Hamilton calibrations are of four types: flat-fields, wavelength calibrations, narrow quartzes, and darks. Though the first three of these are part of most Hammilton programs, there is no standard set of calibrations used by all observers, and individual users will have to decide which types, and how many of each, best meet their program's requirements, approaches to data reduction, and personal preference. Some guidelines are given below, along with instructions on how to make each type of calibration.
Flat FieldsThe flat-field source is a continuum quartz lamp mounted above the entrance slit. It is turned on by selecting "PolarQuartz" from hammotor_guis's "Calibration Lamp" section. Flats are made using an aperture at least twice as tall as that used for observing (typically 5 or 6 arcseconds). This produces flat-field orders wider than the stellar orders, preventing edge effects when performing the flat-field division (you may hear Hamilton flats referred to as "wide flats"). Because of the Hamilton's very large wavelength coverage, combined with the lamp's energy distribution and the detector's response curve, full illumination of all the orders in a single exposure is impossible, except in those unusual cases where wavelegth coverage has been sharply reduced by windowing the CCD. Filters are used to correct the problem of even illumination as much as possible. The standard formula for Hamilton flats covering wide wavelength range combines bg12 and bg13 filters. The exposures through each filter may be taken on separate frames and later combined by adding pairs of frames. Alternatively, the filters may be combined in a single exposure by pausing it part way, changing filters, and completing the exposure. In either case, the ratio of exposure times for bg12 to bg13 is about 10 to 1. Absolute exposure times vary with the age of the lamp, the size of the aperture, and the CCD in use. Keep peak exposure levels within the device's recommended linearity limit.
Hamilton flat fields
At the idl prompt, type autoflat or autoflat_alternate, followed optionally by its keywords. If no keywords are specified, the program will use the default number of exposures (20) and default times for each filter (35 and 3 seconds for bg12 and bg13, respectively). autoflat and autoflat_alternate have the same default numbers and the same keywords. The following options apply to both procedures (substitute autoflat_alternate when running that procedure):
|autoflat,number=n||specify number of exposures for each filter, use default exposure times|
|autoflat,/time||specity exposure times for each filter, use defualt number of exposures|
|autoflat,number=n,/time||specify number of exposures and exposure times|