Photospheric Iron Abundance Research Articles

A MONTE CARLO MARKOV CHAIN BASED INVESTIGATION OF BLACK HOLE SPIN IN THE ACTIVE GALAXY NGC 3783

The analysis of relativistically broadened X-ray spectral features from the inner accretion disk provides a powerful tool for measuring the spin of supermassive black holes (SMBH) in active galactic nuclei (AGN). However, AGN spectra are often complex and careful analysis employing appropriate and self-consistent models are required if one is to obtain robust results. In this paper, we revisit the deep July-2009 Suzaku observation of the Seyfert galaxy NGC3783 in order to study in a rigorous manner the robustness of the inferred black hole spin parameter. Using Monte Carlo Markov Chain (MCMC) techniques, we identify a (partial) modeling degeneracy between the iron abundance of the disk and the black hole spin parameter. We show that the data for NGC3783 strongly require both supersolar iron abundance (Z_Fe=2-4Zsun) and a rapidly spinning black hole (a>0.88). We discuss various astrophysical considerations that can affect the measured abundance. We note that, while the abundance enhancement inferred in NGC3783 is modest, the X-ray analysis of some other objects has found extreme iron abundances. We introduce the hypothesis that the radiative levitation of iron ions in the innermost regions of radiation-dominated AGN disks can enhance the photospheric abundance of iron. We show that radiative levitation is a plausible mechanism in the very inner regions of high accretion rate AGN disks.

Iron abundance in the solar photosphere. Application of a two-component model atmosphere

A realistic two-component model of the quiet Sun is used to determine the solar abundance of iron from the inversion of a number of Fe I and Fe II spectral lines for which accurate atomic parameters (oscillator strengths, central wavelengths, and collisional broadening cross sections) exist. From 33 Fe I lines we infer an abundance of AFe= 7:430:06, whereas we estimate AFe= 7:45 0:08 from 10 Fe II lines. These values are in excellent agreement with the results of analyses based on realistic 3D hydrodynamical simulations of the solar granulation, and imply a low photospheric iron abundance. We investigate the eects of convective motions and granular temperatures and conclude that both are important for reliable abundance determinations. For Fe I lines, the eects of convective motions can be simulated by using a microturbulent velocity of about 1 km s 1 , whereas it is possible to account for temperature inhomogeneities by adopting an average temperature stratification which is cooler than the Holweger & Muller model in the upper layers.

Roles of SN Ia and SN II in ICM Enrichment

Based on ASCA observations Mushotzky et al. (1996, ApJ 466, 686) have recently derived the relative abundance ratios of α-elements to iron, [α/Fe] ≃ 0.2–0.3, for four rich clusters, and have suggested that the origin of metals in an intra-cluster medium (ICM) is not a type-Ia supernovae (SNIa), but a type-II supernovae (SNII). However, these authors used the solar photospheric iron abundance for ASCA data reduction, while the meteoritic iron abundance is usually adopted in chemical-evolution studies. It is true that although the photospheric and meteoritic solar abundances are consistent for most of the elements, a serious discrepancy is known to exist for iron; indeed, the photospheric abundance of iron is NFe/NH = 4.68 · 10−5 by number, while the meteoritic value is 3.24 · 10−5. The argument concerning the relative roles of SNIa and SNII in ICM enrichment is quite sensitive to the precise values of [α/Fe], and one should use an identical solar iron abundance in data reduction as well as in theoretical arguments. We therefore adopt the meteoritic iron abundance, which is consistent with chemical-evolution studies, and shift Mushotzky et al.'s ASCA data by Δ[α/Fe] ≃ −0.16 dex. By comparing the corrected [α/Fe] values with theoretical nucleosynthesis prescriptions of SNIa and SNII, we reach a conclusion that an SNIa iron contribution of 50% or higher in the ICM enrichment could not be ruled out, and might indeed be favored based on the ASCA spectra.

Is the problem of solar iron abundance solved?

We revise the solar photospheric abundance of iron from Fe I lines based on two scales of oscillator strengths gf (Oxford [1–6] and Kiel [7]). In order to answer the question of Holweger et al. [8] why the gf of both scales agree but abundances deviate, we analyse different sources of errors in the solar iron abundance determinations. The most important reason of the abundance discrepancy is connected with the damping enchancement factor, E. However, the results obtained do not allow to infer a final value of the solar iron abundance. The “high” abundance derived from the Oxford scale of gf [2] seems to be more preferable in view of a smaller root mean square error ε in the iron abundance determination and a more pronounced minimum of the function ε( E) in comparison with the “low” abundance case [8].

