Overabundance Of Nitrogen Research Articles

Far-Ultraviolet Spectra of Broad Absorption Line QSOs and Constraints on Models for the Ionization Structure and Metallicity of the BAL-Region Gas

view Abstract Citations (54) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-Ultraviolet Spectra of Broad Absorption Line QSOs and Constraints on Models for the Ionization Structure and Metallicity of the BAL-Region Gas Turnshek, David A. ; Kopko, Michael, Jr. ; Monier, Eric ; Noll, Donette ; Espey, Brian R. ; Weymann, Ray J. Abstract Hubble Space Telescope Faint Object Spectrograph G270H spectra of four moderate-to high-redshift broad absorption line (BAL) QSOs are presented. In addition, evidence is discussed that indicates that the gas that gives rise to the BALs has nonuniform ionization and enhanced abundances. In the context of a photoionization model, ionization parameter fluctuations of at least ~32-16 are needed to explain the observed column densities of different ions of the same element. In such a model, the gas must have very enhanced metal-to-hydrogen abundances relative to solar composition. However, the actual metal-to-hydrogen abundance enhancements are difficult to constrain because they are so model-dependent. For example, in a photoionization model the shape of the photoionizing continuum has a significant influence on the derived metal-to-hydrogen enhancement, but for normally adopted shapes the enhancement is very large, i.e., an enhancement of ~120-230 times solar for nitrogen. If collisional ionization is important, the need for metal-to-hydrogen abundance enhancements would be severely reduced. The derived relative metal abundances are somewhat more robust because the relevant metal-line transitions correspond to similar ionization potentials. In a photoionization model, nitrogen enhancements relative to oxygen and carbon of ~4-3 and 9:-10: times solar values, respectively, are indicated. If normal stellar nucleosynthesis is important, the results may be indicative of star formation with a relatively flat initial mass function, with the nitrogen overabundance produced by secondary processing in massive stars. However, large enhancements of elements like phosphorus in some objects suggest that the enrichment scenario may be more complex. In addition, the results discussed here place constraints on the details of a photoionization model for the BAL-region gas. These constraints are unphysical enough that they may indicate that central- source photoionization is not dominant. Publication: The Astrophysical Journal Pub Date: May 1996 DOI: 10.1086/177227 Bibcode: 1996ApJ...463..110T Keywords: GALAXIES: QUASARS: ABSORPTION LINES; GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: H0059-735; GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: Q0226-024; GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: H0903+1734; GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: Q0932+5006; GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: Q1309-0536 full text sources ADS | data products SIMBAD (7) NED (4) MAST (1) ESA (1)

The "F str 4077" star HD 177645 as a possible barium dwarf star

The abundances of 12 elements in the atmosphere of the "F str 4077" star HD 177645 have been determined from new spectroscopic observations with the CCD camera and the model atmosphere method. The overabundance of nitrogen found for this star indicates its possible relation to barium dwarfs with anomalies in the chemical composition of their atmospheres due to mass transfer from the more evolved companion in a binary system. As an object related to Ba stars and CH subgiants, HD 177645 with an effective temperature Teff=7150K may also have anomalies in the chemical composition characteristic of diffusion processes in chemically peculiar stars of the upper main sequence, as may be indicated by the overabundance of sulfur in its atmosphere.

THE R CORONAE BOREALIS STARS

ABSTRACT This year marks the bicentennial of the discovery of the variability of R Coronae Borealis. The R Coronae Borealis (RCB) stars are distinguished from other hydrogen-deficient objects by their spectacular dust formation episodes. They may decline by up to 8 magnitudes in a few weeks revealing a rich emission-line spectrum. Their atmospheres have unusual abundances with very little hydrogen and an overabundance of carbon and nitrogen. The RCB stars are thought to be the product of a final helium shell flash or the coalescence of a binary white-dwarf system. Dust may form in non-equilibrium conditions created behind shocks caused by pulsations in the atmospheres of these stars. The RCB stars are interesting and important, first because they represent a rare, or short-lived stage of stellar evolution, and second because these stars regularly produce large amounts of dust so they are laboratories for the study of dust formation and evolution.

