To cite HeckmanEM in publications use:

V'ictor Hugo Lachos, Marcos Oliveira Prates, Dipak Kumar Dey (2021). “Heckman selection-t model: Parameter estimation via the EM-algorithm.” Journal of Multivariate Analysis, 184, 104737.

Corresponding BibTeX entry:

  @Article{,
    title = {Heckman selection-t model: Parameter estimation via the
      EM-algorithm},
    author = {{V{'i}ctor Hugo Lachos} and {Marcos Oliveira Prates} and
      {Dipak Kumar Dey}},
    journal = {Journal of Multivariate Analysis},
    volume = {184},
    pages = {104737},
    year = {2021},
  }