43 research outputs found
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
Infrared Imaging of Capella with the IOTA Closure Phase Interferometer
We present infrared aperture synthesis maps produced with the upgraded IOTA
interferometer. Michelson interferograms on the close binary system Capella
(Alpha Aur) were obtained in the H-band between 2002 November 12 and 16 using
the IONIC3 beam combiner. With baselines of 15m < B < 38m, we were able to
determine the relative position of the binary components with milliarcsecond
(mas) precision and to track their movement along the approx. 14 degree arc
covered by our observation run. We briefly describe the algorithms used for
visibility and closure phase estimation. Three different Hybrid Mapping and
Bispectrum Fitting techniques were implemented within one software framework
and used to reconstruct the source brightness distribution. By dividing our
data into subsets, the system could be mapped at three epochs, revealing the
motion of the stars. The precise position of the binary components was also
determined with model fits, which in addition revealed I_Aa/I_Ab=1.49 +/- 0.10
and apparent stellar uniform-disk (UD) diameters of Theta_Aa=8.9 +/- 0.6 mas
and Theta_Ab=5.8 +/- 0.8 mas.
To improve the u, v-plane coverage, we compensated this orbital motion by
applying a rotation-compensating coordinate transformation. The resulting
model-independent map with a beam size of 5.4 x 2.6 mas allows the resolution
of the stellar surfaces of the Capella giants themselves.Comment: Accepted by the Astronomical Journal (2005-03-21
Mid-infrared laser light nulling experiment using single-mode conductive waveguides
Aims: In the context of space interferometry missions devoted to the search
of exo-Earths, this paper investigates the capabilities of new single mode
conductive waveguides at providing modal filtering in an infrared and
monochromatic nulling experiment; Methods: A Michelson laser interferometer
with a co-axial beam combination scheme at 10.6 microns is used. After
introducing a Pi phase shift using a translating mirror, dynamic and static
measurements of the nulling ratio are performed in the two cases where modal
filtering is implemented and suppressed. No additional active control of the
wavefront errors is involved. Results: We achieve on average a statistical
nulling ratio of 2.5e-4 with a 1-sigma upper limit of 6e-4, while a best null
of 5.6e-5 is obtained in static mode. At the moment, the impact of external
vibrations limits our ability to maintain the null to 10 to 20 seconds.;
Conclusions: A positive effect of SM conductive waveguide on modal filtering
has been observed in this study. Further improvement of the null should be
possible with proper mechanical isolation of the setup.Comment: Accepted in A&A, 7 pages, 5 figure
First astronomical unit scale image of the GW Ori triple. Direct detection of a new stellar companion
Young and close multiple systems are unique laboratories to probe the initial
dynamical interactions between forming stellar systems and their dust and gas
environment. Their study is a key building block to understanding the high
frequency of main-sequence multiple systems. However, the number of detected
spectroscopic young multiple systems that allow dynamical studies is limited.
GW Orionis is one such system. It is one of the brightest young T Tauri stars
and is surrounded by a massive disk. Our goal is to probe the GW Orionis
multiplicity at angular scales at which we can spatially resolve the orbit. We
used the IOTA/IONIC3 interferometer to probe the environment of GW Orionis with
an astronomical unit resolution in 2003, 2004, and 2005. By measuring squared
visibilities and closure phases with a good UV coverage we carry out the first
image reconstruction of GW Ori from infrared long-baseline interferometry. We
obtain the first infrared image of a T Tauri multiple system with astronomical
unit resolution. We show that GW Orionis is a triple system, resolve for the
first time the previously known inner pair (separation 1.4 AU) and
reveal a new more distant component (GW Ori C) with a projected separation of
8 AU with direct evidence of motion. Furthermore, the nearly equal (2:1)
H-band flux ratio of the inner components suggests that either GW Ori B is
undergoing a preferential accretion event that increases its disk luminosity or
that the estimate of the masses has to be revisited in favour of a more equal
mass-ratio system that is seen at lower inclination. Accretion disk models of
GW Ori will need to be completely reconsidered because of this outer companion
C and the unexpected brightness of companion B.Comment: 5 pages, 9 figures, accepted Astronomy and Astrophysics Letters. 201
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
Few Skewed Disks Found in First Closure-Phase Survey of Herbig Ae/Be stars
Using the 3-telescope IOTA interferometer on Mt. Hopkins, we report results
from the first near-infrared (lambda=1.65 mu) closure-phase survey of Young
Stellar Objects (YSOs). These closure phases allow us to unambiguously detect
departures from centrosymmetry (i.e., skew) in the emission pattern from YSO
disks on the scale of ~4 milliarcseconds, expected from generic ``flared disk''
models. Six of fourteen targets showed small, yet statistically-significant,
non-zero closure phases, with largest values from the young binary system MWC
361-A and the (pre-main sequence?) Be star HD 45677. Our observations are quite
sensitive to the vertical structure of the inner disk and we confront the
predictions of the ``puffed-up inner wall'' models of Dullemond, Dominik, and
Natta (DDN). Our data support disks models with curved inner rims because the
expected emission appear symmetrically-distributed around the star over a wide
range of inclination angles. In contrast, our results are incompatible with the
models possessing vertical inner walls because they predict extreme skewness
(i.e., large closure phases) from the near-IR disk emission that is not seen in
our data. In addition, we also present the discovery of mysterious H-band
``halos'' (~5-10% of light on scales 0.01-0.50 arcsec) around a few objects, a
preliminary ``parametric imaging'' study for HD 45677, and the first
astrometric orbit for the young binary MWC 361-A.Comment: Accepted for publication in Astrophysical Journa
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
Increasing the imaging capabilities of the VLTI using integrated optics
Several scientific topics linked to the observation of extended structures around astrophysical sources (dust torus around AGN, disks around young stars, envelopes around AGBs) require imaging capability with milli-arcsecond spatial resolution. The current VLTI instruments, AMBER and MIDI, will provide in the coming months the required high angular resolution, yet without actual imaging. As a rule of thumb, the image quality accessible with an optical interferometer is directly related to the number of telescopes used simultaneously: the more the apertures, the better and the faster the reconstruction of the image. We propose an instrument concept to achieve interferometric combination of N telescopes (4 ≤ N ≤ 8) thanks to planar optics technology: 4 x 8-m telescopes in the short term and/or 8 x 1.8-m telescopes in the long term. The foreseen image reconstruction quality in the visible and/or in the near infrared will be equivalent to the one achieved with millimeter radio interferometers. Achievable spatial resolution will be better than the one foreseen with ALMA. This instrument would be able to acquire routinely 1 mas resolution images. A 13 to 20 magnitude sensitivity in spectral ranges from 0.6 to 2.5 μm is expected depending on the choice of the phase referencing guide source. High dynamic range, even on faint objects, is achievable thanks to the high accuracy provided by integrated optics for visibility amplitude and phase measurements. Based on recent validations of integrated optics presented here an imaging instrument concept can be proposed. The results obtained using the VLTI facilities give a demonstration of the potential of the proposed technique
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