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Oke, J. B.

Publications and source records attributed to Oke, J. B..

At least 73 records · Page 4
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NASA NTRS1979

The hydrogen lines in the high-luminosity quasar B2 1225+31

The emission lines H-alpha, H-beta + forbidden O III, and L-alpha have been observed in the high-redshift quasar 1225+31. The ratios of line intensities in 1225+31 are found to be approximately 0.8 for L-alpha/H-alpha, about 4 for H-alpha/(H-beta + forbidden O III), and between 4 and 10 for H-alpha/H-beta. The observed value of L-alpha/H-alpha agrees well with the ratio derived by Baldwin (1977) on the basis of a composite quasar spectrum, as well as with direct determination of this ratio in 3C 273 and PKS 0237-23. The ratio H-alpha/H-beta is in the range of values found for a sample of low-redshift quasars by Baldwin (1975). The low value for the L-alpha/H-alpha ratio cannot be reasonably explained by foreground extinction between the sun and 1225+31.

Soifer, B. T.↗
NASA NTRS1978

Photoelectric spectrophotometry of radio galaxies

The absolute energy distributions from 3200 to 10,000 A of 26 3CR radio galaxies are determined on the basis of spectrophotometric observations with the multichannel spectrometer of the Hale 5-m telescope. It is found that there is a continuous range of emission-line characteristics and UV excess in the sample and that a strong correlation exists between the nonthermal component luminosity and hydrogen emission, which favors the hypothesis that direct photoionization by the nuclear radiation is responsible for the emission lines observed. Calculations are performed which show that in almost all cases the power-law component model provides sufficient UV photons to produce the observed H-beta line. Indications are obtained that the optical nuclear component is related to the radio emission in some complex manner and that strong radio galaxies tend to be accompanied by UV excess and emission lines.

Yee, H. K. C.↗
NASA NTRS1978

The metallicity of globular clusters in the halo of M87

The energy distributions of one 20th and two 21st magnitude globular clusters in the halo of the giant elliptical galaxy M87 (NGC 4486) of the Virgo cluster have been obtained between 0.32 and 1.1 microns with the multichannel spectrophotometer of the Hale 5-m telescope. Comparisons with globular clusters in M31 show line strength indices L ranging from 4 plus or minus 2 to 9.5 plus or minus 2.0, with a mean for the three clusters of 7.5 plus or minus 1.5. On average they thus have metal deficiencies relative to the sun by a factor of about 5. The distribution over abundance in the halo globular clusters of M87 is the same as that in M31, but different from that in the halo of the Galaxy.

Racine, R.↗
NASA NTRS1978

Spectral variations in brightest cluster galaxies

Multichannel-spectrometer scans of 56 of the brightest galaxies in faint clusters have been examined for evidence of color evolution. The dispersion introduced into the sample by some 25% of the galaxies which have unusual spectra is shown to be sufficient to obscure evolutionary variations. On omitting these galaxies it is found that over a time equivalent to a redshift of 0.46, B-V decreases by no more than 0.04 mag. A comparative analysis of the spectral energy distributions suggests that their differences may be due to a combination of the dispersion in metallicity among the members of the sample and to anomalous reddening of individual galaxies.

Wilkinson, A.↗
NASA NTRS1977

Further spectrophotometry of the transient X-ray source A0620-00

Observations of the transient X-ray source A0620-00 in November 1976 show that the optical object had an apparent visual magnitude of 18.35. The spectrum is cool and shows that one component of the light comes from a K5 V to K7 V star. The distance is estimated to be 870 pc if the cool star is normal. Some support for the 7.8-day X-ray period recently found is provided by observations made in 1975 during the outburst. In addition to the cool K star, there is a second radiation source which has a flat spectrum. This source can be modeled by a 10,000-K blackbody with a radius (if spherical) of 17,000 km plus a 4000-K blackbody with a radius of 13,400 km and is probably a residual accretion disk. It is very unlikely that the K star can fill its Roche lobe, so that mass transfer to a neutron-star companion by this mechanism is unlikely. It is possible that the K star is losing mass by processes such as those that occur in T Tauri stars.

Oke, J. B.↗
NASA NTRS1977

Optical spectrum of HDE 245770 /A0535 + 26/

Narrow-band spectrophotometric observations of HDE 245770 with the multichannel spectrometer and slit spectra obtained with the SIT digital spectrograph at the Cassegrain focus of the 5-m Hale telescope indicate that this star is of spectral type B0 with emission at H-alpha, H-beta, and probably 5876 A of He I. There is some evidence that it is of luminosity class III. The reddening is estimated in various ways and corresponds to a B-V color excess of 0.80. If the star is really a giant, its distance is approximately 1.8 kpc. No variations larger than 1% at the reported 104-x X-ray pulse period are evident in the data in visual magnitude, color, or H-alpha emission intensity. This is not surprising, since the optical star is much more luminous than the X-ray object, and the heating effect of the X-ray source (which is assumed to be one component of a binary) on the B0 star's atmosphere can produce at most a few percent modulation in visual light.

