329 research outputs found
Tomorrow optical interferometry: astrophysical prospects and instrumental issues
Interferometry has brought many new constraints in optical astronomy in the
recent years. A major leap in this field is the opening of large
interferometric facilities like the Very Large Telescope Interferometer and the
Keck Interferometer to the astronomical community. Planning for the future is
both easy --most specialists know in which directions to develop
interferometry-- and difficult because of the increasing complexity of the
technique. I present a short status of interferometry today. Then I detail the
possible astrophysical prospects. Finally I address some important instrumental
issues that are decisive for the future of interferometry.Comment: 8 pages, invited review at the "Visions in IR astronomy" conference
held in Paris, 21-23 March 200
Phase closure nulling of HD 59717 with AMBER/VLTI . Detection of the close faint companion
Aims: The detection of close and faint companions is an essential step in
many astrophysical fields, including the search for planetary companions. A new
method called "phase closure nulling" has been proposed for the detection of
such faint and close companions based on interferometric observations when the
system visibility amplitude is close to zero due to the large diameter of the
primary star. We aim at demonstrating this method by analyzing observations
obtained on the spectroscopic binary HD 59717. Methods: Using the AMBER/VLTI
instrument in the K-band with ~1500 spectral resolution, we record the
spectrally dispersed closures phases of the SB1 binary HD 59717 with a
three-baseline combination adequate for applying phase closure methods. After a
careful data reduction, we fit the primary diameter, the binary flux ratio, and
the separation using the phase closure data. Results: We detect the 5-mag
fainter companion of HD 59717 at a distance of 4 stellar radii from the
primary. We determine the diameter of the primary, infer the secondary's
spectral type and determine the masses and sizes of the stars in the binary
system. This is one of the highest contrasts detected by interferometry between
a companion and its parent star. Based on observations collected at the
European Southern Observatory, Paranal, Chile, within the commissioning
programme 60.A-9054(A)
Prospects for near-infrared characterisation of hot Jupiters with VSI
In this paper, we study the feasibility of obtaining near-infrared spectra of
bright extrasolar planets with the 2nd generation VLTI Spectro-Imager
instrument (VSI), which has the required angular resolution to resolve nearby
hot Extrasolar Giant Planets (EGPs) from their host stars. Taking into account
fundamental noises, we simulate closure phase measurements of several
extrasolar systems using four 8-m telescopes at the VLT and a low spectral
resolution (R = 100). Synthetic planetary spectra from T. Barman are used as an
input. Standard chi2-fitting methods are then used to reconstruct planetary
spectra from the simulated data. These simulations show that low-resolution
spectra in the H and K bands can be retrieved with a good fidelity for half a
dozen targets in a reasonable observing time (about 10 hours, spread over a few
nights). Such observations would strongly constrain the planetary temperature
and albedo, the energy redistribution mechanisms, as well as the chemical
composition of their atmospheres. Systematic errors, not included in our
simulations, could be a serious limitation to these performance estimations.
The use of integrated optics is however expected to provide the required
instrumental stability (around 10^-4 on the closure phase) to enable the first
thorough characterisation of extrasolar planetary emission spectra in the
near-infrared.Comment: 10 pages, 8 figures, Proc. SPIE conference 7013 "Optical and Infrared
Interferometry" (Marseille 2008
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
Monte-Carlo radiative transfer simulation of the circumstellar disk of the Herbig Ae star HD 144432
Studies of pre-transitional disks, with a gap region between the inner
infrared-emitting region and the outer disk, are important to improving our
understanding of disk evolution and planet formation. Previous infrared
interferometric observations have shown hints of a gap region in the
protoplanetary disk around the Herbig Ae star HD~144432. We study the dust
distribution around this star with two-dimensional radiative transfer modeling.
We compare the model predictions obtained via the Monte-Carlo radiative
transfer code RADMC-3D with infrared interferometric observations and the
{\SED} of HD~144432. The best-fit model that we found consists of an inner
optically thin component at 0.21\enDash0.32~\AU and an optically thick outer
disk at 1.4\enDash10~\AU. We also found an alternative model in which the
inner sub-AU region consists of an optically thin and an optically thick
component. Our modeling suggests an optically thin component exists in the
inner sub-AU region, although an optically thick component may coexist in the
same region. Our modeling also suggests a gap-like discontinuity in the disk of
HD~144432.Comment: 18 pages, 12 figure
Interferometric science results on young stellar objects
Long-baseline interferometry at infrared wavelengths allows the innermost
regions around young stars to be observed. These observations directly probe
the location of the dust and gas in the disks. The characteristic sizes of
these regions found are larger than previously thought. These results have
motivated in part a new class of models of the inner disk structure, but the
precise understanding of the origin of these low visibilities is still in
debate. Mid-infrared observations probe disk emission over a larger range of
scales revealing mineralogy gradients in the disk. Recent spectrally resolved
observations allow the dust and gas to be studied separately showing that the
Brackett gamma emission can find its origin either in a wind or in a
magnetosphere and that there is probably no correlation between the location of
the Brackett gamma emission and accretion. In a certain number of cases, the
very high spatial resolution reveals very close companions and can determine
their masses. Overall, these results provide essential information on the
structure and the physical properties of close regions surrounding young stars
especially where planet formation is suspected to occur.Comment: 18 pages, 6 figures, invited lecture at the VLTI school on
"Astrometry and Imaging with the Very Large Telescope Interferometer", 2-13
June 2008, Keszthely, Hungary. v2: typos corrected; v3: reference adde
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