Orbital Solution Research Articles

Spectroscopic Follow-up of Gaia Exoplanet Candidates: Impostor Binary Stars Invade the Gaia DR3 Astrometric Exoplanet Candidates

In this paper, we report on the follow-up of six potential exoplanets detected with Gaia astrometry and provide an overview of what is currently known about the nature of the entire Gaia astrometric exoplanet candidate sample, 72 systems in total. We discuss the primary false-positive scenario for astrometric planet detections: binary systems with alike components that produce small photocenter motions, mimicking exoplanets. These false positives can be identified as double-lined binaries (SB2) through analysis of high-resolution spectra. Doing so we find that three systems, Gaia DR3 1916454200349735680, Gaia DR3 2052469973468984192, and Gaia DR3 5122670101678217728, are indeed near-equal-mass double-star systems rather than exoplanetary systems. The spectra of the other two analyzed systems, HD 40503 and HIP 66074, are consistent with the exoplanet scenario in that no second set of lines can be found in the time series of publicly available high-resolution spectra. However, their Gaia astrometric solutions imply radial-velocity semiamplitudes ∼3 (HD 40503) and ∼15 (HIP 66074) larger than what was observed with ground-based spectrographs. The Gaia astrometry orbital solutions and ground-based radial-velocity measurements exhibit inconsistencies in six out of a total of 12 exoplanet candidate systems where such data are available, primarily due to substantial differences between observed ground-based radial-velocity semiamplitudes and those implied by the Gaia orbits. We investigated various hypotheses as to why this might be the case, and although we found no clear perpetrator, we note that a mismatch in orbital inclination offers the most straightforward explanation.

Photometric Study And Orbital Solution For Some Newly Discovered Eclipsing Binary Systems

We present an orbital solution and light curve analysis for the three newly discovered W UMa systems: V0757 And, IK Lyn, and V0996 Per by means of first CCD observations. New times of minima were estimated and the observed light curves were analyzed using the most recent version of Wilson-Devinney modeling code (WD code) based on model atmospheres by Kurucz. The accepted models revealed some parameters describing the orbit of each system which showed that the primary components in all systems are massive and hotter than the secondary components. The spectral types of the systems' components were adopted and the locations of the systems on the theoretical mass-luminosity and mass-radius relations revealed a good fit for all the systems components except the secondary components of the systems V0996 Per and V0757 And are located above the TAMS track. Представлено орбитальное решение и анализ кривых блеска для трех недавно открытых систем W UMa: V0757 And, IK Lyn и V0996 Per с помощью первых ПЗС-наблюдений. Были оценены новые времена минимумов и проанализированы наблюдаемые кривые блеска с использованием самой последней версии кода моделирования Уилсона-Девинни (код WD), основанного на моделях атмосфер Куруца. Принятые модели позволили выявить некоторые параметры, описывающие орбиту каждой системы, которые показали, что первичные компоненты во всех системах массивнее и горячее, чем вторичные компоненты. Спектральные классы компонентов систем и расположение систем по теоретическим соотношениям масса- светимость и масса-радиус показали хорошее соответствие для всех компонентов систем, кроме вторичных компонентов систем V0996 Per и V0757 And, расположенных выше последовательности TAMS.

Revisiting the orbital motion of WR 138

The optical spectrum of WR 138 exhibits emission lines typical of a WN6o star and absorption lines from a rapidly-rotating OB star. Using a large set of spectroscopic data, we establish a new orbital solution of the WN6o star based on the radial velocities of highly-ionized nitrogen lines. We show that the WN6o star moves on a 4.3yr orbit with a comparatively low eccentricity of 0.16. The radial velocities of the OB star display considerable scatter. Our best estimates of the velocities of Hei absorption lines result in a mass-ratio of mWN6o/mOB=0.53±0.09. We disentangle the spectra of the two stars and derive a projected rotational velocity of vsini=350±10kms−1 for the OB star. Our best orbital parameters, combined with the Gaia parallax of WR 138, are at odds with a previous interferometric detection of the companion, suggesting that there is either a bias in this detection or that WR 138 is actually a triple system.

