The distance of WR 21a is not definitely known. There have been estimates from 2.85 kpc to around 8 kpc, with consequent uncertainties in the system luminosity. The larger distance is preferred because of consistency with the derived orbital parameters, but it is still uncertain whether the star is nearer or further than Westerlund 2.
Every 31 days and 16 hours days the two stars in this system revolve around each other. The inclination of the orbit means that we do not see eclipses and the visual brightness of the system is quite stable.
The colliding winds of the two stars produce extremely high temperatures and luminous x-ray emission. The system is also bright at radio wavelengths.
Location of WR 21a (circled) near RCW 49 Credit: ESO
^ abCutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.
^Hur, Hyeonoh; Park, Byeong-Gon; Sung, Hwankyung; Bessell, Michael S.; Lim, Beomdu; Chun, Moo-Young; Sohn, Sangmo Tony (2015). "Reddening, distance, and stellar content of the young open cluster Westerlund 2". Monthly Notices of the Royal Astronomical Society. 446 (4): 3797–3819. arXiv:1411.0879. Bibcode:2015MNRAS.446.3797H. doi:10.1093/mnras/stu2329.
This page is based on a Wikipedia article written by authors
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.