80 research outputs found
Integrated optics for astronomical interferometry. I. Concept and astronomical applications
We propose a new instrumental concept for long-baseline optical single-mode
interferometry using integrated optics which were developed for
telecommunication. Visible and infrared multi-aperture interferometry requires
many optical functions (spatial filtering, beam combination, photometric
calibration, polarization control) to detect astronomical signals at very high
angular resolution. Since the 80's, integrated optics on planar substrate have
become available for telecommunication applications with multiple optical
functions like power dividing, coupling, multiplexing, etc. We present the
concept of an optical / infrared interferometric instrument based on this new
technology. The main advantage is to provide an interferometric combination
unit on a single optical chip. Integrated optics are compact, provide
stability, low sensitivity to external constrains like temperature, pressure or
mechanical stresses, no optical alignment except for coupling, simplicity and
intrinsic polarization control. The integrated optics devices are inexpensive
compared to devices that have the same functionalities in bulk optics. We think
integrated optics will fundamentally change single-mode interferometry.
Integrated optics devices are in particular well-suited for interferometric
combination of numerous beams to achieve aperture synthesis imaging or for
space-based interferometers where stability and a minimum of optical alignments
are wished.Comment: 11 pages, 8 figures, accpeted by Astronomy and Astrophysics
Supplement Serie
The interferometric baselines and GRAVITY astrometric error budget
GRAVITY is a new generation beam combination instrument for the VLTI. Its
goal is to achieve microarsecond astrometric accuracy between objects separated
by a few arcsec. This accuracy on astrometric measurements is the most
important challenge of the instrument, and careful error budget have been
paramount during the technical design of the instrument. In this poster, we
will focus on baselines induced errors, which is part of a larger error budget.Comment: SPIE Meeting 2014 -- Montrea
High spatial resolution monitoring of the activity of BA supergiant winds
There are currently two optical interferometry recombiners that can provide
spectral resolutions better than 10000, AMBER/VLTI operating in the H-K bands,
and VEGA/CHARA, recently commissioned, operating in the visible. These
instruments are well suited to study the wind activity of the brightest AB
supergiants in our vicinity, in lines such as H or BrGamma. We present
here the first observations of this kind, performed on Rigel (B8Ia) and Deneb
(A2Ia). Rigel was monitored by AMBER in two campaigns, in 2006-2007 and
2009-2010, and observed in 2009 by VEGA; whereas Deneb was monitored in
2008-2009 by VEGA. The extension of the Halpha and BrGamma line forming regions
were accurately measured and compared with CMFGEN models of both stars.
Moreover, clear signs of activity were observed in the differential visibility
and phases. These pioneer observations are still limited, but show the path for
a better understanding of the spatial structure and temporal evolution of
localized ejections using optical interferometry.Comment: Proceedings of conf. IAUS272 - Active OB stars - Paris, July 19-23,
201
Characterization of integrated optics components for the second generation of VLTI instruments
Two of the three instruments proposed to ESO for the second generation
instrumentation of the VLTI would use integrated optics for beam combination.
Several design are studied, including co-axial and multi-axial recombination.
An extensive quantity of combiners are therefore under test in our
laboratories. We will present the various components, and the method used to
validate and compare the different combiners. Finally, we will discuss the
performances and their implication for both VSI and Gravity VLTI instruments.Comment: SPIE Astronomical Instrumentation 2008 in Marseille, France --
Equation (7) update
The compact Hα emitting regions of the Herbig Ae/Be stars HD 179218 and HD 141569 from CHARA spectro-interferometry
This work presents CHARA/VEGA Hα spectro-interferometry (R ⌠6000, and λ/2B ⌠1 mas) of HD 179218 and HD 141569, doubling the sample of Herbig Ae/Be (HAeBe) stars for which this type of observations is available so far. The observed Hα emission is spatially unresolved, indicating that the size of the Hα emitting region is smaller than âŒ0.21 and 0.12 au for HD 179218 and HD 141529 (âŒ15 and 16 R*, respectively). This is smaller than for the two other HAeBes previously observed with the same instrumentation. Two different scenarios have been explored in order to explain the compact line emitting regions. A hot, several thousand K, blackbody disc is consistent with the observations of HD 179218 and HD 141569. Magnetospheric accretion (MA) is able to reproduce the bulk of the Hα emission shown by HD 179218, confirming previous estimates from MA shock modelling with a mass accretion rate of 10â8 Mâ yrâ1, and an inclination to the line of sight between 30â and 50â. The Hα profile of HD 141569 cannot be fitted from MA due to the high rotational velocity of this object. Putting the CHARA sample together, a variety of scenarios is required to explain the Hα emission in HAeBe stars â compact or extended, discs, accretion, and winds â in agreement with previous BrÎł spectro-interferometric observations
Integrated optics for astronomical interferometry - VI. Coupling the light of the VLTI in K band
Our objective is to prove that integrated optics (IO) is not only a good
concept for astronomical interferometry but also a working technique with high
performance. We used the commissioning data obtained with the dedicated K-band
integrated optics two-telescope beam combiner which now replaces the fiber
coupler MONA in the VLTI/VINCI instrument. We characterize the behaviour of
this IO device and compare its properties to other single mode beam combiner
like the previously used MONA fiber coupler. The IO combiner provides a high
optical throughput, a contrast of 89% with a night-to-night stability of a few
percent. Even if a dispersive phase is present, we show that it does not bias
the measured Fourier visibility estimate. An upper limit of 0.005 for the
cross-talk between linear polarization states has been measured. We take
advantage of the intrinsic contrast stability to test a new astronomical
prodecure for calibrating diameters of simple stars by simultaneously fitting
the instrumental contrast and the apparent stellar diameters. This method
reaches an accuracy with diameter errors of the order of previous ones but
without the need of an already known calibrator. These results are an important
step of integrated optics and paves the road to incoming imaging interferometer
projects
Characterizing closure-phase measurements at IOTA
We are working towards imaging the surfaces and circumstellar envelopes of Mira stars in the near-infrared, using the IOTA interferometer and the IONIC integrated-optics 3-beam combiner. In order to study atmospheric structures of these stars, we installed 3 narrow-band filters that subdivide H-band into 3 roughly equal-width sub-bands - a central one for continuum, and 2 adjacent ones to sample Mira star's (mostly water) absorption-bands. We present here our characterization of the IOTA 3-Telescope interferometer for closure-phase measurements with broad and narrow-band filters in the H atmospheric window. This includes characterizing the stability, chromaticity, and polarization effects of the present IOTA optics with the IONIC beam-combiner, and characterizing the accuracy of our closure phase measurements
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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