Publication: Optical and ultraviolet observations of a strong flare in the young, single K2 dwarf LQ Hya
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1999-05-01
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We present high-resolution optical echelle spectra and IUE observations during a strong flare on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive phase of the flare, which started sometime between 2:42 ut and 4:07 ut, was characterized by strong optical continuum enhancement and blueshifted emission lines with broad wings. The optical chromospheric lines reached their maximum intensity at ≈ 5:31 ut, by which time the blueshift vanished and the optical continuum enhancement had sharply decreased. Thereafter, the line emission slowly decreased and the lines redshift in a gradual phase that lasted at least two more hours. The Mg II lines behaved similarly. Quiescent C IV flux levels were not recovered until 21 h later, though a data gap and a possible second flare make the interpretation uncertain. In addition to the typically flare-enhanced emission lines (e.g., H α and H β), we observe He I D_3 going into emission, plus excess emission (after subtraction of the quiescent spectrum) in other He I and several strong neutral metal lines (e.g., Mg I b). Flare enhancement of the far-ultraviolet continuum generally agrees with an Si I recombination model. We estimate the total flare energy, and discuss the broad components, asymmetries and Doppler shifts seen in some of the emission lines.
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© 1999 RAS.
The work reported herein is based on observations made with the William Herschel Telescope operated on the island of La Palma by the Royal Greenwich Observatory at the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofósica de Canarias, and on data obtained with the International Ultraviolet Explorer. This work has been partially supported by the Universidad Complutense de Madrid and the Spanish Direccioón General de Enseñanza Superior e Investigacioón Científica (DGESIC) under grant PB97-0259, by NASA grants NAG5-1975 and NAGW-112, HST grant GO-5871.01-94A, and NSF grant AST-9528563. YCU is supported by the Austrian Science Foundation grant S7302. We thank the referee J. G. Doyle for helpful comments, and C. M. Johns-Krull for useful discussions.
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