10 research outputs found
A close encounter of the massive kind
We have used (a) HST ACS imaging and STIS spectroscopy, (b) ground-basedPIONIER/VLT long-baseline interferometry, and (c) ground-basedspectroscopy from different instruments to study the orbit of theextreme multiple system HD 93 129 Aa,Ab, which is composed of (at least)two very massive stars in a long-period orbit with e>0.92 that willpass through periastron in 2017/2018. In several ways, the system is aneta Car precursor. Around the time of periastron passage the two verystrong winds will collide and generate an outburst of non-thermal hardX-ray emission without precedent in an O+O binary since astronomers havebeen able to observe above Earth's atmosphere. A coordinatedmultiwavelength monitoring in the next two years will enable abreakthrough understanding of the wind interactions in such extremeclose encounters. Furthermore, we have found evidence that HD 93 129 Aamay be a binary system itself. In that case, we could witness athree-body interaction that may yield a runaway star or a stellarcollision close to or shortly after the periastron passage. Either ofthose outcomes would be unprecedented, as they are predicted to below-frequency events in the Milky Way.Instituto de AstrofĂsica de La Plat
A close encounter of the massive kind
We have used (a) HST ACS imaging and STIS spectroscopy, (b) ground-basedPIONIER/VLT long-baseline interferometry, and (c) ground-basedspectroscopy from different instruments to study the orbit of theextreme multiple system HD 93 129 Aa,Ab, which is composed of (at least)two very massive stars in a long-period orbit with e>0.92 that willpass through periastron in 2017/2018. In several ways, the system is aneta Car precursor. Around the time of periastron passage the two verystrong winds will collide and generate an outburst of non-thermal hardX-ray emission without precedent in an O+O binary since astronomers havebeen able to observe above Earth's atmosphere. A coordinatedmultiwavelength monitoring in the next two years will enable abreakthrough understanding of the wind interactions in such extremeclose encounters. Furthermore, we have found evidence that HD 93 129 Aamay be a binary system itself. In that case, we could witness athree-body interaction that may yield a runaway star or a stellarcollision close to or shortly after the periastron passage. Either ofthose outcomes would be unprecedented, as they are predicted to below-frequency events in the Milky Way.Instituto de AstrofĂsica de La Plat
Adaptive optics in high-contrast imaging
The development of adaptive optics (AO) played a major role in modern
astronomy over the last three decades. By compensating for the atmospheric
turbulence, these systems enable to reach the diffraction limit on large
telescopes. In this review, we will focus on high contrast applications of
adaptive optics, namely, imaging the close vicinity of bright stellar objects
and revealing regions otherwise hidden within the turbulent halo of the
atmosphere to look for objects with a contrast ratio lower than 10^-4 with
respect to the central star. Such high-contrast AO-corrected observations have
led to fundamental results in our current understanding of planetary formation
and evolution as well as stellar evolution. AO systems equipped three
generations of instruments, from the first pioneering experiments in the
nineties, to the first wave of instruments on 8m-class telescopes in the years
2000, and finally to the extreme AO systems that have recently started
operations. Along with high-contrast techniques, AO enables to reveal the
circumstellar environment: massive protoplanetary disks featuring spiral arms,
gaps or other asymmetries hinting at on-going planet formation, young giant
planets shining in thermal emission, or tenuous debris disks and micron-sized
dust leftover from collisions in massive asteroid-belt analogs. After
introducing the science case and technical requirements, we will review the
architecture of standard and extreme AO systems, before presenting a few
selected science highlights obtained with recent AO instruments.Comment: 24 pages, 14 figure
Constraining the structure of the transition disk HD 135344B (SAO 206462) by simultaneous modeling of multiwavelength gas and dust observations
Context. Constraining the gas and dust disk structure of transition disks, particularly in the inner dust cavity, is a crucial step toward understanding the link between them and planet formation. HD 135344B is an accreting (pre-)transition disk that displays the CO 4.7 Όm emission extending tens of AU inside its 30 AU dust cavity. Aims. We constrain HD 135344B's disk structure from multi-instrument gas and dust observations. Methods. We used the dust radiative transfer code MCFOST and the thermochemical code ProDiMo to derive the disk structure from the simultaneous modeling of the spectral energy distribution (SED), VLT/CRIRES CO P(10) 4.75 Όm, Herschel/PACS [OI] 63 Όm, Spitzer/IRS, and JCMT 12CO J = 3-2 spectra, VLTI/PIONIER H-band visibilities, and constraints from (sub-)mm continuum interferometry and near-IR imaging. Results. We found a disk model able to describe the current gas and dust observations simultaneously. </p
Recent progress and future prospects of the GI2T interferometer
Advances in Stellar Interferometry, SPIE 6268, (2006)International audienc
Spatio-spectral encoding of fringes in optical long baseline interferometry . Example of the 3T and 4T recombining mode of VEGA/CHARA
International audienc
Upgrading the GRAVITY fringe tracker for GRAVITY+ - Tracking the white-light fringe in the non-observable optical path length state-space
