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  • Kervella, P.  (36)
  • Sturm, E.  (36)
  • 1
    Online Resource
    Online Resource
    First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer
    EDP Sciences ; 2017
    In:  Astronomy & Astrophysics Vol. 602 ( 2017-6), p. A94-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 602 ( 2017-6), p. A94-
    Abstract: GRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular resolution and a collecting area of 200 m 2 . The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual-beam operation, and laser metrology. GRAVITY opens up to optical/infrared interferometry the techniques of phase referenced imaging and narrow angle astrometry, in many aspects following the concepts of radio interferometry. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase-tracking on stars as faint as m K ≈ 10 mag, phase-referenced interferometry of objects fainter than m K ≈ 15 mag with a limiting magnitude of m K ≈ 17 mag, minute long coherent integrations, a visibility accuracy of better than 0.25%, and spectro-differential phase and closure phase accuracy better than 0.5°, corresponding to a differential astrometric precision of better than ten microarcseconds ( μ as). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 μ as when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the  Galactic center supermassive black hole and its fast orbiting star S2 for phase referenced dual-beam observations and infrared wavefront sensing, the high mass X-ray binary BP Cru and the active galactic nucleus of PDS 456 for a few μ as spectro-differential astrometry, the T Tauri star S CrA for a spectro-differential visibility analysis, ξ  Tel and 24 Cap for high accuracy visibility observations, and η Car for interferometric imaging with GRAVITY.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201730838
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2017
    detail.hit.zdb_id: 1458466-9
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  • 2
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    GRAVITY chromatic imaging of η Car’s core : Milliarcsecond resolution imaging of the wind-wind collision zone (Br γ , He I)
    EDP Sciences ; 2018
    In:  Astronomy & Astrophysics Vol. 618 ( 2018-10), p. A125-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 618 ( 2018-10), p. A125-
    Abstract: Context . η Car is one of the most intriguing luminous blue variables in the Galaxy. Observations and models of the X-ray, ultraviolet, optical, and infrared emission suggest a central binary in a highly eccentric orbit with a 5.54 yr period residing in its core. 2D and 3D radiative transfer and hydrodynamic simulations predict a primary with a dense and slow stellar wind that interacts with the faster and lower density wind of the secondary. The wind-wind collision scenario suggests that the secondary’s wind penetrates the primary’s wind creating a low-density cavity in it, with dense walls where the two winds interact. However, the morphology of the cavity and its physical properties are not yet fully constrained. Aims . We aim to trace the inner ∼5–50 au structure of η Car’s wind-wind interaction, as seen through Br γ and, for the first time, through the He  I 2s-2p line. Methods . We have used spectro-interferometric observations with the K -band beam-combiner GRAVITY at the VLTI. The analyses of the data include (i) parametrical model-fitting to the interferometric observables, (ii) a CMFGEN model of the source’s spectrum, and (iii) interferometric image reconstruction. Results . Our geometrical modeling of the continuum data allows us to estimate its FWHM angular size close to 2 mas and an elongation ratio ϵ = 1.06 ± 0.05 over a PA = 130° ± 20°. Our CMFGEN modeling of the spectrum helped us to confirm that the role of the secondary should be taken into account to properly reproduce the observed Br γ and He  I lines. Chromatic images across the Br γ line reveal a southeast arc-like feature, possibly associated to the hot post-shocked winds flowing along the cavity wall. The images of the He  I 2s-2p line served to constrain the 20 mas (∼50 au) structure of the line-emitting region. The observed morphology of He  I suggests that the secondary is responsible for the ionized material that produces the line profile. Both the Br γ and the He  I 2s-2p maps are consistent with previous hydrodynamical models of the colliding wind scenario. Future dedicated simulations together with an extensive interferometric campaign are necessary to refine our constraints on the wind and stellar parameters of the binary, which finally will help us predict the evolutionary path of η Car.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201832977
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2018
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 3
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    First light for GRAVITY Wide : Large separation fringe tracking for the Very Large Telescope Interferometer
    EDP Sciences ; 2022
    In:  Astronomy & Astrophysics Vol. 665 ( 2022-9), p. A75-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 665 ( 2022-9), p. A75-
