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FiltersThe light path of INGRID passes through (i) a pupil stop wheel and (ii) two filter wheels. The two filter wheels are identical in design, but the first is dedicated to broad band filters, and the second to narrow band filters. For an overview of the mechanical system click here. For more details see the following sections:
For the afternoon setup and science observations with INGRID, the following configurations are recommended:
SYS> filter ingrid <configuration name>
Both the command line and the GUI will move the filter wheels and pupil stop wheel to the appropriate positions, ensuring that the latter is always repositioned last. (This is because the three wheels are mounted on the same rotational shaft and so the movement of one wheel can slightly influence the position of another one.)
The filter and pupil stop wheels can be controlled individually using either the command line or the 'Mechanism Control' section of the INGRID GUI. Note that while individual control is useful for engineering purposes, the use of the configurations outlined in the previous section is strongly recommend for observing.
The command line syntax for the filter and pupil wheel movements is:
SYS> fwheel1 ingrid <filter name> or <position>
SYS> fwheel2 ingrid <filter name> or <position>
SYS> pstop ingrid <pupil stop name> or <position>
The current options for <filter name> and <pupil stop name> are given in the following section. Note that replacing the name/position by datum will allow one to datum the mechanism.
When moving filters and pupil wheels individually, make sure that the pupil stop is the last mechanism to be moved.
Note that blank indicates that an "aluminium blank" is in the light path (useful for dark frames) while clear means that there is nothing in the light path. See below for more details about the other pupil stops and filters.
The filters have thicknesses of less than 6mm and diameters of 38mm (±0.1mm). They are all angled at 5° to the optical beam to reduce ghosting and are all specified for adaptive optics observations except for the Z filter. The two tables below show the set of filters currently available for INGRID. Note that the J-Barr filter has not been included as it has not been scanned; it is expected to have similar properties to those of the J filter.
All filters were purchased in collaboration with the Gemini filter buying consortium (headed by Alan Tokunaga); more details can be found here. The transmission curves have been measured at room temperature and at 0° angle with respect to the incident light. The central wavelengths of the narrow band filters are sensitive to both temperature and the angle of incidence, so transmission curves have also been estimated at values appropriate for INGRID (ie. 5° incidence and T=77K). See here for more details.
Graphical overview of INGRID broad band filter transmissions
Graphical overview of INGRID K-band filter transmissions
INGRID broad band filters (Filter Wheel 1)
The last column of the above table gives the wavelength of the rest-frame emission line associated with each filter. Please note that the Br-gamma filter is redshifted by ~4nm with respect to the rest-frame wavelength of the corresponding emission line.
INGRID pupil stops
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