Abstract
The Daniel K. Inouye Solar Telescope (DKIST) Visible Spectro-Polarimeter (ViSP) is a traditional slit-scanning spectrograph with the ability to observe solar regions up to a 120times 78~mbox{arcsec}^{2} area. The design implements dual-beam polarimetry, a polychromatic polarization modulator, a high-dispersion echelle grating, and three spectral channels that can be automatically positioned. A defining feature of the instrument is its capability to tune anywhere within the 380 – 900 nm range of the solar spectrum, allowing for a virtually infinite number of combinations of three wavelengths to be observed simultaneously. This enables the ViSP user to pursue well-established spectro-polarimetric studies of the magnetic structure and plasma dynamics of the solar atmosphere, as well as completely novel investigations of the solar spectrum. Within the suite of first-generation instruments at the DKIST, ViSP is the only wavelength-versatile spectro-polarimeter available to the scientific community. It was specifically designed as a discovery instrument to explore new spectroscopic and polarimetric diagnostics and test improved models of polarized line formation through high spatial-, spectral-, and temporal-resolution observations of the Sun’s polarized spectrum. In this instrument article, we describe the science requirements and design drivers of ViSP and present preliminary science data collected during the commissioning of the instrument.
Highlights
The Daniel K. Inouye Solar Telescope (DKIST) positions itself at the forefront of solar science with this suite of instrumentation: spectro-polarimetry is a powerful tool for quantitative diagnostics of the magnetic field in the solar plasma, which is critically important for our understanding of physical processes in the solar atmosphere
Visible Spectro-Polarimeter (ViSP) provides measurements of the full state of polarization simultaneously in up to three wavelength regions within the visible and near-IR solar spectrum with high polarimetric precision and high spectral resolving power. Such measurements provide quantitative diagnostics of the magnetic-field vector as a function of height in the solar atmosphere, along with the associated variation of the thermodynamic properties, which are crucial to addressing many of the DKIST science use cases (Rimmele and the ATST Science Working Group, 2005), such as improving our understanding of solar magnetism and of the trigger mechanisms of solar energetic events that are the main causes of space weather
No spectral diagnostics probing the solar transition region between the chromosphere and the low corona are accessible to ViSP or DKIST, as these all belong to the UV spectrum that lies below the terrestrial atmosphere’s wavelength cutoff
Summary
ViSP is “wavelength versatile”, meaning that it can be set up to observe any wavelength within its spectral range of operation, while simultaneously achieving high spectral, spatial, and temporal resolution It is the only instrument at the DKIST with this capability at this time. Imaging spectro-polarimeters using Fabry–Pérot interferometers have become commonly available at many telescopes, such as the Triple Etalon Solar Spectrometer (Kentischer et al, 1998; Tritschler et al, 2002) at the German Vacuum Tower Telescope (VTT: von der Lühe, 1998), and the CRisp Imaging SpectroPolarimeter (Scharmer et al, 2008) at the Swedish 1-m Solar Telescope (SST: Scharmer et al, 2003) These instruments have the benefit that they simultaneously capture a 2D region of the Sun, but they must scan in wavelength, potentially resulting in spectra that are not temporally coherent. ViSP improves on these instruments in terms of spatial resolution and in its automated configuration of grating and camera-arm angles, significantly reducing setup time while improving repeatability
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