Nitrogen K-shell photoabsorption

Reliable atomic data have been computed for the spectral modeling of the nitrogen K lines, which may lead to useful astrophysical diagnostics. Data sets comprise valence and K-vacancy level energies, wavelengths, Einstein $A$-coefficients, radiative and Auger widths and K-edge photoionization cross sections. An important issue is the lack of measurements which are usually employed to fine-tune calculations so as to attain spectroscopic accuracy. In order to estimate data quality, several atomic structure codes are used and extensive comparisons with previous theoretical data have been carried out. In the calculation of K photoabsorption with the Breit--Pauli $R$-matrix method, both radiation and Auger damping, which cause the smearing of the K edge, are taken into account. This work is part of a wider project to compute atomic data in the X-ray regime to be included in the database of the popular {\sc xstar} modeling code

Accretion onto the Companion of Eta Carinae During the Spectroscopic Event: II. X-Ray Emission Cycle

We calculate the X-ray luminosity and light curve for the stellar binary system Eta Carinae for the entire orbital period of 5.54 years. By using a new approach we find, as suggested before, that the collision of the winds blown by the two stars can explain the X-ray emission and temporal behavior. Most X-ray emission in the 2-10 \kev band results from the shocked secondary stellar wind. The observed rise in X-ray luminosity just before minimum is due to increase in density and subsequent decrease in radiative cooling time of the shocked fast secondary wind. Absorption, particularly of the soft X-rays from the primary wind, increases as the system approaches periastron and the shocks are produced deep inside the primary wind. However, absorption can not account for the drastic X-ray minimum. The 70 day minimum is assumed to result from the collapse of the collision region of the two winds onto the secondary star. This process is assumed to shut down the secondary wind, hence the main X-ray source. We show that this assumption provides a phenomenological description of the X-ray behavior around the minimum.Comment: The Astrophysical Journal, in pres

The Chandra Iron-L X-Ray Line Spectrum of Capella

An analysis of the iron L-shell emission in the publicly available spectrum of the Capella binary system, as obtained by the High Energy Transmission Grating Spectrometer on board the Chandra X-ray Observatory, is presented. The atomic-state model, based on the HULLAC code, is shown to be especially adequate for analyzing high-resolution x-ray spectra of this sort. Almost all of the spectral lines in the 10 - 18 Angstrom wavelength range are identified. It is shown that, for the most part, these lines can be attributed to emission from L-shell iron ions in the Capella coronae. Possibilities for electron temperature diagnostics using line ratios of Fe16+ are demonstrated. It is shown that the observed iron-L spectrum can be reproduced almost entirely by assuming a single electron temperature of kTe= 600 eV. This temperature is consistent with both the measured fractional ion abundances of iron and with the temperature derived from ratios of Fe16+ lines. A volume emission measure of 1053 cm-3 is calculated for the iron L-shell emitting regions of the Capella coronae indicating a rather small volume of 1029 cm3 for the emitting plasma if an electron density of 1012 cm-3 is assumed.Comment: Accepted to Ap