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Keck/MOSFIRE spectroscopy of five ULX counterparts

Heida, M; Jonker, P.G.; Torres, M.A.P.; Roberts, T.P.; Walton, D.J.; Moon, D.-S.; Stern, D.; Harrison, F.A.

Keck/MOSFIRE spectroscopy of five ULX counterparts Thumbnail


M Heida

P.G. Jonker

M.A.P. Torres

D.J. Walton

D.-S. Moon

D. Stern

F.A. Harrison


We present H-band spectra of the candidate counterparts of five ultraluminous X-ray sources (ULXs; two in NGC 925, two in NGC 4136 and Holmberg II X-1) obtained with Keck/MOSFIRE (Multi-Object Spectrometer for Infra-Red Exploration). The candidate counterparts of two ULXs (J022721+333500 in NGC 925 and J120922+295559 in NGC 4136) have spectra consistent with (M-type) red supergiants (RSGs). We obtained two epochs of spectroscopy of the candidate counterpart to J022721+333500, separated by 10 months, but discovered no radial velocity variations with a 2σ upper limit of 40 km s−1. If the RSG is the donor star of the ULX, the most likely options are that either the system is seen at low inclination (<40°) or the black hole mass is less than 100 M⊙, unless the orbital period is longer than 6 years, in which case the obtained limit is not constraining. The spectrum of the counterpart to J120922+295559 shows emission lines on top of its stellar spectrum, and the remaining three counterparts do not show absorption lines that can be associated with the atmosphere of a star; their spectra are instead dominated by emission lines. Those counterparts with RSG spectra may be used in the future to search for radial velocity variations, and, if those are present, determine dynamical constraints on the mass of the accretor.


Heida, M., Jonker, P., Torres, M., Roberts, T., Walton, D., Moon, D., …Harrison, F. (2016). Keck/MOSFIRE spectroscopy of five ULX counterparts. Monthly Notices of the Royal Astronomical Society, 459(1), 771-778.

Journal Article Type Article
Acceptance Date Mar 22, 2016
Online Publication Date Mar 28, 2016
Publication Date Jun 11, 2016
Deposit Date May 31, 2016
Publicly Available Date Jun 2, 2016
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 459
Issue 1
Pages 771-778
Related Public URLs


Published Journal Article (1.9 Mb)

Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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