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At least 703 records · Page 39
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NASA NTRS1987

Spectral classification of emission-line galaxies

A revised method of classification of narrow line active galaxies and H II region-like galaxies is proposed. It involves the line ratios (O III) lambda 5007/H beta, (N II) lambda 6583/H alpha, (S II) (lambda lambda 6716 = 6731)/H alpha, and (O I) lambda 6300/H alpha. These line ratios take full advantage of the physical distinction between the two types of objects and minimize the effects of reddening correction and errors in the flux calibration. Large sets of internally consistent data are used including new previously unpublished measurements. Prediction of recent photoionization models by power law spectra and by hot stars are compared with the observations. The classification is based on the observational data interpreted on the basis of these models.

Veilleux, Sylvain↗
NASA NTRS1986

X-ray emission lines from three Galactic bulge sources

X-ray spectroscopic observations obtained with the Einstein objective grating spectrometer (OGS) and monitor proportional counter (MPC) instruments of three Galactic bulge sources, the globular cluster burst source 1820-30, the burster Serpens X-1, and the GX 9+9 are presented. Joint spectral fits to the OGS and MPC data are consistent for all three sources with either a thermal bremsstrahlung model with temperature ranging from 6 to 10 keV or with a two-component blackbody model, where one component may be associated with the neutron star and one with the accretion disk. The spectra of Serpens X-1 and 1820-30 harden with increases in intensity. The implications of the results for recent models of low-mass X-ray binaries are discussed.

Vrtilek, S. D.↗
NASA NTRS1987

Ultraviolet Al III emission lines and the physics of the solar transition region

Two lines of the solar UV spectrum were identified as due to 3p-3d Al III transitions near 1612 A; the ratios of these lines to the 3s-3p Al III doublet near 1855 A were found to be very sensitive to temperature. Thus, the temperatures of formation of the Al III lines could be determined by using one of the line ratios in two quiet sun regions, a coronal hole, and an active region. The results were found to be consistent with expectations based on the assumption of ionization equilibrium for Al III. It is suggested that S III lines near 1350 A and 1200 A may also serve as a temperature diagnostic.

Doschek, G. A.↗
NASA NTRS1987

The peculiar early-type emission line supergiant S 18/SMC - An optical and ultraviolet study

Spectroscopic observations of S 18/SMC, obtained in the visible at CTIO, the AAT, and ESO and in the UV with the IUE SWP and LWR instruments during 1978-1983, are reported. The data are presented in tables and spectra and characterized in detail. The variability of the object in He II, C IV, N IV, N V, and Si IV and the lack of detectable photometric variation between 120 and 1000 nm are discussed in terms of a stellar-envelope model with mass-loss rate greater than or equal to 0.00001 solar mass/yr and N abundance 3-5 times the solar value, corresponding to a transitional phase between extreme mass loss (near the Humphrey-Davidson limit) and the presupernova stage. The FUV flux is tentatively attributed to an extremely hot He-star or neutron-star companion.

Shore, S. N.↗
NASA NTRS1988

A possible detection of Jupiter's northern auroral S1(1) H2 quadrupole line emission

An upper limit is presently determined for the mean intensity of the Jupiter northern Auroral UV/thermal hot spot's S1(1) H2 quadrupole emission, over an 8 sq arcsec illuminated beam; the value obtained is 4.2 X 10 to the -6th W/sq m per sr. It is suggested that the nonradiative deexitation of the H2 molecules via collisions with H may have been underestimated by Kim and Maguire (1986), due to uncertainties concerning auroral H density.

Trafton, L.↗
NASA NTRS1988

Fe II emission line profiles in the ultraviolet spectrum of cool, luminous stars

The differences between the outer atmospheres of the coronal and noncoronal cool stars and the importance of massive stellar winds to the latter group are summarized. The utility of Fe II as a probe of such winds is indicated and a brief review of previous observations of Fe II in these stars is given. The early results of a current IUE program to study the chromospheres and winds of the noncoronal, late-type stars are presented, including evidence of a strong dependence of the mid-UV Fe II profiles on stellar luminosity. In addition, the dependence of the Fe II profiles on intrinsic line strength in spectra of Alpha Ori and the discovery of a variation of the Fe II profiles with time in spectra of Gamma Cru are discussed.