SMM observations of K-alpha radiation from fluorescence of photospheric iron by solar flare X-rays

High-resolution Fe K-alpha spectra near 1.94 A observed during solar flares with the Bent Crystal Spectrometer on the Solar Maximum Mission are presented. The evidence for two possible excitation mechanisms, electron impact and fluorescence, is examined. It is found that the fluorescence mechanism satisfactorily describes the results, while the observations do not support electron collisional excitation of the Fe K-alpha transitions in low ionization stages (II-XII) of iron. Using Bai's model of the fluorescent excitation process, the photospheric iron abundance relative to that of hydrogen is estimated to be 5-6 x 10 to the -5th. The mean height of the soft X-ray source producing the K-alpha fluorescence is calculated on the basis of this model for about 40 large flares. The solar K-alpha lines are found to be about 25 percent wider than those measured in the laboratory. Weak line features observed at wavelengths shorter than that of the K-alpha lines are discussed.

Fluorescent excitation of photospheric Fe K-α emission during solar flares

The Bent Crystal Spectrometer on the NASA Solar Maximum Mission satellite provides high spectral and temporal resolution observations of the Fe Kα lines. We have analysed spectra from almost 50 solar flares that occurred during 1980. These data strongly support fluorescent excitation of photospheric iron by photons of E > 7.11 keV emitted by the hot coronal plasma produced during the flare. After comparison of the data with a model, we discuss the observed Kα line widths, estimates of the size of the emitting region, the height of the coronal source and the photospheric iron abundance.

Iron K?-fluorescence in solar flares: A probe of the photospheric iron abundance

The X-ray line at 6.4 keV has been observed from solar flares. It is found that Kα-fluorescence of neutral iron in the photosphere due to ‘thermal’ (T ∼ 107 K) X-rays of the gradual phase is its dominant production mechanism. For a given flux and energy spectrum of incident X-rays, the flux at 1 AU of iron Kα-photons depends on the photospheric iron abundance, the height of the X-ray source, and the helio-centric angle between the flare and the observer. Therefore, the flux of iron Kα-photons, when measured simultaneously with the flux and energy spectrum of the X-ray continuum and the flare location, can give us information on the height of the X-ray source and the photospheric iron abundance. Here we present our Monte Carlo calculations of iron Kα-fluorescence efficiencies, so that they might be useful for interpretations of future measurements of the 6.4 keV line (e.g., by a detector to be flown on the Solar Maximum Mission).

The solar photospheric abundance of iron

A new value of the solar photospheric abundance of iron, independent of line-shape parameters, is derived. Our analysis is based on a study of 40 weak infrared lines (0.85<λ<2.5 μ) for which theoretical oscillator strengths (calculated with configuration interactions taken into account) have recently been computed by Kurucz (1974). The abundance obtained, AFe = 7.57±0.11 (in the usual scale where log NH = 12.00) is in agreement with the ‘high’ solar values recently reported in the literature and with the meteoritic abundance.

Relative coronal abundances derived from X-ray observations. III - The effect of cascades on the relative intensity of Fe XVII line fluxes, and a revised iron abundance

