Second generation spectroscopic instrumentation for the STELLA robotic observatory

TL;DR

This paper describes the development of a new suite of specialized spectrographs for the STELLA robotic observatory, covering UV, visual, and NIR bands to enhance spectral capabilities and accuracy.

Contribution

It introduces a second-generation spectroscopic instrumentation suite with three dedicated spectrographs, improving spectral coverage and radial-velocity precision.

Findings

Spectral resolution maintained at 55000 across all three spectrographs.

New UV H&K spectrograph designed for 380-470nm coverage.

Refurbished prime focus corrector enhances UV transmission and fiber feeding.

Abstract

The current STELLA Echelle spectrograph (SES), which records 390nm to 870nm in one shot at a spectral resolution of 55000, will be replaced by a suite of specialized spectrographs in three spectral bands. The UV will be covered by a newly designed H&K spectrograph covering 380nm to 470nm (SES-H&K), the visual band (470nm - 690nm) will be covered by SES-VIS, which is a vacuum-stabilized spectrograph designed for high radial-velocity accuracy, and the NIR will be covered by the current SES spectrograph from 690nm to 1050nm. In order to improve the UV transmission, and to accommodate three different fibre-feeds, the prime focus corrector of the telescope will be refurbished, leading to an optical system with the f/2 1200mm spherical primary, a 4-lens collimator with 2 arcsec aperture, atmospheric dispersion corrector (ADC), and two dichroic beam splitters, feeding 3 separate fibre feeds for the three bands. The newly designed H&K spectrograph will be an Echelle spectrograph, based on a R4-grating with 41.6 l/mm and 110mmx420mm, using a f/5 camera and the cross-disperser in double pass (as in TRAFICOS, MIKE, KPF), using 21 spectral orders. The spectral resolution of all three spectrographs will be comparable to the 55000 of the current SES.