arXiv subjects

H. M. Schmid

Publications and source records attributed to H. M. Schmid.

At least 19 recordsLinked to original sources

arXiv2026

The SPHERE infrared survey for exoplanets (SHINE) V. Full sample characterization

Unbiased surveys of large stellar samples are the prime means through which the prevalence of exoplanets can be derived, and crucial constraints to planet formation models can be set. Direct imaging (DI) is ideally positioned to probe the outer regions (5-300au) of planetary systems, providing complementary information to techniques such as transits and radial velocities. We present the full sample of the SpHere INfrared survey for Exoplanets (SHINE), the second largest DI campaign to date. SHINE observed 460 stars between 2015 and 2023 thanks to the guaranteed time observations (GTO) allocated by ESO to the SPHERE consortium at VLT. The goal of this paper is to homogeneously derive the stellar properties of the targets and to define a subsample of young single hosts to be used as a starting point for the final statistical analysis of the survey. Stellar ages were determined based on kinematic indicators (such as the membership to young moving groups), age diagnostics (lithium abundance, rotation, activity), and isochrone fitting. A thorough vetting for binarity was undertaken combining astrometric, spectroscopic, and imaging data. A subsample of 333 stars, covering a large extent of stellar ages and masses, was constructed. Selection criteria, global features, as well as the properties of individual stars are reported and discussed.

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arXiv2025

Characterization of debris disks observed with SPHERE

This study aims to characterize debris disks observed with SPHERE across multiple programs, with the goal of identifying systematic trends in disk morphology, dust mass, and grain properties as a function of stellar parameters. We analyzed a sample of 161 young stars using SPHERE observations at optical and near-IR wavelengths. Disk geometries were derived from ellipse fitting and model grids, while dust mass and properties were constrained by modified blackbody (MBB) and size distribution (SD) modeling of SEDs. The dynamical modeling was performed to assess whether the observed disk structures can be explained by the presence of unseen planets. We resolved 51 debris disks, including four new detections: HD 36968, BD-20 951, and the inner belts of HR 8799 and HD 36546. In addition, we found a second transiting giant planet in the HD 114082 system, with a radius of 1.29 $R_{\rm Jup}$ and an orbital distance of ~1 au. We identified nine multi-belt systems, with outer-to-inner belt radius ratios of $1.5-2$, and found close agreement between scattered-light and millimeter-continuum belt radii. They scale weakly with stellar luminosity ($R_{\rm belt} \propto L_{\star}^{0.11}$), but show steeper dependencies when separated by CO and CO$_2$ freeze-out regimes. Disk fractional luminosities follow collisional decay trends, declining as $t_{\rm age}^{-1.18}$ for A and $t_{\rm age}^{-0.81}$ for F stars. The inferred dust masses span $10^{-5}-1\,M_\oplus$ from MBB and $0.01-1\,M_\oplus$ from SD modeling. These masses scale as $R_{\rm belt}^n$ with $n>2$ in belt radius and super-linearly with stellar mass, consistent with trends seen in protoplanetary disks. Analysing correlation between disk polarized flux and IR excess, we found an offset of ~1 dex between total-intensity (HST) and polarized fluxes. A new parametric approach to estimate dust albedo and maximum polarization fraction is introduced.

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arXiv2025

Resolution and calibration effects in high contrast polarimetric imaging of circumstellar scattering regions

Many circumstellar dust scattering regions have been detected and investigated with polarimetric imaging. However, the quantitative determination of the intrinsic polarization and of dust properties is difficult because of complex observational effects. This work investigates instrumental convolution and polarimetric calibration effect for high contrast imaging polarimetry with the aim to define procedures for accurate measurements of the circumstellar polarization. For this we simulate the instrumental convolution and polarimetric cancellation effects for a Gaussian PSF and an extended PSF_{AO} typical for a modern adaptive optics system. Further, polarimetric zero-point corrections (zp-corrections) are simulated for different cases like coronagraphic observations or systems with barely resolved circumstellar scattering regions. We find that the PSF convolution reduces the integrated azimuthal polarization Q_phi for the scattering region while the net Stokes signals Q and U are not changed. For non-axisymmetric systems a spurious U_phi-signal is introduced. These effects are strong for compact systems but scattering regions can still be detected down to small separations while unresolved scattering regions can be constrained by the central Stokes Q,U signal. The smearing by PSF_{AO} produces an extended, low surface brightness polarization signal changing the angular distribution of the polarization, but the initial signal can be recovered partly from the Stokes Q and U quadrant pattern. A polarimetric zp-correction applied for the removal of offsets from instrumental or interstellar polarization depends on the selected reference region and can also introduce strong bias effects for the azimuthal distribution of the polarization signal. Strategies for the zp-correction are described for coronagraphic data or observations of partly unresolved systems.

