Astrometric observations of the M9 dwarf TVLM 513$-$46546 taken with the VLBA reveal an astrometric signature consistent with a period of 221 $\pm$ 5 days. The orbital fit implies that the companion has a mass m$_{p}$ = 0.35$-$0.42 $M_{J}$, a circular orbit ($e \simeq 0$), a semi-major axis a = 0.28$-$0.31 AU and an inclination angle i = 71$-$88$^\circ$. The detected companion, TVLM~513$b$, is one of the few giant-mass planets found associated to UCDs. The presence of a Saturn-like planet on a circular orbit, 0.3 AU from a 0.06$-$0.08 $M_\odot$ star, represents a challenge to planet formation theory. This is the first astrometric detection of a planet at radio wavelengths.
We conducted multi-epoch VLBI observations to search for astrometric reflex motion caused by a sub-stellar companion of the M8.5 dwarf TVLM 513-46546. The observations yield an absolute parallax corresponding to a distance of 10.762+/-0.027 pc and a proper motion of 78.09+/-0.17 mas/yr. From the absence of significant residual motion, we place an upper limit to any reflex motion caused by a companion, extending the parameter space covered by previous near-infrared direct-imaging searches. By covering different orbital periods, the data exclude a phase-space of companion masses and orbital peri…
Gaia DR3 astrometric orbit determination with Markov Chain Monte Carlo and Genetic Algorithms. Systems with stellar, substellar, and planetary mass companions
Ultra-Precise Astrometric Search for Exoplanets with SKA-VLBI
International Centre for Radio Astronomy Research (ICRAR), University of Western Australia（西澳大利亚大学国际射电天文研究中心）；Joint Institute for VLBI ERIC (JIVE)（甚长基线干涉测量欧洲研究基础设施合作组织）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）
This note describes an effort to detect additional stellar sources in known transiting exoplanet (TEP) systems, which are unresolved or barely resolved in the Gaia Data Release 2 (DR2) catalogue. The presence of multiple unresolved stars in photometric and spectroscopic observations of a transiting planetary system biases measurements of the planet's radius, mass, and atmospheric conditions. In addition to the effect on individual planetary systems, the presence of unresolved stars across the sample of known exoplanets biases our overall understanding of planetary systems, due to the systemati…
(abridged) A complete census of planetary systems around a volume-limited sample of solar-type stars (FGK dwarfs) in the Solar neighborhood with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics. This fundamental goal can be achieved with a mission concept such as NEAT - the Nearby Earth Astrometric Telescope. NEAT is designed to carry out space-borne extremely-high-precision astrometric measurements sufficient to detect dynamical effects due to orbiting planets of mass even lower than Ea…
Because of the diversity of stellar masses and orbital sizes of binary systems, and the complex interaction between star-star, star-planet and planet-planet, it has been difficult to fully characterize the planetary systems associated with binary systems. Here, we report high-precision astrometric observations of the low-mass binary system GJ 896AB, revealing the presence of a Jupiter-like planetary companion (GJ 896Ab). The planetary companion is associated to the main star GJ 896A, with an estimated mass of 2.3 Jupiter masses and an orbit period of 284.4 days. A simultaneous analysis of the …
The NEAT (Nearby Earth Astrometric Telescope) mission is a proposition submitted to ESA for its 2010 call for M-size mission. The main scientific goal is to detect and characterize planetary systems in an exhaustive way down to 1 Earth mass in the habitable zone and further away, around nearby stars for F, G, and K spectral types. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to that mass limit. Extremely- high-precision astrometry, in space, can detect the dynamica…
The first planetary candidate discovered by Latham et al. (1989) with radial velocities around a solar-like star other than the Sun, HD 114762 b, was detected with a minimum mass of 11 Mjup. The small v sin(i)~0 km/s that is otherwise measured by spectral analysis indicated that this companion of a late-F subgiant star better corresponds to a massive brown dwarf (BD) or even a low-mass M-dwarf seen nearly face-on. To our knowledge, the nature of HD 114762 b is still undetermined. The astrometric noise measured for this system in the first data release, DR1, of the Gaia mission allows us to der…
Radio astronomy observations of close approaches of the Solar system planets to compact radio sources as well as radio source occultations by planets may be of large interest for planetary sciences, dynamical astronomy, and testing gravity theories. In this paper, we present extended lists of occultations of astrometric radio sources observed in the framework of various astrometric and geodetic VLBI programs by planets, and close approaches of planets to radio sources expected in the nearest years. Computations are made making use of the EPOS software package.
