Several luminous stars in the dark cloud (Li 630) containing M78 (NOC 2068) are found to have ages as young as a few times i0 years. The properties of the stellar population apparently associated with this dark cloud are investigated; it appears that star formation has taken place over a period of several million years. A significant number of heavily obscured (A > 10 mag) stars has been found in the course of a 2- survey of selected regions in the Li 630 cloud complex. These objects appear best interpreted as stars of late B and early A spectral type embedded within the dense cloud material. The ratio of total to selective extinction achieves values as high as 5.8 in Li 630; furthermore, the ratio of A4430 band strength to visible extinction is anomalously low in this dense cloud complex. Sabject headings: infrared sources interstellar extinction - nebulae, individual - pre-main-sequence stars - star formation
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Strom et al. (1975) studied this question.