79 research outputs found
Methods for multiple telescope beam imaging and guiding in the near infrared
Atmospheric turbulence and precise measurement of the astrometric baseline
vector between any two telescopes are two major challenges in implementing
phase referenced interferometric astrometry and imaging. They limit the
performance of a fibre-fed interferometer by degrading the instrument
sensitivity and astrometric measurements precision and by introducing image
reconstruction errors due to inaccurate phases. A multiple beam acquisition and
guiding camera was built to meet these challenges for a recently commissioned
four beam combiner instrument, GRAVITY, at the ESO Very Large Telescope
Interferometer. For each telescope beam it measures: a) field tip-tilts by
imaging stars in the sky; b) telescope pupil shifts by imaging pupil reference
laser beacons installed on each telescope using a lenslet; c)
higher order aberrations using a Shack-Hartmann. The telescope
pupils are imaged for a visual monitoring while observing. These measurements
enable active field and pupil guiding by actuating a train of tip-tilt mirrors
placed in the pupil and field planes, respectively. The Shack-Hartmann measured
quasi-static aberrations are used to focus the Auxiliary Telescopes and allow
the possibility of correcting the non-common path errors between the Unit
Telescopes adaptive optics systems and GRAVITY. The guiding stabilizes light
injection into single-mode fibres, increasing sensitivity and reducing the
astrometric and image reconstruction errors. The beam guiding enables to
achieve astrometric error less than as. Here, we report on the data
reduction methods and laboratory tests of the multiple beam acquisition and
guiding camera and its performance on-sky.Comment: 12 pages, 20 figures and 7 tables. Accepted for publication in MNRA
Methods for multiple-telescope beam imaging and guiding in the near-infrared
This is the final version. Available from OUP via the DOI in this recordAtmospheric turbulence and precise measurement of the astrometric baseline vector between any two telescopes are two major challenges in implementing phase-referenced interferometric astrometry and imaging. They limit the performance of a fibre-fed interferometer by degrading the instrument sensitivity and the precision of astrometric measurements and by introducing image reconstruction errors due to inaccurate phases. A multiple-beam acquisition and guiding camera was built to meet these challenges for a recently commissioned four-beam combiner instrument, GRAVITY, at the European Southern Observatory Very Large Telescope Interferometer. For each telescope beam, it measures (a) field tip-tilts by imaging stars in the sky, (b) telescope pupil shifts by imaging pupil reference laser beacons installed on each telescope using a 2×2 lenslet and (c) higher-order aberrations using a 9 ×9 Shack-Hartmann. The telescope pupils are imaged to provide visual monitoring while observing. These measurements enable active field and pupil guiding by actuating a train of tip-tilt mirrors placed in the pupil and field planes, respectively. The Shack-Hartmann measured quasi-static aberrations are used to focus the auxiliary telescopes and allow the possibility of correcting the non-common path errors between the adaptive optics systems of the unit telescopes and GRAVITY. The guiding stabilizes the light injection into single-mode fibres, increasing sensitivity and reducing the astrometric and image reconstruction errors. The beam guiding enables us to achieve an astrometric error of less than 50 μas. Here, we report on the data reduction methods and laboratory tests of the multiple-beam acquisition and guiding camera and its performance on-sky.Fundação para a Ciência e a TecnologiaEuropean Commissio
First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e
To date, infrared interferometry at best achieved contrast ratios of a few
times on bright targets. GRAVITY, with its dual-field mode, is now
capable of high contrast observations, enabling the direct observation of
exoplanets. We demonstrate the technique on HR8799, a young planetary system
composed of four known giant exoplanets. We used the GRAVITY fringe tracker to
lock the fringes on the central star, and integrated off-axis on the HR8799e
planet situated at 390 mas from the star. Data reduction included
post-processing to remove the flux leaking from the central star and to extract
the coherent flux of the planet. The inferred K band spectrum of the planet has
a spectral resolution of 500. We also derive the astrometric position of the
planet relative to the star with a precision on the order of 100as. The
GRAVITY astrometric measurement disfavors perfectly coplanar stable orbital
solutions. A small adjustment of a few degrees to the orbital inclination of HR
8799 e can resolve the tension, implying that the orbits are close to, but not
strictly coplanar. The spectrum, with a signal-to-noise ratio of
per spectral channel, is compatible with a late-type L brown dwarf. Using
Exo-REM synthetic spectra, we derive a temperature of \,K and a
surface gravity of cm/s. This corresponds to a radius
of and a mass of , which is an independent confirmation of mass estimates from evolutionary
models. Our results demonstrate the power of interferometry for the direct
detection and spectroscopic study of exoplanets at close angular separations
from their stars.Comment: published in A&
Dynamical masses of the primary Be star and the secondary sdB star in the single-lined binary kappa Dra (B6 IIIe)
Because many classical Be stars may owe their nature to mass and
angular-momentum transfer in a close binary, the present masses, temperatures,
