SAGE Independent Research Group

There is no one observable that is sensitive to age and age alone. However, some combinations of parameters such as large frequency separation and small frequency separation are more sensitive to age. The age can be better constrained by comparing these observables with parameters extracted from stellar models. Extracting ages from stellar models is an optimization problem that seeks the initial stellar conditions and amount of time elapsed that gives the best fit to a measured set of observables.

Yvonne Elsworth, Sarbani Basu

From its surface proper.es it can be difficult to determine whether a red-giant star is in its Helium-core-burning phase or only burning Hydrogen in a shell around an inert Helium core. Stars in either of these stage can have similar effec.ve temperatures, radii and hence luminosi.es, i.e. they can be located at the same posi.on in the Hertzsprung-Russell diagram. Bedding et al. (2011) showed that with asteroseismic informa.on from the stellar structure it is however possible to iden.fy the evolu.onary state of a red giant. For this technique one relies on the detec.on of the frequencies of mixed pressure-gravity modes. Resolving individual mixed modes is not always feasible in shorter .meseries data such as those of the K2 (Haas et al. 2014) and TESS (Ricker et al. 2015) missions. Here we present two methods that do not rely on the detec.on of the individual mixed modes. These methods have been applied together with the methods by Kallinger et al. (2012) and Mosser et al. (2014) to the APOKASC stars (Pinsonnault et al. in prep; Elsworth et al. in prep) to provide consolidated evolu.onary phases.