Speaker
Description
H$\alpha$ emission is abundant in ultracool dwarfs (UCD), but its origin is unclear. While it may stem from residual star-like, chromospheric emission, it may also be attributed to planet-like magnetospheric emission akin to Jupiter's aurora. A way to resolve this issue is to measure the spatial distribution of H$\alpha$ emission on the UCD. Chromospheric emission would appear distributed in spots, and/or spread out across the entire surface. In contrast, auroral emission would manifest as a ring structure centered on the magnetic axis, produced by particles precipitating along a largely dipolar magnetosphere.
In this talk, I will present the first application of this method using time series of high-resolution spectra of LSR J1835, a young nearby brown dwarf. I will show evidence that the H$\alpha$ emission from LSR J1835 emanates from a combination of an oblique ring with two high-latitude spots, suggesting that the UCD produces a chimera: a residual stellar chromosphere, embedded in a largely dipolar magnetosphere powering the auroral ring. This is consistent with the broader observational record of LSR J1835, which shows both planet-like features like radiation belts and coherent emission at radio frequencies, and star-like flares in its optical photometry.
Finally, I will demonstrate that discriminating different emission structures through forward modeling and Bayesian analysis is possible, but requires high signal-to-noise, high-resolution spectra that place LSR J1835 as the only viable target. However, looking ahead, E-ELT/ANDES will extend our reach to spectral types as late as L3, opening a new window into the magnetic and atmospheric physics of UCDs, and the space weather of planets around them.
| Talk category | NOVA Network 2 |
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