Simultaneous photometric and CARMENES spectroscopic monitoring of fast-rotating M dwarf GJ 3270

Abstract

Context. Active M dwarfs frequently exhibit large flares, which can pose an existential threat to the habitability of any planet in orbit in addition to making said planets more difficult to detect. M dwarfs do not lose angular momentum as easily as earlier-type stars, which maintain the high levels of stellar activity for far longer. Studying young, fast-rotating M dwarfs is key to understanding their near stellar environment and the evolution of activity. Aims. We study stellar activity on the fast-rotating M dwarf GJ 3270. Methods. We analyzed dedicated high cadence, simultaneous, photometric and high-resolution spectroscopic observations obtained with CARMENES of GJ 3270 over 7.7 h, covering a total of eight flares of which two are strong enough to facilitate a detailed analysis. We consult the TESS data, obtained in the month prior to our own observations, to study rotational modulation and to compare the TESS flares to those observed in our campaign. Results. The TESS data exhibit rotational modulation with a period of 0.37 d. The strongest flare covered by our observing campaign released a total energy of about 3.6 × 1032 erg, putting it close to the superflare regime. This flare is visible in the B,V, r, i, and z photometric bands, which allows us to determine a peak temperature of about 10 000 K. The flare also leaves clear marks in the spectral time series. In particular, we observe an evolving, mainly blue asymmetry in chromospheric lines, which we attribute to a post-flare, corotating feature. To our knowledge this is the first time such a feature has been seen on a star other than our Sun. Conclusions. Our photometric and spectroscopic time series covers the eruption of a strong flare followed up by a corotating feature analogous to a post-flare arcadal loop on the Sun with a possible failed ejection of material.

Zodiacal exoplanets in time – XIII. Planet orbits and atmospheres in the V1298 Tau system, a keystone in studies of early planetary evolution

“…However, the change in the steady decline in EW over the 6 h observation interval is inconsistent with the increase expected in declining phase of a flare, and the time-scale is inconsistent with the more rapid (࣠1 h) rise time of flares. 3 Emission is also associated with Doppler shifts of 10s of km s −1 (Johnson et al 2021) which we do not observe.…”

“…He I emission from a flaring region fills in the line core and produces a weakening both of He I at 1083 nm and the D3 line at 587.6 nm that tracks other chromospheric emission indicators such as H α (Johnson et al 2021;Schmidt et al 2012). However, the change in the steady decline in EW over the 6 h observation interval is inconsistent with the increase expected in declining phase of a flare, and the time-scale is inconsistent with the more rapid (࣠1 h) rise time of flares.…”

Zodiacal Exoplanets in Time (ZEIT) XIII: Planet Orbits and Atmospheres in the V1298 Tau System, a Keystone in Studies of Early Planetary Evolution

“…However, the change in the steady decline in EW over the 6 hr observation interval is inconsistent with the increase expected in the declining phase of a flare, and the time scale is inconsistent with the more rapid ( 1 hr) rise time of flares. 3 Emission is also associated with Doppler shifts of 10s of km s −1 (Johnson et al 2021) which we do not observe.…”

“…He I emission from a flaring region fills in the line core and produces a weakening both of He I at 1083 nm and the D3 line at 587.6 nm that tracks other chromospheric emission indicators such as H𝛼 (Schmidt et al 2012;Johnson et al 2021). However, the change in the steady decline in EW over the 6 hr observation interval is inconsistent with the increase expected in the declining phase of a flare, and the time scale is inconsistent with the more rapid ( 1 hr) rise time of flares.…”

Activity of M dwarfs in the CARMENES sample

“…1.12, the enhancement of emission lines during a flare is not necessarily symmetric around the line cores. Line asymmetries are especially prominent in Hα (Fuhrmeister et al 2018) and can be attributed to a Doppler shift caused by the emitting material rising in the chromosphere at the onset of the flare (blue asymmetry) or moving down again during the decay (red asymmetry; Ichimoto & Kurokawa 1984;Cho et al 2016;Johnson et al 2021). Flares were discussed in detail in the reviews by Haisch et al (1991) and Benz & Güdel (2010).…”