2025/10/15 by Anderson, David R., Vines, Jose I., Hesse, Katharine +56 · 1 citation
#Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2510.14083
We report the discovery of NGTS-11 c, a transiting warm Neptune (P ≈ 12.8 d; Mp = 1.2+0.3-0.2 MNep; Rp = 1.24 ± 0.03 RNep), in an orbit interior to the previously reported transiting warm Saturn NGTS-11 b (P ≈ 35.5 d). We also find evidence of a third outer companion orbiting the K-dwarf NGTS-11. We first detected transits of NGTS-11 c in TESS light curves and confirmed them with follow-up transits from NGTS and many other ground-based facilities. Radial-velocity monitoring with the HARPS and FEROS spectrographs revealed the mass of NGTS-11 c and provides evidence for a long-period companion (P > 2300 d; Mp sin i > 3.6 MJup). Taking into account the two additional bodies in our expanded datasets, we find that the mass of NGTS-11 b (Mp = 0.63 ± 0.09 MSat; Rp = 0.97 ± 0.02 RSat) is lower than previously reported (Mp = 1.2 ± 0.3 MSat). Given their near-circular and compact orbits, NGTS-11 c and b are unlikely to have reached their present locations via high-eccentricity migration. Instead, they probably either formed in situ or formed farther out and then underwent disk migration. A comparison of NGTS-11 with the eight other known systems hosting multiple well-characterized warm giants shows that it is most similar to Kepler-56. Finally, we find that the commonly used 10-day boundary between hot and warm Jupiters is empirically well supported.