860 research outputs found
Pupil plane optimization for single-mode multiaxial optical interferometry with a large number of telescopes
Incoming optical interferometers will allow spectro-imaging at high angular
resolution. Non-homothetic Fizeau concept combines good sensitivity and high
spectral resolution capabilities. However, one critical issue is the design of
the beam recombination scheme, at the heart of the instrument. We tackle the
possibility of reducing the number of pixels that are coding the fringes by
compressing the pupil plane. Shrinking the number of pixels -- which
drastically increases with the number of recombined telescopes -- is indeed a
key issue that enables to reach higher limiting magnitude, but also allows to
lower the required spectral resolution and fasten the fringes reading process.
By means of numerical simulations, we study the performances of existing
estimators of the visibility with respect to the compression process. We show
that, not only the model based estimator lead to better signal to noise ratio
(SNR) performances than the Fourier ones, but above all it is the only one
which prevent from introducing baseline mixing biases in the visibilities as
the pupil plane compression rate increases. Furthermore, we show that moderate
compression allows to keep the visibilities SNR unaffected. In the light of
these conclusions, we propose an optimized pupil arrangements for 6 and 8 beam
recombiners
The long period eccentric orbit of the particle accelerator HD167971 revealed by long baseline interferometry
Using optical long baseline interferometry, we resolved for the first time
the two wide components of HD167971, a candidate hierarchical triple system
known to efficiently accelerate particles. Our multi-epoch VLTI observations
provide direct evidence for a gravitational link between the O8 supergiant and
the close eclipsing O + O binary. The separation varies from 8 to 15 mas over
the three-year baseline of our observations, suggesting that the components
evolve on a wide and very eccentric orbit (most probably e>0.5). These results
provide evidence that the wide orbit revealed by our study is not coplanar with
the orbit of the inner eclipsing binary. From our measurements of the
near-infrared luminosity ratio, we constrain the spectral classification of the
components in the close binary to be O6-O7, and confirm that these stars are
likely main-sequence objects. Our results are discussed in the context of the
bright non-thermal radio emission already reported for this system, and we
provide arguments in favour of a maximum radio emission coincident with
periastron passage. HD167971 turns out to be an efficient O-type particle
accelerator that constitutes a valuable target for future high angular
resolution radio imaging using VLBI facilities.Comment: 8 pages, including 4 figures, accepted by Monthly Notices of the
Royal Astronomical Societ
Post-processing the VLTI fringe-tracking data: First measurements of stars
At the Very Large Telescope Interferometer, the purpose of the fringe-tracker
FINITO is to stabilize the optical path differences between the beams, allowing
longer integration times on the scientific instruments AMBER and MIDI. Our goal
is to demonstrate the potential of FINITO for providing H-band interferometric
visibilities, simultaneously and in addition to its normal fringe-tracking
role. We use data obtained during the commissioning of the Reflective Memory
Network Recorder at the Paranal observatory. This device has permitted the
first recording of all relevant real-time data needed for a proper
data-reduction. We show that post-processing the FINITO data allows valuable
scientific visibilities to be measured. Over the several hours of our
engineering experiment, the intrinsic transfer function is stable at the level
of 2%. Such stability would lead to robust measurements of science stars even
without the observation of a calibration star within a short period of time. We
briefly discuss the current limitations and the potential improvements
PIONIER: a status report
The visitor instrument PIONIER provides VLTI with improved imaging capabilities and sensitivity. The instrument started routinely delivering scientic data in November 2010, that is less than 12 months after being approved by the ESO Science and Technical Committee. We recall the challenges that had to be tackled to design, built and commission PIONIER. We summarize the typical performances and some astrophysical results obtained so far. We conclude this paper by summarizing lessons learned
A List of Bright Interferometric Calibrators measured at the ESO VLTI
In a previous publication (Richichi & Percheron 2005) we described a program
of observations of candidate calibrator stars at the ESO Very Large Telescope
Interferometer (VLTI), and presented the main results from a statistical point
of view. In the present paper, we concentrate on establishing a new homogeneous
group of bright interferometric calibrators, based entirely on publicly
available K-band VLTI observations carried out with the VINCI instrument up to
July 2004. For this, we have defined a number of selection criteria for the
quality and volume of the observations, and we have accordingly selected a list
of 17 primary and 47 secondary calibrators. We have developed an approach to a
robust global fit for the angular diameters using the whole volume of
quality-controlled data, largely independent of a priori assumptions. Our
results have been compared with direct measurements, and indirect estimates
based on spectrophotometric methods, and general agreement is found within the
combined uncertainties. The stars in our list cover the range K=-2.9 to +3.0
mag in brightness, and 1.3 to 20.5 milliarcseconds in uniform-disk diameter.
