About: http://webisa.webdatacommons.org/169819832

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	Because they should have essentially pure hydrogen or pure helium atmospheres, if heavier elements (in astronomy described as ???metals???, examples including calcium, magnesium and iron) are found then these must be external pollutants.
http://www.w3.org/ns/prov#wasQuotedFrom	gla.ac.uk