Access to Stellar Population Models in the Virtual Observatory

A great effort is being made by the international Virtual Observatory community to build tools ready to be used by scientists. Presently, providing access to theoretical spectra in general, and synthetic spectra of galaxies in particular, is a matter of current interest in the Virtual Observatory. Several ways of accessing such spectra are available. We present two of them for accessing PEGASE.HR evolutionary synthesis models: HTTP-access to a limited number of parameters using Simple Spectral Access Protocol (SSAP), and full-featured WEB-service based access using Common Execution Architecture (CEA).Comment: 2 pages, 1 figure, to appear in the proceedings of IAU Symposium 241 (Stellar Populations as Building Blocks of Galaxies

Virtual Observatory based identification of AX J194939+2631 as a new cataclysmic variable

We report the discovery of a new cataclysmic variable (CV) among unidentified objects from the ASCA Galactic Plane Survey made using the Virtual Observatory data mining. First, we identified AX J194939+2631 with IPHAS J194938.39+263149.2, the only prominent H-alpha emitter among 400 sources in a 1 arcmin field of the IPHAS survey, then secured as a single faint X-ray source found in an archival Chandra dataset. Spectroscopic follow-up with the 3.5-m Calar Alto telescope confirmed its classification as a CV, possibly of magnetic nature. Our analysis suggests that AX J194939+2631 is a medium distance system (d ~ 0.6 kpc) containing a late-K or early-M type dwarf as a secondary component and a partially disrupted accretion disc revealed by the double-peaked H-alpha line. However, additional deep observations are needed to confirm our tentative classification of this object as an intermediate polar.Comment: 5 pages, 5 figures, 2 tables, accepted to Astronomy and Astrophysic

Explaining the stellar initial mass function with the theory of spatial networks

The distributions of stars and prestellar cores by mass (initial and dense core mass functions, IMF/DCMF) are among the key factors regulating star formation and are the subject of detailed theoretical and observational studies. Results from numerical simulations of star formation qualitatively resemble an observed mass function, a scale-free power law with a sharp decline at low masses. However, most analytic IMF theories critically depend on the empirically chosen input spectrum of mass fluctuations which evolve into dense cores and, subsequently, stars, and on the scaling relation between the amplitude and mass of a fluctuation. Here we propose a new approach exploiting the techniques from the field of network science. We represent a system of dense cores accreting gas from the surrounding diffuse interstellar medium (ISM) as a spatial network growing by preferential attachment and assume that the ISM density has a self-similar fractal distribution following the Kolmogorov turbulence theory. We effectively combine gravoturbulent and competitive accretion approaches and predict the accretion rate to be proportional to the dense core mass: $dM/dt \propto M$. Then we describe the dense core growth and demonstrate that the power-law core mass function emerges independently of the initial distribution of density fluctuations by mass. Our model yields a power law solely defined by the fractal dimensionalities of the ISM and accreting gas. With a proper choice of the low-mass cut-off, it reproduces observations over three decades in mass. We also rule out a low-mass star dominated "bottom-heavy" IMF in a single star-forming region.Comment: 8 pages, 5 figures, v2 matches the published versio