Rubidium abundances of galactic disk stars

Spectroscopic determinations of rubidium abundances were made by applying the spectrum-fitting method to the Rb(i) 7800 line for an extensive sample of similar to 500 late-type dwarfs as well as giants (including Hyades cluster stars) belonging to the galactic disk population, with the aim of establishing the behavior of [Rb/Fe] ratio for disk stars in the metallicity range of -0.6 less than or similar to [Fe/H] less than or similar to +0.3. An inspection of the resulting Rb abundances for Hyades dwarfs revealed that they show a systematic T-eff-dependent trend at greater than or similar to 5,500 K; this means that the results for mid-G to F stars (including the Sun) are not reliable (i.e., more or less overestimated), which might be due to some imperfect treatment of surface convection in classical model atmospheres. As such, it was decided to confine only to late-G and K stars at T-eff less than or similar to 5,500 K and adopt the solar-system (meteoritic) value as the reference Rb abundance. The [Rb/Fe] versus [Fe/H] relations derived for field dwarfs and giants turned out to be consistent with each other, showing a gradual increase of [Rb/Fe] with a decrease in [Fe/H] (with d[Rb/Fe]/d[Fe/H] gradient of similar to -0.4 around the solar metallicity), which compares favorably with the theoretical prediction of chemical evolution models. Accordingly, this study could not confirm the anomalous behavior of [Rb/Fe] ratio (tending to be subsolar but steeply increasing towards supersolar metallicity) recently reported for M dwarf stars of -0.3 less than or similar to [Fe/H] less than or similar to +0.3.

Automated summary

The study used spectroscopic determinations of rubidium abundances to investigate the behavior of [Rb/Fe] ratio for disk stars in the metallicity range of -0.6 to +0.3. Results showed that the reliability of the abundances varied with stellar temperature, leading to the decision to focus on late-G and K stars at temperatures below 5500K. The study found that the [Rb/Fe] ratio gradually increases with decreasing metallicity, consistent with theoretical predictions of chemical evolution models.