Gratings: 2nd Order
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Any of the GMOS gratings can be used in 2nd order; however only a few configurations are potentially interesting and none have been fully characterized. Prompted by a recent inquiry from the user community, we have recently made some daytime testing of the R831 grating in 2nd order. This mode offers higher resolution than delivered by the B1200 grating although the wavelength range is limited by the necessity to use broad-band color filters to block 1st order. Neither GMOS is currently equipped with red-blocking (short-pass) filters.
The configuration tested was R831 in 2nd order, central wavelength = 440 nm, using the g'-filter for order blocking. A Nod&Shuffle 1.0arcsec longslit data was used, which allowed for a characterization of scattered light beyond the edge of the slit. The detector was binned 2x2. The test data are available for download from the Gemini Science Archive. These test data were taken with GMOS-N:
Filename | Grating Configuration | Data Type |
N20110923S0129 | B1200 1st order | GCALflat |
N20110923S0130 | B1200 1st order | CuAr |
N20110923S0467 | R831 2nd order | GCALflat |
N20110923S0468 | R831 2nd order | CuAr |
These daytime tests were encouraging, and users whose science would benefit from higher resolution and do not need full wavelength coverage may wish to consider this combination. The R831 grating efficiency in 2nd order is comparable to that of the B1200 grating in 1st order. The g-filter unfortunately introduces a drop in throughput of about 15% because its peak transmission is 85%. The resolution compared to the B1200 grating increases by about 40% as expected, and the amount of scattered light contribution per pixel is comparable.
Please note: we have yet to confirm the behavior of the Gemini GMOS IRAF data reduction scripts with 2nd order spectral data.
![B1200 1st order GCALflat [B1200 1st order GCALflat]](http://www.gemini.edu/sciops/instruments/gmos/B1200_440_g_1st_flat.jpg)
![R831 2nd order GCALflat [R831 2nd order GCALflat]](http://www.gemini.edu/sciops/instruments/gmos/R831_440_g_2nd_flat.jpg)
![B1200 1st order CuAr [B1200 1st order CuAr]](http://www.gemini.edu/sciops/instruments/gmos/B1200_440_g_1st_CuAr_full.jpg)
![R831 2nd order CuAr [R831 2nd order CuAr]](http://www.gemini.edu/sciops/instruments/gmos/R831_440_g_2nd_CuAr_full.jpg)
![B1200 1st order CuAr (zoomed in) [B1200 1st order CuAr (zoomed in)]](http://www.gemini.edu/sciops/instruments/gmos/B1200_440_g_1st_CuAr_zoom.jpg)
![R831 2nd order CuAr (zoomed in) [R831 2nd order CuAr (zoomed in)]](http://www.gemini.edu/sciops/instruments/gmos/R831_440_g_2nd_CuAr_zoom.jpg)