GAIA Spectroscopy and Radial Velocities

GAIA spectroscopic and radial velocity performancies are reviewed on the base of ground-based test observations and simulations. The prospects for accurate analysis of stellar atmospheres (temperature, gravity, chemical abundances, rotation, peculiarities) and precise radial velocities (single stars, binaries, pulsating stars) are colorful provided the spectral dispersion is high enough. A higher dispersions also favors a given precision of radial velocities to be reached at fainter magnitudes: for example, with current parameters for GAIA spectrograph, a 1 km/sec accuracy on epoch RVs of a K0 star is reached at V~13.0 mag with 0.25 Ang/pix dispersion spectra, at V~10.3 mag for 0.5 Ang/pix, and V~6.7 mag for 1 Ang/pix. GAIA radial velocities for single stars can match the ~0.5 km/sec mean accuracy of tangential motions at V=15 mag, provided the observations are performed at a dispersion not less than 0.5 Ang/pix.Comment: proceedings of Les Houches 2001 summer school "GAIA, an European Space Project", published by Editions De Physique, 14 page

On the narrow emission line components of the LMC novae 2004 (YY Dor) and 2009a

We present early decline spectra of the two Large Magellanic Cloud novae: LMC 2004 (YY Dor) and LMC 2009a and discuss their spectral an line profile evolution with special emphasis on the existence and appearance of a sharp component. We show that the narrow component that characterizes the emission lines in the maximum spectra of nova LMC 2004 originates in the ejecta. The HeII 4686 A, narrow emission which appears at the onset of the nebular phase in both novae is somewhat controversial. Our observations suggest that the corresponding line forming region is physically separated from the rest of the ejecta (the broad line region) and environmentally different. However, the lack of late time observations covering the super-soft source (SSS) phase, the post-SSS phase and the quiescence state does not allow to securely establish any non-ejecta origin/contribution as, instead, in the case of U Sco and KT Eri.Comment: 11 pages, 9 figures. Accepted for publication in Astronomy and Astrophysics on Aug 13 201

A rate-independent model for the isothermal quasi-static evolution of shape-memory materials

This note addresses a three-dimensional model for isothermal stress-induced transformation in shape-memory polycrystalline materials. We treat the problem within the framework of the energetic formulation of rate-independent processes and investigate existence and continuous dependence issues at both the constitutive relation and quasi-static evolution level. Moreover, we focus on time and space approximation as well as on regularization and parameter asymptotics.Comment: 33 pages, 3 figure

Global attractors for gradient flows in metric spaces

We develop the long-time analysis for gradient flow equations in metric spaces. In particular, we consider two notions of solutions for metric gradient flows, namely energy and generalized solutions. While the former concept coincides with the notion of curves of maximal slope, we introduce the latter to include limits of time-incremental approximations constructed via the Minimizing Movements approach. For both notions of solutions we prove the existence of the global attractor. Since the evolutionary problems we consider may lack uniqueness, we rely on the theory of generalized semiflows introduced by J.M. Ball. The notions of generalized and energy solutions are quite flexible and can be used to address gradient flows in a variety of contexts, ranging from Banach spaces to Wasserstein spaces of probability measures. We present applications of our abstract results by proving the existence of the global attractor for the energy solutions both of abstract doubly nonlinear evolution equations in reflexive Banach spaces, and of a class of evolution equations in Wasserstein spaces, as well as for the generalized solutions of some phase-change evolutions driven by mean curvature