TOI-1408: the limb darkening models, photometric and Doppler noises, and the exoplanetary system

Abstract

We perform a self-consistent analysis of Doppler and photometric TESS and ground-based transit observations available for TOI-1408, known to host a system with two planets orbiting near 2:1 mean-motion commensurability and a distant companion. In general we confirm its orbital configuration derived in previous studies, however we found that the likelihood function contains multiple local maxima spread over a wider parametric domain, thus making some model uncertainties significantly larger than deemed before. In particular, the planet b radius still appears poorly constrained (from $\sim 1.2$~$R_{\mathrm{Jup}}$ to $\sim 3.5$~$R_{\mathrm{Jup}}$) because of the near-tangential transit geometry. We also show that the derived model is very prior-dependent regarding the astrophysical (spectrum-derived) constraints on the stellar mass $M_{\star }$ and radius $R_{\star }$. While such estimations may potentially contribute a significant information to the fit, their prior distribution must be accurately specified to be useful. Presently so accurate characterization (e.g. the correlation between $M_{\star }$ and $R_{\star }$) is not available in the literature.

arXiv comment23 pages, 11 figures, 2 tables; accepted by Research in Astronomy & Astrophysics