Identification of a population of X-ray-emitting massive stars in the Galactic plane

Gemma E. Anderson, B. M. Gaensler, David L. Kaplan, Bettina Posselt, Patrick O. Slane, Stephen S. Murray, Jon C. Mauerhan, Robert A. Benjamin, Crystal L. Brogan, Deepto Chakrabarty, Jeremy J. Drake, Janet E. Drew, Jonathan E. Grindlay, Jaesub Hong, T. Joseph W. Lazio, Julia C. Lee, Danny T.H. Steeghs, Marten H. Van Kerkwijk

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Abstract

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.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume727
Issue number2
DOIs
StatePublished - Feb 1 2011

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massive stars
x rays
radio observation
observatories
emitters
observatory
infrared spectroscopy
spectroscopy
accretion
radio
wavelength

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Anderson, G. E., Gaensler, B. M., Kaplan, D. L., Posselt, B., Slane, P. O., Murray, S. S., ... Van Kerkwijk, M. H. (2011). Identification of a population of X-ray-emitting massive stars in the Galactic plane. Astrophysical Journal, 727(2). https://doi.org/10.1088/0004-637X/727/2/105
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. / Identification of a population of X-ray-emitting massive stars in the Galactic plane. In: Astrophysical Journal. 2011 ; Vol. 727, No. 2.
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abstract = "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.",
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Anderson, GE, Gaensler, BM, Kaplan, DL, Posselt, B, Slane, PO, Murray, SS, Mauerhan, JC, Benjamin, RA, Brogan, CL, Chakrabarty, D, Drake, JJ, Drew, JE, Grindlay, JE, Hong, J, Lazio, TJW, Lee, JC, Steeghs, DTH & Van Kerkwijk, MH 2011, 'Identification of a population of X-ray-emitting massive stars in the Galactic plane', Astrophysical Journal, vol. 727, no. 2. https://doi.org/10.1088/0004-637X/727/2/105

Identification of a population of X-ray-emitting massive stars in the Galactic plane. / 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.

In: Astrophysical Journal, Vol. 727, No. 2, 01.02.2011.

Research output: Contribution to journalArticle

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AU - Anderson, Gemma E.

AU - Gaensler, B. M.

AU - Kaplan, David L.

AU - Posselt, Bettina

AU - Slane, Patrick O.

AU - Murray, Stephen S.

AU - Mauerhan, Jon C.

AU - Benjamin, Robert A.

AU - Brogan, Crystal L.

AU - Chakrabarty, Deepto

AU - Drake, Jeremy J.

AU - Drew, Janet E.

AU - Grindlay, Jonathan E.

AU - Hong, Jaesub

AU - Lazio, T. Joseph W.

AU - Lee, Julia C.

AU - Steeghs, Danny T.H.

AU - Van Kerkwijk, Marten H.

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N2 - 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.

AB - 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.

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