Columbia subject headings:
Stars--Classification--Congresses.
Harvard subject headings:
Keenan, Philip C. (Philip Childs), 1908-
Morgan, W. W. (William Wilson), 1906-
Stars--Classification--Congresses.
Princeton subject headings:
Keenan, Philip C. (Philip Childs), 1908-
Morgan, W. W. (William W.)
Stars--Classification--Congresses.
Stars--Spectra--Congresses.