Symposium - International Astronomical Union

Published by Cambridge University Press
Print ISSN: 0074-1809
It is demonstrated that the 1988-90 microlensing events in image A of Q2237+0305 reported by Racine (1992) do not exclude microlensing models with very low average mass, making the source radius larger than the projected Einstein radius $\eta_0$ (Refsdal and Stabell 1991, 1993). This is contrary to what has been claimed by Witt and Mao (1994). Since these events are the best resolved microlensing events recorded in Q2237+0305, further work should not exclude the possibility of a large source when interpreting lightcurve data.
We report multifrequency observations of the $\gamma$-ray blazar 0528+134 with the Effelsberg 100-m telescope, the IRAM 30-m telescope, and the NRL Green Bank Interferometer. 0528+134 underwent a major radio and mm outburst in 1993 a few month after a very strong outburst in high energy $\gamma$-rays. A similar behaviour is indicated for the weaker $\gamma$-ray outburst in May 1991 and the mm activity in the beginning of 1992. This result fits nicely to the general finding that blazars are bright in $\gamma$-rays preferrentially at the beginning of a radio outburst. 0528+134 was observed with a global VLBI array at 22$\,$GHz in November 1992. Within the IRIS-S and EUROPE geodetic VLBI observing campaigns the source was also observed regularly at 8.4$\,$GHz. A new VLBI component which is not present in data at 22 $\,$GHz from 1991 also exhibits superluminal motion. Backextra\-polating in time we find that the new component was expelled from the core in the first half of 1991, near the first $\gamma$-ray outburst in Mai 1991. Newest VLBI data indicate the appearance of another new component in 1994. Although this new component has yet been found only at two epochs, it appears to move superluminally and may have been expelled from the core between fall 1992 and summer 1993, i.e. near the time of the second gamma ray outburst and at the beginning of a strong radio outburst.
We present both low and high-dispersion abundance analyses of giants drawn from the zero proper motion sample near NGC 121. For the sample of 35 stars, the mean metallicity of the SMC field near NGC 121 is [Fe/H]=-1.3 with a real dispersion of 0.4 dex. The most metal-rich stars are at -0.5 dex and the most metal-poor stars at -2.1 dex. The velocity dispersion of the sample is 25 km/s. The dispersion of various kinematic samples in the SMC is independent of age. The RGB colors are consistent with Galactic globular clusters of similar metallicity. The field population, however, does not have an extended blue horizontal branch, and the main sequence turnoff extends 1 magnitude brighter than the turnoff in M5. Evidently active star formation in this region started roughly at the age of the Galactic globular cluster M5 and extended for about 6 Gyrs, and then stopped.
A 21-cm survey at Dwingeloo of a 5° square containing IC 1396 shows several neutral hydrogen concentrations that correspond in shape and position with dust clouds, particularly the bright-rimmed clouds involved with the H II region.
We have made HI 21cm-line absorption measurements using the GMRT towards 15 directions in the Galaxy which are known to have high random velocity clouds as seen in the optical absorption lines of CaII and NaI. For the first time, in 6 out of these 15 directions we detect HI absorption features corresponding to the high random velocity optical absorption lines. The mean optical depth of these detections is ~ 0.08.
Location of M104 GCs. Solid points: new 2dF GCs (April 2002); Open squares: WHT/LDSS-2 GCs [1]; Crosses: Keck GCs [7]. Note that the 2dF GCs extend to a radius of ∼ 20 arcmin (50 kpc)
We have found 56 new globular clusters in M104 from 2dF multi-fiber spectroscopy, doubling the number of confirmed clusters, and extending the spatial coverage to 50 kpc radius. We find no significant rotation in the total sample, or for subsets split by color or radius. However, there are hints that the blue clusters have a higher rotation than the red clusters, and for counter-rotation of clusters at large radius. We find a total mass of M ~ 1 × 10 12 M ⊙ and a (M/L) B =30 out to 50 kpc radius, which is strong evidence for a dark matter halo in M104.
A large single-dish submillimeter-wave telescope equipped with a focal plane array containing ~ 10 4 bolometers and costing about $120M could locate most protogalaxies in the southern sky within a year of operation.
