No abstract

Nearly a century ago it was recognized that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models. A particular problem arose when refined photosphere spectral analysis led to reductions of 30-50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9-2.3 million kelvin and electron densities of (0.7-4.0) × 10(22) per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30-400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

Abstract. Near-infrared spectroscopy is used to study the kinematics and excitation mechanisms of H 2 and [Fe ] lines in a sample of mostly Seyfert 1 galaxies. The spectral coverage allows simultaneous observation of the JHK bands, thus eliminating the aperture and seeing effects that have usually plagued previous works. The H 2 lines are unresolved in all objects in which they were detected while the [Fe ] lines have widths implying gas velocities of up to 650 km s −1 . This suggests that, very likely, the H 2 and [Fe ] emission does not originate from the same parcel of gas. Molecular H 2 lines were detected in 90% of the sample, including PG objects, indicating detectable amounts of molecular material even in objects with low levels of circumnuclear starburst activity. Analysis of the observations favors thermal excitation mechanisms for the H 2 lines. Indeed, in NGC 3227, Mrk 766, NGC 4051 and NGC 4151, the molecular emission is found to be purely thermal but with heating processes that vary between the objects. Thermal excitation is also confirmed by the rather similar vibrational and rotational temperatures in the objects for which data were available. [Fe ] lines are detected in all of the sample AGN. The [Fe ] 1.254 µm/Paβ ratio is compatible with excitation of the [Fe ] lines by the active nucleus in most Seyfert 1 galaxies, but in Mrk 766 the ratio implies a stellar origin. A correlation between H 2 /Brγ and [Fe ]/Paβ is found for our sample objects supplemented by data from the literature. The correlation of these line ratios is a useful diagnostic tool in the NIR to separate emitting line objects by their level of nuclear activity. X-ray excitation models are able to explain the observed H 2 and part of the [Fe ] emission but fail to explain the observations in Seyfert 2 galaxies. Most likely, a combination of X-ray heating, shocks driven by the radio jet and circumnuclear star formation contributes, in different proportions, to the H 2 and [Fe ] lines observed. In most of our sample objects, the [Fe ] 1.257 µm/1.644 µm ratio is found to be 30% lower than the intrinsic value based on current atomic data. This implies either that the extinction towards the [Fe ]-emitting clouds is very similar in most objects or there are possible inaccuracies in the A-values in the Fe  transitions.

Spectroscopy enables the precise study of astronomical objects and phenomena. Bridging the gap between physics and astronomy, this is the first integrated graduate-level textbook on atomic astrophysics. It covers the basics of atomic physics and astrophysics, including state-of-the-art research applications, methods and tools. The content is evenly balanced between the physical foundations of spectroscopy and their applications to astronomical objects and cosmology. An undergraduate knowledge of physics is assumed, and relevant basic material is summarized at the beginning of each chapter. The material is completely self-contained and features sufficient background information for self-study. Advanced users will find it handy for spectroscopic studies. A website hosted by the authors contains updates, corrections, exercises and solutions, as well as news items from physics and astronomy related to spectroscopy. A link to this can be found at www.cambridge.org/9780521825368.

We present theoretical Fe II emission line strengths for physical conditions typical of Active Galactic Nuclei with Broad-Line Regions. The Fe II line strengths were computed with a precise treatment of radiative transfer using extensive and accurate atomic data from the Iron Project. Excitation mechanisms for the Fe II emission included continuum fluorescence, collisional excitation, self-fluorescence amoung the Fe II transitions, and fluorescent excitation by Ly α and Ly β. A large Fe II atomic model consisting of 827 fine structure levels (including states to E ≈ 15 eV) was used to predict fluxes for approximately 23,000 Fe II transitions, covering most of the UV, optical, and IR wavelengths of astrophysical interest. Spectral synthesis for wavelengths from λ 1600Å to 1.2 µm is presented. Applications of present theoretical templates to the analysis of observations are described. In particular, we discuss recent observations of near-IR Fe II lines in the 8500Å-1 µm region which are predicted by the Ly α fluorescence mechanism. We also compare our UV spectral synthesis with an empirical iron template for the prototypical, narrowline Seyfert galaxy I Zw 1. The theoretical Fe II template presented in this work should also applicable to a variety of objects with Fe II spectra formed under similar excitation conditions, such as supernovae and symbiotic stars.

