Imaging
This is a basic mode. It allows the user to take image by using conventional standard broad band or interference filters. Direct Imaging can be performed over the whole FOV of the instrument Pixel Size: 0.125" FOV: 8.53' x 8.53'
Broad Band
Filters:Gunn Sloan
Tunable Imaging
Using TFs and specially devised interference intermediate-band filters as order sorters. Inserting different TFs (one for the blue and another for the red spectral range) shall allow coverage of the full optical spectral range. Tunable imaging can be performed over the whole FOV of the instrument.
Standard
The whole OSIRIS FOV is usable and only one wavelength range is tuned.
Charge-Shuffled continuum subtraction mode
In the charge-shuffled continuum subtraction mode only one third of the FOV shall be usable. In this mode a focal plane mask selects about the central one-third of the CCD lines. Charge is shuffled up and down one third of the CCD length between exposures. One third of the detector is exposed through the TF tuned to the wavelength of the line. The other third is exposed through the TF tuned to the continuum. Line and continuum can be alternated, and if desired, different parts of continuum on both sides of the line can be selected and on-line averaged in the same image. This permits to obtain a line and a continuum image of the same extended source on the same frame, averaging atmospheric transparency /stability effects and possible continuum wavelength-dependence. Hence, a continuum subtracted line image can be obtained by direct pixel-to-pixel subtraction of both images in the same frame. This mode requires a synchronous shutter operation, charge shuffling and TF tuning.
Spectroscopy
Long Slit
The traditional spectroscopy shall be done selecting one of the possible long slits fixed width available in the slit loader to account for different seeing conditions. It can be performed over the OSIRIS FOV in the spatial direction and in part of the OSIRIS FOV parallel to the dispersiondirection, depending on the resolution and spectroscopy image quality.
Multiple-Object Spectroscopy
As in the long slit mode, multi-object spectroscopy shall be possible using customised masks. Multi-object spectroscopy can be performed over the OSIRIS FOV in the spatial direction and in the part of the OSIRIS FOV parallel to the dispersion direction, depending on the resolution and spectroscopy image quality.
Standard
Using slitlets for sky subtraction.
Point source crowded fields
Using slitlets for sky subtraction.
Point source crowded fields
Using pinholes for each object over one section of the spectral usable FOV in the dispersion direction and subtracting sky by combining telescope beam-switching with charge shuffling to obtain sky-spectra, through the same pinhole mask and physical pixels, of an adjacent field. The operation shall be similar to that described on Charge-Shuffled continuum subtraction mode, but the continuum image shall be the sky spectrum. A synchronous operation of shutter, telescope beam switching and charge shuffling shall be needed.
Fast Modes
Fast Spectroscopy
This mode is similar to Long Slit spectroscopy mode, the only difference is that the detector is readout at the fastest speed (thus increasing readout noise and reducing spectra S/N) either full frame or frame transfer mode (half of it is being exposed while the other half is being read-out). Frame transfer mode shall require a special focal plane mask. Detector shall allow frame transfer operation.
Fast Photometry
For fast photometry of point source objects, a long slit mask located on the loader of slits and with the slit projected on one edge of the detector shall be used. After each exposure the charge shall be shuffled a given number of lines equivalent to the projected width of the slit. This shall be done shutter-less. Also for every exposure a TF can be tuned to different wavelength. Once the detector is filled, it is read out (standard read-out mode). Alternatively it shall be possible to read-out the detector while exposing in a continuous mode (shuffling down the charge and read-out), or frame transfer reading out detector boxes.
This mode requires a synchronous operation of TF tuning, or filters change, and charge shuffling.
Fast continuum photometry
The selected filters (TF, conventional filters) remain in the optical path without changes during the whole observing modes.
Fast line photometry
The same as in before, but in this case on-line and continuum exposures are alternatively observed by TF tuning. This allows monitoring line variability.
Alternatively, a filter can be used in combination with a Grism to select the line to be observed avoiding spectra overlapping. The charge is then shuffled the number of lines occupied by the spectra that should include the continuum for subtraction. Since this is a very specialised mode, the filter to select the line should be provided by the observer. In both cases, once the frame is full, it is read-out. This mode requires a synchronous operation of TF tuning and charge shuffling.
Last update January 10, 2006, by Héctor Castañeda