Accretion and magnetism on young eccentric binaries: DQ Tau and AK Sco
arxiv(2024)
摘要
The accretion and ejection of mass in pre-main sequence (PMS) stars are key
processes in stellar evolution as they shape the stellar angular momentum
transport necessary for the stars' stability. Magnetospheric accretion onto
classical T Tauri stars and low-mass PMS stars has been widely studied in the
single-star case. This process can not be directly transferred to PMS binary
systems, as tidal and gravitation effects, and/or accretion from a circumbinary
disc (with variable separation of the components in the case of eccentric
orbits) are in place. This work examines the accretion process of two PMS
eccentric binaries, DQ Tau and AK Sco, using high-resolution
spectropolarimetric time series. We investigate how magnetospheric accretion
can be applied to these systems by studying the accretion-related emission
lines and the magnetic field of each system. We discover that both systems are
showing signs of magnetospheric accretion, despite their slightly different
configurations, and the weak magnetic field of AK Sco. Furthermore, the
magnetic topology of DQ Tau A shows a change relative to the previous orbital
cycle studied: previously dominated by the poloidal component, it is now
dominated by the toroidal component. We also report an increase of the
component's accretion and the absence of an accretion burst at the apastron,
suggesting that the component's magnetic variation might be the cause of the
inter-cycle variations of the system's accretion. We conclude on the presence
of magnetospheric accretion for both systems, together with gravitational
effects, especially for AK Sco, composed of more massive components.
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