学术文献库

We present a photometrically accurate restitution of the K and F coronae from white-light images obtained over 24 Years [1996--2019] by the Large-Angle Spectrometric COronagraph "LASCO-C2" onboard the Solar and Heliospheric Observatory (SOHO). The procedure starts with the data set coming from the polarimetric separation of images of 512 x 512 pixels in which the F-corona and the instrumental stray light are entangled. Disentangling these components proceeds in three stages, each composed of several steps. Stage 1 establishes the distinct variations of the radiance of these components with the Sun--SOHO distance and generate a new data set of median images calculated for each Carrington rotation. Stage 2 achieves the restitution of a set of 36 stray light images reflecting its temporal variation and the periodic rolls of SOHO which started in 2003. Stage 3 achieves the restitution of the F-corona and a time series of daily images is generated. These results allowed us processing the whole set of routine LASCO-C2 images of 1024 x 1024 pixels (approximately 626000 images) and producing calibrated, high resolution images of the K-corona. We extend our past conclusions that the temporal variation of the integrated radiance of the K-corona tracks the solar activity over two solar cycles 23 and 24 and that it is highly correlated with the temporal variation of the total magnetic field. The behaviours of the integrated radiance during the last few years of the declining phases of solar cycles 23 and 24 are remarkably similar, reaching the same floor level and leading to a duration of 11.0 year for the latter cycle, in agreement with the sunspot determination.