BEGIN:VCALENDAR VERSION:2.0 PRODID:-//AIP Calendar//www.aip.de// BEGIN:VEVENT SUMMARY:Colloquium: Ekaterina Dineva (AIP) DTSTART:20211104T133000Z DTEND:20211104T143000Z DTSTAMP:20260405T191725Z UID:www.aip.de-1079 CATEGORIES:Scientific CATEGORIES:Generic Event CATEGORIES:Public CONTACT:Silva Järvinen DESCRIPTION:Sun-as-a-Star with PEPSI: Tracing Solar Activity in Strong Chr omospheric Absorption Lines\nThe Potsdam Echelle Polarimetric and Spectros copic Instrument (PEPSI) is a state-of-the-art\, high-resolution spectrogr aph for the Large Binocular Telescope (LBT) at Mt. Graham\, Arizona\, USA. During daytime\, the 11-millimeter aperture binocular Solar Disk-Integrat ed (SDI) telescope feeds PEPSI with disk-unresolved sunlight. This produce s a quasi-continuous daily record of the Sun-as-a-star spectrum in the bro ad wavelength range 3830 – 9140 Å and with a spectral resolution of R ≈ 250 000. The Sun is the only star\, where spectra can be related to su rface structure and magnetic fields. We present high-resolution\, high-fid elity spectra that were recorded with PEPSI/SDI on 184 &\; 82 days in 2 018 &\; 2019 and derive the Ca II H &\; K emission ratio\, i.e.\, th e S-index. In addition\, we compile excess brightness and area indices bas ed on full-disk Ca II K line-core filtergrams of the Chromospheric Telesco pe (ChroTel) at Observatorio del Teide\, Tenerife\, Spain and full-disk UV 1600 Å images of the Atmospheric Imaging Assembly (AIA) on board the Sol ar Dynamics Observatory (SDO). Thus\, Sun-as-a-star spectral indices are r elated to their counterparts derived from resolved images of the solar chr omosphere. Combining these three types of indices provides evidence that t he minimum towards the end of Solar Cycle 24 is very deep and represents t he lowest level of activity recorded with contemporary instruments\, with a strong activity asymmetry between the two hemispheres. Furthermore\, the spectral profiles of the Fraunhofer Na I D doublet at λ5890/5896 Å was observed with PEPSI during the 2017 August 21 total solar eclipse. Sun-as- a-star spectra are mainly affected by limb darkening\, solar differential rotation\, convective motions\, and magnetic activity. During a solar ecli pse\, the contribution from these features is modified by the passage of t he Moon\, thus causing a transit spectrum signature. The temporal evolutio n of the Na I D doublet is analyzed employing contrast profiles which illu strate subtle changes in the line profile. The line bisectors are used to study the height dependent signature of convective motions. These observat ions are compared to synthetic Na I D spectra computed with the state-of-t he-art Bifrost code combined with a geometrically accurate model of the so lar eclipse.\n LOCATION:Colloquium Zoom room END:VEVENT END:VCALENDAR