Characterising the magnetospheric accretion process of DF Tauri's primary

Abstract

The accretion process in young stellar objects (YSOs) is fundamental to the formation of stellar systems. This process governs the star's mass assembly, the transfer of angular momentum, and the shaping of the protoplanetary disc, thereby influencing planet formation. For classical T Tauri stars (cTTSs), which are low-mass YSOs, accretion is a well-understood process. Their strong, dipolar magnetic field truncates the disc at a few stellar radii. Material is then channelled along these magnetic field lines, creating accretion funnel flows that fall onto the star's surface. However, this paradigm, known as magnetospheric accretion, is limited to isolated stars. The accretion process in multiple systems has not yet been fully understood. This work is part of a series of studies designed to build a framework to understand the accretion process in multiple star systems. The specific goal here is to determine how the magnetospheric accretion model can be used to describe DF Tau, a binary system where only the primary star is accreting material. To investigate how accretion occurs in a system where a single star is orbited by a non-accreting stellar companion, we used a time series of high-resolution spectropolarimetric observations from the ESPaDOnS instrument. This allowed us to study the accretion-related emission line variability, the veiling, and the magnetic field topology of the primary star in the system. Our research concludes that the primary star of the DF Tau system undergoes typical magnetospheric accretion. This process is driven by a strong dipolar magnetic field, which funnels accreting material onto the stellar surface, creating an accretion shock. We also identified a significant difference in the magnetic topology of the two stars querying the influence of accretion of the evolution of the magnetic field, or capture of the secondary star.

Figures (13)

• Figure 1: Variability analysis of Balmer lines. The H$\alpha$, H$\beta$, and H$\gamma$ lines are depicted on the first, second, and third line, respectively. The first column shows the line profiles, each colour corresponding to an observation. The second column are the P2Ds, with the velocity on the x-axis, the frequency on the y-axis, and the power of the periodogram scaled by the colour bar. The white dotted line shows the primary rotation period of 10.5 days derived by Allen17. The mean profile and its variance are shown in black and blue, respectively, along the x-axis of the P2D. The third column present the ACMs. The two lines velocity are on the x and y axes and the colour bar scaled the Pearson correlation coefficient, red being 1, highly correlated, by being $-$1, highly anticorrelated. The two mean and variance profiles are illustrated in black and blue, respectively, along its corresponding axis.
• Figure 2: Variability analysis of the Ca ii IRT line. The top left panel illustrates the line profiles, the top right panel shows the P2D, the bottom left panel present the ACM, and the bottom right panel depicts the CM with H$\gamma$. The colours and figure shapes are the same as used in Fig. \ref{['fig:balmer']}.
• Figure 3: Variability analysis of the He i D$_{3}$ line. The top left panel illustrates the line profiles, the top right panel shows the P2D, the bottom left panel present the CM with the Ca ii IRT, and the bottom right panel depicts the CM with H$\gamma$. The colours and figure shapes are the same as used in Fig. \ref{['fig:balmer']}.
• Figure 4: Veiling values as function of the HJD. The colours indicate the different wavelength windows used.
• Figure 5: Doppler image (brightness maps) of DF Tau on a flattened polar view. The central dot illustrate the rotation pole, the two dotted circles are latitude 60 and 30$^\circ$, and the solid circle represents the equator. The black ticks show the clockwise rotation phases, and the red ticks represent the observed phases. The colour-code indicates the brightness on a linear scale, where a value of 1 represents the quiet photosphere. Values lower than one are darker regions, and values greater than one are bright.