...subdwarfs

Based on observations obtained with the Calar Alto 3.5 m and William Herschel telescopes.

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...O4''

There are isolated cases of subdwarf classifications based on MK spectral types. HD49798 was designated sdO6 by Stickland & Lloyd (1994) following Thackeray's (1970) description of the spectrum as O6. Such cases are sufficiently rare as to be unlikely to cause conflict.

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