257 research outputs found
A two-band approach to n phase error corrections with LBTI's PHASECam
PHASECam is the Large Binocular Telescope Interferometer's (LBTI) phase
sensor, a near-infrared camera which is used to measure tip/tilt and phase
variations between the two AO-corrected apertures of the Large Binocular
Telescope (LBT). Tip/tilt and phase sensing are currently performed in the H
(1.65 m) and K (2.2 m) bands at 1 kHz, and the K band phase telemetry
is used to send tip/tilt and Optical Path Difference (OPD) corrections to the
system. However, phase variations outside the range [-, ] are not
sensed, and thus are not fully corrected during closed-loop operation.
PHASECam's phase unwrapping algorithm, which attempts to mitigate this issue,
still occasionally fails in the case of fast, large phase variations. This can
cause a fringe jump, in which case the unwrapped phase will be incorrect by a
wavelength or more. This can currently be manually corrected by the observer,
but this is inefficient. A more reliable and automated solution is desired,
especially as the LBTI begins to commission further modes which require robust,
active phase control, including controlled multi-axial (Fizeau) interferometry
and dual-aperture non-redundant aperture masking interferometry. We present a
multi-wavelength method of fringe jump capture and correction which involves
direct comparison between the K band and currently unused H band phase
telemetry.Comment: 17 pages, 10 figure
Nulling interferometry: impact of exozodiacal clouds on the performance of future life-finding space missions
Earth-sized planets around nearby stars are being detected for the first time
by ground-based radial velocity and space-based transit surveys. This milestone
is opening the path towards the definition of missions able to directly detect
the light from these planets, with the identification of bio-signatures as one
of the main objectives. In that respect, both ESA and NASA have identified
nulling interferometry as one of the most promising techniques. The ability to
study distant planets will however depend on exozodiacal dust clouds
surrounding the target stars. In this paper, we assess the impact of
exozodiacal dust clouds on the performance of an infrared nulling
interferometer in the Emma X-array configuration. For the nominal mission
architecture with 2-m aperture telescopes, we found that point-symmetric
exozodiacal dust discs about 100 times denser than the solar zodiacal cloud can
be tolerated in order to survey at least 150 targets during the mission
lifetime. Considering modeled resonant structures created by an Earth-like
planet orbiting at 1 AU around a Sun-like star, we show that the tolerable dust
density for planet detection goes down to about 15 times the solar zodiacal
density for face-on systems and decreases with the disc inclination. The upper
limits on the tolerable exozodiacal dust density derived in this study must be
considered as rather pessimistic, but still give a realistic estimation of the
typical sensitivity that we will need to reach on exozodiacal discs in order to
prepare the scientific programme of future Earth-like planet characterisation
missions.Comment: 17 pages, accepted for publication in A&
First Light with ALES: A 2-5 Micron Adaptive Optics Integral Field Spectrograph for the LBT
Integral field spectrographs are an important technology for exoplanet
imaging, due to their ability to take spectra in a high-contrast environment,
and improve planet detection sensitivity through spectral differential imaging.
