TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet

We present the bright (V$_{mag} = 9.12$), multi-planet system TOI-431, characterised with photometry and radial velocities. estimate stellar rotation period to be $30.5 \pm 0.7$ days using archival TOI-431b is a super-Earth of 0.49 days, radius 1.28 $\pm$ 0.04 R$_{\oplus}$, mass $3.07 0.35$ M$_{\oplus}$, density $8.0 1.0$ g cm$^{-3}$; TOI-431d sub-Neptune 12.46 $3.29 0.09$ $9.90^{+1.53}_{-1.49}$ $1.36 0.25$ cm$^{-3}$. find third planet, TOI-431c, in HARPS velocity data, but it not seen transit TESS light curves. It has an $M \sin i$ $2.83^{+0.41}_{-0.34}$ 4.85 days. likely extended atmosphere one most well-suited discoveries for atmospheric characterisation, while may stripped core. These planets straddle gap, presenting interesting case-study evolution, prime discovery study rocky planet phase