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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.

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NASA NTRS1987

The nearby Abell clusters. II - Luminosity and spatial distribution of galaxies in A2175, A2256, and A2384

The luminosity and spatial distributions of galaxies in the nearby Abell clusters A2175, A2256, and A2384 have been studied using an automated object detection, classification, and photometry system. Schecter functions have been fit to the observed luminosity functions of these clusters. Values of the characteristic magnitude Mr(asterisk) at the 'break' in the luminosity function (LF) are found that are within about 0.25 mag of the so-called 'universal' value of Mr(asterisk) for A2256 and A2384. The faint ends of the LFs of these two clusters are fairly flat, with a value of -1.6 that is steeper than the universal value of -1.25. The spatial distributions of galaxies in all three clusters seem to be described fairly well by power laws, with no evidence for constant-density cores, when the cluster center is assumed to be the central D or cD galaxy. These results indicate a strong correlation between the density distribution of galaxies and the presence of a dominant D or cD galaxy in the cluster.

Oegerle, William R.↗
NASA NTRS1987

Rapid variability of the R Coronae Australis reflection nebula NGC 6729

Measurable changes in the surface brightness of the reflection nebula associated with R CrA occur over intervals as short as 24 hours. These and other more extreme variations are demonstrated with CCD images obtained over a 23-day period March 10 to April 2, 1984. During this time span R CrA brightened by 1.3 mag. The alterations in the appearance of the nebula NGC 6729 are apparently caused by the shadowing effects of clouds which are very close to the star, probably well within 1 Au. The spectrum of R CrA may itself vary slightly from night to night, and these changes are echoed by the surrounding nebula with an observable time delay. A photograph showing the complicated filamentary structure in NGC 6729 is reproduced and the relation between the reflection nebula and its illuminating star is discussed.

Graham, J. A.↗
NASA NTRS1987

Flux distribution in the Algol binary system RW Persei

IUE low-dispersion spectra and optical TIS scans of the Algol-type binary system RW Persei show that the primary has a spectrral type of B9.6 and that it is a Be star. The cooler component has a spectral type that is less accurately determined to as K2 III-IV, and it is probably a star of very low mass. The system is heavily reddened, with an E(B-V) color excess of 0.40 + or - 0.05 mag. The present results suggest that the hotter component is actually an opticaly thick accretion disk. The expected W Serpentis-type emission lines are not found in the UV spectrum near mideclipse, although two very broad emissions and several weaker ones seem to be present.

Dobias, Jan J.↗
NASA NTRS1987

The peculiar planetary nebula 75+35 deg 1

The high galactic latitude planetary nebula 75+35 deg 1 was observed in the low-dispersion mode of the IUE satellite. The UV spectrum is characterized by a strong continuum that matches the energy distribution of a blackbody curve of 90,000 K + or - 5000 K. The color temperature of 94,000 K + or - 4000 K is derived from the UV color indices. The spectral type mimics that of an O7.5 V star; a very strong N V 1240-A feature with a P Cygni profile is present, in addition to a very weak C IV P Cygni line. A very slight depression in the 2200-A region suggests very little interstellar absorption with an upper limit of E(B-V) = 0.025 mag, as would be expected for a high galactic latitude object. The ultraviolet observations, in context with the optical data, indicate that this object is not a typical planetary.

Feibelman, Walter A.↗
NASA NTRS1987

A spectrophotometric study of the Algol binary system RX Geminorum

IUE low-dispersion spectra and optical ITS scans of the semidetached Algol-type binary system RX Gem have been obtained. The spectral type of the primary component was determined to be A0, with good accuracy. Since the primary eclipse is only partial, the spectral type of the cooler component has been determined with less accuracy as K2 (+ or - 2). The system is only slightly reddened: its color excess is E(B-V) = 0.04 + or - 0.01 mag. Two models of the system are considered, depending on the luminosity class of the hotter star. Optically, the system is a Be star, since it displays Balmer line emission, visible most clearly during the primary eclipse. The ultraviolet spectrum observed near mideclipse does not display the expected 'W Serpentis-type' emission lines. Probably the main reason is that the primary eclipse is only partial.

