Poster Open Access

Modelling Solar Ca II H&K Emission Variations

Sowmya, Krishnamurthy; Shapiro, Alexander I.; Witzke, Veronika; Nèmec, Nina-E.; Chatzistergos, Theodosis; Yeo, Kok Leng; Krivova, Natalie A.; Solanki, Sami K.


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  "inLanguage": {
    "alternateName": "eng", 
    "@type": "Language", 
    "name": "English"
  }, 
  "description": "<p>The emission in the near ultraviolet Ca II H&amp;K lines, often quantified via the S-index, has been serving as a prime proxy of solar and stellar magnetic activity. Despite the broad usage of the S-index, the link between the coverage of a stellar disk by magnetic features and Ca II&nbsp;H&amp;K emission is not fully understood. In order to fill this gap we developed a physics-based model to calculate the solar S-index. To this end, we made use of the distributions of the solar magnetic features derived from the simulations of magnetic flux emergence and surface transport, together with the Ca II&nbsp;H&amp;K spectra synthesized using a non-local thermodynamic equilibrium (non-LTE) radiative transfer code.</p>\n\n<p>We show that the value of the solar S-index is influenced by the inclination angle between the solar rotation axis and the observer&rsquo;s line-of-sight, i.e. the solar S-index values obtained by an out-of-ecliptic observer are different from those obtained by an ecliptic-bound observer. This is important for comparing the magnetic activity of the Sun to other stars. We computed time series of the S-index as they would be observed at various inclinations dating back to 1700. We find that depending on the inclination and period of observations, the activity cycle in solar S-index can appear weaker or stronger than in stars with a solar-like level of magnetic activity. We show that there is nothing unusual about the solar chromospheric emission variations in the context of stars with near-solar magnetic activity.</p>", 
  "license": "https://creativecommons.org/licenses/by/4.0/legalcode", 
  "creator": [
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0002-3243-1230", 
      "@type": "Person", 
      "name": "Sowmya, Krishnamurthy"
    }, 
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0002-8842-5403", 
      "@type": "Person", 
      "name": "Shapiro, Alexander I."
    }, 
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0002-0929-1612", 
      "@type": "Person", 
      "name": "Witzke, Veronika"
    }, 
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0001-6090-1247", 
      "@type": "Person", 
      "name": "N\u00e8mec, Nina-E."
    }, 
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0002-0335-9831", 
      "@type": "Person", 
      "name": "Chatzistergos, Theodosis"
    }, 
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0003-3851-7323", 
      "@type": "Person", 
      "name": "Yeo, Kok Leng"
    }, 
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0002-1377-3067", 
      "@type": "Person", 
      "name": "Krivova, Natalie A."
    }, 
    {
      "affiliation": "Max Planck Institute for Solar System Research", 
      "@id": "https://orcid.org/0000-0002-3418-8449", 
      "@type": "Person", 
      "name": "Solanki, Sami K."
    }
  ], 
  "url": "https://zenodo.org/record/4564796", 
  "datePublished": "2021-02-26", 
  "keywords": [
    "The Sun and the Heliosphere", 
    "Solar activity", 
    "Solar chromosphere", 
    "Stellar activity"
  ], 
  "@type": "CreativeWork", 
  "contributor": [
    {
      "@type": "Person", 
      "name": "Wolk, Scott"
    }
  ], 
  "@context": "https://schema.org/", 
  "identifier": "https://doi.org/10.5281/zenodo.4564796", 
  "@id": "https://doi.org/10.5281/zenodo.4564796", 
  "workFeatured": {
    "url": "http://coolstars20.cfa.harvard.edu/cs20half/", 
    "alternateName": "CS20.5", 
    "location": "virtually anywhere", 
    "@type": "Event", 
    "name": "The 20.5th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun"
  }, 
  "name": "Modelling Solar Ca II H&K Emission Variations"
}
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