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WR 124
WR 124 is a Wolf–Rayet star in the constellation of Sagitta surrounded by a ring nebula of expelled material known as M1-67. It is one of the fastest runaway stars in the galaxy with a radial velocity around 200 km/s. It was discovered by Paul W. Merrill in 1938, identified as a high velocity Wolf Rayet star. It is listed in the General Catalogue of Variable Stars as variable with a range of 0.08 magnitudes.
==Distance==
WR 124 has a Hipparcos parallax, but the quoted margin of error is much larger than the parallax itself, so it isn't really a useful measurement.
A recent study of WR 124 directly measured the expansion rate of the M1-67 nebula expelled from the star using WFPC2 camera images taken 11 years apart, and compared that rate to the expansion velocity measured by the Doppler shift of the nebular emission lines.〔 This yields a direct geometric measurement of the distance to WR 124, something that has only been done for one other WR star (Gamma Velorum), and which should be less subject to error than other methods of distance measurement.
The distance calculated from the nebular expansion rate is 3.35kpc, which is less than previous studies, and the resulting luminosity of 150,000 times the sun () is much lower than previously calculated. The luminosity is also lower than predicted by models for a star of this spectral class. Previous studies found distances of 5kpc〔 to 8.4kpc,〔 with corresponding luminosities of , as expected for a typical WN8h which is a very young star just moving away from the main sequence. This may be an uncommon post-red-supergiant WN star with some hydrogen still remaining. In this case WR 124 would be much older, around 8.6 million years, but the luminosity is still lower than predicted by theory.〔 WR stars of lower metallicity can form from lower mass progenitors and have lower luminosity, but this would be unusual for a Population I star within the Milky Way.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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