Assessment of Swarm Kinematic Orbit Determination Using Two Different Double-Difference Methods

The Swarm mission aims to study the principle and change regularities of the Earth’s magnetic field. Precise orbit determination is essential to the successful implementation of the mission and relevant scientific research. This article focuses on using two different double-difference methods to improve the accuracy of Swarm kinematic orbit determination. The accuracy of the kinematic orbit determination relies entirely on the space-borne observation data, independent of any dynamic parameters. The article analyzes the data quality of the Swarm space-borne global positioning system (GPS) receiver and presents a detailed introduction to the data pre-processing algorithms. The double-difference observation gathering and the applied orbit determination strategy using two different double-difference methods are discussed. The results of the kinematic orbits under different solar cycle conditions are presented, along with an evaluation based on analysis of GPS carrier phase residuals, subtracting from the post-processed orbits, and assessment with satellite laser ranging (SLR) measurements. The results show that the accuracy of the kinematic orbit determination is at the centimeter level for the three Swarm satellites’ orbit solutions. The daily root mean square (RMS) values of the three satellites’ phase residuals remain at around the 6 mm level. The RMS values of the position residuals between the kinematic orbits and the reduced dynamic orbits released by the European Space Agency (ESA) are at about the 2–3 cm level. The external evaluation with SLR measurements shows a good agreement with the ESA level, with the RMS values of the SLR residuals for kinematic orbits around 2 cm.

The ability of CSST to determine the orbital solutions of SB1s

The single-lined spectroscopic binaries (SB1s) are composed of two components with large difference in masses and in physical properties. The orbital and physical parameters of a large number of such binary systems are unknown due to lack of necessary observations. Compared with SB2s, SB1s can provide much more stringent constraint to stellar evolutionary models at a single age. Besides, the fainter components of SB1s are likely to be compact celestial objects, such as a black hole or a neutron star, it is therefore interesting to determine their masses and physical properties. CSST provides an excellent opportunity to study SB1s especially nearby ones, since it can detect astrometric wobble at milliarcsecond level. This implies that if the motion of the visible components can be detected, the full motion of the SB1s can be determined. In this paper, we aim to analyse the ability of CSST to improve the orbital solutions of nearby SB1s based on the available data by adding simulated CSST data of different observation times. The orbital solutions of binaries determined from non-single-star orbital models for sources compatible with combined astrometric + single lined spectroscopic orbital model of Gaia DR3 are served as the research sample to reproduce the orbital elements by fitting simulated CSST data.

DMPP-3: confirmation of short-period S-type planet(s) in a compact eccentric binary star system, and warnings about long-period RV planet detections

ABSTRACT We present additional HARPS radial velocity observations of the highly eccentric (e ∼ 0.6) binary system DMPP-3AB, which comprises a K0V primary and a low-mass companion at the hydrogen burning limit. The binary has a 507 d orbital period and a 1.2 au semimajor axis. The primary component harbours a known 2.2 M⊕ planet, DMPP-3A b, with a 6.67-d orbit. New HARPS measurements constrain periastron passage for the binary orbit and add further integrity to previously derived solutions for both companion and planet orbits. Gaia astrometry independently confirms the binary orbit and establishes the inclination of the binary is 63.89 ± 0.78°. We performed dynamical simulations that establish that the previously identified ∼800 d RV signal cannot be attributed to an orbiting body. The additional observations, a deviation from strict periodicity, and our new analyses of activity indicators suggest the ∼800 d signal is caused by stellar activity. We conclude that there may be long-period planet ‘detections’ in other systems, which are similar misinterpreted stellar activity artefacts. Without the unusual eccentric binary companion to the planet-hosting star, we could have accepted the ∼800 d signal as a probable planet. Further monitoring of DMPP-3 will reveal which signatures can be used to most efficiently identify these imposters. We also report a threshold detection (0.2 per cent FAP) of a ∼2.26 d periodicity in the RVs, potentially attributed to an Earth-mass S-type planet interior to DMPP-3A b.

