An Explanation of Remarkable Emission-line Profiles in Post-flare Coronal Rain

Lacatus, D. A.; Judge, P. G.; Donea, Alina-Catalina

doi:10.3847/1538-4357/aa725d

Cited by 32 publications

(36 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To see cool flare loops against the solar disk in absorption in the Hα line, the electron density in the loop should not exceed 10 12 cm −3 (Heinzel & Karlicky (1987)). The same loops, however, can be seen in emission in other lines like MgII h & k (Lacatus et al (2017), Mikuła et al (2017)). At such densities or lower, the loops will not be visible in WL against the disk, but can be detected as faint WL loops high above the limb (Saint-Hilaire et al (2014), Krucker et al (2015)).…”

Section: Visibility Of Loops During Solar Flaressupporting

confidence: 57%

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

Heinzel

Shibata

2018

ApJ

View full text Add to dashboard Cite

Since the discovery of stellar superflares by Kepler satellite, these extremely energetic events have been studied in analogy to solar flares. Their white-light (WL) continuum emission has been interpreted as being produced by heated ribbons. In this paper we compute the WL emission from overlying flare loops depending on their density and temperature and show that, under conditions expected during superflares, the continuum brightening due to extended loop arcades can significantly contribute to stellar flux detected by Kepler. This requires electron densities in the loops 10 12 − 10 13 cm −3 or higher. We show that such densities, exceeding those typically present in solar flare loops, can be reached on M-dwarf and solar-type superflare stars with large starspots and much stronger magnetic fields. Quite importantly, the WL radiation of loops is not very sensitive to their temperature and thus both cool as well as hot loops may contribute. We show that the WL intensity emergent from optically-thin loops is lower than the blackbody radiation from flare ribbons, but the contribution of loops to total stellar flux can be quite important due to their significant emitting areas. This new scenario for interpreting superflare emission suggests that the observed WL flux is due to a mixture of the ribbon and loop radiation and can be even loop-dominated during the gradual phase of superflares.

show abstract

Section: Visibility Of Loops During Solar Flaressupporting

confidence: 57%

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

Heinzel

Shibata

2018

ApJ

View full text Add to dashboard Cite

show abstract

“…Along with the red shift, Lacatus et al (2017) observed broad wings with a Doppler width of ≈100 km s −1 , appearing about six minutes after the impulsive flare phase. Their lines are far broader than the net red shift, which is also true for the majority of our measurements.…”

Section: Red Line Asymmetriesmentioning

confidence: 87%

“…As to line asymmetries, Lacatus et al (2017) presented solar Mg ii H&K line profiles with a striking red asymmetry, observed with the Interface Region Imaging Spectrograph (IRIS) following an X2.1-class flare; the relevant data and fits are shown in their Fig. 2.…”

Section: Red Line Asymmetriesmentioning

confidence: 99%

“…While symmetric line broadening can be caused by the Stark effect or turbulence (Švestka 1972;Kowalski et al 2017b), asymmetric line broadening is sometimes attributed to bulk motion, for example in the form of socalled coronal rain (e.g. Antolin & Rouppe van der Voort 2012; Antolin et al 2015;Lacatus et al 2017) or chromospheric condensations (Ichimoto & Kurokawa 1984;Canfield et al 1990; see also Sect. 6.3).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The CARMENES search for exoplanets around M dwarfs

Fuhrmeister

Czesla

Schmitt

et al. 2018

A&A

View full text Add to dashboard Cite

Stellar activity is ubiquitously encountered in M dwarfs and often characterised by the Hα line. In the most active M dwarfs, Hα is found in emission, sometimes with a complex line profile. Previous studies have reported extended wings and asymmetries in the Hα line during flares. We used a total of 473 high-resolution spectra of 28 active M dwarfs obtained by the CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-Earths with Near-infrared and optical Echelle Spectrographs) spectrograph to study the occurrence of broadened and asymmetric Hα line profiles and their association with flares, and examine possible physical explanations. We detected a total of 41 flares and 67 broad, potentially asymmetric, wings in Hα. The broadened Hα lines display a variety of profiles with symmetric cases and both red and blue asymmetries. Although some of these line profiles are found during flares, the majority are at least not obviously associated with flaring. We propose a mechanism similar to coronal rain or chromospheric downward condensations as a cause for the observed red asymmetries; the symmetric cases may also be caused by Stark broadening. We suggest that blue asymmetries are associated with rising material, and our results are consistent with a prevalence of blue asymmetries during the flare onset. Besides the Hα asymmetries, we find some cases of additional line asymmetries in He I D3, Na I D lines, and the He I line at 10 830 Å taken all simultaneously thanks to the large wavelength coverage of CARMENES. Our study shows that asymmetric Hα lines are a rather common phenomenon in M dwarfs and need to be studied in more detail to obtain a better understanding of the atmospheric dynamics in these objects.

show abstract

“…Foukal 1978) and in flare loops at cool temperatures such as Hα (e.g. Jing et al 2016), He II 304Å (Scullion et al 2016), and IRIS slit-jaw images (Lacatus et al 2017). Jing et al (2016) showed, importantly, that the impact of the rain in the chromosphere followed exactly the same path as the flare ribbon and had the same size scale as the ribbon, demonstrating a tight cause and ef-fect between the energy release and formation of rain.…”

Section: Introductionmentioning

confidence: 97%

Electron Beams Cannot Directly Produce Coronal Rain

Reep

Antolin

Bradshaw

2020

ApJ

View full text Add to dashboard Cite

Coronal rain is ubiquitous in flare loops, forming shortly after the onset of the solar flare. Rain is thought to be caused by a thermal instability, a localized runaway cooling of material in the corona. The models that demonstrate this require extremely long duration heating on the order of the radiative cooling time, localized near the footpoints of the loops. In flares, electron beams are thought to be the primary energy transport mechanism, driving strong footpoint heating during the impulsive phase that causes evaporation, filling and heating flare loops. Electron beams, however, do not act for a long period of time, and even supposing that they did, their heating would not remain localized at the footpoints. With a series of numerical experiments, we show directly that these two issues mean that electron beams are incapable of causing the formation of rain in flare loops. This result suggests that either there is another mechanism acting in flare loops responsible for rain, or that the modeling of the cooling of flare loops is somehow deficient. To adequately describe flares, the standard model must address this issue to account for the presence of coronal rain.

show abstract

An Explanation of Remarkable Emission-line Profiles in Post-flare Coronal Rain

Cited by 32 publications

References 38 publications

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

The CARMENES search for exoplanets around M dwarfs

Electron Beams Cannot Directly Produce Coronal Rain

Contact Info

Product

Resources

About