The predictions of Galactic chemical evolution models for D and ³ He are described in connection with those on the other Galactic quantities for which observational constraints are available. Models in agreement with the largest set of data predict deuterium depletions from the Big Bang to the present epoch smaller than a factor of 3 and do not allow for D/H primordial abundances larger than ∼ 4 × 10 —5 . Models predicting higher D consumption do not reproduce other observed features of our Galaxy. If both the primordial D and ³ He are low, models assuming that 90% of low-mass stars experience an extra-mixing during the red giant phase reproduce all the ³ He observed abundances. The same percentage allows to fit also the observed carbon isotopic ratios, thus supporting the self-consistency of the extra-mixing mechanism.
A single merger scenario for making galaxies such as NGC 4550 possessing equal coplanar counter-rotating stellar disks is investigated by collisionless N-body technique. The scenario is successful in producing an axisymmetric disk made of two almost equal counter-rotating populations. The final disk shows a clear bimodal line profile in the outer part, which demonstrates that disk-disk mergers do not always produce ellipticals.
Two aspects of the chemical evolution of 4He in the Galaxy are considered on the basis of a sample of disk planetary nebulae by the application of corrections due to the contamination of 4He from the progenitor stars. First, the He/H radial gradient is analyzed, and then, the helium to heavy element enrichment ratio is determined for metallicities up to the solar value.
The galaxy pair NGC 5194/95 (M 51) is one of the closest and best known interacting systems. Despite its notoriety, however, many of its features are not well studied. Extending westward from NGC 5195 is a low surface brightness tidal tail, which can only be seen in deep broadband exposures. Our previous [O III] lambda 5007 planetary nebulae (PN) survey of M 51 recovered this tidal tail, and presented us with a opportunity to study the kinematics of a galaxy interaction in progress. We report the results of a spectroscopy survey of the PN, aimed at determining their kinematic properties. We then use these data to constrain new self-consistent numerical models of the system.
We discuss a model of the central source in Seyfert 1 galaxy NGC 5548. The model assumes a three phase disk structure consisting of a cold outer disk, a hot central disk constituting a Comptonizing X/gamma source, and an intermediate unstable and complex phase emitting a soft excess component. The model qualitatively explains broad-band spectrum and variability behavior assuming that the soft excess contributes significantly to the continuum emission and drives variability by geometrical changes of the intermediate disk zone.
I use integral field and long-slit spectra from the AAT and the Magellan telescope to investigate the kinematics of several clumps, recently identified along the prominent tidal tail of CG J1720-67.8 and suggested as possile tidal dwarf galaxy (TDG) candidates. A comparison of photometric and spectroscopic data with evolutionary synthesis models suggests burst ages of ~ 6 Myr for these clumps/TDG candidates.
We are studying the properties of the holes and the high velocity gas in NGC 6946. Here we present some puzzling results.
FUSE high resolution spectra of two PG1159 type central stars (K1-16 and NGC 7094) have revealed an unexpected iron deficiency of at least 1 or 2 dex (Miksa et al. 2002). Here we present early results of FUSE spectroscopy of the CSPN Abell 78. It is shown that iron is strongly deficient in this star, too.
A highly homogeneous study of 23 halo field dwarf stars has achieved a Li abundance accuracy of 0.033 dex per star. The work shows that the intrinsic spread of the Li abundances of these stars at a given metallicity is <0.02 dex, and consistent with zero. That is, the Spite Li plateau for halo field dwarfs is incredibly thin. The thinness rules out depletion by more than 0.1 dex by a rotational-induced extra-mixing mechanism. Despite the thinness of the plateau, an increase of Li with [Fe/H] is seen, interpreted as evidence of Galactic chemical evolution (GCE) of Li, primarily due to Galactic cosmic ray (GCR) spallation reactions in the era of halo formation. The rate of Li evolution is concordant with: (1) observations of spallative 6Li in halo dwarfs; (2) GCE models; and (3) data on Li in higher metallicity halo stars. New data have also revealed four new ultra-Li-deficient halo dwarfs, doubling the number known. Based on their propensity to cluster at the halo main sequence turnoff and also to exist redward of the turnoff, we hypothesise that they are the products of binary mergers that ultimately will become blue stragglers. We explain their low Li abundances by normal pre-main-sequence (and possibly main-sequence) destruction in the low mass stars prior to their merging. If this explanation is correct, then such stars need no longer be considered an embarrassment to the existence of negligible Li destruction in the majority of field halo dwarfs.
