A hot ultraviolet flare on the M dwarf star GJ 674

Journal article

As part of the Mega-Measurements of the Ultraviolet Spectral Characteristics of Low-Mass Exoplanetary Systems Hubble Space Telescope (HST) Treasury program, we obtained time-series ultraviolet spectroscopy of the M2.5V star, GJ 674. During the far-ultraviolet (FUV) monitoring observations, the target exhibited several small flares and one large flare (E FUV = 1030.75 erg) that persisted over the entirety of an HST orbit and had an equivalent duration >30,000 s, comparable to the highest relative amplitude event previously recorded in the FUV. The flare spectrum exhibited enhanced line emission from chromospheric, transition region, and coronal transitions and a blue FUV continuum with an unprecedented color temperature of TC sime 40,000 ± 10,000 K. In this Letter, we compare the flare FUV continuum emission with parameterizations of radiative hydrodynamic model atmospheres of M star flares. We find that the observed flare continuum can be reproduced using flare models but only with the ad hoc addition of a hot, dense emitting component. This observation demonstrates that flares with hot FUV continuum temperatures and significant extreme-ultraviolet/FUV energy deposition will continue to be of importance to exoplanet atmospheric chemistry and heating, even as the host M dwarfs age beyond their most active evolutionary phases.

Authors: Froning, CS; Kowalski, A; France, K; Loyd, ROP; Schneider, PC

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IOP Publishing
• Journal: Astrophysical Journal Letters
• Volume: 871
• Issue: 2
• Article number: L26
• Publication date: 2019-01-28
• Acceptance date: 2019-01-18
• DOI: 10.3847/2041-8213/aaffcd
• EISSN: 2041-8213
• ISSN: 2041-8205
• Language: English
• Keywords: stars: individual (GJ 674); stars: flare; stars: activity; stars: chromospheres; stars: low-mass; planets and satellites: atmospheres; FFR