Observation history Wolf–Rayet star

wr 136 wn6 star atmosphere shed during red supergiant phase has been shocked hot fast wr winds form visible bubble nebula

in 1867, using 40 cm foucault telescope @ paris observatory, astronomers charles wolf , georges rayet discovered 3 stars in constellation cygnus (hd 191765, hd 192103 , hd 192641, designated wr 134, wr 135, , wr 137 respectively) displayed broad emission bands on otherwise continuous spectrum. stars display absorption lines or bands in spectra, result of overlying elements absorbing light energy @ specific frequencies, these unusual objects.

the nature of emission bands in spectra of wolf–rayet star remained mystery several decades. edward c. pickering theorized lines caused unusual state of hydrogen, , found pickering series of lines followed pattern similar balmer series, when half-integral quantum numbers substituted. later shown lines resulted presence of helium; chemical element discovered in 1868. pickering noted similarities between wolf–rayet spectra , nebular spectra, , similarity led conclusion or wolf rayet stars central stars of planetary nebulae.

by 1929, width of emission bands being attributed doppler broadening, , hence gas surrounding these stars must moving velocities of 300–2400 km/s along line of sight. conclusion wolf–rayet star continually ejecting gas space, producing expanding envelope of nebulous gas. force ejecting gas @ high velocities observed radiation pressure. known many stars wolf rayet type spectra central stars of planetary nebulae, many not associated obvious planetary nebula or visible nebulousity @ all.

in addition helium, emission lines of carbon, oxygen , nitrogen identified in spectra of wolf–rayet stars. in 1938, international astronomical union classified spectra of wolf–rayet stars types wn , wc, depending on whether spectrum dominated lines of nitrogen or carbon-oxygen respectively.

in 1969, several cspne strong ovi emissions lines grouped under new ovi sequence , or ovi type. these subsequently referred [wo] stars. similar stars not associated planetary nebulae described shortly after , wo classification adopted population wr stars.

the understanding late, , not-so-late, wn stars hydrogen lines in spectra @ different stage of evolution hydrogen-free wr stars has led introduction of term wnh distinguish these stars other wn stars. referred wnl stars, although there late-type wn stars without hydrogen wr stars hydrogen wn5.