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Several M dwarfs are targets of systematical monitoring in searches forDoppler signals caused by low-mass exoplanet companions. As a result, anemerging population of high-multiplicity planetary systems around low-massstars are being detected as well. We optimize classic data analysis methods anddevelop new ones to enhance sensitivity towards low-amplitude planets inhigh-multiplicity systems. We apply these methods to the public HARPSobservations of GJ 676A, a nearby M dwarf with one reported gas giantcompanion. We re-derived Doppler measurements using the template matchingmethod (HARPS-TERRA). We used refined versions of periodograms to assess thepresence of additional low-mass companions. We analyse the same dataset withBayesian tools and compared the performance of both approaches. We confirm thereported massive gas giant candidate and a long period trend, whose curvatureis now well detected. We also find very secure evidence of two new candidatesin close-in orbits and masses in the super-Earth mass regime. Despite theincreased sensitivity of the new periodogram tools, we find that Bayesianmethods are more sensitive in the early detection of candidate signals. Whilehardware development is important, development of data analysis techniques canhelp to reveal new results from existing data sets with significantly fewerresources. This new system holds the record of minimum-mass range (from Msin i= 4.5 M_Earth to 5 M_Jup) and period range (from 3.6 days to more than 10years). Although all the planet candidates are substantially more massive, itis the first exoplanetary system with a general architecture similar to oursolar system. GJ 676A can be happily added to the family of high-multiplicityplanetary systems around M dwarfs.

astronomy and astrophysics

A planetary system with gas giants and super-Earths around the nearby M  dwarf GJ 676A. Optimizing data analysis techniques for the detection of  multi-planetary systems