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Wolf-Rayet stars form a rare group of ~200 supergiants with spectacular emission line spectra. They have exceptional surface temperatures approaching, in some cases, 100,000K and 50 solar masses. Although very brilliant all are so remote that a telescope is needed to view them. With a high mass-loss through a turbulant atmosphere - they show very strong broad emission lines of ionised He and O in addition to nitrogen [WN type] and carbon [WC type] respectively. The Doppler broadening of the lines is only evident at higher resolution.
These lines rise as bright 'peaks' above the
star's background continuum or 'hump' in the intensity plots below. Some
of these stars are binaries and the relative intensity of the emission
lines is affected by the continuum contribution of the companion star.
A concentration of bright WR stars in Cygnus makes it the best site for
northern hemisphere observers.
2000 August 23 - a revisit to some of the Cygnus WR stars using the WPO spectrograph with a dispersion of 1.45A/pixel [x30 > Rainbow spectra below] and confined to the red part of the spectrum.
1999 June 15/16 - some 28 spectra [many duplicates] of 12 WR stars in Cygnus captured in 80 minutes ! It represents a revisit to the same stars captured last August '98 over several evenings via the Mk1a direct-vision prism spectroscope. Resolution is essentially the same with both instruments - the Rainbow grating gives a linear dispersion of ~40A/pixel and exposures are noticeably briefer by a factor of perhaps 2 or 3. In crowded starsfields, like Cygnus, other objects 'pop-up' like the variable BI Cyg [spectral type M4 Iab] near WR141 and included here .