Carpenter, Kenneth G.↗
NASA NTRS1988

A very high resolution study of emission line widths in Galactic and extragalactic H II regions

Very high spectral resolution spectroscopy was performed using the 5007-A forbidden O III line on two Galactic H II regions (NGC 6611 and NGC 7000) and three giant extragalactic H II regions (NGC 588, NGC 604, and IC 133) in M33. Use of the thermally narrow forbidden O III line also aided in the determination of the broadening due to mass motion, although the results are in agreement with the average values obtained in earlier studies primarily done with H-alpha. Evidence is confirmed and found for multiple velocity components in each of the extragalactic systems.

O'Dell, C. R.↗
NASA NTRS1988

X-ray emission lines from cooling flows

Techniques employing individual X-ray line strengths to estimate the rate at which gas cools in the intracluster medium are discussed. It is demonstrated that departures from ionization equilibrium in the cooling plasma are not important at X-ray temperatures. Nonrestrictive upper limits are obtained for four cooling flow clusters. The results favor the existence of substantial cooling flows and argue against the dominance of conduction or other heat sources.

Canizares, Claude R.↗
NASA NTRS1989

Millimeter- and submillimeter-wave surveys of Orion A emission lines in the ranges 200.7-202.3, 203.7-205.3, and 330-360 GHz

A continuous spectral line survey of the Orion A position from 330.5 to 360.1 GHz was carried out. This survey covers nearly the entire 870 micron atmospheric window accessible from ground-based observations. Approximately 160 distinct spectral features composed of about 180 lines were detected, 29 of which could not be readily identified. In addition, Orion A from 200.7 to 202.3 GHz and from 203.7 to 205.3 GHz and 42 distinct new spectral lines were detected, including four that are unidentified at present. These data sets are the first thorough survey results in these spectral regions. The new interstellar lines in the survey bands are tabulated and displayed graphically. Moreover, the data are being made available to the Astronomical Data Center at the Goddard Space Flight Center for distribution by request to the astronomical community.

Jewell, P. R.↗
NASA NTRS1989

Reversed far-infrared line emission from OH in Orion

The fundamental OH rotational transition at 2514 GHz has been observed in the Orion IRc2 region at a spectral resolution of 0.6 km/s. The emission is spatially compact and centered near IRc2. A comparison of the observed profile with spectra of other species known to exist in the region suggests that the entire blueshifted side of the OH profile has been self-absorbed, leaving only a redshifted emission component.

Betz, A. L.↗
NASA NTRS1990

Emission-line variations and broad-line region kinematics of NGC 5548

Sixteen spectroscopic observations of the Seyfert galaxy NGC 5548 were made between March 1979 and June 1984 at Palomar and Steward Observatories. Broad-line flux variations correlated with nonstellar continuum changes were measured. H-beta, H-gamma, and He II 4686A all respond rapidly to continuum variations providing strong evidence for photoionization by a central continuum source. Additionally, H-beta profile variations have occurred during the 1900 day monitoring period. These profile variations also correlate with changes in the continuum, but lag behind by about 90 days or less. A kinematic model that incorporates radial outflow and an internal line opacity source is proposed to explain qualitatively the observed H-beta profile variations.

Rosenblatt, Edward I.↗
NASA NTRS1990

Distances of Galactic WC stars from emission-line fluxes and a quantification of the WC classification

The extent to which later-type WC stars in the Galaxy show constant flux in the carbon lines is assessed. It is found the the WC stars are an extremely 'well-behaved' sequence in terms of quantitative spectroscopic properties. The two classification parameters are closely correlated with a scatter of the order of uncertainty. There appear to be natural breaks in the sequence between subclasses, except between WC5 and 6. The classification is quantified using the C IV 5808 A/C III 5696 A ratio as the principal defining parameter for WC7-9 stars and the C III 5696 A/O V 5590 A ratio as the principal defining parameter for WC4-6 stars. Preliminary calibration of the line fluxes indicate that the flux of C IV 5808 A in Galactic WC stars is constant at F(0) 5808 = -log F(0)(5808) = 8.1 at 1 kpc for subclasses WC5-7. The intrinsic line flux ratio C(0) = log f(0)(5808/4650) is a smooth function of subclass number, decreasing from -0.22 dex for WC4 stars to -0.56 dex for WC9 stars.

Smith, Lindsey F.↗
NASA NTRS1990

The oxygen emission lines in Wolf-Rayet spectra

The statistical equilibrium of oxygen in the line-emitting regions of WR stars is studied using the one-representative point theory of Castor and van Blerkom (1970) for a wider range of the radiation temperature, electron temperature, and electron density. Radiative processes, collisional processes, and electronic recombination are studied for a 59-level model atom. The level populations depart by large factors from those expected for LTE at the electron temperature and electron density. When the parameters have the values found previously by Bhatia and Underhill to be representative for WR stars, the oxygen atoms are strongly concentrated in the lower levels of O(2+), O(3+), and O(4+). The predicted relative energies in typical lines of O III, O IV, and O V for a solar abundance ratio of O to H are compatible with what is observed in WC and WN spectra.

