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)

1 UniFI - Università degli Studi di Firenze = University of Florence = Université de Florence
2 INAF - Istituto Nazionale di Astrofisica
3 OAC - INAF - Osservatorio Astronomico di Capodimonte
4 Unict - Università degli studi di Catania = University of Catania
5 OACT - INAF - Osservatorio Astrofisico di Catania
6 IFN - CNR Istituto di Fotonica e Nanotecnologie [Padova]
7 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
8 Predictive Sciences Inc.
9 OATo - INAF - Osservatorio Astrofisico di Torino
10 ASU / CAS - Astronomical Institute of the Czech Academy of Sciences
11 UNITO - Università degli studi di Torino = University of Turin
12 Unipd - Università degli Studi di Padova = University of Padua
13 IASF-MI - Istituto di Astrofisica Spaziale e Fisica Cosmica - Milano
14 NRL - Naval Research Laboratory
15 Catholic University of America
16 Università degli Studi di Urbino 'Carlo Bo'
17 Università degli studi di Trieste = University of Trieste
18 Polito - Politecnico di Torino = Polytechnic of Turin
19 NASA Headquarters
20 CNR | IEIIT - CNR Institute of Electronics, Computer and Telecommunication Engineering [Torino]
21 ASI - Agenzia Spaziale Italiana
22 IAS - Institut d'astrophysique spatiale
23 Astronomical Institute [Wroclaw]
24 IAPS - Istituto di Astrofisica e Planetologia Spaziali - INAF
25 OAPa - INAF - Osservatorio Astronomico di Palermo
26 HELIOS - LATMOS
27 UNIPV - Università degli Studi di Pavia = University of Pavia
28 Unical - Università della Calabria [Arcavacata di Rende]
29 Università degli studi di Palermo - University of Palermo
30 NKUA - National and Kapodistrian University of Athens
31 UCLA - University of California [Los Angeles]

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.

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]

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, 2021, 656 (December), A32 (9 pp). ⟨10.1051/0004-6361/202140980⟩. ⟨insu-03494483⟩