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Keywords:

  • techniques: spectroscopic;
  • stars: evolution;
  • stars: formation;
  • stars: fundamental parameters;
  • stars: pre-main-sequence;
  • open clusters and associations: general

ABSTRACT

We address the age rank of the nearest pre-main-sequence (PMS) associations, using low-resolution spectrophotometry to measure gravity-sensitive indices in these stars. We compare spectral index-colour sequences for the PMS populations and rank them according to the strength of their gravity-sensitive features. The age rank using the gravity method is in general agreement with the ranking of these groups suggested by colour–magnitude (CM) diagram placement. Several of the groups have a kinematic origin in the Oph-Sco-Cen OB association. For three of them, their age rank is also in agreement with epochs resulting from a formation scenario for the OB association.