Characterization of the HD 108236 system with CHEOPS and TESS Confirmation of a fifth transiting planet

The HD108236 system was first announced with the detection of four small planets based on TESS data. Shortly after, transit an additional planet a period 29.54d serendipitously detected by CHEOPS. In this way, (V=9.2) became one brightest stars known to host five transiting (R$_p$<3R$_{\oplus}$). We characterize planetary using all data available from CHEOPS and space missions. use flexible pointing capabilities follow up transits in system, including fifth body. After updating star parameters results Gaia eDR3, we analyzed 16 43 observed TESS, respectively, derive physical orbital parameters. carried out timing analysis each search for presence variations. derived improved values radius mass (R$_{\star}$=0.876$\pm$0.007 R$_{\odot}$ M$_{\star}$=0.867$_{-0.046}^{+0.047}$ M$_{\odot}$). confirm f orbit. Thus, consists R$_b$=1.587$\pm$0.028, R$_c$=2.122$\pm$0.025, R$_d$=2.629$\pm$0.031, R$_e$=3.008$\pm$0.032, R$_f$=1.89$\pm$0.04 [R$_{\oplus}$]. refine ephemeris find no significant variations c, d, e. For b f, instead, measure deviations their times (up 22 28 min, respectively) non-negligible dispersion 9.6 12.6 min time residuals. evidence potential 10.9d period, as previously suggested. Full abstract PDF file.