Solar and Stellar Flares and their Effects on Planets Proceedings IAU Symposium No. 320, 2015 A.G. Kosovichev, S.L. Hawley & P. Heinzel, eds. c  International Astronomical Union 2016 doi:10.1017/S1743921316000338 Solar X-rays from 0.3 a.u.: the ChemiX Bragg Spectrometer on Interhelioprobe Janusz Sylwester 1 , Marek Siarkowski, Jaros law Ba – ka la, ˙ Zaneta Szaforz, Miros law Kowali´ nski, Marek Ste – ´slicki, Barbara Sylwester, Zbigniew Kordylewski, Oleksiy Dudnik 2 , Vladimir D. Kuznetsov 3 , Valery Polansky 3 , Sergey Kuzin 4 and Kenneth J. H. Phillips 5 1 Space Research Centre, Polish Academy of Sciences, Wroc law, Poland email: js@cbk.pan.wroc.pl 2 Institute of Radio Astronomy, National Academy of Sciences of Ukraine, Kharkiv, Ukraine email: dudnik@rian.kharkov.ua 3 Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, RAS, Moscow Troitsk, Russia email: kvd@izmiran.ru 4 Laboratory of X-ray Astronomy of the Sun, P. N. Lebedev Physical Institute, RAS, Moscow, Russia email: kuzin@sci.lebedev.ru 5 Dept. of Earth Sciences, Natural History Museum, London SW7 5BD, U.K. email: kennethjhphillips@yahoo.com Abstract. ChemiX is a Bragg crystal spectrometer that will fly on the two Interhelioprobe spacecraft due for launch in 2025 and 2026. The spacecraft perihelion will be only 0.3 a.u. and the orbit inclination up to 30 ◦ , and so instruments on board will have a close view of solar active regions and flares and regions near each solar pole. The ChemiX X-ray spectrometer, built by a consortium of groups led by the Space Research Centre, Polish Academy of Sciences, will fly on each of the spacecraft, and observe X-ray spectra in the 1.5 − 9 ˚ A range. Spectral lines in this range include resonance lines of helium-like and hydrogen-like ions of elements such as Fe, Ca, Ar, S, and Si, with less abundant elements such as K and Cl represented by weaker lines which the high sensitivity of ChemiX should be able to detect. The free–free and free–bound continua should also be detected since instrumental background will be eliminated. Three of the seven channels of ChemiX will be in a “dopplerometer” arrangement by which spatial and spectral shifts present in flare impulsive stages can be disentangled. Keywords. techniques: spectroscopic, Sun: abundances, Sun: corona, Sun: flares, Sun: X-rays, gamma rays 1. Introduction X-ray emission is formed in optically thin multi-million Kelvin solar plasmas such as are present in the quiet Sun, active regions, or flares. X-ray spectral lines are emitted by these plasmas and are due to transitions in highly ionized elements such as Mg, Al, Si, S, Ar, Ca, Fe, and Ni, with weaker line emission due to less abundant elements such as K and Cl. Many of the principal emission lines, which are mainly due to transitions in hydrogen- like and helium-like ions of elements, fall in the spectral range 1.5 − 9 ˚ A. There is also a prominent continuum formed of free–free (bremsstrahlung) and free-bound radiation; free-bound emission depends on the plasma composition, with abundant elements being the most important emitters. 442 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921316000338 Downloaded from https://www.cambridge.org/core. IP address: 54.163.42.124, on 08 Jun 2020 at 04:10:22, subject to the Cambridge Core terms of use, available at