The 2006 review of the AAO recommended that a new instrument be designed and built for the AAT in order to maintain the competitiveness of the observatory over the next decade. A Workshop was held in November 2007 to determine the community's scientific priorities for such a new instrument. The HERMES multi-object medium resolution optical spectrograph was selected by AAO in early 2008. The project is now in its final design phase, with start of science observations expected late 2012. Development of the HERMES facility is led by AAO with involvement of the community through the HERMES Science Team.
Unravelling the complex formation history of our Galaxy is the primary science driver for HERMES. This process of “Galactic archaeology”, involves finding groups of stars that were born together in the same cloud of gas and dust through their chemical abundances — a common ‘signature’ that uniquely identifies them. By measuring precise chemical abundances for a million stars it should be possible to identify the clouds from which our Galaxy formed. Combining this ‘chemical tagging’ with ‘kinematical tagging’ using forthcoming (2012-2017) GAIA data will help to reveal a picture of the sequence of events that produced the Milky Way. HERMES will also be able to help make substantial progress in other astrophysical domains, notably the physics and chemistry of the interstellar medium in our Galaxy and in the Magellanic Clouds.
To successfully piece together the formation history of our Galaxy, HERMES must meet challenging technical requirements: a) it must deliver high-resolution (R~28,000), high-quality (S/N=100) spectra for up to V=14 stars in four simultaneous spectral bands covering ~ 100 nm in total to allow precise abundances to be measured for critical elements for a million stars, b) it must be able to get such high S/N spectra for many (400) stars simultaneously in a one-hour exposure to allow this huge sample to be studied in a reasonable amount of time, and c) each frame must cover a large patrol field (2 degree per pointing) so that the Survey can adequately sample the whole accessible Galactic plane.
HERMES operational requirements are equally tough and just as crucial, in particular for the success of the huge GA survey. All observations will be handled at AAT through an end to end process flow, covering object selection, science and calibration exposures, data extraction & quality assessment. This process will be largely automated, albeit with human supervision at key junctures. The final phase of data analysis (extracting abundances & building the huge GA data base) is being prepared and will be handled by the community through the GA Survey Team.
HERMES is able to deliver on all of these requirements by building upon the AAT’s existing two-degree field optical fibre positioner, which allows it to pick the light from up to 400 stars in one go, feeding a powerful new spectrograph that can handle all the requirements, giving precise abundances for many chemical elements at once. Most of the software packages to handle the process flow are already operational and will be completed and merged. Once in operation, the HERMES ‘machine’ will provide a unique and powerful capability for the AAO astronomical community.