113 research outputs found
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
The secondary maximum of T CrB caused by irradiation of the red giant by a cooling white dwarf
Both the 1866 and 1946 outbursts of the recurrent symbiotic nova T CrB have
displayed a mysterious secondary maximum peaking in brightness ~5 months past
the primary one. Common to all previous modeling attempts was the rejection of
plain irradiation of the red giant (RG), on the basis that the secondary
maximum of T CrB would have been out of phase with the transit at superior
conjunction of the RG. Implicit to this line of reasoning is the assumption of
a constant temperature for the white dwarf (WD) irradiating the red giant. I
show by radiative modeling that irradiation of the RG by a cooling WD nicely
reproduces the photometric evolution of the secondary maximum, both in terms of
brightness and color, removes the phasing offset, and provides a
straightforward explanation that will be easy to test at the next and imminent
outburst.Comment: correcting a label in Figure
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