Opacity in the upper atmosphere of AU Mic

Bloomfield, D. Shaun; Mathioudakis, M.; Christian, D. J.; Keenan, F. P.; Linsky, Jeffrey L.

doi:10.1051/0004-6361:20020690

Cited by 20 publications

(44 citation statements)

References 26 publications

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“…As reported in previous publications of these data sets, AD Leo shows two distinct flares (Christian et al 2006), AU Mic (Bloomfield et al 2002) shows one flare, and AB Dor (Dupree et al 2006) shows three flares, two of which appear during observational day-time and are therefore not considered for further analysis. In Fig.…”

Section: Lightcurve Analysismentioning

confidence: 96%

“…Dupree et al (1976) found that the ratio is enhanced for active solar regions. On stars, this ratio was found to be enhanced during flaring (Bloomfield et al 2002;Christian et al 2006). The C iii(λ977 Å) transition region A&A 536, A62 (2011) Notes.…”

Section: Introductionmentioning

confidence: 94%

“…In Sect. 3 where we present and describe stellar lightcurves and spectra, we refer also to the relevant previous studies (for AU Mic: Bloomfield et al 2002;Del Zanna et al 2002, for AD Leo: Christian et al 2006; and for AB Dor: Dupree et al 2006), in which flare detections and values for the C iii(λ1176 Å)/C iii(λ977 Å) line ratio during stellar quiescence and activity have already been presented (except for the AB Dor data set, for which no values for this line ratio have been published so far). In contrast to previous studies we investigate the temporal evolution of the flare lightcurves in greater detail and perform a systematic search for spectral line shifts and enhancements.…”

Section: Introductionmentioning

confidence: 99%

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Search for indications of stellar mass ejections using FUV spectra

Leitzinger

Odert

Ribas

et al. 2011

A&A

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Aims. We search for highly energetic activity phenomena in a small sample of late-type main-sequence stars in the far ultraviolet (FUV) using data from the Far Ultraviolet Spectroscopic Explorer (FUSE). Methods. Because FUSE allows a simultaneous photometric and spectroscopic analysis, we are able to analyze variations in the light curves (flares) and possible, activity-related signatures (line asymmetries, enhancements, and shifts) in the spectra. Furthermore, the computation of the well-known density-sensitive line ratio C iii(λ1176 Å)/C iii(λ977 Å) is also possible, and allows the investigation of its dependence on stellar activity. Results. Three late-type main-sequence stars found in the FUSE archive (HD 36705, HD 197481, and Gl 388) show flares in their light curves. We find no obvious Doppler shifts in the brightest lines of these stars, but the O vi(λ1032 Å) transition region line of AD Leo shows a blue wing enhancement one spectrum after a flare event. This emission feature is shifted by ∼-84 km s −1 from the line core. We can exclude that the spectral feature was caused by a gas cloud co-rotating with the star and favor an interpretation of a mass ejection. In addition we find an increase of the C iii(λ1176 Å)/C iii(λ977 Å) line ratio during all detected flares. We compare this finding to the Sun using solar full-disk spectra from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and SOlar Radiation and Climate Experiment (SORCE) missions, and find that powerful flare events also show an increased C iii(λ1176 Å)/C iii(λ977 Å) line ratio but this result is of low statistical significance. Owing to a lack of perfectly temporally coinciding TIMED/SORCE spectra and a low temporal resolution (∼15 spectra per day) it is not possible to distinguish clearly if this increase is caused by the flares or by the related mass ejections.

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Section: Lightcurve Analysismentioning

confidence: 96%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Search for indications of stellar mass ejections using FUV spectra

Leitzinger

Odert

Ribas

et al. 2011

A&A

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“…As in our previous work (Bloomfield et al 2002;Christian et al 2004Christian et al , 2006 we measured emission line fluxes by fitting Gaussians to the observed line profiles. In general, a single Gaussian profile was sufficient to fit both the O vi transitions.…”

Section: Discussionmentioning

confidence: 99%

“…Hence deviations of the observed line ratio from the optically thin value allows the optical depth and hence parameters of the emitting plasma to be derived. Using this method, several studies have found TR scale heights between 10-100 km for active stars including AU Mic (Bloomfield et al 2002), the flare star Prox Cen (Christian et al 2004) and AD Leo (Christian et al 2006). …”

Section: Introductionmentioning

confidence: 99%

A search for line intensity enhancements in the far-UV spectra of active late-type stars arising from opacity

Keenan¹,

Christian²,

Rose³

et al. 2011

A&A

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Context. Radiative transfer calculations have predicted intensity enhancements for optically thick emission lines, as opposed to the normal intensity reductions, for astrophysical plasmas under certain conditions. In particular, the results are predicted to be dependent both on the geometry of the emitting plasma and the orientation of the observer. Hence in principle the detection of intensity enhancement may provide a way of determining the geometry of an unresolved astronomical source. Aims. To investigate such enhancements we have analysed a sample of active late-type stars observed in the far ultraviolet spectral region. Methods. Emission lines of O vi in the FUSE satellite spectra of Eri, II Peg and Prox Cen were searched for intensity enhancements due to opacity. Results. We have found strong evidence for line intensity enhancements due to opacity during active or flare-like activity for all three stars. The O vi 1032/1038 line intensity ratios, predicted to have a value of 2.0 in the optically thin case, are found to be up to ∼30% larger during several orbital phases. Conclusions. Our measurements, combined with radiative transfer models, allow us to constrain both the geometry of the O vi emitting regions in our stellar sources and the orientation of the observer. A spherical emitting plasma can be ruled out, as this would lead to no intensity enhancement. In addition, the theory tells us that the line-of-sight to the plasma must be close to perpendicular to its surface, as observations at small angles to the surface lead to either no intensity enhancement or the usual line intensity decrease over the optically thin value. For the future, we outline a laboratory experiment, that could be undertaken with current facilities, which would provide an unequivocal test of predictions of line intensity enhancement due to opacity, in particular the dependence on plasma geometry.

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Stellar Activity and CMEs: Important Factors of Planetary Evolution

Khodachenko

2014

Solar Prominences

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Opacity in the upper atmosphere of AU Mic

Cited by 20 publications

References 26 publications

Search for indications of stellar mass ejections using FUV spectra

Search for indications of stellar mass ejections using FUV spectra

A search for line intensity enhancements in the far-UV spectra of active late-type stars arising from opacity

Stellar Activity and CMEs: Important Factors of Planetary Evolution

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