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First light observations of the solar wind in the outer corona with the Metis coronagraph

Marco Romoli 1, 2, * E. Antonucci 2 V. Andretta 3 G. Capuano 4, 5 V. da Deppo 2, 6 Y. de Leo 4, 7 C. Downs 8 S. Fineschi 9 P. Heinzel 10 F. Landini 9 A. Liberatore 9, 11 G. Naletto 2, 6, 12 G. Nicolini 9 M. Pancrazzi 9 C. Sasso 3 D. Spadaro 5 R. Susino 9 D. Telloni 9 L. Teriaca 7 M. Uslenghi 13 Y.-M. Wang 14 A. Bemporad 9 G. Capobianco 9 M. Casti 2, 15 M. Fabi 16 F. Frassati 9 F. Frassetto 2, 6 S. Giordano 9 C. Grimani 16 G. Jerse 17 E. Magli 18 G. Massone 9 M. Messerotti 17 D. Moses 19 M.-G. Pelizzo 20 P. Romano 5 U. Schühle 7 A. Slemer 6 M. Stangalini 2, 21 T. Straus 3 C. Volpicelli 9 L. Zangrilli 9 P. Zuppella 2, 6 L. Abbo 2 F. Auchère 22 R. Aznar Cuadrado 7 A. Berlicki 10, 23 R. Bruno 24 A. Ciaravella 25 R. D’amicis 24 Philippe Lamy 26 A. Lanzafame 2, 4 A. Malvezzi 27 P. Nicolosi 12 G. Nisticò 28 H. Peter 7 C. Plainaki 2, 21 L. Poletto 6 F. Reale 2, 29 S. Solanki 7 L. Strachan 14 G. Tondello 12 K. Tsinganos 30 M. Velli 31 R. Ventura 5 Jean-Claude Vial 22 J. Woch 7 G. Zimbardo 2, 28 
* Corresponding author
20 IEIIT-CNR - Institute of Electronics, Computer and Telecommunication Engineering
Polito - Politecnico di Torino = Polytechnic of Turin , CNR - Consiglio Nazionale delle Ricerche [Torino]
26 HELIOS - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : In this work, we present an investigation of the wind in the solar corona that has been initiated by observations of the resonantly scattered ultraviolet emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations that were performed during solar activity cycle 23 by simultaneously imaging the polarized visible light and the H I Lyman- α corona in order to obtain high spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, taken on May 15, 2020, provide the first H I Lyman- α images of the extended corona and the first instantaneous map of the speed of the coronal plasma outflows during the minimum of solar activity and allow us to identify the layer where the slow wind flow is observed. The polarized visible light (580–640 nm) and the ultraviolet H I Ly α (121.6 nm) coronal emissions, obtained with the two Metis channels, were combined in order to measure the dimming of the UV emission relative to a static corona. This effect is caused by the outward motion of the coronal plasma along the direction of incidence of the chromospheric photons on the coronal neutral hydrogen. The plasma outflow velocity was then derived as a function of the measured Doppler dimming. The static corona UV emission was simulated on the basis of the plasma electron density inferred from the polarized visible light. This study leads to the identification, in the velocity maps of the solar corona, of the high-density layer about ±10° wide, centered on the extension of a quiet equatorial streamer present at the east limb – the coronal origin of the heliospheric current sheet – where the slowest wind flows at about 160 ± 18 km s −1 from 4 R ⊙ to 6 R ⊙ . Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona.
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Submitted on : Sunday, December 19, 2021 - 2:12:03 PM
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Marco Romoli, E. Antonucci, V. Andretta, G. Capuano, V. da Deppo, et al.. First light observations of the solar wind in the outer corona with the Metis coronagraph. Astronomy and Astrophysics - A&A, EDP Sciences, 2021, 656 (December), A32 (9 pp). ⟨10.1051/0004-6361/202140980⟩. ⟨insu-03494483⟩

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