A portable broadband astronomical spectrograph

Astronomical spectroscopy serves as a critical tool for many frontier research fields such as cosmic origin, galaxy evolution, stellar formation, and exoplanet detection. Medium-to-large aperture optical telescopes equipped with various spectrographs are competitive in many large programs. On the other hand, many small-aperture (30~80 cm) telescopes have great potential of quick and flexible observations in astronomical field. This paper presents a portable broadband astronomical spectrograph (ESPEC-2), which features an echelle grating as the main disperser and a group of collimating and imaging lenses to simplify the optical system. For 30~80 cm aperture telescopes, the prototype demonstrates a spectral resolution of R≥6200 across the wavelength range of 400~900nm, with a total weight of only ~3.5kg. It can be directly mounted on telescope focus or fed through optical fiber. Its portability and versatility also enable applications as a general-purpose spectrograph in other scientific experiments. The instrument development demonstrates that such a compact broadband spectrograph could make significant contributions to scientific research, outreach and education.