1,151 research outputs found
"Advanced" data reduction for the AMBER instrument
The amdlib AMBER data reduction software is meant to produce AMBER data
products from the raw data files that are sent to the PIs of different
proposals or that can be found in the ESO data archive. The way defined by ESO
to calibrate the data is to calibrate one science data file with a calibration
one, observed as close in time as possible. Therefore, this scheme does not
take into account instrumental drifts, atmospheric variations or
visibility-loss corrections, in the current AMBER data processing software,
amdlib. In this article, we present our approach to complement this default
calibration scheme, to perform the final steps of data reduction, and to
produce fully calibrated AMBER data products. These additional steps include:
an overnight view of the data structure and data quality, the production of
night transfer functions from the calibration stars observed during the night,
the correction of additional effects not taken into account in the standard
AMBER data reduction software such as the so-called "jitter" effect and the
visibility spectral coherence loss, and finally, the production of fully
calibrated data products. All these new features are beeing implemented in the
modular pipeline script amdlibPipeline, written to complement the amdlib
software.Comment: 10 pages, will be published in the proceeding of the SPIE conference
"astronomical Telescopes and Instrumentation: Optical and Infrared
Interferometry", held in Marseille from 23 to 27 june 200
AMBER closure and differential phases: accuracy and calibration with a Beam Commutation
The first astrophysical results of the VLTI focal instrument AMBER have shown
the importance of the differential and closure phase measures, which are
supposed to be much less sensitive to atmospheric and instrumental biases than
the absolute visibility. However there are artifacts limiting the accuracy of
these measures which can be substantially overcome by a specific calibration
technique called Beam Commutation. This paper reports the observed accuracies
on AMBER/VLTI phases in different modes, discusses some of the instrumental
biases and shows the accuracy gain provided by Beam Commutation on the
Differential Phase as well as on the Closure Phase.Comment: This paper will be published in the proceeding of SPIE ``astronomical
Telescopes and Instrumentation: Optical and Infrared Interferometry'
Differential interferometry of QSO broad line regions I: improving the reverberation mapping model fits and black hole mass estimates
Reverberation mapping estimates the size and kinematics of broad line regions
(BLR) in Quasars and type I AGNs. It yields size-luminosity relation, to make
QSOs standard cosmological candles, and mass-luminosity relation to study the
evolution of black holes and galaxies. The accuracy of these relations is
limited by the unknown geometry of the BLR clouds distribution and velocities.
We analyze the independent BLR structure constraints given by super-resolving
differential interferometry. We developed a three-dimensional BLR model to
compute all differential interferometry and reverberation mapping signals. We
extrapolate realistic noises from our successful observations of the QSO 3C273
with AMBER on the VLTI. These signals and noises quantify the differential
interferometry capacity to discriminate and measure BLR parameters including
angular size, thickness, spatial distribution of clouds, local-to-global and
radial-to-rotation velocity ratios, and finally central black hole mass and BLR
distance. A Markov Chain Monte Carlo model-fit, of data simulated for various
VLTI instruments, gives mass accuracies between 0.06 and 0.13 dex, to be
compared to 0.44 dex for reverberation mapping mass-luminosity fits. We
evaluate the number of QSOs accessible to measures with current (AMBER),
upcoming (GRAVITY) and possible (OASIS with new generation fringe trackers)
VLTI instruments. With available technology, the VLTI could resolve more than
60 BLRs, with a luminosity range larger than four decades, sufficient for a
good calibration of RM mass-luminosity laws, from an analysis of the variation
of BLR parameters with luminosity.Comment: 19 pages, 14 figures, accepted by MNRAS on December 5, 201
Statistical characterization of polychromatic absolute and differential squared visibilities obtained from AMBER/VLTI instrument
In optical interferometry, the visibility squared modulus are generally
assumed to follow a Gaussian distribution and to be independent of each other.
