Two planets around Kapteyn's star : a cold and a temperate super-Earth orbiting the nearest halo red-dwarf
Guillem Anglada-Escud\'e, Pamela Arriagada, Mikko Tuomi, Mathias, Zechmeister, James S. Jenkins, Aviv Ofir, Stefan Dreizler, Enrico Gerlach,, Chris J. Marvin, Ansgar Reiners, Sandra V. Jeffers, R. Paul Butler, Steven S., Vogt, Pedro J. Amado, Cristina Rodr\'iguez-L\'opez

TL;DR
This study reports the detection of two super-Earth planets orbiting Kapteyn's star, including one in the habitable zone, providing insights into planet formation around ancient halo stars.
Contribution
First detection of super-Earth planets around a halo star using combined archival and new Doppler measurements, revealing a potentially habitable planet in an ancient stellar environment.
Findings
Two planets with periods of 48 and 120 days identified.
One planet resides in the star's habitable zone.
Low activity levels suggest planetary signals are not activity-induced.
Abstract
Exoplanets of a few Earth masses can be now detected around nearby low-mass stars using Doppler spectroscopy. In this paper, we investigate the radial velocity variations of Kapteyn's star, which is both a sub-dwarf M-star and the nearest halo object to the Sun. The observations comprise archival and new HARPS, HIRES and PFS Doppler measurements. Two Doppler signals are detected at periods of 48 and 120 days using likelihood periodograms and a Bayesian analysis of the data. Using the same techniques, the activity indicies and archival ASAS-3 photometry show evidence for low-level activity periodicities of the order of several hundred days. However, there are no significant correlations with the radial velocity variations on the same time-scales. The inclusion of planetary Keplerian signals in the model results in levels of correlated and excess white noise that are remarkably low…
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