arXiv subjects

R. Kamlah

Publications and source records attributed to R. Kamlah.

3 recordsLinked to original sources

arXiv2026

Prominence signatures in the Fraunhofer G-band; Testing ionization memory with multi-line prominence diagnostics

The Fraunhofer G-band around 4304 {\AA} is widely used as a photospheric diagnostic and is generally not expected to show signatures of chromospheric or coronal structures. However, recent amateur observations have suggested the presence of off-limb prominence emission in this spectral region. We investigate the origin of the prominence emission in the G-band to determine if this is caused by methylene (CH) or other lines in this band. We also aim to test these lines for the presence of ionization memory effects in neutral lines. We present a case study of two prominences, one obtained with a Solar Explorer (Sol'Ex) spectroheliograph and another with the high-resolution Fast Multi-Line Universal Spectrograph (FaMuLUS) camera system at the echelle spectrograph of the German Vacuum Tower Telescope (VTT). Line widths are measured for simultaneously observed neutral and ionized metal lines, allowing a comparison of thermal and non-thermal broadening components to see if these lines exhibit any ionization memory effects. We report clear prominence emission in several metal lines within the G-band, primarily from Ti II and Ca I lines, while contributions from CH molecular lines are not observed. A comparison of the simultaneously observed ionized and neutral lines reveals no clear evidence for an ionization memory effect. Since the prominence emission does not originate from CH lines, we will not call them "G-band prominences" but rather prominences in the G-band, as they are independent of the primary diagnostic in this spectral window. In addition, the absence of a clear ionization memory effect suggests that such effects may be less pronounced for weak neutral lines.

astro-ph.SR↗

arXiv2025

On the center-to-limb variations of the He I 10 830 \AA\ triplet

We present high-resolution spectroscopic observations of the quiet-Sun center-to-limb variations (CLV) of the He I triplet at 10 830 {\AA} and the nearby Si I 10 827 {\AA} line, observed with GREGOR Infrared Spectrograph (GRIS) and the improved High-resolution Fast Imager (HiFI+). The observations cover the interval $\mu = [0.1,\, 1.0]$, where $\mu$ is the cosine of the heliocentric angle. At each $\mu$-position, the spectra are spatially averaged over 0.02 $\mu$, and the resulting CLVs are given both as these averaged data points and as smooth polynomial curves fitted across each wavelength point. The He I spectra were inverted using the HAnle and ZEeman Light (HAZEL) code, showing an increase in optical depth towards the limb and a reversed convective blueshift for the red component, while the blue component was entirely absent. In addition, we find a strong increase in the steepness of the He I CLV compared to that of the nearby continuum. The Si I showed a behavior more typical of photospheric lines, namely shallower CLV, a reduction in width and depth, and a more typical convective blueshift.

astro-ph.SR↗

arXiv2023

A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N: Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection

Stellar flares cannot be spatially resolved, which complicates ascertaining the physical processes behind particular spectral signatures. Due to their proximity to Earth, solar flares can serve as a stepping stone for understanding their stellar counterparts, especially when using a Sun-as-a-star instrument and in combination with spatially resolved observations. We aim to understand the disk-integrated spectral behaviors of a confined X2.2 solar flare and its eruptive X9.3 successor as measured by HARPS-N. The behavior of multiple photospheric and chromospheric spectral lines are investigated by means of activity indices and contrast profiles. A number of different photospheric lines were also investigated by means of equivalent widths, and radial velocity measures, which are then related to physical processes directly observed in high-resolution observations made with the Swedish 1-meter Solar Telescope and SDO Our findings suggest a relationship between the evolving shapes of contrast profile time and the flare locations, which assists in constraining flare locations in disk-integrated observations. In addition, an upward bias was found in flare statistics based on activity indices derived from the Ca II H & K lines. In this case, much smaller flares cause a similar increase in the activity index as that produced by larger flares. H$\alpha$-based activity indices do not show this bias and are therefore less susceptible to activity jitter. Sodium line profiles show a strongly asymmetric response during flare activity, which is best captured with a newly defined asymmetrical sodium activity index. A strong flare response was detected in Mn I line profiles, which is unexpected and calls for further exploration. Intensity increases in H$\alpha$, H$\beta$, and certain spectral windows of AIA before the flare onset suggest their potential use as short-term flare predictors.

astro-ph.SR↗