ALES is the first integral field spectrograph capable of imaging exoplanets
from 3-5m, and will extend our ability to characterize self-luminous
exoplanets into a wavelength range where they peak in brightness. ALES is
installed inside LBTI/LMIRcam on the Large Binocular Telescope, taking
advantage of existing AO systems, camera optics, and a HAWAII-2RG detector. The
new optics that comprise ALES are a Keplerian magnifier, a silicon lenslet
array with diffraction suppressing pinholes, a direct vision prism, and
calibration optics. All of these components are installed in filter wheels
making ALES a completely modular design. ALES saw first light at the LBT in
June 2015.Comment: 13 pages, 9 figures, Proc. SPI
Nulling Data Reduction and On-sky Performance of the Large Binocular Telescope Interferometer
The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5–13 μm). In this paper, we focus on the mid-infrared (8–13 μm) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star β Leo. This is equivalent to an exozodiacal disk density of 15–30 zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems
Precise radial velocities of giant stars IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system
Context: For over 12 yr, we have carried out a precise radial velocity survey
of a sample of 373 G and K giant stars using the Hamilton \'Echelle
Spectrograph at Lick Observatory. There are, among others, a number of multiple
planetary systems in our sample as well as several planetary candidates in
stellar binaries. Aims: We aim at detecting and characterizing
substellar+stellar companions to the giant star HD 59686 A (HR 2877, HIP
36616). Methods: We obtained high precision radial velocity (RV) measurements
of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in
the RVs, we can assess the nature of companions in the system. In order to
discriminate between RV variations due to non-radial pulsation or stellar spots
we used infrared RVs taken with the CRIRES spectrograph at the Very Large
Telescope. Additionally, to further characterize the system, we obtain
high-resolution images with LMIRCam at the Large Binocular Telescope. Results:
We report the likely discovery of a giant planet with a mass of orbiting at
au from the giant star HD 59686 A. Besides the planetary signal, we discover an
eccentric () binary companion with a mass of
orbiting at a semi-major axis
of just au. Conclusions: The existence of the
planet HD 59686 Ab in a tight eccentric binary system severely challenges
standard giant planet formation theories and requires substantial improvements
to such theories in tight binaries. Otherwise, alternative planet formation
scenarios such as second generation planets or dynamical interactions in an
early phase of the system's lifetime should be seriously considered in order to
better understand the origin of this enigmatic planet.Comment: 14 pages, 11 figures, 2 tables. Accepted for publication in A&A.
Updated version to match the published pape
Models of the η Corvi Debris Disk from the Keck Interferometer, Spitzer, and Herschel
Debris disks are signposts of analogs to small-body populations of the solar system, often, however, with much higher masses and dust production rates. The disk associated with the nearby star η Crv is especially striking, as it shows strong mid- and far-infrared excesses despite an age of ~1.4 Gyr. We undertake constructing a consistent model of the system that can explain a diverse collection of spatial and spectral data. We analyze Keck Interferometer Nuller measurements and revisit Spitzer and additional spectrophotometric data, as well as resolved Herschel images, to determine the dust spatial distribution in the inner exozodi and in the outer belt. We model in detail the two-component disk and the dust properties from the sub-AU scale to the outermost regions by fitting simultaneously all measurements against a large parameter space. The properties of the cold belt are consistent with a collisional cascade in a reservoir of ice-free planetesimals at 133 AU. It shows marginal evidence for asymmetries along the major axis. KIN enables us to establish that the warm dust consists of a ring that peaks between 0.2 and 0.8 AU. To reconcile this location with the ~400 K dust temperature, very high albedo dust must be invoked, and a distribution of forsterite grains starting from micron sizes satisfies this criterion, while providing an excellent fit to the spectrum. We discuss additional constraints from the LBTI and near-infrared spectra, and we present predictions of what James Webb Space Telescope can unveil about this unusual object and whether it can detect unseen planets
Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer
The Large Binocular Telescope Interferometer uses a near-infrared camera to
measure the optical path length variations between the two AO-corrected
apertures and provide high-angular resolution observations for all its science
channels (1.5-13 m). There is however a wavelength dependent component to
the atmospheric turbulence, which can introduce optical path length errors when
observing at a wavelength different from that of the fringe sensing camera.
Water vapor in particular is highly dispersive and its effect must be taken
into account for high-precision infrared interferometric observations as
described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this
paper, we describe the new sensing approach that has been developed at the LBT
to measure and monitor the optical path length fluctuations due to dry air and
water vapor separately. After reviewing the current performance of the system
for dry air seeing compensation, we present simultaneous H-, K-, and N-band
observations that illustrate the feasibility of our feedforward approach to
stabilize the path length fluctuations seen by the LBTI nuller.Comment: SPIE conference proceeding
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