Planetary Companions Research Articles

Is the gap in the DS Tau disc hiding a planet?

ABSTRACT Recent millimetre-wavelength surveys performed with the Atacama Large Millimeter Array (ALMA) have revealed protoplanetary discs characterized by rings and gaps. A possible explanation for the origin of such rings is the tidal interaction with an unseen planetary companion. The protoplanetary disc around DS Tau shows a wide gap in the ALMA observation at 1.3 mm. We construct a hydrodynamical model for the dust continuum observed by ALMA assuming the observed gap is carved by a planet between one and five Jupiter masses. We fit the shape of the radial intensity profile along the disc major axis varying the planet mass, the dust disc mass, and the evolution time of the system. The best-fitting model is obtained for a planet with $M_{\rm p}=3.5\, \mathrm{ M}_{\rm Jup}$ and a disc with $M_{\rm dust}= 9.6\,\times \,10^{-5}\, \mathrm{ M}_{\odot }$. Starting from this result, we also compute the expected signature of the planet in the gas kinematics, as traced by CO emission. We find that such a signature (in the form of a ‘kink’ in the channel maps) could be observed by ALMA with a velocity resolution between $0.2-0.5\, \rm {kms}^{-1}$ and a beam size between 30 and 50 mas.

Spirals inside the millimeter cavity of transition disk SR 21

Context. Hydrodynamical simulations of planet-disk interactions suggest that planets may be responsible for a number of the substructures frequently observed in disks in both scattered light and dust thermal emission. Despite the ubiquity of these features, direct evidence of planets embedded in disks and of the specific interaction features like spiral arms within planetary gaps are still rare. Aims. In this study we discuss recent observational results in the context of hydrodynamical simulations in order to infer the properties of a putative embedded planet in the cavity of a transition disk. Methods. We imaged the transition disk SR 21 in H-band in scattered light with SPHERE/IRDIS and in thermal dust emission with ALMA band 3 (3 mm) observations at a spatial resolution of 0.1″. We combine these datasets with existing Band 9 (430 μm) and Band 7 (870 μm) ALMA continuum data. Results. The Band 3 continuum data reveals a large cavity and a bright ring peaking at 53 au strongly suggestive of dust trapping. The ring shows a pronounced azimuthal asymmetry, with a bright region in the northwest that we interpret as a dust overdensity. A similarly asymmetric ring is revealed at the same location in polarized scattered light, in addition to a set of bright spirals inside the millimeter cavity and a fainter spiral bridging the gap to the outer ring. These features are consistent with a number of previous hydrodynamical models of planet-disk interactions, and suggest the presence of a ∼1 MJup planet at 44 au and PA = 11 deg. This makes SR21 the first disk showing spiral arms inside the millimeter cavity, and the first disk for which the location of a putative planet can be precisely inferred. Conclusions. The main features of SR 21 in both scattered light and thermal emission are consistent with hydrodynamical predictions of planet-disk interactions. With the location of a possible planet being well constrained by observations, it is an ideal candidate for follow-up observations to search for direct evidence of a planetary companion still embedded in its disk.

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

Abstract We present the first discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, a large-scale survey for wide-orbit planetary and substellar companions. We have discovered a comoving system COCONUTS-1, composed of a hydrogen-dominated white dwarf (PSO J058.9855+45.4184; d = 31.5 pc) and a T4 companion (PSO J058.9869+45.4296) at a 40.″6 (1280 au) projected separation. We derive physical properties for COCONUTS-1B from (1) its near-infrared spectrum using cloudless Sonora atmospheric models, and (2) its luminosity and the white dwarf’s age ( Gyr) using Sonora evolutionary models. The two methods give consistent temperatures and radii, but atmospheric models infer a lower surface gravity and therefore an unphysically young age. Assuming evolutionary model parameters ( K, dex, ), we find that cloudless model atmospheres have brighter Y- and J-band fluxes than the data, suggesting that condensate clouds have not fully dispersed around 1300 K. The W2 flux (4.6 μm) of COCONUTS-1B is fainter than models, suggesting non-equilibrium mixing of CO. To investigate the gravity dependence of the L/T transition, we compile all 60 known L6−T6 benchmarks and derive a homogeneous set of temperatures, surface gravities, and masses. As is well known, young, low-gravity late-L dwarfs have significantly fainter, redder near-infrared photometry and ≈200–300 K cooler temperatures than old, high-gravity objects. Our sample now reveals such gravity dependence becomes weaker for T dwarfs, with young objects having comparable near-infrared photometry and ≈100 K cooler temperatures compared to old objects. Finally, we find that young objects have a larger amplitude J-band brightening than old objects, and also brighten at H band as they cross the L/T transition.