ACS observations of massive lensing clusters permit an order of magnitude increase in the numbers of multiply-lensed background galaxies identified behind a given cluster. We have developed a code to take the pixels belonging to any given image and generate counter-images with full resolution, so that multiple systems are convincingly and exhaustively identified. Over 130 images of 35 multiply lensed galaxies are found behind A1689, including many radial arcs and also tiny counter-images projected on the center of mass. The derived mass profile is found to flatten steadily towards the center, like an NFW profile, with a mean slope d(log(Sigma))/d(log(r)) ~ -0.55 +/- 0.1, over the range r<250 kpc/h, which is somewhat steeper than predicted for such a massive halo. We also clearly see the expected geometric increase of bend angles with redshift, however, given the low redshift of A1689, z=0.18, the dependence on cosmological parameters is weak, but using higher redshift clusters from our GTO program we may derive a more competitive constraint. Comment: To appear in Proceedings of IAU Symposium 225: Impact of Gravitational Lensing on Cosmology, 6 pages
AA Dor (LB 3459) is an eclipsing, close binary ( P = 0.26 d) consisting of a sdOB primary star and an unseen secondary with an extraordinary small mass. The secondary is possibly a former planet which may have survived a common-envelope phase and has even gained mass. In order to investigate on an existing discrepancy between the components' mass derived from NLTE spectral analysis and subsequent comparison to evolutionary tracks and masses derived from radial-velocity and the eclipse curves, we performed phase-resolved high-resolution and high-SN spectroscopy with the UVES attached to the ESO VLT. from the obtained spectra, we have determined AA Dor's orbital parameters ( P = 22 600.702±0.005 sec, A = 39.19±0.05 km s –1 , T 0 = 2451917.152690) and the rotational velocity ( v rot = 47±5 km s –1 ) of the primary.
The Hyades: Differences between spectroscopic radial-velocity values from the literature, and astrometric determinations. An increased blueshift of spectral lines in stars somewhat hotter than the Sun (B-V ≃ 0.3 − 0.5) is theoretically expected due to their more vigorous surface convection, causing greater convective blueshifts. Gravitational redshifts of white-dwarf spectra place them far off main-sequence stars. The error bars show the combined spectroscopic and astrometric errors (Madsen et al. 2002)
Accuracies reached in space astrometry now permit the accurate determination of astrometric radial velocities, without any use of spectroscopy. Knowing this true stellar motion, spectral shifts intrinsic to stellar atmospheres can be identified, for instance gravitational redshifts and those caused by velocity fields on stellar surfaces. The astrometric accuracy is independent of any spectral complexity, such as the smeared-out line profiles of rapidly rotating stars. Besides a better determination of stellar velocities, this permits more precise studies of atmospheric dynamics, such as possible modifications of stellar surface convection (granulation) by rotation-induced forces, as well as a potential for observing meridional flows across stellar surfaces.
This article reviews three related topics: the extragalactic background l ight and its sources, evolution models for the dust absorption and emission in galaxies, and empirical constraints on these transfer pr ocesses in nearby starburst galaxies. It is intended that the material presented here will serve as an introduction to this Joint Discussion.
Millimetre-band scans of the frequency space towards optically dim quasars is potentially a highly efficient method for detecting new high redshift molecular absorption systems. Here we describe scans towards 7 quasars over wide bandwidths (up to 23 GHz) with sensitivity limits sufficient to detect the 4 redshifted absorbers already known. With wider frequency bands, highly efficient searches of large numbers of possibly obscured objects will yield many new molecular absorbers.
We review observations of molecular absorption line systems at high redshift toward red quasars and gravitational lenses. Comment: in Cold Dust and Gas at High Redshift, IAU 24, Highlights of Astromony Vol. 12, 2000 (PASP), ed. D. Wilner
SHF OH absorption lines in Cassiopeia A spectrum, noting 1665 and 1667 MHz lines split
It is argued that an important fraction of PNe present large temperature variations that are not due to observational errors nor to incomplete atomic physics. Seven possible causes for these variations are reviewed, one of them is presented for the first time.
Over the last half-century quantitative stellar spectroscopy has made great progress. However, most stellar abundance analyses today still employ rather simplified models, which can introduce severe systematic errors swamping the observational errors. Some of these uncertainties for late-type stars are briefly reviewed here: atomic and molecular data, stellar parameters, model atmospheres and spectral line formation.
The application to main-sequence stars of the rotation-induced mixing theory in the presence of mu-gradients leads to partial mixing in the lithium destruction region, not visible in the atmosphere. The induced lithium depletion becomes visible in the sub-giant phase as soon as the convective zone deepens enough. This may explain why the observed " lithium dilution " is smoother and the final dilution factor larger than obtained in standard models, while the lithium abundance variations are very small on the main sequence.
