Mass segregation in star clusters is not energy equipartition

Mass segregation in star clusters is often thought to indicate the onset of energy equipartition, where the most massive stars impart kinetic energy to the lower-mass stars and brown dwarfs/free floating planets. The predicted net result of this is that the centrally concentrated massive stars should have significantly lower velocities than fast-moving low-mass objects on the periphery of the cluster. We search for energy equipartition in initially spatially and kinematically substructured N-body simulations of star clusters with N = 1500 stars, evolved for 100 Myr. In clusters that show significant mass segregation we find no differences in the proper motions or radial velocities as a function of mass. The kinetic energies of all stars decrease as the clusters relax, but the kinetic energies of the most massive stars do not decrease faster than those of lower-mass stars. These results suggest that dynamical mass segregation -- which is observed in many star clusters -- is not a signature of energy equipartition from two-body relaxation

Was Planet 9 captured in the Sun’s natal star-forming region?

The presence of an unseen ‘Planet 9’ on the outskirts of the Solar system has been invoked to explain the unexpected clustering of the orbits of several Edgeworth–Kuiper Belt Objects. We use N-body simulations to investigate the probability that Planet 9 was a free-floating planet (FFLOP) that was captured by the Sun in its birth star formation environment. We find that only 1–6 per cent of FFLOPs are ensnared by stars, even with the most optimal initial conditions for capture in star-forming regions (one FFLOP per star, and highly correlated stellar velocities to facilitate capture). Depending on the initial conditions of the star-forming regions, only 5–10 of 10 000 planets are captured on to orbits that lie within the constraints for Planet 9. When we apply an additional environmental constraint for Solar system formation – namely the injection of short-lived radioisotopes into the Sun’s protoplanetary disc from supernovae – we find the probability for the capture of Planet 9 to be almost zero

The SPHERE view of the Taurus star-forming region

The sample of planet-forming disks observed by high-contrast imaging campaigns over the last decade is mature enough to enable the demographical analysis of individual star-forming regions. We present the full census of Taurus sources with VLT/SPHERE polarimetric images available. The whole sample sums up to 43 targets (of which 31 have not been previously published) corresponding to one-fifth of the Class II population in Taurus and about half of such objects that are observable. A large fraction of the sample is apparently made up of isolated faint disks (equally divided between small and large self-shadowed disks). Ambient signal is visible in about one-third of the sample. This probes the interaction with the environment and with companions or the outflow activity of the system. The central portion of the Taurus region almost exclusively hosts faint disks, while the periphery also hosts bright disks interacting with their surroundings. The few bright disks are found around apparently older stars. The overall picture is that the Taurus region is in an early evolutionary stage of planet formation. Yet, some objects are discussed individually, as in an intermediate or exceptional stage of the disk evolution. This census provides a first benchmark for the comparison of the disk populations in different star forming regions

Episodic formation of cometary material in the outburst of a solar-like young star

Our Solar System originated in interstellar gas and dust; the latter is in the form of amorphous silicate particles and carbonaceous dust. The composition of cometary material shows that a significant fraction of the amorphous silicates was transformed into crystalline form during the early evolution of the protosolar nebula. How and when this transformation happened has been controversial, with the main options being heating by the young Sun or shock heating. Here we report mid-infrared features in the outburst spectrum of the young solar-like star EX Lupi that were not present in quiescence. We attribute them to crystalline forsterite; the crystals were produced via thermal annealing in the surface layer of the inner disk by heat from the outburst, a process that has hitherto not been considered. The observed lack of cold crystals excludes shock heating at larger radii.Comment: 13 pages of PDF, including Supplementary Informatio

Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk

Context. The observation of planets in their formation stage is a crucial but very challenging step in understanding when, how, and where planets form. PDS 70 is a young pre-main sequence star surrounded by a transition disk, in the gap of which a planetary-mass companion has recently been discovered. This discovery represents the first robust direct detection of such a young planet, possibly still at the stage of formation. Aims. We aim to characterize the orbital and atmospheric properties of PDS 70 b, which was first identified on May 2015 in the course of the SHINE survey with SPHERE, the extreme adaptive-optics instrument at the VLT. Methods. We obtained new deep SPHERE/IRDIS imaging and SPHERE/IFS spectroscopic observations of PDS 70 b. The astrometric baseline now covers 6 yr, which allowed us to perform an orbital analysis. For the first time, we present spectrophotometry of the young planet which covers almost the entire near-infrared range (0.96–3.8 μm). We use different atmospheric models covering a large parameter space in temperature, log g, chemical composition, and cloud properties to characterize the properties of the atmosphere of PDS 70 b. Results. PDS 70 b is most likely orbiting the star on a circular and disk coplanar orbit at ~22 au inside the gap of the disk. We find a range of models that can describe the spectrophotometric data reasonably well in the temperature range 1000–1600 K and log g no larger than 3.5 dex. The planet radius covers a relatively large range between 1.4 and 3.7 RJ with the larger radii being higher than expected from planet evolution models for the age of the planet of 5.4 Myr. Conclusions. This study provides a comprehensive data set on the orbital motion of PDS 70 b, indicating a circular orbit and a motion coplanar with the disk. The first detailed spectral energy distribution of PDS 70 b indicates a temperature typical of young giant planets. The detailed atmospheric analysis indicates that a circumplanetary disk may contribute to the total planetflux

Review and scientific prospects of high-contrast optical stellar interferometry

This is the final version. Available from SPIE via the DOI in this recordSPIE Astronomical Telescopes + Instrumentation conference, 14 - 18 December 2020, Online OnlyHigh-contrast optical stellar interferometry generally refers to instruments able to detect circumstellar emission at least a few hundred times fainter than the host star at high-angular resolution (typically within a few λ/D). While such contrast levels have been enabled by classical modal-filtered interferometric instruments such as VLTI/PIONIER, CHARA/FLUOR, and CHARA/MIRC the development of instruments able to filter out the stellar light has significantly pushed this limit, either by nulling interferometry for on-axis observations (e.g., PFN, LBTI, GLINT) or by off-axis classical interferometry with VLTI/GRAVITY. Achieving such high contrast levels at small angular separation was made possible thanks to significant developments in technology (e.g., adaptive optics, integrated optics), data acquisition (e.g., fringe tracking, phase chopping), and data reduction techniques (e.g., nulling self-calibration). In this paper, we review the current status of high-contrast optical stellar interferometry and present its key scientific results. We then present ongoing activities to improve current ground-based interferometric facilities for high-contrast imaging (e.g., Hi-5/VIKING/BIFROST of the ASGARD instrument suite, GRAVITY+) and the scientific milestones that they would be able to achieve. Finally, we discuss the long-term future of high-contrast stellar interferometry and, in particular, ambitious science cases that would be enabled by space interferometry (e.g., LIFE, space-PFI) and large-scale ground-based projects (PFI).European Research Council (ERC