At the telescope: night time

Here is  a useful log sheet for your own note taking.

Twilight flats. For all the envisaged blocking filters on a given night, it helps to have twilight flats taken in the evening. We observe through TAURUS without the TTF in the beam. We bias subtract and normalize these images in preparation for the TTF data. These images are used to divide out uneven illumination (vignetting) for each of the TTF images. (If we are using the AAT f/15, check that the sky baffle is in.)

Object positions and rotations. Be prepared to give the TO your first object position. Observers should also consider whether instrument rotations are required. It is important to discuss this with the TO at twilight if not before, as TAURUS has a rotation offset, and things can get confusing.  The beginning of the night is a good time to determinen the direction of N and E at the image display.

Telescope focus. We will need to focus the telescope on a bright star near your first field of view. The TTF filters are specified to give the same focus so this need only be done once. It is not advisable to determine a separate focus for other filters. Of course, if you are using the gamut of TTF and UBVRIz filters, it is important to compare the different focus values and consider a course of action. If the focus values were obtained in bad seeing, consider repeating the operation when things improve.

Object wavelengths. Be prepared to give the TTF operator your required wavelengths.These will need to be converted to etalon gap (Z) values.

Stability tests. The main thing to watch is the stability of the TTF. The TTF drift report  demonstrates that the main problem is flexure within the TTF when moving around the sky. It is necessary to redo the TTF calibration for each pointing of the telescope if the movement is more than a few degrees. A secondary effect is temperature drift but this will only matter if (a) you are sticking with one object for several hours, (b) the temperature has drifted by a few degrees during that time.

Required calibrations. You will need spectrophotometric flux standards for each of your filters at each of the Z values used. (Obviously, the TTF should be in the beam.) Choose a bright star with at least V < 11 or so. It is useful -  but not essential - to observe an emission line standard if a calibrated emission line happens to fall within your filter (e.g. the H-alpha PN flux standards in K.R. Lang `Astrophysical Quantities' or Dopita's 'Southern spectrophotometric flux standards' paper.)

At dawn, why not get some more twilight flats, and of course the obligatory dome flats. For the latter, you will need dome flats with the TTF for each of the Z values and filters you have used.