Suppression of the near-infrared OH night-sky lines with fibre Bragg gratings: first results

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Suppression of the near-infrared OH night-sky lines with fibre Bragg gratings: first results

Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/232904

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Title: Suppression of the near-infrared OH night-sky lines with fibre Bragg gratings: first results
Author(s): Ellis, S. C.; Bland-Hawthorn, J.; Lawrence, J.; Horton, A. J.; Trinh, C.; Leon-Saval, S. G.; Shortridge, K.; Bryant, J.; Case, S.; Colless, M.; Couch, W.; Freeman, K.; Gers, L.; Glazebrook, K.; Haynes, R.; Lee, S.; Lohmannsroben, H. G.; O'Byrne, J.; Miziarski, S.; Roth, M.; Schmidt, B.; Tinney, C. G.; Zheng, J.
Abstract: The background noise between 1 and 1.8 μm in ground-based instruments is dominated by atmospheric emission from hydroxyl molecules. We have built and commissioned a new instrument, the Gemini Near-infrared OH Suppression Integral Field Unit (IFU) System (GNOSIS), which suppresses 103 OH doublets between 1.47 and 1.7& 8201;μm by a factor of ≈1000 with a resolving power of ≈10 000. We present the first results from the commissioning of GNOSIS using the IRIS2 spectrograph at the Anglo-Australian Telescope. We present measurements of sensitivity, background and throughput. The combined throughput of the GNOSIS fore-optics, grating unit and relay optics is ≈36 per cent, but this could be improved to ≈46 per cent with a more optimal design. We measure strong suppression of the OH lines, confirming that OH suppression with fibre Bragg gratings will be a powerful technology for low-resolution spectroscopy. The integrated OH suppressed background between 1.5 and 1.7 μm is reduced by a factor of 9 compared to a control spectrum using the same system without suppression. The potential of low-resolution OH-suppressed spectroscopy is illustrated with example observations of Seyfert galaxies and a low-mass star. The GNOSIS background is dominated by detector dark current below 1.67 μm and by thermal emission above 1.67 μm. After subtracting these, we detect an unidentified residual interline component of ≈860 ± 210 photons s−1 m& 8722;2 arcsec−2 μm−1, comparable to previous measurements. This component is equally bright in the suppressed and control spectra. We have investigated the possible source of the interline component, but were unable to discriminate between a possible instrumental artefact and intrinsic atmospheric emission. Resolving the source of this emission is crucial for the design of fully optimized OH suppression spectrographs. The next-generation OH suppression spectrograph will be focused on resolving the source of the interline component, taking advantage of better optimization for a fibre Bragg grating feed incorporating refinements of design based on our findings from GNOSIS. We quantify the necessary improvements for an optimal OH suppressing fibre spectrograph design.
Publication type: Journal article
Research centre: Swinburne University of Technology. Faculty of Information and Communication Technologies. Centre for Astrophysics and Supercomputing
Source: Monthly Notices of the Royal Astronomical Society, Vol. 425, no. 3 (Sep 2012), pp. 1682-1695
Publication year: 2012
FOR Code(s): 0201 Astronomical and Space Sciences
Keyword(s): Atmospheric effects; Instrumentation; Near-infrared wavelengths
Publisher: Wiley-Blackwell Publishing
ISSN: 0035-8711
Publisher URL: http://dx.doi.org/10.1111/j.1365-2966.2012.21602.x
Peer reviewed