A study of the magnetic activity and variability of GJ 436

M. Kumar, R. Fares

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6 Citations (Scopus)


We present a magnetic activity study of GJ 436 using spectroscopic data from HARPS, spanning over 14 yr, and additional data from NARVAL, falling within the HARPS observations. We study the Ca II H&K, He I D3, Na I doublet, H α, and Ca II IRT triplets lines and explore linear correlations between them. Using the full HARPS data set, we found indices H α versus Ca II H&K & H α versus He I to correlate positively. From the NARVAL data set, covering one observing epoch, we found Ca II IRT3 versus Ca II IRT2 & Ca II IRT3 versus H α index to correlate negatively. We investigate long and short-term periodicity in these index variations, using the Generalized Lomb-Scargle periodogram. For Ca II H&K, Na I and H α indices, we detect long-term periods of 2470.7 d (∼ 6.8 yr), 1861.6 d (∼ 5.1 yr), and 2160.9 d (∼ 5.9 yr) respectively, consistent with GJ 436's photometric cycle of ∼ 7.4 yr. Applying the 'Pooled Variance' technique to H α & Na I indices, we found ∼ 2500 d to be the period of an activity cycle mechanism, in good agreement with the detected 2470.7 d period. For Ca II H&K and H α indices, we detect short-term periods of 39.47+0.11−0.15 d and 40.46+0.44−0.52 d, respectively, identified as the stellar rotation period. The stellar rotation is detected after pre-whitening the long-term periodicity. It is detected as well in the analysis of individual observing epochs.

Original languageEnglish
Pages (from-to)3147-3163
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - Jan 1 2023


  • planetary systems
  • stars: activity
  • stars: chromospheres
  • stars: individual: GJ 436

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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