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At least 487 records · Page 27
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NASA NTRS1990

Narrow circumstellar emission lines in SN 1987A

Low and high dispersion short wavelength prime (SWP) spectra of SN 1987A show that the supernova's progenitor was in a post red giant branch stage of evolution at the time of its demise in February 1987. The development of narrow high temperature emission lines of N 5, N 4, N 3, C 3, He 2 and O 3 were followed since May 1987. Observations through April 1990 are presented. The lines are interpreted as arising in a low density gas surrounding the supernova which was photoionized by the extreme UV pulse at shock breakout. In this picture, their temporal evolution is determined primarily by light travel time effects and recombination. Comparison of models of circumstellar environment with the International Ultraviolet Explorer (IUE) observations are discussed.

Sonneborn, George↗
NASA NTRS1986

Fe II emission line profiles in spectra of high luminosity non-coronal stars

The results of a program to study the winds of noncoronal late-type giant and supergiant stars with IUE are presented. The primary data for this study are profiles, fluxes, and velocities of the Fe II emission lines which occur throughout the 2200 to 3230 A region of the IUE long wavelength spectrographs. The apparent dependence of the Fe II profiles on stellar luminosity (surface gravity) and intrinsic line strength is discussed. The discovery of significant changes in the Fe II profiles in spectra of Gamma Crucis (M3 III), during the period 1978 to 1985, that suggest a substantial change in its outer atmosphere is noted.

Carpenter, Kenneth G.↗
NASA NTRS1982

Results of the IUE program of monitoring the ultraviolet emission line fluxes of four binary systems: HR 1099, 2 Peg, AR Lac and By Dra

A program to obtain IUE spectra and optical photometry and spectra of three RS CVn-type binaries (HR 1099, II Peg, and AR Lac) and the prototype BY Dra system is reported. The systems were monitored for at least one orbital phase, and periodic variations in emission line flux from II Peg and HR 1099, indicative of notational modulation of an active region on these stars were detected. It is found that for II Peg the active region is in phase with photometric minimum as expected, but for HR 1099 ultraviolet emission maximum occurs at the time of photometric maximum.

Marstad, M.↗
NASA NTRS1980

X-ray line emission from the Cygnus Loop

The HEAO 1 satellite has observed the X-ray spectrum of the Cygnus Loop in the 0.1-2.0 keV band. The observed count-rate spectrum is deconvolved by the Kahn and Blissett technique to demonstrate conclusively the presence of oxygen- and iron-line emission between 0.6 and 0.9 keV. The spectrum has been fitted with single- and two-component Raymond-Smith plasma emission models. The best-fit dominant X-ray temperature is approximately 3,200,000 K, and the best-fit interstellar column density is approximately a few times 10 to the 20th/sq cm.

Kahn, S. M.↗
DOE OSTI2023

The DESI Survey Validation: Results from Visual Inspection of Bright Galaxies, Luminous Red Galaxies, and Emission-line Galaxies

The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect DESI spectra of approximately 2500 bright galaxies, 3500 luminous red galaxies (LRGs), and 10,000 emission-line galaxies (ELGs) to obtain robust redshift identifications. We then utilize the visually inspected redshift information to characterize the performance of the DESI operation. Based on the visual inspection (VI) catalogs, our results show that the final survey design yields samples of bright galaxies, LRGs, and ELGs with purity greater than 99%. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km s –1 for bright galaxies and ELGs and approximately 40 km s –1 for LRGs. The average redshift accuracy is within 10 km s –1 for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show examples of unexpected real astronomical objects, such as Ly α emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Emission-line studies of young stars. 4: The optical forbidden lines

