2020A&A...643A.170K


Query : 2020A&A...643A.170K

2020A&A...643A.170K - Astronomy and Astrophysics, volume 643A, 170-170 (2020/11-1)

Orbital variability of the optical linear polarization of the γ-ray binary LS I +61° 303 and new constraints on the orbital parameters.

KRAVTSOV V., BERDYUGIN A.V., PIIROLA V., KOSENKOV I.A., TSYGANKOV S.S., CHERNYAKOVA M., MALYSHEV D., SAKANOI T., KAGITANI M., BERDYUGINA S.V. and POUTANEN J.

Abstract (from CDS):

We studied the variability of the linear polarization and brightness of the γ-ray binary LS I +61° 303. High-precision BVR photopolarimetric observations were carried out with the Dipol-2 polarimeter on the 2.2m remotely controlled UH88 telescope at Mauna Kea Observatory and the 60 cm Tohoku telescope at Haleakala bservatory (Hawaii) over 140 nights in 2016-2019. We also determined the degree and angle of the interstellar polarization toward LS I +61° 303 using two out of four nearby field stars that have Gaia's parallaxes. After subtracting the interstellar polarization, we determined the position angle of the intrinsic polarization θ≃11°, which can either be associated with the projection of the Be star's decretion disk axis on the plane of sky, or can differ from it by 90°. Using the Lomb-Scargle method, we performed timing analyses and period searches of our polarimetric and photometric data. We found statistically significant periodic variability of the normalized Stokes parameters q and u in all passbands. The most significant period of variability, PPol=13.244±0.012d, is equal to one half of the orbital period Porb=26.496d. The fits of the polarization variability curves with Fourier series show a dominant contribution from the second harmonic which is typical for binary systems with circular orbits and nearly symmetric distribution of light scattering material with respect to the orbital plane. The continuous change of polarization with the orbital phase implies co-planarity of the orbit of the compact object and the Be star's decretion disk. Using a model of Thomson scattering by a cloud that orbits the Be star, we obtained constraints on the orbital parameters, including a small eccentricity e<0.2 and periastron phase of php≃0.6, which coincides with the peaks in the radio, X-ray, and TeV emission. These constraints are independent of the assumption about the orientation of the decretion disk plane on the sky. We also extensively discuss the apparent inconsistency with the previous measurements of the orbital parameters from radial velocities. By folding the photometry data acquired during a three-year time span with the orbital period, we found a linear phase shift of the moments of the brightness maximum, confirming the possible existence of superorbital variability.

Abstract Copyright: © ESO 2020

Journal keyword(s): binaries: general - gamma rays: stars - polarization - stars: emission-line, Be - stars: individual: LS I +61 303

CDS comments: Fig.1 Field stars not in SIMBAD.

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NAME Heart Nebula HII 02 32.7 +61 27           ~ 293 1
2 IC 1805 OpC 02 32 42 +61 27.0   7.03 6.5     ~ 487 2
3 LS I +61 303 HXB 02 40 31.6641883136 +61 13 45.591138110 11.27 11.61 10.75 10.19 9.55 B0Ve 784 2
4 HD 25443 * 04 06 08.0670623506 +62 06 06.620149609 6.45 6.998 6.766     B0.5III 121 0
5 V* V479 Sct HXB 18 26 15.0561532140 -14 50 54.249464136 12.02 12.23 11.27 11.04   ON6V((f))z 514 2
6 HD 187399 SB* 19 48 41.8756793202 +29 24 08.403071025 6.92 7.38 7.12 6.82 6.66 B7Ia?e 102 0
7 HD 204827 SB* 21 28 57.7601719555 +58 44 23.223287944 8.63 8.74 7.94 7.25 6.76 O9.5IV 317 0
8 HD 218393 Be* 23 07 06.2120465053 +50 11 32.489137162 6.79 7.25 6.92     B3pe+K1III 149 0

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2021.09.22-13:08:05

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