Spectral Standard Stars
The revised Yerkes Atlas system (Johnson & Morgan 1953) listed a dense grid of B-type dwarf spectral standard stars, however not all of these have survived to this day as standards. The "anchor points" of the MK spectral classification system among the B-type main sequence dwarf stars, i.e. those standard stars that have remain unchanged since at least the 1940's, are upsilon Orionis (B0 V), eta Aurigae (B3 V), eta Ursae Majoris (B3 V). Besides these anchor standards, the seminal review of MK classification by Morgan & Keenan (1973) listed "dagger standards" of Tau Scorpii (B0 V), Omega Scorpii (B1 V), 42 Orionis (B1 V), 22 Scorpii (B2 V), Rho Aurigae (B5 V), and 18 Tau (B8 V). The Revised MK Spectra Atlas of Morgan, Abt, & Tapscott (1978) further contributed the standards beta2 Sco (B2 V), 29 Persei (B3 V), HD 36936 (B5 V), and HD 21071 (B7 V). Gray & Garrison (1994) contributed two B9 V standards: omega For A and HR 2328. The only published B4 V standard is 90 Leonis, from Lesh (1968). There has been little agreement in the literature on choice of B6 V standard.
Read more about this topic: B-type Main Sequence Star
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