Issue |
A&A
Volume 686, June 2024
|
|
---|---|---|
Article Number | A304 | |
Number of page(s) | 12 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/202244473 | |
Published online | 21 June 2024 |
High-resolution spectroscopy of the intermediate polar EX Hydrae
II. The inner disk radius⋆,⋆⋆
Institut für Astrophysik und Geophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
e-mail: k.beuermann@t-online.de
Received:
11
July
2022
Accepted:
25
January
2024
EX Hya is one of the best studied, but still enigmatic intermediate polars. We present phase-resolved blue VLT/UVES high-resolution (λ/Δλ ≃ 16.000) spectra of EX Hya taken in January 2004. Our analysis involves a unique decomposition of the Balmer line profiles into the spin-modulated line wings that represent streaming motions in the magnetosphere and the orbital-phase modulated line core that represents the accretion disk. Spectral analysis and tomography show that the division line between the two is solidly located at ∣υrad ∣ ≃ 1200 km s−1, defining the inner edge of the accretion disk at rin ≃ 7 × 109 cm or ∼10R1 (WD radii). This large central hole allows an unimpeded view of the tall accretion curtain at the lower pole with a shock height up to hsh ∼ 1R1 that is required by X-ray and optical observations. Our results contradict models that advocate a small magnetosphere and a small inner disk hole. Equating rin with the magnetospheric radius in the orbital plane allows us to derive a magnetic moment of the WD of μ1 ≃ 1.3 × 1032 G cm3 and a surface field strength B1 ∼ 0.35 MG. Given a polar field strength Bp ≲ 1.0 MG, optical circular polarization is not expected. With an accretion rate Ṁ = 3.9 × 10−11 M⊙ yr−1, the accretion torque is Gacc ≃ 2.2 × 1033 g cm2 s−2. The magnetostatic torque is of similar magnitude, suggesting that EX Hya is not far from being synchronized. We measured the orbital radial-velocity amplitude of the WD, K1 = 58.7 ± 3.9 km s−1, and found a spin-dependent velocity modulation as well. The former is in perfect agreement with the mean velocity amplitude obtained by other researchers, confirming the published component masses M1 ≃ 0.79 M⊙ and M2 ≃ 0.11 M⊙.
Key words: binaries: eclipsing / stars: fundamental parameters / novae, cataclysmic variables / stars: individual: EX hydrae / white dwarfs / X-rays: stars
Reduced spectra are 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/686/A304
© The Authors 2024
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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