An investigation of chromospheric activity spanning the Vaughan--Preston gap: impact on stellar ages

TL;DR

This study investigates chromospheric activity in solar-type stars across different ages, revealing that activity levels do not decline smoothly with age but change rapidly, challenging previous assumptions about stellar aging.

Contribution

The paper provides new high-resolution spectroscopic data showing that chromospheric activity in solar-type stars changes abruptly rather than gradually with age.

Findings

Chromospheric activity remains high in stars up to 1.2 Gyr old.

Stars transition from active to inactive states rapidly, not gradually.

Previous correlations between age and activity may need reevaluation.

Abstract

Chromospheric activity is widely used as an age indicator for solar-type stars based on the early evidence that there is a smooth evolution from young and active to old and inactive stars. We analysed chromospheric activity in five solar-type stars in two open clusters, in order to study how chromospheric activity evolves with time. We took UVES high-resolution, high S/N ratio spectra of 3 stars in IC 4756 and 2 in NGC 5822, which were combined with a previously studied data-set and reanalysed here. The emission core of the deep, photospheric Ca II K line was used as a probe of the chromospheric activity. All of the 5 stars in the new sample, including those in the 1.2 Gyr-old NGC 5822, have activity levels comparable to those of Hyades and Praesepe. A likely interpretation of our data is that solar-type-star chromospheric activity, from the age of the Hyades until that of the Sun, does not evolve smoothly. Stars change from active to inactive on a short timescale. Evolution before and after such a transition is much less significant than cyclical and long-term variations. We show that data presented in the literature to support a correlation between age and activity could be also interpreted differently in the light of our results.