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A candidate super-Earth planet orbiting near the snow line of Barnard's star

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  • M. Kiraga
  • M. Kürster
  • M. J. López-González
  • D. Montes
  • J. Morin
  • A. Ofir
  • E. Pallé
  • R. Rebolo
  • S. Reffert
  • A. Schweitzer
  • W. Seifert
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  • A. Suárez Mascareño
  • Y. Tsapras
  • G. Anglada-Escudé
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Original languageEnglish
Number of pages4
Pages (from-to)365-368
JournalNature
Journal publication date15 Nov 2018
Volume563
Issue7731
Early online date14 Nov 2018
DOIs
Publication statusPublished - 15 Nov 2018

Abstract

Barnard’s star is a red dwarf, and has the largest proper motion (apparent motion across the sky) of all known stars. At a distance of 1.8 parsecs, it is the closest single star to the Sun; only the three stars in the α Centauri system are closer. Barnard’s star is also among the least magnetically active red dwarfs known and has an estimated age older than the Solar System. Its properties make it a prime target for planetary searches; various techniques with different sensitivity limits have been used previously, including radial-velocity imaging, astrometry and direct imaging, but all ultimately led to negative or null results. Here we combine numerous measurements from high-precision radial-velocity instruments, revealing the presence of a low-amplitude periodic signal with a period of 233 days. Independent photometric and spectroscopic monitoring, as well as an analysis of instrumental systematic effects, suggest that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard’s star is a cold super-Earth, with a minimum mass of 3.2 times that of Earth, orbiting near its snow line (the minimum distance from the star at which volatile compounds could condense). The combination of all radial-velocity datasets spanning 20 years of measurements additionally reveals a long-term modulation that could arise from a stellar magnetic-activity cycle or from a more distant planetary object. Because of its proximity to the Sun, the candidate planet has a maximum angular separation of 220 milliarcseconds from Barnard’s star, making it an excellent target for direct imaging and astrometric observations in the future.

Notes

38 pages, 7 figures, 4 tables, author's version of published paper in Nature journal

ID: 15985969