In the Shanti Parva of Mahabharat SECTION CCCXXXVII the following verse is mentioned:
King Uparichara, otherwise called Vasu, became a disciple of Vrihaspati and soon became the foremost of his disciples. Admitted as such, he began to study at the feet of his preceptor that science which was composed by the seven Rishis who were (otherwise) known by the name of Chitrasikhandins.
My question is who were these rishis?