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At least 1,297 records · Page 72
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NASA NTRS1982

Outer atmospheres of cool stars. XII - A survey of IUE ultraviolet emission line spectra of cool dwarf stars

Quantitative information is obtained on the chromospheres and transition regions of M dwarf stars, in order to determine how the outer atmospheres of dMe stars differ from dM stars and how they compare with the outer atmospheres of quiet and active G and K type dwarfs. IUE spectra of six dMe and four dM stars, together with ground-based photometry and spectroscopy of the Balmer and Ca II H and K lines, show no evidence of flares. It is concluded, regarding the quiescent behavior of these stars, that emission-line spectra resemble that of the sun and contain emission lines formed in regions with 4000-20,000 K temperatures that are presumably analogous to the solar chromosphere, as well as regions with temperatures of 20,000-200,000 K that are presumably analogous to the solar transition region. Emission-line surface fluxes are proportional to the emission measure over the range of temperatures at which the lines are formed.

Linsky, J. L.↗
NASA NTRS1983

Determinations of SIII, OIV and NeV abundances in planetary nebulae from IR lines

Airborne observations of the infrared forbidden lines (SIII) 18.71 microns, (NeV) 24.28 microns and (OIV) 25.87 microns were made for twelve planetary nebulae. One or more of the lines was detected in seven of these nebulae and ionic abundances were calculated. These results are insensitive to nebula temperatures, in contrast to the case for optical or UV lines. However, density estimates from optical and UV forbidden lines were required to obtain abundances. The NeV infrared line flux from NGC 7662 was combined with the 3426A flux to obtain a NeV electron temperature of 11,200 (+2000, - 1100) K, which overlaps OIII temperature measurements. Since the ionization potential of NeIV is much greater than that of OII, T sub e (NeV) would be expected to be much greater than T sub e (OIII). In fact, numerical models predict T sub e (NeV) (16-20) x 1000 K. This discrepancy may indicate inaccuracies in currently available atomic parameters for NeV.

Shure, M. A.↗
NASA NTRS1982

He I lines in B stars - Comparison of non-local thermodynamic equilibrium models with observations

Profiles of He gamma-gamma 4026, 4387, 4471, 4713, 5876, and 6678 have been obtained in 17 stars of spectral type B0-B5. Parameters of the nonlocal thermodynamic equilibrium models appropriate to each star are determined from the Stromgren index and fits to H-alpha line profiles. These parameters yield generally good fits to the observed He I line profiles, with the best fits being found for the blue He I lines where departures from local thermodynamic equilibrium are relatively small. For the two red lines it is found that, in the early B stars and in stars with log g less than 3.5, both lines are systematically stronger than predicted by the nonlocal thermodynamic equilibrium models.

Heasley, J. N.↗
NASA NTRS1982

Asymmetric emission-line regions with out-flowing mass in QSOs and the z/ab/ at least equal to z/em/ systems

A heuristic asymmetrical model for a quasar emission-line region, with material streaming out, is described. The physical parameters are essentially the same as those of static models; the geometry turns out to be the dominant factor in determining the emission line profiles. Calculations are carried out for a variety of parameterized flow models and for the Blumenthal and Mathews (1975) theoretical model of a radiatively driven flow. The emission-line profiles are insensitive to the details of the acceleration, the filling factor, and the ionization profile. Absorption is assumed to take place in stationary matter in the QSO's galaxy or associated group or cluster, so that z(ab) is identified with the cosmological redshift. Due to the flow, the emission-lines are shifted with respect to the absorption-lines; in cases of a flow directed towards the observer systems with z(ab) at least equal to z(em) result. The distribution of absorption redshifts is symmetric about z(em).

