The RR Lyrae in Trumpler 5: first direct detection of an RR Lyrae in an intermediate-age cluster

Abstract: RR Lyrae stars have long been considered tracers of exclusively old (>10 Gyr) and metal-poor stellar populations. Recent independent results in different scenarios, however, are challenging this view and pointing at the existence of intermediate-age RR Lyrae, only a few (2–5) Gyrs old. 

In this seminar I will present the first detection of an RR Lyrae star reliably associated to an intermediate-age cluster: the nearby 2-4 Gyr-old Trumpler 5. I will frame this result in the context of recent works on the expected and observed rates of these stars per unit mass, both from observations of  intermediate-age clusters in the Magellanic Clouds and from previous results on possible binary evolution origins for these stars. The association of an RRL star to a decidedly intermediate-age simple stellar population is, so far, the most direct evidence of the existence of these ‘young’ RRLs and adds firm support to the evidence that has been systematically accumulating toward the existence of these highly controverted stars.