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Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

Guarcello, M. G. and Micela, G. and Sciortino, S. and López-Santiago, J. and Argiroffi, C. and Reale, F. and Flaccomio, E. and Alvarado-Gómez, J. D. and Antoniou, V. and Drake, J. J. and Pillitteri, I. and Rebull, L. M. and Stauffer, J. (2019) Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades. Astronomy and Astrophysics, 622 . Art. No. A210. ISSN 0004-6361. doi:10.1051/0004-6361/201834370.

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Context. Flares are powerful events ignited by a sudden release of magnetic energy which triggers a cascade of interconnected phenomena, each resulting in emission in different electromagnetic bands. In fact, in the Sun flares are observed across the whole electromagnetic spectrum. Multi-band observations of stellar flares are instead rare. This limits our ability to extend what we learn from solar flares to the case of flares occurring in stars with different properties. Aims. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. The objective of this paper is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We also aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. Methods. We selected bright X-ray/optical flares that occurred in 12 known members of the Pleiades from their K2 and XMM-Newton light curves. The sample includes ten K-M stars, one F9 star, and one G8 star. Flare average properties were obtained from integrated analysis of the light curves during the flares. The time evolution of the plasma in the magnetic loops is constrained with time-resolved X-ray spectral analysis. Results. Most of the flares studied in this work emitted more energy in optical than in X-rays, as in most solar flares, even if the Pleiades flares output a larger fraction of their total energy in X-rays than typical solar flares do. Additionally, the energy budget in the two bands is weakly correlated. We also found comparable flare duration in optical and X-rays and observed that rapidly rotating stars (e.g., with rotation period shorter than 0.5 days) preferentially host short flares. We estimated the slope of the cooling path of the flares in the log(EM)-vs.-log(T) plane. The values we obtained are affected by large uncertainties, but their nominal values suggest that the flares analyzed in this paper are mainly due to single loops with no sustained heating occurring during the cooling phase. We also observed and analyzed oscillations with a period of 500 s during one of the flares. Conclusions. The flares observed in the Pleiades can be classified as “superflares” based on their energy budget in the optical, and share some of the properties of the flares observed in the Sun, despite being more energetic. For instance, as in most solar flares, more energy is typically released in the optical than in X-rays and the duration of the flares in the two bands is correlated. We have attempted a comparison between the X-ray flares observed in the Pleiades and those observed in clusters with different ages, but to firmly address any evolutionary pattern of flare characteristics, similar and uniform multi-wavelength analyses on more complete samples are necessary.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Guarcello, M. G.0000-0002-3010-2310
Micela, G.0000-0002-9900-4751
Flaccomio, E.0000-0002-3638-5788
Antoniou, V.0000-0001-7539-1593
Drake, J. J.0000-0002-0210-2276
Rebull, L. M.0000-0001-6381-515X
Stauffer, J.0000-0003-3595-7382
Additional Information:© 2019 ESO. Article published by EDP Sciences. Received 3 October 2018; Accepted 8 January 2019; Published online 21 February 2019. We thank the anonymous referee for his/her thoughtful reading and comments, which helped us to improve our paper. For this study we used data from the NASA satellite Kepler and the X-ray observatory XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Funding for the Kepler mission is provided by the NASA Science Mission directorate. Funding for the K2 mission is provided by the NASA Science Mission directorate. M.G.G., G.M., S.S., C.A., E.F., F.R., and I.P. acknowledge modest financial support from the agreement ASI-INAF n.2017-14-H.0. J.J.D. was supported by NASA contract NAS8-03060 to the Chandra X-ray Center. J.D.A.G. was supported by Chandra grants AR4-15000X and GO5-16021X. V.A. acknowledges financial support from the Texas Tech President’s Office.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Agenzia Spaziale Italiana (ASI)2017-14-H.0
Texas Tech UniversityUNSPECIFIED
Subject Keywords:X-rays: stars – stars: flare
Record Number:CaltechAUTHORS:20190307-103305275
Persistent URL:
Official Citation:Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades. M. G. Guarcello, G. Micela, S. Sciortino, J. López-Santiago, C. Argiroffi, F. Reale, E. Flaccomio, J. D. Alvarado-Gómez, V. Antoniou, J. J. Drake, I. Pillitteri, L. M. Rebull and J. Stauffer. A&A, 622 (2019) A210. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93629
Deposited By: Tony Diaz
Deposited On:07 Mar 2019 21:01
Last Modified:16 Nov 2021 16:59

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