IDENTIFICATION OF A POPULATION OF X-RAY-EMITTING MASSIVE STARS IN THE GALACTIC PLANE
- Sydney Institute for Astronomy, School of Physics A29, University of Sydney, NSW 2006 (Australia)
- Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)
- Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
- Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)
- Department of Physics, University of Wisconsin, Whitewater, WI 53190 (United States)
- National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States)
- MIT Kavli Institute for Astrophysics and Space Research and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
- Centre for Astrophysics Research, STRI, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom)
- Naval Research Laboratory, Washington, DC 20375 (United States)
- Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
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{sup +} (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 {approx}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.
- OSTI ID:
- 21567527
- Journal Information:
- Astrophysical Journal, Vol. 727, Issue 2; Other Information: DOI: 10.1088/0004-637X/727/2/105; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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