(130) Elektra Delta – on the stability of the new third moonlet

ABSTRACT The aim of this work is to verify the stability of the proposed orbital solutions for the third moonlet (Delta) taking into account a realistic gravitational potential for the central body of the quadruple system (Alpha). We also aim to estimate the location and size of a stability region inside the orbit of Gamma. First, we created a set of test particles with intervals of semimajor axis, eccentricities, and inclinations that covers the region interior to the orbit of Gamma, including the proposed orbit of Delta and a wide region around it. We considered three different models for the gravitational potential of Alpha: irregular polyhedron, ellipsoidal body, and oblate body. For a second scenario, Delta was considered a massive spherical body and Alpha an irregular polyhedron. Beta and Gamma were assumed as spherical massive bodies in both scenarios. The simulations showed that a large region of space is almost fully stable only when Alpha was modelled simply as an oblate body. For the scenario with Delta as a massive body, the results did not change from those as mass-less particles. Beta and Gamma do not play any relevant role in the dynamics of particles interior to the orbit of Gamma. Delta’s predicted orbital elements are fully unstable and far from the nearest stable region. The primary instability source is Alpha’s elongated shape. Therefore, in the determination of the orbital elements of Delta, it must be taken into account the gravitational potential of Alpha assuming, at least, an ellipsoidal shape.

Timescales of Chaos in the Inner Solar System: Lyapunov Spectrum and Quasi-integrals of Motion

Numerical integrations of the Solar System reveal a remarkable stability of the orbits of the inner planets over billions of years, in spite of their chaotic variations characterized by a Lyapunov time of only 5 million years and the lack of integrals of motion able to constrain their dynamics. To open a window on such long-term behavior, we compute the entire Lyapunov spectrum of a forced secular model of the inner planets. We uncover a hierarchy of characteristic exponents that spans two orders of magnitude, manifesting a slow-fast dynamics with a broad separation of timescales. A systematic analysis of the Fourier harmonics of the Hamiltonian, based on computer algebra, reveals three symmetries that characterize the strongest resonances responsible for the orbital chaos. These symmetries are broken only by weak resonances, leading to the existence of quasi-integrals of motion that are shown to relate to the smallest Lyapunov exponents. A principal component analysis of the orbital solutions independently confirms that the quasi-integrals are among the slowest degrees of freedom of the dynamics. Strong evidence emerges that they effectively constrain the chaotic diffusion of the orbits, playing a crucial role in the statistical stability over the Solar System lifetime.

On precise orbit determination based on DORIS, GPS and SLR using Sentinel-3A/B and -6A and subsequent reference frame determination based on DORIS-only