and radii of their components are of high interest for comparison to stellar
evolution models. Kappa Dra is a 61.5-day single-lined binary with a B6 IIIe
primary. With the CHARA Array instruments MIRC/MIRC-X and MYSTIC, we detected
the secondary at (approximately photospheric) flux ratios of 1.49 +- 0.10% and
1.63 +- 0.09% in the H and K band, respectively. From a large and diverse
optical spectroscopic database only the radial velocity curve of the Be star
could be extracted. However, employing the parallaxes from Hipparcos and Gaia,
which agree within their nominal 1-sigma errors, we could derive the total mass
and found component masses of 3.65 +- 0.48 Msun and 0.426 +- 0.043 Msun for the
Be star and the companion, respectively. Previous cross-correlation of the
observed far-UV spectrum with sdO spectral model templates had not detected a
companion belonging to the hot O-type subdwarf (sdO) population known from ~20
earlier-type Be stars. Guided by our full 3D orbital solution, we found a
strong cross-correlation signal for a stripped subdwarf B-type companion
(far-UV flux ratio of 2.3 +- 0.5%), enabling the first firm characterization of
such a star, and making kappa Dra the first mid- to late-type Be star with a
directly-observed subdwarf companion.Comment: Accepted to ApJ. Figure sets available on reques
Submilliarcsecond Optical Interferometry of the High-mass X-Ray Binary BP Cru with VLTI/GRAVITY
This is the final version. Available from American Astronomical Society via the DOI in this recordWe observe the high-mass X-ray binary (HMXB) BP Cru using interferometry in the near-infrared K band with VLTI/GRAVITY. Continuum visibilities are at most partially resolved, consistent with the predicted size of the hypergiant. Differential visibility amplitude () and phase () signatures are observed across the He i and Brγ lines, the latter seen strongly in emission, unusual for the donor star's spectral type. For a baseline m, the differential phase rms corresponds to an astrometric precision of . We generalize expressions for image centroid displacements and variances in the marginally resolved limit of interferometry to spectrally resolved data, and use them to derive model-independent properties of the emission such as its asymmetry, extension, and strong wavelength dependence. We propose geometric models based on an extended and distorted wind and/or a high-density gas stream, which has long been predicted to be present in this system. The observations show that optical interferometry is now able to resolve HMXBs at the spatial scale where accretion takes place, and therefore to probe the effects of the gravitational and radiation fields of the compact object on its environment
A thesis to probe unique exoplanet regimes with micro-arcsecond astrometry and precision closure phases at CHARA and VLTI
This is the final version. Available from SPIE via the DOI in this recordSPIE Astronomical Telescopes + Instrumentation 2022, 17 - 22 July 2022, Montreal, CanadaIn this thesis work, we exploit the unique capabilities of long baseline interferometry to fill two gaps in exoplanet parameter space: 1) the discovery of new planets around stars more massive than the Sun (Project ARMADA), and 2) the characterization of known planets that are extremely close to their host star (Project PRIME). Current detection methods struggle to find exoplanets around hot (A/B-type) stars. We are pushing the astrometric limits of ground-based optical interferometers to carry out a survey of sub-arcsecond A/B-type binary systems with ARMADA. We are achieving astrometric precision at the few tens of micro-arcsecond level in short observations at CHARA/MIRC-X and VLTI/GRAVITY. This incredible precision allows us to probe the au-regime for giant planets orbiting individual stars of the binary system. We present the status of our survey, including our newly implemented etalon wavelength calibration method at CHARA, detection of new stellar mass companions, and non-detection limits down to a few Jupiter masses in some cases. With Project PRIME, we show that ground-based optical interferometry can be used to measure the orbit-dependent spectra of close-in “hot Jupiter”-type exoplanets with precision closure phases. Detecting the infrared spectra of such planets allows us to place useful constraints on atmosphere circulation models. We perform injection tests with MIRC-X and MYSTIC at CHARA for the hot Jupiter exoplanet Ups And b to show that we are reaching down to a contrast of 2e-4. The promise of both these methods demonstrate that optical interferometers are a valuable tool for probing unique regimes of exoplanet science.NASANational Science Foundation (NSF)European Research Council (ERC)Science and Technology Facilities Council (STFC)European Union Horizon 202
Interferometric detections of sdO companions orbiting three classical Be stars
This is the final version. Available from IOP Publishing via the DOI in this record. Classical Be stars are possible products of close binary evolution, in which the mass donor becomes a hot, stripped O- or B-type subdwarf (sdO/sdB), and the mass gainer spins up and grows a disk to become a Be star. While several Be+sdO binaries have been identified, dynamical masses and other fundamental parameters are available only for a single Be+sdO system, limiting the confrontation with binary evolution models. In this work, we present direct interferometric detections of the sdO companions of three Be stars - 28 Cyg, V2119 Cyg, and 60 Cyg - all of which were previously found in UV spectra. For two of the three Be+sdO systems, we present first orbits and preliminary dynamical masses of the components, revealing that one of them could be the first identified progenitor of a Be/X-ray binary with a neutron star companion. These results provide new sets of fundamental parameters that are crucially needed to establish the evolutionary status and origin of Be stars.European Research CouncilNational Science FoundationSTFC studentshipGeorgia State Universit
