Physical properties of the interstellar medium using high-resolution Chandra spectra: O K-edge absorption

E. Gatuzz (1), J. García (2), C. Mendoza (1,3), T. R. Kallman (4), M. A. Bautista (3), T. W. Gorczyca (3)

(1) Centro de Física, Instituto Venezolano de Investigaciones Científicas (IVIC), PO Box 20632, Caracas 1020A, Venezuela, (2) Harvard-Smithsonian Center for Astrophysics, MS-6, 60 Garden Street, Cambridge, MA 02138, USA, (3) Department of Physics, Western Michigan University, Kalamazoo, MI 49008, USA, (4) NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.

Chandra high-resolution spectra toward eight low-mass Galactic binaries have been analyzed with a photoionization model that is capable of determining the physical state of the interstellar medium. Particular attention is given to the accuracy of the atomic data. Hydrogen column densities are derived with a broadband fit that takes into account pileup effects, and in general are in good agreement with previous results. The dominant features in the oxygen-edge region are O I and O II absorption lines whose simultaneous fits lead to average values of the ionization parameter of log  = 2.90 and oxygen abundance of AO = 0.70. The latter is relative to the standard by Grevesse & Sauval (1998), but a rescaling with the revision by Asplund et al. (2009) would lead to an average abundance value fairly close to solar. The low average oxygen column density (NO = 9.2 × 10^{17}cm^{-2}) suggests a correlation with the low ionization parameters, the latter also being in evidence in the column density ratios O II/O I and O III/O I that are estimated to be less than 0.1. We do not find conclusive evidence for absorption by any other compound but atomic oxygen.

See complete preprint –> http://arxiv.org/abs/1403.2115

 

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