Sun-as-a-star observations of the 2017 August 21 solar eclipse

Abstract

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution spectrograph for the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. During daytime the instrument is fed with sunlight from the 10-millimeter aperture, fully automated, binocular Solar Disk-Integrated (SDI) telescope. The observed Sun-as-a-star spectra contain a multitude of photospheric and chromospheric spectral lines in the wavelength ranges 4200–4800 Å and 5300–6300 Å. One of the advantages of PEPSI is that solar spectra are recorded in the exactly same manner as nighttime targets. Thus, solar and stellar spectra can be directly compared. PEPSI/SDI recorded 116 Sun-as-a-star spectra during the 2017 August 21 solar eclipse. The observed maximum obscuration was 61.6%. The spectra were taken with a spectral resolution of ≈ 250000 and an exposure time of 0.3 s. The high-spectral resolution facilitates detecting subtle changes in the spectra while the Moon passes the solar disk. Sun-as-a-star spectra are affected by changing contributions due to limb darkening and solar differential rotation, and to a lesser extend by supergranular velocity pattern and the presence of active regions on the solar surface. The goal of this study is to investigate the temporal evolution of the chromospheric Na D doublet during the eclipse and to compare observations with synthetic line profiles computed with the state-of-the-art Bifrost code.

Characterization of chromospheric activity based on Sun-as-a-star spectral and disk-resolved activity indices

“…The SOLIS/ISS observations started in 2006 December and comprise a much longer period than the PEPSI/SDI data. Dineva, Denker, Verma, et al (2020) demonstrated that the core of the Ca ii K-line obtained with PEPSI/SDI is deeper compared to SOLIS/ISS for the same day. This difference in depth affects the intensity-based parameters.…”

Characterization of chromospheric activity based on Sun‐as‐a‐star spectral and disk‐resolved activity indices

“…The SOLIS/ISS observations started in 2006 December and comprise a much longer period than the PEPSI/SDI data. Dineva et al (2020b) demonstrated that the core of the Ca ii K‐line obtained with PEPSI/SDI is deeper compared to SOLIS/ISS for the same day. This difference in depth affects the intensity‐based parameters.…”