A dusty veil shading Betelgeuse during its Great Dimming
This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this record.Data availability:
Raw data were generated at the ESO under programs 0102.D-0240(A), 0102.D-0240(D), 104.20UZ and 104.20V6.004. Derived data that support the findings of this study are available at the Centre de Données Astronomiques de Strasbourg (CDS) via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/other/Nat (for the VLT/SPHERE–ZIMPOL images) and at the Optical Interferometry Database (OiDB; for the VLTI/GRAVITY and VLT/SPHERE–IRDIS SAM observations). Source data are provided with this paper.The SPHERE and GRAVITY pipelines are available on the ESO website: http://www.eso.org/sci/software/
pipelines/index.html. The RADMC3D code is publicly available online: https://github.com/dullemond/
radmc3d-2.0Code availability:
The SPHERE and GRAVITY pipelines are available on the ESO website (http://www.eso.org/sci/software/pipelines/index.html). The PyRAF implementation of the Richardson–Lucy deconvolution algorithm is publicly available at https://astroconda.readthedocs.io/en/latest/. The RADMC3D code is publicly available at https://github.com/dullemond/radmc3d-2.0.Red supergiants represent the most common final stage of the evolution of stars with initial masses between 8 and 30-35
times the mass of the Sun. During this phase of lifetime lasting ≈ 105 yrs, they experience substantial mass loss of unknown
mechanism. This mass loss can affect their evolutionary path, collapse, future supernova light curve, and ultimate fate as a
neutron star or a black hole. From November 2019 to March 2020, the second closest red supergiant (RSG, 222+48
−34 pc) Betelgeuse experienced a historic dimming of its visible brightness, witnessed worldwide. Usually between 0.1 and 1.0 mag, it
went down to 1.614±0.008 mag around 7-13 February 2020. Here we report high angular resolution observations showing
that the southern hemisphere of the star was ten times darker than usual in the visible. Observations and modeling support
the scenario of a dust clump recently formed in the vicinity of the star due to a local temperature decrease in a cool patch
appearing on the photosphere. The directly imaged brightness variations of Betelgeuse evolved on a timescale of weeks. This
event suggests that an inhomogeneous component of red supergiant mass loss is linked to a very contrasted and rapidly
changing photosphere.European Research Council (ERC)European Union Horizon 2020Foundation FlandersKU LeuvenNAS
CHARA array adaptive optics: Complex operational software and performance
This is the final version. Available from SPIR via the DOI in this recordSPIE Astronomical Telescopes + Instrumentation conference, 14 - 18 December 2020, Online OnlyThe CHARA Array is the longest baseline optical interferometer in the world. Operated with natural seeing, it has delivered landmark sub-milliarcsecond results in the areas of stellar imaging, binaries, and stellar diameters. However, to achieve ambitious observations of faint targets such as young stellar objects and active galactic nuclei, higher sensitivity is required. For that purpose, adaptive optics are developed to correct atmospheric turbulence and non-common path aberrations between each telescope and the beam combiner lab. This paper describes the AO software and its integration into the CHARA system. We also report initial on-sky tests that demonstrate an increase of scientific throughput by sensitivity gain and by extending useful observing time in worse seeing conditions. Our 6 telescopes and 12 AO systems with tens of critical alignments and control loops pose challenges in operation. We describe our methods enabling a single scientist to operate the entire system.GSU College of Arts and SciencesGSU Office of the Vice President for Research and Economic Developmen
Progress of the CHARA/SPICA project
This is the final version. Available from SPIE via the DOI in this recordSPIE Astronomical Telescopes + Instrumentation conference, 14 - 18 December 2020, Online OnlyCHARA/SPICA (Stellar Parameters and Images with a Cophased Array) is currently being developed at Observatoire de la Cote d'Azur. It will be installed at the visible focus of the CHARA Array by the end of 2021. It has been designed to perform a large survey of fundamental stellar parameters with, in the possible cases, a detailed imaging of the surface or environment of stars. To reach the required precision and sensitivity, CHARA/SPICA combines a low spectral resolution mode R = 140 in the visible and single-mode fibers fed by the AO stages of CHARA. This setup generates additional needs before the interferometric combination: the compensation of atmospheric refraction and longitudinal dispersion, and the fringe stabilization. In this paper, we present the main features of the 6-telescopes fibered visible beam combiner (SPICA-VIS) together with the first laboratory and on-sky results of the fringe tracker (SPICA-FT). We describe also the new fringe-tracker simulator developed in parallel to SPICA-FT.National Science Foundation (NSF)GSU College of Arts and SciencesGSU Office of the Vice President for Research and Economic DevelopmentEuropean Union Horizon 2020Onera’s Direction Scientifique General
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