TOI-2322: two transiting rocky planets close to the stellar rotation period and its first harmonic

Abstract

Context. Active regions on the stellar surface can induce quasi-periodic radial velocity (RV) variations that can mimic planets and mask true planetary signals. These spurious signals can be problematic for RV surveys such as those carried out by the ESPRESSO consortium. Aims. Using ESPRESSO and HARPS RVs and activity indicators, we aim to confirm and characterize two candidate transiting planets from TESS orbiting a K4 star with strong activity signals. Methods. From the ESPRESSO FWHM, TESS photometry, and ASAS-SN photometry, we measure a stellar rotation period of 21.28 $\pm$ 0.08 d. We jointly model the TESS photometry, ESPRESSO and HARPS RVs, and activity indicators, applying a multivariate Gaussian Process (GP) framework to the spectroscopic data. Results. We are able to disentangle the planetary and activity components, finding that TOI-2322 b has a $11.307170_{-0.000079}^{+0.000085}$ d period, close to the first harmonic of the rotation period, a $\le 2.03M_{\oplus }$ mass upper limit and a $0.994_{-0.059}^{+0.057}$ ${\mathrm{R}}_{\oplus }$ radius. TOI-2322 c orbits close to the stellar rotation period, with a $20.225528_{-0.000044}^{+0.000039}$ d period; it has a $18.10_{-5.36}^{+4.34}$ ${\mathrm{M}}_{\oplus }$ mass and a $1.874_{-0.057}^{+0.066}$ ${\mathrm{R}}_{\oplus }$ radius. Conclusions. The multivariate GP framework is crucial to separating the stellar and planetary signals, significantly outperforming a one-dimensional GP. Likewise, the transit data is fundamental to constraining the periods and epochs, enabling the retrieval of the planetary signals in the RVs. The internal structure of TOI-2322 c is very similar to that of Earth, making it one of the most massive planets with an Earth-like composition known.

arXiv comment22 pages, 20 figures. Accepted for publication in A&A

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