Identification of A Population of X-ray-emitting Massive Stars in the Galactic Plane
Author(s)Anderson, Gemma E.; Gaensler, B. M.; Kaplan, David L.; Posselt, Bettina; Slane, Patrick O.; Murray, Stephen S.; Mauerhan, Jon C.; Benjamin, Robert A.; Brogan, Crystal L.; Chakrabarty, Deepto; Drake, Jeremy J.; Drew, Janet E.; Grindlay, Jonathan E.; Hong, Jaesub; Lazio, T. Joseph W.; Lee, Julia C.; Steeghs, Danny T. H.; van Kerkwijk, Marten H.; ... Show more Show less
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We present X-ray, infrared, optical, and radio observations of four previously unidentified Galactic plane X-ray sources: AX J163252-4746, AX J184738-0156, AX J144701-5919, and AX J144547-5931. Detection of each source with the Chandra X-ray Observatory has provided sub-arcsecond localizations, which we use to identify bright infrared counterparts to all four objects. Infrared and optical spectroscopy of these counterparts demonstrate that all four X-ray sources are extremely massive stars, with spectral classifications: Ofpe/WN9 (AX J163252-4746), WN7 (AX J184738-0156 = WR121a), WN7-8h (AX J144701-5919), and OIf+ (AX J144547-5931). AX J163252-4746 and AX J184738-0156 are both luminous, hard, X-ray emitters with strong Fe XXV emission lines in their X-ray spectra at ~6.7 keV. The multi-wavelength properties of AX J163252-4746 and AX J184738-0156 are not consistent with isolated massive stars or accretion onto a compact companion; we conclude that their X-ray emission is most likely generated in a colliding-wind binary (CWB) system. For both AX J144701-5919 and AX J144547-5931, the X-ray emission is an order of magnitude less luminous and with a softer spectrum. These properties are consistent with a CWB interpretation for these two sources also, but other mechanisms for the generation of X-rays cannot be excluded. There are many other as yet unidentified X-ray sources in the Galactic plane, with X-ray properties similar to those seen for AX J163252-4746, AX J184738-0156, AX J144701-5919, and AX J144547-5931. This may indicate a substantial population of X-ray-emitting massive stars and CWBs in the Milky Way.
DepartmentKavli Institute for Astrophysics and Space Research; Massachusetts Institute of Technology. Department of Physics
Institute of Physics Publishing
Anderson, Gemma E. et al. “Identification of A Population of X-ray-emitting Massive Stars in the Galactic Plane.” The Astrophysical Journal 727.2 (2011): 105. Web.
Final published version