view Abstract Citations (45) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relative coronal abundances derived from X-ray observations. III. The effect of cascades on the relative intensity of Fe XVII line fluxes, and a revised iron abundance. Walker, A. B. C., Jr. ; Rugge, H. R. ; Weiss, K. Abstract Observations of the helium-like and hydrogen-like resonance lines of N, 0, Ne, Na, Mg, Al, Si, S' and Ar below 25 A, made from the U.S. Air Force satellites OVI-lO and OV!-17, have previously been used to construct coronal models and to determine the relative abundances of these elements. Lines of Fe xvii are also prominent in the coronal spectrum below 25 A. The intensities of the lines of the 2p-3d transitions near 15 A have also been used in conjunction with these coronal models, and the assumption that the excited states are populated only by collisional excitation from the ground state ("coronal excitation"), to determine the Fe abundance. We have observed eight lines of Fe xvii which originated from the 2p53s, 2p53d, and 2s2p63d configurations in the coronal spectrum between 13 and 18 A. Many of the upper levels are populated by cascade so that the assumption of "coronal excitation" is not a valid one for most of these lines. Recent theoretical work on the spectrum of Fe xvii has taken account of the statistical equilibrium of the first 36 excited states in computing the intensities of the observed lines. Although the theoretical atomic rate constants for Fe xvii (especially the collisional excitation rates) cannot be as accurately calculated as those of the simpler ions, the relative intensities of the 2p-3d Fe xvii lines observed in the corona are now in good agreement with theoretical predictions. The measured flux in the lines from the 2s22p53s levels, which are populated in part by cascade from the 2p63l (1 = 1, 2, 3) levels, have been used to obtain the excitation-rate coefficients for the 2s2p631 3L levels, since the theoretical rate coefficients for these excitations are less accurately known than those for the 2p-31 transitions. Using this more complete theoretical model, and higher-resolution observations which allow a number of line blends to be resolved, we have revised our earlier calculation of the coronal abundance of Fe. We find an iron abundance relative to hydrogen of 26 x 10-6, which is in excellent agreement with the photospheric iron abundance. Subject headings: abundances, solar - atomic and molecular processes - coronal lines - line identifications - spectra, solar - X-rays, solar Publication: The Astrophysical Journal Pub Date: December 1974 DOI: 10.1086/153264 Bibcode: 1974ApJ...194..471W Keywords: Abundance; Iron; Line Spectra; Solar Corona; Solar X-Rays; Atmospheric Models; Electron Transitions; Integral Equations; Radiant Flux Density; Solar Spectra; X Ray Astronomy; Solar Physics full text sources ADS |

Opacity of the Solar Core

view Abstract Citations (8) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Opacity of the Solar Core Watson, William D. Abstract The influence of individual heavy elements on the opacity of the solar core is investigated. Increases and decreases in abundances are considered quantitatively. The recently revised photospheric iron abundance and the possible effects of diffusion are included. Together, these two changes may increase the opacity at the solar center by almost 50 percent relative to that obtained with a Lambert-Warner photospheric composition. A discussion of the uncertainty in the physical theory is given. Improved opacities are provided in a form that is convenient for solar evolutionary calculations. For opacity considerations, the conditions within main-sequence Population I models having radiative cores are similar to those of the Sun, and the discussion here is relevant for such stars. Publication: The Astrophysical Journal Pub Date: July 1970 DOI: 10.1086/150519 Bibcode: 1970ApJ...161..139W full text sources ADS |

The photospheric abundance of iron

The center-to-limb variation of equivalent widths of 198 Fei lines in the spectral region 5500 to 7000 A was studied with five photospheric models. The gf-values of Corliss and Warner (1964) were used in the analysis. The photospheric iron abundance was found to vary with excitation potential. This can be explained by a systematic error in the gf-values of high excitation lines and an error of 250 to 500K in the temperature of the arcs used for measuring the gf-values. Departures from LTE in the solar Fei lines are also a possibility. The adopted photospheric abundance of iron, log(N Fe/N H) is - 5.2.

Photospheric Abundance of Iron.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photospheric Abundance of Iron. Withbroe, George L. Abstract The center-limb variation of the equivalent widths of 198 Fe I lines in the spectral region 5500 to 7000 A have been studied with four photospheric models. The gf values of Corliss and Warner (Astrophys. J. Suppi. 8, 395, 1964) were used in the analysis. The photospheric abundance of iron was determined as a function of limb position and as a function of excitation potential Xe of the lines. The abundance does not vary significantly with position on the solar disk; however, it does seem to depend upcn excitation potential. The iron abundance decreases with increasing excitation potential for 1 ~ X~~ 4 V and increases for 4&Xex~5 V. The minimum in abundance at Xe 4 V corresponds closely to an ~nflection point in the calibration curve used to de~ne the absolute scale of Corliss and Warner's gf values. Huber and Tobey (Scientific Report Xo. 16, Harvard College Observatory Shock Tube Spectroscopy Laboratory, 1967) have found evidence that this calibration curve is incorrect for lines with X~> 6 V, where Xa is the excitation potential of the upper level of a transition. If Corliss and Warner's gf values are changed in the manner suggested by Huber and Tobey's data, the solar iron abundance decreases with increasing Xex over the range 1 ~ X~& 5 V. The results suggest that the excitation temperature of the Fe I lines is 5000K cooler than the photospheric local electron temperature or that there is a corresponding temperaturedependent error in the gf values. Publication: The Astronomical Journal Pub Date: 1967 DOI: 10.1086/110581 Bibcode: 1967AJ.....72T.837W full text sources ADS |