Optical forbidden line strengths and profiles are discussed for a sample of 30 T Tauri stars and 12 Herbig Ae-Be stars. Transitions of (C I), (N II), (O I), (O II), (S II), (Ca II), (Cr II), (Fe II), and (Ni II) are detected. Profile variability occurred in DG Tau and probably other sources. The ensemble profiles can be divided into four generic components that may represent distinct emitting regions; (1) narrow rest-velocity lines, (2) 'low'-velocity lines (peaking at less than or approximately +/- 50 km s(exp -1)), (3) 'high'-velocity (usually greater than or approximately +/- 100 km s(exp -1)) blueshifted peaks or wings, and (4) high-velocity redshifted peaks. Among T Tauri stars, the rest-velocity lines appear most often in sources with weak and narrow permitted lines, such as the Ca II triplet. The low- and high-velocity blueshifted components usually appear together in sources with strong and broad Ca II triplet lines. If the velocity-shifted lines form in jets, the smallest (full) opening angles required by the profiles are less than or approximately 20 deg for the narrow, blueshifted (Ca II) lines of DG Tau and HL Tau. Other lines in DG Tau are much broader, implying larger opening angles or greater velocity dispersions. The variability in DG Tau also implies significant changes in the collimation or velocity coherence on timescales of a few years. RW Aur and AS 353A have blue- and redshifted line peaks that could form in oppositely directed jets. The strong (S II) lambda 6716 and lambda 6731 lines in RW Aur are exclusively redshifted and require opening angles less than or approximately 60 deg. Measurements of different profiles in the same spectrum show that the physical conditions change with the line-of-sight velocities. The most persistent trends are for more (N II) and (O II) and less (O I) lambda 5577 flux at high velocities. Constraints on the physical conditions are derived by modeling the emission lines via multilevel ions in 'coronal ionization equilibrium.' A single temperature and density cannot fully describe the line spectra in any velocity interval. Temperatures in the (O I) region are 9000 less than or approximately T(sub e) less than 14,000 K, and the ionization fraction (of H) is less than 35%. The densities derived from (O I) include n(sub e) less than or approximately 5 x 10(exp 5) to approximately 10(exp 7) cm(exp -3), but n(sub e) greater than or approximately 10(exp 6) cm(exp -3) obtains only at low velocities. In the (S II) regions the densities are lower, 10(exp 3) less than or approximately n(sub e) less than or approximately 7 x 10(exp 4) cm(exp -3), and the temperatures are probably higher, T(sub e) greater than or approximately 13,000 K. At high velocities (only) there is additional hot gas that produces (N II) and (O II), possibly most of the (S II), and little (O I). This region is characterized by T(sub e) greater than or approximately 15,000 K, n(sub e) less than or approximately 10(exp 5) cm(exp -3), and an ionization fraction greater than or approximately 50%. When combined with the spatially segregated emitting regions observed by others by spectral imaging, these results suggest decreasing n(sub e) and increasing T(sub e) away from the star in at least the high velocity gas.

Hamann, Fred↗
NASA NTRS1976

Intensity of the Fe XV emission line corona, the level of geomagnetic activity, and the velocity of the solar wind

The method of superposed epochs is used to determine the average solar wind velocity and the Kp index following central meridian passage of coronal weak and bright features identified from OSO 7 isophotograms of the Fe XV (284 A) emission line. It is found that bright coronal regions possess magnetic fields of closed configuration, thus reducing particle escape, while coronal holes possess open magnetic field lines favorable to particle escape or enhanced outflow of the solar wind.

Bell, B.↗
DOE OSTI2023

Searching for Dwarf H$α$ Emission-line Galaxies within Voids. I. Survey Methods and First Observations

The population density of dwarf galaxies in low-density voids is likely determined by the dark matter halo mass function and how galaxy formation proceeds in smaller halos. This depends on the nature of dark matter itself, making the dwarf galaxy population a tracer of its properties. While dwarfs have been found in smaller, closer voids, they have proven difficult to find in larger, more distant voids through magnitude-limited spectroscopic surveys. This is because these surveys detect an overwhelmingly large number of objects behind the voids that must be verified spectroscopically, making void surveys prohibitively inefficient and expensive in terms of large-telescope time. Narrowband imaging for emission lines such as Hα reduces the number of background objects, although the overall number remains large. If imaging is done through a filter set with overlapping transmission wings, then object redshift can be estimated from photometry alone. The precision possible is an order of magnitude greater than single-band photometry, with the caveat that the captured line must be identified through other means. Broadband photometry can be used to reject enough objects with emission of an unwanted type to make obtaining spectra of the remaining objects feasible. In this study, we present an Hα survey for dwarf galaxies with M r ' fainter than -14 mag through the center 4.3 square degrees of the void FN8. Using Sloan $g^{\prime} ,r^{\prime} ,i^{\prime}$ photometry, we exclude enough [O II ] and [O III ] emitters that follow-up spectra of only a few dozen objects are required to statistically estimate the void population density.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

Variability of emission lines in the planetary nebulae IC 4997 and NGC 6572

New IUE high-dispersion data and recent ground-based spectra of the planetary nebulae IC 4997 and NGC 6572 are compared with equivalent IUE observations taken in 1980 and optical data taken in 1974-1990. Significant changes are detected in many emission-line fluxes in IC 4997, and primarily in He II and C IV for NGC 6572. These changes are interpreted as due to recent temperature increases in the central stars of the planetaries which are known to belong to a small set which have shown variability in the past.

