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Schneider, D. P.

Publications and source records attributed to Schneider, D. P..

35 records · Page 2
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NASA NTRS1987

The surface-brightness-effective-size relation for elliptical galaxies in the cores of clusters

Surface photometry of 372 elliptical galaxies has been performed using CCD images of the centers of 97 nearby rich Abell clusters. The strong correlation between surface brightness and effective size, originally found by Kormendy (1977), is clear in the data. Brightest cluster galaxies show much less scatter about the mean relation defined by these data than do lower-luminosity cluster ellipticals, and the slope of the relation is shallower for the brightest galaxies; these two results are tentative, however, because of uncertain selection and environmental effects. When combined with published central velocity dispersions, the photometry yields a relation for brightest cluster galaxies that is in good agreement with the mean relation for elliptical galaxies found by Djorgovski and Davis (1987). Use of the surface-brightness/scale-length relation to measure the lookback luminosity evolution of the stellar content in galaxies is promising.

Hoessel, J. G.↗
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.↗
NASA NTRS1987

The triple radio source 0023 + 171 - A candidate for a dark gravitational lens

In the course of a radio-optical search for gravitational lenses, a multiple radio source, 0023 + 171, was discovered, which has two optical counterparts at z = 0.946 separated by 5 arcsec. Their redshifts are the same within the measurement error, and their optical spectra show the same emission lines with the same relative intensities. One interpretation of these measurements is that the images of 0023 + 171 are gravitationally lensed. However, because the radio morphology is complex and the optical objects are faint, the existing data cannot exclude another interpretation, i.e., that the components of 0023 + 171 are two physically associated radio galaxies or two components of a single galaxy. The only possible evidence in favor of a lensing object is extremely faint optical emission located approximately 1 arcsec from one of the images. If this multiple source is indeed gravitationally lensed, the combination of available data imply a mass-to-light ratio for the lensing matter equal to about 1000.

Hewitt, J. N.↗
NASA NTRS1987

Spectroscopy of the extranuclear line-emitting regions associated with the gravitational lens system 2016 + 112

Moderate-resolution slit spectroscopy of the extended emission-line objects A1 and B1 located within 5 arcsec of the triple radio source 2016 + 112 shows that at least one is physically associated with the z = 3.273 quasar thought to be multiply imaged by a foreground galaxy. The data and theoretical models unanimously favor the identification of A1 and B1 with two separate clouds of ionized gas that lie within a few kiloparsecs of the primary A/B QSO and radio source. The available evidence does not support the view that they are multiple images of a single object or their classification as separate (companion) galaxies.

Schneider, D. P.↗
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 NTRS1986

Three-color CCD photometry of the distant cluster of galaxies Cl 0024 + 1654

Photometry of 265 galaxies in rich cluster Cl 0024 + 1654 (z = 0.39), based on CCD imaging in three filters, is presented. The luminosity of this system ranks it among the richest known clusters, and it has a blue mass-to-light ratio of about 210. The color-magnitude diagram has a prominent E/S0 sequence. There are essentially no blue cluster members brighter than r equals about 19.3, and only very red galaxies inhabit the central 30 arcsec of the cluster. The blue cluster members have sizes and surface brightnesses similar to spiral galaxies in nearby clusters.

Schneider, D. P.↗
NASA NTRS1986

UGC 8508 - A dwarf galaxy associated with the M 101 group

Two-color CCD photometry of UGC 8508 has resolved the system into stars. The color-magnitude diagram shows blue and red supergiants, the apparent magnitudes of the brightest stars indicate that UGC 8508 lies within 2 Mpc of the adopted 6 Mpc distance of the M 101 group. The galaxy contains a significant color gradient; star formation is confined to the central 1.5 scale lengths (0.8 kpc). UGC 8508 has a central surface brightness intermediate between bursting and quiescent dwarf irregular galaxies.

