On the validity of the spectroscopic age indicators [Y/Mg], [Y/Al], [Y/Si], [Y/Ca], and [Y/Ti] for giant stars

TL;DR

This study evaluates the effectiveness of specific yttrium-based abundance ratios as chemical clocks for giant stars in open clusters, confirming their variable reliability compared to dwarf stars and highlighting the non-universality of spectroscopic age indicators.

Contribution

It provides the first systematic validation of Y-based abundance ratios as age indicators for giant stars in open clusters, revealing their limitations and differences from dwarf star calibrations.

Findings

Y/Mg, Y/Al, Y/Si are effective for field dwarf stars.

Y/Ca and Y/Ti do not correlate with age in field giants.

Chemical clocks show high scatter at early ages.

Abstract

The abundance ratios [Y$/$Mg], [Y$/$Al], [Y$/$Si], [Y$/$Ca], and [Y$/$Ti] have been suggested as chemical clocks for solar-metallicity dwarf stars in the field as well as for giant stars in open clusters. To verify this last hypothesis, we derive these abundances ratios of 50 giant stars belonging to seven open clusters. To calculate the abundances, we analyze FEROS spectra assuming the LTE-hypothesis. We confirm that [Y$/$Mg], [Y$/$Al], [Y$/$Si], [Y$/$Ca], and [Y$/$Ti] work as chemical clocks for field dwarf stars at the local region (d $<$ 1 kpc) whereas for the field giants the [Y$/$Mg], [Y$/$Al] and [Y$/$Si] also present trends with the ages but high scattering. [Y$/$Ca] and [Y$/$Ti] do not present any correlation with ages in the field giants. In Our open clusters, the behaviour is similar, [Y$/$Mg], [Y$/$Al] and [Y$/$Si] present evident trends, whereas [Y$/$Ca] vs. Ages is a flat and [Y$/$Ti] vs. Ages is less steep. We also confirm that the chemical clocks have high scatter at the early ages. In the case of the compiled sample, the chemical clocks are similar to our results but in some situations there are important differences. Several relations between abundance ratios and ages may be obtained when dwarfs and giants are analyzed, confirming the non-universality of the spectroscopic age indicators.