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Identification of a Population of X-ray-emitting Massive Stars in the Galactic Plane

Anderson, Gemma E. and Gaensler, B. M. and Kaplan, David L. and Posselt, Bettina and Slane, Patrick O. and Murray, Stephen S. and Mauerhan, Jon C. and Benjamin, Robert A. and Brogan, Crystal L. and Chakrabarty, Deepto and Drake, Jeremy J. and Drew, Janet E. and Grindlay, Jonathan E. and Hong, Jaesub and Lazio, T. Joseph W. and Lee, Julia C. and Steeghs, Danny T. H. and van Kerkwijk, Marten H. (2011) Identification of a Population of X-ray-emitting Massive Stars in the Galactic Plane. Astrophysical Journal, 727 (2). Art. No. 105. ISSN 0004-637X.

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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 ofX-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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Gaensler, B. M.0000-0002-3382-9558
Kaplan, David L.0000-0001-6295-2881
Brogan, Crystal L.0000-0002-6558-7653
Chakrabarty, Deepto0000-0001-8804-8946
Grindlay, Jonathan E.0000-0002-1323-5314
Lazio, T. Joseph W.0000-0002-3873-5497
Additional Information:© 2011 American Astronomical Society. Received 2010 August 31; accepted 2010 November 11; published 2011 January 11. Special thanks goes to Michael Muno for his encouragement, expertise, and participation in this project. We also thank Sean Farrell, Stan Owocki, and Nathan Smith for their advice and help with this research and the referee for his or her constructive response and suggestions. G.E.A acknowledges the support of an Australian Postgraduate Award. B.M.G. acknowledges the support of a Federation Fellowship from the Australian Research Council through grant FF0561298. D.L.K. was supported by NASA through Hubble Fellowship grant 51230.01-A awarded by the STScI, which is operated by AURA, for NASA, under contract NAS 5-26555. P.O.S. acknowledges partial support from NASA Contract NAS8- 03060. D.T.H.S. acknowledges an STFC Advanced Fellowship. J.J.D was supported by NASA contract NAS8-39073 to the Chandra X-ray Center (CXC). Basic research in radio astronomy at the NRL is supported by 6.1 Base funding. Support for this work was also provided by NASA through Chandra Award Number GO9-0155X issued by the CXC, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA. This research makes use of data obtained with the Chandra X-ray Observatory, and software provided by the CXC in the application packages CIAO and Sherpa. OSIRIS is a collaborative project between Ohio State University and CTIO. Observing time on the 6.5m Clay and Baade Magellan Telescopes, located at Las Campanas Observatory, was allocated through the Harvard-Smithsonian Center for Astrophysics. The ATCA, part of the Australia Telescope, is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. This publication makes use of data products from the second catalogue of serendipitous X-ray sources (2XMMi) from the European Space Agency’s (ESA) XMM-Newton observatory. These data were accessed through the Leicester Database and Archive Service at Leicester University, UK. 2MASS is a joint project of the University of Massachusetts and the IPAC/Caltech, funded by the NASA and NFS. GLIMPSE survey data are part of the Spitzer Legacy Program. The Spitzer Space Telescope is operated by the JPL/ Caltech under a contract with NASA. This research has made use of NASA’s Astrophysics Data System.
Funding AgencyGrant Number
Australian Postgraduate AwardUNSPECIFIED
Australian Research CouncilFF0561298
NASA Hubble Fellowship51230.01-A
NASANAS 5-26555
Subject Keywords:stars: winds, outflows; stars: Wolf-Rayet; supergiants; X-rays: binaries; X-rays: individual (AX J163252-4746, AX J184738-0156, AX J144701-5919, AX J144547-5931); X-rays: stars
Issue or Number:2
Classification Code:PACS: 98.35.Ln; 97.30.Eh; 97.80.Jp; 97.20.Pm; 97.60.Jd
Record Number:CaltechAUTHORS:20110307-093952112
Persistent URL:
Official Citation:Gemma E. Anderson et al. 2011 ApJ 727 105 doi: 10.1088/0004-637X/727/2/105
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22682
Deposited By: Ruth Sustaita
Deposited On:08 Mar 2011 21:22
Last Modified:22 Nov 2019 19:28

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