Astronomers Discover Trio Of Planets Orbiting An M-Dwarf Star (Planetary Science)

A team of international astronomers reported on the discovery of one super-Earth- (TOI-1749b) and two sub-Neptune-sized planets (TOI1749c and TOI-1749d) transiting an early M dwarf TOI-1749 at a distance of 100 pc. Their study recently appeared in Arxiv.

Astronomers first identified these systems as planetary candidates using data from the TESS photometric survey. Later, they have followed up this system from the ground by means of multiband transit photometry, adaptive-optics imaging, and low-resolution spectroscopy, from which they have validated the planetary nature of the candidates.

They found that TOI-1749 b, c, and d have orbital periods of 2.39, 4.49, and 9.05 days, and radii of 1.4, 2.1, and 2.5 R, respectively. (More derived parameters are given in Table 1 below)

Table 1: Derived parameters from the results of photodynamical analysis. © Fukui et al.

In addition, using photodynamical models they have been able to place 95% confidence level upper limits on the masses of TOI-1749b, TOI-1749c, and TOI-1749d of 57, 14, and 15 M, respectively.

Figure 1: Period and radius diagram for planets around M dwarfs. The gray dots are known planets around M dwarfs taken from the NASA Exoplanet Archive. The magenta squares and black dots are for planets in the TOI-1749 and TOI-270 systems, respectively. The orange dashed line indicates the location of the proposed radius valley for M dwarf planets by Van Eylen et al. (2021). © Fukui et al.

The periods, sizes, and tentative masses of these planets are in line with a scenario in which all three planets initially had a hydrogen envelope on top of a rocky core, and only the envelope of the innermost planet has been stripped away by photoevaporation and/or core-powered mass loss mechanisms.

“The compositions of the innermost planet and the outer two planets can be explained by a bare rocky core and a rocky core + thin hydrogen envelope respectively.”

In addition, they have confirmed that the system is dynamically stable for at least 109 orbits of the innermost planet.

Figure 2. Period ratios of planetary trios including a near 2:1 commensurability pair. P1, P2, and P3 denote the orbital period of the inner planet in a near 2:1 commensurability pair, that of the outer planet in the same pair, and that of another planet inside (left panels) or outside (right panels) of the near 2:1 commensurability pair, respectively. Top and bottom panels show planetary trios around M dwarfs (Teff ≤ 4000K) and FGK dwarfs (Teff > 4000K), respectively. The gray dashed, dash-dotted, and dotted lines indicate the locations of the exact 2:1, 2:3, and 3:5 commensurabilities, respectively. This figure shows that additional planets to planetary pairs near 2:1 commensurability around M (FGK) dwarfs tend to have an inside (outside) orbit. Note that the TOI-178 system shows an opposite property; the host star however has an effective temperature that is close to the boundary (Teff = 4316K) © Fukui et al.

The outer planetary pair has a period ratio very close to the 2:1 commensurability (2.015), sharing the orbital architecture with the other M dwarf systems TOI-270 and TOI-175. This characteristic architecture might be a consequence of common planetary formation and migration processes in these systems.

“Further follow-up observations of this system would be worth pursuing to characterize the system in more detail.”

— concluded authors of the study

Featured image credit: Getty Images

Reference: A. Fukui, J. Korth, J. H. Livingston, J. D. Twicken, M. R. Zapatero Osorio, J. M. Jenkins, M. Mori, F. Murgas, M. Ogihara, N. Narita, E. Pallé, K. G. Stassun, G. Nowak, D. R. Ciardi, L. Alvarez-Hernandez, V. J. S. Béjar, N. Casasayas-Barris, N. Crouzet, J. P. de Leon, E. Esparza-Borges, D. Hidalgo Soto, K. Isogai, K. Kawauchi, P. Klagyivik, T. Kodama, S. Kurita, N. Kusakabe, R. Luque, A. Madrigal-Aguado, P. Montanes Rodriguez, G. Morello, T. Nishiumi, J. Orell-Miquel, M. Oshagh, H. Parviainen, M. Sánchez-Benavente, M. Stangret, N. Watanabe, G. Chen, M. Tamura, P. Bosch-Cabot, M. Bowen, K. Eastridge, L. Freour, E. Gonzales, P. Guerra, Y. Jundiyeh, T. K. Kim, L. V. Kroer, A. M. Levine, E. H. Morgan, M. Reefe, R. Tronsgaard, C. K. Wedderkopp, J. Wittrock, K. A. Collins, K. Hesse, D. W. Latham, G. R. Ricker, S. Seager, R. Vanderspek, J. Winn, E. Bachelet, M. Bowman, C. McCully, M. Daily, D. Harbeck, N. H. Volgenau, “TOI-1749: an M dwarf with a Trio of Planets including a Near-Resonant Pair”, Arxiv, pp. 1-30, 2021.

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