{
  "id": "2209.11258",
  "version": "v1",
  "published": "2022-09-22T18:05:58.000Z",
  "updated": "2022-09-22T18:05:58.000Z",
  "title": "A Study of the Magnetic Activity and Variability of GJ 436",
  "authors": [
    "M. Kumar",
    "R. Fares"
  ],
  "comment": "Accepted for publication in MNRAS. 13 pages, with additional online material",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We present a magnetic activity study of GJ 436 using spectroscopic data from HARPS, spanning over 14 years, and additional data from NARVAL, falling within the HARPS observations. We study the CaII H&K, HeID3, NaI doublet, H$\\alpha$ and CaII IRT triplets lines and explore linear correlations between them. Using the full HARPS dataset, we found indices H$\\alpha$ vs CaII H&K & H$\\alpha$ vs HeI to correlate positively. From the NARVAL dataset, covering one observing epoch, we found CaII IRT$_{3}$ vs CaII IRT$_{2}$ & CaII IRT$_{3}$ vs H$\\alpha$ index to correlate negatively. We investigate long and short-term periodicity in these index variations using the Generalised Lomb-Scargle periodogram. For CaII H&K, NaI and H$\\alpha$ indices, we detect long-term periods of 2470.7d (~ 6.8 years), 1861.6d (~ 5.1 years) and 2160.9d (~ 5.9 years) respectively, consistent with GJ 436's photometric cycle of ~ 7.4 years. Applying the \"Pooled Variance\" technique to H$\\alpha$ & NaI indices, we found ~ 2500d to be the period of an activity cycle mechanism, in good agreement with the detected 2470.7d period. For CaII H&K and H$\\alpha$ 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 prewhitening the long-term periodicity. It is detected as well in the analysis of individual observing epochs.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-09-22T18:05:58.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "variability",
      "gj 436s photometric cycle",
      "caii irt triplets lines",
      "detect short-term periods",
      "full harps dataset"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 13,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}