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NASA NTRS1980

Discovery of low-redshift X-ray selected quasars - New clues to the QSO phenomenon

The identification of six X-ray sources discovered by the Einstein Observatory with X-ray quasars is reported, and the properties of these X-ray selected quasars are discussed. The four high-latitude fields of 1 sq deg each in which the Einstein imaging proportional counter detected serendipitous X-ray sources at intermediate exposures of 10,000 sec were observed by 4-m and 1.5-m telescopes, and optical sources with uv excesses and emission line spectra typical of many low-redshift quasars and Seyfert 1 galaxies were found within the 1-arcsec error boxes of the X-ray sources. All six quasars identified were found to be radio quiet, with low redshift and relatively faint optical magnitudes, and to be similar in space density, colors and magnitude versus redshift relation to an optically selected sample at the same mean magnitude. X-ray luminosity was found to be well correlated with both continuum and broad-line emission luminosities for the known radio-quiet quasars and Seyfert 1 galaxies, and it was observed that the five objects with the lowest redshifts have very similar X-ray/optical luminosity ratios despite tenfold variations in X-ray luminosity. It is concluded that photoionization by a continuum extending to X-ray energies is the dominant excitation mechanism in radio-quiet quasars.

Grindlay, J. E.↗

NASA NTRS1981

Optical spectral variability of the N galaxies 3C 382 and 3C 390.3

Multichannel spectrophotometry data acquired from 1969 to 1980 are used to study the absolute energy distribution and emission line variability of the N galaxies 3C 382 and 3C 390.3. It is shown that: (1) the continuum spectra can be decomposed into a nuclear nonthermal component of constant spectral shape and a constant elliptical galaxy component; (2) apparent visual magnitudes within a 10 arcsec aperture are derived for underlying galaxies, 3C 382 being 15.27 and 3C 390.3, 16.04; (3) forbidden lines and narrow Balmer lines do not change with the central continuum, but (4) the intensity variations of the broad Balmer lines are correlated nonlinearly with changes in the luminosity of the central continuum source. This correlation can be explained by a time-lag effect if there are two components of broad-line emission, one varying on a time scale of a few months and the other over a few years.

Yee, H. K. C.↗

NASA NTRS1982

The chromospheres of classical Cepheids. I - Low resolution IUE spectra

A program to study the behavior of chromospheres in classical Cepheids using both ground-based and satellite-based observations. Five stars, delta Cep, nu Aql, beta Dor, zeta Gem, and l Car, have been included, and where possible the various types of data have been obtained simultaneously. The first part of this investigation concerns low dispersion spectra from the IUE satellite. Fine error sensor (FES) magnitudes are presented for the five Cepheids and, in the case of one, nu Aql, are used to rediscuss the period. The 'artificial viscosity dip' predicted by some theoretical calculations may be present in the FES light curve of delta Cep. The low dispersion spectra have been used to determine continuum magnitudes at various UV wavelengths, and light curves are shown. The amplitude increases with decreasing wavelength except around 1550 A. Line emission in the short wavelength region is observed in three of the Cepheids and is found to be phase dependent. Some correspondence is found between the variation of the emission lines and the appearance of bumps on the UV light curves.

Schmidt, E. G.↗

NASA NTRS1982

Goddard X-ray astronomy contributions to the IAU/COSPAR (1982)

The relation of X-ray flux to both the continuum flux in the optical and radio bands, and to the line emission properties of these objects were studied. The Einstein Observatory, because of increased sensitivity and improved angular resolution, increased substantially the number of known X-ray emitting active galactic nuclei. The Einstein imaging instruments detected morphology in AGN X-ray emission, in particular from jetlike structures in Cen-A, M87, and 3C273. The improved energy resolution and sensitivity of the spectrometers onboard the Observatory provide information on the geometry and ionization structure of the region responsible for the broad optical emission lines in a few AGN's. This information, combined with theoretical modeling and IUE and optical observations, allows the construction of a moderately detailed picture of the broad line region in these objects.

Holt, S. S.↗

NASA NTRS1983

Two new possible planetary nebulae

Two new possible planetary nebulae have been identified using the Parker, Gull, and Kirshner (1979) emission-line survey of the galactic plane. Both objects exhibit very strong forbidden O III lambda 5007 line emission, a symmetrical morphology, and a faint blue central star.

