Georgieya and colleagues in their recently published paper in arxiv, presented the discovery and characterization of two sub-Neptunes: TOI-1260 b and TOI-1260 c, in close orbits, as well as a tentative outer planet of a similar size, orbiting TOI-1260 – a low metallicity K6 V dwarf star. The system TOI-1260 is observed by TESS in sectors 14 and 21.
Apart from space-based photometry from TESS, they obtained ground-based follow-up photometry from the Las Cumbres Observatory Global Telescope. They searched for stellar companions using Adaptive Optics (AO) and speckle imaging. To measure the planetary masses they observed TOI-1260 with HARPS-N.
Photometry from TESS yields radii of 𝑅b = 2.33 𝑅 and 𝑅c = 2.82 R, and periods of 3.13 and 7.49 days for TOI-1260 b and TOI-1260 c, respectively. They combined the TESS data with a series of ground-based follow-up observations to characterize the planetary system. From HARPS-N high-precision radial velocities they obtained 𝑀b = 8.61 𝑀 and 𝑀c = 11.84 𝑀. (for more refer Table 1 below)
They also found that the star is moderately active with a complex activity pattern, which necessitated the use of Gaussian process regression for both the light curve detrending and the radial velocity modelling, in the latter case guided by suitable activity indicators. They successfully disentangle the stellar-induced signal from the planetary signals, underlining the importance and usefulness of the Gaussian Process approach.
Finally, they performed simulations to evaluate the possibility of hydrodynamic atmospheric mass loss, which demonstrated the difficulty in constraining the structure and composition of planets in 2 – 3 𝑅 radius range. Their discussion thus emphasizes the fact that solely from the mass and radius we cannot distinguish between a planet being H2O-dominated or a rocky planet with a significant envelope.
Another constraint to their insight into similar systems is the large uncertainty on the systems’ ages. This could be remedied from a large sample of planet systems with well-determined ages, such as is attempted to be achieved by the core sample of the PLATO mission, with projected uncertainties in its age determinations to be within 10%.
In this paper, we further demonstrated the need to study close-in planets around low-mass stars to help constrain composition models and mass-loss mechanisms. We add that the precision to which planetary masses are measured today is often insufficient to accomplish this to a satisfactory level, complicating our overall understanding of exoplanet demographics.— concluded authors of the study
Featured image: TOI-1260 b and TOI-1260 c transits. The panels show a flattened LCOGT and TESS light curves with residuals folded to the orbital periods of the planets. Black lines show the best-fitting transit models. The LCO and TESS radius estimates for planet b agree to nearly 1𝜎. Data are shown in the nominal 2-min cadence mode and binned to 10 min. Typical error bar for nominal data is shown at the bottom right for each panel. © Georgieya et al.
Reference: I. Y. Georgieva, C. M. Persson, O. Barragán, G. Nowak, M. Fridlund, D. Locci, E. Palle, R. Luque, I. Carleo, D. Gandolfi, S. R. Kane, J. Korth, K. G. Stassun, J. Livingston, E. C. Matthews, K. A. Collins, S. B. Howell, L. M. Serrano, S. Albrecht, A. Bieryla, C. E. Brasseur, D. Ciardi, W. D. Cochran, K. D. Colon, I. J. M. Crossfield, Sz. Csizmadia, H. J. Deeg, M. Esposito, E. Furlan, T. Gan, E. Goffo, E. Gonzales, S. Grziwa, E. .W. Guenther, P. Guerra, T. Hirano, J. M. Jenkins, E. L. N. Jensen, P. Kabáth, E. Knudstrup, K. W. F. Lam, D. W. Latham, A. M. Levine, R. A. Matson, S. McDermott, H. L. M. Osborne, M. Paegert, S. N .Quinn, S. Redfield, G. R. Ricker, J. E. Schlieder, N. J. Scott, S. Seager, A. M. S. Smith, P. Tenenbaum, J. D. Twicken, R. Vanderspek, V. Van Eylen, J. N. Winn, “Hot planets around cool stars — two short-period mini-Neptunes transiting the late K-dwarf TOI-1260”, Arxiv, pp. 1-20, 2021. https://arxiv.org/abs/2104.05653
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