Simultaneous photometric and CARMENES spectroscopic monitoring of fast-rotating M dwarf GJ 3270: Discovery of a post-flare corotating feature

Full list of authors: Johnson, E. N.; Czesla, S.; Fuhrmeister, B.; Schöfer, P.; Shan, Y.; Cardona Guillén, C.; Reiners, A.; Jeffers, S. V.; Lalitha, S.; Luque, R.; Rodríguez, E.; Béjar, V. J. S.; Caballero, J. A.; Tal-Or, L.; Zechmeister, M.; Ribas, I.; Amado, P. J.; Quirrenbach, A.; Cortés-Contreras, M.; Dreizler, S.; Fukui, A. ; López-González, M. J.; Hatzes, A. P.; Henning, Th.; Kaminski, A.; Kürster, M.; Lafarga, M.; Montes, D.; Morales, J. C.; Murgas, F.; Narita, N.; Pallé, E.; Parviainen, H.; Pedraz, S.; Pollacco, D.; Sota, A.--This is an Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.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. © E.N. Johnson et al. 2021.This project was funded principally by the Deutsche Forschungsgemeinschaft through the Major Research Instrumentation Programme and Research Unit FOR2544 "Blue Planets around Red Stars". CARMENES is an instrument at the Centro Astronomico Hispano-Aleman (CAHA) at Calar Alto (Almeria, Spain), operated jointly by the Junta de Andalucia and the Instituto de Astrofisica de Andalucia (CSIC). The authors wish to express their sincere thanks to all members of the Calar Alto staff for their expert support of the instrument and telescope operation. CARMENES was funded by the Max-Planck-Gesellschaft (MPG), the Consejo Superior de Investigaciones Cientificas (CSIC), the Ministerio de Economia y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS-2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut fur Astronomie, Instituto de Astrofisica de Andalucia, Landessternwarte Konigstuhl, Institut de Ciencies de l'Espai, Institut fur Astrophysik Gottingen, Universidad Complutense de Madrid, Thuringer Landessternwarte Tautenburg, Instituto de Astrofisica de Canarias, Hamburger Sternwarte, Centro de Astrobiologia and Centro Astronomico Hispano-Aleman), with additional contributions by the MINECO, the Klaus Tschira Stiftung, the states of Baden-Wurttemberg and Niedersachsen and by the Junta de Andalucia. We acknowledge financial support from the Agencia Estatal de Investigacion of the Ministerio de Ciencia, Innovacion y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033 and PGC2018-098153-B-C33 and the Centre of Excellence "Severo Ochoa" and "Maria de Maeztu" awards to the Instituto de Astrofisica de Canarias (SEV-2015-0548), Instituto de Astrofisica de Andalucia (SEV-2017-0709), and Centro de Astrobiologia (MDM-2017-0737), the Generalitat de Catalunya/CERCA programme, JSPS KAKENHI via grants JP18H01265 and JP18H05439, and JST PRESTO via grant JPMJPR1775. This work was based on data from the CARMENES data archive at CAB (CSIC-INTA). Data were partly collected with the 150 cm and 90 cm telescopes at the Observatorio de Sierra Nevada (SNO) operated by the Instituto de Astrofifica de Andalucia (IAA-CSIC). This article is based on observations made with the MuSCAT2 instrument, developed by ABC, at Telescopio Carlos Sanchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide.Peer reviewe