241 research outputs found
Projet collectif de recherche : cartographie de l'espace parisien
Rapport final d'activité du PCR 2005-200
A resolved, au-scale gas disk around the B[e] star HD 50138
articleHD 50138 is a B[e] star surrounded by a large amount of circumstellar gas and dust. Its spectrum shows characteristics which may indicate either a pre- or a post-main-sequence system. Mapping the kinematics of the gas in the inner few au of the system contributes to a better understanding of its physical nature. We present the first high spatial and spectral resolution interferometric observations of the BrÎł line of HD 50138, obtained with VLTI/AMBER. The line emission originates in a region more compact (up to 3 au) than the continuum-emitting region. Blue- and red-shifted emission originates from the two different hemispheres of an elongated structure perpendicular to the polarization angle. The velocity of the emitting medium decreases radially. An overall offset along the NW direction between the line- and continuum-emitting regions is observed. We compare the data with a geometric model of a thin Keplerian disk and a spherical halo on top of a Gaussian continuum. Most of the data are well reproduced by this model, except for the variability, the global offset and the visibility at the systemic velocity. The evolutionary state of the system is discussed; most diagnostics are ambiguous and may point either to a post-main-sequence or a pre-main-sequence nature.National Science FoundationGeorgia State UniversityW.M. Keck FoundationDavid and Lucile Packard FoundationFizeau ProgramCNRS-PICS progra
VSI: a milli-arcsec spectro-imager for the VLTI
VLTi Spectro-Imager (VSI) is a proposition for a second generation VLTI
instrument which is aimed at providing the ESO community with the capability of
performing image synthesis at milli-arcsecond angular resolution. VSI provides
the VLTI with an instrument able to combine 4 telescopes in a baseline version
and optionally up to 6 telescopes in the near-infrared spectral domain with
moderate to high spectral resolution. The instrument contains its own fringe
tracker in order to relax the constraints onto the VLTI infrastructure. VSI
will do imaging at the milli-arcsecond scale with spectral resolution of: a)
the close environments of young stars probing the initial conditions for planet
formation; b) the surfaces of stars; c) the environment of evolved stars,
stellar remnants and stellar winds, and d) the central region of active
galactic nuclei and supermassive black holes. The science cases allowed us to
specify the astrophysical requirements of the instrument and to define the
necessary studies of the science group for phase A.Comment: 12 page
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
FU Orionis disk outburst: evidence for a gravitational instability scenario triggered in a magnetically dead zone
Context: FUors outbursts are a crucial stage of accretion in young stars.
However a complete mechanism at the origin of the outburst still remains
missing. Aims: We aim at constraining the instability mechanism in FU Orionis
star itself, by directly probing the size and the evolution in time of the
outburst region with near-infrared interferometry, and to confront it to
physical models of this region. Methods: FU Orionis has been a regular target
of near-infrared interferometry. In this paper, we analyze more than 20 years
of interferometric observations to perform a temporal monitoring of the region
of the outburst, and compare it to the spatial structure deduced from 1D MHD
simulations. Results: We measure from the interferometric observations that the
size variation of the outburst region is compatible with a constant or slightly
decreasing size over time in the H and K band. The temporal variation and the
mean sizes are consistently reproduced by our 1D MHD simulations. We find that
the most compatible scenario is a model of an outburst occurring in a
magnetically layered disk, where a Magneto-Rotational Instability (MRI) is
triggered by a Gravitational Instability (GI) at the outer edge of a dead-zone.
The scenario of a pure Thermal Instability (TI) fails to reproduce our
interferometric sizes since it can only be sustained in a very compact zone of
the disk <0.1 AU. The scenario of MRI-GI could be compatible with an external
perturbation enhancing the GI, such as tidal interactions with a stellar
companion, or a planet at the outer edge of the dead-zone. Conclusions: The
layered disk model driven by MRI turbulence is favored to interpret the spatial
structure and temporal evolution of FU Orionis outburst region. Understanding
this phase gives a crucial link between the early phase of disk evolution and
the process of planet formation in the first inner AUs.Comment: Accepted for publication in A&
A new interferometric study of four exoplanet host stars : {\theta} Cygni, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis
Studying exoplanet host stars is of the utmost importance to establish the
link between the presence of exoplanets around various types of stars and to
understand the respective evolution of stars and exoplanets.
