A study of the magnetic activity and variability of GJ 436

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