THE NATURE OF THE UV/OPTICAL EMISSION OF THE ULTRALUMINOUS X-RAY SOURCE IN HOLMBERG II

Journal Article · Thu May 10 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/750/2/110· OSTI ID:22034527

Lian, Tao; Hua, Feng ^[1]; Kaaret, Philip; Grise, Fabien ^[2]

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1. Department of Engineering Physics and Center for Astrophysics, Tsinghua University, Beijing 100084 (China)
2. Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242 (United States)

We report on UV and X-ray spectroscopy and broadband optical observations of the ultraluminous X-ray source in Holmberg II. Fitting various stellar spectral models to the combined, non-simultaneous data set, we find that normal metallicity stellar spectra are ruled out by the data, while low-metallicity, Z = 0.1 Z{sub Sun }, late O-star spectra provide marginally acceptable fits, if we allow for the fact that X-ray ionization from the compact object may reduce or eliminate UV absorption/emission lines from the stellar wind. By contrast, an irradiated disk model fits both UV and optical data with {chi}{sup 2}/dof = 175.9/178, and matches the nebular extinction with a reddening of E(B - V) = 0.05{sup +0.05}{sub -0.04}. These results suggest that the UV/optical flux of Holmberg II X-1 may be dominated by X-ray irradiated disk emission.

• OSTI ID: 22034527
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 750; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTRA
ACCRETION DISKS
ASTROPHYSICS
BLACK HOLES
COSMIC X-RAY SOURCES
EMISSION SPECTRA
GALAXIES
GAMMA ASTRONOMY
IONIZATION
PHOTON EMISSION
STARS
STELLAR WINDS
X RADIATION
X-RAY SPECTROSCOPY