The Helmholtz-Zentrum Potsdam GFZ German Research Centre for Geosciences is one of the Associate Analysis Centers of the International Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) Service (IDS). In the framework of a recent reprocessing campaign for the International Terrestrial Reference Frame (ITRF) the suite of DORIS-derived satellite products was extended and improved with respect to reference frame determination. Among others the Copernicus Sentinel-3A/3B and 6A Michael Freilich (MF) satellites were used for this purpose. The orbits were generated based on DORIS-only and on the combination of DORIS and Satellite Laser Ranging (SLR) observations, and attempts were made to optimize their accuracy. Also for these satellites, GFZ generates Global Positioning System (GPS) based orbits within the Copernicus Precise Orbit Determination (CPOD) quality working group (CPOD-QWG). The GPS orbits contribute to a combined CPOD orbit solution, which is assumed to have superior absolute accuracy and minimal residual systematic errors. The DORIS-only, the combined DORIS and SLR, and the GPS-only orbits are compared to the CPOD combined solution serving as reference solution. The accuracy of the orbits shows up in radial direction for all techniques and combinations with values of 0.60 to 0.82 cm. In transverse and normal direction the RMS values achieved with GPS are up to around 50% lower as with DORIS, which sizes at around 1.5–2 cm. Subsequently the reference points of the observation techniques were estimated. With a multi-technique approach, a center-of-mass deviation according to Montenbruck et al. (2017) could be reproduced for Sentinel-3A. In addition, for both Sentinel-3 satellites the DORIS reference point values show a deviation in normal direction of 8–9 mm and a drift in radial direction of about 3 mm/year with respect to manufacturer’s data, reference point values for Sentinel-6A (MF) show a good agreement. With the confidence gained on the DORIS-only orbit solutions, weekly local reference frames are computed for each of the three satellites as well as a combined solution and evaluated in terms of the reference frame defining parameters, i.e. origin, scale, and orientation. The accuracy achieved here is in the range of a few mm to cm region. The scale remains stable, except for Sentinel-3A, which shows a scale drift of about −1.5 mm/year, whose cause is not clear yet. Standard deviations of station coordinate residuals (North, East, Up) are in the range of 2–4 mm, 5–9 mm and 5–7 mm respectively.

Extending the GPS IIIA antenna calibration for precise orbit determination of low Earth orbit satellites

High-precision applications of GNSS require accurate calibrations to correct for phase variations of the transmitting antennas. Calibrations distributed by the International GNSS Service (IGS), based upon observations from the global network of ground stations, are often used as the source of the transmitter calibrations as they are inherently linked to a specific definition of the International Terrestrial Reference Frame. The IGS provides antenna phase variations as a function of boresight angle for each basic block of navigation satellite. To support scientific missions operating in low Earth orbit, the antenna calibrations must be extended beyond the 14-degrees limit that can be observed by GNSS receivers on the Earth. Extended antenna calibrations to accommodate low Earth orbiting satellites have already been derived for the GPS Block II satellites. This paper derives an extension solution for the new GPS IIIA antenna calibration, based on a year of observations from the Sentinel-6 Michael Freilich altimetry mission and validated using Jason-3. These solutions are inherently consistent with the IGS-provided models of the Block II antenna calibrations. We use the new model for the GPS IIIA transmitter antenna calibration extensions to evaluate the impact on precise orbit solutions of both Sentinel-6 MF and Jason-3.

New insight into the massive eccentric binary HD 165052: self-consistent orbital solution, apsidal motion, and fundamental parameters

ABSTRACT HD 165052 is a short-period massive eccentric binary system that undergoes apsidal motion. As the rate of apsidal motion is directly related to the internal structure constants of the binary components, its study allows getting insight into the internal structure of the stars. We use medium- and high-resolution spectroscopic observations of HD 165052 to provide constraints on the fundamental properties of the binary system and the evolutionary state of its components. We apply a spectral disentangling code to reconstruct artefact-free spectra of the individual stars and derive the radial velocities (RVs) at the times of the observations. We perform the first analysis of the disentangled spectra with the non-local thermodynamic equilibrium model atmosphere code CMFGEN to determine the stellar properties. We derive the first self-consistent orbital solution of all existing RV data, including those reported in the literature, accounting for apsidal motion. We build, for the very first time, dedicated stellar evolution tracks with the Clés code requesting the theoretical effective temperatures and luminosities to match those obtained from our spectroscopic analysis. The binary system HD 165052, consisting of an O6.5 V((f)) primary ($T_\text{eff,P}=37\, 500 \pm 1000$ K) and an O7 V((f)) secondary ($T_\text{eff,S}=36\, 000 \pm 1000$ K), displays apsidal motion at a rate of $(11.30^{+0.64}_{-0.49})^\circ$ yr−1. Evolutionary masses are compared to minimum dynamical masses to constrain the orbital inclination. Evolutionary masses $M_\text{ev,P}=24.8\pm 1.0\, \mathrm{M}_\odot$ and $M_\text{ev,S}=20.9\pm 1.0\, \mathrm{M}_\odot$ and radii $R_\text{ev,P}=7.0^{+0.5}_{-0.4}\, \mathrm{R}_\odot$ and $R_\text{ev,S}=6.2^{+0.4}_{-0.3}\, \mathrm{R}_\odot$ are derived, and the inclination is constrained to 22.1° ≤ i ≤ 23.3°. Theoretical apsidal motion rates, derived assuming an age of 2.0 ± 0.5 Myr for the binary, are in agreement with the observational determination. The agreement with theoretical apsidal motion rates enforces the inferred values of the evolutionary stellar masses and radii.