Shadowing and multiple rings in the protoplanetary disk of HD 139614

Context. Shadows in scattered light images of protoplanetary disks are a common feature and support the presence of warps or misalignments between disk regions. These warps are possibly caused by an inclined (sub-)stellar companion embedded in the disk. Aims. We aim to study the morphology of the protoplanetary disk around the Herbig Ae star HD 139614 based on the first scattered light observations of this disk, which we model with the radiative transfer code MCMax3D. Methods. We obtained J- and H-band observations that show strong azimuthal asymmetries in polarized scattered light with VLT/SPHERE. In the outer disk, beyond ~30 au, a broad shadow spans a range of ~240 deg in position angle, in the east. A bright ring at ~16 au also shows an azimuthally asymmetric brightness, with the faintest side roughly coincidental with the brightest region of the outer disk. Additionally, two arcs are detected at ~34 and ~50 au. We created a simple four-zone approximation to a warped disk model of HD 139614 in order to qualitatively reproduce these features. The location and misalignment of the disk components were constrained from the shape and location of the shadows they cast. Results. We find that the shadow on the outer disk covers a range of position angles too wide to be explained by a single inner misaligned component. Our model requires a minimum of two separate misaligned zones – or a continuously warped region – to cast this broad shadow on the outer disk. A small misalignment of ~4° between adjacent components can reproduce most of the observed shadow features. Conclusions. Multiple misaligned disk zones, potentially mimicking a warp, can explain the observed broad shadows in the HD 139614 disk. A planetary mass companion in the disk, located on an inclined orbit, could be responsible for such a feature and for the dust-depleted gap responsible for a dip in the SED.

A multiplicity study of transiting exoplanet host stars

Context. Many main-sequence stars are part of multiple systems. The effect of stellar multiplicity on planet formation and migration, however, is poorly understood. Aims. We study the multiplicity of stars hosting known transiting extra-solar planets to test competing theories on the formation mechanisms of hot Jupiters. Methods. We observed 45 exoplanet host stars using the infrared dual imaging spectrograph of the Spectro-Polarimetric High-Contrast Exoplanet Research (SPHERE) instrument at the Very Large Telescope to search for potential companions. For each identified candidate companion we determined the probability that it is gravitationally bound to its host by performing common proper motion checks and modelling of synthetic stellar populations around the host. In addition, we derived contrast limits as a function of angular separation to set upper limits on further companions in these systems. We converted the derived contrast into mass thresholds using AMES-Cond, AMES-Dusty, and BT-Settl models. Results. We detected new candidate companions around K2-38, WASP-72, WASP-80, WASP-87, WASP-88, WASP-108, WASP-118, WASP-120, WASP-122, WASP123, WASP-130, WASP-131, and WASP-137. The closest candidates were detected at separations of 0.′′124±0.′′007 and 0.′′189±0.′′003 around WASP-108 and WASP-131; the measured K-band contrasts indicate that these are stellar companions of 0.35 ± 0.02 M⊙ and 0.62−0.04+0.05 M⊙, respectively. Including the re-detection and confirmation of previously known companions in 13 other systems, we derived a multiplicity fraction of 55.4−9.4+5.9%. For the representative sub-sample of 40 hot Jupiter host stars among our targets, the derived multiplicity rate is 54.8−9.9+6.3%. Our data do not confirm any trend that systems with eccentric planetary companions are preferably part of multiple systems. On average, we reached a magnitude contrast of 8.5 ± 0.9 mag at an angular separation of 0.′′5. This allows us to exclude additional stellar companions with masses higher than 0.08M⊙ for almost all observed systems; around the closest and youngest systems, this sensitivity is achieved at physical separations as small as 10 au. Conclusions. Our study shows that SPHERE is an ideal instrument for detecting and characterising close companions to exoplanetary host stars. Although the second data release of the Gaia mission also provides useful constraints for some of the systems, the achieved sensitivity provided by the current data release of this mission is not good enough to measure parallaxes and proper motions for all detected candidates. For 14 identified companion candidates further astrometric epochs are required to confirm their common proper motion at 5σ significance.