Fesen, R. A.↗

NASA NTRS1984

X-ray observations of broad absorption-line quasars

The present 0.1-4 keV observer frame data was obtained for three broad absorption-line quasars with the imaging proportional counter on the Einstein Observatory. Data for one object, UM 232, are sufficiently good to tell that absorption at 1 keV is unimportant (quasar rest frame), which leads to an upper limit to the column density of absorbing gas of 10 to the 22nd/sq cm. Because this gas absorbs optical continuum and line emission, it must have a size of 10 to the 19th cm or greater, and therefore a density of less than 1000/cu cm. This absorbing gas is unlike the much denser clouds responsible for the broad emission lines. It is also calculated that the mass of absorbing gas is greater than 1 solar mass, and that it is at least 300 pc distant from the ionizing continuum source. Free-free absorption, which is calculated to be unimportant at frequencies above 2 GHz, is probably not the cause of the radio-quiet nature of this quasar in the 5 and 10.7 GHz survey of Strittmatter et al. (1980).

Bregman, J. N.↗

NASA NTRS1985

An analysis of scattered light in low dispersion IUE spectra

A detailed numerical simulation of light scattering from the low-resolution grating in the short wavelength spectrograph of the IUE Observatory was developed, in order to quantitatively analyze the effects of scattering on both continuum and line emission spectra. It is found that: (1) the redistribution of light by grating scattering did not appreciably alter either the shape or the absolute flux level of continuum spectra for A-F stars; (2) late-type stellar continua showed a tendency to flatten when observed in scattered light toward the shorter wavelengths; and (3) the effect of grating scattering on emission lines is to decrease measured line intensities by an increasing percentage toward the shorter wavelengths. The spectra obtained from scattering experiments for solar-type and late type stars are reproduced in graphic form.

Basri, G.↗

NASA NTRS1986

X-ray, UV, and optical observations of the dwarf nova BV Puppis

Exosat, IUE, optical spectroscopic, and broad-band photometric data on BV Pup are presented and analyzed in order to study the system characteristics and their relation to the high excitation of the emission lines. It is observed that: (1) at quiescence and outburst, the He II 4686 A/H-beta ratio for the star is larger than for other observed dwarf novae; (2) the X-ray flux is high for a system at outbursts and the X-ray flux correlates with an increased He II flux over the quiescent values; (3) the flat slope of the flux distribution at quiescence implies relatively low accretion rate; and (4) the abnormal UV line spectrum suggests a different geometry/opacity for the line emission zone compared to normal dwarf novae.

Szkody, Paula↗

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

A five-level program for ions of astrophysical interest

An interactive FORTRAN program is presented which determines the physical conditions in a nebula given an appropriate emission-line intensity ratio, or the line emissivities given a density and temperature. A method for estimating ionic abundances based on the H-beta emissivity is also included. The relevant underlying physics is reviewed and a detailed description of the operation of the program given. Uncertainties in the interpretation of the results are discussed briefly.

De Robertis, M. M.↗

NASA NTRS1989

The double-nucleus galactic merger Mkn 463

Deep CCD imaging in broadband and forbidden O III wavelengths of the twin-nucleus active galaxy Markarian 463 is presented. These data show that the system has triple curved tails indicative of a strong tidal interaction and probable merger. Colors, morphology, and their implications are discussed. The forbidden O III line emission is seen to be extended and linear, perhaps filling twin cones with apex at the eastern optical nucleus. It is argued that this indicates nonisotropic radiation from an obscured AGN. Spatially resolved spectroscopy on and off the nuclei reveals that the radial velocities of the gas lie in a small range, unlike some other multiple nucleus systems. The nature of the emission-line regions is discussed, along with the evolutionary state of the system indicated by the present data and IR and radio data.

Hutchings, J. B.↗

NASA NTRS1989

Time-resolved spectroscopy and photometry of the eclipsing AM Herculis binary EXO 033319 - 2554.2

Time-resolved optical observations of the eclipsing AM Herculis binary EXO 033319 - 2554.2 are presented. High-speed photometry of an eclipse is presented and used to derive a new ephemeris for the system and to estimate the size of the region responsible for the cyclotron emission. Optical spectra that span the orbital cycle are presented, the cyclotron emission in these spectra is discussed, and the flux and radial velocity variations of H-beta, H-gamma, and He II 4686 A are examined. Models of the flux and radial velocity variations of the emission lines indicate that about half the line emission comes from low-velocity material that is about 1.4 x 10 to the 10th cm from the white dwarf. The rest comes from high-velocity material that is about 10 to the 10th cm from the white dwarf and is moving toward it at about 600 km/s.

