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The HERMES Project
A High Efficiency and Resolution Multi-Element Spectrograph for the AAT
HERMES will be the next major instrument for the 3.9-m AAT, and is currently under construction at AAO. It will provide a unique and powerful new facility for multi-object astronomy. The concept was first presented at a 2007 workshop held to determine the astronomical community's priorities for new AAT instrumentation.
The HERMES system is built upon the AAT’s existing two-degree field (2dF) optical fibre positioner, which can collect the light from 400 stars at a time (there are 8 guide fibres and 392 fibres that can allocated to targets) . The positioner feeds a powerful new spectrograph which covers four optical bands simultaneously at a spectral resolution of ~28,000. The fibres have a core diameter of 140 microns, which corresponds to approximately 2 arcseconds on the sky (median AAT seeing is > 1.5 arcsec), and are positioned to better than 20 microns (rms error around 10 microns).
HERMES will provide simultaneous observations in the following bands:
Blue: 471.8 - 490.3 nm
Green: 564.9 - 587.3 nm
Red: 648.1 - 673.9 nm
IR: 759.0 - 789.0 nm
A high resolution mask will provide R ~ 50,000 at ~ 50% light loss. All detectors are from the E2V CCD231-84 family, and are 4096 x 4112, 15um pixel devices, with a nominal operating temperature of 170K. The "blue" and "green" detectors are both 16 micron, standard silicon devices with broadband and mid band coatings. The "red" detector is a 40 micron, deep depletion device with fringe suppression and an ER1 coating. The "infrared" detector is a 100 micron bulk silicon device with fringe suppression and a "Multi-9" coating.
All detectors so far received ("blue", "green" and "red") are grade-0 cosmetic quality (the highest available quality).
The efficiency target is to achieve a SNR of 100 per resolution element for a V = 14th magnitude star within an hour's exposure. The corresponding efficiency requirements per channel are given in the plots below in colour and the expected instrument efficiency per channel is shown in black.
There are graphs available showing the resolving power of HERMES in all four channels.
The AAO will provide an associated reduction pipeline which will provide spectra with the instrument signature removed and wavelength calibrated.
The primary HERMES science project is the ‘Galactic Archaeology‘ (GA) Survey, which aims to reconstruct the history of our Galaxy's formation from precise multi-element abundances of 1 million stars derived from HERMES spectra. This survey is being prepared and will be handled by the GA Survey Team.
The AAO has documented the HERMES assembly, integration and test phases with a time-lapse camera. See the following movies:
Low resolution HERMES integration movie 17M (Last updated 9 May 2013)
High resolution HERMES integration movie 78M (Last updated 9 May 2013)
For more details on the project please use the left navigation bar.