T. Zwitter

A Computational Guide to Physics of Eclipsing Binaries. I. Demonstrations and Perspectives

PHOEBE (PHysics Of Eclipsing BinariEs) is a modeling package for eclipsing binary stars, built on top of the widely used WD program of Wilson & Devinney. This introductory paper gives an overview of the most important scientific extensions (incorporating observational spectra of eclipsing binaries into the solution-seeking process, extracting individual temperatures from observed color indices, main-sequence constraining, and proper treatment of the reddening), numerical innovations (suggested improvements to WDs differential corrections method, the new Nelder & Mead downhill simplex method), and technical aspects (back-end scripter structure, graphical user interface). While PHOEBE retains 100% WD compatibility, its add-ons are a powerful way to enhance WD by encompassing even more physics and solution reliability. The operability of all these extensions is demonstrated on a synthetic main-sequence test binary; applications to real data will be published in follow-up papers. PHOEBE is released under the GNU General Public License, which guarantees it to be free and open to anyone interested in joining in on future development.

An extensive library of 2500-10 500 A synthetic spectra

We present a complete library of synthetic spectra based on Kurucz’s codes that covers the 2500–10 500 A wavelength range at resolving powers RP = 20 000, 11 500 (≡GAIA), 8500 (≡RAVE), 2000 (≡SLOAN) and uniform dispersions of 1 and 10 A/pix. The library maps the whole HR diagram, exploring 51 288 combinations of atmospheric parameters spanning the ranges: 3500 ≤ Teff ≤ 47 500 K, 0.0 ≤ log g ≤ 5.0, −2.5 ≤ [M/H] ≤ 0.5, [α/Fe] = 0.0,+0.4, ξ = 1, 2, 4 km s −1 ,0 ≤ Vrot ≤ 500 km s −1 . The spectra are available both as absolute fluxes as well as continuum normalized. Performance tests and spectroscopic applications of the library are discussed, including automatic classification of data from spectroscopic surveys like RAVE, SLOAN, GAIA. The entire library of synthetic spectra is accessible via the web.

Eigenvector 1: An Optimal Correlation Space for Active Galactic Nuclei.

We identify a correlation space involving optical and UV emission-line parameters as well as the soft X-ray spectral index that provides optimal discrimination between all principal classes of active galactic nuclei (AGNs). Most of the sources in our three high-quality data samples show a strong intercorrelation with narrow-line Seyfert 1 (NLSy1) galaxies and steep-spectrum radio galaxies occupying opposite extrema in the space. NLSy1 sources show a clear continuity with broader line sources, indicating that they are not a disjoint class of AGN as is sometimes suggested. We interpret the principal intercorrelation in the parameter space as being driven by the AGN luminosity-to-black hole mass ratio (L&solm0;M is proportional to the Eddington ratio). Source orientation no doubt also plays an important role, but it is not yet clear whether FWHM Hbeta or C iv lambda1549 line shift is the better indicator. We tentatively identify two radio-quiet populations: an almost pure radio-quiet population A, with FWHM</=4000, and population B, which occupies the same parameter domain as the flat-spectrum radio-loud sources. A possible interpretation sees population A/NLSy1 as lower mass/high accretion rate sources and population B/radio-loud sources as the opposite.

The wobbly Galaxy: kinematics north and south with RAVE red-clump giants

The RAdial Velocity Experiment survey, combined with proper motions and distance estimates, can be used to study in detail stellar kinematics in the extended solar neighbourhood (solar suburb). Using 72 365 red-clump stars, we examine the mean velocity components in 3D between 6 <R <10 kpc and -2 <Z <2 kpc, concentrating on north-south differences. Simple parametric fits to the (R, Z) trends for Vφ and the velocity dispersions are presented. We confirm the recently discovered gradient in mean Galactocentric radial velocity, VR, finding that the gradient is marked below the plane (δ/δR = -8 km s-1 kpc-1 for Z <0, vanishing to zero above the plane), with a Z gradient thus also present. The vertical velocity, VZ, also shows clear, large-amplitude (|VZ| = 17 km s-1) structure, with indications of a rarefaction-compression pattern, suggestive of wave-like behaviour. We perform a rigorous error analysis, tracing sources of both systematic and random errors. We confirm the north-south differences in VR and VZ along the line of sight, with the VR estimated independent of the proper motions. The complex three-dimensional structure of velocity space presents challenges for future modelling of the Galactic disc, with the Galactic bar, spiral arms and excitation of wave-like structures all probably playing a role.

The mysterious eruption of V838 Mon

V838 Mon is marking one of the most mysterious stellar outbursts on record. The spectral energy distribution of the progenitor resembles an under-luminous F main sequence star (at V =1 5:6 mag), that erupted into a cool supergiant following a complex and multi-maxima lightcurve (peaking at V =6 :7 mag). The outburst spectrum show BaII, LiI and lines of several s elements, with wide P-Cyg proles and a moderate and retracing emission in the Balmer lines. A light-echo discovered expanding around the object helped to constrain the distance (d = 790 30 pc), providing MV =+ 4:45 in quiescence and MV = 4:35 at optical maximum (somewhat dependent on the still uncertain EB V =0 :5 reddening). The general outburst trend is toward lower temperatures and larger luminosities, and continuing so at the time of writing. The object properties conflict with a classication within already existing categories: the progenitor was not on a post-AGB track and thus the similarities with the born-again AGB stars FG Sge, V605 Aql and Sakurais object are limited to the cool giant spectrum at maximum; the cool spectrum, the moderate wind velocity (500 km s 1 and progressively reducing) and the monotonic decreasing of the low ionization condition argues against a classical nova scenario. The closest similarity is with a star that erupted into an M-type supergiant discovered in M 31 by Rich et al. (1989), that became however much brighter by peaking at MV = 9:95, and with V4332 Sgr that too erupted into an M-type giant (Martini et al. 1999) and that attained a lower luminosity, closer to that of V838 Mon. M 31-RedVar, V4332 Sgr and V838 Mon could be all manifestations of a new class of astronomical objects.

