New X-ray observatories (Chandra and XMM-Newton) are providing a wealth of high-resolution X-ray spectra in which hydrogen- and helium-like ions are usually strong features. We present results from a new collisional-radiative plasma code, the Astrophysical Plasma Emission Code (APEC), which uses atomic data in the companion Astrophysical Plasma Emission Database (APED) to calculate spectral models for hot plasmas. APED contains the requisite atomic data such as collisional and radiative rates, recombination cross sections, dielectronic recombination rates, and satellite line wavelengths. We compare the APEC results to other plasma codes for hydrogen- and helium-like diagnostics, and test the sensitivity of our results to the number of levels included in the models. We find that dielectronic recombination with hydrogen-like ions into high (n=6-10) principal quantum numbers affects some helium-like line ratios from low-lying (n=2) transitions.Comment: 5 pages, 6 figures, accepted by ApJ Letter

(Abridged) Using a 100 ks XMM-Newton exposure of NGC 4051, we show that the time evolution of the ionization state of the X-ray absorbers in response to the rapid and highly variable X-ray continuum constrains all the main physical and geometrical properties of an AGN Warm Absorber wind. The absorber consists of two different ionization components. By tracking the response in the opacity of the gas in each component to changes in the ionizing continuum, we were able to constrain the electron density of the system. The measured densities require that the high and low ionization absorbing components of NGC 4051 must be compact, at distances 0.5-1.0 l-d (2200 - 4400Rs) and < 3.5 l-d (< 15800Rs) from the continuum source, respectively. This rules out an origin in the dusty obscuring torus, as the dust sublimation radius is at least an order of magnitude larger (>12 l-d). An accretion disk origin for the warm absorber wind is strongly suggested, and an association with the high ionization, HeII emitting, broad emission line region (radius <2 l-d) is possible. The two detected phases are consistent with pressure equilibrium, which suggests that the absorber consists of a two phase medium. A radial flow in a spherical geometry is unlikely, and a conical wind geometry is preferred. The implied mass outflow rate from this wind, can be well constrained, and is 2-5% of the mass accretion rate. If the mass outflow rate scaling with accretion rate is representative of all quasars, our results imply that warm absorbers in powerful quasars are unlikely to produce important evolutionary effects on their larger environment, unless we are observing the winds before they get fully accelerated. Only in such a scenario can AGN winds be important for cosmic feedback.Comment: Accepted for publication on ApJ on Dec 15, 2006. 13 Figures, 4 Table

We present a detailed model for the ionized absorbing gas evident in the 900 ksec Chandra HETGS spectrum of NGC 3783. The analysis was carried out with PHASE a new tool designed to model X-ray and UV absorption features in ionized plasmas. The 0.5-10 keV intrinsic continuum of the source is well represented by a single power law (Gamma=1.53) and a soft black-body component (kT=10 keV). The spectrum contains over 100 features, which are well fit by PHASE with just six free parameters. The model consists of a simple two phase absorber with difference of 35 in the ionization parameter and difference of 4 in the column density of the phases. The two absorption components turned out to be in pressure equilibrium, and are consistent with a single outflow (750 kms-1) an a single turbulent velocity (300 km s-1), and with solar elemental abundances. The main features of the low ionization phase are an Fe M-shell unresolved transition array (UTA) and the OVII lines. The OVII features, usualy identified with the OVIII and a warm absorber, are instead produced in a cooler medium also producing OVI lines. The UTA sets tight constraints on the ionization degree of the absorbers, making the model more reliable. The high ionization phase is required by the OVII and the Fe L-shell lines, and there is evidence for an even more ionized component in the spectrum. A continuous range of ionization parameters is disfavored by the fits, particularly to the UTA. The low ionizaton phase can be decomposed into three subcomponents based on the outflow velocity, FWHM, and H column densities found for three out of the four UV absorbers detected in NGC 3783. However, the ionization parametes are systematically smaller in our model than derived from UV data, indicating a lower degree of ionization.Comment: 42 pages, 7 tables and 17 figures. Replaced with version accepted for publication in Ap

High resolution spectra of the active binary Capella (G8 III + G1 III) covering the energy range 0.4-8.0 keV (1.5-30 Angstroms) show a large number of emission lines, demonstrating the performance of the HETGS. A preliminary application of plasma diagnostics provides information on coronal temperatures and densities. Lines arising from different elements in a range of ionization states indicate that Capella has plasma with a broad range of temperatures, from log T = 6.3 to 7.2, generally consistent with recent results from observations with the Extreme Ultraviolet Explorer (EUVE) and the Advanced Satellite for Cosmology and Astrophysics (ASCA). The electron density is determined from He-like O VII lines, giving the value N_e=10^10 cm^-3 at T_e=2*10^6 K; He-like lines formed at higher temperatures give only upper limits to the electron density. The density and emission measure from O VII lines together indicate that the coronal loops are significantly smaller than the stellar radius.Comment: 9 pages, 3 figures (1 color) accepted for ApJ