Bhatia, A. K.↗
NASA NTRS1991

An optical catalog of extragalactic emission-line objects similar to quasi-stellar objects

A catalog of 935 galaxies which have optical properties similar to those of QSOs is given. A subsidiary table of cross-identifications enables the reader to relate the name of a given object to its coordinate name. Most of the objects appear to be nonstellar. The majority, more than 700, have redshifts z = 0.2 or less, and have mostly been classified as Seyfert galaxies, N systems, or radio galaxies. The Hubble diagram for all of the objects with z = 0.2 or less is shown. The redshift distribution peaks at z = 0.025, but there are about 200 powerful radio galaxies in the extended tail of the distribution which have z greater than 0.2. There is a separate and distinct peak in the redshift distribution at z = 0.06.

Hewitt, A.↗
NASA NTRS1991

Optical coronal emission lines from cooling flows in elliptical galaxies and galaxy clusters

Luminosities, surface brightnesses, and line profiles of the coronal lines predicted by standard models for cooling flows in clusters of galaxies and in individual early-type galaxies are presented. The coronal line luminosities of cooling flows depend primarily on the total rate at which gas is cooling. In homogeneous cooling flow models (HMs) in which all of the gas flows into the central regions, the coronal lines are very centrally concentrated, coming mainly from a limb-brightened shell lying just within the sonic radius of the inflow. For HMs, the central surface brightnesses of the stronger coronal lines from nearby clusters with large cooling rates are expected to be about 6 x 10 to the -17th ergs/sq cm/s/sq arcsec. For inhomogeneous models (IMs) in which gas cools out of the flow at large radii, the surface brightness profiles of the coronal lines are more extended, and the central surface brightness is much lower. The integrated line profiles of the HMs are very wide and flat and the central line profiles are double-peaked. The IMs have nearly Gaussian line profiles.

Sarazin, Craig L.↗
NASA NTRS1992

The origin of broad emission lines in the extragalactic giant H II region NGC 2363

High signal-to-noise long-slit spectra have been obtained of the giant H II region NGC 2363 located in the dwarf SBm galaxy NGC 2366. A discovery of low-intensity broad spectral components (FWHM is approximately equal to 40 A or 2400 km/s) in the bright nebular lines H-alpha, H-beta, and forbidden O III is reported. The broad spectral components are detected over a large spatial extent (not less than 500 pc) centered on the nebula. Several mechanisms for broadening nebular lines are explored: stellar winds, Thomson scattering by hot gas, supernova remnants, and superbubble blowout. All mechanisms have problems. Superbubble blowout, which is the only known mechanism capable of accelerating interstellar gas over such a volume of space, does not appear consistent with the physical properties of the H II region NGC 2363 or with the nature of the host galaxy. It is concluded that the broad nebular lines are probably due to very high velocity gas whose origin is, at present, unknown.

Roy, Jean-Rene↗
NASA NTRS1992

The broad emission line and continuum variations of Seyfert galaxies. I - Time scales and amplitudes

Spectroscopic observations of 13 Seyfert 1 galaxies made from 1979 to 1984 at Palomar and Steward Observatories were analyzed for Balmer-line and optical continuum variability. The majority of the galaxies showed significant variations, particularly in the continuum. Typical peak-to-peak changes for H-beta and H-gamma integrated line fluxes were 100-200 percent, while the continua varied by 200-350 percent. In several cases, Balmer-line and continuum variations were found to be strongly correlated, as expected for photoionization by a central continuum source. However, these correlations were found to be highly nonlinear. Significant correlations were found between variability amplitude and global AGN properties such as luminosity. Moreover, a significant number of variations occurring on short time scales constrains the size of the broad-line region in Seyfert galaxies to about 90 lt-days across or less.

Rosenblatt, Edward I.↗
NASA NTRS1992

The narrow emission lines from SN 1987 A

Observations of the narrow lines from SN 1987 A have been reviewed, along with model interpretations of these observations. In addition, a discussion is provided on characteristics of the radiation from the supernova outburst, and how this affects the thermal structure of the circumstellar gas. Preliminary results from 2D hydrodynamical calculations for the circumstellar structure are also presented.

Lundqvist, Peter↗