The relative accuracy of the angular diameter values is on average 0.4% and 2%
for the primary and secondary calibrators respectively. Our calibrators are
well suited for interferometric observations in the near-infrared on baselines
between ~20m and ~200m, and their accuracy is superior, at least for the
primary calibrators, to other similar catalogues. Therefore, the present list
of calibrators has the potential to lead to significantly improved
interferometric scientific results
Masses and age of the Chemically Peculiar double-lined binary ~Lupi
We aim at measuring the stellar parameters of the two Chemically Peculiar
components of the B9.5Vp HgMn + A2 Vm double-lined spectroscopic binary
HD141556, whose period is 15.25 days. We combined historical radial velocity
measurements with new spatially resolved astrometric observations from
PIONIER/VLTI to reconstruct the three-dimensional orbit of the binary, and thus
obtained the individual masses. We fit the available photometric points
together with the flux ratios provided by interferometry to constrain the
individual sizes, which we compared to predictions from evolutionary models.The
individual masses of the components are \Ma = 2.84 \pm 0.12\ \Msun and \Mb =
1.94 \pm 0.09\ \Msun. The dynamical distance is compatible with the Hipparcos
parallax. We find linear stellar radii of \Ra=2.85 \pm 0.15\ \Rsun and
\Rb=1.75 \pm 0.18\ \Rsun. This result validates a posteriori the flux ratio
used in previous detailed abundance studies. We determine a sub-solar initial
metallicity and an age of years. Our
results imply that the primary rotates more slowly than its synchronous
velocity, while the secondary is probably synchronous. We show that strong
tidal coupling during the pre-main sequence evolution followed by a full
decoupling at zero-age main sequence provides a plausible explanation for these
very low rotation rates.Comment: 8 pages, accepted in Aand
Refined masses and distance of the young binary Haro 1-14 C
We aim to refine the dynamical masses of the individual component of the
low-mass pre-main sequence binary Haro 1-14 C. We combine the data of the
preliminary orbit presented previously with new interferometric observations
obtained with the four 8m telescopes of the Very Large Telescope
Interferometer. The derived masses are M_a=0.905\pm0.043\,\Msun and
M_b=0.308\pm0.011\,\Msun for the primary and secondary components,
respectively. This is about five times better than the uncertainties of the
preliminary orbit. Moreover, the possibility of larger masses is now securely
discarded. The new dynamical distance, pc, is smaller than the
distance to the Ophiuchus core with a significance of . Fitting
the spectral energy distribution yields apparent diameters of
\phi_a=0.13\pm0.01\mas and \phi_b=0.10\pm0.01\mas (corresponding to
\Ra=1.50\,\Rsun and \Rb=1.13\,\Rsun) and a visual extinction of
. Although the revised orbit has a nearly edge-on geometry, the
system is unlikely to be a long-period eclipsing binary. The secondary in
Haro~1-14C is one of the few low-mass, pre-main sequence stars with an
accurately determined dynamical mass and distance
A PIONIER View on Mass-Transferring Red Giants
Symbiotic stars display absorption lines of a cool red giant together with
emission lines of a nebula ionized by a hotter star, indicative of an active
binary star system in which mass transfer is occurring. PIONIER at the VLT has
been used to combine the light of four telescopes at a time to study in
unprecedented detail how mass is transferred in symbiotic stars. The results of
a mini-survey of symbiotic stars with PIONIER are summarised and some tentative
general results about the role of Roche lobe overflow are presented.Comment: Report for the ESO Messenger June issu
Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements
The distance to pulsating stars is classically estimated using the
parallax-of-pulsation (PoP) method, which combines spectroscopic radial
velocity measurements and angular diameter estimates to derive the distance of
the star. An important application of this method is the determination of
Cepheid distances, in view of the calibration of their distance scale. However,
the conversion of radial to pulsational velocities in the PoP method relies on
a poorly calibrated parameter, the projection factor (p-factor). We aim to
measure empirically the value of the p-factors of a homogeneous sample of nine
Galactic Cepheids for which trigonometric parallaxes were measured with the
Hubble Space Telescope Fine Guidance Sensor. We use the SPIPS algorithm, a
robust implementation of the PoP method that combines photometry,
interferometry, and radial velocity measurements in a global modeling of the
pulsation. We obtained new interferometric angular diameters using the PIONIER
instrument at the Very Large Telescope Interferometer, completed by data from
the literature. Using the known distance as an input, we derive the value of
the p-factor and study its dependence with the pulsation period. We find the
following p-factors: 1.20 0.12 for RT Aur, 1.48 0.18 for T Vul,
1.14 0.10 for FF Aql, 1.31 0.19 for Y Sgr, 1.39 0.09 for X
Sgr, 1.35 0.13 for W Sgr, 1.36 0.08 for Dor, 1.41
0.10 for Gem, and 1.23 0.12 for Car. These values are
consistently close to p = 1.324 0.024. We observe some dispersion around
this average value, but the observed distribution is statistically consistent
with a constant value of the p-factor as a function of the pulsation period.
The error budget of our determination of the p-factor values is presently
dominated by the uncertainty on the parallax, a limitation that will soon be
waived by Gaia.Comment: 18 pages, 13 figure
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