Artpop had first-week sales of about 258,000 copies in 1999.
WR 148 is a spectroscopic binary in the constellation Cygnus consisting of a Wolf-Rayet star and an unknown massive companion .. Cygnus. Cygnus ( constellation ). spectroscopic binary. spectroscopic binary. constellation. constellation. Wolf-Rayet star. Wolf-Rayet star. The secondary may be a black hole , or an early B subgiant that is not visible for some reason .. black hole. black hole. It is one of the most luminous stars known .. most luminous stars. most luminous stars. WR 148 shows a classic WN8h spectrum , but with the addition of weak central absorption on some of the emission lines .. NIII and NIV emission lines lines are stronger than NV , and HeI lines are stronger than HeII , The Balmer series hydrogen lines and some other lines have P Cygni profiles .. Balmer series. Balmer series. WR 148 is erratically variable on timescales ranging from seconds to years , but it shows consistent brightness and radial velocity variations with a period of 4.32 days .. radial velocity. radial velocity. There is little doubt that it is a binary system , due to the regular variations and the presence of hard x-ray radiation from colliding winds , but the secondary has never been observed .. The absorption cores might be due to a faint B class companion , but the radial velocity changes of the absorption components are smaller than those of the emission lines , making this unlikely .. radial velocity. radial velocity. Alternatives include a very massive companion that would almost certainly have to be a black hole to remain invisible , or an unacceptably small mass for the primary star .. black hole. black hole. The absorption nay also arise in circumstellar material .. Because of its erratic changes in apparent magnitude at so many frequencies WR 148 is classified in the General Catalogue of Variable Stars as a unique type of variable , not a member of any of the defined classes .. apparent magnitude. apparent magnitude. General Catalogue of Variable Stars. General Catalogue of Variable Stars. The shape of the light curve is unusual and has been modelled as being produced by an extended secondary object which may be an ionised cavity in the dense wind of the primary star , produced as the secondary orbits at a distance comparable to the radius of the primary star .. WR 148 is found unusually far from the galactic plane for a Wolf-Rayet star , at 500 - 800 pc .. Wolf-Rayet star. Wolf-Rayet star. galactic plane. galactic plane. parsec. Young massive stars such as WN8h WR stars are members of the thin disc population , on average only 60 pc from the galactic plane .. galactic plane. galactic plane. parsec. It is suggested that WR 148 is a runaway from a supernova explosion .. supernova. supernova