Prominence signatures in the Fraunhofer G-band

Testing ionization memory with multi-line prominence diagnostics

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
² Independent Researcher, Cluj-Napoca, Romania
³ Universität Potsdam, Institut für Physik und Astronomie, Karl-Liebknecht-Straße 24/25, 14476 Potsdam, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 6 February 2026
Accepted: 12 April 2026

Abstract

Context. The Fraunhofer G-band around 4304 Å 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.

Aims. We investigated the origin of the prominence emission in the G-band to determine whether this is caused by methylene (CH) or other lines in this band. We also tested these lines for the presence of ionization memory effects in neutral lines.

Methods. We present a case study of two prominences, one obtained with a Solar Explorer (Sol’Ex) spectroheliograph, and the other with the high-resolution Fast Multi-Line Universal Spectrograph (FaMuLUS) camera system at the echelle spectrograph of the German Vacuum Tower Telescope (VTT). The line widths were measured for simultaneously observed neutral and ionized metal lines, allowing a comparison of thermal and nonthermal broadening components to determine whether these lines exhibit any ionization memory effects.

Results. 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 revealed no clear evidence of an ionization memory effect.

Conclusions. Since the prominence emission does not originate from CH lines, we do not call them G-band prominences, but 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 these effects may be less pronounced for weak neutral lines.