Journal Article

Evidence of accretion triggered oscillations in the pre-main-sequence interacting binary AK Sco

de Castro Ana I. Gómez, Javier López-Santiago and Antonio Talavera

in Monthly Notices of the Royal Astronomical Society: Letters

Published on behalf of The Royal Astronomical Society

Volume 429, issue 1, pages L1-L4
Published in print February 2013 |
Published online November 2012 | e-ISSN: 1745-3933 | DOI: http://dx.doi.org/10.1093/mnrasl/sls012

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Pre-main sequence (PMS) binaries are surrounded by circumbinary discs from which matter falls on to both components. The material dragged from the circumbinary disc flows on to each star through independent streams channelled by the variable gravitational field. The action of the bar-like potential is most prominent in high eccentricity systems made of two equal mass stars. AK Sco is a unique PMS system composed of two F5 stars in an orbit with e = 0.47. Henceforth, it is an ideal laboratory to study matter infall in binaries and its role in orbit circularization. In this Letter, we report the detection of a 1.3 mHz ultra low-frequency oscillation in the ultraviolet light curve at periastron passage. This oscillation lasts 7 ks being most likely fed by the gravitational energy released when the stream's tails spiralling on to each star get in contact at periastron passage enhancing the accretion flow; this unveils a new mechanism for angular momentum loss during PMS evolution and a new type of interacting binary.

Keywords: accretion, accretion discs; binaries: close; binaries: spectroscopic; circumstellar matter; stars: pre-main-sequence; stars: individual: AK Sco; stars: variables: T Tauri, Herbig Ae/Be

Journal Article.  2542 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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