Dobias, Jan J.↗
NASA NTRS1987

Observations of SN 1986J in NGC 891

Supernova SN 1986J was discovered at radio wavelengths with the VLA. The object is currently strongest at 6 cm wavelength and probably turned on at 6 cm wavelength in early 1984 and at 20 cm wavelength one or two years later. H I absorption-line observations show that the SN is about 7.7 kpc from the center and within 170 pc of the plane of NGC 891. SN 1986J is, in the radio, both the brightest and most luminous supernova yet found.The supernova has been identified optically with a 20th-magnitude (September, 1986) point source in NGC 891, and was approximately 1 mag brighter in January, 1984. The spectrum is dominated by emission lines; H I, He I, forbidden O I, and probably Fe I and Fe II are seen. The Balmer decrement is very large, with an H-alpha/H-beta flux ratio of about 60. The He I line spectrum and the current optical brightness both suggest that only a small amount of this decrement can be attributed to extinction. The spectrum is similar to those seen in the late phases of type II supernovae; however, the small linewidth (FWHM of about 1000 km/s) suggests that SN 1986J is actually type V.

Rupen, M. P.↗
NASA NTRS1987

Giant H II regions in M81

H-alpha and VLA radio continuum observations at wavelengths of 6 and 20 cm are used to study the distribution of extinction and the distribution of giant radio H II regions along the spiral arms in M81. The radial distribution of visual extinction Av in the plane of M81 shows no trend, with an upper limit 0.1 mag/kpc for the radial extinction gradient and a mean Av of 1.1 + or - 0.4 mag. Nearly all the giant radio H II regions lie along the spiral arms or the inner H I ring. The radial distribution of the set of giant radio H II regions exhibits a strong maximum at a galactocentric distance R roughly 300 arcsec. Unless molecular hydrogen in M81 is also concentrated near R roughly 300 arcsec, the data disagree with Visser's (1980) model for star formation associated with a density wave. Some suggestions are made about how to change the ballistic particle model of Leisawitz and Bash to agree with the observed radial distribution of giant radio H II regions.

Kaufman, Michele↗
NASA NTRS1987

Coordinated observations of asteroids 1219 Britta and 1972 Yi Xing

A coordinated observational program conducted for asteroids 1219 Britta and 1972 Yi Xing has yielded a sidereal rotation period of 5.57497 + or - 0.00013 h for the former, which has retrograde rotation and may be classified as an S-type asteroid on the basis of its spectra and albedo. The 1972 Yi Xing synodic period is found to be 14.183 + or - 0.003 h, with an observed light-curve amplitude amplitude of 0.18 mag; its five-color measurements also appear consistent with an S-type classification. A light-curve maximum absolute magnitude of 13.32 + or - 0.01 is also obtained.

Binzel, Richard P.↗
NASA NTRS1987

Optical spectroscopy of IRAS sources with infrared emission bands. 1: IRAS 21282+5050 and the diffuse interstellar bands

Spectroscopy of the starlike optical counterpart to IRAS 21282+5050, a source with the hydrocarbon infrared emission band spectrum, shows an 07(f)-(WC11) planetary nebula nucleus suffering an extinction of 5.7 mag. Emission line widths in the WC spectrum are only approx. 100 km/s, indicating a very slow stellar wind. Optical diffuse interstellar bands (DIBs) are prominent. Five DIBs are strongly enhanced, namely lamda lamda 5797, 6196, 6203, 6283, and 6613. The presence of circumstellar hydrocarbon molecules may explain both the infrared emission bands and the enhanced DIBs.

Cohen, Martin↗
NASA NTRS1987

Observations of faint field galaxies

Number counts, colors, and angular correlations of field galaxies fainter than 20th mag are summarized. Resulting conclusions regarding the presence and nature of luminosity, spectral, and clustering evolution remain contraversial. Preliminary analysis of two major spectroscopic surveys near completion suggests that by z approximately 0.5, larger numbers of very blue galaxies of moderate luminosities are found than today. The skewer-like surveys also provide new probes of galaxy clustering on scales previously unexplored (larger than 200 Mpc) and over lookback times of several billion years.

Koo, David C.↗
NASA NTRS1987

The Perseus Flasher and satellite glints

The Perseus Flasher (PF) is claimed to be an astrophysical source which frequently emits bright optical flashes (Katz et al. 1986). These flashes have all been detected by the naked eye, with the exception of one photographed flash for which an accurate position is measured. Notable properties of the PF are its large amplitude (greater than 19 mag), short duration (about 1 s), and frequent occurrence (a flash every 12 hr). Here, evidence is presented that the PF is not an astrophysical source but is merely the observation of glints of reflected sunlight from artificial earth satellites. This conclusion is supported by the following facts: (1) a total of 3400 hr of photographic, video, and CCD observations have detected no flashes in or near the small PF error box, despite the claim of one bright flash every 12 hr; (2) thirteen of the 26 flashes are shown to be nonastrophysical in origin; and (3) both the observational and theoretical glint rates indicate that most, if not all, PF observations are caused by satellite glints.