The Main Problem of Lunar Orbit Revisited

A novel algorithm based on the Lindstedt–Poincaré method is proposed to construct an analytical solution of the lunar orbit. Based on the analytical solution, a numerical fitting algorithm is proposed to improve the coefficients of the analytical solution so that its accuracy can reach the level of a few kilometers within 20 yr. By fitting our solution to the long-term JPL ephemerides, we are able to recover the receding speed of the Moon from the Earth due to tidal effects. The proposed algorithm also provides a general way to treat the third-body perturbation in rectangular coordinates.

The quantitative analysis of homoclinic orbits from quadratic isochronous systems

In this paper, we investigate a pair of symmetric homoclinic orbits given by a Perturbation-Incremental (PI) method for the quadratic isochronous systems, which can bifurcate from the periodic orbits of the quadratic isochronous centers. The existing researches on the isochronous system are mostly from a qualitative perspective, while we have studied the quadratic isochronous system through the quantitative analysis method. As a quantitative analysis method, the PI method can not only determine the position of the limit cycle and the homoclinic (heteroclinic) orbit, but also provide an analytical expression of the asymptotic solution. At the same time, this method combines the significant characteristics of the perturbation method and the parameter incremental method. By utilizing the perturbation method, we obtain the analytic expressions of the zero-order perturbation solutions of homoclinic orbits when the parameters of systems are small. Then, the approximate analytical expressions of homoclinic orbits can be obtained by using the parameter incremental method when they are iterated from small parameters to large parameters. The numerical results will be compared with those from the Runge–Kutta method. The theoretical results agree very well with numerical simulation.

The Neptunian gravity estimated from the motion of Triton based on astrometric observations

Context. Accurate gravity and ephemerides estimations for Neptune and its satellites are necessary for the forthcoming deep space exploration missions targeting its system. In addition, these estimations are also meaningful for the modeling of Neptune's interior and for solar system dynamics studies. The body of astrometric data concerning Triton has been accumulating for about two hundred years, but more accurate updates to the ephemerides of this moon and revisions to the relevant gravity parameters would be possible with more precise astrometric data. The new Gaia catalog of star positions plus observations from Voyager 2 and the Hubble Space Telescope provide such a basis for high-precision astrometry and to complement and extend the existing body of data. Aims. We aim to report integrated orbital fits for Triton based on all the available astrometric data from 1847 to 2020, including observations from Earth-based telescopes, Voyager 2, and the Hubble Space Telescope. We also estimate the Neptunian gravity using the motion of Triton. Methods. Triton’s orbital solution was determined by a weighted least-squares method to fit the model to the most complete astrometric data set to date. The DOP853 algorithm was adopted in the numerical integration calculations. For the dynamical model parameters, our orbital model for Triton is similar to the NEP081 but with an update. The perturbations from the inner satellites (Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, and Hippocamp) were considered by adding corrections to J2 and J4 for Neptune. As the gravitational oblateness coefficient of Neptune is correlated with its orientation, the pole parameters were thus kept fixed in the integration when estimating Neptunian gravity. A Monte Carlo analysis was performed, however, to obtain reliable accuracy estimations and to assess the uncertainty of pole parameters on the results’ formal error. Results. We provide a new orbit and dynamical model values for Triton. The estimated accuracy of the model we built and updated fit all the astrometric data. The RMS of the residuals was 0.074 arcsec in the right ascension and 0.071 arcsec in declination. The RMS was 0.102 arcsec for X and 0.139 arcsec for Y in differential coordinates. The RMS for the position angle was 0.834 degrees, and the angular separation distance was 0.257 arcsec for the data collected before 1960. The orbit of Triton was well determined with the orbit differences from NEP081 and NEP097 (so far the latest Triton ephemerides from Jet Propulsion Laboratory) as being less than 300 km (about 15 mas) during the observation coverage period of this study. The large body of astrometric data for Triton over a time interval from 1847 to 2020 was used to constrain its position at the initial epoch, allowing us to reduce formal uncertainty to about 3 km. Based on the most complete weighting astrometric observations of Triton, the estimated mass of the Neptune system is GMs = 6 836 525.210 ±19.526 km3 s−2. Our revised gravity model yields J2 = 3401.655 ±1.850 × 10−6 and J4 = −33.294 ±10.000 × 10−6. The astrometric observations showed little sensitivity to GMs and J4, but acted well on J2. A Monte Carlo method was used to analyze the error caused by a variation in the pole parameters and showed that J2 = 3401.655 ± 3.994 × 10−6 was a more realistic error.

