On the Influence of Hinode/SOT NFI instrumental effects on the visibility of simulated prominence fine structures in H-alpha

The models, which simulate prominences with their numerous fine structures distributed within the prominence magnetic field, such as the 3D Whole-Prominence Fine Structure (WPFS) models of Gunár and Mackay (2015) and Gunár et al. (2018), use approximate radiative transfer techniques to visualize the simulated prominences. However, to properly understand both large and small-scale morphological features and dynamics of prominences, we need to accurately compare synthetic images of simulated prominences with observations and to precisely analyze the visibility of even the faintest prominence features. To do so, we need to consider how the properties of instruments used for observations would affect the synthetic spectra and images.

In the presented work, we study how synthetic H-alpha spectra of simulated prominences will be influenced by the instrumental effects induced by the Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT) on-board the Hinode satellite. To process the synthetic H-alpha images provided by the 3D WPFS models into SOT-like synthetic H-alpha images, we take into account the effects of the integration over the NFI transmission profile, the stray-light and PSF of Hinode/SOT and the observed noise level. This allows us to compare the visibility of the prominence fine structures in the SOT-like synthetic H-alpha images with the synthetic H-alpha line-centre images used by the 3D models and a pair of Hinode/SOT NFI observations of quiescent prominences.

The comparison between the SOT-like synthetic H-alpha images and the synthetic H-alpha line-centre images shows that all large and small-scale features are very similar in both visualizations and that the same very faint prominence fine structures can be discerned in both. This confirms that the computationally efficient H-alpha line-centre visualization technique can be reliably used for the purpose of visualization of complex 3D prominence models. In addition, the comparison between the SOT-like synthetic images and the observations shows that the 3D WPFS models can reproduce large-scale prominence features rather well. However, the distribution of the prominence fine structures is significantly more diffuse in the observations than in the models. Moreover, the diffuse intensity areas surrounding the observed prominences are also not present in the synthetic images. We also found that the maximum intensities reached in the models are about twice as high as those present in the observations--an indication that the mass-loading assumed in the present 3D WPFS models might be too large.