Abstract
Asteroseismic methods offer a means to investigate stellar activity and activity cycles as well as to identify those properties of stars which are crucial for the operation of stellar dynamos. With data from CoRoT and \textit{Kepler}, signatures of magnetic activity have been found in the seismic properties of a few dozen stars. Now, NASA's Transiting Exoplanet Survey Satellite (TESS) mission offers the possibility to expand this, so far, rather exclusive group of stars. This promises to deliver new insight into the parameters that govern stellar magnetic activity as a function of stellar mass, age, and rotation rate. We derive a new scaling relation for the amplitude of the activity-related acoustic (p-mode) frequency shifts that can be expected over a full stellar cycle. Building on a catalogue of synthetic TESS time series, we use the shifts obtained from this relation and simulate the yield of detectable frequency shifts in an extended TESS mission. We find that, according to our scaling relation, we can expect to find significant p-mode frequency shifts for a couple hundred main-sequence and early subgiant stars and for a few thousand late subgiant and low-luminosity red giant stars.
Highlights
The primary seismic signature of stellar activity and activity cycles is a systematic change in mode frequencies over timescales associated with activity cycles, which are typically of the order of months to decades (Baliunas et al, 1995; Saar and Brandenburg, 1999; Vida et al, 2014)
To simulate the yield of seismic signatures of activity that can be expected from Transiting Exoplanet Survey Satellite (TESS), we use the synthetic catalog of Ball et al (2018), which consists of light curves that realistically mimic the properties of the TESS targets in short-cadence data (120 s
We note that the sensitivity of modes we find with Equation (11) is very similar to that found by Metcalfe et al (2007) and quoted by Karoff et al (2009) in their Equation (14)
Summary
The primary seismic signature of stellar activity and activity cycles is a systematic change in mode frequencies over timescales associated with activity cycles, which are typically of the order of months to decades (Baliunas et al, 1995; Saar and Brandenburg, 1999; Vida et al, 2014) Measuring this phenomenon for stars is primarily limited by the baseline length of the observations. For the Sun, we have Sun-as-a-star helioseismic observations lasting for decades, covering several 11-year solar activity cycles From these data it is found that the frequency of low-degree modes close to the frequency of maximum oscillation power νmax change by approximately 0.4 μHz between activity minimum and maximum (e.g., Jiménez-Reyes et al, 1998; Broomhall, 2017). This paper is aimed at a prediction of how many detections of activity-related frequency shifts we can expect in an extended TESS mission
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