56,650 research outputs found
The SIMBAD astronomical database
Simbad is the reference database for identification and bibliography of
astronomical objects. It contains identifications, `basic data', bibliography,
and selected observational measurements for several million astronomical
objects. Simbad is developed and maintained by CDS, Strasbourg. Building the
database contents is achieved with the help of several contributing institutes.
Scanning the bibliography is the result of the collaboration of CDS with
bibliographers in Observatoire de Paris (DASGAL), Institut d'Astrophysique de
Paris, and Observatoire de Bordeaux. When selecting catalogues and tables for
inclusion, priority is given to optimal multi-wavelength coverage of the
database, and to support of research developments linked to large projects. In
parallel, the systematic scanning of the bibliography reflects the diversity
and general trends of astronomical research.
A WWW interface to Simbad is available at: http://simbad.u-strasbg.fr/SimbadComment: 14 pages, 5 Postscript figures; to be published in A&A
Intermediate Mass Stars <--> Massive Stars. A workshop around causes and consequences of differing evolutionary paths
The post-main sequence evolution of stars of intermediate or large masses is
notoriously complex. In the recent past, a number of workshops and meetings
have focused on either the Asymptotic Giant Branch of intermediate mass stars,
or the evolution of massive stars. But how well defined is the boundary between
these categories of objects defined? How would an observer proceed to classify
stars into one or the other category? How do objects near the boundary evolve,
die, and contribute to the chemical evolution of their environment? During this
3-day international workshop, 26 high quality presentations were given by
specialists in the relevant fields of astrophysics, and stimulating discussions
followed. It is technically impossible to provide an exhaustive census of the
results and ideas that emerged. In this brief article, we choose to point to
key elements of the workshop, some of which are now the topic of new
collaborations and will lead to publications elsewhere. For the sake of
brevity, we deliberately cite only the contributors to the workshop and no
external references. Many bibliographic references can be found in the original
presentations, which can be retrieved through:
http://astro.u-strasbg.fr/observatoire/obs/stars2009/stars2009.html The
programme workshop, which includes the titles of the individual contributions,
is provided as an appendix.Comment: 8 pages, 4 figure
[alpha/Fe] in the thin and the thick disk towards an automatic parametrization of stellar spectra
We test an automatic procedure to measure [Fe/H] and [alpha/Fe] on high
resolution spectra. The test sample is the intersection of the ELODIE library
and a catalogue of 830 stars having well determined abundances.Comment: Three-dimensional Universe with Gaia, 4-7 October 2004, Observatoire
de Paris-Meudon, France (ESA SP-576), eds M. Perryman & C. Turo
Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution
The larger number of models of asteroid shapes and their rotational states
derived by the lightcurve inversion give us better insight into both the nature
of individual objects and the whole asteroid population. With a larger
statistical sample we can study the physical properties of asteroid
populations, such as main-belt asteroids or individual asteroid families, in
more detail. Shape models can also be used in combination with other types of
observational data (IR, adaptive optics images, stellar occultations), e.g., to
determine sizes and thermal properties. We use all available photometric data
of asteroids to derive their physical models by the lightcurve inversion method
and compare the observed pole latitude distributions of all asteroids with
known convex shape models with the simulated pole latitude distributions. We
used classical dense photometric lightcurves from several sources and
sparse-in-time photometry from the U.S. Naval Observatory in Flagstaff,
Catalina Sky Survey, and La Palma surveys (IAU codes 689, 703, 950) in the
lightcurve inversion method to determine asteroid convex models and their
rotational states. We also extended a simple dynamical model for the spin
evolution of asteroids used in our previous paper. We present 119 new asteroid
models derived from combined dense and sparse-in-time photometry. We discuss
the reliability of asteroid shape models derived only from Catalina Sky Survey
data (IAU code 703) and present 20 such models. By using different values for a
scaling parameter cYORP (corresponds to the magnitude of the YORP momentum) in
the dynamical model for the spin evolution and by comparing synthetics and
observed pole-latitude distributions, we were able to constrain the typical
values of the cYORP parameter as between 0.05 and 0.6.Comment: Accepted for publication in A&A, January 15, 201
Formation of rings in galactic discs by infalling small companions
We use N-body simulations to study the formation of rings in a disc galaxy by
the impact of a small spherical companion. Both barred and nonbarred target
discs are considered. We discuss the effect of the properties of the target
disc (distribution of mass in the disc, velocity dispersion, etc.) as well as
of the mass and orbit of the companion on the properties of the rings, such as
their amplitude, width, shape, expansion velocity and lifetime. In particular
the amplitude, width, lifetime and expansion velocity of the first ring
increase considerably with companion mass, and so does the expansion velocity
of the particles in it and the total extent of the disc after the interaction.
We also discuss the formation and evolution of spokes and show that they can be
caused by companions of relatively small mass. In our three examples of oblique
impacts on barred target galaxies we note important transient displacements of
the bar, as well as changes of its pattern speed and size. An asymmetric
pseudoring is formed in each case, and during the first stages of its evolution
the bar forms part of it.Comment: 21 pages Latex, 22 figures, of which 7 as separate gif-files.
Requires mn.sty, accepted for publication in MNRAS. High resolution version
at http://www-obs.cnrs-mrs.fr/dynamique/pap/ring.htm
GYES, a multifibre spectrograph for the CFHT
We have chosen the name of GYES, one of the mythological giants with one
hundred arms, offspring of Gaia and Uranus, for our instrument study of a
multifibre spectrograph for the prime focus of the Canada-France-Hawaii
Telescope. Such an instrument could provide an excellent ground-based
complement for the Gaia mission and a northern complement to the HERMES project
on the AAT. The CFHT is well known for providing a stable prime focus
environment, with a large field of view, which has hosted several imaging
instruments, but has never hosted a multifibre spectrograph. Building upon the
experience gained at GEPI with FLAMES-Giraffe and X-Shooter, we are
investigating the feasibility of a high multiplex spectrograph (about 500
fibres) over a field of view 1 degree in diameter. We are investigating an
instrument with resolution in the range 15000 to 30000, which should provide
accurate chemical abundances for stars down to 16th magnitude and radial
velocities, accurate to 1 km/s for fainter stars. The study is led by
GEPI-Observatoire de Paris with a contribution from Oxford for the study of the
positioner. The financing for the study comes from INSU CSAA and Observatoire
de Paris. The conceptual study will be delivered to CFHT for review by October
1st 2010.Comment: Contributed talk at the Gaia ELSA conference 2010, S\`evres 7-11 June
2010, to be published on the EAS Series, Editors: C. Turon, F. Arenou & F.
Meynadie
High-resolution optical frequency dissemination on a telecommunication network with data traffic
We transferred the frequency of an ultra-stable laser over a 108 km urban
fiber link comprising 22 km of optical communications network fiber
simultaneously carrying Internet data traffic. The metrological signal and the
digital data signal are transferred on two different frequency channels in a
dense wavelength division multiplexing scheme. The metrological signal is
inserted into and extracted from the communications network by using
bidirectional off-the-shelf optical add-drop multiplexers. The link-induced
phase noise is measured and cancelled with round-trip technique using an
all-fiber-based interferometer. The compensated link shows an Allan deviation
of a few 10-16 at one second and below 10-19 at 10,000 seconds. This opens the
way to a wide dissemination of ultra stable optical clock signals between
distant laboratories via the Internet network
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