75 research outputs found
Radii, masses, and ages of 18 bright stars using interferometry and new estimations of exoplanetary parameters
Accurate stellar parameters are needed in numerous domains of astrophysics.
The position of stars on the H-R diagram is an important indication of their
structure and evolution, and it helps improve stellar models. Furthermore, the
age and mass of stars hosting planets are required elements for studying
exoplanetary systems. We aim at determining accurate parameters of a set of 18
bright exoplanet host and potential host stars from interferometric
measurements, photometry, and stellar models. Using the VEGA/CHARA
interferometer, we measured the angular diameters of 18 stars, ten of which
host exoplanets. We combined them with their distances to estimate their radii.
We used photometry to derive their bolometric flux and, then, their effective
temperature and luminosity to place them on the H-R diagram. We then used the
PARSEC models to derive their best fit ages and masses, with error bars derived
from MC calculations. Our interferometric measurements lead to an average of
1.9% uncertainty on angular diameters and 3% on stellar radii. There is good
agreement between measured and indirect estimations of angular diameters (from
SED fitting or SB relations) for MS stars, but not as good for more evolved
stars. For each star, we provide a likelihood map in the mass-age plane;
typically, two distinct sets of solutions appear (an old and a young age). The
errors on the ages and masses that we provide account for the metallicity
uncertainties, which are often neglected by other works. From measurements of
its radius and density, we also provide the mass of 55 Cnc independently of
models. From the stellar masses, we provide new estimates of semi-major axes
and minimum masses of exoplanets with reliable uncertainties. We also derive
the radius, density, and mass of 55 Cnc e, a super-Earth that transits its
stellar host. Our exoplanetary parameters reflect the known population of
exoplanets.Comment: 23 pages, 9 figures, published in A&A. (This version includes proof
corrections.
First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics
Context. Classical Be stars are hot non-supergiant stars surrounded by a
gaseous circumstellar disk that is responsible for the observed infrared-excess
and emission lines. The phenomena involved in the disk formation still remain
highly debated. Aims. To progress in the understanding of the physical process
or processes responsible for the mass ejections and test the hypothesis that
they depend on the stellar parameters, we initiated a survey on the
circumstellar environment of the brightest Be stars. Methods. To achieve this
goal, we used spectro-interferometry, the only technique that combines high
spectral (R=12000) and high spatial (=4\,mas) resolutions.
Observations were carried out at the Paranal observatory with the VLTI/AMBER
instrument. We concentrated our observations on the Br emission line to
be able to study the kinematics within the circumstellar disk. Our sample is
composed of eight bright classical Be stars : Col, CMa,
Car, p Car, Cen, Cen, Ara, and \textit{o} Aqr.
Results. We managed to determine the disk extension in the line and the nearby
continuum for most targets. We also constrained the disk kinematics, showing
that it is dominated by rotation with a rotation law close to the Keplerian
one. Our survey also suggests that these stars are rotating at a mean velocity
of V/V\,=\,0.82\,\,0.08. This corresponds to a rotational rate
of \,=\,0.95\,\,0.02 Conclusions. We did not detect
any correlation between the stellar parameters and the structure of the
circumstellar environment. Moreover, it seems that a simple model of a
geometrically thin Keplerian disk can explain most of our spectrally resolved
K-band data. Nevertheless, some small departures from this model have been
detected for at least two objects (i.e, CMa and Col).
Finally, our Be stars sample suggests that rotation is the main physical
process driving the mass-ejection. Nevertheless, smaller effects from other
mechanisms have to be taken into account to fully explain how the residual
gravity is compensated.Comment: Astronomy and Astrophysics (2011) Accepte
VITRUV - Science Cases
VITRUV is a second generation spectro-imager for the PRIMA enabled Very Large
Telescope Interferometer. By combining simultaneously up to 8 telescopes VITRUV
makes the VLTI up to 6 times more efficient. This operational gain allows two
novel scientific methodologies: 1) massive surveys of sizes; 2) routine
interferometric imaging. The science cases presented concentrate on the
qualitatively new routine interferometric imaging methodology. The science
cases are not exhaustive but complementary to the PRIMA reference mission. The
focus is on: a) the close environment of young stars probing for the initial
conditions of planet formation and disk evolution; b) the surfaces of stars
tackling dynamos, activity, pulsation, mass-loss and evolution; c) revealing
the origin of the extraordinary morphologies of Planetary Nebulae and related
stars; d) studying the accretion-ejection structures of stellar black-holes
(microquasars) in our galaxy; e) unveiling the different interacting components
(torus, jets, BLRs) of Active Galactic Nuclei; and f) probing the environment
of nearby supermassive black-holes and relativistic effects in the Galactic
Center black-hole.Comment: 15 pages. The Power of Optical/IR Interferometry: Recent Scientific
Results and 2nd Generation VLTI Instrumentation, Allemagne (2005) in pres
The metrology system of the VLTI instrument GRAVITY
The VLTI instrument GRAVITY combines the beams from four telescopes and
provides phase-referenced imaging as well as precision-astrometry of order 10
microarcseconds by observing two celestial objects in dual-field mode. Their
angular separation can be determined from their differential OPD (dOPD) when
the internal dOPDs in the interferometer are known. Here, we present the
general overview of the novel metrology system which performs these
measurements. The metrology consists of a three-beam laser system and a
homodyne detection scheme for three-beam interference using phase-shifting
interferometry in combination with lock-in amplifiers. Via this approach the
metrology system measures dOPDs on a nanometer-level.Comment: 9 pages, 5 figure
VITRUV - Imaging close environments of stars and galaxies with the VLTI at milli-arcsec resolution
The VITRUV project has the objective to deliver milli-arcsecond
spectro-images of the environment of compact sources like young stars, active
galaxies and evolved stars to the community. This instrument of the VLTI second
generation based on the integrated optics technology is able to combine from 4
to 8 beams from the VLT telescopes. Working primarily in the near infrared, it
will provide intermediate to high spectral resolutions and eventually
polarization analysis. This paper summarizes the result from the concept study
led within the Joint Research Activity advanced instruments of the OPTICON
program.Comment: In "The Power of Optical/IR Interferometry: Recent Scientific Results
and 2nd Generation VLTI Instrumentation", Allemagne (2005) in pres
The GRAVITY instrument software / High-level software
GRAVITY is the four-beam, near- infrared, AO-assisted, fringe tracking,
astrometric and imaging instrument for the Very Large Telescope Interferometer
(VLTI). It is requiring the development of one of the most complex instrument
software systems ever built for an ESO instrument. Apart from its many
interfaces and interdependencies, one of the most challenging aspects is the
overall performance and stability of this complex system. The three infrared
detectors and the fast reflective memory network (RMN) recorder contribute a
total data rate of up to 20 MiB/s accumulating to a maximum of 250 GiB of data
per night. The detectors, the two instrument Local Control Units (LCUs) as well
as the five LCUs running applications under TAC (Tools for Advanced Control)
architecture, are interconnected with fast Ethernet, RMN fibers and dedicated
fiber connections as well as signals for the time synchronization. Here we give
a simplified overview of all subsystems of GRAVITY and their interfaces and
discuss two examples of high-level applications during observations: the
acquisition procedure and the gathering and merging of data to the final FITS
file.Comment: 8 pages, 7 figures, published in Proc. SPIE 9146, Optical and
Infrared Interferometry IV, 91462
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