Search

Located at less than two pc away, Luhman 16 AB (WISE J104915.57-531906.1) is the closest pair of brown dwarfs and the third closest "stellar" system to Earth. An exoplanet candidate in the Luhman 16 binary system was reported in 2017 based on a weak astrometric signature in the analysis of 12 HST epochs. An additional epoch collected in 2018 and re-analysis of the data with more advanced methods further increased the significance level of the candidate, consistent with a Neptune-mass exoplanet orbiting one of the Luhman 16 brown dwarf components. We report the joint analysis of these previous data together with two new astrometric HST epochs we obtained to confirm or disprove this astrometric signature. Our new analysis rules out the presence of a planet orbiting one component of the Luhman 16 AB system for masses 1.5 M (Neptune masses) and periods between 400 and 5000 days. However, the presence of third bodies with masses 3 M and periods between 2 and 400 days (~1.1 years) cannot be excluded. Our measurements make significant improvements to the characterization of this sub-stellar binary, including its mass-ratio 0.8305±0.0006, individual component masses 35.4±0.2M and 29.4±0.2M (Jupiter masses), and parallax distance 1.9960 pc ± 50 AU. Comparison of the masses and luminosities of Luhman 16 AB to several evolutionary models shows persistent discrepancies in the ages of the two components, but strengthens the case that this system is a member of the 510±95 Myr Oceanus Moving Group. [ABSTRACT FROM AUTHOR]

The last decade of direct imaging (DI) searches for sub-stellar companions has uncovered a widely diverse sample that challenges the current formation models, while highlighting the intrinsically low occurrence rate of wide companions, especially at the lower end of the mass distribution. These results clearly show how blind surveys, crucial to constrain the underlying planet and sub-stellar companion population, are not an efficient way to increase the sample of DI companions. It is therefore becoming clear that efficient target selection methods are essential to ensure a larger number of detections. We present the results of the COPAINS Survey conducted with SPHERE/VLT, searching for sub-stellar companions to stars showing significant proper motion differences (Δμ) between different astrometric catalogues. We observed 25 stars and detected ten companions, including four new BDs: HIP 21152 B, HIP 29724 B, HD 60584 B, and HIP 63734 B. Our results clearly demonstrate how astrometric signatures, in the past only giving access to stellar companions, can now thanks to Gaia reveal companions well in the sub-stellar regime. We also introduce FORECAST (Finely Optimised REtrieval of Companions of Accelerating STars), a tool which allows to check the agreement between position and mass of the detected companions with the measured Δμ. Given the agreement between the values of the masses of the new sub-stellar companions from the photometry with the model-independent ones obtained with FORECAST, the results of COPAINS represent a significant increase in the number of potential benchmarks for BD and planet formation and evolution theories. [ABSTRACT FROM AUTHOR]

Recent observations of resolved cold debris discs at tens of au have revealed that gaps could be a common feature in these Kuiper-belt analogues. Such gaps could be evidence for the presence of planets within the gaps or closer in near the edges of the disc. We present SPHERE observations of HD 92945 and HD 107146, two systems with detected gaps. We constrained the mass of possible companions responsible for the gap to 1–2  M Jup for planets located inside the gap and to less than 5  M Jup for separations down to 20 au from the host star. These limits allow us to exclude some of the possible configurations of the planetary systems proposed to explain the shape of the discs around these two stars. In order to put tighter limits on the mass at very short separations from the star, where direct-imaging data are less effective, we also combined our data with astrometric measurements from Hipparcos and Gaia and radial-velocity measurements. We were able to limit the separation and the mass of the companion potentially responsible for the proper-motion anomaly of HD 107146 to values of 2–7 au and 2–5  M Jup, respectively. [ABSTRACT FROM AUTHOR]

Context. Recent surveys indicate that planets in binary systems are more abundant than previously thought, which is in agreement with theoretical work on disc dynamics and planet formation in binaries. So far, most observational surveys, however, have focused on short-period planets in binaries, thus little is known about the occurrence rates of planets on longer periods (≥10 au). Aims. In order to measure the abundance and physical characteristics of wide-orbit giant exoplanets in binary systems, we have designed the "VIsual Binary Exoplanet survey with Sphere" (VIBES) to search for planets in visual binaries. It uses the SPHERE instrument at VLT to search for planets in 23 visual binary and four visual triple systems with ages of <145 Myr and distances of <150 pc. Methods. We used the IRDIS dual-band imager on SPHERE to acquire high-contrast images of the sample targets. For each binary, the two components were observed at the same time with a coronagraph masking only the primary star. For the triple star, the tight components were treated as a single star for data reduction. This enabled us to effectively search for companions around 50 individual stars in binaries and four binaries in triples. Results. We derived upper limits of <13.7% for the frequency of sub-stellar companions around primaries in visual binaries, <26.5% for the fraction of sub-stellar companions around secondaries in visual binaries, and an occurrence rate of <9.0% for giant planets and brown dwarfs around either component of visual binaries. We have combined our observations with literature measurements to astrometrically confirm, for the first time, that 20 binaries and two triple systems, which were previously known, are indeed physically bound. Finally, we discovered a third component of the binary HD 121336. Conclusions. The upper limits we derived are compatible with planet formation through the core accretion and the gravitational instability processes in binaries. These limits are also in line with limits found for single star and circumbinary planet search surveys. [ABSTRACT FROM AUTHOR]