A quantitative analysis of the relevance of such assumptions is important to
help improving the exploitation of existing and upcoming multi-wavelength
interferometric instruments. Analyze the statistical behaviour of both the
absolute and the colour-differential squared visibilities: distribution laws,
correlations and cross-correlations between different baselines. We use
observations of stellar calibrators obtained with AMBER instrument on VLTI in
different instrumental and observing configurations, from which we extract the
frame-by-frame transfer function. Statistical hypotheses tests and diagnostics
are then systematically applied. For both absolute and differential squared
visibilities and under all instrumental and observing conditions, we find a
better fit for the Student distribution than for the Gaussian, log-normal and
Cauchy distributions. We find and analyze clear correlation effects caused by
atmospheric perturbations. The differential squared visibilities allow to keep
a larger fraction of data with respect to selected absolute squared
visibilities and thus benefit from reduced temporal dispersion, while their
distribution is more clearly characterized. The frame selection based on the
criterion of a fixed SNR value might result in either a biased sample of frames
or in a too severe selection.Comment: A&A, 13 pages and 9 figure
DISCO: a Spatio-Spectral Recombiner for Pupil Remapping Interferometry
Pupil-remapping is a new high-dynamic range imaging technique that has
recently demonstrated feasibility on sky. The current prototypes present
however deceiving limiting magnitude, restricting the current use to the
brightest stars in the sky. We propose to combine pupil-remapping with
spatio-spectral encoding, a technique first applied to the VEGA/CHARA
interferometer. The result is an instrument proposal, called "Dividing
Interferometer for Stars Characterizations and Observations" (DISCO). The idea
is to take profit of wavelength multiplexing when using a spectrograph in order
to pack as much as possible the available information, yet providing a
potential boost of 1.5 magnitude if used in existing prototypes. We detail in
this paper the potential of such a concept.Comment: Improving the performances of current optical interferometers \&
future designs, France (2013
Wolf-Rayet stars probed by AMBER/VLTI
Massive stars deeply influence their surroundings by their luminosity and the
injection of kinetic energy. So far, they have mostly been studied with
spatially unresolved observations, although evidence of geometrical complexity
of their wind are numerous. Interferometry can provide spatially resolved
observations of massive stars and their immediate vicinity. Specific geometries
(disks, jets, latitude-dependent winds) can be probed by this technique. The
first observation of a Wolf-Rayet (WR) star (\gamma^2 Vel) with the AMBER/VLTI
instrument yielded to a re-evaluation of its distance and an improved
characterization of the stellar components, from a very limited data-set. This
motivated our team to increase the number of WR targets observed with AMBER. We
present here new preliminary results that encompass several spectral types,
ranging from early WN to evolved dusty WC. We present unpublished data on
WR79a, a massive star probably at the boundary between the O and Wolf- Rayet
type, evidencing some Wolf-Rayet broad emission lines from an optically thin
wind. We also present new data obtained on \gamma^2 Vel that can be compared to
the up-to-date interferometry-based orbital parameters from North et al.
(2007). We discuss the presence of a wind-wind collision zone in the system and
provide preliminary analysis suggesting the presence of such a structure in the
data. Then, we present data obtained on 2 dusty Wolf-Rayet stars: WR48a-b and
WR118, the latter exhibiting some clues of a pinwheel-like structure from the
visibility variations.Comment: This paper will be published in the proceeding of SPIE ``astronomical
Telescopes and Instrumentation: Optical and Infrared Interferometry'
High spectral resolution imaging of the dynamical atmosphere of the red supergiant Antares in the CO first overtone lines with VLTI/AMBER
We present high spectral resolution aperture-synthesis imaging of the red
supergiant Antares (alpha Sco) in individual CO first overtone lines with
VLTI/AMBER. The reconstructed images reveal that the star appears differently
in the blue wing, line center, and red wing and shows an asymmetrically
extended component. The appearance of the star within the CO lines changes
drastically within one year, implying a significant change in the velocity
field in the atmosphere. Our modeling suggests an outer atmosphere (MOLsphere)
extending to 1.2--1.4 stellar radii with CO column densities of
(0.5--1)x10^{20} cm^{-2} and a temperature of ~2000 K. While the velocity field
in 2009 is characterized by strong upwelling motions at 20--30 km/s, it changed
to strong downdrafts in 2010. On the other hand, the AMBER data in the
continuum show only a slight deviation from limb-darkened disks and only
marginal time variations. We derive a limb-darkened disk diameter of
37.38+/-0.06 mas and a power-law-type limb-darkening parameter of
(8.7+/-1.6)x10^{-2} (2009) and 37.31+/-0.09 mas and (1.5+/-0.2)x10^{-1} (2010).
We also obtain Teff = 3660+/-120 K and log L/Lsun = 4.88+/-0.23, which suggests
a mass of 15+/-5 Msun with an age of 11-15 Myr. This age is consistent with the
recently estimated age for the Upper Scorpius OB association. The properties of
the outer atmosphere of Antares are similar to those of another well-studied
red supergiant, Betelgeuse. The density of the extended outer atmosphere of
Antares and Betelgeuse is higher than predicted by the current 3-D convection
simulations by at least six orders of magnitude, implying that convection alone
cannot explain the formation of the extended outer atmosphere.Comment: 18 pages, 16 figures, accepted for publication in Astronomy and
Astrophysics, short discussion on the age of Antares and the Upper Scorpius
OB association added, movies of the reconstructed images available at
http://www.mpifr-bonn.mpg.de/staff/kohnaka
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