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arXiv2025

Multiwavelength analysis of polarized light in HD 100453

HD 100453 disk is a prototypical companion-disk interaction system hosting a pair of spirals and a substellar companion. We present new noncoronagraphic high-contrast imaging observations of HD 100453 with $V$ filter on SPHERE/ZIMPOL. We combined high-contrast imaging data of the reflected light from 0.55 to 2.2 $μm$ using the $V$, $I'$, $J$, and $Ks$ band data of ZIMPOL and IRDIS at VLT/SPHERE. For each observational epoch, we corrected for the smearing effect to derive the intrinsic disk-integrated polarized flux. We derived a steady increase with wavelengths from $\hat{Q}_φ/I_{\star}(V)=0.3\%$ to $\hat{Q}_φ/I_{\star}(K)=1.2\%$. We applied reference differential imaging to extract the disk intensity for the $V$ and $Ks$ bands using star hopping observations. We obtained the first $V$-band total intensity for HD 100453 with ZIMPOL star hopping. The integrated total flux $I_{\rm disk}/I_{\star}(V)=1.5\%$ increases to $I_{\rm disk}/I_{\star}(K)=4.8\%$. Both the total intensity and the polarization fraction show red colors, and the intrinsic maximum degree of polarization increases moderately from $40\%$ to $55\%$. We then used RADMC-3D radiative transfer modeling with a parametrized Henyey-Greenstein phase function to constrain the dust properties. From the $V$ to $Ks$ band, the dominating dust in the outer disk has an increasing scattering albedo and degree of polarization, while the asymmetry parameter slightly decreases. The outer disk of HD 100453 contains sub-micron-sized low porosity grains/aggregates. The cavity in scattered light is not empty and is replenished with optically thin dust with a maximum size of $\leq 0.1μm$. The linear polarization is higher in the spiral region than in the other regions, suggesting different dust properties in those regions.

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arXiv2025

The SPHERE infrared survey for exoplanets (SHINE). V. Complete observations, data reduction and analysis, detection performances, and final results

During the past decade, state-of-the-art planet-finder instruments like SPHERE@VLT, coupling coronagraphic devices and extreme adaptive optics systems, unveiled, thanks to large surveys, around 20 planetary mass companions at semi-major axis greater than 10 astronomical units. Direct imaging being the only detection technique to be able to probe this outer region of planetary systems, the SPHERE infrared survey for exoplanets (SHINE) was designed and conducted from 2015 to 2021 to study the demographics of such young gas giant planets around 400 young nearby solar-type stars. In this paper, we present the observing strategy, the data quality, and the point sources analysis of the full SHINE statistical sample as well as snapSHINE. Both surveys used the SPHERE@VLT instrument with the IRDIS dual band imager in conjunction with the integral field spectrograph IFS and the angular differential imaging observing technique. All SHINE data (650 datasets), corresponding to 400 stars, including the targets of the F150 survey, are processed in a uniform manner with an advanced post-processing algorithm called PACO ASDI. An emphasis is put on the classification and identification of the most promising candidate companions. Compared to the previous early analysis SHINE F150, the use of advanced post-processing techniques significantly improved by one or 2 magnitudes (x3-x6) the contrast detection limits, which will allow us to put even tighter constraints on the radial distribution of young gas giants. This increased sensitivity directly places SHINE as the largest and deepest direct imaging survey ever conducted. We detected and classified more than 3500 physical sources. One additional substellar companion has been confirmed during the second phase of the survey (HIP 74865 B), and several new promising candidate companions are awaiting second epoch confirmations.

