![]() Mass and LuminosityĪccurate knowledge of the luminosity of these stars is important for comparing masses derived from stellar evolutionary models with those derived from stellar atmosphere models, for determining initial mass functions, and for studying stellar evolution in the high luminosity/high mass region of the Hertzsprung-Russell Diagram. HDE 313846 and HD 152408, “the appearance of P Cygni profiles and strengthened emission components in both H and HeI lines seems to suggest they are in a transition phase between Of and Ofpe/WN9” (Nota et al. We actually see a continuous sequence between Of and pure absorption O, and intermediate types have been introduced: O(f) for stars with N III emission and no l4686 at all, and O((f)) for those with the nitrogen lines still bright, but with l4686 now dark” (Kaler 1989, p. 206). ![]() are much more significant and are known as Of. “O stars with emission may be called Oe, but those with bright lines of He II at l4686 and N III at l4634and l4640, such as ζ Puppis. The hottest O-type stars display high ionisation (N III, He II) features. This is the only main sequence spectral type in which ionised helium can be seen only O stars are sufficiently hot to produce the 24ev required to ionise helium. Their spectra exhibit rather weak hydrogen lines, atomic helium, and also ionised helium (HeII – helium atoms which have lost one electron). O is the earliest spectral type, radiating strongly at short wavelengths thus their light appears bluish to the human eye. However, such stars, which spend most of their short lives as H-burning O-type stars, play an important role in galactic structure and evolution. Only a small fraction of stars in the Galaxy are more massive than 20 solar masses. ![]() In the solar vicinity, dwarf (luminosity class V) O type stars dominate the massive star population, leading to the conclusion that this is the most prolonged evolutionary phase in the lifetime of massive stars (Nota et al. They are the bluest of the of the main sequence stars.Īlthough various individual properties, such as temperature, may be exceeded by more exotic objects such as white dwarf or Wolf-Rayet stars, type O stars are extreme by the standards of ‘normal’ stars, and they are by far the rarest members of the main sequence. O-type stars are massive, bright, hot stars. ![]() The characteristic properties of type O stars – including spectra, mass, and luminosity – are briefly described, followed by notes about a few well-known examples. Spectral Type O Stars Peripatus Home Page Astronomy and Astrophysics > Spectral Type O Stars ![]()
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