First light observations of the solar wind in the outer corona with the Metis coronagraph
Abstract
The investigation of the wind in the solar corona initiated with the observations of the resonantly scattered UV emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying the Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations, performed during solar activity cycle 23, by simultaneously imaging the polarized visible light and the HI Ly-alpha corona in order to obtain high-spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, on May 15, 2020, provide the first HI Ly-alpha 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 UV HI Ly-alpha (121.6 nm) coronal emissions, obtained with the two Metis channels, are 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 is then derived as a function of the measured Doppler dimming. The static corona UV emission is 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 deg wide, centered on the extension of a quiet equatorial streamer present at the East limb where the slowest wind flows at about (160 +/- 18) km/s from 4 Rs to 6 Rs. Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona.
Keywords
Cite
@article{arxiv.2106.13344,
title = {First light observations of the solar wind in the outer corona with the Metis coronagraph},
author = {M. Romoli and E. Antonucci and V. Andretta and G. E. Capuano and V. Da Deppo and Y. De Leo and C. Downs and S. Fineschi and P. Heinzel and F. Landini and A. Liberatore and G. Naletto and G. Nicolini and M. Pancrazzi and C. Sasso and D. Spadaro and R. Susino and D. Telloni and L. Teriaca and M. Uslenghi and Y. M. Wang and A. Bemporad and G. Capobianco and M. Casti and M. Fabi and F. Frassati and F. Frassetto and S. Giordano and C. Grimani and G. Jerse and E. Magli and G. Massone and M. Messerotti and D. Moses and M. G. Pelizzo and P. Romano and U. Schühle and A. Slemer and M. Stangalini and T. Straus and C. A. Volpicelli and L. Zangrilli and P. Zuppella and L. Abbo and F. Auchére and R. Aznar Cuadrado and A. Berlicki and R. Bruno and A. Ciaravella and R. D'Amicis and P. Lamy and A. Lanzafame and A. M. Malvezzi and P. Nicolosi and G. Nisticò and H. Peter and C. Plainaki and L. Poletto and F. Reale and S. K. Solanki and L. Strachan and G. Tondello and K. Tsinganos and M. Velli and R. Ventura and J. C. Vial and J. Woch and G. Zimbardo},
journal= {arXiv preprint arXiv:2106.13344},
year = {2021}
}