Astrometric view of companions in the inner dust cavities of protoplanetary disks
European Southern Observatory（欧洲南方天文台）；School of Physics and Astronomy, University of Leeds（利兹大学物理与天文学学院）；Dipartimento di Fisica, Università degli Studi di Milano（米兰大学物理系）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理学研究所）；Max-Planck-Institut für Astronomie (MPIA)（马克斯·普朗克天文学研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；INAF - Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）；Centro de Astrobiología (CAB), CSIC-INTA（西班牙国家研究委员会-国家航空航天技术研究所天体生物学中心）；Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London（伦敦大学玛丽女王学院物理与天文学学院天文学单元）
We present constraints on the presence of substellar companions to the nearby ($d\sim7.6$ pc), young ($440\pm40$ Myr) K4Ve star TW Piscis Austrini, the wide ($\sim$0.3 pc) companion to the A4V star Fomalhaut. We combined absolute astrometry from Hipparcos and Gaia with literature radial velocity measurements and dedicated high-contrast imaging observations obtained with Keck/NIRC2 to achieve sensitivity to brown dwarf and planetary-mass companions ($\gtrsim2$ M$_{\rm Jup}$) over many decades of orbital period ($\lesssim 10^3$ yr). The significant astrometric acceleration measured between the H…
Transit photometry of the M8V dwarf star TRAPPIST-1 (2MASS J23062928-0502285) has revealed the presence of at least seven planets with masses and radii similar to that of Earth orbiting at distances that might allow liquid water to be present on their surfaces. We have been following TRAPPIST-1 since 2011 with the CAPSCam astrometric camera on the 2.5-m du Pont telescope at the Las Campanas Observatory in Chile. In 2016 we noted that TRAPPIST-1 lies slightly farther away than previously thought, at 12.49 pc, rather than 12.1 pc. Here we examine fifteen epochs of CAPSCam observations of TRAPPIS…
In its all-sky survey, the ESA global astrometry mission Gaia will perform high-precision astrometry and photometry for 1 billion stars down to $V = 20$ mag. The data collected in the Gaia catalogue, to be published by the end of the next decade, will likely revolutionize our understanding of many aspects of stellar and Galactic astrophysics. One of the relevant areas in which the Gaia observations will have great impact is the astrophysics of planetary systems. This summary focuses on a) the complex technical problems related to and challenges inherent in correctly modelling the signals of pl…
We present the Exoplanet Simple Orbit Fitting Toolbox (ExoSOFT), a new, open-source suite to fit the orbital elements of planetary or stellar mass companions to any combination of radial velocity and astrometric data. To explore the parameter space of Keplerian models, ExoSOFT may be operated with its own multi-stage sampling approach, or interfaced with third-party tools such as emcee. In addition, ExoSOFT is packaged with a collection of post-processing tools to analyze and summarize the results. Although only a few systems have been observed with both the radial velocity and direct imaging …
HR\,8799 is a young planetary system composed of 4 planets and a double debris belt. Being the first multi-planetary system discovered with the direct imaging technique, it has been observed extensively since 1998. This wide baseline of astrometric measurements, counting over 50 observations in 20 years, permits a detailed orbital and dynamical analysis of the system. To explore the orbital parameters of the planets, their dynamical history, and the planet-to-disk interaction, we made follow-up observations of the system during the VLT/SPHERE GTO program. We obtained 21 observations, most of t…
Astrometric microlensing can be used to make precise measurements of the masses of lens stars that are independent of their assumed internal physics. Such direct mass measurements, obtained purely by observing the gravitational effects of the stars on external objects, are crucial for validating theoretical stellar models. Specifically, astrometric microlensing provides a channel to direct mass measurements of single stars for which so few measurements exist. To use the astrometric solutions and photometric measurements of ~1.7 billion stars from Gaia Data Release 2 to predict microlensing eve…
We report here the discovery of the first planet around an ultracool dwarf star. It is also the first extrasolar giant planet (EGP) astrometrically discovered around a main-sequence star. The statistical significance of the detection is shown in two ways. First, there is a 2 x 10^-8 probability that the astrometric motion fits a parallax-and-proper-motion-only model. Second, periodogram analysis shows a false alarm probability of 3 x 10^-5 that the discovered period is randomly generated. The planetary mass is M2 = 6.4 (+2.6,-3.1) Jupiter-masses (MJ), and the orbital period is P = 0.744 (+0.01…
The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for the discovery and study of planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years and to detect their barycentric motions due to orbiting planets. We present the operation principle, the instrument's implementation, and the results of a first series of test observations. A comprehensive overview of the instrument infrastructure is given and the observation strategy for dual-field relative astr…