Here we describe some of our latest results from measuring detailed abundances in Local Group dwarf galaxies with the VLT. Combining spectroscopic abundances with Color-Magnitude diagrams allows the effective measurement of detailed chemical evolution with time in these galaxies. Although there are not yet significant numbers of individual stars observed in local group dwarf galaxies, the uniformity of the abundance patterns of the majority of stars in galaxies with very different star formation histories must hint at general properties of all star formation in these small systems.
The strong activity of radio galaxies should have led to a nearly ubiquitous presence of fossil radio plasma in the denser regions of the inter-galactic medium as clusters, groups and filaments of galaxies. This fossil radio plasma can contain large quantities of relativistic particles (electrons and possibly protons) by magnetic confinement. These particles might be released and/or re-energized under environmental influences as turbulence and shock waves. Possible connections of such processes to the formation of the observed sources of diffuse radio emission in clusters of galaxies (the cluster radio halos and the cluster radio relics) are discussed.
I give a synopsis of two aspects of the Galactic Cosmic Ray (GCR) acceleration problem: the importance of the medium energy gamma-ray window, and several specific astrophysical sources which merit further investigation.
In a review written in December 1965, the author of this report has summarized the state of observational X-ray astronomy at that time. Further data that have become available since then have produced important advances in several directions. New sources have been discovered, some of which have been tentatively identified with known galactic or extra-galactic objects. Evidence has been presented for variability of the X-ray flux received from at least one of the sources. New spectral information has been obtained. New observations of the strong X-ray source in Scorpius, Sco X-1, have greatly reduced the previous upper limit for its angular size and have provided a much more accurate determination of its celestial coordinates. This determination has led to the identification of Sco X-1 with a faint visible object whose peculiar properties had, until then, escaped the attention of astronomers.
We model the nucleosynthesis during a radiative interpulse phase of a rotating 3Msun Asymptotic Giant Branch (AGB) star. We find an enhanced production of the neutron source species C13 compared to non-rotating models due to shear mixing of protons and C12 at the core-envelope interface. We estimate that the resulting total production of heavy elements by slow neutron capture s-process is too low to account for most observations. This due to the fact that rotationally induced mixing during the interpulse phase causes a pollution of the C13 pocket layer with the neutron poison N14. As a result we find a maximum neutron exposure of tau_max=0.04mbarn^{-1} in the s-process layer of our solar metallicity model with rotation. This is about a factor of 5 to 10 less than required to reproduce the observed stellar s-process abundance patterns. We compare our results with models that include hydrodynamic overshooting mixing, and with simple parametric models including the combined effects of overshooting and mixing in the interpulse. Within the parametric model a range of mixing efficiencies during the interpulse phase correlates with a spread in the s-process efficiency. Such a spread is observed in AGB and post-AGB stars as well as in pre-solar SiC grains.
Infrared observations of complete samples of active galactic nuclei (AGN) have shown that a substantial fraction of their bolometric luminosity is emitted at wavelengths ~8-1000microns. In radio-loud and Blazar-like objects much of this emission appears to be direct non-thermal synchrotron radiation. However, in the much larger numbers of radio-quiet AGN it is now clear that thermal dust emission is responsible for the bulk of radiation from the near-infrared through submillimeter wavelengths. Luminous infrared-selected AGN are often surrounded by powerful nuclear starbursts, both of which appear to be fueled by enormous supplies of molecular gas and dust funneled into the nuclear region during the strong interaction/merger of gas rich disks. All-sky surveys in the infrared show that luminous infrared AGN are at least as numerous as optically-selected AGN of comparable bolometric luminosity, suggesting that AGN may spend a substantial fraction of their lifetime in a dust-enshrouded phase. The space density of luminous infrared AGN at high redshift may be sufficient to account for much of the X-Ray background, and for a substantial fraction of the far-infrared background as well. These objects plausibly represent a major epoch in the formation of spheroids and massive black holes (MBH).
Winds and outflows in starburst galaxies and AGN provide important information on the physics of the "central engine", the presence and evolution of (nuclear) starbursts, and the metal enrichment of the nuclear environment and the intergalactic medium. Here, we concentrate on two examples, X-ray observations of the (U)LIRG NGC6240 and the BAL quasar APM08279+5255.