We report the discovery of strong soft X-ray emission lines and a hard continuum above 2 keV in the narrow-line Seyfert 1 galaxy Mrk 335 during an extremely low X-ray flux state. Mrk 335 was observed for 22 ks by XMM-Newton in 2007 July as a Target of Opportunity to examine it in its X-ray low flux state, which was discovered with Swift. Long-term light curves suggest that this is the lowest flux state this AGN has ever been seen in. However, Mrk 335 is still sufficiently bright that its X-ray properties can be studied in detail. The X-ray continuum spectrum is very complex and requires several components to model. Statistically, partial covering and blurred reflection models work well. We confirm the presence of a strong narrow Fe line at 6.4 keV. High-resolution spectroscopy with the XMMNewton RGS reveals strong, soft X-ray emission lines not detected in previous, higher signal-to-noise ratio, XMMNewton observations, such as highly ionized Fe lines, O vii, and Ne ix and Mg xi lines. The optical /UV fluxes are similar to those previously measured with Swift. Optical spectroscopy taken in 2007 September does not show any changes to optical spectra obtained 8 years earlier.

We present the discovery of an outflowing ionized wind in the Seyfert 1 Galaxy Mrk 335. Despite having been extensively observed by most of the largest X-ray observatories in the last decade, this bright source was not known to host warm absorber gas until recent XMM-Newton observations in combination with a long-term Swift monitoring program have shown extreme flux and spectral variability. High resolution spectra obtained by the XMM-Newton RGS detector reveal that the wind consists of three distinct ionization components, all outflowing at a velocity of ∼5000 km/s. This wind is clearly revealed when the source is observed at an intermediate flux state (2-5×10 −12 ergs cm −2 s −1 ). The analysis of multi-epoch RGS spectra allowed us to compare the absorber properties at three very different flux states of the source. No correlation between the warm absorber variability and the X-ray flux has been determined. The two higher ionization components of the gas (logξ∼2.3 and 3.3) may be consistent with photoionization equilibrium, but we can exclude this for the only ionization component that is consistently present in all flux states (logξ∼1.8). We have included archival, non-simultaneous UV data from HST (FOS, STIS, COS) with the aim of searching for any signature of absorption in this source that so far was known for being absorption-free in the UV band. In the COS spectra obtained a few months after the X-ray observations we found broad absorption in CIV lines intrinsic to the AGN and blueshifted by a velocity roughly comparable to the X-ray outflow. The global behavior of the gas in both bands can be explained by variation of the covering factor and/or column density, possibly due to transverse motion of absorbing clouds moving out of the line of sight at Broad Line Region scale.

A unified treatment for electron-ion recombination has been developed and applied to detailed calculations for cross sections and total recombination rate coefficients for a number of atoms and ions. The ab initio calculations are carried out in the close-coupling approximation employing the R-matrix method for the bound and the continuum states of the electron-ion system. All final states of the recombined system are taken into account and the present method subsumes both the radiative and the dielectronic recombination (RR and DR) processes over all energy and temperature ranges of practical importance. Recombined states of the electron-ion system are divided into two groups: (a) n ~ no and (b) no < n ~ 00. Photoionization cross sections are calculated for all bound states of group (a), typically a few hundred bound states, referred to as low-n states, including a detailed energy resolution of the several infinite series of autoionizing resonances converging onto the various excited states of the core ion included in the close-coupling expansion. High-n states of group (b) are treated primarily through the theory of DR developed by Bell and Seaton [J. Phys. B 18, 1589Phys. B 18, (1985]. DR collision strengths with detailed resonance structures are presented. The detailed and the resonance-averaged DR collision strengths show characteristic peaks at the target thresholds of the core ion corresponding to dipoleallowed transitions. Individual bound states of the e +ion system with dominant contribution to lowenergy recombination are described. The present results demonstrate the importance of (i) recombinations to excited states (particularly the metastable states), and (ii) low-energy autoionizing resonances, both of which result in large contributions to effective electron-ion recombination. The individual contributions of the excited bound states of the e + ion system are calculated and their relative contribution to the total are discussed. The general pattern of the recombination rate, as a function of electron temperature, is studied along an isoelectronic sequence. It is found that while the low-energy (temperature) recombination increases with ion charge z, the relative high-energy (temperature) contribution to the total decreases; i.e., viewed as independent processes, the RR part increases while the DR decreases with z. Total recombination rate coefficients for several atoms and ions (C II, S II, C II, N II, 0 III, F IV, N e v, and Si IX) are obtained over the entire temperature range of possible interest in applications. Comparisons are made with earlier works on RR and DR. PACS number(s): 34.80. Kw, 32.80.Dz, 32.80.Fb