Trio of super-Earth candidates orbiting K-dwarf HD 48948: a new habitable zone candidate

We present the discovery of three super-Earth candidates orbiting HD 48948, a bright K-dwarf star with an apparent magnitude of m_V = 8.58 mag. As part of the HARPS-N Rocky Planet Search programme, we collect 189 high-precision radial velocity measurements using the HARPS-N spectrograph from 2013 October 6, to 2023 April 16. Various methodologies are applied to extract the radial velocities from the spectra, and we conduct a comprehensive comparative analysis of the outcomes obtained through these diverse extraction techniques. To ensure the robustness of our findings, we employ several methods to address stellar variability, with a focus on Gaussian Process regression. To account for the impact of stellar variability and correlated noise in the radial velocity data set, we include activity indicators, such as log R'_HK and bisector span, in the multidimensional Gaussian Process regression. Our analysis reveals three planetary candidates with orbital periods of 7.3, 38, and 151 d, and minimum masses estimated at 4.88±0.21 M_⊕⁠, 7.27±0.70 M_⊕, and 10.59±1.00 M_⊕⁠, respectively. The outermost planet resides within the (temperate) habitable zone, positioned at a projected distance of 0.029 arcsec from its star. Given the close proximity of this planetary system, situated at a distance of 16.8 parsecs, HD 48498 emerges as a promising target (closest super-Earth around FGK stars) for future high-contrast direct imaging and high-resolution spectroscopic studies.