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arXiv2024

Temporal and chromatic variation of polarized scattered light in the outer disk of PDS 70

PDS 70 is a unique system as it hosts a protoplanetary disk with two confirmed forming planets, making it an ideal target for characterizing dust in such disks. We present new high-contrast polarimetric differential imaging of PDS 70 using the $N\_R$ filter on SPHERE/ZIMPOL, combined with archival VLT/SPHERE data across five wavelengths ($N\_R$, $VBB$, $J$, $H$, and $Ks$) spanning seven epochs over eight years. For each epoch, we corrected smearing effects from instrument resolution, analyzed azimuthal brightness profiles, and derived intrinsic disk-integrated polarized reflectivity and brightness contrasts. Our analysis reveals significant temporal variability in both integrated polarized reflectivity and azimuthal brightness profiles, suggesting variable shadowing on the outer disk from unresolved inner disk structures. Nonetheless, we observe a systematic wavelength-dependent contrast between the near and far sides of the inclined disk, highlighting the need to consider shadowing from the inner disk and surface geometry of the reflecting disk in data interpretation.

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arXiv2024

SPHERE RefPlanets: Search for epsilon Eridani b and warm dust

We carried out very deep VLT/SPHERE imaging polarimetry of the nearby system Eps Eri based on 38.5 hours of integration time with a 600 - 900 nm broadband filter to search for polarized scattered light from a planet or from circumstellar dust using AO, coronagraphy, high precision differential polarimetry, and angular differential imaging. We have improved several data reduction and post-processing techniques and also developed new ones to further increase the sensitivity of SPHERE/ZIMPOL. The data provide unprecedented contrast limits, but no significant detection of a point source or an extended signal from circumstellar dust. For each observing epoch, we obtained a point source contrast for the polarized intensity between $2\cdot 10^{-8}$ and $4\cdot 10^{-8}$ at the expected separation of the planet Eps Eri b of 1'' near quadrature phase. The polarimetric contrast limits are about six to 50 times better than the intensity limits because polarimetric imaging is much more efficient in speckle suppression. Combining the entire 14-month data set to the search for a planet moving on a Keplerian orbit with the K-Stacker software further improves the contrast limits by a factor of about two, to about $8 \cdot 10^{-9}$ at 1''. This would allow the detection of a planet with a radius of about 2.5 Jupiter radii. The surface brightness contrast limits achieved for the polarized intensity from an extended scattering region are about 15 mag arcsec$^{-2}$ at 1'', or up to 3 mag arcsec$^{-2}$ deeper than previous limits. For Eps Eri, these limits exclude the presence of a narrow dust ring and they constrain the dust properties. This study shows that the polarimetric contrast limits for reflecting planets with SPHERE/ZIMPOL can be improved to a level $<10^{-8}$ simply by collecting more data over many nights and using the K-Stacker software.

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arXiv2024

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.

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arXiv2023

Color measurements of the polarized light scattered by the dust in protoplanetary disks

Ground-based high-contrast instruments have yielded reflected light images of protoplanetary disks. Quantitative measurements of the reflected radiation provide strong constraints on the scattering dust which can clarify the dust particle evolution in these disks and the composition of the forming planets. This study aimed to derive the wavelength dependence of polarized reflectivity $(\hat{Q}_φ/I_\star)_λ$ for 11 disks, constraining dust properties and identifying systematic differences. Using ESO archive data from SPHERE/ZIMPOL and SPHERE/IRDIS instruments, we obtained accurate intrinsic polarized reflectivity $\hat{Q}_φ/I_\star$ values at wavelengths from 0.62$μ$m to 2.2$μ$m. Polarized reflectivities ranged from $Q_φ/I_\star\approx 0.1\%$ to 1.0$\%$, with PSF-corrected values averaging 1.6 times higher than observed. Accurate PSF calibrations reduced systematic errors to $Δ\hat{Q}_φ/\hat{Q}_φ\approx 10\%$ or less. For each disk, we derived a polarized reflectivity color $η_{V/IR}$ between a visible band $λ<1~μ$m and a near-IR band $λ>1~μ$m and other wavelength combinations. Wavelength gradients $η$ varied significantly among objects. Disks around Herbig stars (HD 169142, HD 135334B, HD 100453, MWC 758, and HD 142527) showed a red color $η_{\rm V/IR}>0.5$, suggesting rather compact dust grains. T-Tauri star disks (PDS 70, TW Hya, RX J1615, and PDS 66) were predominantly gray $-0.5<η_{\rm V/IR}<0.5$, with an absence of blue colors incompatible with porous aggregates. Exceptional red colors for LkCa15 and MWC758 were attributed to potential extra reddening from hot dust near the star. Future studies incorporating parameters like fractional polarization $\langle p_φ\rangle$ hold promise for advancing our understanding of dust properties within protoplanetary disks.

