Letter to the Editor

The first coronal mass ejection observed in both visible-light and UV H I Ly-α channels of the Metis coronagraph on board Solar Orbiter^⋆

¹ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
e-mail: vincenzo.andretta@inaf.it
² INAF – Osservatorio Astrofisico di Torino, Turin, Italy
³ Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
⁴ INAF – Osservatorio Astronomico di Trieste, Trieste, Italy
⁵ Royal Observatory of Belgium, Brussels, Belgium
⁶ Institute of Geodynamics of the Romanian Academy, Bucharest, Romania
⁷ Università di Padova – Dip. Fisica e Astronomia “Galileo Galilei”, Padua, Italy
⁸ CNR – Istituto di Fotonica e Nanotecnologie, Padua, Italy
⁹ INAF – Associate Scientist, Italy
¹⁰ Università di Firenze – Dip. Fisica e Astronomia, Florence, Italy
¹¹ INAF – Osservatorio Astrofisico di Catania, Catania, Italy
¹² KU Leuven, Leuven, Belgium
¹³ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan, Italy
¹⁴ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, Orsay, France
¹⁵ University of Wrocław – Astronomical Institute, Poland
¹⁶ Università di Catania – Dip. Fisica e Astronomia “Ettore Majorana”, Catania, Italy
¹⁷ Università di Padova – CISAS, Padua, Italy
¹⁸ Catholic University of America, Washington, DC, USA
¹⁹ Università di Urbino “Carlo Bo” – DiSPeA, Urbino, Italy
²⁰ INFN – Sez. Firenze, Florence, Italy
²¹ Astronomical Institute of the Czech Academy of Sciences, Ondřejov, Czech Republic
²² Università di Torino, Turin, Italy
²³ Politecnico di Torino – DET, Turin, Italy
²⁴ NASA HQ, Washington, DC, USA
²⁵ CNR – IEIIT, Padua, Italy
²⁶ Agenzia Spaziale Italiana, Roma, Italy
²⁷ INAF – Istituto di Astrofisica e Planetologia Spaziali di Roma, Rome, Italy
²⁸ INAF – Osservatorio Astronomico di Palermo, Palermo, Italy
²⁹ Laboratoire Atmosphères, Milieux et Observations Spatiales, Guyancourt, France
³⁰ Università di Pavia, Pavia, Italy
³¹ Università di Padova, Padua, Italy
³² Università della Calabria – Dip, Fisica, Italy
³³ Università di Palermo – Dip. Fisica e Chimica “Emilio Segrè”, Palermo, Italy
³⁴ Naval Research Laboratory, Washington, DC, USA
³⁵ University of Athens, Dep. Physics, Athens, Greece
³⁶ University of California, Los Angeles, California, USA

Received: 11 October 2021
Accepted: 28 October 2021

Abstract

Context. The Metis coronagraph on board Solar Orbiter offers a new view of coronal mass ejections (CMEs), observing them for the first time with simultaneous images acquired with a broad-band filter in the visible-light interval and with a narrow-band filter around the H I Ly-α line at 121.567 nm, the so-called Metis UV channel.

Aims. We show the first Metis observations of a CME, obtained on 16 and 17 January 2021. The event was also observed by the EUI/FSI imager on board Solar Orbiter, as well as by other space-based coronagraphs, such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here with Metis data.

Methods. Different images are analysed here to reconstruct the 3D orientation of the expanding CME flux rope using the graduated cylindrical shell model. This also allows us to identify the possible location of the source region. Measurements of the CME kinematics allow us to quantify the expected Doppler dimming in the Ly-α channel.

Results. Observations show that most CME features seen in the visible-light images are also seen in the Ly-α images, although some features in the latter channel appear more structured than their visible-light counterparts. We estimated the expansion velocity of this event to be below 140 km s⁻¹. Hence, these observations can be understood by assuming that Doppler dimming effects do not strongly reduce the Ly-α emission from the CME. These velocities are comparable with or smaller than the radial velocities inferred from the same data in a similar coronal structure on the east side of the Sun.

Conclusions. The first observations by Metis of a CME demonstrate the capability of the instrument to provide valuable and novel information on the structure and dynamics of these coronal events. Considering also its diagnostics capabilities regarding the conditions of the ambient corona, Metis promises to significantly advance our knowledge of such phenomena.