Actualités du Laboratoire

Ref Arxiv: 2402.01419
DOI: 10.1093/mnras/stae383
Ref. & Cit.: NASA ADS
Résumé:

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.

Commentaires: 21 pages, 24 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society

Ref HAL: hal-04414704_v1
DOI: 10.1039/d3cp03575a
Exporter : BibTex | endNote

Ref Arxiv: 2311.05039
DOI: 10.1093/mnras/stad3472
Ref. & Cit.: NASA ADS
Résumé:

In this paper, we study six slowly rotating mid-to-late M~dwarfs (rotation period $P_{\mathrm{rot}} \approx 40-190\,\mathrm{dy}$) by analysing spectropolarimetric data collected with SPIRou at the Canada-France-Hawaii Telescope as part of the SPIRou Legacy Survey from 2019 to 2022. From $\approx$100--200 Least-Squares-Deconvolved (LSD) profiles of circularly polarised spectra of each star, we confirm the stellar rotation periods of the six M~dwarfs and explore their large-scale magnetic field topology and its evolution with time using both the method based on Principal Component Analysis (PCA) proposed recently and Zeeman-Doppler Imaging. All M~dwarfs show large-scale field variations on the time-scale of their rotation periods, directly seen from the circularly polarised LSD profiles using the PCA method. We detect a magnetic polarity reversal for the fully-convective M~dwarf GJ~1151, and a possible inversion in progress for Gl~905. The four fully-convective M~dwarfs of our small sample (Gl~905, GJ~1289, GJ~1151, GJ~1286) show a larger amount of temporal variations (mainly in field strength and axisymmetry) than the two partly-convective ones (Gl~617B, Gl~408). Surprisingly, the six M~dwarfs show large-scale field strengths in the range between 20 to 200\,G similar to those of M~dwarfs rotating significantly faster. Our findings imply that the large-scale fields of very slowly rotating M~dwarfs are likely generated through dynamo processes operating in a different regime than those of the faster rotators that have been magnetically characterized so far.

Commentaires: 16 pages, 35 figures, published in MNRAS