A number of monitoring observations of continuum emission from Active Galactic Nuclei (AGNs) have been made in optical-X-ray bands. The results obtained so far show (i) random up and down on timescales longer than decades, (ii) no typical timescales of variability on shorter timescales and (iii) decreasing amplitudes as timescales become shorter. The second feature indicates that any successful model must produce a wide variety of shot-amplitudes and -durations over a few orders in their light curves. In this sense, we conclude that the disk instability model is favored over the starburst model, since fluctuations on days are hard to produce by the latter model. Inter-band correlations and time lags also impose great constraints on models. Thus, constructing wavelength and time dependent models remains as future work.
The need for high angular resolution is emphasised, especially in the context of programs to understand massive black holes and the processes in their environment.
Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature accelerates protons and photons to energies in excess of 10 20 and 10 13 eV, respectively. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the reach of its extension, IceCube.
We discuss the transport of angular momentum induced by tidal effects in a disk surrounding a star in a pre-main sequence binary system. We consider the effect of both density and bending waves. Although tidal effects are important for truncating protostellar disks and for determining their size, it is unlikely that tidally-induced angular momentum transport plays a dominant role in the evolution of protostellar disks. Where the disk is magnetized, transport of angular momentum is probably governed by MHD turbulence. In a non self-gravitating laminar disk, the amount of transport provided by tidal waves is probably too small to account for the lifetime of protostellar disks. In addition, tidal effects tend to be localized in the disk outer regions.
I review of the observational properties of Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs), two unusual manifestations of neutron stars. I summarize the reasoning for SGRs being "magnetars," neutron stars powered by the decay of a very large magnetic field, and the now compelling evidence that SGRs and AXPs are in fact members of the same source class, as predicted uniquely by the magnetar model. I discuss some open issues in the magnetar model, and the prospects for future work.
On examining the historical development of astrophysical science at the bottom of the world from the early 20th century until today we find three temporally overlapping eras of which each has a rather distinct beginning. These are the eras of Astrogeology, High Energy Astrophysics and Photon Astronomy. A full version of this paper will be submitted to PASA.
The Crab Nebula demonstrates that neutron stars can interact with their environments in spectacular fashion, their relativistic winds generating nebulae observable across the electromagnetic spectrum. At many previous conferences, astronomers have discussed, debated and puzzled over the complicated structures seen in the Crab, but have been limited to treating most other pulsar wind nebulae (PWNe) as simple calorimeters for a pulsar's spin-down energy. However, with the wealth of high-quality data which have now become available, this situation has changed dramatically. I here review some of the main observational themes which have emerged from these new measurements. Highlights include the ubiquity of pulsar termination shocks, the unambiguous presence of relativistic jets in PWNe, complicated time variability seen in PWN structures, and the use of bow shocks to probe the interaction of pulsar winds with the ambient medium.
Recent observational studies of intermediate- and high-mass star-forming regions at submillimeter and infrared wavelengths are reviewed, and chemical diagnostics of the different physical components associated with young stellar objects are summarized. Procedures for determining the temperature, density and abundance profiles in the envelopes are outlined. A detailed study of a set of infrared-bright massive young stars reveals systematic increases in the gas/solid ratios, the abundances of evaporated molecules, and the fraction of heated ices with increasing temperature. Since these diverse phenomena involve a range of temperatures from < 100 K to 1000 K, the enhanced temperatures must be communicated to both the inner and outer parts of the envelopes. This `global heating' plausibly results from the gradual dispersion of the envelopes with time. Similarities and differences with low-mass YSOs are discussed. The availability of accurate physical models will allow chemical models of ice evaporation followed by `hot core' chemistry to be tested in detail.
In the context of the luminosity calibration of the nearer stars I discuss the Hipparcos results on distances to nearby OB associations and open clusters. The shortcomings and assumptions in the analyses used to derive these results are pointed out and for the open clusters a comparison is made with results obtained from main sequence fitting. I conclude that given the considerable uncertainties in the latter technique there is no convincing evidence that the Hipparcos based distances to open clusters beyond the Hyades should not be trusted.
AST/RO is a 1.7m diameter submillimeter-wave telescope at the geographic South Pole. A key AST/RO project is the mapping of CI and CO J = 4→3 and J = 7 → 6 emission from the inner Milky Way (Martin et al. 2003). These data are released for general use.