Wade, R. A.↗
NASA NTRS1977

The nebulosity near the quasar 3C 249.1

Spectroscopic observations made 2 arcsec away from 3C 249.1 with a cooled SIT camera spectrograph and with a multichannel spectrometer yield convincing evidence for the presence of fairly narrow emission lines of forbidden O II, forbidden O III, forbidden Ne III, and perhaps H-beta. The redshift of these emission lines, z = 0.3125, is, within the accuracy of the observations, the same as that of the broad emission lines in the quasar itself; this appears to rule out a gravitational-redshift interpretation for the quasar redshift. The main difficulty in making models for the extended emission-line region is that of understanding the strong forbidden O II lines. For this purpose, shell, cloud, and disk models are discussed, as is time-dependent ultraviolet illumination of the nebula. Simple models, in which the nebular is exposed to the unaltered extrapolated quasar continuum flux, fail to produce the observed line ratios.

Richstone, D. O.↗
NASA NTRS1977

Spectrophotometry of the transient X-ray source A0620-00

Optical observations of the transient X-ray source A0620-00 over the wavelength range from about 3200 to 6600 A are analyzed which were made with the 5-m Hale telescope using a multichannel spectrometer, a digital spectrograph with a cooled integrating SIT vidicon, and an image photon-counting system attached to the camera of the coude spectrograph. Infrared observations at 1.65, 2.2, and 3.5 microns are also examined. Individual spectral lines of special interest are discussed, the E(B-V) color excess is estimated to be about 0.40, and a distance of 1200 pc is adopted. Analysis of the continuous spectrum yields several simple binary models. A specific model is proposed in which one of the continuum sources is an optically thick object characterized by a model atmosphere at a temperature of 25,000 to 30,000 K and the second source is either a cool black body at 4000 K or a partially optically thick source of bound-free plus free-free radiation from a hydrogen gas with an electron temperature of at least 100,000 K. Some possible parameters of these sources and of the accretion disk are considered.

Oke, J. B.↗
NASA NTRS1976

Spectrophotometry of the X-ray binary HZ Herculis

An extensive set of absolute spectrophotometric observations of HZ Her over the wavelength range from 3300 to 10,000 A is presented and analyzed to determine to what extent the observations can be interpreted in terms of a model for the system. The specific model to be tested consists of a large star (HZ Her) with a hot cap beneath the X-ray source, an accretion disk around the X-ray source, and a gas stream flowing between the primary star and the disk. It is found that the model is compatible to a large extent with the detailed observations and that the physical characteristics of the various components can be derived. The mass, luminosity, and radius of the primary star, the mass of the X-ray object, and the orbital dimensions are obtained by analyzing the energy distribution at minimum light and X-ray eclipse data. The angle and effective temperature of the hot cap on the primary are also determined along with the energy distribution, diameter, and thickness of the accretion disk. It is concluded that HZ Her fills its Roche lobe and is an A7 V star, that the logarithm of its surface gravity is about 3.6, and that the mass of the X-ray object is 1.95 solar masses.

Oke, J. B.↗
NASA NTRS1976

Seyfert galaxies with strong Fe II emission

Measurements are reported for the spectral energy distributions of the Seyfert galaxies Zw 2130+09 and Zw 0051+12 as well as the quasar 3C 273 over the wavelength range from 3300 to 10,760 A. Absolute emission-line intensities are derived for numerous Fe II blends and the O I line at 8446 A. Several new Fe II emission features are identified, the absence of Fe III emission is noted, and interesting properties of the individual spectra are described. Constraints on the ionizing continuum and on the geometry and velocity field of the emission-line regions are discussed. The observations show that Seyfert galaxies with strong Fe II emission also have strong O I 8446-A emission and that a flat continuum in the near-UV appears to be common in such objects. Assuming photoionization, it is suggested that both the Fe II and the O I emission could result from continuum fluorescence in an outer, optically thick H I zone in an emission-line region about 1 pc in radius and consisting of many small high-velocity filaments.

Oke, J. B.↗
NASA NTRS1976

Color gradients in the nuclear region of M31

Spectrophotometric measurements of the nuclear region of M31 under conditions of excellent seeing with M31 near the zenith and using a 3.8-9.9-in. diameter entrance annulus for the bulge along with a 3.6-in. aperture for the nucleus, show that the nuclear region is only slightly redder and shows marginally stronger CN blends than the bulge. The data can be interpreted in terms of an increase in heavy-element abundance toward the center of M31 by a factor substantially less than two.

