Astronomers Revealed Mass and True Nature Of TOI-263b (Planetary Science)

The TESS mission is dedicated to the search for transiting extrasolar planets around the brightest and closest stars in the sky. It was launched on April 18th 2018, and has recently completed its initial survey of (almost) the entire sky with 26 pointings over 2 years. Many of the new exciting planets discovered by TESS are excellent targets for precise radial velocity (RV) follow-up to determine accurate masses and bulk properties, and later explore the characterization of their atmospheres.

However, despite the thousands of planets discovered to date, many questions remain about their dominant formation mechanism(s) and the underlying statistical properties of the different exoplanet populations. Thus, new objects displaying extreme properties may deliver critical knowledge to understand the formation and evolution of planetary systems. One of those extreme systems is TOI-263 b (Gaia DR2 5119203027983398656).

TOI-263 b is a validated ultra-short period substellar object in a 0.56-day orbit around a faint (V = 18.97) M3.5 dwarf star. The substellar nature of TOI-263 b was explored using multi-color photometry, which determined a true radius of 0.87 ± 0.21RJ , establishing TOI-263 b’s nature ranging from an inflated Neptune to a brown dwarf. The orbital period-radius parameter space occupied by TOI-263 b is quite unique, which prompted a further characterization of its true nature.

We report radial velocity measurements of TOI-263 obtained with 3 VLT units and the ESPRESSO spectrograph to retrieve the mass of TOI-263b.

— told Palle, first author of the study.

Now, Palle and colleagues reported on the ESPRESSO 3-UT mode observations of the TOI263 system, and found that TOI-263 b is low-mass brown dwarf with a mass of 61.6 ± 4.0 MJup (61.6 times that of the mass of the Jupiter). With an ultra-short period of 0.56 days, TOI-263 b is the shortest period known brown dwarf around any stellar type, and a unique and extreme inhabitant of the so-called “brown dwarf desert”. It is also one of the lightest among transiting brown dwarfs found so far around stars of cold (Teff < 4000 K) stellar type.

They found that the orbital period of TOI-263 b is synchronized to the rotation period of the host star, indicative of interaction between the star and the brown dwarf than spun the stellar rotation, and that the star is relatively active. All these findings combined, suggested that the system formation history might be explained via disc fragmentation and later migration to close-in orbits.

These mechanisms have not yet been proven to occur for brown dwarfs, making TOI-263 an excellent system to study in detail.

Featured image credit: An artist impression of brown dwarf orbiting star © Mashable

Reference: E. Palle, R. Luque, M. R. Zapatero Osorio, H. Parviainen, M. Ikoma, H. M. Tabernero, M. Zechmeister, A.J. Mustill, V.S.J. Bejar, N. Narita, F. Murgas, “ESPRESSO Mass determination of TOI-263b: An extreme inhabitant of the brown dwarf desert”, ArXiv, pp. 1-9, 2021.

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