Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7: System properties, accretion, and evolution. (arXiv:2208.07773v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ramachandran_V/0/1/0/all/0/1">V. Ramachandran</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oskinova_L/0/1/0/all/0/1">L. M. Oskinova</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hamann_W/0/1/0/all/0/1">W.-R. Hamann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sander_A/0/1/0/all/0/1">A. A. C. Sander</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Todt_H/0/1/0/all/0/1">H. Todt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pauli_D/0/1/0/all/0/1">D. Pauli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shenar_T/0/1/0/all/0/1">T. Shenar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Torrejon_J/0/1/0/all/0/1">J. M. Torrej&#xf3;n</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Postnov_K/0/1/0/all/0/1">K. A. Postnov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blondin_J/0/1/0/all/0/1">J. M. Blondin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bozzo_E/0/1/0/all/0/1">E. Bozzo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hainich_R/0/1/0/all/0/1">R. Hainich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Massa_D/0/1/0/all/0/1">D. Massa</a>

M33 X-7 is the only known eclipsing black hole high mass X-ray binary. The
system is reported to contain a very massive O supergiant donor and a massive
black hole in a short orbit. The high X-ray luminosity and its location in the
metal-poor galaxy M33 make it a unique laboratory for studying the winds of
metal-poor donor stars with black hole companions and it helps us to understand
the potential progenitors of black hole mergers. Using phase-resolved
simultaneous HST- and XMM-Newton-observations, we traced the interaction of the
stellar wind with the black hole. Our comprehensive spectroscopic investigation
of the donor star (X-ray+UV+optical) yields new stellar and wind parameters for
the system that differs significantly from previous estimates. In particular,
the masses of the components are considerably reduced to 38 for the O-star
donor and 11.4 for the black hole. The O giant is overfilling its Roche lobe
and shows surface He enrichment. The donor shows a densely clumped wind with a
mass-loss rate that matches theoretical predictions. We investigated the
wind-driving contributions from different ions and the changes in the
ionization structure due to X-ray illumination. Toward the black hole, the wind
is strongly quenched due to strong X-ray illumination. For this system, the
standard wind-fed accretion scenario alone cannot explain the observed X-ray
luminosity, pointing toward an additional mass overflow, which is in line with
our acceleration calculations. The X-ray photoionization creates an He II
emission region emitting $10^{47}$ ph/s. We computed binary evolutionary tracks
for the system using MESA. Currently, the system is transitioning toward an
unstable mass transfer phase, resulting in a common envelope of the black hole
and donor. Since the mass ratio is q~3.3 and the period is short, the system is
unlikely to survive the common envelope, but will rather merge.

M33 X-7 is the only known eclipsing black hole high mass X-ray binary. The
system is reported to contain a very massive O supergiant donor and a massive
black hole in a short orbit. The high X-ray luminosity and its location in the
metal-poor galaxy M33 make it a unique laboratory for studying the winds of
metal-poor donor stars with black hole companions and it helps us to understand
the potential progenitors of black hole mergers. Using phase-resolved
simultaneous HST- and XMM-Newton-observations, we traced the interaction of the
stellar wind with the black hole. Our comprehensive spectroscopic investigation
of the donor star (X-ray+UV+optical) yields new stellar and wind parameters for
the system that differs significantly from previous estimates. In particular,
the masses of the components are considerably reduced to 38 for the O-star
donor and 11.4 for the black hole. The O giant is overfilling its Roche lobe
and shows surface He enrichment. The donor shows a densely clumped wind with a
mass-loss rate that matches theoretical predictions. We investigated the
wind-driving contributions from different ions and the changes in the
ionization structure due to X-ray illumination. Toward the black hole, the wind
is strongly quenched due to strong X-ray illumination. For this system, the
standard wind-fed accretion scenario alone cannot explain the observed X-ray
luminosity, pointing toward an additional mass overflow, which is in line with
our acceleration calculations. The X-ray photoionization creates an He II
emission region emitting $10^{47}$ ph/s. We computed binary evolutionary tracks
for the system using MESA. Currently, the system is transitioning toward an
unstable mass transfer phase, resulting in a common envelope of the black hole
and donor. Since the mass ratio is q~3.3 and the period is short, the system is
unlikely to survive the common envelope, but will rather merge.

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