Photometric Study and Orbital Solution for Some Newly Discovered Eclipsing Binary Systems

Photometric Study and Orbital Solution for Some Newly Discovered Eclipsing Binary Systems

Chaotic diffusion of the fundamental frequencies in the Solar System (Corrigendum)

The long-term variations in the orbit of the Earth govern the insolation on its surface and hence its climate. The use of the astronomical signal, whose imprint has been recovered in the geological records, has revolutionized the determination of the geological timescales. However, the orbital variations beyond 60 Myr cannot be reliably predicted because of the chaotic dynamics of the planetary orbits in the Solar System. Taking this dynamical uncertainty into account is necessary for a complete astronomical calibration of geological records. Our work addresses this problem with a statistical analysis of 120 000 orbital solutions of the secular model of the Solar System ranging from 500 Myr to 5 Gyr. We obtain the marginal probability density functions of the fundamental secular frequencies using kernel density estimation. The uncertainty of the density estimation is also obtained here in the form of confidence intervals determined by the moving block bootstrap method. The results of the secular model are shown to be in good agreement with those of the direct integrations of a comprehensive model of the Solar System. Application of our work is illustrated on two geological data sets: the Newark-Hartford records and the Libsack core.

Dust as a solar shield

We revisit dust placed near the Earth–Sun L1 Lagrange point as a possible climate-change mitigation measure. Our calculations include variations in grain properties and orbit solutions with lunar and planetary perturbations. To achieve sunlight attenuation of 1.8%, equivalent to about 6 days per year of an obscured Sun, the mass of dust in the scenarios we consider must exceed 1010 kg. The more promising approaches include using high-porosity, fluffy grains to increase the extinction efficiency per unit mass, and launching this material in directed jets from a platform orbiting at L1. A simpler approach is to ballistically eject dust grains from the Moon’s surface on a free trajectory toward L1, providing sun shade for several days or more. Advantages compared to an Earth launch include a ready reservoir of dust on the lunar surface and less kinetic energy required to achieve a sun-shielding orbit.

Accelerations of stars in the central 2–7 arcsec from Sgr A*

This work presents the results from extending the long-term monitoring program of stellar motions within the Galactic Center to include stars with separations of 2–7 arcsec from the compact radio source, Sgr A*. In comparison to the well studied inner 2 arcsec, a longer baseline in time is required to study these stars. With 17 years of data, a sufficient number of positions along the orbits of these outer stars can now be measured. This was achieved by designing a source finder to track the positions of ∼2000 stars in NACO/VLT adaptive-optics-assisted images of the Galactic Center from 2002 to 2019. Of the studied stars, 54 exhibit significant accelerations toward Sgr A*, most of which have separations of between 2 and 3 arcsec from the black hole. A further 20 of these stars have measurable radial velocities from SINFONI/VLT stellar spectra, which allows for the calculation of the orbital elements for these stars, thus increasing the number of known orbits in the Galactic Center by ∼40%. With orbits, we can consider which structural features within the Galactic Center nuclear star cluster these stars belong to. Most of the stars have orbital solutions that are consistent with the known clockwise rotating disk feature. Further, by employing Monte Carlo sampling for stars without radial velocity measurements, we show that many stars have a subset of possible orbits that are consistent with one of the known disk features within the Galactic Center.

