Discovery Of A Directly Imaged Planet To The Young Solar Analog YSES 2


Multi-epoch observations of YSES 2 and its planetary-mass companion. Final data products of the SPHERE observations collected in the H band (left panel) and Ks band (right panel) are presented. For both filters, the stellar PSF is modeled by 50 principal components that were derived from a reference library of YSES targets. These PSF models were subtracted and the residuals rotated such that north points up and east toward the left. In the presented images the median of these de-rotated residuals is shown. For the Ks band data, uncorrected residuals of a wind-driven halo are detected that extend from the northeast to southwest. The planet YSES 2b is highlighted by white arrows. The primary is located at the origin of the coordinate system and we artificially masked the inner region up to the radial extent of the coronagraphic mask of 100 mas. To assess the spatial extent of the instrumental PSF, the median combination of the non-coronagraphic flux images of the primary star are shown in the lower left of each panel. The intensity of each flux image is rescaled to match the maximum and minimum counts in the corresponding residual science image, and we display both images with the same spatial and color scales.

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.

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 (RDI) using the other targets in the survey in combination with principal component analysis.

We report the discovery of YSES 2b, a planetary-mass companion to the K1 star YSES 2 (TYC 8984-2245-1). The primary has a Gaia EDR3 distance of 110 pc, and we derive a revised mass of 1.1M⊙ 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. We derive a photometric planet mass of 6.3+1.6−0.9MJup 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. 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.

Alexander J. Bohn, Christian Ginski, Matthew A. Kenworthy, Eric E. Mamajek, Mark J. Pecaut, Markus Mugrauer, Nikolaus Vogt, Christian Adam, Tiffany Meshkat, Maddalena Reggiani, Frans Snik
Abbreviated.

Comments: Accepted for publication in A&A (15 pages, 7 figures, 5 tables)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Journal reference: A&A 648, A73 (2021)
DOI: 10.1051/0004-6361/202140508
Cite as: arXiv:2104.08285 [astro-ph.EP] (or arXiv:2104.08285v1 [astro-ph.EP] for this version)
Submission history
From: Alexander Bohn
[v1] Fri, 16 Apr 2021 18:00:01 UTC (7,599 KB)
https://arxiv.org/abs/2104.08285
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