Broadband Low-Resolution Spectrograph - SpectrumMate LR

TL;DR

By addressing barriers of cost and complexity, the paper presents SpectrumMate LR, a broadband, low-resolution spectrograph for small telescopes that covers $3400$–$7000$ Å with practical resolving power. The approach combines a $300$ grooves/mm grating, $80$ mm collimator and objective lenses, achromatic doublets, and a largely modular, 3D-printed mechanical design to achieve compact, affordable spectroscopy. Validation includes star spectral typing across O–M and Wolf-Rayet classes, Wien's law temperature tests on incandescent sources, and optical-filter transmission checks (g'r'i'z' bands), showing the instrument can classify stars, estimate source temperatures, and test filters with sufficient accuracy for education and citizen science. The results indicate that practical performance is slightly below theory due to minor misalignments and manufacturing variances, but the device remains a capable, accessible tool to broaden participation in astronomy.

Abstract

This paper presents the development and application of SpectrumMate LR, a broadband, low-resolution spectrograph for small telescope use. SpectrumMate LR is designed to offer affordable, accessible spectroscopic capabilities for amateur astronomers and educators, inspired by the need for versatile instruments in amateur and educational settings. Utilising a 300 grooves/mm grating, 80 mm collimator and objective lenses, SpectrumMate LR is optimised to perform analyses across the visible spectrum, enabling users to classify stars by spectral type, measure stellar temperatures, and test filter transmission ranges. Tests demonstrate SpectrumMate LR's ability to capture accurate spectral data, validating its efficacy in observing both celestial and terrestrial light sources. This instrument fills a niche for cost-effective spectroscopy, empowering a broader audience to engage in detailed observational astronomy.

Figures (13)

• Figure 1: SpectrumMate LR optical system. Compared to SpectrumMate, the lenses and the grating are the main differences.
• Figure 2: Grating geometry by palmerdiff.
• Figure 3: 3D model of SpectrumMate LR.
• Figure 4: SpectrumMate LR equipped with accessories. (1) is a guiding camera, that allows the user to see what the slit is pointing to by looking at the guider (2). (3) is a helical focuser, used for precisely changing the focus of the main camera (4), which captures the spectra.
• Figure 5: FOV of the spectrograph through the guider. The black line in the middle is the slit. The light of the object that the slit is pointing to will go inside the spectrograph. In this case, light from the ring of Saturn.