HD 183579b: A Warm Sub-Neptune Transiting a Solar Twin Detected by TESS

We report the discovery and characterization of a transiting warm sub-Neptune planet around the nearby bright (\(V=8.75\) mag, \(K=7.15\) mag) solar twin HD 183579, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located \(56.8\pm0.1\) pc away with a radius of \(R_{\ast}=0.97\pm0.02\ R_{\odot}\) and a mass of \(M_{\ast}=1.03\pm0.05\ M_{\odot}\). We confirm the planetary nature by combining space and ground-based photometry, spectroscopy, and imaging. We find that HD 183579b (TOI-1055b) has a radius of \(R_{p}=3.53\pm0.13\ R_{\oplus}\) on a \(17.47\) day orbit with a mass of \(M_{p}=11.2\pm5.4\ M_{\oplus}\) (\(3\sigma\) mass upper limit of \(27.4\ M_{\oplus}\)). HD 183579b is the fifth brightest known sub-Neptune planet system in the sky, making it an excellent target for future studies of the interior structure and atmospheric properties. By performing a line-by-line differential analysis using the high resolution and signal-to-noise ratio HARPS spectra, we find that HD 183579 joins the typical solar twin sample, without a statistically significant refractory element depletion.