Additional Doppler Monitoring Corroborates HAT-P-11 c as a Planet

TL;DR

Extended Doppler monitoring over 17 years provides strong evidence that HAT-P-11c is a genuine planet, corroborating previous findings and ruling out stellar activity as the cause of its signal.

Contribution

This study extends the Doppler dataset for HAT-P-11, confirming HAT-P-11c as a planet through multiple periastron observations and astrometric data.

Findings

Two periastron passages observed of HAT-P-11c

No coherent stellar activity signature detected

Astrometric acceleration supports planetary nature

Abstract

In 2010, Bakos and collaborators discovered a Neptune-sized planet transiting the K-dwarf HAT-P-11 every five days. Later in 2018, Yee and collaborators reported an additional Jovian-mass companion on a nine year orbit based on a decade of Doppler monitoring. The eccentric outer giant HAT-P-11c may be responsible for the peculiar polar orbit of the inner planet HAT-P-11b. However, Basilicata et al. (2024) recently suggested that the HAT-P-11c Doppler signal could be caused by stellar activity. In this research note, we extend the Yee et al. (2018) Doppler time series by six years. The combined dataset spanning 17 years covers nearly two orbits of the outer planet. Importantly, we observe two periastron passages of planet c and do not observe a coherent activity signature. Together with the previously reported astrometric acceleration of HAT-P-11 from Hipparcos and Gaia, we believe there is strong evidence for HAT-P-11c as a bona fide planet.