On the Interpretation of the Ultraviolet Spectra of Symbiotic Stars and Recurrent Novae. II. The 1985 Outburst of RS Ophiuchi

view Abstract Citations (65) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Interpretation of the Ultraviolet Spectra of Symbiotic Stars and Recurrent Novae. II. The 1985 Outburst of RS Ophiuchi Shore, Steven N. ; Kenyon, Scott J. ; Starrfield, Sumner ; Sonneborn, G. Abstract We discuss the 1985 outburst of the symbiotic recurrent nova RS Oph using spectra obtained with the International Ultraviolet Explorer satellite and contemporaneous ground-based optical spectra. The low- resolution integrated fluxes show that a short-lived constant bolometric luminosity phase existed in the early outburst. If this reached the Eddington luminosity, it implies a minimum mass for the white dwarf of 1.2 Msun. This and the lack of evidence for eclipses in ultraviolet low-resolution spectra obtained in quiescence support the orbital solution of Dobrzycka & Kenyon (1994), in particular the low inclination of the system and the low mass, 0.5 Msun, of the red giant. The high-resolution optical and ultraviolet line profiles showed the development of two separate contributors. One was a broad-line component produced by emission from the high- velocity ejecta. The other was a narrow-line component produced in the portion of the red giant wind that was ionized by the UV pulse from the explosion and by radiation from the shock produced by the passage of the ejecta through the wind. The expanding Strömgren sphere had two effects. The strength of the line absorption from the overlying wind decreased against the ejecta and the ionized emitting gas, and the emission measure increased within the expanding H II region. We model these effects using the techniques developed in Shore & Aufdenberg (1993) to show how the column density of the cool material decreased with time. We show that the increased ionization of the wind accounts for changes in the absorption line components in the ultraviolet and use this decrease and the narrow emission-line ratios to determine the physical parameters for the line-forming region in the wind. From this, we derive the mass-loss rate for the red giant. In addition, we find evidence for a nitrogen overabundance in the wind using the time development of the N V 1240 Å doublet. The primary source for ionizing the red giant wind was radiation produced by the shocked ejecta as they traversed the stellar wind. The shock-generated emission also produced and powered the coronal species until about 100 days after outburst at which time shock breakout occurred. The ionized wind subsequently recombined, although a hot source was still present on the white dwarf on the basis of continued visibility of the ultraviolet O III fluorescence lines and the IR He I 1.08 microns line. Finally, we discuss how many of the techniques developed in this study of a photoionizing pulse propagating into a dense environment can be applied to the analysis of active galactic nuclei. Publication: The Astrophysical Journal Pub Date: January 1996 DOI: 10.1086/176692 Bibcode: 1996ApJ...456..717S Keywords: STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: INDIVIDUAL CONSTELLATION NAME: RHO OPHIUCHI; STARS: BINARIES: SYMBIOTIC; GALAXIES: NUCLEI full text sources ADS | data products SIMBAD (11) MAST (1) INES (1)

Nova Cygni 1992: spectral development in the near-infrared at maximum light ⋆

Spectroscopic observations of Nova Cygni 1992 in the range 0.64-1.15 μm from 1992 February 22 to 24 show a strong increase of emission in the H I, O I and N I lines, and the onset of the two absorption systems on February 23. There are indications of a strong overabundance of nitrogen

CN anomalies in extremely metal-deficient red giants

New photometric and UV spectroscopic data for the metal-deficient red giants CD -38 deg 245 and BD -18 deg 5550 are presented and discussed in light of recently noted photometric anomalies. From the IUE spectra it is aparent that the UV excess found in BD -18 deg 5550 is not the result of a hot companion. The IUE spectra, in conjunction with other observations, point to anomalous nitrogen abundances as the source of the discrepancies between the photometric and spectroscopic abundances for these stars. CD -38 deg 245 appears to be exceptionally nitrogen-rich while BD -18 deg 5550 is anomalously nitrogen-poor with respect to stars of comparable metallicities. While BD -18 deg 5550 appears to be an exception to the rule for its metallicity, the confirmation of a similar photometric pattern for CS 22885-96 may be an indication that the nitrogen overabundance in CD -38 deg 245 is typical for giants of extreme metal-deficiency.