Goldman, I.↗
NASA NTRS1983

A survey of ultraviolet interstellar absorption lines

A telescope-spectrometer on the Copernicus spacecraft made possible the measurement of many ultraviolet absorption lines produced by the interstellar gas. The present survey provides data on ultraviolet absorption lines in the spectra of 88 early-type stars. The stars observed are divided into four classes, including reddened stars, unreddened bright stars, moderately reddened bright stars, and unreddened and moderately reddened faint stars. Data are presented for equivalent width, W, radial velocity V, and rms line width, D, taking into account some 10 to 20 lines of N I, O I, Si II, P II, S II, Cl I, Cl II, Mn II, Fe II, Ni II, Cu II, and H2. The data are based on multiple scans for each line. Attention is given to details of observations, the data reduction procedure, and the computation of equivalent width, mean velocity, and velocity dispersion.

Bohlin, R. C.↗
NASA NTRS1983

X-ray and optical studies of emission-line Markarian galaxies

The X-ray and optical properties of a selection of compact nucleus, emission line Markarian galaxies have been studied. Observations with the Einstein Observatory have detected X-rays from all the Seyfert galaxies and none of the narrow emission line galaxies in the sample. This result supports the idea that powerful X-ray emission is correlated with the presence of a broad optical emission line component. The emission line spectra of the Seyfert galaxies show much higher excitation than do the narrow-line galaxies, whose spectra are similar to those of H II regions. Both the optical properties and the radio and X-ray upper limits of the non-Seyfert galaxies are consistent with the suggestion that those objects have undergone bursts of massive star formation.

Ulvestad, J. S.↗
NASA NTRS1983

Observations of the line profile of Paschen alpha in 3C 273

Within the uncertainties, the P-alpha line profile is the same as those of H-beta, L-alpha, and C IV. It is therefore contended that if current models of broad-line-emitting clouds in quasars are correct, then the similarity of the P-alpha line profile to the L-alpha profile argues against a velocity field dominated by radial inflow or outflow. It is noted, however, that if the cloud motions are predominantly due to radial inflow or outflow, then the clouds must radiate more isotropically in L-alpha then current models predict. The observed similarity of the line profiles of P-alpha at 1.875 microns and of C IV at 1550 A leads to the conclusion that there is no differential reddening caused by dust between clouds moving at different velocities within the broad line region of 3C 273.

Sellgren, K.↗
NASA NTRS1983

Profiles and intensity ratios of the C IV lambda 1548, 1550 emission lines in planetary nebulae

The C IV resonance doublet at lambda 1548, 1550 is an important diagnostic tool in the study of planetary nebulae. The predicted theoretical intensity ratio of 2:1 is, however, rarely observed in the high dispersion IUE spectrograms. Values of 0.8-2.0 are observed for a sampling of 11 planetary nebulae of various excitation classes and for three proto-planetary nebulae. A diversity of line profiles is observed. In addition to the C IV doublet, weak subsidiary lines are seen. The spacing between these pseudo-lines happens to correspond to the separation of the C IV lines but are believed to be due to hot pixels and do not conform to the radial velocity displacement of the C IV lines.

Feibelman, W. A.↗
NASA NTRS1983

Characteristics of gamma-ray line flares as observed in hard X-ray emissions and other phenomena

Solar Maximum Mission observations of gamma-ray lines from solar flares indicate that energetic proton and heavy ions are accelerated during the impulsive phase. Attention is given to the characteristics of flares from which gamma-ray lines have been observed, as well as intense, hard X-ray flares lacking gamma-ray line emissions. It is found that most of the gamma-ray line flares produced intense, type II and IV radio bursts, and that the time profiles of the high energy hard X-rays are delayed for several seconds relative to those of low energy hard X-rays. The hard X-ray spectral of the gamma-ray line flares are generally flatter (harder) than those of flares without gamma-ray emission.

Bai, T.↗
NASA NTRS1984

Cosmic rays and the emission line regions of active galactic nuclei

The effects that the synchrotron emitting relativistic electrons could have on the emission line regions which characterize active nuclei are discussed. Detailed models of both the inner, dense, broad line region and the outer, lower density, narrow line region are presented, together with the first models of the optically emitting gas often found within extended radio lobes. If the relativistic gas which produces the synchrotron radio emission is mixed with the emission line region gas then significant changes in the emission line spectrum will result. The effects of the synchrotron emitting electrons on filaments in the Crab Nebula are discussed in an appendix, along with a comparison between the experimental calculations, which employ the mean escape probability formalism, and recent Hubbard and Puetter models.

