Solar magnetism eXplorer (SolmeX)

Abstract

The magnetic field plays a pivotal role in many fields of Astrophysics. This is especially true for the physics of the solar atmosphere. Measuring the magnetic field in the upper solar atmosphere is crucial to understand the nature of the underlying physical processes that drive the violent dynamics of the solar coronathat can also affect life on Earth.SolmeX, a fully equipped solar space observatory for remote-sensing observations, will provide the first comprehensive measurements of the strength and direction of the magnetic field in the upper solar atmosphere. The mission consists of two spacecraft, one carrying the instruments, and another one in formation flight at a distance of about 200 m carrying the occulter to provide an artificial total solar eclipse. This will ensure high-quality coronagraphic observations above the solar limb SolmeX integrates two spectro-polarimetric coronagraphs for off-limb observations, one in the EUV and one in the IR, and three instruments for observations on the disk. The latter comprises one imaging polarimeter in the EUV for coronal studies, a spectro-polarimeter in the EUV to investigate the low corona, and an imaging spectro-polarimeter in the UV for chromospheric studies.SOHO and other existing missions have investigated the emission of the upper atmosphere in detail (not considering polarization), and as this will be the case also for missions planned for the near future. Therefore it is timely that SolmeX provides the final piece of the observational quest by measuring the magnetic field in the upper atmosphere through polarimetric observations.

Testing spectropolarimetry in the extreme ultraviolet to infer the solar coronal magnetic field

“…A spectropolarimetric measurement using Zeeman magnetometry by Lin et al (2004) found a LOS coronal magnetic field at 1.1 R above an active region to have a flux density of about 4 G. This value is very much in line with many other estimates shown in Fig. 5 of Peter et al (2012), and we therefore do not expect the flux density to be more than at most two or three times the nominal values given by our coronal model, i.e., 10 G. We note, however, that the only way of reproducing the full range of measurements plus uncertainties found by SUMER/SOHO, is by increasing the flux to the values cited in the previous paragraph.…”

Neutral Hydrogen and Its Emission Lines in the Solar Corona

“…The ratio Lβ/Lα is about 10 −3 as in Labrosse, Li, and Li (2006) at 3 R ⊙ but it is about 10 −1 instead of 10 −2 in Labrosse, Li, and Li (2006) for 1 R ⊙ . With the quiet-Sun (Allen) model, the Lβ/Lα ratio is lower than 10 −1 at 1 R ⊙ and 2 × 10 −3 at 2.5 R ⊙ , which means that polarization measurements in the Lβ line (Peter et al, 2012) will face serious difficulties because of the low signal-to-noise ratio. Third, as far as the Hα intensity is concerned, Figures 5 and 6 provide a useful information on the proper line emission (lower than the Lβ line by a factor eight).…”

Prospects of Solar Magnetometry—From Ground and in Space

“…Lyman alpha polarimeters have been proposed twice as strawman instruments for ESA missions, first for the COMPASS mission proposed in response to the call for the M2 slot (Fineschi et al 2007), later as part of the SOLMEX mission proposed in 2008 in response to ESAs M3 call (Peter et al 2012). It is obvious that -given the explorative character of such an instrument -a demonstration of the principle including the successful interpretation of the harvested data is mandatory.…”