HR8799 is so far the only directly imaged multiple exoplanet system. The orbital configuration would, if better known, provide valuable insight into the formation and dynamical evolution of wide-orbit planetary systems. We present L'-band observations of the HR8799 system obtained with NACO at VLT, adding to the astrometric monitoring of the planets HR8799b, c and d. We investigate how well the two simple cases of (i) a circular orbit and (ii) a face-on orbit fit the astrometric data for HR8799d over a total time baseline of ~2 years. The results indicate that the orbit of HR8799d is inclined …
A low-amplitude periodic signal in the radial velocity (RV) time series of Barnard's Star was recently attributed to a planetary companion with a minimum mass of ${\sim}$3.2 $M_\oplus$ at an orbital period of $\sim$233 days. The relatively long orbital period and the proximity of Barnard's Star to the Sun raises the question whether the true mass of the planet can be constrained by accurate astrometric measurements. By combining the assumption of an isotropic probability distribution of the orbital orientation with the RV-analysis results, we calculated the probability density function of the …
Astrometry as a technique has so far proved of limited utility when employed as either a follow-up tool or to independently search for planetary mass companions orbiting nearby stars. However, this is bound to change during the next decade. In this review, I start by summarizing past and present efforts to detect planets via milli-arcsecond astrometry. Next, I provide an overview of the variety of technical, statistical, and astrophysical challenges that must be met by future ground-based and space-borne efforts in order to achieve the required degree of astrometric measurement precision. Then…
Astrometric observations of the radio source occultations by solar system bodies may be of large interest for testing gravity theories, dynamical astronomy, and planetary physics. In this paper, we present an updated list of the occultations of astrometric radio sources by planets expected in the nearest years. Such events, like the solar eclipses, generally speaking, can be only observed in a limited region. The map of the shadow path is provided for the events occurred in regions with several VLBI stations and hence the most interesting for radio astronomy experiments.
Astrometry is less sensitive to stellar activity than the radial velocity technique when attempting to detect Earth mass planets in the habitable zone of solar-type stars. This is due to a smaller number of physical processes affecting the signal, and a larger ratio of the amplitude of the planetary signal to the stellar signal. A few high-precision astrometric missions have therefore been proposed over the past two decades. We aim to re-estimate the detection limits in astrometry for the nearby stars which are the main targets proposed for the THEIA astrometric mission, the most elaborate mis…
A Century of Radial Velocity and Astrometric Monitoring of 70 Oph AB: New PFS Data and Constraints on Planetary Companions
University of Michigan（密歇根大学）；University of California, Riverside（加州大学河滨分校）；Carnegie Institution for Science（卡内基科学研究所）；California Institute of Technology（加州理工学院）
The Closeby Habitable Exoplanet Survey (CHES) mission is proposed to discover habitable-zone Earth-like planets of the nearby solar-type stars ($\sim 10~\mathrm{pc}$ away from our solar system) via micro-arcsecond relative astrometry. The major scientific objectives of CHES are: to search for Earth Twins or terrestrial planets in habitable zones orbiting 100 FGK nearby stars; further to conduct a comprehensive survey and extensively characterize the nearby planetary systems. The primary payload is a high-quality, low-distortion, high-stability telescope. The optical subsystem is a coaxial thre…
Astrometric exomoon detection by means of optical interferometry
European Southern Observatory（欧洲南方天文台）；LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎天文台 LIRA 实验室，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎大学）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；Department of Physics & Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文学系）；Space Telescope Science Institute（太空望远镜科学研究所）；Max Planck Institute for extraterrestrial Physics（马克斯·普朗克地外物理学研究所）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）
Using astrometric measurements obtained with the FORS2/VLT camera, we are searching for low-mass companions around 20 nearby ultracool dwarfs. With a single-measurement precision of 0.1 milli-arcseconds, our survey is sensitive to a wide range of companion masses from planetary companions to binary systems. Here, we report the discovery and orbit characterisation of a new ultracool binary at a distance of 19.5 pc from Earth that is composed of the M8.5-dwarf primary DE0630-18 and a substellar companion. The nearly edge-on orbit is moderately eccentric (e=0.23) with an orbital period of 1120 d,…
A system of four super-Jupiter planets around HR 8799 is the first multi-planet configuration discovered via the direct imaging technique. Despite over decade of research, the system's architecture remains not fully resolved. The main difficulty comes from still narrow observing window of ~20 years that covers small arcs of orbits with periods from roughly 50 to 500 years. Soon after the discovery it became clear that unconstrained best-fitting astrometric configurations self-disrupt rapidly, due to strong mutual gravitational interactions between ~10-Jupiter-mass companions. Recently, we show…
