Measuring the Density Structure of an Accretion Hot Spot

Abstract

Magnetospheric accretion models predict that matter from protoplanetary disks accretes onto the star via funnel flows which follow the stellar field lines and shock on the stellar surface leaving a hot spot with a density gradient. Previous work has inferred different densities in the hot spot, but has not been sensitive to the radial density distribution. Attempts have been made to measure this with X-ray observations, but X-ray emission only traces a fraction of the hot spot and also coronal emission. Here we report periodic ultraviolet and optical light curves of the accreting star GM Aur that display a time lag of about 1 day between their peaks. The periodicity arises as the source of the ultraviolet and optical emission moves into and out of view as it rotates along with the star. The time-lag indicates a difference in the spatial distribution of ultraviolet and optical brightness over the stellar surface. Within the framework of the magnetospheric accretion model, this indicates a radial density gradient in a hot spot on the stellar surface since different density parts of the hot spot are expected to emit radiation at different wavelengths. These results are the first observational confirmation of the magnetospheric accretion model's prediction of a density gradient in the hot spot and demonstrate the insights gained from focusing on the wavelengths where the bulk of the accretion energy can be observed.

published in Nature; open access link: https://www.nature.com/articles/s41586-021-03751-5

References in corpus (10)

• Accretion to Magnetized Stars through the Rayleigh-Taylor Instability: Global Three-Dimensional Simulations
• Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph
• On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds
• CSI 2264: Characterizing Young Stars in NGC 2264 with Short-Duration, Periodic Flux Dips in their Light Curves
• The non-dipolar magnetic fields of accreting T Tauri stars
• Multi-epoch Ultraviolet HST Observations of Accreting Low-mass Stars
• A measure of the size of the magnetospheric accretion region in TW Hydrae
• The magnetic obliquity of accreting T Tauri stars
• Magnetohydrodynamic modeling of the accretion shocks in classical T Tauri stars: the role of local absorption on the X-ray emission
• Using Multiwavelength Variability to Explore the Connection between X-ray Emission, the Far-Ultraviolet H2 Bump, and Accretion in T Tauri Stars

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• Hydrogen Emission from Accretion and Outflow in T Tauri Stars
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• Correlation between the optical veiling and accretion properties: A case study of the classical T Tauri star DK Tau
• Understanding Accretion Variability Through TESS Observations of Taurus