The current knowledge of neutrino properties has been derived from measurements performed with both astrophysical and terrestrial sources. Observations of neutrino flavor change have been made with neutrinos generated in the solar core, through cosmic ray interactions in the atmosphere and in nuclear reactors. A summary is presented of the current knowledge of neutrino properties and a description is provided for future measurements that could provide more complete information on neutrino properties.
We propose a new dynamical mechanism to account for the bar off-centering observed in many barred galaxies. It is based on the presence of a m=1 density wave, non-linearly excited by the strong m=2 component due to the linearly unstable bar and by a m=3 mode. N-body simulations suggest that this mechanism is at work in the centers of galaxies, and provide a natural explanation by spontaneously producing bar off-centering which amounts to several tens of parsecs.
We have numerically investigated the dynamics of how a close stellar fly-by encounter of a symmetrical circumstellar planetesimal disc can give rise to the many kinds of asymmetries and substructures attributed to the dusty disc of Beta Pic. We find three recognizable groupings of test particles that can be related to the morphology of the Beta Pic disc. These are: highly eccentric and inclined orbit particles that reach apocentre in the southwest, moderately eccentric and inclined orbit particles that reach apocentre in the northeast, and a relatively unperturbed region inside ~200au radius.
Recent advances in the modelling of stellar winds driven by radiation pressure make it possible to fit many wind-sensitive features in the UV spectra of hot stars, opening the way for a hydrodynamically consistent determination of stellar radii, masses, and luminosities from the UV spectrum alone. It is thus no longer necessary to assume a theoretical mass-luminosity relation. As the method has been shown to work for massive O-stars, we are now able to test predictions from the post-AGB evolutionary calculations quantitatively for the first time. Here we present the first rather surprising consequences of using the new generation of model atmospheres for the analysis of a sample of central stars of planetary nebulae.
Clouds and hazes are important throughout our solar system and in the atmospheres of brown dwarfs and extrasolar giant planets. Among the brown dwarfs, clouds control the colors and spectra of the L-dwarfs; the disappearance of clouds helps herald the arrival of the T-dwarfs. The structure and composition of clouds will be among the first remote-sensing results from the direct detection of extrasolar giant planets.
The atmospheres of M stars are dominated by a small number of very strong molecular compounds (H$_2$O, TiO, H$_2$, CO, VO). Most of the hydrogen is locked in molecular H$_2$, most of the carbon in CO; and H$_2$O, TiO and VO opacities define a pseudo-continuum covering the entire flux distribution of these stars. The optical ``continuum'' is due to TiO vibrational bands which are often used as temperature indicators for these stars. These may be the depth of the bands relative to the troughs in between them; or the depth of the VO bands; or of the atomic lines relative to the local ``continuum''; or even the strength of the infrared water bands; all of these depend on the strength of the TiO bands and the amount of flux-redistribution to longer wavelengths exerted by them. Departures from LTE of the Ti I atom, and thus the concentration of the important TiO molecule, could, therefore, have severe and measurable consequences on the atmospheric structure and spectra of these stars. In this paper we discuss NLTE effects of Ti I in fully self-consistent models for a few representative M/Brown dwarf and M giant model atmospheres and spectra.
A hot central star illuminating the surrounding ionized H II region usually produces very rich atomic spectra resulting from basic atomic processes: photoionization, electron-ion recombination, bound-bound radiative transitions, and collisional excitation of ions. Precise diagnostics of nebular spectra depend on accurate atomic parameters for these processes. Latest developments in theoretical computations are described, especially under two international collaborations known as the Opacity Project (OP) and the Iron Project (IP), that have yielded accurate and large-scale data for photoionization cross sections, transition probabilities, and collision strengths for electron impact excitation of most astrophysically abundant ions. As an extension of the two projects, a self-consistent and unified theoretical treatment of photoionization and electron-ion recombination has been developed where both the radiative and the dielectronic recombination processes are considered in an unified manner. Results from the Ohio State atomic-astrophysics group, and from the OP and IP collaborations, are presented. A description of the electronic web-interactive database, TIPTOPBASE, with the OP and the IP data, and a compilation of recommended data for effective collision strengths, is given.
Top-cited authors
Edward P. J. van den Heuvel
  • University of Amsterdam
Gunther Hasinger
  • European Space Agency
Wolfgang Voges
  • Max Planck Institute for Extraterrestrial Physics
Elmar Pfeffermann
  • Max Planck Institute for Extraterrestrial Physics
U. G. Briel
  • Max Planck Institute for Extraterrestrial Physics