A New Age–Activity Relation For Solar Analogs that Accounts for Metallicity

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Abstract
Determining stellar ages is challenging, particularly for cooler main-sequence (MS) stars. Magnetic evolution offers an observational alternative for age estimation via the age–chromospheric activity (AC) relation. We evaluate the impact of metallicity on this relation using near one-solar-mass stars across a wide metallicity range. We analyze a sample of 358 solar-type stars with precise spectroscopic parameters determined through a line-by-line differential technique and with ages derived using Yonsei–Yale isochrones. We measured chromospheric activity (S-index) using high-quality High Accuracy Radial Velocity Planet Searcher spectra, calibrated to the Mount Wilson system and converted to the R HK ′ ( T eff ) index with a temperature-based photospheric correction. Our findings show that the AC relation for R HK ′ ( T eff ) is strongly influenced by metallicity. We propose a new age–activity–metallicity relation for solar-type MS stars ( log g ≳ 4.2 ) with temperatures 5370 ≲ T eff ≲ 6530 K and metallicities from −0.7 to +0.3 dex. We show that taking metallicity into account significantly enhances chromospheric ages’ reliability, reducing the residuals’ rms relative to isochronal ages from 2.6 to 0.92 Gyr. This reflects a considerable improvement in the errors of chromospheric ages, from 53% to 15%. The precision level achieved in this work is also consistent with previous age–activity calibration from our group using solar twins.
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Funding Information
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2021/01303-3)
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2023/16319-8)
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2018/04055-8)
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2022/05833-0)
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2022/10325-3)

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