Ferland, G. J.↗
NASA NTRS1984

Investigation of arc cloud lines

The natural mechanisms that lead to the development of deep convective storms through the integration of radio scan satellite data with research aircraft observations is discussed. The aircraft measurements are designed to provide detailed air motion and thermodynamic data near and in the arc cloud line region at the same time GOES rapid scan data is taken. Inspection of the data indicates: (1) Arc cloud lines are important in both the production of convergence and vorticity, and in the interaction with intense thunderstorms which may act to trigger tornado activity. (2) The lateral extent of the vertical motion field compared to the cloud scale indicates that the main driving force for the initial cloud development along the arc-line is controlled by the thunderstorm outflow(s) interacting with the convectively unstable air of the environment. (3) Arc cloud lines and their associated DSL region can pose extreme hazards to aircraft operations. (4) An arc cloud line's major threat to space shuttle operations lie in its ability to generate new thunderstorm activity along the shuttle glide path.

Purdom, J. F. W.↗
NASA NTRS1983

Laboratory absorption strengths and line shape parameters in the 4-0, 5-0, and 6-0 vibration bands of HD

Experimental values for the visible vibration-dipole bands of HD are improved through a study of weak, unsaturated absorption lines of HD against a well-defined white light continuum at low gas densities between 0.3 and 1.7 amagats. Spectral resolution was high enough to allow recovery of line profiles with only minor corrections for instrumental effects, so line strengths and shapes are determined directly without recourse to theoretical assumptions regarding the curve of growth, and the unusual phenomenon of collision narrowing in HD is directly observed in the line shape for the first time. Accurate line strengths are reported, the behavior of spectral profiles as a function of gas density is discussed, and the pressure shift coefficients are determined. These are compared with previous laboratory work done either at lower spectral resolving power or at higher gas densities.

Trauger, J. T.↗
NASA NTRS1983

Redshifts of high-temperature emission lines in the far-ultraviolet spectra of late-type stars

High-dispersion IUE spectra of six late-type stars exhibit small but statistically significant differential redshifts of high-temperature emission lines, like Si IV and C IV, with respect to low-temperature lines like S I and O I. A well-exposed, small-aperture spectrum of the active chromosphere binary Capella (Alpha Aurigae A: G6 II+F9 III) establishes that the high-temperature lines are redshifted in an absolute sense with respect to the accurately determined photospheric velocity of the system at single-line phase 0.50. Several possible explanations for the stellar redshifts are discused, including a warm wind (100,000 K) in which aparent redshifts are produced in optically thick lines by an accelerating outfow, and the downflowing component of a vertical circulation system for which the up-leg portion of the flow is too cool, too hot, or too tenuous to be visible in Si IV and C IV. If the second scenario is true, the stellar redshifts may provide an important phenomenological link to the downflows observed in 100,000 K species over magnetic active regions in the sun.

Ayres, T. R.↗
NASA NTRS1984

The high-ionization and excited-state interstellar lines in the Carina Nebula - A giant H II region in absorption

The dominant component of the highly ionized and excited-state interstellar species seen in the ultraviolet toward stars within the Carina Nebula has been found to have a heliocentric radial velocity of about -30 km/s. This velocity is known to correspond to the near edge of the expanding H II region, as shown by the double optical nebular emission lines and the single He I lambda 3889 nebular absorption line. It is also seen as a (nondominant) component in both the optical and ultraviolet low-ionization interstellar lines, discussed previously. Hence, the Carina Nebula provides a clear case in which the principal high-ionization interstellar features are associated with the hot stars against which they are observed; and a considerable range of absorption lines can provide physical information about the H II region. Also, the weaker zero-velocity, line-of-sight component in the high-ionization species can be measured in this direction relatively free from confusion by the material associated with the stars. There is, in addition, a pervasive high-ionization feature with a velocity of -90 km/s in this region, which has the relatively large value of N(C IV)/N(Si IV) = 4.5.

