  The spin evolution of main sequence stars has long been of interest for basic
stellar evolution, stellar aging, stellar activity, and consequent influence on
companion planets. Observations of older than solar late-type main-sequence
stars have been interpreted to imply that a change from a dipole-dominated
magnetic field to one with more prominent higher multipoles might be necessary
to account for the data. The spin-down models that lead to this inference are
essentially tuned to the sun. Here we take a different approach which considers
individual stars as fixed points rather than just the Sun. We use a
time-dependent theoretical model to solve for the spin evolution of low-mass
main-sequence stars that includes a Parker-type wind and a time-evolving
magnetic field coupled to the spin. Because the wind is exponentially sensitive
to the stellar mass over radius and the coronal base temperature, the use of
each observed star as a separate fixed point is more appropriate and, in turn,
produces a set of solution curves that produces a solution envelope rather than
a simple line. This envelope of solution curves, unlike a single line fit, is
consistent with the data and does not unambiguously require a modal transition
in the magnetic field to explain it.
