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Context. The diverse morphology among protoplanetary disks may result from planet-disk interactions, suggesting the presence of planets undergoing formation. The characterization of disks can provide information on the formation environments of planets. To date, most imaging campaigns have probed the polarized light from disks, which is only a fraction of the total scattered light and not very sensitive to planetary emission. Aims. We aim to observe and characterize protoplanetary disk systems in the near-infrared in both polarized and total intensity light to carry out an unprecedented study of the dust scattering properties of disks, as well as of any possible planetary companions. Methods. Using the star-hopping mode of the SPHERE instrument at the Very Large Telescope, we observed 29 young stars hosting protoplanetary disks and their reference stars in the Ks-band polarized light. We extracted disk signals in total intensity by removing stellar light using the corresponding reference star observations, by adopting the data imputation concept with sequential non-negative matrix factorization (DI-sNMF). For well-recovered disks in both polarized and total intensity light, we parameterized the polarization fraction phase functions using a scaled beta distribution. We investigated the empirical DI-sNMF detectability of disks using logistic regression. For systems with SPHERE data in the Y, J, and H bands, we have summarized their polarized color at an approximately 90° scattering angle. Results. We obtained high-quality disk images in total intensity for 15 systems and in polarized light for 23 systems. The total intensity detectability of disks primarily depends on the host star brightness, which determines adaptive-optics control ring imagery and thus stellar signals capture using DI-sNMF. The peak of polarization fraction tentatively correlates with the peak scattering angle, which could be reproduced using certain composition for compact dust, yet more detailed modeling studies are needed. Most of the disks are blue in polarized J – Ks color and the fact that they are relatively redder as stellar luminosity increases indicates larger scatterers. Conclusions. High-quality disk imagery in both total intensity and polarized light allows for disk characterizations in the polarization fraction. Combining these techniques reduces the confusion between the disk and planetary signals.
Context. The diverse morphology among protoplanetary disks may result from planet-disk interactions, suggesting the presence of planets undergoing formation. The characterization of disks can provide information on the formation environments of planets. To date, most imaging campaigns have probed the polarized light from disks, which is only a fraction of the total scattered light and not very sensitive to planetary emission. Aims. We aim to observe and characterize protoplanetary disk systems in the near-infrared in both polarized and total intensity light to carry out an unprecedented study of the dust scattering properties of disks, as well as of any possible planetary companions. Methods. Using the star-hopping mode of the SPHERE instrument at the Very Large Telescope, we observed 29 young stars hosting protoplanetary disks and their reference stars in the Ks-band polarized light. We extracted disk signals in total intensity by removing stellar light using the corresponding reference star observations, by adopting the data imputation concept with sequential non-negative matrix factorization (DI-sNMF). For well-recovered disks in both polarized and total intensity light, we parameterized the polarization fraction phase functions using a scaled beta distribution. We investigated the empirical DI-sNMF detectability of disks using logistic regression. For systems with SPHERE data in the Y, J, and H bands, we have summarized their polarized color at an approximately 90° scattering angle. Results. We obtained high-quality disk images in total intensity for 15 systems and in polarized light for 23 systems. The total intensity detectability of disks primarily depends on the host star brightness, which determines adaptive-optics control ring imagery and thus stellar signals capture using DI-sNMF. The peak of polarization fraction tentatively correlates with the peak scattering angle, which could be reproduced using certain composition for compact dust, yet more detailed modeling studies are needed. Most of the disks are blue in polarized J – Ks color and the fact that they are relatively redder as stellar luminosity increases indicates larger scatterers. Conclusions. High-quality disk imagery in both total intensity and polarized light allows for disk characterizations in the polarization fraction. Combining these techniques reduces the confusion between the disk and planetary signals.
Accreting protoplanets are windows into planet formation processes, and high-contrast differential imaging is an effective way to identify them. We report results from the Giant Accreting Protoplanet Survey (GAPlanetS), which collected Hα differential imagery of 14 transitional disk host stars with the Magellan Adaptive Optics System. To address the twin challenges of morphological complexity and point-spread function instability, GAPlanetS required novel approaches for frame selection and optimization of the Karhounen–Loéve Image Processing algorithm pyKLIP. We detect one new candidate, CS Cha “c,” at a separation of 68 mas and a modest Δmag of 2.3. We recover the HD 142527 B and HD 100453 B accreting stellar companions in several epochs, and the protoplanet PDS 70 c in 2017 imagery, extending its astrometric record by nine months. Though we cannot rule out scattered light structure, we also recover LkCa 15 “b,” at Hα; its presence inside the disk cavity, absence in Continuum imagery, and consistency with a forward-modeled point source suggest that it remains a viable protoplanet candidate. Through targeted optimization, we tentatively recover PDS 70 c at two additional epochs and PDS 70 b in one epoch. Despite numerous previously reported companion candidates around GAplanetS targets, we recover no additional point sources. Our moderate Hα contrasts do not preclude most protoplanets, and we report limiting Hα contrasts at unrecovered candidate locations. We find an overall detection rate of ∼36 − 22 + 26 % , considerably higher than most direct imaging surveys, speaking to both GAPlanetS’s highly targeted nature and the promise of Hα differential imaging for protoplanet identification.
Giant planets grow by accreting gas through circumplanetary disks, but little is known about the timescale and mechanisms involved in the planet-assembly process because few accreting protoplanets have been discovered. Recent visible and infrared imaging revealed a potential accreting protoplanet within the transition disk around the young intermediate-mass Herbig Ae star, AB Aurigae (AB Aur). Additional imaging in Hα probed for accretion and found agreement between the line-to-continuum flux ratio of the star and companion, raising the possibility that the emission source could be a compact disk feature seen in scattered starlight. We present new deep Keck/NIRC2 high-contrast imaging of AB Aur to characterize emission in Paβ, another accretion tracer less subject to extinction. Our narrow band observations reach a 5σ contrast of 9.6 mag at 0.″6, but we do not detect significant emission at the expected location of the companion, nor from other any other source in the system. Our upper limit on Paβ emission suggests that if AB Aur b is a protoplanet, it is not heavily accreting or accretion is stochastic and was weak during the observations.
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