Observations of circumstellar environments that look for the direct signal of exoplanets and the scattered light from disks have significant instrumental implications. In the past 15 years, major developments in adaptive optics, coronagraphy, optical manufacturing, wavefront sensing, and data processing, together with a consistent global system analysis have brought about a new generation of high-contrast imagers and spectrographs on large ground-based telescopes with much better performance. One of the most productive imagers is the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE), which was designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE includes an extreme adaptive optics system, a highly stable common path interface, several types of coronagraphs, and three science instruments. Two of them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager and Spectrograph (IRDIS), were designed to efficiently cover the near-infrared range in a single observation for an efficient search of young planets. The third instrument, ZIMPOL, was designed for visible polarimetric observation to look for the reflected light of exoplanets and the light scattered by debris disks. These three scientific instruments enable the study of circumstellar environments at unprecedented angular resolution, both in the visible and the near-infrared. In this work, we thoroughly present SPHERE and its on-sky performance after four years of operations at the VLT.

/pdf/sphere-the-exoplanet-imager-for-the-very-large-telescope-1mlo24tsno.pdf

SPHERE: the exoplanet imager for the Very Large Telescope

We report the results of a ~4 yr direct imaging survey of 104 stars to resolve and characterize circumstellar debris disks in scattered light as part of the Gemini Planet Imager (GPI) Exoplanet Survey We targeted nearby (≲150 pc), young (≲500 Myr) stars with high infrared (IR) excesses (L_(IR)/L★ > 10⁻⁵), including 38 with previously resolved disks Observations were made using the GPI high-contrast integral field spectrograph in H-band (16 μm) coronagraphic polarimetry mode to measure both polarized and total intensities We resolved 26 debris disks and 3 protoplanetary/transitional disks Seven debris disks were resolved in scattered light for the first time, including newly presented HD 117214 and HD 156623, and we quantified basic morphologies of five of them using radiative transfer models All of our detected debris disks except HD 156623 have dust-poor inner holes, and their scattered-light radii are generally larger than corresponding radii measured from resolved thermal emission and those inferred from spectral energy distributions To assess sensitivity, we report contrasts and consider causes of nondetections Detections were strongly correlated with high IR excess and high inclination, although polarimetry outperformed total intensity angular differential imaging for detecting low-inclination disks (≲70°) Based on postsurvey statistics, we improved upon our presurvey target prioritization metric predicting polarimetric disk detectability We also examined scattered-light disks in the contexts of gas, far-IR, and millimeter detections Comparing H-band and ALMA fluxes for two disks revealed tentative evidence for differing grain properties Finally, we found no preference for debris disks to be detected in scattered light if wide-separation substellar companions were present

https://iopscience.iop.org/article/10.3847/1538-3881/ab9199/pdf

Debris Disk Results from the Gemini Planet Imager Exoplanet Survey's Polarimetric Imaging Campaign

Over the past three decades, we have witnessed one of the great revolutions in our understanding of the cosmos - the dawn of the Exoplanet Era. Where once we knew of just one planetary system (the Solar system), we now know of thousands, with new systems being announced on a weekly basis. Of the thousands of planetary systems we have found to date, however, there is only one that we can study up-close and personal - the Solar system. 
In this review, we describe our current understanding of the Solar system for the exoplanetary science community - with a focus on the processes thought to have shaped the system we see today. In section one, we introduce the Solar system as a single well studied example of the many planetary systems now observed. In section two, we describe the Solar system's small body populations as we know them today - from the two hundred and five known planetary satellites to the various populations of small bodies that serve as a reminder of the system's formation and early evolution. In section three, we consider our current knowledge of the Solar system's planets, as physical bodies. In section four, we discuss the research that has been carried out into the Solar system's formation and evolution, with a focus on the information gleaned as a result of detailed studies of the system's small body populations. In section five, we discuss our current knowledge of planetary systems beyond our own - both in terms of the planets they host, and in terms of the debris that we observe orbiting their host stars. 
As we learn ever more about the diversity and ubiquity of other planetary systems, our Solar system will remain the key touchstone that facilitates our understanding and modelling of those newly found systems, and we finish section five with a discussion of the future surveys that will further expand that knowledge.

Solar System Physics for Exoplanet Research

We present a velocimetric and spectropolarimetric analysis of 27 observations of the 22-Myr M1 star AU Microscopii (Au Mic) collected with the high-resolution $YJHK$ (0.98-2.35 $\mu$m) spectropolarimeter SPIRou from 2019 September 18 to November 14. Our radial velocity (RV) time-series exhibits activity-induced fluctuations of 45 m/s RMS, about three times smaller than those measured in the optical domain, that we filter using Gaussian Process Regression. We report a 3.9$\sigma$-detection of the recently-discovered 8.46-d transiting planet AU Mic b, with an estimated mass of $17.1^{+4.7}_{-4.5}$ M$_{\odot}$ and a bulk density of $1.3 \pm 0.4$ g/cm$^{-3}$, inducing a RV signature of semi-amplitude $K=8.5^{+2.3}_{-2.2}$ m/s in the spectrum of its host star. A consistent detection is independently obtained when we simultaneously image stellar surface inhomogeneities and estimate the planet parameters with Zeeman-Doppler Imaging (ZDI). Using ZDI, we invert the time series of unpolarized and circularly-polarized spectra into surface brightness and large-scale magnetic maps. We find a mainly poloidal and axisymmetric field of 475 G, featuring, in particular, a dipole of 450 G tilted at 19° to the rotation axis. Moreover, we detect a strong differential rotation of d$\Omega = 0.167 \pm 0.009$ rad/d shearing the large-scale field, about twice stronger than that shearing the brightness distribution, suggesting that both observables probe different layers of the convective zone. Even though we caution that more RV measurements are needed to accurately pin down the planet mass, AU Mic b already appears as a prime target for constraining planet formation models, studying the interactions with the surrounding debris disk, and characterizing its atmosphere with upcoming space- and ground-based missions.