Feibelman, Walter A.↗
NASA NTRS1994

The broad emission line and continuum variations of Seyfert galaxies. 2: Broad-line region structure and kinematics

Spectroscopic observations of 13 Seyfert 1 galaxies made from 1979 to 1984 at Palomar and Steward Observatories were analyzed for H beta line profile variations. Significant profile changes were detected in five galaxies. These variations are often associated with changes in continuum and/or H beta strength, suggesting a causal connection between variations in the continuum source and changes in emission-line profiles. Moreover, the overall strength of H beta line flux variations is strongly correlated with line width in the far wings, whereas no such correlation was found in the line core. This finding is consistent with previous observations (Shuder 1982) which suggest that higher velocity gas lies closer to the central continuum source, since this inner gas would be expected to track variations more closely. In each of the five galaxies in which H beta line profile variations were detected, particularly NGC 5548 and Mrk 6, only two distinct line profile shapes were observed. Since intermediate profile types were not detected, the transition from one type to the other must occur rapidly (within a few months). These rapid line profile variations are thus consistent with numerous other studies which strongly point to a small broad-line region (BLR) size in Seyfert galaxies. Observational models of BLR kinematics and structure for each of the galaxies in the present sample are presented. Line asymmetries suggest that radial motions exist in the BLRs of most of these objects. Chaotic motions also appear to be quite common. However, evidence for rotational motion was observed in only one case. A model that is consistent with the majority of this sample incorporates both radial and chaotic motions combined with some form of external obscuration such as an optically and geometrically thick torus.

Rosenblatt, Edward I.↗
NASA NTRS1990

A survey of the profiles of narrow emission lines in Seyfert galaxies

An atlas of the nuclear spectra of 58 Seyfert galaxies and six galaxies with nuclear H II regions is presented. For all but three galaxies, the range of rest wavelengths covered is about 6000-6800 A, with spectral resolution at H-alpha either 45 km/s or 130 km/s. Widths are given for the emission lines forbidden Fe VII 6086 A, forbidden O I 6300 A, H-alpha, forbidden N II 6584, and forbidden S II 6717,6731 A. In all, widths for some 210 lines in 53 galaxies are listed. A comparison is made between the present and previous line width measurements.

Wilson, A. S.↗
NASA NTRS2002

Broad-Band Continuum and Line Emission of the gamma-Ray Blazar PKS 0537-441

PKS 0537-441, a bright gamma ray emitting blazar was observed at radio, optical, UV and X-ray frequencies during various EGRET paintings, often quasi-simultaneously. In 1995 the object was found in an intense emission state at all wavelengths. BeppoSAX observations made in 1998, non-simultaneously with exposures at other frequencies, allow us to characterize precisely the spectral shape of the high energy blazer component, which we attribute to inverse Compton scatter in The optical-to-gamma-ray spectral energy distributions at the different epochs show that the gamma-ray luminosity dominates the barometric output. This, together with the presence of optical and UV line emission, suggests that, besides the synchrotron self-Compton mechanism, the Compton upscattering of photons external to the jet (e.g., in the broad line region) may have a significant role for high energy radiation. The multiwavelength variability can be reproduced by changes of the plasma bulk Lorentz factor. The spectrum secured by ICE in 1995 appears to be partially absorbed shortward of approximately 1700 Angstroms. However, this signature is not detected in the HST spectrum taker during a lower state of the source. The presence of intervening absorbers is not supported by optical imaging and spectroscopy of the field.

Pian, E.↗
NASA NTRS1994

X-ray continuum and iron K emission line from the radio galaxy 3C 390.3

X-ray properties of the radio galaxy 3C 390.3 were investigated using the European X-ray Observatory Satellite (EXOSAT) and Ginga satellites. Long-term, large-amplitude X-ray intensity changes were detected over a period extending from 1984 through 1991, and high-quality X-ray spectra were obtained especially with Ginga. The X-ray continuum spectra were described with power-law model with photon slope in the range 1.5-1.8, and the slope flattened as the 2-20 keV luminosity decreased by 40%. There was a first detection of the iron emission line from this source at the 90% confidence level. An upper limit was derived on the thermal X-ray component. X-ray emission mechanisms and possible origins of the long-term variation are discussed.

