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At least 1,333 records · Page 74
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NASA NTRS1988

A statistical study of properties of Seyfert and starburst galaxies

Spectral and morphological data for 282 Seyfert and emission-line galaxies spanning radio to X-ray wavelengths are compiled. The data include a large number of optical emission-line measurements which have not been reported previously. These data are intended to provide a convenient summary of the relevant properties of these galaxies, as well as a data base to search for correlations among the various parameters in order to obtain a better understanding of the active galaxy phenomenon. The paper presents the data and analyzes the distributions of various properties of Seyfert 1 and Seyfert 2 galaxies and starburst galaxies. It is found that Seyferts 2s have a higher 60 micron/forbidden O III 5007 A flux ratio than Seyfert 1s. This result, combined with the fact that Seyfert 2s are more heavily reddened, indicate that they have a higher dust content. It is also found that starburst nuclei are comparable to Seyfert 2s in far-infrared and 20 cm luminosities, although their optical spectra are markedly different.

Dahari, Oved↗
NASA NTRS1988

The analysis of spectra of novae taken near maximum

A project to analyze ultraviolet spectra of novae obtained at or near maximum optical light is presented. These spectra are characterized by a relatively cool continuum with superimposed permitted emission lines from ions such as Fe II, Mg II, and Si II. Spectra obtained late in the outburst show only emission lines from highly ionized species and in many cases these are forbidden lines. The ultraviolet data will be used with calculations of spherical, expanding, stellar atmospheres for novae to determine elemental abundances by spectral line synthesis. This method is extremely sensitive to the abundances and completely independent of the nebular analyses usually used to obtain novae abundances.

Stryker, L. L.↗
NASA NTRS1994

Charge transfer in helium-rich supernova plasma

Charge transfer rate coefficients are estimated using Landau-Zener and modified Demkov approximations. The coefficients, augmented by those available from the literature, are used in statistical equilibrium equations describing the state of helium-rich supernova plasma. Such a plasma may describe both Type Ib and Type Ic supernova ejecta. The hypothesis that extensive mixing of metals with helium in Type Ic supernovae may provide a catalyst for rapid charge transfer that weakens the helium line emission by altering the excitation balance is tested. It is shown that charge transfer as a mechanism for suppressing helium line emission is ineffective unless the metal abundance is comparable to or larger than the helium abundance. This result supports an earlier conclusion that Type Ic supernovae must be helium poor relative to Type Ib events.

Swartz, Douglas A.↗
NASA NTRS1995

Blue lobes in the Hydra A cluster central galaxy

We present new U- and I-band images of the centrally dominant galaxy in the Hydra A cluster, obtained with the 2.5 m Isaac Newton Telescope at La Palma. The galaxy is centered in a poor, X-ray-luminous cluster whose gaseous intracluster medium is apparently cooling at a rate of m-dot(sub CF) approximately 3000 solar masses/yr. The galaxy's structure is that of a normal giant elliptical galaxy, apart from the central approximately 8 x 6 arcsec (approximately 12 x 9 kpc) region which contains an unusually blue, lobelike structure that is spatially coincident with a luminous emission-line nebula in rotation about the nucleus. Based on near spatial coincidence of the central continuum structure and the emission-line nebula, we suggest that the blue continuum is due to a warm stellar population in a central disk. In order to isolate and study the structure of the disk, we have subtracted a smooth galactic background model from the U-band image. The disk's surface brightness profiles along its major and minor axes decline roughly exponentially with radius. The disk's axial ratio is consistent with a nearly edge-on thick disk or a thin disk that is inclined with respect to the line of sight. The bluest regions, located a few arcsec on either side of the nucleus (giving the lobelike appearance), may be due to locally enhanced star formation or a seeing-blurred ring of young stars embedded in the disk observed nearly edge-on. If star-formation is occurring with the local initial mass function, the central color, surface brightness, and dynamical mass would be consistent with models for star formation at a rate of less than and approximately 1 solar masses/yr which has persisted for the past approximately 10(exp 9) yr, a short burst (10(exp 7) yr) of star formation at a rate of approximately 30 solar masses/yr which occurred less than and approximately 10(exp 8) yr ago, or an instantaneous burst of star formation which occurred approximately 5 x 10(exp 7) yr ago. While the young population contributes approximately 30%-40% of the central U-band luminosity, its mass would be less than and approximately 1% to less than and approximately 10% (10(exp 8) solar masses - 2 x 10(exp 9) solar masses of the galaxy's central dynamical mass. We consider a number of possible origins for the disk material.

