Stars earlier than about F5 (
~ 8000 K) donŐt have
convective envelopes and donŐt have any X-ray emissionÉ
Except that O and early B stars
have X-ray emission
they are strong sources of soft X-rays.
And they have
Wind broadened and blueshifted UV
absorption lines of an O and a B star.
HST image of
Car; an extreme
example of a hot star wind.