HD 117214 debris disk: scattered-light images and constraints on the presence of planets

Context. Young stars with debris disks are the most promising targets for an exoplanet search because debris indicate a successful formation of planetary bodies. Debris disks can be shaped by planets into ring structures that give valuable indications on the presence and location of planets in the disk. Aims. We performed observations of the Sco-Cen F star HD 117214 to search for planetary companions and to characterize the debris disk structure. Methods. HD 117214 was observed with the SPHERE subsystems IRDIS, IFS, and ZIMPOL at optical and near-IR wavelengths using angular and polarimetric differential imaging techniques. This provided the first images of scattered light from the debris disk with the highest spatial resolution of 25 mas and an inner working angle <0.1″. With the observations with IRDIS and IFS we derived detection limits for substellar companions. The geometrical parameters of the detected disk were constrained by fitting 3D models for the scattering of an optically thin dust disk. Investigating the possible origin of the disk gap, we introduced putative planets therein and modeled the planet–disk and planet–planet dynamical interactions. The obtained planetary architectures were compared with the detection limit curves. Results. The debris disk has an axisymmetric ring structure with a radius of 0.42(±0.01)″ or ~45 au and an inclination of 71(±2.5)° and exhibits a 0.4″ (~40 au) wide inner cavity. From the polarimetric data, we derive a polarized flux contrast for the disk of (Fpol)disk/F∗ = (3.1 ± 1.2) × 10−4 in the RI band. Conclusions. The fractional scattered polarized flux of the disk is eight times lower than the fractional IR flux excess. This ratio is similar to the one obtained for the debris disk HIP 79977, indicating that dust radiation properties are similar for these two disks. Inside the disk cavity we achieve high-sensitivity limits on planetary companions with a mass down to ~4 MJ at projected radial separations between 0.2″ and 0.4″. We can exclude stellar companions at a radial separation larger than 75 mas from the star.

Mutual Inclination Excitation by Stellar Oblateness

Abstract Ultra-short-period planets (USPs) provide important clues to planetary formation and migration. It was recently found that the mutual inclinations of the planetary systems are larger if the inner orbits are closer (≲5R *) and if the planetary period ratios are larger (P 2/P 1 ≳ 5). This suggests that the USPs experienced both inclination excitation and orbital shrinkage. Here we investigate the increase in the mutual inclination due to stellar oblateness. We find that the stellar oblateness (within ∼1 Gyr) is sufficient to enhance the mutual inclination to explain the observed signatures. This suggests that the USPs can migrate closer to the host star in a near coplanar configuration with their planetary companions (e.g., disk migration+tides or in situ+tides), before mutual inclination gets excited due to stellar oblateness.

No Massive Companion to the Coherent Radio-emitting M Dwarf GJ 1151

Abstract The recent detection of circularly polarized, long-duration (>8 hr), low-frequency (∼150 MHz) radio emission from the M4.5 dwarf GJ 1151 has been interpreted as arising from a star–planet interaction via the electron cyclotron maser instability. The existence or parameters of the proposed planets have not been determined. Using 20 new HARPS-N observations, we put 99th-percentile upper limits on the mass of any close companion to GJ 1151 at . With no stellar, brown dwarf, or giant planet companion likely in a close orbit, our data are consistent with detected radio emission emerging from a magnetic interaction between a short-period terrestrial-mass planet and GJ 1151 (https://github.com/benjaminpope/video).