    Abstract: GRAVITY+ is the upgrade for GRAVITY and the Very Large Telescope Interferometer (VLTI) with wide-separation fringe tracking, new adaptive optics, and laser guide stars on all four 8 m Unit Telescopes (UTs) to enable ever-fainter, all-sky, high-contrast, milliarcsecond interferometry. Here we present the design and first results of the first phase of GRAVITY+, known as GRAVITY Wide. GRAVITY Wide combines the dual-beam capabilities of the VLTI and the GRAVITY instrument to increase the maximum separation between the science target and the reference star from 2 arcseconds with the 8 m UTs up to several 10 arcseconds, limited only by the Earth’s turbulent atmosphere. This increases the sky-coverage of GRAVITY by two orders of magnitude, opening up milliarcsecond resolution observations of faint objects and, in particular, the extragalactic sky. The first observations in 2019–2022 include the first infrared interferometry of two redshift z ~ 2 quasars, interferometric imaging of the binary system HD 105913A, and repeat observations of multiple star systems in the Orion Trapezium Cluster. We find the coherence loss between the science object and fringe-tracking reference star well described by the turbulence of the Earth’s atmosphere. We confirm that the larger apertures of the UTs result in higher visibilities for a given separation due to the broader overlap of the projected pupils on the sky and provide predictions for visibility loss as a function of separation to be used for future planning.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202243941
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2022
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 4
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    First direct detection of an exoplanet by optical interferometry : Astrometry and K -band spectroscopy of HR 8799 e
    EDP Sciences ; 2019
    In:  Astronomy & Astrophysics Vol. 623 ( 2019-03), p. L11-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 623 ( 2019-03), p. L11-
    Abstract: Aims . To date, infrared interferometry at best achieved contrast ratios of a few times 10 −4 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 HR 8799, a young planetary system composed of four known giant exoplanets. Methods . We used the GRAVITY fringe tracker to lock the fringes on the central star, and integrated off-axis on the HR 8799 e 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 100  μ as. Results . 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 ≈5 per spectral channel, is compatible with a late-type L brown dwarf. Using Exo-REM synthetic spectra, we derive a temperature of 1150 ± 50 K and a surface gravity of 10 4.3 ± 0.3  cm s 2 . This corresponds to a radius of 1.17 −0.11 +0.13 R Jup and a mass of 10 −4 +7 M Jup , 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.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201935253
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2019
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 5
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    GRAVITY K -band spectroscopy of HD 206893 B : Brown dwarf or exoplanet
    EDP Sciences ; 2021
    In:  Astronomy & Astrophysics Vol. 652 ( 2021-8), p. A57-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 652 ( 2021-8), p. A57-
    Abstract: Context. Near-infrared interferometry has become a powerful tool for studying the orbital and atmospheric parameters of substellar companions. Aims. We aim to reveal the nature of the reddest known substellar companion HD 206893 B by studying its near-infrared colors and spectral morphology and by investigating its orbital motion. Methods. We fit atmospheric models for giant planets and brown dwarfs and perform spectral retrievals with petitRADTRANS and ATMO on the observed GRAVITY, SPHERE, and GPI spectra of HD 206893 B. To recover its unusual spectral features, first and foremost its extremely red near-infrared color, we include additional extinction by high-altitude dust clouds made of enstatite grains in the atmospheric model fits. However, forsterite, corundum, and iron grains predict similar extinction curves for the grain sizes considered here. We also infer the orbital parameters of HD 206893 B by combining the ~100 μas precision astrometry from GRAVITY with data from the literature and constrain the mass and position of HD 206893 C based on the Gaia proper motion anomaly of the system. Results. The extremely red color and the very shallow 1.4 μm water absorption feature of HD 206893 B can be fit well with the adapted atmospheric models and spectral retrievals. By comparison with AMES-Cond evolutionary tracks, we find that only some atmosphericmodels predict physically plausible objects. Altogether, our analysis suggests an age of ~ 3–300 Myr and a mass of ~ 5–30  M Jup for HD 206893 B, which is consistent with previous estimates but extends the parameter space to younger and lower-mass objects. The GRAVITY astrometry points to an eccentric orbit ( e  = 0.29 −0.11 +0.06 ) with a mutual inclination of 〈 34.4 deg with respectto the debris disk of the system. Conclusions. While HD 206893 B could in principle be a planetary-mass companion, this possibility hinges on the unknown influence of the inner companion on the mass estimate of 10 −4 +5   M Jup from radial velocity and Gaia as well as a relatively small but significant Argus moving group membership probability of ~ 61%. However, we find that if the mass of HD 206893 B is 〈 30  M Jup , then the inner companion HD 206893 C should have a mass between ~ 8–15  M Jup . Finally, further spectroscopic or photometric observations at higher signal-to-noise and longer wavelengths are required to learn more about the composition and dust cloud properties of HD 206893 B.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202140749