Peering into the young planetary system AB Pic

Aims. We aim to revisit the formation pathway of AB Pic b, an imaged companion that straddles the exoplanet/brown-dwarf boundary. We based this study on a rich set of observations, which allows us to investigate its orbital and atmospheric properties.Methods. We composed a spectrum of AB Pic b by merging archival medium-resolution (~4000) VLT/SINFONI K band (1.96–2.45 µm) data with published spectra atJandHbands from SINFONI,Lpband from Magellan-AO/CLIO2, and photometric measurements from HST (visible) andSpitzer(mid-infrared). We modeled the spectrum with ForMoSA, following a forward-modeling approach based on two atmospheric models: ExoREM and BT-SETTL13. In parallel, we determined the orbital properties of AB Pic b fitting orbital solutions to astrometric measurements from NaCo (2003 and 2004) and SPHERE (2015).Results. The orbital solutions favor a semi-major axis of 190-50+200au on a highly inclined orbit (edge-on), but with a poorly constrained eccentricity. From the atmospheric modeling with Exo-REM, we derive an effective temperature of 1700 ± 50 K and surface gravity of 4.5 ± 0.3 dex, which are consistent with previous findings, and we report for the first time a c/o ratio of 0.58 ± 0.08, consistent with the value for the Sun. The posteriors are sensitive to the wavelength interval and the family of models used. Given the published rotation period of 2.1 h and our derivedυsin(i) of 73-27+11km s−1, we estimate for the first time the true obliquity of AB Pic b to be between 45 and 135 deg, indicating a rather significant misalignment between the spin and orbit orientations of the planet. Finally, the existence of a proper-motion anomaly between the HIPPARCOSandGaiaEarly Data Release 3 compared to our SPHERE detection limits and adapted radial velocity limits indicates the potential existence of a ~6MJupinner planet orbiting from 2 to 10 au (40–200 mas).Conclusions. The possible existence of an inner companion and the likely misalignment of the spin-axis orientation strongly favor a formation path by gravitational instability or core accretion within a protoplanetary disk at a smaller orbital radius followed by a dynamical interaction which scattered AB Pic b to its current location. Confirmation and characterization of this unseen inner exoplanet and access to a broader wavelength coverage and higher spectral resolution for the characterization of AB Picb will be essential for probing the uncertainties associated with the atmospheric and orbital parameters.

The orbital solution and dynamical masses of the binary system V* PX Virginis

Abstract V* PX Vir is a nearby single-lined spectroscopic binary with the primary being a variable of a BY Dra-type star. It has a period of ∼216 d and the components of the system are two low-mass pre-main-sequence stars. By a simultaneous least-squares fit to the radial velocities, the relative positions, and the revised Hipparcos intermediate astrometric data, the complete orbital solution is derived and the precision is improved significantly. In addition, the Hipparcos parallax is revised as 46.06±0.69 mas. Taking advantage of the resulting orbital elements and parallax, the component masses are calculated to be 0.74±0.06 M⊙ and 0.47±0.02 M⊙, respectively. The absolute magnitudes in the K and H bands are determined as 4.32±0.14, 4.42±0.03 for the primary and 5.63±0.46, 6.08±0.03 for the secondary, respectively. According to the derived physical parameters, the two components of the system lie very close to the same isochrone age 0.1–0.14 Gyr by comparison with pre-main-sequence evolution tracks.