[astro-ph.EP] Hot Neptunes are close-in exoplanets that occupy a sparsely populated region of parameter space known as the “hot-Neptune desert”.
Their presence in this extreme environment is puzzling as it implies a complex history involving intense stellar radiation, atmospheric loss, and unique migration patterns, different from Neptunes at larger orbital periods.
We are running an observational programme conceived to enlarge the number of close-in Neptune-sized planets, with well-measured physical and orbital parameters, with the aim of contributing to obtaining a statistically significant sample needed to clarify what the formation and migration pathways of this class of exoplanets are.
We used currently available TESS photometry, along with new (HARPS-N) and archival (HIRES) high-precision radial-velocity measurements, to review the main properties of the planetary systems TOI-1272 and TOI-1694 by means of joint-fit analyses that, in the case of TOI-1272, included Gaussian-process regressions for carefully modelling stellar activity. Our final estimates of the parameters of the two systems are consistent with previous measurements but have smaller uncertainties.
We identified the radial-velocity variation of TOI-1272 found in the HIRES data as stellar activity rather than planetary in nature and, therefore, rejected the non-transiting planet TOI-1272c. This opens up the possibility that TOI-1272b’s eccentricity is the result of high-eccentricity migration.
The larger number of data at our disposal also allowed us to point out that both TOI-1694b and TOI-1694c move on slightly eccentric orbits. The current orbital architecture of TOI-1694 suggests a history of migration driven by both disc and dynamical interactions.
Comparison of exoplanetary systems’ architectures that have at least one Neptunian planet (defined as having a mass between 10 and 40 M⊕) with Porb ≲ 5.7 d, therefore inside the ridge (delimited by the two dashed lines) and the desert. TOI-1272 and TOI-1694 are highlighted. Host stars’ metallicity and size are illustrated by color and circle size, respectively. Planets’ orbital eccentricity and mass are illustrated by color and circle size, respectively. Note that the TOI-1272 system hosts only one planet now. The red cross marks the wrong position of TOI-1694 c reported in the exoplanet archives up to now (June 2026). — astro-ph.EP
L. Mancini, L. Naponiello, M. Damasso, K. Biazzo, A. S. Bonomo, A. F. Lanza, J. Lillo-Box, M. Pinamonti, R. Cosentino, A. Bignamini, W. Boschin, A. Fiorenzano, P. Giacobbe, F. Manni, M. Rainer, G. Scandariato, A. Sozzetti
Comments: 20 pages, 13 figures, accepted for publication in Astronomy & Astrophysics. This version contains HARPS-N RV data points and activity indices not available in the published paper, but present in the CDS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2606.21625 [astro-ph.EP] (or arXiv:2606.21625v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.21625
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Submission history
From: Luigi Mancini
[v1] Fri, 19 Jun 2026 17:29:44 UTC (6,657 KB)
https://arxiv.org/abs/2606.21625
Astrobiology, exoplanet,
