The Rate of Star Formation. II. The Rate of Formation of Stars of Different Mass.

The rate of formation of stars of different mass as a function of time is investigated. Considerations involving the present observed main-sequence luminosity function suggest that the average past formation rate of stars of around 1 solar mass has been, at most, three times their present rate of formation. The past formation history of bright stars is investigated through its effect on the distribution of ultraviolet excesses among late G-type dwarfs The observed distribution does not admit a time-independent birth luminosity function; it shows that in the past relatively more bright stars were formed. The average past formation rate of bright stars may have been some twenty times larger than their present formation rate. A brief explanation of the methods used is given in Section I.