HADES RV Programme With HARPS-N At TNG. XVI. A super-Earth In The Habitable Zone Of The GJ 3998 Multi-planet System

The low masses of M dwarfs create attractive opportunities for exoplanet radial-velocity (RV) detections. These stars, however, exhibit strong stellar activity that may attenuate or mimic planetary signals.

We present a velocimetric analysis on one such M dwarf, GJ 3998 (d=18.2pc), with two published short-period super-Earths: GJ 3998 b and GJ 3998 c. We use additional data from the HARPS-N spectrograph to confirm these two planets and to look for more. We carry out joint modelling of: (i) RV planetary signals, (ii) stellar rotation in RV and activity indicators through Gaussian processes, (iii) long-term trends in RV and activity indicators.

We constrain the rotational period of GJ 3998 to Prot=30.2±0.3d and discover long-term sinusoidal imprints in RV and FWHM of period Pcyc=316+14−8d. We confirm GJ 3998 b and GJ 3998 c, and detect a third planet: GJ 3998 d, whose signal had been previously attributed to stellar activity.

GJ 3998 d has an orbital period of 41.78±0.05d, a minimum mass of 6.07+1.00−0.96M_⊕ and a mean insolation flux of 1.2+0.3−0.2Φ_⊕. This makes it one of the few known planets receiving Earth-like insolation flux.

A. K. Stefanov, A. Suárez Mascareño, J. I. González Hernández, N. Nari, R. Rebolo, L. Affer, G. Micela, I. Ribas, A. Sozzetti, M. Perger, M. Pinamonti, M. Damasso, J. Maldonado, E. González Álvarez, G. Scandariato

Comments: Published in A&A. 27 pages, 27 figures, 10 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2503.08405 [astro-ph.EP] (or arXiv:2503.08405v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2503.08405
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Related DOI:
https://doi.org/10.1051/0004-6361/202452630
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Submission history
From: Atanas K. Stefanov
[v1] Tue, 11 Mar 2025 13:09:15 UTC (2,994 KB)
https://arxiv.org/abs/2503.08405
Astrobiology,