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Class S stars have excess amounts of zirconium and other elements produced by the s-process, and have more similar carbon and oxygen abundances to class M or carbon stars. Like carbon stars, nearly all known class S stars are asymptotic-giant-branch stars. The spectral type is formed by the letter S and a number between zero and ten.
The Henry Draper Catalogue (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension (HDE), published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the Henry Draper Extension Charts (HDEC), published from 1937 to 1949 in the form of charts ...
Stars numbered 1–225300 are from the original catalogue and are numbered in order of right ascension for the 1900.0 epoch. Stars in the range 225301–359083 are from the 1949 extension of the catalogue. The notation HDE can be used for stars in this extension, but they are usually denoted HD as the numbering ensures that there can be no ...
Only a tiny minority of known stars have proper names; all others have only designations from various catalogues or lists, or no identifier at all. Hipparchus in the 2nd century BC enumerated about 850 naked-eye stars. Johann Bayer in 1603 listed about twice this number. Only in the 19th century did star catalogues list the naked-eye stars ...
As a result, the core temperature of main sequence stars only varies from 4 million kelvin for a small M-class star to 40 million kelvin for a massive O-class star. [ 171 ] In the Sun, with a 16-million-kelvin core, hydrogen fuses to form helium in the proton–proton chain reaction : [ 210 ]
Young associations will contain 10–100 massive stars of spectral class O and B, and are known as OB associations. These are believed to form within the same small volume inside a giant molecular cloud. Once the surrounding dust and gas is blown away, the remaining stars become unbound and begin to drift apart. [7]
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System ← → ← → Star or (sub-) brown dwarf Distance ()Constellation Coordinates: RA, Dec (Ep J2000, Eq J2000)Stellar class Apparent magnitude (V) Parallax (Notes and additional references