docs: def triple_fraction(self,query='mass_A > 0', unc=False):
          """
          Triple fraction of stars following given query
          """
          subdf = self.stars.query(query)
          ntriples = ((subdf['mass_B'] > 0) & (subdf['mass_C'] > 0)).sum()
          frac = ntriples/len(subdf)
          if unc:
              return frac, frac/np.sqrt(ntriples)
          else:
              return frac