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