Investigating the young AU Mic system with SPIRou: large-scale stellar magnetic field and close-in planet mass

Context. The nearby and young M star AU Mic is surrounded by a debris disk in which we previously identified a series of large-scale arch-like structures that have never been seen before in any other debris disk and that move outward at high velocities.Aims. We initiated a monitoring program with the following objectives: (1) track the location of the structures and better constrain their projected speeds, (2) search for new features emerging closer in, and ultimately (3) understand the mechanism responsible for the motion and production of the disk features.Methods. AU Mic was observed at 11 different epochs between August 2014 and October 2017 with the IR camera and spectrograph of SPHERE. These high-contrast imaging data were processed with a variety of angular, spectral, and polarimetric differential imaging techniques to reveal the faintest structures in the disk. We measured the projected separations of the features in a systematic way for all epochs. We also applied the very same measurements to older observations from the Hubble Space Telescope (HST) with the visible cameras STIS and ACS.Results. The main outcomes of this work are (1) the recovery of the five southeastern broad arch-like structures we identified in our first study, and confirmation of their fast motion (projected speed in the range 4–12 km s−1 ); (2) the confirmation that the very first structures observed in 2004 with ACS are indeed connected to those observed later with STIS and now SPHERE; (3) the discovery of two new very compact structures at the northwest side of the disk (at 0.40′′ and 0.55′′ in May 2015) that move to the southeast at low speed; and (4) the identification of a new arch-like structure that might be emerging at the southeast side at about 0.4′′ from the star (as of May 2016).Conclusions. Although the exquisite sensitivity of SPHERE allows one to follow the evolution not only of the projected separation, but also of the specific morphology of each individual feature, it remains difficult to distinguish between possible dynamical scenarios that may explain the observations. Understanding the exact origin of these features, the way they are generated, and their evolution over time is certainly a significant challenge in the context of planetary system formation around M stars.

/pdf/observations-of-fast-moving-features-in-the-debris-disk-of-29addybw0a.pdf

Observations of fast-moving features in the debris disk of AU Mic on a three-year timescale : Confirmation and new discoveries

Context. Recent observations of the edge-on debris disk of AU Mic have revealed asymmetric, fast outward-moving arch-like structures above the disk midplane. Although asymmetries are frequent in debris disks, no model can readily explain the characteristics of these features. Aims. We present a model aiming to reproduce the dynamics of these structures, more specifically their high projected speeds and their apparent position. We test the hypothesis of dust emitted by a point source and then expelled from the system by the strong stellar wind of this young M-type star. In this model we make the assumption that the dust grains follow the same dynamics as the structures, i.e., they are not local density enhancements. Methods. We perform numerical simulations of test particle trajectories to explore the available parameter space, in particular the radial location R 0 of the dust producing parent body and the size of the dust grains as parameterized by the value of β (ratio of stellar wind and radiation pressure forces over gravitation). We consider the cases of a static and of an orbiting parent body. Results. We find that for all considered scenarios (static or moving parent body), there is always a set of ( R 0 ,β ) parameters able to fit the observed features. The common characteristics of these solutions is that they all require a high value of β , of around 6. This means that the star is probably very active, and the grains composing the structures are submicronic in order for observable grains to reach such high β values. We find that the location of the hypothetical parent body is closer in than the planetesimal belt, around 8 ± 2 au (orbiting case) or 28 ± 7 au (static case). A nearly periodic process of dust emission appears, of 2 yr in the orbiting scenarios and 7 yr in the static case. Conclusions. We show that the scenario of sequential dust releases by an unseen point-source parent body is able to explain the radial behavior of the observed structures. We predict the evolution of the structures to help future observations discriminate between the different parent body configurations that have been considered. In the orbiting parent body scenario, we expect new structures to appear on the northwest side of the disk in the coming years.

/pdf/expelled-grains-from-an-unseen-parent-body-around-au-4t76sbewid.pdf

Expelled grains from an unseen parent body around AU Microscopii

ESO 
CNRS (France) 
MPIA (Germany) 
INAF (Italy) 
FINES (Switzerland) 
NOVA (Netherlands) 
European Commission Sixth Framework Programme as part of the Optical Infrared Coordination Network for Astronomy (OPTICON) 	
RII3-Ct-2004-001566 
226604 
312430 
European Commission Seventh Framework Programme as part of the Optical Infrared Coordination Network for Astronomy (OPTICON) 	
RII3-Ct-2004-001566 
226604 
312430 
LabEx OSUG@2020, Investissement d'avenir 	
ANR10 LABX56 
"Progetti Premiali" funding scheme of the Italian Ministry of Education, University, and Research 
project PRIN-INAF The Cradle of Life - GENESIS- SKA (General Conditions in Early Planetary Systems for the rise of life with SKA) 
ICM Nucleo Milenio de Formacion Planetaria, NPF 
Universidad de Valparaiso 
"Programme National de Planetologie" (PNP) of CNRS/INSU - CNES 
European Union's Horizon research and innovation programme under the Marie Sklodowska-Curie grant 	
664931 
STFC via the Institute of Astronomy, Cambridge Consolidated Grant 
ANR of France 	
ANR-16-CE31-0013 
Spanish MICINN 	
AyA2011-24052

/pdf/new-disk-discovered-with-vlt-sphere-around-the-m-star-gsc-4xxmffjaje.pdf

New disk discovered with VLT/SPHERE around the M star GSC 07396-00759

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Expelled grains from an unseen parent body around AU Microscopii

New disk discovered with VLT/SPHERE around the M star GSC 07396-00759