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At least 1,279 records · Page 71
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NASA NTRS1979

The Balmer 9 and Balmer 11 lines of He II in the sun

The Balmer 9 and 11 lines of He II at 959 A and 942 A in solar spectra are identified. These lines are produced mainly by recombination following photoionization of He II by coronal XUV radiation. From analysis of the line intensities, the theoretical model of Avrett et al. (1976), is confirmed where it was found that an appreciable amount of He (2+) is present at temperatures of 1 - 2 x 10 to the 4th K and that the anomalously strong He II 304 line is produced primarily by collisional excitation. The suggestion of Kohl (1977) that the photoionization-recombination process is more important in active regions than in the quiet sun is confirmed, and we find that the 304-A line is produced largely by recombination in solar flares.

Raymond, J. C.↗
NASA NTRS1980

A study of the Jovian forbidden line S II nebula at high spectral resolution

Observations of forbidden line S II 6716-6731 A emissions from the Jovian magnetosphere have been carried out with a PEPSIOS spectrometer at the Hale 5 m telescope. Spectral resolving power was sufficient to resolve the forbidden line S II line widths. From measured 6716-6731 A doublet ratios and spectral line widths a thermal plasma is found characterized by temperatures about 2 x 10 to the 4th K and electron densities about 2000 cu cm. The source of forbidden line S II emissions was centered within a toroidal region of radius 5 Jupiter radii (inside the orbit of Io), with tight latitudinal confinement near the equilibrium equator for ions in the tilted corotating Jovian magnetic field, and significant long-lived longitudinal structure.

Trauger, J. T.↗
NASA NTRS1980

Two micron spectroscopy and 2.7 mm CO line observations of V645 Cygni

Spectroscopy of V645 Cyg from 1.5 to 2.5 microns and CO line observations at 2.7 mm are presented. A kinematic distance of 6 kpc is derived from the CO line velocity. The strengths of the observed members of the hydrogen Brackett recombination line series are consistent with a spectral type of O9 and an extinction of 4-5 mag to both the line-emitting region and to the exciting star. The infrared continuum is probably produced by thermal emission from hot (about 1000 K) dust. The star is embedded in a 20 pc diameter molecular cloud with a mass not less than 2500 solar masses. The cloud shows CO line broadening in the vicinity of the star and a velocity gradient perpendicular to the plane of polarization of the stellar optical emission. The system has many similarities to R Mon.

Harvey, P. M.↗
NASA NTRS1980

Formation of chromospheric resonance line profiles in supergiants

The formation of chromospheric resonance line profiles is examined for the case of the relatively low-density atmospheres appropriate to late-type supergiants. The effects of partial frequency redistribution control the emergent line profiles, to the extent that even an isothermal atmosphere can give rise to apparent emission features. Schematic model chromospheres are used to demonstrate the effects of different velocity fields and temperature-density structures on the line profiles, as a first step toward a clearer understanding of the chromospheric line profiles and why supergiants have broad emission lines (the Wilson-Bappu effect). Neither the Doppler nor the mass column density explanation alone can explain the Wilson-Bappu effect in supergiants, but both theories may play a role.

Basri, G. S.↗
NASA NTRS1981

X-ray heating and ionization of broad-line emission regions in QSOs and active galaxies

The absorption of X-rays deep within the broad-line emitting clouds in quasars and the nuclei of active galaxies produces extensive zones of warm (about 10,000 K), partially ionized gas. Because Lyman-alpha photons are trapped in these regions, the X-ray energy is efficiently channeled into Balmer lines collisionally excited from the n = 2 level. These H I regions and the H II regions created by UV photons illuminating the surfaces of the clouds gives rise to integrated Lyman-alpha/H-alpha lines emission ratios between 1 and 2. Enhanced Mg II line emission from the H I regions gives rise to integrated Mg II/H-alpha ratios near 0.5. The O I line at 8446 A is efficiently pumped by trapped H-alpha photons; and an intensity ratio of I(8446 A)/I(H-alpha) of approximately equal to and not greater than 0.1 is calculated for the X-ray heated zone.

Weisheit, J. C.↗
NASA NTRS1981

A survey of X-ray line emission from the supernova remnant Puppis A

Initial results from the first high-resolution study of the X-ray spectrum of a supernova remnant are reported. The spectrum of Puppis A between 500 and 1100 eV has been surveyed with the Focal Plane Crystal Spectrometer on the Einstein Observatory and the flux in eight lines and three line blends from various transitions of highly ionized nitrogen, oxygen, neon, and iron has been measured. The spectrum resembles that of active regions in the solar corona, but the neon lines seem enhanced relative to the oxygen lines, and both are enhanced relative to iron. The observed line strengths serve as diagnostics of the physical conditions in the emitting material. Without a priori assumptions, the ionization temperatures of O (2.2 million K) and Ne (4 million K) and the dominant ionization stage of Fe (Fe XVII) are deduced. Isothermal equilibrium plasmas or homogeneous nonequilibrium plasmas as descriptions of the source are ruled out. It is concluded that Puppis A must contain plasma over a temperature range 2-million to 5-million K with an intervening absorption column of 4 x 10 to the 21st/sq cm.

