Preparing for a 2dF/AAOmega observing run
Contact your support astronomer (see the Schedule).
Fill out your AAO visitors travel form, which will also make reservations at the ANU lodge on the mountain.
Read the Configure program guide. This is the software used to optimally configure fibre placement for an observation and prepare files for the telescope to observe.
Choose your central observing wavelength to which fibres will be positioned. The Chromatic Variation in Distortion (CVD; an optical effect of the prime focus corrector optics) issue is described in more detail in the CVD web page.
Create a number of target files for the Configure software. Test them in Configure. E-mail a few example fields to your support astronomer to confirm that the format and contents are okay.
Discuss your proposed strategy with your support astronomer and confirm your requested gratings, central wavelengths and blaze angles.
In order to achieve a wide field of view and good image quality over that entire field of view the 2dF prime focus corrector suffers from Chromatics Variation in Distortion (CVD). This means that while the Atmospheric Distortion Corrector (ADC) accounts for the effect of the atmosphere on your target object's white light apparent positions, the prime focus corrector moves your target on the field plate as a function of wavelength. The effects can be quite large, up to 2 arcsec in the worst case when considered over the full wavelength range accessible to 2dF and over the full 2degree field. 2dF knows about CVD and so you must specify for what wavelength you want 2dF to put the fibres in the correct position. This must be the compromise which best suits your program goals (e.g. 400nm for Ca H+K and the Balmer lines, 860nm for Ca Triplet work, 600nm for low-resolution broad-band redshift measurements with the 570nm dichroic or 670nm for low-resolution broad-band redshift measurements with the 670nm dichroic).
The atmosphere acts as a giant, time variable (due to changing Hour Angle, HA) chromatic lens. The 2dF top end is equipped with an Atmospheric Dispersion Corrector (ADC) which corrects for the chromatic component, but atmospheric refraction changes the plate scale of the 2dF field plates as a function of HA (or rather Zenith Distance, ZD) and there is no way to account for this stretch of the field (Differential Atmospheric Refraction, DAR) during an observations. Each 2dF configuration has a specified mid point for which the field is setup, accounting for the effects of DAR at that time. For a full 2degree field, a configuration is typically valid for +/- 1hour either side of this mid point. Smaller fields are valid for longer, fields at high airmass are only valid for short time periods. Losses due to fibre position mismatches (this is in no way an error within 2dF, it is the Earth's atmosphere which is at fault) can be significant outside of this time window. An excellent paper discussing the full horrors of the effect is Newman 2002 PASP 114 918.
AAOmega data is reduced using the 2dfdr software environment. Reduction facilities are available at the AAT, but users may wish to download and run the software elsewhere. The 2dfdr page provides all necessary links and information for the data reduction task.
Sarah Brough (firstname.lastname@example.org)