H. Parviainen & colleagues, reported the discovery of TOI-519 b, a transiting substellar object, having a radius of 1.07 times that of the radius of the Jupiter (RJup), orbiting a faint M dwarf (TIC 218795833) on a very short-period orbit of 1.26 day.
Brown dwarfs and massive planets orbiting M dwarfs on short-period orbits are rare, but more have already been discovered than expected from planet formation models. TOI-519 is a valuable addition into this group of unlikely systems, and adds towards our understanding of the boundaries of planet formation.
The object was originally identified in the TESS Sector 7 photometry by the TESS Science Processing Operations Center (SPOC) pipeline, and was later followed up from the ground using multicolour transit photometry and low-resolution spectroscopy.
Astronomers estimated the radius of the transiting object using multicolour transit modelling, and set upper limits for its mass, effective temperature, and Bond albedo using a phase curve model that includes Doppler boosting, ellipsoidal variations, thermal emission, and reflected light components.
The radius, effective temperature, and mass constraints from the multicolour and phase curve analyses validate TOI-519 b is a substellar object with a radius posterior median of 1.07 RJup and 5th and 95th percentiles of 0.66 and 1.20 RJup, respectively, where most of the uncertainty comes from the uncertainty in the stellar radius. The phase curve analysis sets an upper effective temperature limit of 1800 K, an upper Bond albedo limit of 0.49, and a companion mass upper limit of 14 MJup.
After estimating the companion radius, they combined it with the effective temperature (Teff) and mass limits which suggested that the companion is more likely a planet than a brown dwarf, but a brown-dwarf scenario is more likely a priori given the lack of known massive planets in ≈ 1 day orbits around M dwarfs with Teff < 3800 K, and the existence of some (but few) brown dwarfs.
“We note that giant planets and brown dwarfs seem to be found orbiting distinct spectral types. All large objects (R > 0.5 RJup) around the coolest dwarfs (Teff < 3400 K) are brown dwarfs, except for HATS- 71 A b, and these transiting brown dwarfs seem to be clustered orbiting cool dwarfs with Teff ∼ 3100-3400 K. On the contrary, giant planets are found around spectral types with Teff > 3700 K. For the spectral types with Teff ∼ 3400-3700 K there is a desert of any companions with a R > 0.5 RJup. Whether this apparent clustering is of any significance needs to be verified by more hot Jupiter and brown dwarf discoveries around cool dwarfs.”, wrote authors in their research paper.
According to authors, “Further research is needed in order to confirm whether TOI-519b is a low mass brown dwarf or a massive planet.”
References: H. Parviainen, E. Palle, M.R. Zapatero-Osorio, G. Nowak, A. Fukui, F. Murgas, N. Narita, K.G. Stassun, J.H. Livingston, K.A. Collins, D. Hidalgo Soto, V.J.S. Béjar, J. Korth, M. Monelli, P. Montanes Rodriguez, N. Casasayas-Barris, G. Chen, N. Crouzet, J.P. de Leon, A. Hernandez, K. Kawauchi, P. Klagyivik, N. Kusakabe, R. Luque, M. Mori, T. Nishiumi, J. Prieto-Arranz, M. Tamura, N. Watanabe, T. Gan, K.I. Collins, E.L.N. Jensen, T. Barclay, J.P. Doty, J.M. Jenkins, D.W. Latham, M. Paegert, G. Ricker, D.R. Rodriguez, S. Seager, A. Shporer, R. Vanderspek, J. Villaseñor, J.N. Winn, B. Wohler, I. Wong, “TOI-519 b: a short-period substellar object around an M dwarf validated using multicolour photometry and phase curve analysis”, ArXiv, pp. 1-15, 2020. https://arxiv.org/abs/2011.11458v1
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