Winkler, P. F.↗
NASA NTRS1981

Galactic disk absorption lines in the spectrum of the quasar 3C 273

It is pointed out that the line of sight to 3C 273 is unique because of the possibility of obtaining both radio and optical absorption line measurements. This information may make it possible to understand in detail the structure of the interstellar medium along the line of sight. To take advantage of this possibility, high-resolution optical spectra were obtained of 3C 273. The observations were made using the echelle spectrograph at the Cassegrain focus of the 4 m telescope at the Cerro Tololo Inter-American Observatory in 1980 January. Both Na D and Ca K lines were obtained on the same plate. In the visual lines, the galactic disk absorption shows a main component at 20 km/sec with a trailing wing in the negative velocities.

Cowie, L. L.↗
NASA NTRS1981

Assignment of the /Li-7/2 optically pumped laser transitions pumped by Ar/+/ and Kr/+/ laser lines

Welling and Wellegehausen (1977) have reported a list of Na2 and Li2 lines (belonging to B-X and A-X systems) which lase when vapors of these dimers are pumped with an Ar(+) or Kr(+) laser. A description is presented of a fluorescence study of the A-X system of the (Li-7)2 molecule excited by a Kr(+) laser (6471 A). The optically pumped laser lines are identified as P and R doublets in two different fluorescence series. The conditions which favor lasing action of these lines are pointed out. All but one of the known optically pumped laser lines of (Li-7)2 along with their assignments are presented in a table. For each pumping line, several additional wavelengths are listed which satisfy the condition for laser oscillations and which might well lase well under slightly improved conditions.

Verma, K. K.↗
NASA NTRS1981

Infrared line and continuum views of G333.6-0.2

A 1-micron CCD picture and maps of the Ne II and Ar III fine-structure lines have been obtained in a region roughly one arcmin in size centered on the core of the compact H II region G333.6 - 0.2. The two emission-line maps show nearly identical intensity distributions, although much different fluxes. The maps are similar to the 1-micron picture smoothed to their angular resolutions. The infrared line of S IV also was detected and appears to have a spatial intensity distribution similar to that of the other fine-structure lines. The 1-micron picture reveals a small number of objects of nearly stellar appearance in the core, suggesting that G333.6 - 0.2 is powered by a compact cluster of sources. Stellar continuum radiation probably is responsible in part for the low equivalent width of the B-gamma line in the core.

Geballe, T. R.↗
NASA NTRS1982

N2 pressure - broadened O3 line widths and strengths near 1129.4 cm-1

A Beer's Law experiment was performed with a tunable diode laser to find the N2 pressure broadening characteristics of a single 03 absorption line at 1129.426 cm for N2 pressures from 10 to 100 torr (O3 pressure = 3.16 torr). SO2 line positions were used for wavelength calibration. Line shapes were interatively fitted to a Lorentz function. Results were delta (HWHM in MHz) = 47.44 (+ or - 5.34) MHz + 1.730 (+ or - 0.088) MHz/torr *p(torr) with sigma = 0.9897. This intercept compares well with the Doppler O3 - O3 broadened (at 3.16 torr) width of 44.52 Hz. This result in a HWHM line width of 0.44 cm atm at 760 torr and 285 K. The line strengths integrated over delta nu = 0.55 cm were found to be N2 pressure dependent.

Copeland, G. E.↗
NASA NTRS1981

Detection of forbidden line O I 63 micron emission from the galactic center

The detection of the 63 micron line of forbidden line O I is reported for three positions in the H II region complex Sgr A at the galactic center. Velocity resolution of the line indicates that the emitting material has both rotational and radial motion of magnitude similar to that of the ionized gas in the core, and that a substantial amount of the emitting material lies within the central few parsecs of the Galaxy. A model in which forbidden line O I is collisionally excited by neutral hydrogen, either from the warm region ahead of an ionization front or behind a shock, is proposed and gives a total mass of hot, neutral gas within the central 3 pc of the Galaxy of between 10 and 1000 solar mass. A limit on the flux of this line has been set for Sgr B2.

Lester, D. F.↗
NASA NTRS1981

HEAO 3 measurements of the atmospheric positron annihilation line

The atmospheric positron annihilation line at 511 keV was the first gamma-ray line observed which originates from processes of astrophysical importance. Measurements of the properties of a positron annihilation line make it possible to determine many of the physical conditions present at the source of emission. An investigation was conducted of the 511-keV line measured with the HEAO C-1 experiment. The HEAO C-1 experiment consisted of a cluster of four, large, high-purity germanium detectors surrounded by an active anticoincidence CsI shield. A strong atmospheric line was measured at 511.07 + or - 0.10 keV. The net atmospheric emission has been accurately determined as a function of geomagnetic latitude and varies from 0.01 photons/sq cm-sec-sr near the magnetic equator to 0.035 photons/sq cm-sec-sr at a latitude of 55 deg.