Inda, M.↗
NASA NTRS2011

Uncovering the Spectral Energy Distribution in Active Galaxies Using High Ionization Mid-Infrared Emission Lines

The shape of the spectral energy distribution of active galaxies in the EUV soft X-ray band (13.6 eV to 1 keV) is uncertain because obscuration by dust and gas can hamper our view of the continuum. To investigate the shape of the spectral energy distribution in this energy band, we have generated a set of photoionization models which reproduce the small dispersion found in correlations between high-ionization mid-infrared emission lines in a sample of hard X-ray selected AGN. Our calculations show that a broken power-law continuum model is sufficient to reproduce the [Ne V]14.32 microns/[Ne III], [Ne V]24.32 microns/[O IV]25.89 micron and [O IV] 25.89 microns/[Ne III] ratios, and does not require the addition of a "big bump" EUV model component. We constrain the EUV-soft X-ray slope, alpha(sub i), to be between 1.5 - 2.0 and derive a best fit of alpha(sub i) approx. 1.9 for Seyfert 1 galaxies, consistent with previous studies of intermediate redshift quasars. If we assume a blue bump model, most sources in our sample have derived temperatures between T(sub BB) = 10(exp 5.18) K to 10(exp 5.7) K, suggesting that the peak of this component spans a large range of energies extending from approx. (Lambda)600 A to > (Lambda)1900 A. In this case, the best fitting peak energy that matches the mid-infrared line ratios of Seyfert 1 galaxies occurs between approx. (Lambda)700-(Lambda)1000 A. Despite the fact that our results do not rule out the presence of an EUV bump, we conclude that our power-law model produces enough photons with energies > 4 Ry to generate the observed amount of mid-infrared emission in our sample of BAT AGN.

Melendez, M.↗
NASA NTRS1983

Prominent ultraviolet emission lines from Type 1 Seyfert galaxies

IUE Explorer data with a 6-A resolution are reported for Ly-alpha, C IV 1550 A, C III semiforbidden line 1909 A, and Mg II 2800 A, as well as the continuum at 1450 A, for 20 Seyfert galaxies and one quasar. Good correlation is found between the continuum and the line fluxes, indicating that photoionization is the dominant heating mechanism for these active galactic nuclei. A combination of the data for Seyferts and high redshift quasars covering five orders of magnitude in continuum luminosity shows the lower luminosity objects to have higher equivalent widths for their emission lines, suggesting that the covering factor increases with decreasing luminosity.

Wu, C.-C.↗
NASA NTRS1990

Emission-line properties of the composite Seyfert/Starbust galaxy IC 5135

The galaxy IC 5135 is host for Seyfert activity and vigorous star formation in its nucleus. Results of a study based on optical spectroscopy and imaging are presented that reveal the ionization properties of the nucleus and near-nucleus region, as well as the global morphology of this galaxy. The dual nature of the nucleus is evident in emission-line profiles, which show two kinematic components. Line intensity ratios in the nucleus are typical of Seyfert 2 galaxies, but evolve with increasing radius to values generally characteristic of H II regions. IC 5135 provides an illustration of the importance of the O I 6300 forbidden line as a tracer of a hard-spectrum, photoionizing continuum; the presence at large radii of ionizing radiation from nucleus is clearly revealed by the relative strength of this line.

Shields, Joseph C.↗
NASA NTRS1994

ASCA detection of iron line emission from the distant galaxy cluster Abell 370

ASCA observations of the gravitational lens and Butcher-Oemler cluster Abell 370 (z = 0.37) give kT = 8.8 +/- 0.8 keV and A = 0.5 +/- 0.1 cosmic. If the gas were isothermal the implied cluster mass would be M(sub vir) = (1.5 +/- 0.4) x 10(exp 15) solar masses, a value consistent with the optically-determined virial mass. We detect iron K line emission with high confidence. This measurement increases, by a large factor, the lookback time at which the presence of iron in the intracluster medium has been established. The iron abundance is marginally higher than that of low-redshift clusters of similar temperature, so our results are consistent with models in which all enrichment occurs before the epoch corresponding to z = 0.37.

Bautz, Marshall W.↗