Romina Petrucci
Characterizing flares in ultra-cool dwarfs and their impact on potentially habitable planets
Ultra-cool dwarfs (UCDs) are objects with effective temperatures below 3000 K, including fully convective very low-mass stars and brown dwarfs. They are particularly interesting because it is easier and more likely to detect Earth-like planets in their habitable zone than around stars of any other spectral type. However, a key aspect to assess whether planets orbiting UCDs would be able to promote the emergence of life on their surfaces is to characterize the host’s magnetic activity.
With this in mind, in this contribution, we present the characterization of the photometric variability of 208 ultra-cool dwarfs with spectral types between M4 and L4 using 20-s and 2-min cadence data from the TESS space mission. We computed the rotation period of 87 UCDs and detected 778 flares in 103 of them. The analysis of these data allows us to conclude that the correlations among the measured flare characteristics, namely the slope of the cumulative flare frequency distribution, flare amplitude, duration, and energy, are consistent with those measured for dwarf stars of earlier spectral types. Our findings indicate that UCD flares are similar to those produced by FGK and earlier M dwarfs. According to traditional understanding, magnetic fields in stars with partially convective envelopes are seated at the tachocline, which fully convective UCDs do not have. In this context, our results suggest that the physical mechanism that produces flares might be similar in these very differently structured dwarfs.
Additionally, flares are thought to initiate abiogenesis in terrestrial planets. We explore this possibility and find that the UV energy emitted during flaring events in the UCDs of our sample is not enough to drive prebiotic chemistry on any terrestrial planet orbiting them.
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Characterizing flares in ultra-cool dwarfs and their impact on potentially habitable planets
