Institut für Astronomie und Astrophysik Abteilung Astronomie Sand 1, D-72076 Tübingen, Germany
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Preprint 04/03

The near-synchronous polar V1432 Aql (RX J1940.1-1025): Accretion geometry and synchronization time scale

R. Staubert (1), S. Friedrich (2,3), K. Pottschmidt (3,4), S. Benlloch (1), S.L. Schuh (1), P. Kroll (5), E. Splittgerber (5), R. Rothschild (6)

(1) Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(2) Institut für Theoretische Physik und Astrophysik, Universität Kiel, Leibnizstr. 15, D-24098 Kiel, Germany
(3) Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr., D-85748 Garching, Germany
(4) Integral Science Data Center, 16 Chemin d'Ecogia, CH-1290 Sauverny, Switzerland
(5) Sternwarte Sonneberg, Sternwartestr. 32, D-96515 Sonneberg, Germany
(6) Center for Astrophysics and Space Science (CASS), Univ. California, San Diego, California, USA

A&A 407, 987 (2003)

Abstract. The magnetic Cataclysmic Variable (mCV) V1432 Aql (RXJ1940.1-1025) belongs to the four-member subclass of near-synchronous polars with a slight non-synchronism (<2%) between the spin period of the white dwarf and the binary period. In these systems the accretion geometry changes periodically with phase of the beat cycle. We present the application of a dipole accretion model for near-synchronous systems developed by Geckeler & Staubert (1997a) to extended optical and X-ray data. We detect a significant secular change of the white dwarf spin period in V1432 Aql of dP_spin/dt = -5.4 (+3.7/-3.2) 10^-9s/s from the optical data set alone. This corresponds to a synchronization time scale tau_sync = 199 (+441/-75) yr, comparable to the time scale of 170 yr for V1500 Cyg. The synchronization time scale in V1432 Aql is in excellent agreement with the theoretical prediction from the dominating magnetic torque in near-synchronous systems. We also present period analyses of optical CCD photometry and RXTE X-ray data, which argue against the existence of a 4000s period and an interpretation of V1432 Aql as an intermediate polar. The dipole accretion model also allows to constrain the relevant parameters of the accretion geometry in this system: the optical data allow an estimate of the dimensionless parameter (R'_t0/R_wd)^1/2 sin(beta) = 3.6 (+2.7/-1.1), with a lower limit for the threading radius of R'_t0 < 10 R_wd (68% confidence).
 
Key words: cataclysmic variables - binaries: eclipsing - stars: individual: V1432 Aql; RX J1940.1-1025 - stars: magnetic fields - X-rays: stars

Preprint (1,18 Mb PDF file including figures)
Astrophysics (astro-ph): astro-ph/0306072

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