Far-ultraviolet Flares on Accreting Protostars: Weak and Classical T Tauri Stellar Pair Analysis

Abstract

The far-ultraviolet (FUV) emission of classical T Tauri stars (CTTSs) is known to play an important role in protoplanetary disk dispersal and giant planet formation, yet the role played by protostellar flares in these processes is largely unknown. We use nearby star-forming regions as laboratories to probe the FUV flare characteristics of CTTSs and test whether flares may be masked underneath accretion luminosity. Using AD Leo as our archetypal flare template, we pilot a novel analysis technique on three weak-lined T Tauri star (WTTS) and CTTS pairs: TWA-7/TWA Hya, RECX-1/RECX-11, and LkCa19/GM Aur. We find that flares contribute an upper limit of 0.064% ± 0.002%, 3.1% ± 0.1%, and 2.7% ± 0.3% to the total FUV energy budgets of TW Hya, RECX-11, and GM Aur, respectively. We also present predicted CTTS flare rates, which suggest that we would expect to observe roughly one 5σ flare on each of the CTTS archival light curves. We find one 5σ flare on TW Hya with E(1380–1745 Å) = (6.1 ± 0.7) × 1031 erg, but none are found on RECX-11 or GM Aur. Longer monitoring campaigns are required to provide more concrete constraints on the FUV flare frequency of accreting protostars. Optical TESS data of the targets were also analyzed to contextualize these results. Lastly, we report the first FUV flare on a WTTS (RECX-1), which is also the most energetic FUV flare event observed with the Hubble Space Telescope to date with E(1135–1429 Å) = (2.1 ± 0.1) × 1032 erg.