Astrometry can detect rocky planets in a broad range of masses and orbital distances and measure their masses and three-dimensional orbital parameters, including eccentricity and inclination, to provide the properties of terrestrial planets. The masses of both the new planets and the known gas giants can be measured unambiguously, allowing a direct calculation of the gravitational interactions, both past and future. Such dynamical interactions inform theories of the formation and evolution of planetary systems, including Earth-like planets. Astrometry is the only technique technologically read…
In its all-sky survey, Gaia will monitor astrometrically hundreds of thousands of main-sequence stars within $\approx200$ pc, looking for the presence of giant planetary companions within a few AUs from their host stars. Indeed, Gaia observations will have great impact is the astrophysics of planetary systems (e.g., Casertano et al. 2008), in particular when seen as a complement to other techniques for planet detection and characterization (e.g., Sozzetti 2011). In this paper, I briefly address some of the relevant technical issues associated with the precise and accurate determination of astr…
Closeby Habitable Exoplanet Survey (CHES). IV. Synergy between astrometry and direct imaging missions of the Habitable World Observatory for detecting Earth-like planets
Extrasolar planet searches targeting very low-mass stars and brown dwarfs are hampered by intrinsic or instrumental limitations. Time series of astrometric measurements with precisions better than one milli-arcsecond can yield new evidence on the planet occurrence around these objects. We present first results of an astrometric search for planets around 20 nearby dwarf stars with spectral types M8-L2. Over a timespan of two years, we obtained I-band images of the target fields with the FORS2 camera at the Very Large Telescope. Using background stars as references, we monitored the targets' ast…
HR 8799 harbors arguably the first and best-studied directly-imaged planets. In this brief article, I describe how the HR 8799 planetary system is a benchmark system for studying the atmospheres, orbital properties, dynamical stability, and formation of young superjovian planets. Multi-wavelength photometry and spectroscopy show that HR 8799 bcde appear to have thicker clouds than do field brown dwarfs of similar effective temperatures and exhibit evidence for non-equilibrium carbon chemistry, features that are likely connected to the planets' low surface gravities. Over 17 years of astrometri…
We present COPAINS (Code for Orbital Parametrisation of Astrometrically Inferred New Systems), an innovative tool developed to identify previously undiscovered companions detectable via direct imaging, based on changes in stellar proper motions across multiple astrometric catalogues. This powerful procedure allows for dynamical predictions of the possible masses and separations of unseen companions compatible with observed astrometric trends, marginalised over unknown orbital elements. Validating our approach using well-constrained systems, we found that our tool provides a good indication of …
(Abridged) Hubble Space Telescope (HST) Fine Guidance Sensor astrometric observations of the G4 IV star HD 38529 are combined with the results of the analysis of extensive ground-based radial velocity data to determine the mass of the outermost of two previously known companions. Our new radial velocities obtained with the Hobby-Eberly Telescope and velocities from the Carnegie-California group now span over eleven years. With these data we obtain improved RV orbital elements for both the inner companion, HD 38529 b and the outer companion, HD 38529 c. We identify a rotational period of HD 385…
We present new radial velocity measurements for three low-metallicity solar-like stars observed with the SOPHIE spectrograph and its predecessor ELODIE, both installed at the 193 cm telescope of the Haute-Provence Observatory, allowing the detection and characterization of three new giant extrasolar planets in intermediate periods of 1.7 to 3.7 years. All three stars, HD17674, HD42012 and HD29021 present single giant planetary companions with minimum masses between 0.9 and 2.5 MJup. The range of periods and masses of these companions, along with the distance of their host stars, make them good…
GJ676A is an M0 dwarf hosting both gas-giant and super-Earth-type planets discovered with radial-velocity measurements. Using FORS2/VLT, we obtained position measurements of the star in the plane of the sky that tightly constrain its astrometric reflex motion caused by the super-Jupiter planet `b` in a 1052-day orbit. This allows us to determine the mass of this planet to $M_\mathrm{b} = 6.7^{+1.8}_{-1.5}\,M_\mathrm{J}$, which is $\sim$40 \% higher than the minimum mass inferred from the radial-velocity orbit. Using new HARPS radial-velocity measurements, we improve upon the orbital parameters…
