code: def tauc_from_mass (mass_g):
      
      m = mass_g / cgs.msun
      return np.piecewise (m,
                           [m < 1.3,
                            m < 0.82,
                            m < 0.65,
                            m < 0.1],
                           [lambda x: 61.7 - 44.7 * x,
                            25.,
                            lambda x: 86.9 - 94.3 * x,
                            70.,
                            np.nan]) * 86400.
docs: Estimate the convective turnover time from mass, using the method described
      in Cook+ (2014ApJ...785...10C).
  
      mass_g - UCD mass in grams.
  
      Returns: the convective turnover timescale in seconds.
  
      Masses larger than 1.3 Msun are out of range and yield NaN. If the mass is
      <0.1 Msun, the turnover time is fixed at 70 days.
  
      The Cook method was inspired by the description in McLean+
      (2012ApJ...746...23M). It is a hybrid of the method described in Reiners &
      Basri (2010ApJ...710..924R) and the data shown in Kiraga & Stepien
      (2007AcA....57..149K). However, this version imposes the 70-day cutoff in
      terms of mass, not spectral type, so that it is entirely defined in terms
      of a single quantity.
  
      There are discontinuities between the different break points! Any future
      use should tweak the coefficients to make everything smooth.