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Constraints on the Compact Object Mass in the Eclipsing High-mass X-Ray Binary XMMU J013236.7+303228 in M 33

Bhalerao, Varun B. and van Kerkwijk, Marten H. and Harrison, Fiona A. (2012) Constraints on the Compact Object Mass in the Eclipsing High-mass X-Ray Binary XMMU J013236.7+303228 in M 33. Astrophysical Journal, 757 (1). Art. No. 10. ISSN 0004-637X. doi:10.1088/0004-637X/757/1/10.

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We present optical spectroscopic measurements of the eclipsing high-mass X-ray binary (HMXB) XMMU J013236.7+303228 in M 33. Based on spectra taken at multiple epochs of the 1.73 day binary orbital period we determine physical as well as orbital parameters for the donor star. We find the donor to be a B1.5IV subgiant with effective temperature T = 22, 000-23, 000 K. From the luminosity, temperature, and known distance to M 33 we derive a radius of R = 8.9 ± 0.5 R_☉. From the radial-velocity measurements, we determine a velocity semi-amplitude of K_opt = 63 ± 12 km s^(–1). Using the physical properties of the B star determined from the optical spectrum, we estimate the star's mass to be M_opt = 11 ± 1 M_☉. Based on the X-ray spectrum, the compact companion is likely a neutron star, although no pulsations have yet been detected. Using the spectroscopically derived B star mass we find the neutron star companion mass to be M_X = 2.0 ± 0.4 M_☉, consistent with the neutron star mass in the HMXB Vela X-1, but heavier than the canonical value of 1.4 M_☉ found for many millisecond pulsars. We attempt to use as an additional constraint that the B star radius inferred from temperature, flux, and distance should equate to the Roche radius, since the system accretes by Roche lobe overflow. This leads to substantially larger masses, but by trying to apply the technique to known systems, we find that the masses are consistently overestimated. Attempting to account for that in our uncertainties, we derive M_X = 2.2^(+0.8)_(–0.6) M_☉ and M opt = 13 ± 4 M_☉. We conclude that precise constraints require detailed modeling of the shape of the Roche surface.

Item Type:Article
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Bhalerao, Varun B.0000-0002-6112-7609
Harrison, Fiona A.0000-0003-2992-8024
Additional Information:© 2012 American Astronomical Society. Received 2012 May 8; accepted 2012 June 28; published 2012 August 29. We thank Brian Grefenstette for helping us to interpret the XMM data. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency.
Group:Space Radiation Laboratory
Subject Keywords:binaries: eclipsing; stars: individual: XMMU J013236.7+303228; X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20121107-110334183
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Official Citation:Constraints on the Compact Object Mass in the Eclipsing High-mass X-Ray Binary XMMU J013236.7+303228 in M 33 Varun B. Bhalerao et al. 2012 ApJ 757 10
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35332
Deposited By: Jason Perez
Deposited On:07 Nov 2012 19:31
Last Modified:09 Nov 2021 23:14

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