Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1K080

AK Sco: evidence of tide driven filling of the inner gap in the circumbinary disk

Gomez de Castro, Ana I. (AEGORA, Universidad Complutense de Madrid)
Lopez-Santiago, Javier (AEGORA, Universidad Complutense de Madrid)
Talavera, Antonio (European Space Astronomy Center)
Sytov, A.Yu. (Institute of Astronomy of the Russian Academy of Sciences)
Bisikalo, Dmitri (Institute of Astronomy of the Russian Academy of Sciences)

AK Sco stands out among pre­main sequence binaries because of its prominent ultraviolet excess, the high eccentricity of its orbit and the strong tides driven by it. AK Sco is made of two F5 type stars that get as close as 11R* at periastron passage. The presence of a dense (ne ~ 1011 cm­3) extended envelope has been unveiled recently. In this article, we report the results from a XMM­Newton based, monitoring of the system. We show that at periastron, X­ray and UV fluxes are enhanced by a factor of ~3 with respect to the apastron values. The X­ray radiation is produced in an optically thin plasma with T~6.4 MK and it is found that the NH column rises from 0.35 1021 cm­2 at periastron to 1.11 1021 cm­2 at apastron, in good agreement with previous polarimetric observations. The UV emission detected in the OM band seems to be caused by the reprocessing of the high energy magnetospheric radiation on the circumstellar material. Moreover, further evidence of the strong magnetospheric disturbances is provided by the detection of line broadening of 279 km s­1 in the N V line with HST/STIS. Numerical simulations of the mass flow from the circumbinary disk to the components have been carried out. They provide a consistent scenario 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 ring­like structures around each component of the system. At periastron, the ring­like structures get in contact, leading to angular momentum annihilation, and thus producing an accretion outburst. These results are published in Gómez de Castro et al. 2013, ApJ, 766, 62 We have also discovered a 780 s period oscillation in the UV continuum light curve triggered at periastron passage (Gómez de Castro, Lopez-Santiago & Talavera, 2013, MNRAS, 429, L1).

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