Chemical abundances of 1111 FGK stars from the HARPS-GTO planet search sample

Context. Elemental abundances are of prime importance to help us reconstruct the origin and evolution of stars and galaxies in our Universe. Sulfur abundances have not been as heavily studied as other elements, so some details regarding their behaviour are still unclear. Aims. We aim to investigate [S/Fe] ratios in stars of the solar neighbourhood in order to analyse the chemical evolution of sulfur and probe for possible differences in abundances of planet host and non-planet host stars. Methods. We used the code MOOG to perform spectral synthesis and derive v sin i values and [S/Fe] ratios for 719 FGK stars with high-resolution (R ~ 115 000) and high-quality spectra from the HARPS-GTO programme. We found the best fit and corresponding parameter values by performing χ2 minimisation of the deviation between synthetic profiles and observational spectra. Results. Our results reveal that sulfur behaves as a typical α-element, with low abundances in young thin disc stars and high abundances in old thick disc stars, following what was expected from our understanding of the Galactic chemical evolution (GCE). Nevertheless, further studies into the abundances of sulfur in very metal-poor stars are required as our sample only derived sulfur abundances of stars with metallicity as low as [Fe/H] = − 1.13 dex. High-α metal rich stars are more enhanced in sulfur compared to their thin disc counterparts at the same metallicity. We compare our results to GCE models from other authors in the [S/Fe] versus [Fe/H] plane. The [S/Fe]-age relationship is a good proxy for time, just as is the case with other α-elements. We report no differences in the abundances of sulfur between stars with and without planetary companions in the metallicity range [Fe/H] ≥−0.3 dex.

VMC J021140.41–735320.4—An Extremely Red L Dwarf Candidate Member of the AB Doradus Young Moving Group

We report the discovery of VMC J021140.41-735320.4, a faint ($J=19.9$ mag) and extremely red ($J-K_s=3.0$ mag, $W1-W2=0.45$ mag, $J-W2=4.7$ mag) high proper motion object in front of the Magellanic Bridge region. It is even redder in the near-infrared than the reddest L7 dwarfs ($J-K_s \gtrsim 2.8$ mag) found in the survey of Schneider et al. (2017) and its colours do also not match exactly those of other peculiar red L7.5 dwarfs. Therefore, we consider its photometric distance estimate of about 73 pc as uncertain. A preliminary combined proper motion and parallax solution involving 20 epochs from the Visible and Infrared Survey Telescope for Astronomy (VISTA) survey of the Magellanic Clouds (VMC), the VISTA hemisphere survey (VHS), and the Wide-field Infrared Survey Explorer (WISE) yields $\mu_{\alpha}\cos{\delta}=+74.3\pm3.4$ mas/yr, $\mu_{\delta}=+22.3\pm3.4$ mas/yr, and $\pi=21.0\pm7.1$ mas. Applying the BANYAN tool (this http URL) to these results we find a $\approx$68% membership probability of this object in the AB Doradus young moving group (YMG). With its trignometric distance of $\approx$48 pc, VMC J021140.41-735320.4 has a similar absolute magnitude of $M_{K_s}\approx13.4$ mag as the planetary mass companion of another AB Doradus YMG member candidate, 2MASS J22362452+4751425. Follow-up classification spectroscopy and astrometric monitoring are recommended.

A HARPS RV search for planets around young nearby stars

Context. Young nearby stars are good candidates in the search for planets with both radial velocity (RV) and direct imaging techniques. This, in turn, allows for the computation of the giant planet occurrence rates at all separations. The RV search around young stars is a challenge as they are generally faster rotators than older stars of similar spectral types and they exhibit signatures of magnetic activity (spots) or pulsation in their RV time series. Specific analyses are necessary to characterize, and possibly correct for, this activity. Aims. Our aim is to search for planets around young nearby stars and to estimate the giant planet (GP) occurrence rates for periods up to 1000 days. Methods. We used the HARPS spectrograph on the 3.6 m telescope at La Silla Observatory to observe 89 A−M young (<600 Myr) stars. We used our SAFIR (Spectroscopic data via Analysis of the Fourier Interspectrum Radial velocities) software to compute the RV and other spectroscopic observables. Then, we computed the companion occurrence rates on this sample. Results. We confirm the binary nature of HD 177171, HD 181321 and HD 186704. We report the detection of a close low mass stellar companion for HIP 36985. No planetary companion was detected. We obtain upper limits on the GP (<13 MJup) and BD (∈ [13;80] MJup) occurrence rates based on 83 young stars for periods less than 1000 days, which are set, 2−2+3 and 1−1+3%.

