Optical and ultraviolet observations of a strong flare in the young, single K2 dwarf LQ Hya

Abstract

A B S T R A C TWe present high-resolution optical echelle spectra and IUE observations during a strong¯are on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive phase of the¯are, 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 ux levels were not recovered until 21 h later, though a data gap and a possible second¯are make the interpretation uncertain. In addition to the typically¯are-enhanced emission lines (e.g., Ha and Hb), 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¯are energy, and discuss the broad components, asymmetries and Doppler shifts seen in some of the emission lines. Figure 7. IUE SWP-lo spectra showing¯uxes at earth (A Ê À1 ) for the mean quiescent phase (average of 10 spectra; heavy solid), the early impulsive phase (JD 244 9343.568; thin solid) and the near-maximum phase (JD 244 9343.783; dotted). The spectra have been smoothed by a three-pixel running mean.

A multi-wavelength view of AB Doradus outer atmosphere

“…For the He i lines at 3819.6, 4026.2, and 6678.1 Å the line amplitudes are not strong enough to reveal a broad component, although the latter at least shows a second component. These broad component has been noted mostly in M-dwarf flares (Crespo-Chacón et al 2006;Fuhrmeister et al 2008Fuhrmeister et al , 2011, but also for young K-dwarfs (Montes et al 1999 and references therein). They can be blue-or (more often) red-shifted, and are often ascribed to a moving turbulent plasma component.…”

“…Also Kowalski et al (2010) observed a white light mega-flare on YZ CMi with a resolving power below 1000 but a cadence of 30 s covering a wavelength range from 3350 to 9260 Å. Prominent examples of good spectral resolution but lower cadence are Montes et al (1999), who observed a major flare on LQ Hya during decay and about half an hour before its onset with R ∼ 35 000 and a cadence of six to seven minutes in the wavelength range between 4842 to 7725 Å. Fuhrmeister et al (2008) observed CN Leo during a mega-flare with a cadence of about 15 min and R ∼ 50 000.…”

The Characteristics of Solar X-Class Flares and CMEs: A Paradigm for Stellar Superflares and Eruptions?

“…Ottmann and Schmitt, 1996;Tsuboi et al, 1998), perhaps due to the presence of cool material from erupting filaments. Blue-shifted Hα emission during flares, indicating velocities of order 100 km s −1 , also support the presence of CMEs (Montes et al, 1999;Fuhrmeister and Schmitt, 2004). Complex behavior of optical and ultraviolet lines during a large flare on the M dwarf AD Leo was interpreted in terms of various phases of a mass ejection including motion of filaments, chromospheric condensation, prominence oscillations, and the prominence eruption itself (Houdebine et al, 1993).…”

Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit

“…Similarly, Johns-Krull et al (1997) report on a GOES M7.7 class solar flare also finding the He i D3 line to be in absorption throughout the entire event and absent during quies-During flares on other stars the He i D3 line has been observed in emission. For instance, Crespo-Chacón et al (2006) detect the line studying flares on the active M-type star AD Leo and Montes et al (1999) report He i D3 emission during a flare on the K2 dwarf LQ Hya. Our observations indicate a potential small increase in the He i D3 flux during the rise phase of the flare, which would be consistent with observations of strong flares on the Sun, thereafter a phase of increasing absorption follows.…”