On the ratio [N II]/Hα in the nucleus of Seyfert 2 and LINER galaxies

The dependence of the [N II]/Hα ratio of 180 Seyfert 2 and LINER nuclei on the aperture used in the observations is investigated and quantified. When the aperture effect is taken into account, it can be conclued that the majority of Seyfert 2 and LINER galaxies present [N I]/Hα > 1.5, which means an overabundance of nitrogen in the nucleus, according to results of previous works. The relationship of [N II]/Hα to nuclear compact radio emission, absolute magnitude and morphological type of parent galaxy are also investigated.

Kinematics and ionization of extended gas in active galaxies. VI - The Seyfert 2 galaxy NGC 1386

We present the results of direct imaging with a CCD detector and long-slit medium- and low-dispersion spectroscopy of the spatially extended narrow line-emitting gas in the highly inclined nearby Seyfert 2 galaxy NGC 1386. The images and spectra have been used to investigate the distribution, kinematics, and ionization structure of the excited gas in the regions surrounding the nucleus out to a distance of approximately 1.0 kpc. An elongated high-excitation nebulosity extends 6" (~ 500 pc) N and S of the nucleus, where it ends abruptly. Further out, emission lines from H II regions in spiral arms are seen. Within the high-excitation region, line widths of up to 1500 km s^-1^ are found, and the sense of line asymmetry switches across the nucleus. The velocity field is interpreted in terms of a combination of a normally rotating component (which dominates the line peaks) and a component undergoing high-velocity infall or outflow (which is responsible for the wings). The optical nucleus is displaced by 1"-1.5" (80-120 pc) from the kinematic center of the rotation curve. The nature of this displacement is briefly discussed. Line ratio diagnostics show that the spectrum at the nucleus is typical of Seyfert 2 nuclei. The ratio [O III] {λ5007/Hβ_corr_ remains high (more than about 10) over the high-excitation nebulosity. However, the ratio [N II] λ6583/Hα_corr_ increases toward the NE and SW edges of the nebulosity, where values as high as 2.9 are found, and where the spectrum is LINER-like. We suggest that this increase in [N II] λ6583/Hα_corr_ may reflect either: (1) photoionization with a decrease in the ionization parameter with increasing distance from the nucleus, along with a general overabundance of nitrogen; or (2) photoionization plus effects of shock heating near the edges of the high-excitation nebulosity, where the ratios are the highest. These edges, where the width of [N II] λ6583 is >= 200 km s^- 1^, may be transition zones resulting from shock fronts at the interface between the outflowing Seyfert-excited gas and ambient gas in the galaxy disk.

Narrow ultraviolet emission lines from SN 1987A - Evidence for CNO processing in the progenitor

Results from UV observations of SN 1987A with the IUE satellite are presented, showing that emission lines of He II, C III, N III, N IV, N V, and O III increase in strength with time after May 24, 1987. It is found that increased emission originated in a photoionized low-density circumstellar gas, lost by the progenitor in its red supergiant phase. A nebular analysis reveals a large nitrogen overabundance, indicating that the gas has undergone substantial CNO processing. This suggests that the progenitor of SN 1987A lost much of its hydrogen envelope before the explosion. The findings are consistent with models in which a red supergiant evolves to the blue supergiant stage before exploding.

High and medium resolution spectroscopy of the X-ray transient 4U1543-47

Preliminary results of an EXOSAT observation of the transient X-ray source 4U1543-47 are presented. The source was observed in August 1983, during a high state, following a Tenma alert that the source was again active. Results from the GSPC and the LE 1000 l/mm grating are presented. The spectrum is complex, but in the 2–10 keV energy range can be well described by a Comptonised thermal distribution. Extrapolating the same model into the lower energy band of the grating requires an absorption column density equivalent to 2 × 1021 H cm2. A marked under-abundance of Oxygen and overabundance of Nitrogen, along with a strong, unidentified line feature at 9.8 A, are necessary to model the grating data.