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arXiv2023

The high-albedo, low polarization disk around HD 114082 harbouring a Jupiter-sized transiting planet

We present new optical and near-IR images of debris disk around the F-type star HD 114082. We obtained direct imaging observations and analysed the TESS photometric time series data of this target with a goal to search for planetary companions and to characterise the morphology of the debris disk and the scattering properties of dust particles. HD 114082 was observed with the VLT/SPHERE instrument: the IRDIS camera in the K band together with the IFS in the Y, J and H band using the ADI technique as well as IRDIS in the H band and ZIMPOL in the I_PRIME band using the PDI technique. The scattered light images were fitted with a 3D model for single scattering in an optically thin dust disk. We performed aperture photometry in order to derive the scattering and polarized phase functions, polarization fraction and spectral scattering albedo for the dust particles in the disk. This method was also used to obtain the reflectance spectrum of the disk to retrieve the disk color and study the dust reflectivity in comparison to the debris disk HD 117214. We also performed the modeling of the HD 114082 light curve measured by TESS using the models for planet transit and stellar activity to put constraints on radius of the detected planet and its orbit. The debris disk appears as an axisymmetric debris belt with a radius of ~0.37$"$ (35 au), inclination of ~83$^\circ$ and a wide inner cavity. Dust particles in HD 114082 have a maximum polarization fraction of ~17% and a high reflectivity which results in a spectral scattering albedo of 0.65. The analysis of TESS photometric data reveals a transiting planetary companion to HD 114082 with a radius of $\sim$1~$\rm R_{J}$ on an orbit with a semi-major axis of $0.7 \pm 0.4$ au. Combining different data, we reach deep sensitivity limits in terms of companion masses down to ~5$M_{\rm Jup}$ at 50 au, and ~10 $M_{\rm Jup}$ at 30 au from the central star.

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arXiv2022

Searching for H$_α$-emitting sources in the gaps of five transitional disks. SPHERE/ZIMPOL high-contrast imaging

(Pre-)transitional disks show gaps and cavities that can be related with on-going planet formation. According to theory, young embedded planets can accrete material from the circumplanetary and circumstellar disks, so that they could be detected in accretion tracers, like the H$_α$ emission line. In this work, we present spectral angular differential imaging AO-assisted observations of five (pre-)transitional disks obtained with SPHERE/ZIMPOL at the Very Large Telescope (VLT). They were obtained in the H$_α$ line and the adjacent continuum. We have combined spectral and angular differential imaging techniques to increase the contrast in the innermost regions close to the star, and search for the signature of young accreting protoplanets. As a result, the reduced images do not show any clear H$_α$ point source around any of the targets. We report faint H$_α$ emissions around TW Hya and HD163296: while the former is most probably an artifact related with a spike, the nature of the latter remains unclear. The spectral and angular differential images yield contrasts of 6--8 magnitudes at separations of $\sim$ 100 mas from the central stars, except in the case of LkCa15, with values of $\sim$3 mag. We have estimated upper limits to the accretion luminosity of potential protoplanets, obtaining that planetary models provide an average value of $L_{\rm acc} \sim 10^{-4}$ $L_{\odot}$ at 200 mas, which is $\sim$2 orders of magnitude higher than the $L_{\rm acc}$ estimated from the extrapolation of the $L_{H_α}$ - $L_{acc}$ stellar relationship. We explain the lack of protoplanet detections as a combination of different factors, like e.g. episodic accretion, extinction from the circumstellar and circumplanetray disks, and/or a majority of low-mass, low-accreting planets.

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arXiv2022

Near-IR and visual high resolution polarimetric imaging with AO systems

Many spectacular polarimetric images have been obtained in recent years with adaptive optics (AO) instruments at large telescopes because they profit significantly from the high spatial resolution. This paper summarizes some basic principles for AO polarimetry, discusses challenges and limitations of these systems, and describes results which illustrate the performance of AO polarimeters for the investigation of circumstellar disks, of dusty winds from evolved stars, and for the search of reflecting extra-solar planets.

