Particle monitoring capability of the Solar Orbiter Metis coronagraph through the increasing phase of solar cycle 25

¹ DiSPeA, University of Urbino Carlo Bo, Via S. Chiara 27, 61029 Urbino (PU), Italy
e-mail: catia.grimani@uniurb.it
² INFN, Via Bruno Rossi 1, 50019 Sesto Fiorentino, Florence, Italy
³ INAF - Astronomical Observatory of Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
⁴ INAF - Astrophysical Observatory of Turin, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
⁵ CNR - IFN, Via Trasea 7, 35131 Padova, Italy
⁶ CISAS, Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”, via Venezia 15, 35131 Padova, Italy
⁷ Solar-Terrestrial Centre of Excellence - SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, 1180 Brussels, Belgium
⁸ INAF - Astrophysical Observatory of Trieste, Via Giambattista Tiepolo 11, 34149 Trieste, Italy
⁹ Dip. di Fisica e Astronomia “Galileo Galilei”, Universitá di Padova, Via G. Marzolo, 8, 35131 Padova, Italy
¹⁰ Politecnico di Milano, Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
¹¹ European Space Agency, ESAC, Camino Bajo del Castillo s/n, Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
¹² ASI - Italian Space Agency, Via del Politecnico snc, 00133 Rome, Italy
¹³ University of Florence, Physics and Astronomy Department, Largo E. Fermi 2, 50125 Florence, Italy
¹⁴ INAF - Arcetri Astrophysical Observatory, Largo Enrico Fermi 5, 50125 Florence, Italy
¹⁵ INAF - Catania Astrophysical Observatory, Via Santa Sofia 78, 95123 Catania, Italy
¹⁶ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
¹⁷ National Institute for Astrophysics, Institute of Space Astrophysics and Cosmic Physics of Milan, Via Alfonso Corti 12, 20133 Milano, Italy

Received: 17 April 2023
Accepted: 10 July 2023

Abstract

Context. Galactic cosmic rays (GCRs) and solar particles with energies greater than tens of MeV penetrate spacecraft and instruments hosted aboard space missions. The Solar Orbiter Metis coronagraph is aimed at observing the solar corona in both visible (VL) and ultraviolet (UV) light. Particle tracks are observed in the Metis images of the corona. An algorithm has been implemented in the Metis processing electronics to detect the VL image pixels crossed by cosmic rays. This algorithm was initially enabled for the VL instrument only, since the process of separating the particle tracks in the UV images has proven to be very challenging.

Aims. We study the impact of the overall bulk of particles of galactic and solar origin on the Metis coronagraph images. We discuss the effects of the increasing solar activity after the Solar Orbiter mission launch on the secondary particle production in the spacecraft.

Methods. We compared Monte Carlo simulations of GCRs crossing or interacting in the Metis VL CMOS sensor to observations gathered in 2020 and 2022. We also evaluated the impact of solar energetic particle events of different intensities on the Metis images.

Results. The study of the role of abundant and rare cosmic rays in firing pixels in the Metis VL images of the corona allows us to estimate the efficiency of the algorithm applied for cosmic-ray track removal from the images and to demonstrate that the instrument performance had remained unchanged during the first two years of the Solar Orbiter operations. The outcome of this work can be used to estimate the Solar Orbiter instrument’s deep charging and the order of magnitude for energetic particles crossing the images of Metis and other instruments such as STIX and EUI.