Search for Nearby Earth Analogs. II. Detection of Five New Planets, Eight Planet Candidates, and Confirmation of Three Planets around Nine Nearby M Dwarfs*

Abstract Zechmeister et al. surveyed 38 nearby M dwarfs from 2000 to 2007 March with VLT2 and the Ultraviolet and Visual Echelle Spectrograph (UVES) spectrometer. These data have recently been reanalyzed, yielding a significant improvement in the Doppler velocity precision. Spurred by this, we have combined the UVES data with velocity sets from High Accuracy Radial velocity Planet Searcher, Magellan/Planet Finder Spectrograph, and Keck/High Resolution Echelle Spectrometer. Sixteen planet candidates have been uncovered orbiting nine M dwarfs. Five of them are new planets corresponding to radial velocity signals, which are not sensitive to the choice of noise models and are identified in multiple data sets over various time spans. Eight candidate planets require additional observation to be confirmed. We also confirm three previously reported planets. Among the new planets, GJ 180 d and GJ 229A c are super-Earths located in the conservative habitable zones of their host stars. We investigate their dynamical stability using the Monte Carlo approach and find both planetary orbits are robust to the gravitational perturbations of the companion planets. Due to their proximity to the Sun, the angular separation between the host stars and the potentially habitable planets in these two systems is 25 and 59 mas, respectively. They are thus good candidates for future direct imaging by James Webb Space Telescope and E-ELT. In addition, we find GJ 433 c, a cold super-Neptune belonging to an unexplored population of Neptune-like planets. With a separation of 0.″5 from its host star, GJ 433 c is probably the first realistic candidate for the direct imaging of cold Neptunes. A comprehensive survey of these planets is important for the studies of planet formation.

Are inner disc misalignments common? ALMA reveals an isotropic outer disc inclination distribution for young dipper stars

ABSTRACT Dippers are a common class of young variable star exhibiting day-long dimmings with depths of up to several tens of per cent. A standard explanation is that dippers host nearly edge-on (id ≈ 70°) protoplanetary discs that allow close-in (<1 au) dust lifted slightly out of the mid-plane to partially occult the star. The identification of a face-on dipper disc and growing evidence of inner disc misalignments brings this scenario into question. Thus, we uniformly (re)derive the inclinations of 24 dipper discs resolved with (sub-)mm interferometry from ALMA. We find that dipper disc inclinations are consistent with an isotropic distribution over id ≈ 0−75°, above which the occurrence rate declines (likely an observational selection effect due to optically thick disc mid-planes blocking their host stars). These findings indicate that the dipper phenomenon is unrelated to the outer (>10 au) disc resolved by ALMA and that inner disc misalignments may be common during the protoplanetary phase. More than one mechanism may contribute to the dipper phenomenon, including accretion-driven warps and ‘broken’ discs caused by inclined (sub-)stellar or planetary companions.

VLT/SPHERE exploration of the young multiplanetary system PDS70

Context. PDS 70 is a young (5.4 Myr), nearby (~113 pc) star hosting a known transition disk with a large gap. Recent observations with SPHERE and NACO in the near-infrared (NIR) allowed us to detect a planetary mass companion, PDS 70 b, within the disk cavity. Moreover, observations in Hα with MagAO and MUSE revealed emission associated to PDS 70 b and to another new companion candidate, PDS 70 c, at a larger separation from the star. PDS 70 is the only multiple planetary system at its formation stage detected so far through direct imaging. Aims. Our aim is to confirm the discovery of the second planet PDS 70 c using SPHERE at VLT, to further characterize its physical properties, and search for additional point sources in this young planetary system. Methods. We re-analyzed archival SPHERE NIR observations and obtained new data in Y, J, H and K spectral bands for a total of four different epochs. The data were reduced using the data reduction and handling pipeline and the SPHERE data center. We then applied custom routines (e.g., ANDROMEDA and PACO) to subtract the starlight. Results. We re-detect both PDS 70 b and c and confirm that PDS 70 c is gravitationally bound to the star. We estimate this second planet to be less massive than 5 MJup and with a Teff around 900 K. Also, it has a low gravity with logg between 3.0 and 3.5 dex. In addition, a third object has been identified at short separation (~0.12′′) from the star and gravitationally bound to the star. Its spectrum is however very blue, meaning that we are probably seeing stellar light reflected by dust and our analysis seems to demonstrate that it is a feature of the inner disk. We cannot however completely exclude the possibility that it is a planetary mass object enshrouded by a dust envelope. In this latter case, its mass should be of the order of a few tens of M⊕. Moreover, we propose a possible structure for the planetary system based on our data, and find that this structure cannot be stable on a long timescale.