We present COPAINS (Code for Orbital Parametrization 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, marginalized over unknown orbital elements. Validating our approach using well-constrained systems, we found that our tool provides a good indication of the region of the parameter space where undetected secondaries may be located. Comparing the output of the code to the measured or expected sensitivity from various imaging instruments, this in turn enables us to robustly select the most promising targets for direct imaging campaigns searching for low-mass companions. Such an informed selection method promises to reduce the null detection rates from current programmes and will significantly increase the current census of wide brown dwarfs and planetary companions to stars, which remain extremely rare in the surveys conducted so far. [ABSTRACT FROM AUTHOR]

Aims. HD 142527 is one of the most frequently studied Herbig Ae/Be stars with a transitional disk that hosts a large cavity that is up to about 100 au in radius. For this reason, it has been included in the guaranteed time observation (GTO) SpHere INfrared survey for Exoplanets (SHINE) as part of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT) in order to search for low-mass companions that might explain the presence of the gap. SHINE is a large survey within about 600 young nearby stars are observed with SPHERE with the aim to constrain the occurrence and orbital properties of the giant planet population at large (> 5 au) orbital separation around young stars. Methods. We used the IRDIFS observing mode of SPHERE (IRDIS short for infrared dual imaging and spectrograph plus IFS or integral field spectrograph) without any coronagraph in order to search for and characterize companions as close as 30 mas of the star. Furthermore, we present the first observations that ever used the sparse aperture mask (SAM) for SPHERE both in IRDIFS and IRDIFS_EXT modes. All the data were reduced using the dedicated SPHERE pipeline and dedicated algorithms that make use of the principal component analysis (PCA) and reference differential imaging (RDI) techniques. Results. We detect the accreting low–mass companion HD 142527B at a separation of 73 mas (11.4 au) from the star. No other companions with mass greater than 10 MJ are visible in the field of view of IFS (∼100 au centered on the star) or in the IRDIS field of view (∼400 au centered on the star). Measurements from IFS, SAM IFS, and IRDIS suggest an M6 spectral type for HD 142527B, with an uncertainty of one spectral subtype, compatible with an object of M = 0.11 ± 0.06 M⊙ and R = 0.15 ± 0.07 R⊙. The determination of the mass remains a challenge using contemporary evolutionary models, as they do not account for the energy input due to accretion from infalling material. We consider that the spectral type of the secondary may also be earlier than the type we derived from IFS spectra. From dynamical considerations, we further constrain the mass to 0.26+0.16−0.14 0. 26 − 0.14 + 0.16 $ 0.26^{+0.16}_{-0.14} $ M⊙, which is consistent with both our spectroscopic analysis and the values reported in the literature. Following previous methods, the lower and upper dynamical mass values correspond to a spectral type between M2.5 and M5.5 for the companion. By fitting the astrometric points, we find the following orbital parameters: a period of P = 35 − 137 yr; an inclination of i = 121 − 130°, a value of Ω = 124 − 135° for the longitude of node, and an 68% confidence interval of ∼18 − 57 au for the separation at periapsis. Eccentricity and time at periapsis passage exhibit two groups of values: ∼0.2–0.45 and ∼0.45–0.7 for e, and ∼2015–2020 and ∼2020–2022 for T0. While these orbital parameters might at first suggest that HD 142527B is not the companion responsible for the outer disk truncation, a previous hydrodynamical analysis of this system showed that they are compatible with a companion that is able to produce the large cavity and other observed features. [ABSTRACT FROM AUTHOR]

One field containing WISE J154151.65− 225024.9 was observed by Hubble Space Telescope at three different epochs taken in ∼5 yr. We measured positions of sources in all images and successfully linked these positions to the Gaia DR2 absolute system to derive the astrometric parameters for this faint close-by Y1 brown dwarf. The developed procedure avoids traditional limitations of relative imaging-astrometry with narrow-field cameras, extending Gaia DR2 to fainter magnitudes. We found (μαcos δ, μδ, π) = (−902.62 ± 0.35 mas yr−1, −88.26 ± 0.35 mas yr−1, 168.4 ± 2.2 mas), which represent a sizable improvement over recent determinations in the literature. Applying a correction from relative (π) to absolute parallax (ϖ) we found ϖ = 169 ± 2 mas, corresponding to a distance of 5.9 ± 0.1 pc. [ABSTRACT FROM AUTHOR]