New paper: Magnetic activity of old cool stars ?>

New paper: Magnetic activity of old cool stars

Magnetic activity, measured as X-ray luminosity divided by stellar surface, as a function of stellar age. The decline of activity steepens for stars older than a gigayear. From Booth et al. (2017).

Happy to report that my PhD student Rachel Booth has successfully published her first paper! It’s a very interesting analysis of the magnetic activity of old cool stars, with a surprising find about the decline of activity at old stellar ages. Our paper has also been featured on the Astrobites blog:

Here’s the abstract of the paper:

Stars with convective envelopes display magnetic activity, which decreases over time due to the magnetic braking of the star. This age-dependence of magnetic activity is well-studied for younger stars, but the nature of this dependence for older stars is not well understood. This is mainly because absolute stellar ages for older stars are hard to measure. However, relatively accurate stellar ages have recently come into reach through asteroseismology. In this work we present X-ray luminosities, which are a measure for magnetic activity displayed by the stellar coronae, for 24 stars with well-determined ages older than a gigayear. We find 14 stars with detectable X-ray luminosities and use these to calibrate the age-activity relationship. We find a relationship between stellar X-ray luminosity, normalized by stellar surface area, and age that is steeper than the relationships found for younger stars, with an exponent of -2.80 +- 0.72. Previous studies have found values for the exponent of the age-activity relationship ranging between -1.09 to -1.40, dependent on spectral type, for younger stars. Given that there are recent reports of a flattening relationship between age and rotational period for old cool stars, one possible explanation is that we witness a strong steepening of the relationship between activity and rotation.

“An Improved Age-Activity Relationship for Cool Stars older than a Gigayear”, accepted for publication by MNRAS (2017), R. S. Booth, K. Poppenhaeger, C. A. Watson, V. Silva Aguirre, S. J. Wolk.

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