Discovery of a directly imaged planet to the young solar analog YSES 2

Abstract

Context. To understand the origin and formation pathway of wide-orbit gas giant planets, it is necessary to expand the limited sample of these objects. The mass of exoplanets derived with spectrophotometry, however, varies strongly as a function of the age of the system and the mass of the primary star. Aims. By selecting stars with similar ages and masses, the Young Suns Exoplanet Survey (YSES) aims to detect and characterize planetary-mass companions to solar-type host stars in the Scorpius-Centaurus association. Methods. Our survey is carried out with VLT/SPHERE with short exposure sequences on the order of 5 min per star per filter. The subtraction of the stellar point spread function (PSF) is based on reference star differential imaging using the other targets (with similar colors and magnitudes) in the survey in combination with principal component analysis. Two astrometric epochs that are separated by more than one year are used to confirm co-moving companions by proper motion analysis. Results. We report the discovery of YSES 2b, a co-moving, planetary-mass companion to the K1 star YSES 2 (TYC 8984-2245-1, 2MASS J11275535-6626046). The primary has a Gaia EDR3 distance of 110 pc, and we derive a revised mass of 1.1 M⊙ and an age of approximately 14 Myr. We detect the companion in two observing epochs southwest of the star at a position angle of 205° and with a separation of ~1.′′05, which translates to a minimum physical separation of 115 au at the distance of the system. Photometric measurements in the H and Ks bands are indicative of a late L spectral type, similar to the innermost planets around HR 8799. We derive a photometric planet mass of 6.3−0.9+1.6 MJup using AMES-COND and AMES-dusty evolutionary models; this mass corresponds to a mass ratio of q = (0.5 ± 0.1)% with the primary. This is the lowest mass ratio of a direct imaging planet around a solar-type star to date. We discuss potential formation mechanisms and find that the current position of the planet is compatible with formation by disk gravitational instability, but its mass is lower than expected from numerical simulations. Formation via core accretion must have occurred closer to the star, yet we do not find evidence that supports the required outward migration, such as via scattering off another undiscovered companion in the system. We can exclude additional companions with masses greater than 13 MJup in the full field of view of the detector (0.′′15<ρ<5.′′50), at 0.′′5 we can rule out further objects that are more massive than 6 MJup, and for projected separations ρ >2′′ we are sensitive to planets with masses as low as 2 MJup. Conclusions. YSES 2b is an ideal target for follow-up observations to further the understanding of the physical and chemical formation mechanisms of wide-orbit Jovian planets. The YSES strategy of short snapshot observations (≤5 min) and PSF subtraction based on a large reference library proves to be extremely efficient and should be considered for future direct imaging surveys.

The Scorpion Planet Survey: Wide-Orbit Giant Planets Around Young A-type Stars

“…We also aim to discover additional planets and substellar companions whose orbits and atmospheres are accessible to direct characterization. Finally, the results of this survey will be directly comparable to the demographics of planets around A-stars in the closer (but slightly older) moving groups targeted largely by past surveys (e.g., Nielsen et al 2019;Vigan et al 2021), and also to lower-mass members of the Sco OB2 association (Bohn et al 2020(Bohn et al , 2021−enabling trends in exoplanet properties to be identified across host star age, mass, and formation environment.…”

“…Finally, our results offer a complementary sample to past studies that were largely focused on lower-mass stellar hosts in the solar neighborhood, and also to other ongoing surveys of both higher and lower-mass stars in Sco OB2. Taken in combination with GPIES (Nielsen et al 2019) and SHINE (Vigan et al 2021), the BEASTS survey of B-type stars (Janson et al 2021), and YSES survey (Bohn et al 2020(Bohn et al , 2021 of solar-type stars (both also focused on Sco OB2), these surveys provide a rich and comprehensive view of wide-orbit giant plants around nearby young stars. Together, they inform our understanding of exoplanet demographics, and perhaps of equal importance, enable the yield of future exoplanet imaging surveys to be enhanced by targeting stars around which detectable planets are more likely to exist.…”

“…The systems mentioned above were followed up by discoveries of several other planets 1 Steward Observatory, University of Arizona 2 NASA NExSS Alien Earths Team 3 NASA Hubble Fellowship Program − Sagan Fellow 4 Lunar and Planetary Laboratory, University of Arizona 5 European Southern Observatory, Germany 6 University of Leiden, Netherlands 7 Space Telescope Science Institute Correspondence to: kevinwagner@email.arizona.edu around A-type stars−including those orbiting HD 95086 (Rameau et al 2013), HD 106906b (Bailey et al 2014), 51 Eri (Macintosh et al 2015), and HIP65426 (Chauvin et al 2017). It's also worth noting that an increasing number of planets have been imaged around lower-mass stars−including the two planets orbiting the K7 (0.76 M ) star PDS 70 (Keppler et al 2018;Haffert et al 2019) and three planets around Kstars from the Young Suns Exoplanet Survey (YSES: Bohn et al 2020Bohn et al , 2021. While the number of imaged planets around FGK stars has increased in recent years, there remain fewer than those around A-type stars.…”

Zodiacal Exoplanets in Time (ZEIT) XII: A Directly-Imaged Planetary-Mass Companion to a Young Taurus M Dwarf Star

“…2M0437b is much younger, and therefore likely to be significantly less massive than HIP 65426b. YSES-2b is a similar planet orbiting a member of the same association; it is less luminous than HIP 65426b, and thus predicted to be less massive (∼6M JUP , Bohn et al 2021). Other comparable objects include the four known planets (bcde) of the HR 8799 system.…”

Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope

“…been discovered to date (e.g. Marois et al 2008Marois et al , 2010Lagrange et al 2010;Bohn et al 2020Bohn et al , 2021.…”