Science with SHARK-VIS

The detection of extrasolar planets is one of the most exciting goals of the modern astronomy. Direct imaging is the only technique that efficiently probe the distribution of gaseous giant exoplanets on wide orbits (> 5au) and is therefore complementary to the methods based on radial velocities and transits, which are most sensitive exoplanets close to their hosting star. State-of-the-art extreme Adaptive Optics (ExAO)-assisted instruments, such as SPHERE and GPI, can provide contrasts down to 10^-5-10^-6  in the near-infrared at angular separations larger than ~100-150 mas, i.e. typically >10-20au from their parent star. Despite these remarkable performances, the total number of directly imaged planets still amounts to only about 20, likely because the bulk of the population of giant planets form at separation smaller than 10-20 au by core accretion. Improving the contrast capabilities at very small angular separations is therefore a fundamental step to characterize the population of giant planets. By observing at optical wavelengths SHARK-VIS will benefit from improved angular resolution (λ/D ~ 20 mas) and will give us the unique opportunity to probe very young planets (<10 Myr) still in formation within their parental disk by using their Hα line emission, which is a tracer of gas accretion and offers a much enhanced contrast with respect to the optical continuum. SHARK-VIS Hα observations will allow us to observe the planet formation phase and the interaction between planets and protoplanetary disks, which is essential to ultimately set constraints on the mechanisms and time-scales of planet formation and draw a picture of the assembly of planetary system architectures. The huge potential of the Hα observations has been testified by the recent detection of two actively accreting planets within the disk of the young PDS-70 system. The main scientific program of SHARK-VIS, which will be carried out in synergy with the companion instrument SHARK-NIR, is focused on the search and characterization of planetary mass companions of young sources in the Taurus-Auriga star-forming region.

Protoplanetary disks around newly born stars are the site where planets form through the assembly of growing dust grains. Submm observations with ALMA, sensistive to mm-sized dust grains, have recently  revealed a large variety of disk sub-structures (cavities, rings, spirals) potentially due to the gravitational interaction with planets in many young sources, which suggest that planet formation occurs very rapidly. Optical and NIR observations of the disks, which are sensitive to micron-sized grains, provide highly complementary data to those of ALMA that can be efficiently used to constrain the mutual interplay between small dust (and therefore gas since these components are well coupled), large dust, and forming planets. In this respect, the Taurus-Auriga star-forming region that will be investigated by SHARK-VIS and SHARK-NIR is a perfect laboratory to carry out a census of very young disks (1-2 Myr). We expect that these observations will reveal the morphology of many disks and link the observed substructures to the presence of sub-stellar and/or planetary companions, hopefully even directly detected by the SHARKs themselves. Additional targets, but on the final end of disk evolution, are debris disks, which correspond to the final evolutionary stage of circumstellar disks around young stars. Debris disks are almost totally composed of dust, which is continuously regenerated through collisions of planetesimals. Resolved images of debris disks in scattered-light with SHARK-VIS will allow us to identify specific structures (e.g. rings, warps, asymmetries) that are possibly the imprints of unseen planets (not otherwise detectable) and thus provide crucial insights into the evolution of planetary systems.

Jets and outflows are ubiquitously observed in Young Stellar Objects. The ejection of matter is indeed tightly connected with the accretion process (from the circumstellar disk onto the central star) that characterizes the early phases of a star's life.  Jets are believed to be launched from the innermost regions of the circumstellar disk, through the action of a large-scale magnetic field that is anchored in the rotating star-disk system.  As such, jets can have a major role in extracting the angular momentum from the system and heavily affect the properties of the inner disk region in which planets are going to form. Observing the jet as close as possible to the star is therefore fundamental to directly probe and measure the jet formation region and assess the jet launching mechanism, which will allow us to eventually determine the jet feedback on the disk. However, the regions where the jets are believed to originate have spatial scales spanning from fractions to a few astronomical units. This means that angular resolutions at least better than 70 mas (corresponding to about 10 au at a distance of 150 pc) are required for studying the base of the jets in the closest jet-driving sources of the Taurus-Auriga star-forming region. SHARK-VIS has the potential to achieve these angular resolutions and deliver unprecedented images of the jet formation region in the Hα and [OI] 6300Å lines, which are typical jet tracers.

