| 1 | Begin the night with 25 zeros. Obtain at least 10 zeros every 90 minutes thereafter, ending the night with 25 zeros. |
| 2 | Engage the CLEAR filter slot, making sure that there really is no filter in the optical path. Use no filter in any of the following steps. |
| 3 | Get at least five twilight skyflats with about 25000 counts. Make sure to offset the telescope between flats. |
| 4 | Focus the telescope. You will probably need to refocus the telescope at least two more times during the night. Keep track of the FWHM of the stellar PSFs (use imexam and the r key) as the night progresses, and re-focus when the FWHM changes significantly (0.5 pixel). |
| 5 | Choose a list of observable objects from the provided airmass tables. The exposure times provided are no more than rough guides. Shoot for 25000 counts in the PSF peak.
|
| 6 | Several approaches are possible:
| A. | Take successive exposures of one program star throughout the night, or as long as it is observable. On the next night repeat the procedure with a new star. This approach will reveal luminosity variability on the shortest (hours,minutes, and seconds) timescales; |
| B. | Take exposures of several stars in a sequence that can be repeated throughout the night. Some of the stars will be observable only for part of the night, so the sequence may change membership. The idea is to get several exposures of each star on as many nights as possible to monitor luminosity variability over hours, days, weeks, and months; |
| C. | The preferred strategy is to follow option A above on as many nights as possible, taking the first and last part of each night to obtain single exposures of 1/3 or so of the other stars (no more than 1 hour in the evening and 1 hour in the morning). Shift to another 1/3 of the program stars on successive nights so that all the program stars are observed at least twice every three nights. |
|
| 7 | Good guiding is crucial to accurate photometry. Images that contain elongated stellar profiles will not produce the most accurate results. |
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