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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 is documenting the HERMES assembly with a time-lapse camera. See the following movies:
For more details on the project please use the left
navigation bar.