Mould, J. R.↗
NASA NTRS1986

Spectroscopic CCD surveys for quasars at large redshift. I - A deep PFUEI survey

A survey for faint quasars has been conducted using slitless spectroscopy with the PFUEI at the 200 inch (5 m) telescope. The survey covers a total of 0.91 sq deg in 113 fields at galactic latitudes above 30 deg. Calibrated spectra in the range 4500-7200 A were obtained for more than 9000 objects. Emission-line candidates were selected on the basis of two criteria: the equivalent width must exceed 50 A, and the signal-to-noise ratio of the detection of the line versus the sky background should be larger than 7. Among 45 candidates so selected, subsequent slit spectroscopy confirmed 27 emission-line objects. Among these, 17 are emission-line galaxies with redshifts in the range 0.04-0.31, and 10 are quasars with redshifts between 0.91 and 2.66. The well-defined selection criteria for these objects, together with the distribution of rest frame equivalent widths of the emission lines, allow derivation of the area of sky covered as a function of the continuum limiting magnitude. The observed number of quasars in the redshift range 0.7-2.7 agrees well with that predicted by the luminosity function models published by Schmidt and Green in 1983. It is concluded that quasars with an absolute magnitude of M(B) = -25 suffer a redshift cutoff near or below a redshift of 3.

Schmidt, M.↗
NASA NTRS1986

An apparent gravitational lens with an image separation of 2.6 arc min

Observations are reported which confirm Paczynski's 1986 speculation that the previously known (Arp and Hazard, 1980) pair of 19th magnitude quasars 1146+111B,C are actually two images of a single object produced by a gravitational lens. The image split is 157 arcsec, more than 20 times greater than any previously reported, thus indicating an exceptionally massive lensing object. The data supporting the lens hypothesis are remarkably similar, high signal-to-noise, moderate resolution spectra of the two components. Both spectra show strong Mg II 2798-angstrom emission at z = 1.012 plus or minus 0.001 with indistinguishable redshifts (delta v = 126 plus or minus 309 km/s), widths (FWHM = 64 plus or minus 4 angstroms) and detailed profile shapes. Both spectra also show broad troughs at 6180 angstroms and several weaker continuum features. Neither object exhibits the O II 3727-A forbidden line which is frequently strong in Mg II emission objects. If the foreground galaxy clustering apparent in a deep R band charge-coupled device image proves insufficient to explain the large image splitting, other possibilities such as massive dark objects (e.g. a black hole of about 10 to the 15th solar masses) or a cosmic string may be indicated.

Turner, E. L.↗
NASA NTRS1986

The third image, the redshift of the lens, and new components of the gravitational lens 2016 + 112

Three new observations of the gravitational lens system 2016 + 112 are reported. A new, more sensitive spectrograph has produced a redshift for the red galaxy D, and direct imaging through a narrowband filter centered on the Lyman alpha line of the lensed object has detected a previously unknown point source and two radio-quiet extended emission line regions, all apparently at the redshift of the two brighter images A and B. Some preliminary results from a new VLA map of the system are reported, and the implications of the results for models of gravitational lenses are discussed.

Schneider, D. P.↗
NASA NTRS1985

CCD observations of Abell clusters. IV - Surface photometry of 175 brightest cluster galaxies

The present data from a consistent body of CCD aperture and surface photometry for the brightest galaxies in 175 clusters from the Abell catalog confirm the dispersion in the aperture luminosities for first-ranked cluster galaxies of about 0.32 mag, as well as the documented trends of luminosity with Bautz-Morgan class and cluster richness. Half of these objects are multiple-nucleus systems; multiplicity is not strongly correlated with cluster morphology or richness, and the fraction of multiples is 2-10 times higher than would be produced by random projection in the cores of Hubble-law clusters. The average distance of the secondary nuclei from the luminosity center of the galaxy is significantly less than the value expected from random projections.

