sts which
  allows the user to store the results of back-projecting or nowcasting
  surveillance time seriesA class inheriting from class sts, but with additional slots
  to store the result and associated confidence intervals from back
  projection of a sts object.
The slots are as for "sts". However, two
  additional slots exists.
ci:An array containing the upper and lower limit of the confidence interval.
lambda:Back projection component
The methods are the same as for "sts".
signature(from = "sts", to = "stsBP"):
      convert an object of class sts to class stsBP.
M. Höhle