Phase-locked polarization by photospheric reflection in the semidetached eclipsing binary $mu^1$ Sco. (arXiv:2007.05249v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Cotton_D/0/1/0/all/0/1">Daniel V. Cotton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bailey_J/0/1/0/all/0/1">Jeremy Bailey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kedziora_Chudczer_L/0/1/0/all/0/1">Lucyna Kedziora-Chudczer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Horta_A/0/1/0/all/0/1">Ain De Horta</a>

We report the detection of phase-locked polarization in the bright
($m_V$=2.98-3.24) semidetached eclipsing binary $mu^1$ Sco (HD 151890). The
phenomenon was observed in multiple photometric bands using two different
HIPPI-class (HIgh Precision Polarimetric Instrument)polarimeters with
telescopes ranging in size from 35-cm to 3.9-m. The peak-to-trough amplitude of
the polarization is wavelength dependent and large, $sim$700 parts-per-million
in green light, and is easily seen with even the smallest telescope. We fit the
polarization phase curve with a SYNSPEC/VLIDORT polarized radiative transfer
model and a Wilson-Devinney geometric formalism, which we describe in detail.
Light from each star reflected by the photosphere of the other, together with a
much smaller contribution from tidal distortion and eclipse effects, wholly
accounts for the polarization amplitude. In the past polarization in
semidetached binaries has been attributed mostly to scattering from
extra-stellar gas. Our new interpretation facilitates determining masses of
such stars in non-eclipsing systems.

We report the detection of phase-locked polarization in the bright
($m_V$=2.98-3.24) semidetached eclipsing binary $mu^1$ Sco (HD 151890). The
phenomenon was observed in multiple photometric bands using two different
HIPPI-class (HIgh Precision Polarimetric Instrument)polarimeters with
telescopes ranging in size from 35-cm to 3.9-m. The peak-to-trough amplitude of
the polarization is wavelength dependent and large, $sim$700 parts-per-million
in green light, and is easily seen with even the smallest telescope. We fit the
polarization phase curve with a SYNSPEC/VLIDORT polarized radiative transfer
model and a Wilson-Devinney geometric formalism, which we describe in detail.
Light from each star reflected by the photosphere of the other, together with a
much smaller contribution from tidal distortion and eclipse effects, wholly
accounts for the polarization amplitude. In the past polarization in
semidetached binaries has been attributed mostly to scattering from
extra-stellar gas. Our new interpretation facilitates determining masses of
such stars in non-eclipsing systems.

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