Abstract
We report the discovery and validation of four extrasolar planets hosted
by the nearby, bright, Sun-like (G3V) star HD~108236
using data from the Transiting Exoplanet Survey Satellite (TESS). We
present transit photometry, reconnaissance and precise Doppler
spectroscopy as well as high-resolution imaging, to validate the
planetary nature of the objects transiting HD~108236,
also known as the TESS Object of Interest (TOI) 1233. The innermost
planet is a possibly-rocky super-Earth with a period of
3.79523+0.00047−0.00044 days and has a radius of 1.586±0.098 R⊕. The
outer planets are sub-Neptunes, with potential gaseous envelopes, having
radii of 2.068+0.10−0.091 R⊕, 2.72±0.11 R⊕, and 3.12+0.13−0.12 R⊕ and
periods of 6.20370+0.00064−0.00052 days, 14.17555+0.00099−0.0011 days,
and 19.5917+0.0022−0.0020 days, respectively. With V and Ks magnitudes
of 9.2 and 7.6, respectively, the bright host star makes the transiting
planets favorable targets for mass measurements and, potentially, for
atmospheric characterization via transmission spectroscopy.
HD~108236 is the brightest Sun-like star in the visual
(V) band known to host four or more transiting exoplanets. The
discovered planets span a broad range of planetary radii and equilibrium
temperatures, and share a common history of insolation from a Sun-like
star (R⋆=0.888±0.017 R⊙, Teff=5730±50 K), making HD 108236 an exciting,
opportune cosmic laboratory for testing models of planet formation and
evolution.