First Light Results from the Hermes Spectrograph at the AAT

TL;DR

The paper reports the initial performance and results of the HERMES spectrograph at the AAT, designed for Galactic Archaeology, demonstrating its capabilities for detailed chemical analysis of stars in the Milky Way.

Contribution

It presents the first-light commissioning results of HERMES, including throughput, resolution, and reliability, supporting the GALAH survey's goal of studying galaxy formation.

Findings

Achieved spectral resolution of 28,000 in standard mode and 40,000-50,000 in high-resolution mode.

Demonstrated instrument throughput and stability during initial commissioning.

Successfully began the GALAH survey targeting one million stars.

Abstract

The High Efficiency and Resolution Multi Element Spectrograph, HERMES, is a facility-class optical spectrograph for the Anglo-Australian Telescope (AAT). It is designed primarily for Galactic Archaeology, the first major attempt to create a detailed understanding of galaxy formation and evolution by studying the history of our own galaxy, the Milky Way. The goal of the GALAH survey is to reconstruct the mass assembly history of the Milky Way through a detailed chemical abundance study of one million stars. The spectrograph is based at the AAT and is fed by the existing 2dF robotic fiber positioning system. The spectrograph uses volume phase holographic gratings to achieve a spectral resolving power of 28,000 in standard mode and also provides a high-resolution mode ranging between 40,000 and 50,000 using a slit mask. The GALAH survey requires an SNR greater than 100 for a star brightness of V ?= 14 in an exposure time of one hour. The total spectral coverage of the four channels is about 100 nm between 370 and 1000 nm for up to 392 simultaneous targets within the 2-degree field of view. HERMES has been commissioned over three runs, during bright time in October, November, and December 2013, in parallel with the beginning of the GALAH pilot survey, which started in November 2013. We present the first-light results from the commissioning run and the beginning of the GALAH survey, including performance results such as throughput and resolution, as well as instrument reliability.