The myriads of small bodies in our solar system are leftovers of the building blocks that accreted to form planets and can therefore provide crucial insights on the conditions found 4.5 Gyr ago in the protoplanetary disk around the Sun. Visible-light observations with SHARK-VIS will naturally provide sharper images than those currently obtainable with near-infrared AO-assisted instruments. With a maximum angular resolution around 15 mas, SHARK-VIS can attain spatial resolutions of about 35, 55, 110, and 220 km for objects at distances of 3, 5, 10, and 20 au, respectively, so that it will be able to spatially resolve not only many asteroids of the main belt, but also the largest objects in the outer Solar System. For asteroids, SHARK-VIS will directly measure the size of the targets (hence their volume) and will spot possible satellites, which can be used to derive a refined estimate of their mass. This will provide an accurate estimate of their density, which is key to understand the asteroid inner structure and composition. The size determination provided by SHARK-VIS is a crucial measurement in this regard, as errors in volume usually dominate asteroid density estimates. In addition, SHARK-VIS has the potential to obtain the first spatially resolved images of the largest Trans-Neptunian Objects (TNOs) in the outer Solar System, providing images sharper than those acquired by HST. Direct imaging in different bands and the related color analysis can effectively probe for the first time these remote targets, providing insights on their surface heterogeneity, which is a fundamental piece of information to understand their nature and formation, and on the presence of possible satellites. Suitable TNO targets are dwarf planets Makemake (~1500 km at ~50 au), Haumea (~2000 km at ~50 au), and Quaoar (~1100 km at about 40 au).

Active Galaxy Nuclei (AGN) are a unique laboratory to study gas flows, both inflows and outflows. It is in fact still unclear what is the mechanism responsible for driving gas towards the innermost region of the galaxy in order to feed the Super Massive Black Hole (SMBH). AGN-galaxy co-evolutionary models predict a phase in which the AGN energy output drives powerful winds which can shock against the surrounding gas leading to the formation of galaxy scale outflows. If and how such material acts on the host galaxy is still unclear. High resolution imaging of the gas flows in optical and NIR bands is fundamental to study the inner region of these galaxies hosting a SMBH and constrain both the fueling and the feedback on star formation and nuclear activity in nearby galaxies. SHARK-VIS offers a unique opportunity for a breakthrough in these fields with improved resolution (a factor of three better than HST) and contrast with respect to present optical instrumentation. Its images will allow us to discover and characterize AGN close pairs, to constrain the Black Hole feeding mechanism (e.g. supernovae driven winds vs gravitational asymmetries) in local Seyfert galaxies and to map, through the [OIII] emission line (5007Å), the AGN driven outflows of the ionized gas component, expanding from the central nucleus up to kpc-scales.  SHARK-VIS will allow us to study the innermost region of the galaxy down to angular scales of about 100 mas, which, for an object at z≈0.1, corresponds to d≈0.2 kpc from the nucleus. Color maps from wide-band observations and Hα images will be used to derive information on the feedback effects, by constraining the star-formation rate, age, and metallicity.

Io is the most volcanically active body in our Solar System. Having studied Io through multiple spacecraft encounters and ground-based monitoring for 40 years, we are now moving from a basic understanding of Io's volcanism to investigations of greater significance, concerning internal structure, volcanic advection, and temporal evolution. Ground-based monitoring programs observing in the M-band have been gradually filling in this picture. Resolution for these programs on 8-10 meter telescopes is about 500 km on Io’s surface. SHARK-VIS will provide a much higher resolution down to about 60 km, which will enable us to monitor the Io surface in great detail  and identify areas of volcanic activity by changes in surface albedo or color, so as to study the effects induced by volcanic activity. In addition, visible wavelength observations will be able to detect the highest temperature features that are sufficiently bright in nighttime or eclipse images or even in daylight, to reveal volcanic plumes against the blackness of space by both forward- and backscattered light, and to identify the style of eruption (lava flow as opposed to lava lake, for example) for many volcanic systems.

Disks are commonly detected around post-Asymptotic Giant Branch (post-AGB)  binaries with binary orbital time scales of the order of 1 yr. The evolution of the (binary) star and the formation and evolution of the disk are closely coupled: the primary's AGB phase is believed to be terminated due to mass loss induced by a poorly understood binary interaction process and part of the ejected material is then forced into a circumbinary disk. The unique angular resolution of SHARK-VIS can be used to obtain spatially resolved images at different wavelengths of such disks, which is a critical step in the characterization of these binary stars. The first step will be to measure the disk extent, brightness, and color in scattered light to constrain its mass and dust grain size, and thus its evolutionary state. Imaging a sample of such disks will allow us to connect these properties to the luminosity (thus initial mass) and temperature (thus evolutionary state), and the binary orbit. Structures in the disk (even shadows in edge-on disks) can be linked to binary-disk interaction as well as outflows recently detected, which originate either from stellar mass loss or from disk dispersal. SHARK-VIS will be the only AO system in the Northern Hemisphere that can observe a relevant sample of such stars. It will measure the radial extent of the disk and possibly identify the outflows perpendicular to the disk mid-plane. In addition, combining images in different bands will allow us to derive color information which provides indication on the dominating dust grain sizes in the disk and on the origin of the outflow. Finally, monitoring of detected disk structures or shadows that may move on time scales as short as the binary orbital time scale will allow us to study binary-disk interaction directly.