Mcnamara, Brian R.↗
NASA NTRS2008

Constraints on Black Hole Spin in a Sample of Broad Iron Line AGN

We present a uniform X-ray spectral analysis of nine type-1 active galactic nuclei (AGN) that have been previously found to harbor relativistically broadened iron emission lines. We show that the need for relativistic effects in the spectrum is robust even when one includes continuum "reflection" from the accretion disk. We then proceed to model these relativistic effects in order to constrain the spin of the supermassive black holes in these AGN. Our principal assumption, supported by recent simulations of geometrically-thin accretion disks, is that no iron line emission (or any associated Xray reflection features) can originate from the disk within the innermost stable circular orbit. Under this assumption, which tends to lead to constraints in the form of lower limits on the spin parameter, we obtain non-trivial spin constraints on five AGN. The spin parameters of these sources range from moderate (a approximates 0.6) to high (a > 0.96). Our results allow, for the first time, an observational constraint on the spin distribution function of local supermassive black holes. Parameterizing this as a power-law in dimensionless spin parameter (f(a) varies as absolute value of (a) exp zeta), we present the probability distribution for zeta implied by our results. Our results suggest 90% and 95% confidence limits of zeta > -0.09 and zeta > -0.3 respectively.

Brenneman, Laura W.↗
NASA NTRS1978

Lines in the 2736-3303 A spectrum of Arcturus

Results are reported for a study of the near-UV spectrum of Arcturus as recorded with a balloon-borne echelle spectrograph-vidicon detector system in the spectral region from 2700 to 3300 A at 0.1-A resolution. A condensed version of the Arcturus spectrum is provided along with profile descriptions and identifications for 383 absorption features detected in the near-UV. Elements definitely present include Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, and La. Elements with spectral features indicating possible presence include Be, O, S, K, Ga, Ge, Nb, Sn, Gd, and Bi. Line blocking is shown to be extensive in the spectral region studied, and eight possible continuum 'windows' are found in the near-UV. Emission lines of chromospheric origin due to Mg II, Fe I, Fe II, and possibly Cr II are also identified in the region from 2736 to 3303 A. It is noted that the Fe I emission lines at 2823 and 2844 A are optically pumped.

Stencel, R. E.↗
NASA NTRS1982

The great galactic centre mystery

Gamma-ray observations of the center of the Galaxy show a varying positron-electron annihilation radiation emission, while at radio wavelengths a non-thermal compact source surrounded by ionized gas moving at high velocities can be seen. Line emission maps for atomic and ionized hydrogen and molecular gas suggest gas expulsion and a massive collapsed object. IR observations show that ionized gas in the central few parsecs of the Galactic center is concentrated in at least 14 small clouds. Charge-coupled device images show a pair of faint, very red sources within a few arc seconds of IRS 16 and the compact non-thermal radio source. The positron-electron annihilation line emission implies an annihilation rate of 10 to the 43rd per sec, compared with an observed luminosity at IR wavelengths of 10 to the 40 erg per sec. Some models are briefly discussed.

Riegler, G. R.↗
NASA NTRS1992

A spectroscopic search for colliding stellar winds in O-type close binary systems. II - Plaskett's star (HD 47129)

New evidence for colliding winds in the massive O-type binary system Plaskett's star is reported. High S/N ratio spectra of the H-alpha and He I 6678 emission lines are presented, and their orbital phase-related variations are examined in order to derive the locations and motions of the high-density gas in the system. Radial velocity cures for several absorption and emission lines associated with the photosphere of the primary are also provided. The H-alpha emission profiles are complex, with very broad wings and a sharp spikelike feature that approximately follows the motion of the primary star. The radial velocity curve for this spike lags behind the photospheric velocity curve of the primary by 0.066 in phase. It is suggested that the high-velocity H-alpha emission is related to instabilities in the intershock region between the two component stars. The H-alpha phase-related variations are compared with those observed in the UV wind lines in IUE archival spectra.

Wiggs, Michael S.↗
NASA NTRS1982

A first look at the eclipsing cataclysmic variable Lanning 10

Photometry and spectroscopy of a new cataclysmic variable star, Lanning 10 are presented. The star is shown to be an eclipsing binary with a 7h 42m orbital period. Blue flickering is observed to occur on a time scale of 10 minutes. The light curve is analyzed with a numerical simulation of the eclipse of the accretion disk by the lobe-filling star. The disk nearly spans the Roche lobe of the white dwarf, and its surface brightness is a steep function of radius. Spectra show broad H alpha and He I 6678 A emission lines from the accretion disk and a weak absorption feature from the red dwarf. Radial velocity measurements of the H alpha emission line vary systematically with binary phase. The observed velocity amplitude 240 km/s, gives the mass function 0.46 solar masses. A phase shift of the velocity curve relative to the eclipse ephemeris indicates that a brightness asymmetry exists in the inner parts of the disk.