Super-Earth ingestion can explain the anomalously high metal abundances of M67 Y2235

Abstract We investigate the hypothesis that ingestion of a terrestrial or super-Earth planet could cause the anomalously high metal abundances seen in a turn-off star in the open cluster M67, when compared to other turn-off stars in the same cluster. We show that the mass of the convective envelope of the star is likely only 3.45 × 10−3 M⊙, and hence 5.2 M⊕ of rock is required to obtain the observed 0.128 dex metal enhancement. Rocky planets dissolve entirely in the convective envelope if they enter it with sufficiently tangential orbits: we find that the critical condition for dissolution is that the planet’s radial velocity must be less than 40% of its total velocity at the stellar surface; or, equivalently, the impact parameter must be greater than about 0.9. We model the delivery of rocky planets to the stellar surface both by planet-planet scattering in a realistic multi-planet system, and by Lidov–Kozai cycles driven by a more massive planetary or stellar companion. In both cases almost all planets that are ingested arrive at the star on grazing orbits and hence will dissolve in the surface convection zone. We conclude that super-Earth ingestion is a good explanation for the metal enhancement in M67 Y2235, and that a high-resolution spectroscopic survey of stellar abundances around the turn-off and main sequence of M67 has the potential to constrain the frequency of late-time dynamical instability in planetary systems.

In situ scattering of warm Jupiters and implications for dynamical histories

ABSTRACT Many warm Jupiters (WJs) have substantial eccentricities, which are linked to their formation and migration histories. This paper explores eccentricity excitation of WJs due to planet–planet scattering, beginning with three to four planets in unstable orbits, with the innermost planet placed in the range (0.1−1) au. Such a setup is consistent with either in situ formation or arrival at sub-au orbits due to disc migration. Most previous N-body experiments have focused on ‘cold’ Jupiters at several au, where scattering results in planet ejections, efficiently exciting the eccentricities of surviving planets. In contrast, scattering at sub-au distances results in a mixture of collisions and ejections, and the final eccentricities of surviving planets are unclear. We conduct scattering experiments for a range of planet masses and initial spacings, including the effect of general relativistic apsidal precession, and systematically catalogue the scattering outcomes and properties of surviving planets. A comparable number of one-planet and two-planet systems are produced. Two-planet systems arise exclusively through planet–planet collisions, and tend to have low eccentricities/mutual inclinations and compact configurations. One-planet systems arise through a combination of ejections and collisions, resulting in higher eccentricities. The observed eccentricity distribution of solitary WJs (lacking detection of a giant planet companion) is consistent with roughly $60 {{\ \rm per\ cent}}$ of the systems having undergone in situ scattering, and the remaining experiencing a quiescent history.

Precise radial velocities of giant stars

We report the discovery of a second planet orbiting the K giant star 7 CMa based on 166 high-precision radial velocities obtained with Lick, HARPS, UCLES, and SONG. The periodogram analysis reveals two periodic signals of approximately 745 and 980 d, associated with planetary companions. A double-Keplerian orbital fit of the data reveals two Jupiter-like planets with minimum masses mb sini ~ 1.9 MJ and mc sini ~ 0.9 MJ, orbiting at semimajor axes of ab ~ 1.75 au and ac ~ 2.15 au, respectively. Given the small orbital separation and the large minimum masses of the planets, close encounters may occur within the time baseline of the observations; thus, a more accurate N-body dynamical modeling of the available data is performed. The dynamical best-fit solution leads to collision of the planets and we explore the long-term stable configuration of the system in a Bayesian framework, confirming that 13% of the posterior samples are stable for at least 10 Myr. The result from the stability analysis indicates that the two planets are trapped in a low-eccentricity 4:3 mean motion resonance. This is only the third discovered system to be inside a 4:3 resonance, making this discovery very valuable for planet formation and orbital evolution models.