Thuan, T. X.↗
NASA NTRS1976

Optical and infrared spectrophotometry of 18 Markarian galaxies

Slit spectra, spectrophotometric scans, and infrared broad-band observations are presented for 18 Markarian galaxies with emission lines. Eight of the program galaxies can be classified as Seyfert galaxies. Arguments are given that thermal, nonthermal, and stellar radiation components are present. Broadly speaking, one group of Seyfert galaxies is characterized both by the presence of a high-density region of gas and by a continuum dominated by nonthermal radiation. The continua of the remaining program Seyferts, which do not have a high-density region of gas, are dominated by thermal radiation from dust and a stellar continuum. The 10 galaxies which are not Seyfert galaxies are shown to be examples of extragalactic H II regions; there is evidence for thermal emission from dust being present at 10 microns in four of these galaxies.

Neugebauer, G.↗
NASA NTRS1975

The spectral energy distribution of NGC 1275

An analysis of absolute spectral energy distributions for NGC 1275 (Per A) covering the wavelength interval from 3300 A to 10,800 A is presented. The data are consistent with the heavy reddening discovered by Wampler (1971). The H-alpha intensity varied by less than 10% between the times of Wampler's earlier measurements and the two occasions of the present observations. The line-emitting region has a characteristic density of about 10 to the 4.5 power per cu cm, a mass of about 10 to the 5.5 power solar masses, and a volume filling factor of about 10 to the -6th power. The gas may be ionized by shock waves or by nonthermal or stellar radiation. It is suggested, in the vein of Minkowski's (1957) original proposal, that the high-velocity emission-line knots described by Minkowski are H II regions in a Perseus-cluster galaxy or intergalactic gas cloud seen in projection against NGC 1275.

Shields, G. A.↗
NASA NTRS1975

Further observations of BL Lacertae

Spectrophotometric observations of BL Lac have been obtained under conditions of fair to excellent seeing with BL Lac near the zenith. The nucleus was faint for all observations. Four absorption features identified as the Mg I and MgH band, the 4410-A band, the G-band, and H and K of Ca II, are observed. The redshift is approximately 0.070, in agreement with results in a previous paper. When the effects of the radiation from the central bright source are removed as well as possible, the residual spectral energy distribution is found to be very similar to that of a standard giant elliptical galaxy redshifted by 0.070 and reddened by a factor corresponding to a color excess of 0.28 to 0.40. The absolute visual magnitude of the underlying galaxy is -22.6 if the Hubble constant is 60 km/s per Mpc and the color excess is 0.28.

Thuan, T. X.↗
NASA NTRS1975

Supernova 1972e in NGC 5253

Absolute energy distributions of the Type I supernova 1972e in NGC 5253 extending to about 700 days after maximum light have been obtained. A physical model of the expanding envelope, based on the identification of the feature at 6550 A with H-alpha is proposed. It consists of a differentially expanding atmosphere, with electron density ranging from 10 billion near maximum light to about 10 million 340 days later, illuminated by a photosphere with temperature in the range from 10,000 K to 7000 K. Under these conditions, the identifications of Ca II 8600-A, H, and K lines, the Na D lines, and the Mg I b lines forming P Cygni lines are quite plausible. More than 200 days after maximum, the spectrum is dominated by four features between 4200 and 5500 A. Three of these four features match the blended emissions from over 100 Fe II forbidden lines. If this identification is correct, the envelope requires about 0.01 solar mass of iron, which corresponds to an Fe/H ratio about 20 times higher than the cosmic abundance. Possible identifications of the fourth feature with the Mg I 4571-A line or permitted lines of Fe II are also discussed.

Kirshner, R. P.↗
NASA NTRS1975

Absolute spectrophotometry in M31 and M32

For a number of places in the bulge of M31, and for two places in M32, photometric scans from lambda = 3300 A to lambda = 10,600 A have been obtained with the multichannel spectrometer on the 5-m Hale telescope. The scans show that in both objects the color temperature (particularly shortward of 5000 A) decreases toward the center, and that the strength of the CN bands increases toward the center in both objects, in agreement with other earlier observations. The new data can all be interpreted in terms of an increase of heavy-element abundance toward the center in both objects by a factor probably less than 2, and by an excess of heavy elements in M31 compared with M32 by a factor probably greater than 2, in qualitative agreement with earlier conclusions of other observers.

Oke, J. B.↗
NASA NTRS1975

Spectrophotometry of faint cluster galaxies and the Hubble diagram - An approach to cosmology

New spectrophotometric data are presented for large-redshift galaxies in clusters. A new approach to aperture corrections and the analysis of the Hubble diagram is outlined, including the explicit incorporation of evolutionary effects. The importance of selection effects on the usual methods of analysis are in principle overcome in the analysis, although the heterogeneity of the sample still makes conclusions about cosmology slightly suspect. Formal values of the deceleration parameter are derived under several sets of assumptions, yielding results between +0.33 and -1.27 with formal standard deviations of order 0.7.

Gunn, J. E.↗