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

authors

  • GUARCELLO, M. G.
  • MICELA, G.
  • SCIORTINO, SALVATORE
  • LÓPEZ SANTIAGO, JAVIER
  • ARGIROFFI, C.
  • REALE, FABIO
  • FLACCOMIO, ETTORE
  • ALVARADO GOMEZ, J. D.
  • ANTONIOU, V.
  • DRAKE, J. J.
  • PILLITTERI, I.
  • REBULL, L. M.
  • STAUFFER, J.

publication date

  • February 2019

start page

  • 1

end page

  • 24

volume

  • 622

International Standard Serial Number (ISSN)

  • 0004-6361

Electronic International Standard Serial Number (EISSN)

  • 1432-0746

abstract

  • 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. 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.

keywords

  • x-rays stars; stars flare