Twisted debris: how differential secular perturbations shape debris disks

Context. Resolved images suggest that asymmetric structures are a common feature of cold debris disks. While planets close to these disks are rarely detected, their hidden presence and gravitational perturbations provide plausible explanations for some of these features. Aims. To put constraints on the properties of yet undetected planetary companions, we aim to predict what features such a planet imprints in debris disks undergoing continuous collisional evolution. Methods. We discuss the basic equations, analytic approximations and timescales governing collisions, radiation pressure and secular perturbations. In addition, we combine our numerical model of the collisional evolution of the size and spatial distributions in debris disks with the gravitational perturbation by a single planet. Results. We find that the distributions of orbital elements in the disks are strongly dependent on grain sizes. Secular precession is differential with respect to involved semi-major axes and grain sizes. This leads to observable differences between the big grains tracing the parent belt and the small grains in the trailing halo. Observations at different wavelengths can be used to constrain the properties of a possible planet.

Discarding orbital decay in WASP-19b after one decade of transit observations★†

Abstract We present a empirical study of orbital decay for the exoplanet WASP-19b, based on mid-time measurements of 74 complete transits (12 newly obtained by our team and 62 from the literature), covering a 10-year baseline. A linear ephemeris best represents the mid-transit times as a function of epoch. Thus, we detect no evidence of the shortening of WASP-19b’s orbital period and establish an upper limit of its steady changing rate, $\dot{P}=-2.294$ ms yr−1, and a lower limit for the modified tidal quality factor $Q^{\prime }_{\star } = (1.23 \pm 0.231) \times 10^{6}$. Both are in agreement with previous works. This is the first estimation of $Q^{\prime }_{\star }$ directly derived from the mid-times of WASP-19b obtained through homogeneously analyzed transit measurements. Additionally, we do not detect periodic variations in the transit timings within the measured uncertainties in the mid-times of transit. We are therefore able to discard the existence of planetary companions in the system down to a few M⊕ in the first order mean-motion resonances 1:2 and 2:1 with WASP-19b, in the most conservative case of circular orbits. Finally, we measure the empirical $Q^{\prime }_{\star }$ values of 15 exoplanet host stars which suggest that stars with Teff ≲ 5600K dissipate tidal energy more efficiently than hotter stars. This tentative trend needs to be confirmed with a larger sample of empirically measured $Q^{\prime }_{\star }$.

Detection of Hα emission from PZ Telescopii B using SPHERE/ZIMPOL

Hα is a powerful tracer of accretion and chromospheric activity, which has been detected in the case of young brown dwarfs and even recently in planetary mass companions (e.g. PDS70 b and c). Hα detections and characterisation of brown dwarf and planet companions can further our knowledge of their formation and evolution, and expanding such a sample is therefore our primary goal. We used the Zurich Imaging POLarimeter (ZIMPOL) of the SPHERE instrument at the Very Large Telescope (VLT) to observe the known 38−72 MJ companion orbiting PZ Tel, obtaining simultaneous angular differential imaging observations in both continuum and narrow Hα band. We detect Hα emission from the companion, making this only the second Hα detection of a companion using the SPHERE instrument. We used our newly added astrometric measurements to update the orbital analysis of PZ Tel B, and we used our photometric measurements to evaluate the Hα line flux. Given the estimated bolometric luminosity, we obtained an Hα activity (log(LHα/Lbol)) between −4.16 and −4.31. The Hα activity of PZ Tel B is consistent with known average activity levels for M dwarf of the same spectral type. Given the absence of a known gaseous disk and the relatively old age of the system (24 Myr), we conclude that the Hα emission around PZ Tel B is likely due to chromospheric activity.