Accurate positional measurements of planets and satellites are used to improve our knowledge of their dynamics and to infer the accuracy of planet and satellite ephemerides. In the framework of the FP7 ESPaCE project, we provide the positions of Mars, Phobos, and Deimos taken with the U.S. Naval Observatory 26-inch refractor during the 1971 opposition of the planet. These plates were measured with the digitizer of the Royal Observatory of Belgium and reduced through an optimal process that includes image, instrumental, and spherical corrections to provide the most accurate data. We compared th…
Exoplanets which are detected using the radial velocity technique have a well-known ambiguity of their true mass, caused by the unknown inclination of the planetary orbit with respect to the plane of the sky. Constraints on the inclination are aided by astrometric follow-up in rare cases or, in ideal situations, through subsequent detection of a planetary transit. As the predicted inclination decreases, the mass of the companion increases leading to a change in the predicted properties. Here we investigate the changes in the mass, radius, and atmospheric properties as the inclination pushes th…
The recent discovery of a three-planet extrasolar system of HR 8799 by Marois et al. is a breakthrough in the field of the direct imaging. This great achievement raises questions on the formation and dynamical stability of the HR 8799 system, because Keplerian fits to astrometric data are strongly unstable during ~0.2Myr. We search for stable, self-consistent N-body orbits with the so called GAMP method that incorporates stability constraints into the optimization algorithm. Our searches reveal only small regions of stable motions in the phase space of three-planet, coplanar configurations. Mo…
The Astrometric Resoeccentric Degeneracy: Eccentric Single Planets Mimic 2:1 Resonant Planet Pairs in Astrometry
Center for Computational Astrophysics, Flatiron Institute（计算天体物理学中心，平顿研究所）；Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（卡弗里天体物理与空间研究所，麻省理工学院）；Department of Physics and Astronomy, Stony Brook University（物理与天文系，石溪大学）；School of Physics & Astronomy, Monash University（物理与天文学院，蒙纳士大学）
The $\sim500$\, Myr A2IV star HR 1645 has one of the most significant low-amplitude accelerations of nearby early-type stars measured from a comparison of the {\it Hipparcos} and {\it Gaia} astrometric catalogues. This signal is consistent with either a stellar companion with a moderate mass ratio ($q\sim0.5$) on a short period ($P<1$\,yr), or a substellar companion at a separation wide enough to be resolved with ground-based high contrast imaging instruments; long-period equal mass ratio stellar companions that are also consistent with the measured acceleration are excluded with previous imag…
A Planetary Illusion's Funeral: Non-detection of a Gaia DR3 Exoplanet Candidate, and the Role of Intermediate-precision Radial Velocities in Gaia Exoplanet Follow-up
Centre for Astrophysics, University of Southern Queensland（南昆士兰大学天体物理中心）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森尼天体物理中心）
[abridged] We carry out numerical simulations to gauge the Gaia potential for precision astrometry of exoplanets orbiting a sample of known dM stars within 30 pc from the Sun. (1) It will be possible to accurately determine orbits and masses for Jupiter-mass planets with orbital periods in the range 0.2<P<6.0 yr and with an astrometric signal-to-noise ratio > 10. Given present-day estimates of the planet fraction f_p around M dwarfs, 100 giant planets could be found by Gaia around the sample. Comprehensive screening by Gaia of the reservoir of 4x10^5 M dwarfs within 100 pc could result in 2600…
The formation of massive planetary or brown dwarf companions at large projected separations from their host star is not yet well understood. In order to put constraints on formation scenarios we search for signatures in the orbit dynamics of the systems. We are specifically interested in the eccentricities and inclinations since those parameters might tell us about the dynamic history of the systems and where to look for additional low-mass sub-stellar companions. For this purpose we utilized VLT/NACO to take several well calibrated high resolution images of 6 target systems and analyze them t…
A crucial diagnostic that can tell us about processes involved in the formation and dynamical evolutionof planetary systems is the angle between the rotation axis of a star and a planet's orbital angular momentum vector ("spin-orbit" alignment or "obliquity"). Here we present the first spin-orbit alignment measurement for a wide-separation exoplanetary system, namely on the directly-imaged planet $β$ Pictoris b. We use VLTI/GRAVITY spectro-interferometry with an astrometric accuracy of 1 $μ$as (microarcsecond) in the Br$γ$ photospheric absorption line to measure the photocenter displacement as…
We present new astrometric measurements from our ongoing monitoring campaign of the HR 8799 directly imaged planetary system. These new data points were obtained with NIRC2 on the W.M. Keck II 10 meter telescope between 2009 and 2014. In addition, we present updated astrometry from previously published observations in 2007 and 2008. All data were reduced using the SOSIE algorithm, which accounts for systematic biases present in previously published observations. This allows us to construct a self-consistent data set derived entirely from NIRC2 data alone. From this dataset, we detect accelerat…