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 1458466-9
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  • 6
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    Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY ∗
    American Astronomical Society ; 2021
    In:  The Astronomical Journal Vol. 161, No. 3 ( 2021-03-01), p. 148-
    Details
    In: The Astronomical Journal, American Astronomical Society, Vol. 161, No. 3 ( 2021-03-01), p. 148-
    Abstract: We present K -band interferometric observations of the PDS 70 protoplanets along with their host star using VLTI/GRAVITY. We obtained K -band spectra and 100 μ as precision astrometry of both PDS 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. Rejecting unstable orbits, we found a nonzero eccentricity for PDS 70 b of 0.17 ± 0.06, a near-circular orbit for PDS 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. Enforcing dynamical stability, we obtained a 95% upper limit on the mass of PDS 70 b of 10 M Jup , while the mass of PDS 70 c was unconstrained. The GRAVITY K -band spectra rules out pure blackbody models for the photospheres of both planets. Instead, the models with the most support from the data are planetary atmospheres that are dusty, but the nature of the dust is unclear. Any circumplanetary dust around these planets is not well constrained by the planets’ 1–5 μ m spectral energy distributions (SEDs) and requires longer wavelength data to probe with SED analysis. However with VLTI/GRAVITY, we made the first observations of a circumplanetary environment with sub-astronomical-unit spatial resolution, placing an upper limit of 0.3 au on the size of a bright disk around PDS 70 b.
    Type of Medium: Online Resource
    ISSN: 0004-6256 , 1538-3881
    URL: Article
    DOI: 10.3847/1538-3881/abdb2d
    RVK:
    US 1090
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207625-6
    detail.hit.zdb_id: 2003104-X
    SSG: 16,12
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  • 7
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    Direct confirmation of the radial-velocity planet β Pictoris c
    EDP Sciences ; 2020
    In:  Astronomy & Astrophysics Vol. 642 ( 2020-10), p. L2-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 642 ( 2020-10), p. L2-
    Abstract: Context. Methods used to detect giant exoplanets can be broadly divided into two categories: indirect and direct. Indirect methods are more sensitive to planets with a small orbital period, whereas direct detection is more sensitive to planets orbiting at a large distance from their host star. This dichotomy makes it difficult to combine the two techniques on a single target at once. Aims. Simultaneous measurements made by direct and indirect techniques offer the possibility of determining the mass and luminosity of planets and a method of testing formation models. Here, we aim to show how long-baseline interferometric observations guided by radial-velocity can be used in such a way. Methods. We observed the recently-discovered giant planet β Pictoris c with GRAVITY, mounted on the Very Large Telescope Interferometer. Results. This study constitutes the first direct confirmation of a planet discovered through radial velocity. We find that the planet has a temperature of T  = 1250 ± 50 K and a dynamical mass of M  = 8.2 ± 0.8  M Jup . At 18.5 ± 2.5 Myr, this puts β Pic c close to a ‘hot start’ track, which is usually associated with formation via disk instability. Conversely, the planet orbits at a distance of 2.7 au, which is too close for disk instability to occur. The low apparent magnitude ( M K  = 14.3 ± 0.1) favours a core accretion scenario. Conclusions. We suggest that this apparent contradiction is a sign of hot core accretion, for example, due to the mass of the planetary core or the existence of a high-temperature accretion shock during formation.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202039039
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2020
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 8
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    The wind and the magnetospheric accretion onto the T Tauri star S Coronae Australis at sub-au resolution
    EDP Sciences ; 2017
    In:  Astronomy & Astrophysics Vol. 608 ( 2017-12), p. A78-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 608 ( 2017-12), p. A78-
