An improved age–activity relationship for cool stars older than a gigayear

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      Stars with convective envelopes display magnetic activity, which decreases over time due to the magnetic braking of the star. This age-dependence of magnetic activity is well-studied for younger stars,but the nature of this dependence for older stars is not well understood. This is mainly because absolute stellar ages for older stars are hard to measure. However, relatively accurate stellar ages have recently come into reach through asteroseismology. In this work we present X-ray luminosities, which are a measure for magnetic activity displayed by the stellar coronae, for 24 stars with well-determined agesolder than a gigayear. We find 14 stars with detectable X-ray luminosities and use these to calibrate the age-activity relationship.We find a relationship between stellar X-ray luminosity, normalized by stellar surface area, and age that is steeper than the relationships found for younger stars, with an exponent of -2.80+-0.72. Previous studies have found values for the exponent of the age-activity relationship ranging between -1.09 to -1.40, dependent on spectral type,for younger stars. Given that there are recent reports of a flattening relationship between age and rotational period for old cool stars, one possible explanation is that we witness a strong steepening of the relationship between activity and rotation.

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      Original languageEnglish
      Number of pages14
      Pages (from-to)1012-1025
      JournalMonthly Notices of the Royal Astronomical Society
      Journal publication date11 Oct 2017
      Issue number1
      Volume471
      Early online date29 Jun 2017
      DOIs
      StatePublished - 11 Oct 2017

        Research areas

      • Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Earth and Planetary Astrophysics

      ID: 131772658