79 research outputs found
PISCO2: the new speckle camera of the Nice 76-cm refractor
We present the new speckle camera PISCO2 made in 2010-2012, for the 76-cm
refractor of C\^ote d'Azur Observatory. It is a focal instrument dedicated to
the observation of visual binary stars using high angular resolution speckle
interferometry techniques to partly overcome the degradation caused by the
atmospheric turbulence. Fitted with an EMCCD detector, PISCO2 allows the
acquisition of short exposure images that are processed in real time by our
specially designed software. Two Risley prisms are used for correcting the
atmospheric dispersion. All optical settings are remotely controlled. We have
already been able to observe faint, close binary stars with angular separations
as small as 0".16, and visual magnitudes of about 16. We also have measured
some particularly difficult systems with a magnitude difference between the two
components of about 4 magnitudes. This level of performance is very promising
for the detection and study of large sets of yet unknown (or partly measured)
binaries with close separation and/or large magnitude difference.Comment: 13 pages, 12 figure
Diameter and photospheric structures of Canopus from AMBER/VLTI interferometry
International audience% Context {Direct measurements of fundamental parameters and photospheric structures of post-main-sequence intermediate-mass stars are required for a deeper understanding of their evolution. } % Aims {Based on near-IR long-baseline interferometry we aim to resolve the stellar surface of the F0 supergiant star Canopus, and to precisely measure its angular diameter and related physical parameters.} % Methods {We used the AMBER/VLTI instrument to record interferometric data on Canopus: visibilities and closure phases in the H and K bands with a spectral resolution of 35. The available baselines (~m) and the high quality of the AMBER/VLTI observations allowed us to measure fringe visibilities as far as in the third visibility lobe.} % Results {We determined an angular diameter of \diameter=6.93\pm0.15~mas by adopting a linearly limb-darkened disk model. From this angular diameter and Hipparcos distance we derived a stellar radius R=71.4\pm4.0 R_{\sun}. Depending on bolometric fluxes existing in the literature, the measured \diameter provides two estimates of the effective temperature: ~K and ~K.} % Conclusions {In addition to providing the most precise angular diameter obtained to date, the AMBER interferometric data point towards additional photospheric structures on Canopus beyond the limb-darkened model alone. A promising explanation for such surface structures is the presence of convection cells. We checked such a hypothesis using first order star-cell models and concluded that the AMBER observations are compatible with the presence of surface convective structures. This direct detection of convective cells on Canopus from interferometry can provide strong constraints to radiation-hydrodynamics models of photospheres of F-type supergiant
Apodized Lyot Coronagraph for VLT-SPHERE: Laboratory tests and performances of a first prototype in the visible
We present some of the High Dynamic Range Imaging activities developed around
the coronagraphic test-bench of the Laboratoire A. H. Fizeau (Nice). They
concern research and development of an Apodized Lyot Coronagraph (ALC) for the
VLT-SPHERE instrument and experimental results from our testbed working in the
visible domain. We determined by numerical simulations the specifications of
the apodizing filter and searched the best technological process to manufacture
it. We present the results of the experimental tests on the first apodizer
prototype in the visible and the resulting ALC nulling performances. The tests
concern particularly the apodizer characterization (average transmission radial
profile, global reflectivity and transmittivity in the visible), ALC nulling
performances compared with expectations, sensitivity of the ALC performances to
misalignments of its components
Combined spectroscopy and intensity interferometry to determine the distances of the blue supergiants P Cygni and Rigel
In this paper, we report on the spatial intensity interferometry measurements
within the H line on two stars: the Luminous Blue Variable (LBV)
supergiant \PCygni\,and the late-type B supergiant Rigel. The experimental
setup has been upgraded to allow simultaneous measurement of two polarization
channels and the zero baseline correlation function. Combined with simultaneous
spectra measurements and based on radiative transfer models calculated with the
code CMFGEN, we were able to fit our measured visibility curves to extract the
stellar distances. Our distance determinations for both \PCygni\ (1.61
0.18 kpc) and Rigel (0.26 0.02 kpc) agree very well with the values
provided by astrometry with the Gaia and Hipparcos missions, respectively. This
is the first successful step towards extending the application of the Wind
Momentum Luminosity Relation method for distance calibration from an LBV
supergiant to a more normal late-type B supergiant
A binary engine fuelling HD87643' s complex circumstellar environment, using AMBER/VLTI
International audienceContext. The star HD 87643, exhibiting the “B[e] phenomenon”, has one of the most extreme infrared excesses for this object class. It harbours a large amount of both hot and cold dust, and is surrounded by an extended reflection nebula. Aims. One of our major goals was to investigate the presence of a companion in HD87643. In addition, the presence of close dusty material was tested through a combination of multi-wavelength high spatial resolution observations. Methods. We observed HD 87643 with high spatial resolution techniques, using the near-IR AMBER/VLTI interferometer with baselines ranging from 60 m to 130 m and the mid-IR MIDI/VLTI interferometer with baselines ranging from 25 m to 65 m. These observations are complemented by NACO/VLT adaptive-optics-corrected images in the K and L-bands, ESO-2.2m optical Wide-Field Imager large-scale images in the B, V and R-bands, Results. We report the direct detection of a companion to HD 87643 by means of image synthesis using the AMBER/VLTI instrument. The presence of the companion is confirmed by the MIDI and NACO data, although with a lower confidence. The companion is separated by ∼ 34 mas with a roughly north-south orientation. The period must be large (several tens of years) and hence the orbital parameters are not determined yet. Binarity with high eccentricity might be the key to interpreting the extreme characteristics of this system, namely a dusty circumstellar envelope around the primary, a compact dust nebulosity around the binary system and a complex extended nebula witnessing past violent ejections
Interferometrie Optique a Grande Base: Resultats Astrophysiques et Perspectives
SIGLEINIST TD 19859 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
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