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Register a new userMulti-Aperture Imaging of Extrasolar Planetary Systems
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O. Absil
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In this paper, we review the various ways in which an infrared stellar interferometer can be used to perform direct detection of extrasolar planetary systems. We first review the techniques based on classical stellar interferometry, where (complex) visibilities are measured, and then describe how higher dynamic ranges can be achieved with nulling interferometry. The application of nulling interferometry to the study of exozodiacal discs and extrasolar planets is then discussed and illustrated with a few examples.
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The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential formation pathway. Additionally, contaminating light from both binary companions and unassociated stars can significantly bias the results of planet characterisation studies, but can be corrected for if the properties of the contaminating star are known. We search for binary companions to known transiting exoplanet host stars, in order to determine the multiplicity properties of hot Jupiter host stars. We also characterise unassociated stars along the line of sight, allowing photometric and spectroscopic observations of the planetary system to be corrected for contaminating light. We analyse lucky imaging observations of 97 Southern hemisphere exoplanet host stars, using the Two Colour Instrument on the Danish 1.54m telescope. For each detected companion star, we determine flux ratios relative to the planet host star in two passbands, and measure the relative position of the companion. The probability of each companion being physically associated was determined using our two-colour photometry. A catalogue of close companion stars is presented, including flux ratios, position measurements, and estimated companion star temperature. For companions that are potential binary companions, we review archival and catalogue data for further evidence. For WASP-77AB and WASP-85AB, we combine our data with historical measurements to determine the binary orbits, showing them to be moderately eccentric and inclined to the line of sight and planetary orbital axis. Combining our survey with the similar Friends of Hot Jupiters survey, we conclude that known hot Jupiter host stars show a deficit of high mass stellar companions compared to the field star population; however, this may be a result of the biases in detection and target selection by ground-based surveys.
Planetary radars have obtained unique science measurements about solar system bodies and they have provided orbit determinations allowing spacecraft to be navigated throughout the solar system. Notable results have been on Venus, Earths twin, and small bodies, which are the constituents of the Suns debris disk. Together, these results have served as ground truth from the solar system for studies of extrasolar planets. The Nations planetary radar infrastructure, indeed the worlds planetary radar infrastructure, is based on astronomical and deep space telecommunications infrastructure, namely the radar transmitters at the Arecibo Observatory and the Goldstone Solar System Radar, part of NASAs Deep Space Network, along with the Green Bank Telescope as a receiving element. This white paper summarizes the state of this infrastructure and potential technical developments that should be sustained in order to enable continued studies of solar system bodies for comparison and contrast with extrasolar planetary systems. Because the planetary radar observations leverage existing infrastructure largely developed for other purposes, only operations and maintenance funding is required, though modest investments could yield more reliable systems; in the case of the Green Bank Telescope, additional funding for operations is required.
Significant advances in the discovery and characterization of the planetary systems of nearby stars can be accomplished with a moderate aperture high performance coronagraphic space mission that could be started in the next decade. Its observations would make significant progress in studying terrestrial planets in their habitable zones to giant planets and circumstellar debris disks, also informing the design of a more capable future mission. It is quite exciting that such fundamental exoplanet science can be done with relatively modest capabilities.
We place the first constraints on the obliquity of a planetary-mass companion (PMC) outside of the Solar System. Our target is the directly imaged system 2MASS J01225093-2439505 (2M0122), which consists of a 120 Myr 0.4 M_sun star hosting a 12-27 M_J companion at 50 AU. We constrain all three of the systems angular momentum vectors: how the companion spin axis, the stellar spin axis, and the orbit normal are inclined relative to our line of sight. To accomplish this, we measure projected rotation rates (vsini) for both the star and the companion using new near-infrared high-resolution spectra with NIRSPEC at Keck Observatory. We combine these with a new stellar photometric rotation period from TESS and a published companion rotation period from HST to obtain spin axis inclinations for both objects. We also fitted multiple epochs of astrometry, including a new observation with NIRC2/Keck, to measure 2M0122bs orbital inclination. The three line-of-sight inclinations place limits on the true de-projected companion obliquity and stellar obliquity. We find that while the stellar obliquity marginally prefers alignment, the companion obliquity tentatively favors misalignment. We evaluate possible origin scenarios. While collisions, secular spin-orbit resonances, and Kozai-Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk - the scenario favored for brown dwarf companions to stars - appears promising.
Gravitational waves have opened a new observational window through which some of the most exotic objects in the Universe, as well as some of the secrets of gravitation itself, can now be revealed. Among all these new discoveries, we recently demonstrated [N. Tamanini & C. Danielski, Nat. Astron., 3(9), 858 (2019)] that space-based gravitational wave observations will have the potential to detect a new population of massive circumbinary exoplanets everywhere inside our Galaxy. In this essay we argue that these circumbinary planetary systems can also be detected outside the Milky Way, in particular within its satellite galaxies. Space-based gravitational wave observations might thus constitute the mean to detect the first extra-galactic planetary system, a target beyond the reach of standard electromagnetic searches.
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