Engineering topics

Gunn, J. E.

Publications and source records attributed to Gunn, J. E..

At least 19 records

NASA NTRS1995

Morphology classification of galaxies in CL 0939+4713 using a ground-based telescope image

Morphological classification is studied for galaxies in cluster CL 0939+4712 at z = 0.407 using simple photometric parameters obtained from a ground-based telescope image with seeing of 1-2 arcseconds full width at half maximim (FWHM). By ploting the galaxies in a plane of the concentration parameter versus mean surface brightness, we find a good correlation between the location on the plane and galaxy colors, which are known to correlate with morphological types from a recent Hubble Space Telescope (HST) study. Using the present method, we expect a success rate of classification into early and late types of about 70% or possibly more.

Fukugita, M.↗

NASA NTRS1992

Infrared emission and mass loss from evolved stars in elliptical galaxies

Small aperture 10.2-micron measurements of normal elliptical galaxies show that for almost all of these galaxies the 12-micron emission seen by IRAS is extended on the scale of the galaxy. NGC 1052 and NGC 3998 are exceptions to this; much of their 10-12-micron emission comes from the inner regions of the galaxies and may be associated with their active nuclei, as is the case for many radio galaxies. The distribution of the IR light and the IR colors of elliptical galaxies suggest that the most plausible source of the 12-micron emission is photospheric and circumstellear emission from cool evolved red giant stars. The 12-micron emission is well in excess of that expected from photospheric emission alone; about 40 percent of it probably comes from circumstellar dust.

Knapp, G. R.↗

NASA NTRS1988

A radial-velocity survey of the Hyades

Photoelectric radial-velocity measurements, obtained with external error as small as 0.1 km/s using the 200-inch Hale telescope at Palomar Observatory during the period 1971-1986, are reported for over 400 candidate members (with V magnitude between 6 and 14) of the Hyades cluster. The history of Hyades observations is recalled; the Palomar instrumentation and observing program are described; the data-reduction and standardization procedures are discussed in detail; and the data are presented in extensive tables and graphs. About 200 of the stars are classified as cluster members, including 60 spectroscopic binaries.

Griffin, R. F.↗

NASA NTRS1988

High-resolution CCD imaging and derived gravitational lens models of 2237+0305

Images of the gravitational lens 2237+0305 acquired in good seeing have resolved the system into at least five components within the central few arsec of the object: the galaxy nucleus and four point sources in a ringlike formation approximately centered on the galaxy. It is found that the four point sources are distinctly bluer than the galaxy, but that they do not have identical colors. The observed configuration is well reproduced by a simple model that assumes that the four objects are images of the quasar and that the lens is a constant mass-to-light ratio, elliptical, de Vaucouleurs bulge.

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 NTRS1987

The Palomar Observatory CCD camera

Standard designs for Dewars and electronics which have been developed for the Palomar Observatory CCD camera are described in detail. The Dewars described have holding times of about 17 to 24 hours. In-operation readout-noise levels of about 8 electrons are achieved for TI 800 x 800 CCDs; tests of these CCDs reveal that, over their range of operation, the amplifiers and A/D converters are linear to better than 0.2 percent.

Gunn, J. E.↗

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

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

A systematic survey for distant galaxy clusters

A photographic survey for faint clusters of galaxies has been carried out with fine-grained photographic emulsions using the 1.2 m Schmidt and 5 m Hale telescopes, as well as the 4 m Mayall telescope. A total of 418 clusters have been found with redshifts mostly in the range from 0.15 to 0.92. The survey was planned to minimize distance-dependent selection effects in the resulting catalog. In areas of sky where the deepest search was made, the sample is complete to about z = 0.50; there are 11 clusters per square degree at this limit. At a redshift of 1.0 there should be 63 or 45 clusters per square degree depending on whether q0 is 0.0 or 0.5, provided there is no evolution.

Gunn, J. E.↗

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 NTRS1986

The dust and gas surrounding LkH-alpha 101

The linear polarization of the reflection nebula NGC 1579 and the CO (1 to 0) emission from the associated molecular gas have been mapped for several minutes of arc around the exciting star LkH-alpha 101. These maps show conclusively that LkH-alpha 101 is the sole significant source of illumination in the region. The dust in the reflection nebula appears to be uniform over the illuminated region and is uniformly illuminated by LkH-alpha 101. Despite the patchy obscuration, the dark cloud which obscures LkH-alpha 101 does not surround the star. LkH-alpha 101 may have formed out of a placental cloud whose remnants now include four molecular cloud fragments, two in front of and two behind the reflection nebula, as well as an H I cloud previously detected in the region.

Redman, R. O.↗

NASA NTRS1985

Spectroscopic orbits for 16 more binaries in the Hyades field

A photoelectric survey of the radial velocities of Hyades candidates has provided data for 16 spectroscopic binary orbits, in addition to the 11 known binaries in the Hyades field. The majority of photoelectric observations in the survey were carried out at the Cambridge and Palomar Observatories using different data reduction techniques for determining radial velocities. It is found that two of the objects, vB 164 and J336, are definitely not members of the Hyades cluster; two other objects, HD 16909 and J301, appear to be located far from the center of the cluster, but still deserve classification as Hyades members. The gamma-velocity of HD 16909 differed slightly from the value expected for a member of the Hyades cluster. An additional twelve systems were definitely identified as members of the Hyades. The radial velocity values for all the candidate stars are given in a series of tables.

Griffin, R. F.↗

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

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 NTRS1982

Evolution of the cluster X-ray luminosity function slope

The results of an X-ray survey of 58 clusters of galaxies at moderate and high redshifts are reported. Using a luminosity-limited subsample of 25 objects, it is found that to a redshift of 0.5 the slope of the luminosity function of distant clusters is independent of redshift and consistent with that of nearby clusters. The time scale for change in the slope must be greater than 9 billion years. The implications of the data for theoretical models are discussed. In particular, Perrenod's models (1980) with high Omega are excluded by the present data.

Henry, J. P.↗