International audienceContext. The GRAVITY beam-combiner at the Very Large Telescope Interferometer has recently made important contributions to many different fields of astronomy, from observations of the Galactic centre to the study of massive stars, young stellar objects, exoplanet atmospheres, and active galactic nuclei. These achievements were only made possible by the development of several key technologies, including the development of reliable and high-performance fringe trackers. These systems compensate for disturbances ranging from atmospheric turbulence to vibrations in the optical system, enabling long exposures and ensuring the stability of interferometric measurements.Aims. As part of the ongoing GRAVITY+ upgrade of the Very Large Telescope Interferometer infrastructure, we aim to improve the performance of the GRAVITY fringe tracker, and to enable its use by other instruments.Methods. We modified the group-delay controller to consistently maintain tracking in the white-light fringe, which is characterised by a minimum group delay. Additionally, we introduced a novel approach in which fringe-tracking is performed in the non-observable optical path length state-space using a covariance-weighted Kalman filter and an auto-regressive model of the disturbance. We outline this new state-space representation and the formalism we used to propagate the state vector and generate the control signal. While our approach is presented specifically in the context of GRAVITY/GRAVITY+, it can easily be adapted to other instruments or interfero-metric facilities.Results. We successfully demonstrate phase-delay tracking within a single fringe, with any spurious phase jumps detected and corrected in less than 100 ms. We also report a significant performance improvement, as shown by a reduction of ~30 to 40% in phase residuals, and a much better behaviour under sub-optimal atmospheric conditions. Compared to what was observed in 2019, the median residuals have decreased from 150 nm to 100 nm on the Auxiliary Telescopes and from 250 nm to 150 nm on the Unit Telescopes.Conclusions. The improved phase-delay tracking combined with white-light fringe tracking means that from now on, the GRAVITY fringe tracker can be used by other instruments operating in different wavebands. The only limitation remains the need for an adjustment of the optical path dispersion.Key words: instrumentation: high angular resolution / instrumentation: interferometers / techniques: interferometricâ
These authors contributed equally
Where intermediate-mass black holes could hide in the Galactic Centre - A full parameter study with the S2 orbit
International audienceContext. In the Milky Way the central massive black hole, Sgr A*, coexists with a compact nuclear star cluster that contains a sub-parsec concentration of fast-moving young stars called S-stars. Their location and age are not easily explained by current star formation models, and in several scenarios the presence of an intermediate-mass black hole (IMBH) has been invoked.Aims. We use GRAVITY astrometric and SINFONI, KECK, and GNIRS spectroscopic data of S2, the best known S-star, to investigate whether a second massive object could be present deep in the Galactic Centre (GC) in the form of an IMBH binary companion to Sgr A*.Methods. To solve the three-body problem, we used a post-Newtonian framework and consider two types of settings: (i) a hierarchical set-up where the star S2 orbits the Sgr A*âIMBH binary and (ii) a non-hierarchical set-up where the IMBH trajectory lies outside the S2 orbit. In both cases we explore the full 20-dimensional parameter space by employing a Bayesian dynamic nested sampling method.Results. For the hierarchical case we find the strongest constraints: IMBH masses > 2000 Mâ on orbits with smaller semi-major axes than S2 are largely excluded. For the non-hierarchical case, the chaotic nature of the problem becomes significant: the parameter space contains several pockets of valid IMBH solutions. However, a closer analysis of their impact on the resident stars reveals that IMBHs on semi-major axes larger than S2 tend to disrupt the S-star cluster in less than a million years. This makes the existence of an IMBH among the S-stars highly unlikely.Conclusions. The current S2 data do not formally require the presence of an IMBH. If an IMBH hides in the GC, it has to be either a low-mass IMBH inside the S2 orbit that moves on a short and significantly inclined trajectory or an IMBH with a semi-major axis > 1âł. We provide the parameter maps of valid IMBH solutions in the GC and discuss the general structure of our results and how future observations can help to put even stronger constraints on the properties of IMBHs in the GC.Key words: black hole physics / gravitation / Galaxy: center / Galaxy: nucleus / Galaxy: kinematics and dynamics / Galaxy: structureNote to the reader: affiliations have been corrected on 7 April 2023.â GRAVITY is developed in a collaboration by MPE, LESIA of Paris Observatory/CNRS/Sorbonne UniversitĂ©/Univ. Paris Diderot and IPAG of UniversitĂ© Grenoble Alpes/CNRS, MPIA, Univ. of Cologne, CENTRA â Centro de Astrofisica e Gravitação, and ESO.ââ Corresponding author: O. Straub (e-mail: [email protected]
Using the motion of S2 to constrain scalar clouds around SgrA
International audienceThe motion of S2, one of the stars closest to the Galactic Centre, has been measured accurately and used to study the compact object at the centre of the Milky Way. It is commonly accepted that this object is a supermassive black hole but the nature of its environment is open to discussion. Here, we investigate the possibility that dark matter in the form of an ultralight scalar field ``cloud'' clusters around Sgr~A*. We use the available data for S2 to perform a Markov Chain Monte Carlo analysis and find the best-fit estimates for a scalar cloud structure. Our results show no substantial evidence for such structures. When the cloud size is of the order of the size of the orbit of S2, we are able to constrain its mass to be smaller than of the central mass, setting a strong bound on the presence of new fields in the galactic centre