XMM-Newton monitoring of the close pre-main-sequence binary AK Sco. Evidence of tide-driven filling of the inner gap in the circumbinary disk



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Gómez de Castro, Ana Inés and López Santiago, Javier and Talavera, A. and Sytov, A. Y. and Bisikalo, D. (2013) XMM-Newton monitoring of the close pre-main-sequence binary AK Sco. Evidence of tide-driven filling of the inner gap in the circumbinary disk. Astrophysical journal, 766 (1). ISSN 0004-637X

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Official URL: http://iopscience.iop.org/0004-637X/766/1/62/pdf/0004-637X_766_1_62.pdf


AK Sco stands out among pre-main-sequence binaries because of its prominent ultraviolet excess, the high eccentricity of its orbit, and the strong tides driven by it. AK Sco consists of two F5-type stars that get as close as 11 R-* at periastron passage. The presence of a dense (n(e) similar to 10(11) cm(-3)) extended envelope has been unveiled recently. In this article, we report the results from an XMM-Newton-based monitoring of the system. We show that at periastron, X-ray and UV fluxes are enhanced by a factor of similar to 3 with respect to the apastron values. The X-ray radiation is produced in an optically thin plasma with T similar to 6.4 x 10(6) K and it is found that the N-H column density rises from 0.35 x 10(21) cm(-2) at periastron to 1.11 x 10(21) cm(-2) at apastron, in good agreement with previous polarimetric observations. The UV emission detected in the Optical Monitor band seems to be caused by the reprocessing of the high-energy magnetospheric radiation on the circumstellar material. Further evidence of the strong magnetospheric disturbances is provided by the detection of line broadening of 278.7 km s(-1) in the Nv line with Hubble Space Telescope/Space Telescope Imaging Spectrograph. Numerical simulations of the mass flow from the circumbinary disk to the components have been carried out. They provide a consistent scenario with which to interpret AK Sco observations. We show that the eccentric orbit acts like a gravitational piston. At apastron, matter is dragged efficiently from the inner disk border, filling the inner gap and producing accretion streams that end as ring-like structures around each component of the system. At periastron, the ring-like structures come into contact, leading to angular momentum loss, and thus producing an accretion outburst.

Item Type:Article
Uncontrolled Keywords:binaries: spectroscopic; magnetic fields; stars: pre-main sequence; T-tauri stars; x-ray-emission; system kh 15d; wavelength dependence; accretion shocks; mg-ii; scorpii; polarization; simulations; extinction
Subjects:Sciences > Mathematics > Astronomy
ID Code:21229
Deposited On:06 May 2013 11:43
Last Modified:26 Jun 2018 07:29

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