Local stellar kinematics from RAVE data – I. Local standard of rest

We analyze a sample of 82850 stars from the RAVE survey, with well-determined velocities and stellar parameters, to isolate a sample of 18026 high-probability thin-disc dwarfs within 600 pc of the Sun. We derive space motions for these stars, and deduce the solar space velocity with respect to the Local Standard of Rest. The peculiar solar

A multi-epoch spectrophotometric atlas of symbiotic stars ?;??;???

A multi-epoch, absolute-fluxed spectral atlas extending from about 3200 to 9000 A is presented for 130 symbiotic stars, including members of the LMC, SMC and Draco dwarf galaxies. The fluxes are accurate to better than 5% as shown by comparison with Tycho and ground-based photometric data. The spectra of 40 reference objects (MKK cool giant standards, Mira and Carbon stars, planetary nebulae, white dwarfs, hot sub-dwarfs, Wolf-Rayet stars, classical novae, VV Cep and Herbig Ae/Be objects) are provided to assist the interpretation of symbiotic star spectra. Astrometric positions and counterparts in astrometric catalogues are derived for all program symbiotic stars. The spectra are available in electronic form from the authors.

Spectroscopic survey of the Galaxy with Gaia– II. The expected science yield from the Radial Velocity Spectrometer

The Gaia mission is designed as a Galaxy explorer, and will measure simultaneously, in a survey mode, the five or six phase-space parameters of all stars brighter than 20th magnitude, as well as providing a description of their astrophysical characteristics. These measurements are obtained by combining an astrometric instrument with micro-arcsecond capabilities, a photometric system giving the magnitudes and colours in 15 bands and a medium-resolution spectrograph named the Radial Velocity Spectrometer (RVS). The latter instrument will produce spectra in the 848- to 874-nm wavelength range, with a resolving power R = 11500, from which radial velocities, rotational velocities, atmospheric parameters and abundances can be derived. A companion paper has presented the characteristics of the RVS and its performance. The present paper details the outstanding scientific impact of this important part of the Gaia satellite on some key open questions in present-day astrophysics. The unbiased and simultaneous acquisition of multi-epoch radial velocities and individual abundances of key elements in parallel with the astrometric parameters is essential for the determination of the dynamical state and formation history of our Galaxy. Moreover, for stars brighter than V similar or equal to 15, the resolving power of the RVS will give information about most of the effects that influence the position of a star in the Hertzsprung-Russell diagram, placing unprecedented constraints on the age, internal structure and evolution of stars of all types. Finally, the RVS multi-epoch observations are ideally suited to the identification, classification and characterization of the many types of double, multiple and variable stars.

THE RAVE CATALOG OF STELLAR ELEMENTAL ABUNDANCES: FIRST DATA RELEASE

We present chemical elemental abundances for 36,561 stars observed by the RAdial Velocity Experiment (RAVE), an ambitious spectroscopic survey of our Galaxy at Galactic latitudes vertical bar b vertical bar > 25 degrees and with magnitudes in the range 9 <I(DENIS) <13. RAVE spectra cover the Ca-triplet region at 8410-8795 angstrom with resolving power R similar to 7500. This first data release of the RAVE chemical catalog is complementary to the third RAVE data release of radial velocities and stellar parameters, and it contains chemical abundances for the elements Mg, Al, Si, Ca, Ti, Fe, and Ni, with a mean error of similar to 0.2 dex, as judged from accuracy tests performed on synthetic and real spectra. Abundances are estimated through a dedicated processing pipeline in which the curve of growth of individual lines is obtained from a library of absorption line equivalent widths to construct a model spectrum that is then matched to the observed spectrum via a chi(2) minimization technique. We plan to extend this pipeline to include estimates for other elements, such as oxygen and sulfur, in future data releases.

Constraints on the Galactic bar from the Hercules stream as traced with RAVE across the Galaxy

Non-axisymmetries in the Galactic potential (spiral arms and bar) induce kinematic groups such as the Hercules stream. Assuming that Hercules is caused by the effects of the outer Lindblad resonance of the Galactic bar, we model analytically its properties as a function of position in the Galaxy and its dependence on the bars pattern speed and orientation. Using data from the RAVE survey we find that the azimuthal velocity of the Hercules structure decreases as a function of Galactocentric radius, in a manner consistent with our analytical model. This allows us to obtain new estimates of the parameters of the Milky Ways bar. The combined likelihood function of the bars pattern speed and angle has its maximum for a pattern speed of Ωb = (1.89 ± 0.08) × Ω0, where Ω0 is the local circular frequency. Assuming a solar radius of 8.05 kpc and a local circular velocity of 238 km s-1, this corresponds to Ωb = 56 ± 2 km s-1 kpc-1. On the other hand, the bars orientation φb cannot be constrained with the available data. In fact, the likelihood function shows that a tight correlation exists between the pattern speed and the orientation, implying that a better description of our best fit results is given by the linear relation Ωb/Ω0 = 1.91 + 0.0044(φb(deg) - 48), with standard deviation of 0.02. For example, for an angle of φb = 30 deg the pattern speed is 54.0 ± 0.5 km s-1 kpc-1. These results are not very sensitive to the other Galactic parameters such as the circular velocity curve or the peculiar motion of the Sun, and are robust to biases in distance. Appendices are available in electronic form at http://www.aanda.org