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Calibration of the [C/N] and [Y/Mg] chemical clocks with asteroseismic ages from the TESS space mission

E. Pakštienė, G. Tautvaišienė, V. Bagdonas, H. Kjeldsen, M. L. Winther, A. Drazdauskas, C. Viscasillas Vázquez, Y. Chorniy, Š. Mikolaitis, R. Minkevičiūtė, E. Stonkutė

Abstract

Context. Stellar ages are typically very difficult to estimate for field stars. New empirical methods, based on abundance ratios of chemical elements, are emerging and need to be calibrated. Aims. Our main aim is to contribute to revealing relations between [C/N] and [Y/Mg] ratios and stellar ages by determining astroseismic ages and non-local thermodynamic equilibrium (NLTE) abundances, and accounting for stellar evolutionary stages and birth places in the Galaxy. Methods. We searched for solar pulsations in a sample of 1250 bright F, G, and K giants using data from the TESS space telescope and determined asteroseismic ages using the BASTA and PARAM codes. For the [Y/Mg] relations with age, we determined abundances accounting for deviations from the local thermodynamic equilibrium. For the [C/N] relations with age, we separated stars according to their evolutionary stages. Results. We determined asteroseismic ages for 218 giants and derived [Y/Mg] and [C/N] relations with age for subsamples of stars in three regions of the Galactic thin disc and the thick disc. Conclusions. The [Y/Mg]-age relation exhibits a clear radial dependence across the Galactic disc, with a steeper trend in the outer disc, progressively flatter relations towards the inner disc, and a very flat trend in the thick disc. NLTE abundances of Mg and especially of Y have to be used in order to obtain a more precise stellar age evaluation from [Y/Mg] ratios. When using [C/N] abundance ratios as stellar age indicators, evolutionary stages of stars have to be taken into account.

Calibration of the [C/N] and [Y/Mg] chemical clocks with asteroseismic ages from the TESS space mission

Abstract

Context. Stellar ages are typically very difficult to estimate for field stars. New empirical methods, based on abundance ratios of chemical elements, are emerging and need to be calibrated. Aims. Our main aim is to contribute to revealing relations between [C/N] and [Y/Mg] ratios and stellar ages by determining astroseismic ages and non-local thermodynamic equilibrium (NLTE) abundances, and accounting for stellar evolutionary stages and birth places in the Galaxy. Methods. We searched for solar pulsations in a sample of 1250 bright F, G, and K giants using data from the TESS space telescope and determined asteroseismic ages using the BASTA and PARAM codes. For the [Y/Mg] relations with age, we determined abundances accounting for deviations from the local thermodynamic equilibrium. For the [C/N] relations with age, we separated stars according to their evolutionary stages. Results. We determined asteroseismic ages for 218 giants and derived [Y/Mg] and [C/N] relations with age for subsamples of stars in three regions of the Galactic thin disc and the thick disc. Conclusions. The [Y/Mg]-age relation exhibits a clear radial dependence across the Galactic disc, with a steeper trend in the outer disc, progressively flatter relations towards the inner disc, and a very flat trend in the thick disc. NLTE abundances of Mg and especially of Y have to be used in order to obtain a more precise stellar age evaluation from [Y/Mg] ratios. When using [C/N] abundance ratios as stellar age indicators, evolutionary stages of stars have to be taken into account.
Paper Structure (16 sections, 4 equations, 13 figures)

This paper contains 16 sections, 4 equations, 13 figures.

Table of Contents

  1. Introduction
  2. Stellar sample and method of analysis
  3. Galactocentric distances and isochronal ages
  4. Stellar atmospheric parameters and abundances of chemical elements
  5. Non-local thermodynamic equilibrium effects
  6. Asteroseismic ages
  7. Age determinations with PARAM
  8. Age determinations with BASTA
  9. Evolutionary stages
  10. Results and discussion
  11. Comparison of asteroseismic and classical isochronal ages
  12. Relation of [Y/Mg] with age
  13. Relation of [C/N] with age
  14. Comparison of C and N abundances with evolutionary models
  15. Summary and conclusions
  16. ...and 1 more sections

Figures (13)

  • Figure 1: Distribution of stars according to mean galactocentric distance, $R_{\rm mean}$, and maximum height from the Galactic plane, |$z_{\rm max}$|.
  • Figure 2: Distribution of stars according to $T_{\rm eff}$ and [Fe/H].
  • Figure 3: NLTE corrections of [Mg/H] and [Y/H] for the investigated stars.
  • Figure 4: Distribution of stars according to frequency at maximum power, $\nu_{\rm{max}}$, and the large frequency separation, $\Delta\nu$, derived in this study.
  • Figure 5: Distribution of stars according to their asteroseismic masses and ages determined in this study.
  • ...and 8 more figures