Speaker
Description
Stellar activity cycles are generally studied using observations spanning a decade or more. However, shorter time series may be sufficient to investigate activity-related variations in rapidly rotating F-type stars. The relationship between stellar rotation period and activity-cycle length is well established, but F-type stars occupy an intermediate position between the active and inactive branches of the observed rotation–cycle relation, and their cycle properties remain poorly characterized. Since magnetic activity can produce shifts in solar-like p-mode frequencies (e.g. Fletcher et al., 2006), asteroseismology provides a means of probing these variations.
I investigate temporal p-mode frequency shifts in three F-type stars using Kepler/K2 short-cadence photometry spanning at least one year. The first target, KIC 10355856, is an F5V star with an effective temperature of approximately 6560 K, a rotation period of about 7.2 days, and an observational time span of 1.232 years. Previous work reported an approximately 30-day modulation in its magnetic properties (Régulo et al., 2016).
I employ two complementary approaches. First, I cross-correlate power spectra from consecutive 30-day segments to measure average frequency shifts across the p-mode power-excess region, using the first segment as the reference. The frequency range investigated is 90–130 c/d (approximately 1042–1505 µHz). The resulting shifts are on the order of a few hundredths of a c/d (corresponding to a few tenths of a µHz). Second, I fit individual p-modes in the segmented power spectra and track their frequencies over time. Preliminary results from the individual-mode analysis show shifts of a similar magnitude, although further refinement and improved p-mode identification are required.
I plan to perform p-mode identification using open-source asteroseismology software as well. Results should also be compared with independent stellar activity indicators. The analysis will then be extended to two additional F-type stars with different rotation periods. This will allow me to investigate the relationship between rotation period and activity cycle. Further work may also involve stellar evolution models to gain further insights into the internal properties of these stars.
Summary
I have two ongoing but separate research projects on stellar activity, and I’ve written an abstract for each (see my second abstract in the Comments). I can talk about either one or both.