The primary objective of this campaign is to cross calibrate the Fe I 630 nm spectropolarimeters of the Hinode satellite (the SOT/SP) and the Facility IR Spectropolarimeter (FIRS) of the Dunn Solar Telescope (DST) of the National Solar Observatory (NSO), to prepare these two instruments for future coordinated science observations.
Understanding of solar magnetism, from the smallest spatial and the shortest time scale permitted by current telescopes and instruments to the active region and global scale magnetic fields with the solar cycle or longer time scale requires accurate measurement and interpretation of the polarized spectra of magnetically sensitive spectral lines formed at different level of the solar atmosphere. The Facility IR Spectropolarimeter (FIRS, http://kopiko.ifa.hawaii.edu/firs/) is a newly commissioned facility spectropolarimeter for the DST specifically designed for this task. It can simultaneously obtain the full Stokes spectra of the Fe I 630 nm and Fe I 1565 nm lines. A second wavelength combination includes the Fe I 630 nm and He I 1083 nm. It can also operate simultaneously with the IBIS (Interferometric Bidirectional Imaging Spectrometer, Cavallini 2006) instrument observing the Ca II 854 nm line. Additionally, FIRS employees a multiple-slit (four slits) design that enables it to scan the target fields at high cadence. The combination of multipleheight coverage and high temporal resolution capability makes FIRS an ideal instrument for the study of the dynamics of photospheric and chromospheric magnetism.
The multi-wavelength capability of FR IS naturally complement the high-resolution photospheric SOT/SP. Many recent observations, in particular, those obtained by the Hinode SOT/SP instrument have revealed a broad spectrum of small-scale dynamic magnetohydrodynamic (MHD) phenomena. Some of these are considered to be candidates of small-scale magnetic reconnection events and may have important effects on the heating of the upper atmosphere; or, they may drive the dynamics of the chromosphere. Obviously direct observations of the effects of these energetic events at the chromospheric levels will be critical for the understanding of their physical mechanism and can now be provided by FIRS.
While FIRS is capable of diffraction-limited observation at the Fe I 630 nm wavelength with the assistance of the high-order Adaptive Optics (AO) system of the DST, the actual spatial resolution achieved still depends strongly on the atmospheric seeing condition during the time of observaiton, and diffraction-limited performance is not guarranteed all the time. In the infrared wavelength, however, the high-order AO system is capable of providing diffraction-limited performance over a large field of view (FOV). The Hinode SOT/SP therefore is the most critical and most reliable instrument to provide high-resolution data for the study of the dynamics of small-scale magnetic fields. We envision that the Hinode SOT/SP, DST FIRS and IBIS combination will become one of the most powerful instrument for the study of solar magnetism in the near future. |
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