Hydrogen-Poor Binary Stars

AbstractHydrogen-poor and helium-rich stars are easy to produce in interacting binaries. Thus they should be found among Population I binaries, in which a large-scale mass transfer has occurred between the components (possibly associated with mass loss from the system). For in such cases, those layers are now on the surface of the “loser” (and, most likely, also on the surface of the “gainer”) that were subject to hydrogen burning and the associated mixing of processed material. Helium overabundance in these objects will be accompanied by an overabundance of nitrogen and underabundance of carbon, as a result of the CNO process. All the Algol-like semidetached binaries should be mild helium stars; so far this has been demonstrated only in β Lyrae, for the He/H ratio is not extreme in such cases. Extreme helium stars require a more complex process, with two stages of mass transfer and/or loss (“case BB”); υ Sagittarii and KS Persei seem to be good examples of this process. The optically invisible components of these two stars seem to have been detected with the IUE. Good model atmospheres do not exist yet, so caution must be exercised in interpreting the UV data.

Observations of two peculiar emission objects in the Large Magellanic Cloud

Ultraviolet and visual wavelength spectra were obtained of two peculiar emission objects, Henize S63 and Sanduleak's star in the Large Magellanic Cloud. Previously not observed in the near- or far-ultraviolet, both objects exhibit strong permitted and semiforbidden line emissions. Estimates based on the absolute continuum flux of the hot companion star in Hen S63 indicate that it rivals the luminosity of the carbon star primary. The emission-line profile structure in both objects does not suggest Wolf-Rayet type emission. Carbon in Sanduleak's star (LMC anonymous) is conspicuously absent, while N V, semiforbidden N IV, and semiforbidden N III dominate the UV emission-line spectrum. Nitrogen is overabundant with respect to carbon and oxygen in both objects. The large overabundance of nitrogen in Sanduleak's star suggests evidence for CNO processes material similar to that seen in Nu Car.

Nitrogen overabundances in Population II dwarfs

view Abstract Citations (65) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nitrogen overabundances in population II dwarfs. Bessell, M. S. ; Norris, J. Abstract From a survey and spectrum synthesis analysis of the NH features in the spectra of some 25 Population II dwarfs, two objects have been found in which nitrogen is overabundant relative to the heavy elements by a factor of about 50-100 (i.e., N/Fe approximately equal to 1.7-2.0). The two stars are HD 74000 and HD 160617, which are well-known, extremely metal-deficient subdwarfs with Fe/H of about -2.0. Unless one is willing to invoke mixing during the main-sequence phase, or nitrogen-enhanced mass transfer in a binary system (both of which are believed to be unlikely explanations), the available data suggest a decoupling of nitrogen and heavy element production during the first stellar generations, and indicate that, in the early universe, nitrogen was produced as a primary element. Publication: The Astrophysical Journal Pub Date: December 1982 DOI: 10.1086/183917 Bibcode: 1982ApJ...263L..29B Keywords: Cosmochemistry; Dwarf Stars; Nitrogen; Nuclear Fusion; Abundance; Iron; Spectrum Analysis; Stellar Mass; Astrophysics full text sources ADS | data products SIMBAD (5)

Spectrophotometric observations of a peculiar nitrogen-rich planetary nebula NGC 2440

By using the Boller and Chivens spectrograph with a moderate dispersion (59 a mm-1) in the red spectral region, we obtained 65 spectra covering the whole surface of the planetary nebula NGC 2440. Intensities of Hα, [N II] λλ 6548–6584 and [S II] λλ 6717–6731 lines are derived using the IDS system available at the ESO in La Silva (Chile). The nebula is known to be a nitrogen-rich nebula (Peimbert 1978) surrounded by secondary structures (Minkowski 1964). The unusual high value of the [N II]/Hα in the central core (~ 30) is certainly due to the nitrogen overabundance occurring in that part of the nebula. Its variations from scale ionization structure (Capriotti, Cromwell and Williams 1971). The observations show clearly an outward increase of both [NII]/Hα andI(6717)/I(6713) ratios.

