Issue |
A&A
Volume 670, February 2023
|
|
---|---|---|
Article Number | A176 | |
Number of page(s) | 9 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202245452 | |
Published online | 23 February 2023 |
High-precision broadband linear polarimetry of early-type binaries
III. AO Cassiopeiae revisited★
1
Department of Physics and Astronomy, University of Turku,
20014
Turku, Finland
e-mail: yasir.abdulqadir@utu.fi
2
Graduate School of Sciences, Tohoku University,
Aoba-ku,
980-8578
Sendai, Japan
Received:
12
November
2022
Accepted:
17
January
2023
Aims. The fact that the O-type close binary star system AO Cassiopeiae exhibits variable phase-locked linear polarization has been known since the mid-1970s. In this work, we re-observe the polarization arising from this system more than 50 yr later to better estimate the interstellar polarization and to independently derive the orbital parameters, such as inclination, i, orientation, Ω, and the direction of the rotation for the inner orbit from the phase-folded polarization curves of the Stokes q and u parameters.
Methods. The Dipol-2 polarimeter was used to obtain linear polarization measurements of AO Cassiopeiae in the B, V, and R passbands with the T60 remotely controlled telescope at an unprecedented accuracy level of ~0.003%. We have obtained the first proper quantification of the interstellar polarization in the direction heading towards AO Cas by observing the polarization of three neighboring field stars. We employed a Lomb-Scargle algorithm and detected a clear periodic signal for the orbital period of AO Cas. The standard analytical method based on a two-harmonics Fourier fit was used to obtain the inclination and orientation of the binary orbit.
Results. Our polarimetric data exhibited an unambiguous periodic signal at 1.76 days, thus confirming the orbital period of the binary system of 3.52 days. Most of the observed polarization is of interstellar origin. The de-biased values of the orbital inclination are i = 63° + 2°/−3° and orientation of Ω = 29º(209º) ± 8°. The direction of the binary system rotation on the plane of the sky is clockwise.
Key words: stars: individual: AO Cassiopeiae / polarization / techniques: polarimetric / binaries: close / instrumentation: polarimeters / binaries: eclipsing
The polarization data for AO Cas is only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/670/A176
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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