Patrick Palmeri

Photoionization Modeling and the K Lines of Iron

We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density, and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7‐9 keV energy band. We show that the

Photoionization modeling and the K lines of iron

We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density, and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7‐9 keV energy band. We show that the

Modeling of iron K lines: Radiative and Auger decay data for Fe II-Fe IX

A detailed analysis of the radiative and Auger de-excitation channels of K-shell vacancy states in Fe ii-Fe ix has been carried out. Level energies, wavelengths, A-values, Auger rates and fluorescence yields have been calculated for the lowest fine-structure levels populated by photoionization of the ground state of the parent ion. Dierent branching ratios, namely K2/K1 ,K /K ,K LM/KLL, KMM/KLL, and the total K-shell fluorescence yields, !K, obtained in the present work have been compared with other theoretical data and solid-state measurements, finding good general agreement with the latter. The K2/K1 ratio is found to be sensitive to the excitation mechanism. From these comparisons it has been possible to estimate an accuracy of10% for the present transition probabilities.

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

A new database of astrophysical interest

The aim of the new database D.R.E.A.M. is to supply the astrophysicists with accurate atomic data (wavelengths, energy levels, oscillator strengths, radiative lifetimes) of neutral, singly or multiply ionized lanthanides. Up to now, it contains about 50000 lines but it will be updated and extended in the near future.

K-Shell Photoabsorption of Oxygen Ions

Extensive calculations of the atomic data required for the spectral modeling of the K-shell photoabsorption of oxygen ions have been carried out in a multicode approach. The present level energies and wavelengths for the highly ionized species (electron occupancies 2 ≤ N ≤ 4) are accurate to within 0.5 eV and 0.02 A, respectively. For N > 4, lack of measurements, wide experimental scatter, and discrepancies among theoretical values are handicaps in reliable accuracy assessments. The radiative and Auger rates are expected to be accurate to 10% and 20%, respectively, except for transitions involving strongly mixed levels. Radiative and Auger dampings have been taken into account in the calculation of photoabsorption cross sections in the K-threshold region, leading to overlapping Lorentzian shaped resonances of constant widths that cause edge smearing. The behavior of the improved opacities in this region has been studied with the XSTAR modeling code using simple constant density slab models and is displayed for a range of ionization parameters.

SPECTRUM SYNTHESIS MODELING OF THE X-RAY SPECTRUM OF GRO J1655-40 TAKEN DURING THE 2005 OUTBURST

The spectrum from the black hole X-ray transient GRO J1655-40 obtained using the Chandra High Energy Transmission Grating in 2005 is notable as a laboratory for the study of warm absorbers, and for the presence of many lines from odd-Z elements between Na and Co (and Ti and Cr) not previously observed in X-rays. We present synthetic spectral models which can be used to constrain these element abundances and other parameters describing the outflow from the warm absorber in this object. We present results of fitting to the spectrum using various tools and techniques, including automated line fitting, phenomenological models, and photoionization modeling. We show that the behavior of the curves of growth of lines from H-like and Li-like ions indicate that the lines are either saturated or affected by filling-in from scattered or a partially covered continuum source. We confirm the conclusion of previous work by Miller et al., which shows that the ionization conditions are not consistent with wind driving due to thermal expansion. The spectrum provides the opportunity to measure abundances for several elements not typically observable in the X-ray band. These show a pattern of enhancement for iron peak elements, and solar or subsolar values for elements lighter than calcium. Models show that this is consistent with enrichment by a core-collapse supernova. We discuss the implications of these values for the evolutionary history of this system.

Atomic data for x-ray astrophysics

The available atomic data used for interpreting and modeling x-ray observations are reviewed. The applications for these data can be divided into several levels of detail, ranging from compilations which can be used with direct inspection of raw data, such as line finding lists, to synthetic spectra which attempt to fit to an entire observed dataset simultaneously. This review covers cosmic sources driven by both electron ionization and photoionization and touches briefly on planetary surfaces and atmospheres. The applications to x-ray astronomy, the available data, and recommendations for astronomical users are all reviewed, and an attempt to point out the applications where the shortcomings are greatest is also given.

Experimental and theoretical radiative lifetimes, branching fractions, and oscillator strengths for Lu I and experimental lifetimes for Lu II and Lu III

Radiative lifetimes, accurate in most cases to ±5%, from time-resolved, laser-induced fluorescence measurements on a slow beam of lutetium atoms and ions are reported for 22 odd-parity levels and 4 even-parity levels of Lu I and 14 odd-parity levels of Lu II. In addition, we report the radiative lifetime of one odd-parity level and an upper bound on the radiative lifetime of a second odd-parity level of Lu III. Experimental branching fractions for Lu I from emission spectra covering the near ultraviolet to the near infrared and recorded using the US National Solar Observatory 1.0 m Fourier transform spectrometer are reported. The branching fractions are combined with the radiative lifetimes to produce 44 experimentally determined transition probabilities or oscillator strengths, accurate generally to ±10%, for Lu I. New theoretical values for Lu I radiative lifetimes and branching fractions from a relativistic Hartree-Fock calculation that includes core polarization effects are also reported. These experimental and theoretical results, as well as older published results, are compared.

Radiative and Auger Decay of K-Vacancy Levels in the Ne, Mg, Si, S, Ar, and Ca Isonuclear Sequences

The HFR and AUTOSTRUCTURE atomic structure codes are used to compute complete data sets of level energies, wavelengths, A-values, and radiative and Auger widths for K-vacancy states of the Ne, Mg, Si, S, Ar, and Ca isonuclear sequences. Ions with electron number N > 9 are treated for the first time. Detailed comparisons with previous measurements and theoretical data for ions with N ≤ 9 are carried out in order to estimate reliable accuracy ratings.