Welcome to IAU Colloquium 187.

SS 433 was catalogued twenty five years ago, and yet, very little is known about the true identity of the compact component. We present a brief review of the behaviour of this enigmatic object with a special emphasis on the more recent results and their interpretation. We also speculate on some of the properties of the observed jet components.

The X-ray characteristics of SS 433 are reviewed together with results of recent multi-wavelength observing campaigns.

The coming GAIA Cornerstone mission by ESA will provide micro-arcsec astrometry, ∼10 bands photometry and far-red spectroscopy for a huge number of stars in the Galaxy (109). GAIA spectroscopy will cover the range 8480–8740 Å which includes the CaII triplet and the head of the Paschen series. In this paper we address the diagnostic potential of this wavelength range toward detection of peculiar stars.

The general importance and capabilities of observations of eclipsing binaries by the forthcoming ESA mission GAIA are discussed. Availability of spectroscopic observations and a large number of photometric bands on board will make it possible to reliably determine physical parameters for ∼ 105 binary stars. It is stressed that current methods of object by object analysis will have to be modified and included in an automatic analysis pipeline.

I describe three eclipsing double-lined binaries whose fundamental data (spectra, masses etc.) are totally out of line with theoretical concepts. Accepting the data at face value, they seem to imply that (i) a massive star (about 10 – 30 M⊙) in a moderately wide binary (P ≈ 50 – 250 d) can eject almost its entire envelope to infinity, without shrinking its period substantially, (b) some formerly triple systems can become binaries through the merger of two of the three components, and (c) a red giant can be stimulated to lose half its mass in a stellar wind before reaching its Roche lobe.

We present an analysis of short-wave, high-dispersion ultraviolet spectra of the triple star δ Ori A from the International Ultraviolet Explorer Satellite’s (IUE) Final Archive. These spectra were cross-correlated against AE Aur to find the components’ radial velocities, which were then used to produce the system’s orbital elements. The long-period tertiary star in the δ Ori A system was not seen in the resulting cross-correlation functions (CCFs). The close binary’s eclipses allow the orbit’s inclination to be estimated by modeling of its Hipparcos light curve. The primary star appears to have a mass of 11.2 M⊙ and the secondary seems to have a mass of 5.6 M⊙, both of which are about 1/3 of the expected values for stars of their MK types. Although we expected the massive close binary in the δ Ori A system to be a pre-Roche lobe overflow (RLOF) system, these masses appear to require that it be a post-RLOF system. The full description of this work, including the tomographic separation of the spectra for the close binary’s components, appears in Harvin et al. (2002).

V652 Herculis is a pulsating B star with a mass of about 0.6 M⊙ and a luminosity of some 1000 L⊙. Its uniqueness is defined by a surface which is predominantly (99%) CNO-processed helium. Precise measurements of its pulsation properties have provided direct tests for stellar pulsation and evolution models. Simulations of the merger of two helium white dwarfs are very successful in explaining its origin.

The star BI Lyn = PG 0900+400 was previously classified as an evolved binary system containing either a hot subdwarf or white dwarf and a thick accretion disk. We have analyzed new intermediate dispersion spectra and demonstrated that both views are wrong. BI Lyn is a highly-evolved system containing a luminous low-mass helium star and a rapidly rotating G-type giant. It may be closely related to the evolved sdO+G binary HD 128220.

The 5.07-d eclipsing system RT Lacertae is at the interface of Algol systems and RS CVn-type systems. Three strong lines of evidence support its Algolid nature: gas streaming; the close proximity of the larger star to its Roche lobe; and evidence of circumstellar material. Supporting the stellar activity model are moderately successful, if non-unique, modeling of light curve anomalies and ‘migration waves’ with star spot models, and a general expectation based on similarities to RS CVn-like systems. Recent work by Lanza et al. (2002) provides support for the latter class of models, but other light curve analyses and non-optical passband studies are examined below and directions for the resolutions of the problems and paradoxes presented by the RT Lac system are provided. An observational campaign to acquire simultaneous spectroscopic, photometric, and polarimetric data is suggested.

GLAST, the next U.S. general gamma-ray astrophysics mission scheduled to be launched into low Earth orbit in April, 2006, for 5–10 years of operation, is described. A product of a NASA/DOE and international collaboration, the Large Area Telescope (LAT) is the primary instrument that covers the < 20 MeV to > 300 GeV band with an effective area > 8000 cm2. The angular resolution ranges from < 3.5° at 100 MeV to < 0.15° at 10 GeV. The GLAST Burst Monitor (GBM) consists of a group of NaI and BGO detectors to extend GLAST’s sensitivity to gamma-ray bursts to the < 10 keV to > 25 MeV band. GLAST’s localizations enables us to identify the X-ray, optical and radio counterparts of thousands of gamma-ray sources and to determine their nature.

The very name of η Carinae conjures up the spectre of unsolved problems and challenging physics in the minds of many stellar astrophysicists. High spatial resolution spectroscopy and imaging of η Car during the past few years have answered some questions, but new and even more puzzling ones have appeared. In this review we highlight some of the recent discoveries and the still outstanding questions - what causes its 5.5 year spectroscopic cycle, what is the origin of its famous “great eruption,” and what is the underlying source of its instability?

IRC+10420 is a post–red supergiant at the empirical luminosity boundary in the HR diagram. It has now reached a stage in its blueward evolution where increasing opacity and partial ionization destabilize its atmosphere leading to rapid mass loss. Indeed, its wind is so dense that it is opaque and hides the underlying star. We have obtained HST/STIS spectroscopy with spatial resolution good enough to separate the star from its complex ejecta with numerous arcs, knots and jet-like features. The ejecta form essentially a reflection nebula, allowing us to view the star from a range of directions. The kinematics of the ejecta cannot be reconciled with existing models with either an equatorial disk or a bipolar outflow. Therefore we propose a model with a uniform spherically symmetric outflow of gas with random, asymmetric ejections superimposed. In our model, local instabilities allow for inflowing and outflowing material to coexist.

We describe the first long-baseline interferometric measurement ever made of the luminous blue variable η Carinae. η Car was observed with the Very Large Telescope Interferometer (VLTI) with the 8.2 m Unit Telescopes as well as with the 40 cm test siderostats on three different baselines. We will detail the measurements and data analysis and discuss briefly the implications of the derived visibility on the morphology of the central source. Furthermore we will discuss the future possibilities of interferometric observations and will show that η Car is one of the prime candidates for imaging with the VLTI.

The Homunculus reflection nebula around η Carinae provides a rare opportunity to observe a star from more than one direction. For η Car, the nebula’s geometry is known well enough to infer how wind profiles vary with latitude. STIS spectra of the Homunculus show directly that η Car has an aspherical stellar wind. P Cygni absorption in Balmer lines depends on latitude, with relatively high velocities and strong absorption near the polar axis. Stronger absorption at high latitudes is surprising, and it suggests higher mass flux toward the poles, perhaps resulting from equatorial gravity darkening on a rotating star. Reflected profiles of He I lines are more puzzling, and offer clues to η Car’s circumstellar structure. The bipolar wind geometry may imply that intrinsically asymmetric ejection helped form the Homunculus. It is also critical for understanding this star’s variability and evolution.

In light of recent N-body simulations performed using the GRAPE-6 special-purpose hardware we discuss the role of the star cluster environment in producing unusual stellar populations and the possibility that stars labelled exotic in the solar neighbourhood may be commonplace within star clusters.