Mahoney, W. A.↗
NASA NTRS1981

IUE observations of pre-main-sequence stars. I - Mg II and Ca II resonance line fluxes for T Tauri stars

IUE satellite and Lick 3 m reflector image tube scanner measurements of the Mg II and Ca II resonance lines in a sample of T Tauri stars are the basis of a discussion of the Mg II h and k line emission and the Ca II H and K line emission, within the context of stellar chromospheres. Corroborative evidence is presented for the chromospheric origin of these resonance lines, and chromospheric radiative loss rates in the Mg II and Ca II resonance lines are derived. It is found that the degree of nonradiative heating present in the outer atmospheres of T Tauri stars generally exceeds that of the RS CVn systems, as well as the dMe stars and other active chromospheric dwarfs, and it is inferred that the surfaces of such pre-main sequence stars are covered by regions similar to solar plages. The mean chromospheric electron density of T Tauri stars is determined as 10 to the 11th/cu cm.

Giampapa n, M. S.↗
NASA NTRS1982

The effects on the MHD stability of field line tying to the end faces of a cylindrical magnetic loop

The ideal MHD energy equation is used to derive a stability equation for a specific class of perturbations, in an examination of magnetic loop MHD stability which takes field line tying at its root points into account. It is found that the field line tying effect is negligible to the m=1 kink mode, but important to the localized modes, in the case of a loop of aspect ratio greater than 10. The stability criterion for high-m value localized modes is derived, and compared with the Suydam criterion, to show that there are two field line tying effects for the perturbation of the class studied: (1) a field line bending effect, which is always stabilizing, and (2) a shear effect which is stabilizing or destabilizing depending on the sign of the gradient of the potential magnetic field. The net effect of field line tying is determined by the sum of these two effects.

An, C. Y.↗
NASA NTRS1982

Mass loss from alpha Cyg /A2Ia/ derived from the profiles of low excitation Fe II lines

The low-excitation Fe II lines in the spectral region 2000-3000 A are studied in the spectrum of alpha-Cyg. The profiles of the resonance lines are described by four representative parameters, and a preliminary model is derived from the dependence of these parameters on theoretical line strength, taking into account the influence of blending photospheric lines in an overall and qualitative way. At least 11% of all iron in the wind is once ionized, unless a non-thermal heating source enhances the fraction Fe(++) without destroying much Al(+). It is shown that the contribution of blending photospheric absorption lines to weaker P Cygni profiles has been previously largely underestimated. The mass loss rate corresponding to the model is derived, and is smaller by a factor of 500 than the one derived from the infrared excess by Barlow and Cohen (1977).

Hensberge, H.↗
NASA NTRS1982

Observations of Paschen alpha in the broad-line radio galaxy 3C 445

P alpha line flux measurements of the broad-line radio galaxy 3C 445 made at the NASA IR Telescope Facility in September 1981 are discussed. Broad-band measurements were obtained at H of 1.65 micron and K of 2.2 microns. A line flux of P alpha was found at 3.4 times 10 to the -13th ergs/sq cm sec. No discernable variation was detectable regarding measurements made in 1976. Substantial reddening was concluded to exist, although the H gamma lines observed were not due to reddening. The total H alpha luminosity was determined to be 4 x 10 to the 43rd ergs/sec. Steep Balmer line decrements are concluded to be due to interposed dust.

Rudy, R. J.↗
NASA NTRS1982

Evidence of redshifts in the average solar line profiles of C IV and Si IV from OSO-8 observations

Line profiles of C IV and Si V obtained by the Colorado spectrometer on OSO-8 are presented. It is shown that the mean profiles are redshifted with a magnitude varying from 6-20 km/s, and with a mean of 12 km/s. An apparent average downflow of material in the 50,000-100,000 K temperature range is measured. The redshifts are observed in the line center positions of spatially and temporally averaged profiles and are measured either relative to chromospheric Si I lines or from a comparison of sun center and limb profiles. The observations of 6-20 km/s redshifts place constraints on the mechanisms that dominate EUV line emission since it requires a strong weighting of the emission in regions of downward moving material, and since there is little evidence for corresponding upward moving materials in these lines.

Roussel-Dupre, D.↗
NASA NTRS1982

Spectroscopic line parameters of NH3 and PH3 in the far infrared

NH3 and PH3 rotation and rotation-inversion line parameters in the far to medium IR are calculated for remote sounding purposes of planetary atmospheres; 1607 lines of (N-14)H3, 362 lines of (N-15)H3 and 325 lines of PH3 are compiled. The absolute intensity formulation has been reviewed in the case of rotation and rotation-inversion lines of molecules with C(3v) symmetry. The justification for the general agreement between the authors, and comparisons with other published expressions are given.

Husson, N.↗