Transit timings variations in the three-planet system: TOI-270

Abstract

We present ground and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a bright (K-mag=8.25) M3V dwarf. The planets orbit near low-order mean-motion resonances (5:3 and 2:1), and are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using 8 different observatories between 2018 and 2020, we now report a clear detection of TTVs for planets c and d, with amplitudes of ∼10 minutes and a super-period of ∼3 years, as well as significantly refined estimates of the radii and mean orbital periods of all three planets. Dynamical modeling of the TTVs alone puts strong constraints on the mass ratio of planets c and d and on their eccentricities. When incorporating recently published constraints from radial velocity observations, we obtain masses of $M_{\mathrm{b}}=1.48\pm 0.18\, M_{\oplus}$, $M_{\mathrm{c}}=6.20\pm 0.31\, M_{\oplus}$ and $M_{\mathrm{d}}=4.20\pm 0.16\, M_{\oplus}$ for planets b, c and d, respectively. We also detect small, but significant eccentricities for all three planets : eb = 0.0167 ± 0.0084, ec = 0.0044 ± 0.0006 and ed = 0.0066 ± 0.0020. Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H2O atmosphere for the outer two. TOI-270 is now one of the best-constrained systems of small transiting planets, and it remains an excellent target for atmospheric characterization.

The Ariel Target List: The Impact of TESS and the Potential for Characterising Multiple Planets Within a System

“…Barnes & Haswell 2021;Demangeon et al submitted) and the ongoing work of radial velocity teams, both within the Ariel consortium and outside of it (e.g. Lillo-Box et al 2020;Chontos et al 2021;Nielsen et al 2020;Kaye et al 2021;Van Eylen et al 2021), are ensuring that the best targets for atmospheric characterisation are followed-up. Nevertheless, it may not be possible to conduct detailed follow-up of all the TPCs which may be of interest to the Ariel mission.…”

The Ariel Target List: The Impact of TESS and the Potential for Characterizing Multiple Planets within a System

“…Accurately knowing the planet's mass is also useful, particularly for smaller or cloudier worlds (Batalha et al 2019;Changeat et al 2020b). Several studies have explored the time needed to provide the radial velocity measurements necessary to constrain planet masses for Ariel (e.g., Barnes & Haswell 2021;Demangeon et al 2022), and the ongoing work of the radial velocity teams, both within the Ariel consortium and outside of it (e.g., Lillo-Box et al 2020;Nielsen et al 2020;Chontos et al 2021;Kaye et al 2021;Van Eylen et al 2021), is ensuring that the best targets for atmospheric characterization are followed up. Nevertheless, it may not be Figure 14.…”

Observation scheduling and automatic data reduction for the Antarctic telescope, ASTEP+

“…The optimal calibrated lightcurve is then extracted using a set of comparison stars. This pipeline has served its purpose well and has allowed ASTEP to contribute to many publications since we joined TFOP in 2020 12,13,16,17 ). However, the cost of IDL and its declining usage means that maintenance of the pipeline is becoming highly specialised knowledge.…”

“…This configuration means their gravitational interaction are detectable (producing Transit Timing Variations, TTVs), and would allow us to measure the planet's masses such as done already in papers where ASTEP observations were crucial. 17,21 In addition, ASTEP+ has produced the first ground-based detection of a circumbinary planet transit (Triaud et al in prep). To support this science, measuring Eclipse Timing Variations (ETVs) produced by the eclipsing binary stars at centre of such system is also a source of information about the planets.…”

“…8 With the successful launch of TESS (Transiting Exoplanet Survey Satellite), 11 the ASTEP observation program naturally transitioned to a follow-up of transiting exoplanet candidates, focusing on those with long orbital periods (10-100+ days) and contributing to many discoveries. [12][13][14][15][16][17][18][19][20][21] The geographic location of ASTEP is extremely interesting in complement to several key exoplanetary space missions. Of course, the Antarctic polar night is highly favorable for an efficient observation of transiting planets, in particular for those with long orbital periods and for those with long transit durations (the two being correlated).…”