High-precision broad-band linear polarimetry of early-type binaries. II. Variable, phase-locked polarization in triple Algol-type system λ Tauri
Berdyugin A., Piirola V., Sakanoi T., Kagitani M., Yoneda M.
https://urn.fi/URN:NBN:fi-fe2021042820801
Tiivistelmä
Aim. To study the binary geometry of the classic Algol-type triple
system λ Tau, we have searched for polarization variations over
the orbital cycle of the inner semi-detached binary, arising from light
scattering in the circumstellar material formed from ongoing mass
transfer. Phase-locked polarization curves provide an independent
estimate for the inclination i, orientation Ω, and the direction
of the rotation for the inner orbit.
Methods: Linear polarization
measurements of λ Tau in the B, V , and R passbands with the
high-precision Dipol-2 polarimeter have been carried out. The data have
been obtained on the 60 cm KVA (Observatory Roque de los Muchachos, La
Palma, Spain) and Tohoku 60 cm (Haleakala, Hawaii, USA) remotely
controlled telescopes over 69 observing nights. Analytic and numerical
modelling codes are used to interpret the data.
Results: Optical
polarimetry revealed small intrinsic polarization in λ Tau with
0.05% peak-to-peak variation over the orbital period of 3.95 d. The
variability pattern is typical for binary systems showing strong second
harmonic of the orbital period. We apply a standard analytical method
and our own light scattering models to derive parameters of the inner
binary orbit from the fit to the observed variability of the normalized
Stokes parameters. From the analytical method, the average for three
passband values of orbit inclination i = 76° +
1°/-2° and orientation Ω =
15°(195°) ± 2° are
obtained. Scattering models give similar inclination values i =
72-76° and orbit orientation ranging from Ω =
16°(196°) to Ω =
19°(199°), depending on the geometry of
the scattering cloud. The rotation of the inner system, as seen on the
plane of the sky, is clockwise. We have found that with the scattering
model the best fit is obtained for the scattering cloud located between
the primary and the secondary, near the inner Lagrangian point or along
the Roche lobe surface of the secondary facing the primary. The
inclination i, inferred from polarimetry, agrees with the previously
made conclusion on the semi-detached nature of the inner binary, whose
secondary component is filling its Roche lobe. The non-periodic scatter,
which is also present in the polarization data, can be interpreted as
being due to sporadic changes in the mass transfer rate.
The polarization data for λ Tauri are only available at the CDS
via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A69
Kokoelmat
- Rinnakkaistallenteet [19207]