Walborn, N. R.↗
NASA NTRS1984

Observational tests of X-ray heating in the broad-line region of quasars and Seyfert galaxies

Baldwin (1977) has inferred that the Ly-alpha/H-alpha line ratio in quasars was a factor of 10 lower than predicted by case B recombination theory, and direct observations of the Ly-alpha line in low-redshift quasars and Seyfert galaxies and of the Balmer lines in high-redshift quasars have confirmed this discrepancy. The present investigation is concerned with the Ly-alpha/H-alpha and Fe II/H-beta line ratios of a larger sample of quasars and Seyfert galaxies, taking into account the possibility of X-ray heating. Attention is given to details regarding the data set and to tests of X-ray heating in the broad-line region. The significance of the tests for the predictions of a model considered by Kwan and Krolik (1981) is evaluated.

Kriss, G. A.↗
NASA NTRS1984

Measurements of transition probabilities for spin-changing lines of atomic ions used in diagnostics of astrophysical plasmas

The intensities of ultraviolet, spin-changing, 'intersystem' lines of low-Z atomic ions are frequently used in determinations of electron densities and temperatures in astrophysical plasmas as well as in measurements of element abundances in the interstellar gas. The transition probabilities (A-values) of these lines, which are about five orders of magnitude weaker than allowed lines, have not been measured heretofore and various calculations produce A-values for these lines that differ by as much as 50 percent A radio-frequency ion trap has been used for the first measurements of transition probabilities for intersystem lines seen in astronomical spectra. The measurement procedure is discussed and results for Si III, O III, N II, and C III are reviewed and compared to calculated values. Discrepancies exist; these indicate that some of the calculated A-values may be less reliable than has been beleived and that revisions to the electron densities determined for some astrophysical plasmas may be required.

Smith, P. L.↗
NASA NTRS1985

Far-infrared line emission from the galaxy

The diffuse 157.74 micron (CII) emission from the Galaxy was sampled at several galactic longitudes near the galactic plane including complete scan across the plane at (II) = 2.16 deg and (II) = 7.28 deg. The observed (CII) emission profiles follow closely the nearby (12)CO (J=1to0) emission profiles. The (CII) emission probably arises in neutral photodissociation regions near the edges of giant moleclar clouds (GMC's). These regions have densities of approximately 350 cm(-3) and temperatures of approximately 300 K, and amount to 4x10(8) solar mass of hydrogen in the inner Galaxy. The total 157.74 micron luminosity of the Galaxy is estimated to be 6x10(7) solar luminosity. Estimates were also made of the galactic emission in other far-infrared (FIR) cooling lines. The (CII) line was found to be the dominant FIR emission line from the galaxy and the primary coolant for the warm neutral gas near the galactic plane. Other cooling lines predicted to be prominent in the galactic spectrum are discussed. The 145.53 micron (OI) emission line from the Orion nebula was also measured.

Stacey, G. J.↗
NASA NTRS1984

Observations of Absorption Lines from Highly Ionized Atoms

In the ultraviolet spectra of hot stars, absorption lines can be seen from highly ionized species in the interstellar medium. Observations of these features which have been very influential in revising the perception of the medium's various physical states, are discussed. The pervasiveness of O 6 absorption lines, coupled with complementary observations of a diffuse background in soft X-rays and EUV radiation, shows that there is an extensive network of low density gas (n approx. fewX 0.001/cucm) existing at coronal temperatures, 5.3 or = log T or = 6.3. Shocks created by supernova explosions or mass loss from early-type stars can propagate freely through space and eventually transfer a large amount of energy to the medium. To create the coronal temperatures, the shocks must have velocities in excess of 150 km/sec; shocks at somewhat lower velocity 9v or = 100 km/sec) can be directly observed in the lines of Si3. Observations of other lines in the ultraviolet, such as Si 4V and C 5, may highlight the widespread presence of energetic uv radiation from very hot, dward stars. More advanced techniques in visible and X-ray astronomical spectroscopy may open up for inspection selected lines from atoms in much higher stages of ionization.

Jenkins, E. B.↗