Hoessel, J. G.↗
NASA NTRS1985

Unidentified IRAS sources - Ultrahigh-luminosity galaxies

Optical imaging and spectroscopy measurements were obtained for six of the high galactic latitude infrared sources reported by Houck, et al. (1984) from the IRAS survey to have no obvious optical counterparts on the POSS prints. All are identified with visually faint galaxies that have total luminosities in the range 5 x 10 to the 11th power stellar luminosity to 5 x 10 to the 12th power stellar luminosity. This luminosity emerges virtually entirely in the infrared. The origin of the luminosity, which is one to two orders of magnitude greater than that of normal galaxies, is not known at this time.

Houck, J. R.↗
NASA NTRS1985

Unidentified IRAS sources: Ultrahigh luminosity galaxies

Optical imaging and spectroscopy measurements were obtained for six of the high galactic latitude infrared sources reported by Houck, et al. (1984) from the IRAS survey to have no obvious optical counterparts on the POSS prints. All are identified with visually faint galaxies that have total luminosities in the range 5 x 10 to the 11th power stellar luminosity to 5 x 10 to the 12th power stellar luminosity. This luminosity emerges virtually entirely in the infrared. The origin of the luminosity, which is one to two orders of magnitude greater than that of normal galaxies, is not known at this time.

Houck, J. R.↗
NASA NTRS1983

CCD photometry of Abell clusters. II - Surface photometry of 249 cluster galaxies

The luminosity of the brightest cluster galaxies remains the best standard candle for observational cosmology. Studies of over 250 relatively nearby clusters show that the luminosity of these objects within an aperture of constant metric diameter has a dispersion of only 0.35 mag. The observations considered by Schneider et al. (1983) were acquired to measure the aperture luminosities of the brightest cluster galaxies. However, the data base, because of its high signal-to-noise ratio and large spatial coverage, allows several other investigations to be performed. In the present investigation, surface photometry of the brightness three galaxies within approximately 250 kpc of the cluster center is presented, taking into account the cores of 83 Abell clusters. The relevance of the photometry to cosmological studies is also discussed. It is found that dynamical friction does play an extremely important role in determining properties of brightest cluster galaxies and cluster morphology.

Schneider, D. P.↗
NASA NTRS1983

CCD photometry of Abell clusters. I - Magnitudes and redshifts for 84 brightest cluster galaxies

The way in which the luminosity of brightest cluster galaxy varies with cluster parameters is investigated in a sample of 84 Abell clusters of moderate redshift and of richness classes in the zero-to-5 range. A photometric system is used which is well matched with the low noise CCD detector employed, as well as to the arrangement of galaxies with different redshifts on a standard system. The data, together with measurements from earlier work which forms a low redshift sample of the 199 brightest cluster galaxies, confirm that the luminosity dispersion in first-rank cluster galaxies is about 0.34 mag. The colors of giant ellipticals have not changed since redshifts of 0.25, and the richness correction is well established at 0.10 mag/Abell richness class. Application of these corrections reduces the luminosity dispersion to 0.29 mag.

Schneider, D. P.↗
NASA NTRS1979

High time resolution spectrophotometry of nova DQ Herculis /1934/

Thirty-four spectra of DQ Her are analyzed which were obtained with a time resolution greater than 0.01 cycle. It is found that: (1) the 18th mag visual companion of DQ Her has an energy distribution similar to that of a late F star and is not likely to be a member of the system; (2) the time of minimum has no wavelength dependence and agrees better with the elements of Patterson et al. (1978) than with a linear ephemeris; (3) only very weak evidence exists for the detection of a late-type star, which is of spectral type M4 or later, even at mideclipse; (4) the spectrum of the residual light at mideclipse can be represented by optically thin free-free plus bound-free emission at a temperature of 35,000 K, an electron density of (1-10) trillion per cu cm, and a star contributing about 90% of the red flux; and (5) there is a definite asymmetry in the light curve, as well as strong evidence for a localized bright spot on the side of the disk eclipsed last.

Schneider, D. P.↗