THE OPTICAL SPECTRUM OF W 50.

ABSTRACT Spectrophotometry of a faint filament near the position of the radio source W50 is presented. Emission lines that are characteristic of supernova remnants are seen with a radial velocity of about +100 km/s relative to the local standard of rest. The line-intensity measurements indicate that W50 is an old supernova remnant, perhaps having a nitrogen over-abundance.

Radial variations of line ratios across NGC 5236

The ionized gas in NGC 5236 was studied by spectroscopic means. The radial behaviour of the line ratios [Nii]/[Sii], Hα/[Sii] suggest a real nitrogen overabundance in the central regions of that galaxy.

Supermetallicity and the strong-lined binary systems

view Abstract Citations (20) References (72) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Supermetallicity and the strong-lined binary systems. Deming, D. ; Butler, D. Abstract The present discussion deals with visual binary systems that contain a strong-CN K giant and a strong-lined main sequence companion. It is argued that enhancement of the blue CN bands is associated with genuine supermetallicity, rather than with an overabundance of nitrogen. The arguments for supermetallicity are based on the principle, according to which two noninteracting stars of common origin and of greatly differing temperatures and surface gravities are unlikely to be affected in the same way by any agent that spuriously increases line strengths, other than the simple possibility of genuine heavy-element overabundance relative to hydrogen. Publication: The Astronomical Journal Pub Date: June 1979 DOI: 10.1086/112486 Bibcode: 1979AJ.....84..839D Keywords: Abundance; Binary Stars; Giant Stars; K Stars; Main Sequence Stars; Metallic Stars; Stellar Atmospheres; Astronomical Models; Cosmology; Galactic Evolution; Gravitational Effects; Heavy Elements; Hydrogen; Astrophysics; Metal-Rich Stars:Photometry; Metal-Rich Stars:Spectra; Metal-Rich Stars:Visual Binaries; Orbits:Visual Binaries full text sources ADS | data products SIMBAD (6) GCPD (1)

PK 6-2o1, a remarkable nitrogen-rich southern planetary nebula

Photoelectric spectrophotometry with the IDS on the 3.9 m Anglo-Australian Telescope has shown the planetary nebula PK 6-2o1 to be unique in its overabundance of nitrogen and helium, strong reddening and broad range of excitation conditions. It is suggested that here we see part of the massive envelope of a Wolf-Rayet star of the nitrogen sequence which is still embedded in its placental interstellar cloud.

The abundance of nitrogen in QSOs

Models of photoionized QSO emission-line regions show that measurements of O iii/N iv/C iv or N iii/C iii can yield the C/N/O ratios to an accuracy of a factor 2 or better. The N iii/C iii intensity ratios observed for the QSO PKS 1756+237 (z=1.72) implies a N/C abundance ratio 5 times larger than the solar value. This is comparable with the nitrogen overabundance in the nuclei of nearby galaxies, and it points to advanced chemical evolution in this QSO, with Zapproximately-greater-thanZ/sub sun/. Such a large abundance of nitrogen appears to be exceptional; composite spectra indicate that most QSOs have (N/O) approximately one-fourth to one-half the solar value. (AIP)

THE EFFECTS OF A VARIATION IN THE CNO ABUNDANCES ON THE POSITION OF INITIAL HORIZONTAL-BRANCH MODELS

ABSTRACT From the results of horizontal-branch model computations in which the nitrogen abundance was varied from 0.1 to 10 times normal we conclude, following the suggestion of Hartwick and McClure, that a nitrogen overabundance of 10 times normal can explain the anomalous red horizontal branch in the globular cluster NGC 7006. Key words: stellar evolution - horizontal-branch medels - CNO abundance