A comparative study of the long-term light variations of six young irregular variablesJ. Gürtler, C. Friedemann, H.-G. Reimann, E. Splittgerber and E. RudolphAstron. Astrophys. Suppl. Ser., 140 3 (1999) 293-307DOI: https://doi.org/10.1051/aas:1999423