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arXiv2022

Distribution of solids in the rings of the HD 163296 disk: a multiwavelength study

In this paper we analyze new observations from ALMA and VLA, at a high angular resolution corresponding to 5 - 8 au, of the protoplanetary disk around HD 163296 to determine the dust spatial distribution and grain properties. We fit the spectral energy distribution as a function of the radius at five wavelengths from 0.9 to 9\,mm, using a simple power law and a physical model based on an analytic description of radiative transfer that includes isothermal scattering. We considered eight dust populations and compared the models' performance using Bayesian evidence. Our analysis shows that the moderately high optical depth ($τ$>1) at $λ\leq$ 1.3 mm in the dust rings artificially lower the millimeter spectral index, which should therefore not be considered as a reliable direct proxy of the dust properties and especially the grain size. We find that the outer disk is composed of small grains on the order of 200 $μ$m with no significant difference between rings at 66 and 100 au and the adjacent gaps, while in the innermost 30 au, larger grains ($\geq$mm) could be present. We show that the assumptions on the dust composition have a strong impact on the derived surface densities and grain size. In particular, increasing the porosity of the grains to 80\% results in a total dust mass about five times higher with respect to grains with 25\% porosity. Finally, we find that the derived opacities as a function of frequency deviate from a simple power law and that grains with a lower porosity seem to better reproduce the observations of HD163296. While we do not find evidence of differential trapping in the rings of HD163296, our overall results are consistent with the postulated presence of giant planets affecting the dust temperature structure and surface density, and possibly originating a second-generation dust population of small grains.

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arXiv2022

A model grid for the reflected light from transition disks

The dust in protoplanetary disks is an important ingredient in planet formation and can be investigated with model simulations and quantitative imaging polarimetry of the scattered stellar light. This study explores circumstellar disks with calculations for the intensity and polarization of the reflected light. The photon scattering and absorption by the disk are calculated with a Monte Carlo method for a grid of simple, rotationally symmetric models approximated at each point by a plane-parallel dusty atmosphere. The results of our simple disk models reproduce well the measurements for the intensity $I/I_{\star}$, azimuthal polarization $Q_φ/I_{\star}$, and fractional polarization $p_φ$ reported for well-observed transition disks. They describe the dependencies of the scattered radiation on the disk geometry and the dust scattering parameters in detail. Particularly strong constraints on disk properties can be obtained from certain diagnostic quantities. Therefore, they can be used as a diagnostic tool for the analysis of quantitative measurements, specifically in constraining or even determining the scattering properties of the dust particles in disks. Collecting and comparing such information for many systems is required to understand the nature of the scattering dust in planet-forming disks.

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arXiv2021

Quadrant polarization parameters for the scattered light of circumstellar disks. Analysis of debris disk models and observations of HR 4796A

This paper introduces the quadrant polarization parameters $Q_{000}$, $Q_{090}$, $Q_{180}$, $Q_{270}$ for Stokes $Q$ and $U_{045}$, $U_{135}$, $U_{225}$, $U_{315}$ for Stokes $U$ for the characterization of the azimuthal dependence of the scattering polarization of spatially resolved circumstellar disks illuminated by the central star. These parameters are based on the natural Stokes $Q$ and $U$ quadrant pattern produced by circumstellar scattering. They provide a simple test of the deviations of the disk geometry from axisymmetry and can be used to constrain the scattering phase function for optically thin disks without detailed model fitting of disk images. The parameters are easy to derive from observations and model calculations and are therefore well suited to systematic studies of the dust scattering in circumstellar disks. It is shown for models of optically thin and rotationally symmetric debris disks that the quadrant parameters normalized to the integrated azimuthal polarization or quadrant ratios like $Q_{000}/Q_{180}$ depend only on the disk inclination $i$ and the polarized scattering phase function of the dust, and they do not depend on the radial distribution of the scattering emissivity. Because $i$ is usually well known for resolved disk, we can derive the shape of the phase function for the sampled scattering angle range. This finding also applies to models with vertical extensions as observed for debris disks. Diagnostic diagrams are calculated for normalized quadrant parameters and quadrant ratios for the determination of the asymmetry parameter $g$ of the polarized Henyey-Greenstein scattering phase function. We apply these diagrams to measurements of HR 4796A, and find that a phase function with only one parameter does not reproduce the data well, but find a better solution with a three-parameter phase function.

