High-resolution Observations of Hα Spectra with a Subtractive Double Pass

• Published in: Solar physics Vol. 293; no. 2; pp. 1 - 24
• Main Authors: Beck, C., Rezaei, R., Choudhary, D. P., Gosain, S., Tritschler, A., Louis, R. E.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.02.2018; Springer Nature B.V
• Subjects: Adaptive systems; Astrophysics and Astroparticles; Atmospheric Sciences; Construction costs; Field of view; Filaments; H alpha line; High resolution; Image resolution; Interferometers; Multi-conjugate adaptive optics; Opacity; Optics; Physics; Physics and Astronomy; Polarity; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Space telescopes; Spatial resolution; Spectra; Spectral resolution; Spectroscopy; Spectrum analysis; Telescopes; Techniques: spectroscopic; Line: profiles; Sun: chromosphere
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-018-1252-2

High-resolution imaging spectroscopy in solar physics has relied on Fabry–Pérot interferometers (FPIs) in recent years. FPI systems, however, become technically challenging and expensive for telescopes larger than the 1 m class. A conventional slit spectrograph with a diffraction-limited performance over a large field of view (FOV) can be built at much lower cost and effort. It can be converted into an imaging spectro(polari)meter using the concept of a subtractive double pass (SDP). We demonstrate that an SDP system can reach a similar performance as FPI-based systems with a high spatial and moderate spectral resolution across a FOV of 100 ″ × 100 ″ with a spectral coverage of 1 nm. We use H α spectra taken with an SDP system at the Dunn Solar Telescope and complementary full-disc data to infer the properties of small-scale superpenumbral filaments. We find that the majority of all filaments end in patches of opposite-polarity fields. The internal fine-structure in the line-core intensity of H α at spatial scales of about 0 . ″ 5 exceeds that in other parameters such as the line width, indicating small-scale opacity effects in a larger-scale structure with common properties. We conclude that SDP systems in combination with (multi-conjugate) adaptive optics are a valid alternative to FPI systems when high spatial resolution and a large FOV are required. They can also reach a cadence that is comparable to that of FPI systems, while providing a much larger spectral range and a simultaneous multi-line capability.