Giunta, A. ; Grundy, T. ; Andretta, V. ; Auchère, F. ; Buchlin, É. ; Peter, H. ; Berghmans, D. ; Carlsson, M. ; Fludra, A. ; Harra, L. ; Hassler, D. ; Long, D.M. ; Rochus, P. ; Schühle, U. ; Aznar Cuadrado, R. ; Caldwell, M. ; Caminade, S. ; DeForest, C. ; De Groof, A. ; Fredvik, T. ; Gissot, S. ; Heerlein, K. ; Janvier, M. ; Kraaikamp, E. ; Kucera, T. A. ; Müller, D. ; Parenti, S. ; Schmutz, W. ; Sidher, S. ; Smith, P.J. ; Stegen, K. ; Thompson, W.T. ; Verbeeck, C. ; Walsh, A.P. ; Watson, C.J. ; Williams, D. ; Young, P.

Poster presented at Solar Orbiter 8, Belfast on 2022-09-12

Abstract: Stars with known and stable vacuum ultraviolet spectral irradiances can be used to verify and monitor the radiometric calibration of instruments operating in space. In particular, stars from early spectral types are the best candidates for calibration and characterization of instruments operating above 92 nm (below which radiation is absorbed by interstellar hydrogen). Since the beginning of the cruise phase, Solar Orbiter has made dedicated observing campaigns where the spacecraft points to the solar limb to allow some of the high- resolution instruments to observe the ingress and/or the egress of the target star occultation by the solar disk. The stars are chosen because their luminosity and early spectral type ensure high and stable flux at wavelengths between 100 nm and 122 nm, a range observed by the High Resolution EUI Lyman-α telescope (HRILYA) and by the long wavelength (LW) channel of the SPICE spectrometer. At the time of writing, three such campaigns have been conducted targeting α Leo on June 16th 2020, θ Oph on March 27th 2021 and ω Sco on June 12th 2022. We took images and spectra of each of these stars to determine the radiometric response of the instruments by comparing the observed counts to measured reference fluxes and to measure the instruments' spatial point spread function (PSF) by measuring the spatial profile of the image produced by the star. For SPICE-LW we obtained a first assessment of the radiometric calibration factor and an estimate of the width of the spatial PSF. For HRILYA it has been so far not possible to detect the stars which helps providing a lower limit to its spatial PSF. These campaigns are the first of several that will be carried-out during the Solar Orbiter mission phases.

Keyword(s): Solar Orbiter ; EUI
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