    Abstract: Aims. To investigate the inner regions of protoplanetary discs, we performed near-infrared interferometric observations of the classical T Tauri binary system S CrA. Methods. We present the first VLTI-GRAVITY high spectral resolution ( R ~ 4000) observations of a classical T Tauri binary, S CrA (composed of S CrA N and S CrA S and separated by ~1.̋4), combining the four 8m telescopes in dual-field mode. Results. Our observations in the near-infrared K -band continuum reveal a disc around each binary component, with similar half-flux radii of about 0.1 au at d ~ 130 pc, inclinations ( i = 28 ± 3° and i = 22 ± 6°), and position angles (PA = 0°± 6° and PA = –2°± 12°), suggesting that they formed from the fragmentation of a common disc. The S CrA N spectrum shows bright He  i and Br γ line emission exhibiting inverse P Cygni profiles, typically associated with infalling gas. The continuum-compensated Br γ line visibilities of S CrA N show the presence of a compact Br γ emitting region whose radius is about ~0.06 au, which is twice as big as the truncation radius. This component is mostly tracing a wind. Moreover, a slight radius change between the blue- and red-shifted Br γ line components is marginally detected. Conclusions. The presence of an inverse P Cygni profile in the He  i and Br γ lines, along with the tentative detection of a slightly larger size of the blue-shifted Br γ line component, hint at the simultaneous presence of a wind and magnetospheric accretion in S CrA N.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201731058
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2017
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 9
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    Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
    EDP Sciences ; 2018
    In:  Astronomy & Astrophysics Vol. 615 ( 2018-07), p. L15-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 615 ( 2018-07), p. L15-
    Abstract: The highly elliptical, 16-year-period orbit of the star S2 around the massive black hole candidate Sgr A ✻ is a sensitive probe of the gravitational field in the Galactic centre. Near pericentre at 120 AU ≈ 1400 Schwarzschild radii, the star has an orbital speed of ≈7650 km s −1 , such that the first-order effects of Special and General Relativity have now become detectable with current capabilities. Over the past 26 years, we have monitored the radial velocity and motion on the sky of S2, mainly with the SINFONI and NACO adaptive optics instruments on the ESO Very Large Telescope, and since 2016 and leading up to the pericentre approach in May 2018, with the four-telescope interferometric beam-combiner instrument GRAVITY. From data up to and including pericentre, we robustly detect the combined gravitational redshift and relativistic transverse Doppler effect for S2 of z = Δ λ / λ ≈ 200 km s −1 / c with different statistical analysis methods. When parameterising the post-Newtonian contribution from these effects by a factor f , with f = 0 and f = 1 corresponding to the Newtonian and general relativistic limits, respectively, we find from posterior fitting with different weighting schemes f = 0.90 ± 0.09| stat ± 0.15| sys . The S2 data are inconsistent with pure Newtonian dynamics.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201833718
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2018
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 10
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    Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA*
    EDP Sciences ; 2018
    In:  Astronomy & Astrophysics Vol. 618 ( 2018-10), p. L10-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 618 ( 2018-10), p. L10-
    Abstract: We report the detection of continuous positional and polarization changes of the compact source SgrA* in high states (“flares”) of its variable near-infrared emission with the near-infrared GRAVITY-Very Large Telescope Interferometer (VLTI) beam-combining instrument. In three prominent bright flares, the position centroids exhibit clockwise looped motion on the sky, on scales of typically 150 μ as over a few tens of minutes, corresponding to about 30% the speed of light. At the same time, the flares exhibit continuous rotation of the polarization angle, with about the same 45(±15) min period as that of the centroid motions. Modelling with relativistic ray tracing shows that these findings are all consistent with a near face-on, circular orbit of a compact polarized “hot spot” of infrared synchrotron emission at approximately six to ten times the gravitational radius of a black hole of 4 million solar masses. This corresponds to the region just outside the innermost, stable, prograde circular orbit (ISCO) of a Schwarzschild–Kerr black hole, or near the retrograde ISCO of a highly spun-up Kerr hole. The polarization signature is consistent with orbital motion in a strong poloidal magnetic field.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201834294
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2018
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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