Electron temperatures of flare plasmas from emission line fluxes

Houdebine, E. R.; Butler, C. J.; Rodono, M.; Panagi, P. M.; Foing, B. H.

doi:10.1017/s0252921100153801

Cited by 63 publications

(100 citation statements)

References 3 publications

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“…On the other hand, in stellar flares evidence of mass motions has also been reported. In particular, a large enhancement in the far blue wings of Balmer lines during the impulsive phase of a stellar flare was interpreted as a high‐velocity mass ejection (Houdebine, Foing & Rodonó 1990), or high‐velocity chromospheric evaporation (Gunn et al 1994b), and red asymmetries in the wings of Balmer lines are reported by Houdebine et al (1993) as evidence of CDC. Broadening and shifts in UV lines during stellar flares, also interpreted as mass motions, have been reported by Simon, Linsky & Schiffer (1980), and Linsky et al (1989).…”

Section: Description Of the Flarementioning

confidence: 96%

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

Montes

Saar

Cameron

et al. 1999

Monthly Notices of the Royal Astronomical Society

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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.

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Section: Description Of the Flarementioning

confidence: 96%

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

Montes

Saar

Cameron

et al. 1999

Monthly Notices of the Royal Astronomical Society

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“…Giampapa et al (1982) used Ca II observations to model M dwarf chromospheres, with limited success. Houdebine & Panagi (1990) investigated the effects of changing the model hydrogen atom used in the calculations, but they did not fit their models to data. Hawley & Fisher (1994) have developed chromospheric flare models, which incorporate a full nonlocal thermodynamic equilibrium (NLTE) treatment of the statistical equilibrium and radiative transfer in the important optically thick chromospheric lines and a helium ionization equilibrium computed self-consistently with the downward X-ray flux from the corona.…”

Section: Stellar Activitymentioning

confidence: 99%

Model Atmospheres of Very Low Mass Stars and Brown Dwarfs

Allard

Hauschildt

Alexander

et al. 1997

Annu. Rev. Astron. Astrophys.

353

343

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As progressively cooler stellar and substellar objects are discovered, the presence first of molecules and then of condensed particulates greatly complicates the understanding of their physical properties. Accurate model atmospheres that include these processes are the key to establishing their atmospheric parameters. They play a crucial role in determining structural characteristics by setting the surface conditions of model interiors and providing transformations to the various observational planes. They can reveal the spectroscopic properties of brown dwarfs and help establish their detectability. In this paper, we review the current state-of-the-art theory and modeling of the atmospheres of very low mass stars, including the coolest known M dwarfs, M subdwarfs, and brown dwarfs, i.e. T eff ≤ 4,000 K and −4.0 ≤ [M/H] ≤ +0.0. We discuss ongoing efforts to incorporate molecular and grain opacities in cool stellar spectra, as well as the latest progress in (a) deriving the effective temperature scale of M dwarfs, (b) reproducing the lower main sequences of metal-poor subdwarfs in the halo and globular clusters, and (c) results of the models related to the search for brown dwarfs.

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“…The asymmetries of the Balmer lines are usually interpreted as a consequence of plasma turbulence or directed mass motions. Houdebine et al (1990) found a large enhancement in the far blue wings of Balmer lines during the impulsive phase of a flare on AD Leo, that they attribute to a mass ejection. Houdebine et al (1993) found in the same flare redshifted Balmer line cores that were interpreted as a chromospheric downward condensation.…”

Section: Hα Line Asymmetries: Possible Mass Ejectionmentioning

confidence: 95%

Short-term evolution and coexistence of spots, plages and flare activity on LQ Hydrae

Soriano

Strassmeier

2017

A&A

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Aims. We aim to study the short-term evolution of the chromospheric and photospheric activity of the young, single K2 dwarf LQ Hya. Methods. Four months of quasi-simultaneous spectroscopic and photometric observations were used to study the variations of the photometric light curve, the evolution of the chromospheric activity from the Hα and Hβ lines, and the distribution of cool spots from Doppler maps. Results. During our observations one side of the star was more active than the other. The equivalent width of the Hα line from the least active hemisphere increased from ≈0.7 Å at the beginning of the observation to 1.0 Å at the end. The basal emission of the most active hemisphere remained roughly constant at EW Hα ≈ 1.0 Å. Intense flare activity was observed during the first twenty days, where at least four different events were detected. The line asymmetries of the Hα line suggest that one of the flares could have produced a mass ejection with a maximum projected speed of 70 km s −1 . The rotational modulation of the V-band photometry showed clear anti-correlation with the chromospheric activity. The difference in brightness between the opposite hemispheres decreased from 0 m . 16 to 0 m . 09 in two months. Three spots gradually moving apart from each other are dominating the photospheric Doppler maps. The comparison between the maps and the Hα line as the star rotates reveals the spatial coexistence of chromospheric Hα emission and photospheric spots. Conclusions. Our results indicate that the active regions of LQ Hya can live for at least four months. The detected changes in the photometric light curve and the spectroscopic Doppler images seem to be more a consequence of the spatial redistribution of the active regions rather than due to changes in their strength. Only one of the active regions shows significant changes in its chromospheric emission.

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Electron temperatures of flare plasmas from emission line fluxes

Cited by 63 publications

References 3 publications

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

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

Model Atmospheres of Very Low Mass Stars and Brown Dwarfs

Short-term evolution and coexistence of spots, plages and flare activity on LQ Hydrae

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