Characteristics of Solar Flare Doppler Shift Oscillations Observed with the Bragg Crystal Spectrometer on Yohkoh

This paper reports the results of a survey of Doppler shift oscillations measured during solar flares in emission lines of S XV and Ca XIX with the Bragg Crystal Spectrometer (BCS) on Yohkoh. Data from 20 flares that show oscillatory behavior in the measured Doppler shifts have been fitted to determine the properties of the oscillations. Results from both BCS channels show average oscillation periods of 5.5 +/- 2.7 minutes, decay times of 5.0 +/-2.5 minutes, amplitudes of 17.1 +/- 17.0 km/s, and inferred displacements of 1070 +/- 1710 km, where the listed errors are the standard deviations of the sample means. For some of the flares, intensity fluctuations are also observed. These lag the Doppler shift oscillations by 1/4 period, strongly suggesting that the oscillations are standing slow mode waves. The relationship between the oscillation period and the decay time is consistent with conductive damping of the oscillations.Comment: Accepted for publication in Ap

X-ray Line Diagnostics of Hot Accretion Flows around Black Holes

We compute X-ray emission lines from thermal plasma in hot accretion flows. We show that line profiles are strong probes of the gas dynamics, and we present line-ratio diagnostics which are sensitive to the distribution of mass with temperature in the flow. We show how these can be used to constrain the run of density with radius, and the size of the hot region. We also present diagnostics which are primarily sensitive to the importance of recombination versus collisional ionization, and which could help discriminate ADAFs from photoionization-dominated accretion disk coronae. We apply our results to the Galactic center source Sagittarius A* and to the nucleus of M87. We find that the brightest predicted lines are within the detection capability of current $X$-ray instruments.Comment: 16 pages, 1 table, 9 figures, accepted to Ap

Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. V. Relativistic calculations for Fe XXIV and Fe XXV for X-ray modeling

Photoionization and recombination cross sections and rate coefficients are calculated for Li-like Fe XXIV and He-like Fe XXV using the Breit-Pauli R-matrix (BPRM) method. A complete set of total and level-specific parameters is obtained to enable X-ray photoionization and spectral modeling. The ab initio calculations for the unified (e + ion) recombination rate coefficients include both the non-resonant and the resonant recombination (radiative and di-electronic recombination, RR and DR, respectively) for (e + Fe XXV) -> Fe XXIV and (e + Fe XXVI) -> Fe XXV. The level specific rates are computed for all fine structure levels up to n = 10, enabling accurate computation of recombination-cascade matrices and effective rates for the X-ray lines. The total recombination rate coefficients for both Fe XXIV and Fe XXV differ considerably, by several factors, from the sum of RR and DR rates currently used to compute ionization fractions in astrophysical models. As the photoionization/recombination calculations are carried out using an identical eigenfunction expansion, the cross sections for both processes are theoretically self-consistent; the overall uncertainty is estimated to be about 10-20%. All data for Fe XXIV and Fe XXV (and also for H-like Fe XXVI, included for completeness) are available electronically.Comment: 31 pages, 10fug

K-shell dielectronic resonances in photoabsorption: differential oscillator strengths for Li-like C IV, O VI, and Fe XXIV

Recently X-ray photoabsorption in KLL resonances of O VI was predicted [Pradhan, Astrophys.J. Lett. 545, L165 (2000)], and detected by the Chandra X-ray Observatory [Lee et al, Astrophys. J. {\it Lett.}, submitted]. The required resonance oscillator strengths f_r, are evaluated in terms of the differential oscillator strength df/de that relates bound and continuum absorption. We present the f_r values from radiatively damped and undamped photoionization cross sections for Li-like C,O, and Fe calculated using relativistic close coupling Breit-Pauli R-matrix method. The KLL resonances of interest here are: 1s2p (^3P^o) 2s [^4P^o_{1/2,3/2}, ^2P^o_{1/2,3/2}] and 1s2p (^1P^o) 2s [^2P^o_{1/2,3/2}]. The KLL photoabsorption resonances in Fe XXIV are fully resolved up to natural autoionization profiles for the first time. It is demonstrated that the undamped f_r independently yield the resonance radiative decay rates, and thereby provide a precise check on the resolution of photoionization calculations in general. The predicted photoabsorption features should be detectable by the X-ray space observatories and enable column densities in highly ionized astrophysical plasmas to be determined from the calculated f_r. The dielectronic satellites may appear as redward broadening of resonances lines in emission and absorption.Comment: 9 pages, 2 figurs, Phys. Rev. A, Rapid Communication (submitted

Ni XXVII THEORETICAL SPECTRUM

Des spectres de haute résolution du Nickel viennent d'être obtenus au J.E.T. dans le domaine de longueur d'onde 1.584 - 1.615 Å à partir d'un spectromètre à cristal courbe. On présente ici les premières données atomiques nécessaires à leur interprétation, elles correspondent aux raies de résonance du Ni XXVII et aux raies satellites des Ni XXVI et Ni XXV qu'elles soient diélectroniques ou d'excitation d'électrons de couches internes.High resolution spectra of Nickel in the wavelength interval from 1.584 to 1.615 Å have been obtained recently at J.E.T. using a bent crystal spectrometer. Atomic parameters for resonance lines (Ni XXVII) and dielectronic and innershell satellite lines (Ni XXVI and Ni XXV) have been calculated for their interpretation

The Structure and Origin of Solar Plumes: Network Plumes

Astrophysical Journal, 700, pp. 551-558 (2009)International audienc

THE DIAGNOSTICS OF ASTROPHYSICAL PLASMAS, USING THE OXYGEN VII SOFT X-RAY LINES

Les paramètres atomiques correspondant aux processus de population et de dépopulation des niveaux d'énergie responsables des raies d'émission de l'O VII ont été recalculés. Ils permettent de réévaluer les mesures de densité électronique dans les éruptions solaires ainsi que d'examiner le spectre d'un reste de supernova Puppis À. Le rapport anormal d'intensité observé pour Puppis À a donné lieu à un premier modèle basé sur un plasma thermique de haute température hors équilibre d'ionisation. Nous proposons un autre modèle basé sur la présence d'un faible pourcentage d'électrons très énergétiques dans un plasma thermique plus froid. Ce modèle explique le rapport d'intensité sans invoquer des écarts à l'équilibre d'ionisation.We present a revised theory and atomic model for the line intensities emitted by O VII, taking into account all of the processes responsible for the emission. This is used to provide a revision of the density measurements made during solar flares, as well as in an attempt to understand the spectrum of the Puppis À supernova remnant. In order to explain the strange intensity ratios observed from Puppis À, previous authors have proposed an interpretation based upon a high temperature thermal plasma ( >5 106 K), in a non-equilibrium ionisation state. We present here an alternative model, based upon the assumed presence of a proportion of fast non-thermal electrons imbedded in an otherwise thermal plasma at a temperature of below 1 106 K. This can adequately explain the observations, without the necessity of invoking departures from ionisation balance