The Disk Veiling Effect of the Black Hole Low-Mass X-ray Binary A0620-00

Kavli Affiliate: Luis C. Ho

| First 5 Authors: Wan-Min Zheng, Qiaoya Wu, Jianfeng Wu, Song Wang, Mouyuan Sun

| Summary:

The optical light curves of quiescent black hole low-mass X-ray binaries
often exhibit significant non-ellipsoidal variabilities, showing the
photospheric radiation of the companion star is veiled by other source of
optical emission. Assessing this "veiling" effect is critical to the black hole
mass measurement. Here in this work, we carry out a strictly simultaneous
spectroscopic and photometric campaign on the prototype of black hole low-mass
X-ray binary A0620-00. We find that for each observation epoch, the extra
optical flux beyond a pure ellipsoidal modulation is positively correlated with
the fraction of veiling emission, indicating the accretion disk contributes
most of the non-ellipsoidal variations. Meanwhile, we also obtain a K2V
spectral classification of the companion, as well as the measurements of the
companion’s rotational velocity $v sin i = 83.8pm1.9$ km s$^{-1}$ and the
mass ratio between the companion and the black hole $q=0.063pm0.004$.

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