The GRAVITY fringe tracker

Lacour, S.; Dembet, R.; Abuter, R.; Fédou, P.; Perrin, G.; Choquet, Élodie; Pfuhl, O.; Eisenhauer, F.; Woillez, J.; Cassaing, F.; Wieprecht, E.; Ott, Thomas; Wiezorrek, E.; Tristram, K. R. W.; Wolff, B.; Ramírez, Andrés; Haubois, X.; Perraut, K.; Straubmeier, C.; Brandner, W.; Amorim, A.

doi:10.1051/0004-6361/201834981

Cited by 73 publications

(65 citation statements)

References 24 publications

(32 reference statements)

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“…After the MACAO adaptive optics correction, the flux of the source is split and feeds the fringe tracker and science instrument simultaneously. We collected exposures with coherent integrations of 0.85 ms on the fringe tracker to freeze the atmospheric effects (Lacour et al 2019). Once the fringes were stabilized, we recorded successive sequences of 5 minutes, namely 10 exposures of 30 s each, on the object with the science instrument in its high spectral resolution mode (R∼4,000).…”

Section: Observationsmentioning

confidence: 99%

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

Bouvier

Perraut

Bouquin

et al. 2020

A&A

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Context. Young stellar objects are thought to accrete material from their circumstellar disks through their strong stellar magnetospheres. Aims. We aim to directly probe the magnetospheric accretion region on a scale of a few 0.01 au in a young stellar system using long-baseline optical interferometry. Methods. We observed the pre-transitional disk system DoAr 44 with VLTI/GRAVITY on two consecutive nights in the K-band. We computed interferometric visibilities and phases in the continuum and in the Brγ line in order to constrain the extent and geometry of the emitting regions. Results. We resolve the continuum emission of the inner dusty disk and measure a half-flux radius of 0.14 au. We derive the inclination and position angle of the inner disk, which provides direct evidence that the inner and outer disks are misaligned in this pre-transitional system. This may account for the shadows previously detected in the outer disk. We show that Brγ emission arises from an even more compact region than the inner disk, with an upper limit of 0.047 au (∼5 R ). Differential phase measurements between the Brγ line and the continuum allow us to measure the astrometric displacement of the Brγ line-emitting region relative to the continuum on a scale of a few tens of microarcsec, corresponding to a fraction of the stellar radius. Conclusions. Our results can be accounted for by a simple geometric model where the Brγ line emission arises from a compact region interior to the inner disk edge, on a scale of a few stellar radii, fully consistent with the concept of magnetospheric accretion process in low-mass young stellar systems.

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Section: Observationsmentioning

confidence: 99%

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

Bouvier

Perraut

Bouquin

et al. 2020

A&A

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“…The observing strategy was similar to the one described in Gravity Collaboration (2019): the fringe-tracker (Lacour et al 2019) was using the flux from the central star during the observing sequence, while the position of the science fiber was changed at each exposure, alternating between the central star and the position of the planet. Since the planet was not visible on the acquisition camera, the position used to center the fiber during the planet exposures was a theoretical position, based on predictions from previous monitoring (Wang et al 2016;Lagrange et al 2018).…”

Section: Observationsmentioning

confidence: 99%

Peering into the formation history of β Pictoris b with VLTI/GRAVITY long-baseline interferometry

Nowak¹,

Lacour²,

Mollière³

et al. 2020

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Context. β Pictoris is arguably one of the most studied stellar systems outside of our own. Some 30 yr of observations have revealed a highly-structured circumstellar disk, with rings, belts, and a giant planet: β Pictoris b. However very little is known about how this system came into being. Aims. Our objective is to estimate the C/O ratio in the atmosphere of β Pictoris b and obtain an estimate of the dynamical mass of the planet, as well as to refine its orbital parameters using high-precision astrometry. Methods. We used the GRAVITY instrument with the four 8.2 m telescopes of the Very Large Telescope Interferometer to obtain K-band spectro-interferometric data on β Pic b. We extracted a medium resolution (R = 500) K-band spectrum of the planet and a high-precision astrometric position. We estimated the planetary C/O ratio using two different approaches (forward modeling and free retrieval) from two different codes (ExoREM and petitRADTRANS, respectively). Finally, we used a simplified model of two formation scenarios (gravitational collapse and core-accretion) to determine which can best explain the measured C/O ratio. Results. Our new astrometry disfavors a circular orbit for β Pic b (e = 0.15−0.04+0.05). Combined with previous results and with HIPPARCOS/Gaia measurements, this astrometry points to a planet mass of M = 12.7 ± 2.2 MJup. This value is compatible with the mass derived with the free-retrieval code petitRADTRANS using spectral data only. The forward modeling and free-retrieval approches yield very similar results regarding the atmosphere of β Pic b. In particular, the C/O ratios derived with the two codes are identical (0.43 ± 0.05 vs. 0.43−0.03+0.04). We argue that if the stellar C/O in β Pic is Solar, then this combination of a very high mass and a low C/O ratio for the planet suggests a formation through core-accretion, with strong planetesimal enrichment.

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“…In a "normal" singlefield observation, the light of the science target is split 50/50 and fed into two channels, the fringe-tracker and the science spectrometer. The fringe-tracker is used to correct the fast atmospheric optical path variations with typical integration times of 1-10 milli-seconds (Lacour et al 2019). This allows coherent integration times with the science spectrometer up to ∼100 s. The interferometric observations of NGC 1068 are challenging due to the complex nature of the object.…”

Section: Interferometric Observationsmentioning

confidence: 99%

An image of the dust sublimation region in the nucleus of NGC 1068

Pfuhl

Davies

Dexter

et al. 2020

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We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the GRAVITY instrument on the European Southern Observatory Very Large Telescope Interferometer. The extensive baseline coverage from 5 to 60 Mλ allowed us to reconstruct a continuum image of the nucleus with an unrivaled 0.2 pc resolution in the K-band. We find a thin ring-like structure of emission with a radius r = 0.24 ± 0.03 pc, inclination i = 70 ± 5°, position angle PA = −50 ± 4°, and h/r < 0.14, which we associate with the dust sublimation region. The observed morphology is inconsistent with the expected signatures of a geometrically and optically thick torus. Instead, the infrared emission shows a striking resemblance to the 22 GHz maser disc, which suggests they share a common region of origin. The near-infrared spectral energy distribution indicates a bolometric luminosity of (0.4–4.7) × 1045 erg s−1, behind a large AK ≈ 5.5 (AV ≈ 90) screen of extinction that also appears to contribute significantly to obscuring the broad line region.

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The GRAVITY fringe tracker

Cited by 73 publications

References 24 publications

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

Peering into the formation history of β Pictoris b with VLTI/GRAVITY long-baseline interferometry

An image of the dust sublimation region in the nucleus of NGC 1068

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