Horne, K.↗
NASA NTRS1982

The ultraviolet spectrum of the Crab Nebula

Ultraviolet spectroscopy of the Crab Nebula done by the International Ultraviolet Explorer satellite is described, and an estimate of the carbon abundance is made, noting data reduction to remove spectral defects caused by radiation hits. The important C IV 1549, He II 1640, and semiforbidden C III 1908 emission line intensities were measured and upper limits placed on other ultraviolet features for the brightest filamentary region in the Nebula. The emission lines imply an average ionic abundance ratio n(C+2)/n(O+2) in the range from 0.4 to 1.5 in the observed gaseous condensations. The elemental abundance ratio of carbon to oxygen is probably in the same range. Analysis shows that there is no perceptible excess of carbon due to presupernova nucleosynthesis in the observed region. The large helium abundance, small carbon and oxygen abundances, and presence of a neutron star in the Crab Nebula suggest that the presupernova star had a mass close to eight solar masses.

Davidson, K.↗
NASA NTRS1988

The Algol-like binary TT Hydrae - The stars, circumstellar matter, and superionized plasma

This paper reports on superionized UV emission lines discovered in TT Hydrae (HD 97528), a semidetached eclipsing binary system in the Southern-Hemisphere sky. The list of emission lines observed is typical for interacting nondegenerate binaries of the Algol type, but with system-specific relative-intensity characteristics. The primary component of the system is a B9.5 V main-sequence star with effective temperature of 9800 K. Its mass equals 2.25 solar masses; the radius is 1.9 solar radii; and surface gravity log g equals 4.23. The secondary star has a mass of 0.41 solar mass and fills its critical Roche lobe. Evidence obtained on mass interaction supports the conclusion that HD 97528 is a normal semidetached system.

Plavec, Mirek J.↗
NASA NTRS2016

SU Lyncis, a Hard X-Ray Bright M Giant: Clues Point to a Large Hidden Population of Symbiotic Stars

Symbiotic star surveys have traditionally relied almost exclusively on low resolution optical spectroscopy. However, we can obtain amore reliable estimate of their total Galactic population by using all available signatures of the symbiotic phenomenon. Here we report the discovery of a hard X-ray source, 4PBC J0642.9+5528, in the Swift hard X-ray all-sky survey, and identify it with a poorly studied red giant, SU Lyn, using pointed Swift observations and ground-based optical spectroscopy. The X-ray spectrum, the optical to UV spectrum, and the rapid UV variability of SU Lyn are all consistent with our interpretation that it is a symbiotic star containing an accreting white dwarf. The symbiotic nature of SU Lyn went unnoticed until now, because it does not exhibit emission lines strong enough to be obvious in low resolution spectra. We argue that symbiotic stars without shell-burning have weak emission lines, and that the current lists of symbiotic stars are biased in favour of shell-burning systems. We conclude that the true population of symbiotic stars has been underestimated, potentially by a large factor.

binaries: symbiotic aEuro" stars: individual: SU L↗
NASA NTRS1986

NGC 6212 - An X-ray-selected active elliptical galaxy

Optical and X-ray data on the elliptical galaxy NGC 6212 are reported. The X-ray flux varies by a factor of four on a time scale of months. The optical spectrum shows broad Balmer emission lines and narrow forbidden lines which are typical of low-luminosity X-ray selected Seyfert galaxies. The continuum is predominantly stellar, with no evidence for a nonthermal contribution. Narrow emission lines extend at least 11 kpc from the nucleus and are used to derive a rotation curve. The X-ray variability and relatively weak radio emission of NGC 6212 are not unusual for Seyfert galaxies.

Halpern, J. P.↗
DOE OSTI2022

SDSS-IV MaNGA: the chemical co-evolution of gas and stars in spiral galaxies

ABSTRACT We investigate archaeologically how the metallicity in both stellar and gaseous components of spiral galaxies of differing masses evolve with time, using data from the SDSS-IV MaNGA survey. For the stellar component, we can measure this evolution directly by decomposing the galaxy absorption-line spectra into populations of different ages and determining their metallicities. For the gaseous component, we can only measure the present-day metallicity directly from emission lines. However, there is a well-established relationship between gas metallicity, stellar mass, and star formation rate which does not evolve significantly with redshift; since the latter two quantities can be determined directly for any epoch from the decomposition of the absorption-line spectra, we can use this relationship to infer the variation in gas metallicity over cosmic time. Comparison of present-day values derived in this way with those obtained directly from the emission lines confirms the validity of the method. Application of this approach to a sample of 1619 spiral galaxies reveals how the metallicity of these systems has changed over the last 10 billion yr since cosmic noon. For lower-mass galaxies, both stellar and gaseous metallicity increase together, as one might expect in well-mixed fairly isolated systems. In higher-mass systems, the average stellar metallicity has not increased in step with the inferred gas metallicity, and actually decreases with time. Such disjoint behaviour is what one might expect if these more massive systems have accreted significant amounts of largely pristine gas over their lifetimes, and this material has not been well mixed into the galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2000

