6,775 research outputs found
GAIA accuracy on radial velocities assessed from a synthetic spectra database
Spectrograph aboard the GAIA satellite operates in the near-IR, in the 8490--
8740 \AA window accessible also from the ground. The most important parameter
yet to be determined is the spectral resolution. Realistic estimates of the
zodiacal light background are obtained and a total of
correlation runs are used to study the accuracy of radial velocity measured by
the spectrograph as a function of resolution, magnitude of the target, its
spectral type and luminosity class. Accuracy better than 2 km/s is achievable
for bright stars if a high enough dispersion is chosen. Radial velocity error
of 5 km/s is at for Cepheids and at 17.7 for horizontal branch stars.
Even for very faint objects, with spectra dominated by background and readout
noise, the optimal dispersion is still in the 0.25 / 0.75 \AA/pix range. This
is also true for complicated cases such as spectroscopic binaries or if
information other than radial velocity, i.e. abundances of individual elements
or stellar rotation velocity, is sought after. The results can be scaled to
assess performance of future ground based instruments.Comment: accepted for publication in Astronomy and Astrophysics, 8 pages, 4
figure
Evaluating GAIA performances on eclipsing binaries. I. Orbits and stellar parameters for V505 Per, V570 Per and OO Peg
The orbits and physical parameters of three detached, double-lined A-F
eclipsing binaries have been derived combining H_P, V_T, B_T photometry from
the Hipparcos/Tycho mission with 8500-8750 Ang ground-based spectroscopy,
mimicking the photometric+spectroscopic observations that should be obtained by
GAIA, the approved Cornerstone 6 mission by ESA. This study has two main
objectives, namely (a) to derive reasonable orbits for a number of new
eclipsing binaries and (b) to evaluate the expected performances by GAIA on
eclipsing binaries and the accuracy achievable on the determination of
fundamental stellar parameters like masses and radii. It is shown that a 1%
precision in the basic stellar parameters can be achieved by GAIA on well
observed detached eclipsing binaries provided that the spectroscopic
observations are performed at high enough resolution. Other types of eclipsing
binaries (including semi-detached and contact types) and different spectral
types will be investigated in following papers along this series.Comment: A&A, 11 pages, 5 figures, 5 table
A high resolution, multi-epoch spectral atlas of peculiar stars including RAVE, GAIA and HERMES wavelength ranges
We present an Echelle+CCD, high S/N, high resolution (R = 20\,000)
spectroscopic atlas of 108 well-known objects representative of the most common
types of peculiar and variable stars. The wavelength interval extends from 4600
to 9400 Ang, and includes the RAVE, Gaia and HERMES wavelength ranges.
Multi-epoch spectra are provided for the majority of observed stars. A total of
425 spectra of peculiar stars are presented, which have been collected during
56 observing nights between November 1998 and August 2002. The spectra are
given in FITS format and heliocentric wavelengths, with accurate subtraction of
both the sky background and the scattered light. Auxiliary material useful for
custom applications (telluric dividers, spectro-photometric stars, flat-field
tracings) is also provided. The atlas aims to provide a homogeneous database of
the spectral appearance of stellar peculiarities, a tool useful both for
classification purposes and inter-comparison studies. It could also serve the
planning for and training of automated classification algorithms designed for
RAVE, Gaia, HERMES and other large scale spectral surveys. The spectrum of XX
Oph is discussed in some detail as an example of the content of the present
atlas.Comment: AJ in press (issue 140:6 December 2010
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
UBVRI photometric comparison sequences for symbiotic stars
We present accurate UBVRI photometric comparison sequences around 20
symbiotic stars. The sequences extend over wide brightness and color ranges,
and are suited to cover quiescence as well as outburst phases. The sequences
are intended to assist both present time photometry as well as measurement of
photographic plates from historical archives. The types of variability
presented by symbiotic stars are reviewed. Individual notes on the known
photometric behaviour of the program stars are provided.Comment: in press in Astron.Astrophys.Supp
Properties, evolution and morpho-kinematical modelling of the very fast nova V2672 Oph (Nova Oph 2009), a clone of U Sco
V2672 Oph reached maximum brightness V=11.35 on 2009 August 16.5. With
observed t2(V)=2.3 and t3(V)=4.2 days decline times, it is one of the fastest
known novae, being rivalled only by V1500 Cyg (1975) and V838 Her (1991) among
classical novae, and U Sco among the recurrent ones. The line of sight to the
nova passes within a few degrees of the Galactic centre. The reddening of V2672
Oph is E(B-V)=1.6 +/-0.1, and its distance ~19 kpc places it on the other side
of the Galactic centre at a galacto-centric distance larger than the solar one.
The lack of an infrared counterpart for the progenitor excludes the donor star
from being a cool giant like in RS Oph or T CrB. With close similarity to U
Sco, V2672 Oph displayed a photometric plateau phase, a He/N spectrum
classification, extreme expansion velocities and triple peaked emission line
profiles during advanced decline. The full width at zero intensity of Halpha
was 12,000 km/s at maximum, and declined linearly in time with a slope very
similar to that observed in U Sco. We infer a WD mass close to the
Chandrasekhar limit and a possible final fate as a SNIa. Morpho-kinematical
modelling of the evolution of the Halpha profile suggests that the overall
structure of the ejecta is that of a prolate system with polar blobs and an
equatorial ring. The density in the prolate system appeared to decline faster
than that in the other components. V2672 Oph is seen pole-on, with an
inclination of 0+/-6 deg and an expansion velocity of the polar blobs of 4800
+900/-800 km/s. On the basis of its remarkable similarity to U Sco, we suspect
this nova may be a recurrent. Given the southern declination, the faintness at
maximum, the extremely rapid decline and its close proximity to the Ecliptic,
it is quite possible that previous outbursts of V2672 Oph have been missed.Comment: in press in MNRA
The first three years of the outburst and light-echo evolution of V838 Mon and the nature of its progenitor
V838 Mon has undergone one of the most mysterious stellar outbursts on
record, with (a) a large amplitude (Delta B ~ 10 mag) and multi-maxima
photometric pattern, (b) a cool spectral type at maximum becoming cooler and
cooler with time during the descent, until it reached the never-seen-before
realm of L-type supergiants, never passing through optically thin or nebular
stages, (c) the development of a spectacular, monotonically expanding
light-echo in the circumstellar material, and (d) the identification of a
massive and young B3V companion, unaffected by the outburst. In this talk we
review the photometric and spectroscopic evolution during the first three full
years of outburst, the light-echo development and infer the nature of the
progenitor, which was brighter and hotter in quiescence than the B3V companion
and with an inferred ZAMS mass of about 65 Msun.Comment: to appear in the Proceedings of the Colloquium "Interacting Binaries:
Accretion, Evolution and Outcome", held in Cefalu' (Sicily) July 4-10, 2004,
L.A. Antonelli et al. eds., American Institute of Physics Conf. Proc. series,
in press. 6 pages, 4 figure
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