Allen, Richard G.↗

NASA NTRS1989

Spectrometer system for diffuse extreme ultraviolet radiation

A unique grazing incidence spectrometer system has been designed to study diffuse line emission between 80 and 650 A with 10-30 A resolution. The minimum detectable emission line strength during a 5-min observation ranges from 100-2000 ph/sq cm sec str. The instrument uses mechanically ruled reflection gratings placed in front of a linear array of mirrors. These mirrors focus the spectral image on microchannel plate detectors located behind thin filters. The field of view is 40 min of arc by 15 deg, and there is no spatial imaging. This instrument has been fabricated, calibrated, and successfully flown on a sounding rocket to observe the astronomical background radiation.

Labov, Simon E.↗

NASA NTRS1991

New results concerning the Galactic fountain

The time-dependent nonequilibrium thermal and ionization history is traced of hot optically-thin radiatively-cooling gas in a 1D planar steady-state flow model of the Galactic fountain. The calculation of such a flow which neglects photoionization is found to be unable to simultaneously reproduce the observed C IV, Si IV, and N V column densities through Galactic halo gas. It is shown that, when photoionization is taken into account, a fountain flow can match the observations of both UV absorption and emission lines for a range of ionizing fluxes which depends on the characteristic size of the cooling regions within the flow. What levels of the external photoionizing flux, such as that contributed by Galactic starlight, supernova remnants, and the metagalactic radiation background, can produce agreement with observational results are determined. The ionizing radiation emitted by the cooling gas itself is found to be sufficient to cause the flow to match the observed column densities and line emission.

Shapiro, Paul R.↗

NASA NTRS1993

Two searches for primeval galaxies

A number of active galaxies are now known at very large redshifts, some of them even have properties suggestive of galaxies in the process of formation. They commonly show strong Ly-alpha emission, at least some of which appears to be ionized by young stars. Inferred star formation rates are in the range approximately = 100-500 solar mass/yr. An important question is: are there radio-quiet, field counterparts of these systems at comparable redshifts? Whereas, we are probably already observing some evolutionary and formative processes of distant radio galaxies, the ultimate goal is to observe normal galaxies at the epoch when most of their stars form. We have, thus, started a search for emission-line objects at large redshifts, ostensibly young and forming galaxies. Our method is to search for strong line emission (hopefully Ly alpha) employing two techniques: a direct, narrow-band imaging search, using a Fabry-Perot interferometer; and a serendipitous long-slit spectroscopic search.

Thompson, D.↗

NASA NTRS1992

Observations of R Coronae Borealis stars in decline - Empirical arguments for dust formation near the stellar surface

We present new IUE observations which monitor the spectroscopic evolution of RY Sgr through a deep decline. These data, along with other IUE, visible, and infrared observations of declines in RY Sgr, R CrB, and V854 Cen, are considered in an attempt to understand the dust formation process and the source of the narrow- and broad-line emission seen during declines. Spectroscopic, photometric, and polarimetric data covering 10 declines of these stars have been analyzed. The evolution of the UV emission spectrum is similar to that found in the visible. Previous models of dust formation assume that dust forms around 20 stellar radii, where gas ejected from the star is cool enough to condense. However, the spectral evolution, and the dispersal times of dust implied by the light curve are consistent with dust forming within a few stellar radii and moving outward due to radiation pressure. The expanding dust cloud eclipses the photosphere and parts of the emission line region, causing the observed spectral evolution.

Clayton, Geoffrey C.↗

NASA NTRS1992

How old is the z = 3.4 radio galaxy B2 0902+34?

The redshift 3.395 radio galaxy B2 0902+34 has been observed at K and in a 0.09 micron wide 2.21 micron filter which includes the redshifted forbidden O III 4959 and 5007 A emission lines. A value of m(K) = 19.9 +/- 0.3 is found in a 4 arcsec aperture, a magnitude fainter than Lilly's (1988) value, while the narrow-band image reveals that most of this flux is actually due to line emission. After correcting for forbidden O III 4959 and 5007A, a color is found which is consistent with the flat F(v) spectrum considered characteristic of a protogalaxy. Ages for the galaxy derived from stellar population models based on the limit R - K less than 3.8 are much younger than those for the I - K = 4.5 value reported by Lilly.

Eisenhardt, Peter↗

NASA NTRS1994

ASCA observations of NGC 1068

With the high sensitivity and spectral resolution of the Advanced Satellite for Cosmology and Astrophysics (ASCA) satellite, we have discovered strong emission lines from the H-like and/or He-like ions of Ne, Mg, Si, and S as well as Fe L and confirmed the complex structure of Fe K line emission in the Seyfert II galaxy NGC 1068. The continuum emission above 3 keV exhibits rather flat shape with no evidence of low energy absorption. The overall X-ray spectrum can be well explained with a model involving starburst activity plus an obscured active galactic nucleus.

Ueno, Shiro↗