectral type is near M3 and that it contributes about 15%-25% of the total light near 6500 A; the resulting H-alpha emission is twice as strong as in Feige 24, with an equivalent width of 37-61 A with respect to the red dwarf continuum. EUVE 2013+400 is an important addition to the class of close binary stars discovered in EUV all-sky surveys.

Thorstensen, John R.↗
NASA NTRS2003

Simultaneous X-Ray/Ultraviolet Timing of 4U 1626-67

The science results from our observation have been published (Chakrabarty et al. 2001, ApJ, 562, 985). We detected large-amplitude 0.3- 1.2 mHz quasi-periodic oscillations (QPOs) from the low-mass X-ray binary pulsar 4U 1626--67, using ultraviolet photometry from the Hubble Space Telescope and ground-based optical photometry. These 1 mHz QPOs, which have coherence (nu/Delta_nu) = 8, are entirely distinct from the 130 mHz pulsar spin frequency, a previously known 48 mHz QPO, and the 42 min binary period (independently confirmed here). Unlike the 48 mHz and 130 mHz oscillations which are present in both the optical/UV and the X-ray emission, the 1 mHz QPOs are not detected in simultaneous observations with the X-Ray Timing Explorer. The rms amplitude of the mHz QPO decreases from 15% in the far UV to 3% in the optical, while the upper limit on a corresponding X-ray QPO is as low as 0.8\%. We suggest that the mHz oscillations are due to warping of the inner accretion disk. We also report the detection of coherent upper and lower sidebands of the 130 mHz optical pulsations, with unequal amplitude and a spacing of 1.93 mHz around the main pulsation. The origin of these sidebands remains unclear.

Chakrabarty, Deepto↗
NASA NTRS2009

The First Detection of [O IV] from an Ultraluminous X-ray Source with Spitzer. I. Observational Results for Holmberg II ULX

We presen the first Spitzer Infrared Spectrograph (IRS) observations of the [O IV] 25.89 um emission line detected from the ultraluminous X-ray source (ULX) in Holmberg II. This line is a well established signature of high excitation usually associated with AGN. Its detection suggests that the ULX has a strong impact on the surrounding gas. A Spitzer high resolution spectral map shows that the [O IV] is coincident with the X-ray position of the ULX. The ratios of the [O IV] to lower ionization lines are similar to those observed in AGN, suggesting that a strong UV and X-ray source is responsible for the, photoionization. The best XMM-Newton data is used to model the X-ray band which is then extrapolated into the UV. We perform infrared and ultraviolet photometry, and use its previously published optical and radio data to construct the full SED for the ULX and its companion. The preferred model to describe the SED includes an accretion disk which dominates the soft X-rays but contributes little at UV and optical wavelengths. The optical counterpart is consistent with a B supergiant as previously suggested in other studies. The bolometric luminosity of the ULX suggests the presence of an intermediate-mass black hole with mass >85 M for sub-Eddington accretion or, alternatively, a stellar-mass black hole that is accreting at super-Eddington rates. In a follow-up second paper we perform detailed photoionization modeling of the infrared lines in order to constrain the bolometric luminosity of the ULX.

Berghea, C. T.↗
NASA NTRS1972

Mariner 6 and 7 ultraviolet spectrometer experiment - Photometry and topography of Mars.

From data obtained by the ultraviolet spectrometers aboard the Mariner 6 and 7 Mars missions the reflectivity of the illuminated disk of Mars was found to have two distinct spectral types, associated with polar and nonpolar regions. In this work the characteristic spectrum of nonpolar regions on Mars is discussed. An interpretation of the variation of the intensity at 3050 A due to surface pressure variations is given. A comparison of the ultraviolet observations with pressures inferred by the infrared spectrometer is used to test this interpretation and to determine physical parameters of Mars which lead to the observed reflectance. Earth based pressures obtained by broadening of the one-micron band of CO2 and radar topography are compared with the ultraviolet results.

Hord, C. W.↗