Using the limb-darkened diameter (LDD) obtained from interferometric data, we
determine the fundamental parameters of four exoplanet host stars. We are
particularly interested in the F4 main-sequence star, {\theta} Cyg, for which
Kepler has recently revealed solar-like oscillations that are unexpected for
this type of star. Furthermore, recent photometric and spectroscopic
measurements with SOPHIE and ELODIE (OHP) show evidence of a quasi-periodic
radial velocity of \sim150 days. Models of this periodic change in radial
velocity predict either a complex planetary system orbiting the star, or a new
and unidentified stellar pulsation mode.
We performed interferometric observations of {\theta} Cyg, 14 Andromedae,
{\upsilon} Andromedae and 42 Draconis for two years with VEGA/CHARA (Mount
Wilson, California) in several three-telescope configurations. We measured
accurate limb darkened diameters and derived their radius, mass and temperature
using empirical laws.
We obtain new accurate fundamental parameters for stars 14 And, {\upsilon}
And and 42 Dra. We also obtained limb darkened diameters with a minimum
precision of \sim 1.3%, leading to minimum planet masses of Msini=5.33\pm 0.57,
0.62 \pm 0.09 and 3.79\pm0.29 MJup for 14 And b, {\upsilon} And b and 42 Dra b,
respectively. The interferometric measurements of {\theta} Cyg show a
significant diameter variability that remains unexplained up to now. We propose
that the presence of these discrepancies in the interferometric data is caused
by either an intrinsic variation of the star or an unknown close companion
orbiting around it.Comment: 10 pages + 2 pages appendix, 16 figures, accepted for publication in
A&
Milli-arcsecond astrophysics with VSI, the VLTI spectro-imager in the ELT era
Nowadays, compact sources like surfaces of nearby stars, circumstellar
environments of stars from early stages to the most evolved ones and
surroundings of active galactic nuclei can be investigated at milli-arcsecond
scales only with the VLT in its interferometric mode. We propose a
spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe
these sources both over spatial and spectral scales in the near-infrared
domain. This instrument will provide information complementary to what is
obtained at the same time with ALMA at different wavelengths and the extreme
large telescopes.Comment: 8 pages. To be published in the proceedings of the ESO workshop
"Science with the VLT in the ELT Era", held in Garching (Germany) on 8-12
October 2007, A. Moorwood edito
VSI: the VLTI spectro-imager
The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument
of the Very Large Telescope Interferometer providing the ESO community with
spectrally-resolved, near-infrared images at angular resolutions down to 1.1
milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13
will be imaged without requiring a brighter nearby reference object. The unique
combination of high-dynamic-range imaging at high angular resolution and high
spectral resolution enables a scientific program which serves a broad user
community and at the same time provides the opportunity for breakthroughs in
many areas of astrophysic including: probing the initial conditions for planet
formation in the AU-scale environments of young stars; imaging convective cells
and other phenomena on the surfaces of stars; mapping the chemical and physical
environments of evolved stars, stellar remnants, and stellar winds; and
disentangling the central regions of active galactic nuclei and supermassive
black holes. VSI will provide these new capabilities using technologies which
have been extensively tested in the past and VSI requires little in terms of
new infrastructure on the VLTI. At the same time, VSI will be able to make
maximum use of new infrastructure as it becomes available; for example, by
combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the
measurement of up to 28 visibilities in every wavelength channel within a few
minutes. The current studies are focused on a 4-telescope version with an
upgrade to a 6-telescope one. The instrument contains its own fringe tracker
and tip-tilt control in order to reduce the constraints on the VLTI
infrastructure and maximize the scientific return.Comment: 12 pages, to be published in Proc. SPIE conference 7013 "Optical and
Infrared Interferometry", Schoeller, Danchi, and Delplancke, F. (eds.). See
also http://vsi.obs.ujf-grenoble.f
First AMBER/VLTI observations of hot massive stars
AMBER is the first near infrared focal instrument of the VLTI. It combines
three telescopes and produces spectrally resolved interferometric measures.
This paper discusses some preliminary results of the first scientific
observations of AMBER with three Unit Telescopes at medium (1500) and high
(12000) spectral resolution. We derive a first set of constraints on the
structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum
and the LBV Eta Carinae
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