NO EVIDENCE FOR ACTIVITY CORRELATIONS IN THE RADIAL VELOCITIES OF KAPTEYN'S STAR

Research output: Contribution to journalResearch articleContributedpeer-review

Contributors

  • Guillem Anglada-Escude - , Queen Mary University of London (Author)
  • M. Tuomi - , University of Hertfordshire (Author)
  • P. Arriagada - , Carnegie Institution of Science, Washington (Author)
  • M. Zechmeister - , Queen Mary University of London (Author)
  • J. S. Jenkins - , Universidad de Chile (Author)
  • A. Ofir - , Weizmann Institute of Science (Author)
  • S. Dreizler - , University of Göttingen (Author)
  • E. Gerlach - , Research Group for Astronomy (Author)
  • C. J. Marvin - , University of Göttingen (Author)
  • A. Reiners - , University of Göttingen (Author)
  • S. V. Jeffers - , University of Göttingen (Author)
  • R. Paul Butler - , Carnegie Institution of Science, Washington (Author)
  • P. J. Amado - , Spanish National Research Council (Author)
  • C. Rodriguez-Lopez - , Spanish National Research Council (Author)
  • Z. M. Berdinas - , Spanish National Research Council (Author)
  • J. Morin - , University of Montpellier (Author)
  • J. D. Crane - , Carnegie Institution of Science, Washington (Author)
  • S. A. Shectman - , Carnegie Institution of Science, Washington (Author)
  • M. R. Diaz - , Universidad de Chile (Author)
  • L. F. Sarmiento - , University of Göttingen (Author)
  • H. R. A. Jones - , University of Hertfordshire (Author)
  • University of California at Santa Cruz

Abstract

Stellar activity may induce Doppler variability at the level of a few m s(-1) which can then be confused by the Doppler signal of an exoplanet orbiting the star. To first order, linear correlations between radial velocity measurements and activity indices have been proposed to account for any such correlation. The likely presence of two super-Earths orbiting Kapteyn's star was reported in Anglada-Escude et al., but this claim was recently challenged by Robertson et al., who argued for evidence of a rotation period (143 days) at three times the orbital period of one of the proposed planets (Kapteyn's b, P = 48.6 days) and the existence of strong linear correlations between its Doppler signal and activity data. By re-analyzing the data using global statistics and model comparison, we show that such a claim is incorrect given that (1) the choice of a rotation period at 143 days is unjustified, and (2) the presence of linear correlations is not supported by the data. We conclude that the radial velocity signals of Kapteyn's star remain more simply explained by the presence of two super-Earth candidates orbiting it. We note that analysis of time series of activity indices must be executed with the same care as Doppler time series. We also advocate for the use of global optimization procedures and objective arguments, instead of claims based on residual analyses which are prone to biases and incorrect interpretations.

Details

Original languageEnglish
Article number74
Number of pages7
JournalAstrophysical Journal
Volume830
Issue number2
Publication statusPublished - 20 Oct 2016
Peer-reviewedYes

External IDs

Scopus 84992695553

Keywords

Keywords

  • techniques: radial velocities, stars: individual (Kapteyn's star), planetary systems, methods: data analysis, EXTRA-SOLAR PLANETS, DWARF GLIESE 581, STELLAR ACTIVITY, HABITABLE-ZONE, HARPS SEARCH, MASS PLANETS, SUPER-EARTHS, SPACED DATA, RED NOISE, HD 41248