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arXiv2021

Quantitative polarimetry of the disk around HD 169142

We investigate high resolution imaging polarimetry of HD 169142 taken in the R' and I' bands with the SPHERE/ZIMPOL instrument for an accurate quantitative measurement of the radiation scattered by the circumstellar disk. We observe a strong dependence of the disk polarimetry on the atmospheric turbulences, which strongly impact the AO performance. With our non-coronagraphic data we can analyze the polarimetric signal of the disk simultaneously with the strongly variable stellar PSF, correct for the convolution effects to determine the intrinsic polarization of the disk with high precision. We also extract the disk intensity signal and derive the fractional polarization. We compare the scattered flux from the inner and outer disk rings with the corresponding thermal dust emissions measured in the IR and estimate the ratio between scattered and absorbed radiation. We obtain ratios between the integrated disk polarization flux and total system flux of 0.43% for the R' band and 0.55% for the I' band. This indicates a reddish color for the light reflection by the dust. The inner disk ring contributes about 75% to the total disk flux. The obtained fractional polarization for the bright inner disk ring is 23.6% for the I' band and similar for the R' band. The ratio between scattered disk flux and star flux is about 2.3%. This is much smaller than the derived IR excess of 17.6% for the disk components observed in scattered light. This indicates that only a small fraction of the radiation illuminating the disk is scattered; most is absorbed and reemitted in the IR. We conclude that accurate, quantitative measurements of the scattered light from circumstellar disks are possible with ground based high contrast AO systems, if the PSF convolution effects are properly taken into account, and this provides important new constraints on the properties of the scattering dust.

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arXiv2021

HD142527: Quantitative disk polarimetry with SPHERE

We present high-precision photometry and polarimetry for the protoplanetary disk around HD142527, with a focus on determining the light scattering parameters of the dust. We re-reduced polarimetric differential imaging data of HD142527 in the VBB (735 nm) and H-band (1625 nm) from the ZIMPOL and IRDIS subinstruments of SPHERE/VLT. With polarimetry and photometry based on reference star differential imaging, we were able to measure the linearly polarized intensity and the total intensity of the light scattered by the circumstellar disk with high precision. We used simple Monte Carlo simulations of multiple light scattering by the disk surface to derive constraints for three scattering parameters of the dust: the maximum polarization of $P_{\rm max}$, the asymmetry parameter $g$, and the single-scattering albedo $ω$. We measure a reflected total intensity of $51.4\pm1.5$ mJy and $206\pm12$ mJy and a polarized intensity of $11.3\pm0.3$ mJy and $55.1\pm3.3$ mJy in the VBB and H-band, respectively. We also find in the visual range a degree of polarization that varies between $28\%$ on the far side of the disk and $17\%$ on the near side. The disk shows a red color for the scattered light intensity and the polarized intensity, which are about twice as high in the near-infrared when compared to the visual. We determine with model calculations the scattering properties of the dust particles and find evidence for strong forward scattering ($g\approx 0.5-0.75$), relatively low single-scattering albedo ($ω\approx 0.2-0.5$), and high maximum polarization ($P_{\rm max} \approx 0.5-0.75$) at the surface on the far side of the disk for both observed wavelengths. The optical parameters indicate the presence of large aggregate dust particles, which are necessary to explain the high maximum polarization, the strong forward-scattering nature of the dust, and the observed red disk color.

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arXiv2021

The SPHERE infrared survey for exoplanets (SHINE)- I Sample definition and target characterization

Large surveys with new-generation high-contrast imaging instruments are needed to derive the frequency and properties of exoplanet populations with separations from $\sim$5 to 300 AU. A careful assessment of the stellar properties is crucial for a proper understanding of when, where, and how frequently planets form, and how they evolve. The sensitivity of detection limits to stellar age makes this a key parameter for direct imaging surveys. We describe the SpHere INfrared survey for Exoplanets (SHINE), the largest direct imaging planet-search campaign initiated at the VLT in 2015 in the context of the SPHERE Guaranteed Time Observations of the SPHERE consortium. In this first paper we present the selection and the properties of the complete sample of stars surveyed with SHINE, focusing on the targets observed during the first phase of the survey (from February 2015 to February 2017). This early sample composed of 150 stars is used to perform a preliminary statistical analysis of the SHINE data, deferred to two companion papers presenting the survey performance, main discoveries, and the preliminary statistical constraints set by SHINE. Based on a large database collecting the stellar properties of all young nearby stars in the solar vicinity (including kinematics, membership to moving groups, isochrones, lithium abundance, rotation, and activity), we selected the original sample of 800 stars that were ranked in order of priority according to their sensitivity for planet detection in direct imaging with SPHERE. The properties of the stars that are part of the early statistical sample were revisited, including for instance measurements from the GAIA Data Release 2.

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