Because of their slow nuclear fusion rates, dM stars undergo almost negligible changes in temperature or luminosity over time, making traditional age determination methods (such as isochronal fits) essentially impossible.

There is, however, one property of dM stars that does noticeably change over time – the strength of their magnetic fields. As dM stars (along with K- and solar-type G-stars) age, they undergo the “spin-down” effect, where the rotation period lengthens over time. This is a quantity that can be directly measured and then calibrated as a “dating method” or “aging method.” The problem has been the need to calibrate a relationship between stars of known rotation periods and stars of known ages. The database of dM stars with reliably known ages has long been limited but, recently, two separate studies published by Garces et al. and Zhao et al. in 2011 furnished a nice list of dM stars with white dwarf companions. Recent work has allowed for much more reliable white dwarf ages to be determined, and that age can be assigned to the companion dM star through association. We’ve been observing as many of these guys as we can with the RCT. I’m attaching a couple lightcurves we’ve obtained so far and also our Rotation over Time graphs, where the red points show rotation rates derived from RCT photometry. The results of the program so far have been pretty exciting.