Negative flare in the He i 10830 Å line in facula

Abstract

A small-scale flare SOL2012-09-21T02:19 (B2) occurred in a spotless active region that we observed at a groundbased telescope equipped with a spectrograph. During the flare, we registered an increase in absorption in the He i 10830Å line by 25%, while other chromospheric and coronal spectral lines demonstrated increase in brightness at the same location. This phenomenon called negative flare had rarely been observed at the Sun before. In this paper, we describe the morphology of this flare and investigate its dynamics based on our spectral observations and space imaging data. The Hα and He i 10830Å lines reach their extreme intensities 5 and 6 minutes after the 171Å line. The brightening first occurred in the 171Å and 193Å Solar Dynamics Observatory (SDO) channels followed by the 94Å, 304Å, and 1600Å signals ∼2 minutes after (for the maximum phases). However, the abrupt changes in line-of-sight (LOS) velocities in the chromospheric lines occur simultaneously with the intensity changes in the 304Å and 1600Å lines: we observed a downward motion that was followed by two upward motions. The measured horizontal speed of the perturbation propagation was close to 70 km s −1 both in the chromospheric and coronal lines.We assume that we observed the photoionization-recombination process caused by UV radiation from the transition region during the coronal flare. With this, we point out the difficulties in interpreting the time lag between the emission maximum in the SDO UV channels and the second absorption maximum in the He i 10830Å line.

Oscillations Accompanying a He i 10830 Å Negative Flare in a Solar Facula

“…Earlier, Botha et al (2011) emphasized and important role of the chromosphere resonator in the three-minute oscillation formation. As Kobanov et al (2018) noted, a series of impulse movements (up to 10-12 km s −1 ) followed the studied flare. In the 02:15-02:30 interval, the 3-minute oscillation period slightly increases over time, which agrees with Kwak et al (2016).…”

“…In this paper, we study the characteristics of photospheric and chromospheric oscillations within an iso-lated facular region, where a small-scale flare occurred during the observations. Due to an anomalous (up to 25%) absorption increase in the He i 10830Å line, we identified this flare as a negative flare (Kobanov et al 2018). Such solar events are rarely observed (Henoux et al 1990;Xu et al 2016), and a study of oscillation processes related to this flare, which is the aim of the paper, is of great interest.…”

The CARMENES search for exoplanets around M dwarfs

“…A more detailed picture is obtainable from solar data, where spatially-resolved flare observations by Kobanov et al (2018) can be interpreted in terms of the PR process. In particular, the He I IR line was strengthened in terms of absorption, while other chromospheric and coronal lines brightened.…”

Multi-Passband Observations of A Solar Flare over the He I 10830 Å line

“…The helium triplet around 10830 Å are among the most important diagnostics of the chromosphere. Flare observations using He I 10830 Å line started several decades ago (Harvey & Recely 1984), however, there have not been many events observed with this line since then (You & Oertel 1992;Penn & Kuhn 1995;Li et al 2006;Zeng et al 2014;Xu et al 2016;Kobanov et al 2018). Most of the reported flares show emission similar to the observations in other chromospheric wavelengths, such as Hα.…”