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GMOS-N Filters

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The GMOS filters u', g', r', i' and z' are similar to the filters used by the Sloan Digital Sky Survey (SDSS). A description of the SDSS photometric system is presented in Fukugita et al. (1996, AJ, 111, 1748). See the description of optical photometric standard stars for details on the photometric standard calibration. Please note that due to filter degradation discovered in semester 2004A the u' filter is no longer available for science use on GMOS-N. At this time there are no plans to replace the damaged filter.

The filter CaT is a 150nm broad-band filter approximately centered on the Ca Triplet.

The filters Ha, HaC, OIII, OIIIC, SII, HeII, and HeIIC are narrow-band filters for H-alpha, H-alpha continuum, ionized oxygen, ionized oxygen continuum, ionized sulphur, ionized helium, and ionized helium continuum, respectively.

The filter DS920 is a narrow-band filter centered on a wavelength region of very low sky background.

The filters GG455, OG515 and RG615 are 5mm thick Schott glass filters. These are long-pass filters which can be used to block 2nd-order contamination of the spectra or limit the wavelength range to allow multiple slit-banks in the multi-aperture mode.

Transmission curves based on lab measurements are available for the filters.

The table lists the properties of the filters based on laboratory measurements. The wavelength interval given in the tables is the interval within which the transmission is larger than 50 per cent. For the long-pass filters and the filter z_G0304 the wavelength at the 50 per cent transmission at short wavelength edge is given.

Some of the filters can be combined, the allowed combinations are listed last in the table. The combinations are useful for using the IFU in 2 slit mode with the higher dispersion gratings, e.g. R831_G5302 with the filter combination r_G0303 + RG610_G0307.

Imaging with GMOS requires use of either a color filter (griz, CaT) or a narrow band filter. The long-pass filters GG455, OG515, and RG615 are not suitable for imaging. Also imaging without a filter is not available.

Users may supply their own filters for queue observations; see filter policy and specifications for details.


GMOS-N Filters
Broad Band Imaging Filters
G0308 u_G0308
(no longer available)
350 336-385 data GMOS-N
G0301 g_G0301 475 398-552 data GMOS-N
G0303 r_G0303 630 562-698 data GMOS-N
G0302 i_G0302 780 706-850 data GMOS-N
G0309 CaT_G0309 860 780-933 data GMOS-N
G0304 z_G0304 >=925 >=848 data GMOS-N
Narrow Band Imaging Filters
G0320 HeII_G0320 468 464-472 data GMOS-N
G0321 HeIIC_G0321 478 474-482 data GMOS-N
G0318 OIII_G0318 499 496.5-501.5 data GMOS-N
G0319 OIIIC_G0319 514 509.0-519.0 data GMOS-N
G0310 Ha_G0310 655 654.2-661.1 data GMOS-N
G0311 HaC_G0311 662 659.8-666.6 data GMOS-N
G0317 SII_G0317 672 669.4-673.7 data GMOS-N
G0312 DS920_G0312 920 912.8-931.4 data GMOS-N
Spectroscopy Blocking Filters
G0305 GG455_G0305 >=555 >=460 data GMOS-N
G0306 OG515_G0306 >=615 >=520 data GMOS-N
G0307 RG610_G0307 >=710 >=615 data GMOS-N
Allowed Filter Combinations
  g_G0301 + GG455_G0305 506 460-552   GMOS-N
  g_G0301 + OG515_G0306 536 520-552   GMOS-N
  r_G0303 + RG610_G0307 657 615-698   GMOS-N
  i_G0302 + CaT_G0309 815 780-850   GMOS-N
  z_G0304 + CaT_G0309 890 848-933   GMOS-N

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