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 $10^{-4}$ 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 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 100$\,\mu$as. 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 $\approx 5$ per spectral channel, is compatible with a late-type L brown dwarf. Using Exo-REM synthetic spectra, we derive a temperature of $1150\pm50$\,K and a surface gravity of $10^{4.3\pm0.3}\,$cm/s$^{2}$. This corresponds to a radius of $1.17^{+0.13}_{-0.11}\,R_{\rm Jup}$ and a mass of $10^{+7}_{-4}\,M_{\rm Jup}$, 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.Comment: published in A&

Accretion-ejection morphology of the microquasar SS 433 resolved at sub-au scale

This is the author accepted manuscript. the final version is available from EDP Sciences via the DOI in this recordWe present the first optical observation of the microquasar SS 433 at sub-milliarcsecond (mas) scale obtained with the GRAVITY instrument on the Very Large Telescope interferometer (VLTI). The 3.5-h exposure reveals a rich K-band spectrum dominated by hydrogen Brγand He i lines, as well as (red-shifted)emission lines coming from the jets. The K-band-continuum-emitting region is dominated by a marginally resolved point source (<1 mas) embedded inside a diffuse background accounting for 10% of the total flux. The jet line positions agree well with the ones expected from the jet kinematic model, an interpretation also supported by the consistent sign (i.e., negative/positive for the receding/approaching jet component) of the phase shifts observed in the lines. The significant visibility drop across the jet lines, together with the small and nearly identical phases for all baselines, point toward a jet that is offset by less than 0.5 mas from the continuum source and resolved in the direction of propagation, with a typical size of 2 mas. The jet position angle of ~80° is consistent with the expected one at the observation date. Jet emission so close to the central binary system would suggest that line locking, if relevant to explain the amplitude and stability of the 0.26c jet velocity, operates on elements heavier than hydrogen. The Brγprofile is broad and double peaked. It is better resolved than the continuum and the change of the phase signal sign across the line on all baselines suggests an East-West-oriented geometry similar to the jet direction and supporting a (polar) disk wind origin.Centre National d’Etudes Spatiales (CNES)Programme National Hautes Energies (PNHE)Humboldt FoundationNAS

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

The wind and the magnetospheric accretion onto the T Tauri star S Coronae Australis at sub-Au resolution

This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.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 CrAN and S CrAS and separated by -10:04), 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 halfflux 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 CrAN spectrum shows bright He i and Br line emission exhibiting inverse P Cygni profiles, typically associated with infalling gas. The continuum-compensated Br line visibilities of S CrAN show the presence of a compact Br 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 line components is marginally detected. Conclusions. The presence of an inverse P Cygni profile in the He i and Br lines, along with the tentative detection of a slightly larger size of the blue-shifted Br line component, hint at the simultaneous presence of a wind and magnetospheric accretion in S CrA N.Science Foundation IrelandAlexander von Humboldt Foundation Fellowship ProgrammeFrench PNPSLabEx OSUG@202

Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole

This is the author accepted manuscript. the final version is available from EDP Sciences via the DOI in this recordThe 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 = Δλ / 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

MOJAVE. X. Parsec-Scale Jet Orientation Variations and Superluminal Motion in AGN

We describe the parsec-scale kinematics of 200 AGN jets based on 15 GHz VLBA data obtained between 1994 Aug 31 and 2011 May 1. We present new VLBA 15 GHz images of these and 59 additional AGN from the MOJAVE and 2 cm Survey programs. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12 to 16 year interval, ranging from 10º to 150º on the sky, corresponding to intrinsic variations of ∼0.5º to ∼2º. The BL Lac jets show smaller variations than quasars. Roughly half of the heavily observed jets show systematic position angle trends with time, and 20 show indications of oscillatory behavior. The time spans of the data sets are too short compared to the fitted periods (5 to 12 y), however, to reliably establish periodicity. The rapid changes and large jumps in position angle seen in many cases suggest that the superluminal AGN jet features occupy only a portion of the entire jet cross section, and may be energized portions of thin instability structures within the jet. We have derived vector proper motions for 887 moving features in 200 jets having at least five VLBA epochs. For 557 well-sampled features, there are sufficient data to additionally study possible accelerations. We find that the moving features are generally non-ballistic, with 70% of the well-sampled features showing either significant accelerations or non-radial motions. Inward motions are rare (2% of all features), are slow (<0.1 mas per y), are more prevalent in BL Lac jets, and are typically found within 1 mas of the unresolved core feature. There is a general trend of increasing apparent speed with distance down the jet for both radio galaxies and BL Lac objects. In most jets, the speeds of the features cluster around a characteristic value, yet there is a considerable dispersion in the distribution. Orientation variations within the jet cannot fully account for the dispersion, implying that the features have a range of Lorentz factor and/or pattern speed. Very slow pattern speed features are rare, comprising only 4% of the sample, and are more prevalent in radio galaxy and BL Lac jets. We confirm a previously reported upper envelope to the distribution of speed versus beamed luminosity for moving jet features. Below 10^26 W Hz−1 there is a fall-off in maximum speed with decreasing 15 GHz radio luminosity. The general shape of the envelope implies that the most intrinsically powerful AGN jets have a wide range of Lorentz factors up to ∼40, while intrinsically weak jets are only mildly relativistic

Multiple star systems in the Orion nebula

This is the author accepted manuscript. The final fersion is available from EDP Sciences via the DOI in this record.This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.Marie Skłodowska-Curie Grant AgreementFCT-PortugalERC Starting Gran

A dynamical measure of the black hole mass in a quasar 11 billion years ago

Tight relationships exist in the local universe between the central stellar properties of galaxies and the mass of their supermassive black hole. These suggest galaxies and black holes co-evolve, with the main regulation mechanism being energetic feedback from accretion onto the black hole during its quasar phase. A crucial question is how the relationship between black holes and galaxies evolves with time; a key epoch to probe this relationship is at the peaks of star formation and black hole growth 8-12 billion years ago (redshifts 1-3). Here we report a dynamical measurement of the mass of the black hole in a luminous quasar at a redshift of 2, with a look back time of 11 billion years, by spatially resolving the broad line region. We detect a 40 micro-arcsecond (0.31 pc) spatial offset between the red and blue photocenters of the H$\alpha$ line that traces the velocity gradient of a rotating broad line region. The flux and differential phase spectra are well reproduced by a thick, moderately inclined disk of gas clouds within the sphere of influence of a central black hole with a mass of 3.2x10$^{8}$ solar masses. Molecular gas data reveal a dynamical mass for the host galaxy of 6x10$^{11}$ solar masses, which indicates an under-massive black hole accreting at a super-Eddington rate. This suggests a host galaxy that grew faster than the supermassive black hole, indicating a delay between galaxy and black hole formation for some systems.Comment: 5 pages Main text, 8 figures, 2 tables, to be published in Nature, under embargo until 29 January 2024 16:00 (London

The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.Comment: Published in the ESO Messenge