摘要：Of the two solar lines, K ID1andD2, almost all attention so far has been devoted to theD1line, asD2is severely affected by an O2atmospheric band. This, however, makes the latter appealing for balloon and space observations from above (most of) the Earth’s atmosphere. We estimate the residual effect of the O2band on the K ID2line at altitudes typical for stratospheric balloons. Our aim is to study the feasibility of observing the 770 nm window. Specifically, this paper serves as a preparation for the third flight of the Sunrise balloon-borne observatory. The results indicate that the absorption by O2is still present, albeit much weaker, at the expected balloon altitude. We applied the obtained O2transmittance to K ID2synthetic polarimetric spectra and found that in the absence of line-of-sight motions, the residual O2has a negligible effect on the K ID2line. On the other hand, for Doppler-shifted K ID2data, the residual O2might alter the shape of the Stokes profiles. However, the residual O2absorption is sufficiently weak at stratospheric levels that it can be divided out if appropriate measurements are made, something that is impossible at ground level. Therefore, for the first time with Sunrise III, we will be able to perform polarimetric observations of the K ID2line and, consequently, we will have improved access to the thermodynamics and magnetic properties of the upper photosphere from observations of the K Ilines.
关键词：Key wordsenSun: magnetic fieldstechniques: polarimetricatmospheric effectsballoons