Schaefer, Bradley E.↗
NASA NTRS1987

The low-luminosity X-ray sources in Omega Centauri

UBV observations of three X-ray sources in Omega Cen (sources A, D, and E of Hertz and Grindlay, 1983), obtained with a CCD detector on the 4-m telescope at CTIO in February and August 1985, are reported. The results are presented in images, graphs, and tables and characterized in detail. No optical cataclysmic variable candidates are found down to V = 24.5 mag, corresponding to M(V) = 10.6 in the cluster. It is inferred that these low-luminosity sources, located outside the globular cluster, may be superposed unrelated objects rather than close mass-exchange binaries.

Margon, Bruce↗
NASA NTRS1987

Optical spectroscopy of IRAS sources with infrared emission bands - IRAS 21282+5050 and the diffuse interstellar bands

Spectroscopy of the starlike optical counterpart to IRAS 21282+5050, a source with the 'hydrocarbon' IR emission band spectrum, shows an O7(f)-(WC 11) planetary nebula nucleus suffering an extinction of 5.7 mag. Emission-line widths in the WC spectrum are only about 100 km/s, indicating a very slow stellar wind. Optical diffuse interstellar bands (DIBs) are prominent, and five DIBs are strongly enhanced. The presence of circumstellar hydrocarbon molecules may explain both the IR emission bands and the enhanced DIBs.

Cohen, Martin↗
NASA NTRS1987

X-ray and optical observations of X-ray-selected BL Laceratae objects

Results from several X-ray and optical observations of five X-ray-selected BL Lacertae objects are reported. X-ray light curves covering periods of up to 6 yr reveal that the X-ray flux from these objects does not show large-amplitude trends over this time scale. Variations of up to 2 mag have been observed in the optical. The soft X-ray spectra of three objects have been measured with the Exosat Medium Energy detectors. Energy spectral indices range between one and two. In one case (1E 1415.6 + 2557), evidence for photoelectric absorption in excess of that due to the local interstellar medium has been found. A new optical flare from 1E 1402.3 + 0416, with rise and decay time of order of a few weeks, has been detected.

Giommi, P.↗
NASA NTRS1987

The progenitor of SN 1987A - Spatially resolved ultraviolet spectroscopy of the supernova field

Careful deconvolution of spatially resolved IUE ultraviolet spectra shows that only two of the three stars detected in plate material before 1987 are now present near the site of SN 1987A. The separation, magnitudes, and spectra of these two are consistent with their identification as star 2 and star 3 of the Sanduleak -69 deg 202 trio. The clear implication is that star 1, the 12th mag B3 I star, has disappeared, and it may be identified as the progenitor of SN 1987A.

Sonneborn, George↗
NASA NTRS1987

Light echoes - Supernovae 1987A and 1986G

The sudden brilliance of a supernova (SN) eruption will be reflected on surrounding dust grains to create a phantom nebula. The paper presents a series of calculations in which the apparent brightness of this 'light echo' is predicted for a variety of situations where the dust is part of the interstellar medium (ISM). It is found that the supernova 1987 A will have a very bright echo off the ISM that may perhaps be visible with binoculars for many years. At a time of 400 days past maximum, the SN 1986G is found to be 2.7 mag brighter than would be predicted by an extrapolation of its light curve. This unique property has an easy explanation as a light echo off the dust in the dust lane of Cen A.

Schaefer, Bradley E.↗
NASA NTRS1988

The separate spectra of Pluto and its satellite Charon

The March 3, 1987 occultation of Charon by Pluto was observed spectroscopically from 5400 to 10,200 A at a resolution of 12 A. The midpoint of the event occurred at 11:06 UT; the depth of the event at 6800 A was 0.162 mag. The spectrum of Charon is completely featureless and almost perfectly flat; the red slope and the CH4 absorption features can be attributed solely to Pluto.

Fink, Uwe↗
NASA NTRS1987

Optical observations of SN 1987D in UGC 7370

This paper presents optical photometry and spectroscopy of SN 1987D, a Type Ia supernova in the nearby galaxy UGC 7370, during the period immediately subsequent to its discovery. The distance modulus of the galaxy, independently determined by the redshift and the Tully-Fisher (1977) relation, is 32.3 + or - 1.0. The maximum brightness of SN 1987D was V about 13.2 and occurred on April 18, 1987, + or - 4 days; the absolute luminosity is about 0.6 mag brighter than the average for SNe Ia. The spectrum of SN 1987D is typical of SNe Ia, but the expansion velocity (9600 km/s) is considerably lower than average.

Schneider, D. P.↗