Mapping the X-Ray-Emitting Ejecta in Cassiopeia A with Chandra

We present X-ray emission-line equivalent width images of the bright Galactic supernova remnant Cassiopeia A for the elements Si, S, Ar, Ca, and Fe using a 50,000 s observation with the Advanced CCD Imaging Spectrometer on the Chandra X-Ray Observatory. The images essentially map the bulk of detectable ejecta of these elements over a wide range of surface brightnesses and show morphologies distinctly different from that of the broadband X-ray emission and the 4-6 keV continuum emission. The Si, S, Ar, and Ca maps, while different in turn from those of Fe, are similar to the distribution of fast optical ejecta knots in that they clearly delineate the X-ray counterpart of the northeast optical jet. Low surface brightness regions just outside the bright shell in the north and west are also shown to have strong line emission. The strong Fe emission is exterior to that of other elements in the east, as previously noted, but is generally coincident elsewhere. The projected interior has relatively little emission traced by high line equivalent widths.

Hwang, Una↗
NASA NTRS1984

Detection of shocked atomic gas in the Kleinmann-Low nebula

The 63 micrometer (3)p(1)-(3)P(2) fine structure line emission of neutral atomic oxygen at the center of the Orion nebula with a resolution of 30" is presented. There are three main emission peaks. One is associated with the region of strongest thermal radio continuum radiation close to the Trapezium cluster, and probably arises at the interface between the HII region and the dense Orion molecular cloud. The other two line emission peaks, associated with the Kleinmann Low nebula, are similar in both distribution and velocity to those of the 2 micrometer S(1) line of molecular hydrogen and of the high velocity wings of rotational CO emission. The OI emission from the KL nebula can be produced in the shocked gas associated with the mass outflows in this region and is an important coolant of the shocked gas.

Werner, M.↗
NASA NTRS1995

Broad NE 8 lambda 774 emission from quasars in the HST-FOS snapshot survey (ABSNAP)

We discuss the strength and frequency of broad Ne VIII lambda 774 emission from quasars measured in the Hubble Space Telescope Faint Object Spectrograph (HST-FOS) snapshot survey (Absnap). Five sources in the survey have suitable redshifts (0.86 less than or equal to Z(sub em) less than or equal to 1.31), signal-to-noise ratios and no Lyman limit absorptions. Three of the five sources have a strong broad emission line near 774 A (rest), and the remaining two sources have a less securely measured line near this wavelength. We identify these lines with Ne VIII lambda 774 based on the measured wavelengths and theoretical estimates of various line fluxes (Hamann et al. 1995a). Secure Ne VIII detections occur in both radio-loud and radio-quiet sources. We tentatively conclude that broad Ne VIII lambda 774 emission is common in quasars, with typical strengths between approximately 25% and approximately 200% of O VI lambda 1034. These Ne VIII lambda 774 measurements imply that the broad emission line regions have a much hotter and more highly ionized component than previously recognized. They also suggest that quasar continua have substantial ionizing flux out to energies greater than 207 eV (greater than 15.2 ryd, lambda less than 60 A). Photoionization calculations using standard incident spectra indicate that the Ne VIII emission requires ionization parameters U greater than or = 5, total column densities N(sub H) greater than or = 10(sub 22)/sq cm and covering factors greater than or = 25%. The temperatures could be as high as approximately 10(exp 5) K. If the gas is instead collisionally ionized, strong Ne VIII would imply equilibrium temperatures in the range approximately 400,000 less than or approximately = T(sub e) less than or approximately = 10(exp 6) K. In either case, the highly ionized Ne VIII emission regions would appear as X-ray 'warm absorbers' if they lie along our line of sight to the X-ray continuum source.

Hamann, Fred↗
NASA NTRS1979

Bragg crystal spectroscopy on the OSO 8 satellite

Results are reported for high-resolution OSO 8 Bragg-crystal spectroscopy of a variety of cosmic X-ray sources in the energy range from 2 to 10 keV. A continuous spectrum of Sco X-1 is examined, and results of a search for narrow line emission due to iron near 6.7 keV are presented for 32 galactic X-ray sources, including Sco X-1, Cyg X-3, and Cen X-3. It is noted that the strongest evidence for iron line emission has been obtained for Cyg X-3 and that evidence for an iron line feature has also been found in the spectrum of Cen X-3.

Long, K. S.↗