@prefix rdf: . @prefix xsd: . @prefix dcterms: . @prefix skos: . @prefix rdfs: . @prefix api: . @prefix foaf: . skos:broader . skos:broader . skos:broader . a rdfs:Resource , skos:Concept ; dcterms:contributor ; dcterms:modified "2020-11-03T19:46:55.553Z"^^xsd:dateTime ; skos:altLabel "Class O stars"@en , "O-type stars"@en ; skos:broader , ; skos:definition "A luminous, hot, blue star whose spectrum is dominated by the lines of hydrogen, atomic helium, and ionized helium; also known as O-type star. This is the earliest spectral type and the only main sequence star in which ionized helium is present. The effective temperatures of these stars range from about 30,000 K to 50,000 K, their luminosities from 50,000 to 1,000,000 times that of solar luminosity, and their masses from about 20 to 100 solar masses. The hottest O-type stars display high ionization emission features such as N III and He II, Of star. They are divided into subtypes O2, the hottest, to O9.7, the coldest. O-type stars are relatively rare, for each star of 100 solar masses there are 10^6 stars of solar mass. They are relatively short-lived since they spend only a few million years on the main sequence. The brightest O-type star in the sky visible with naked eye is Alnitak."@en ; skos:narrower , , , , , , , ; skos:prefLabel "O stars"@en ; skos:related . skos:related . skos:broader . skos:broader . skos:broader . skos:broader . skos:narrower . skos:narrower . skos:broader . a api:ItemEndpoint , api:Page ; api:definition ; api:extendedMetadataVersion ; foaf:primaryTopic .