Flat Fields Adds noise to every science frame Goal: 10x lower noise contribution from flats compared to object Typical fwhm area = 10pix, so for 0.01mag error, want flat pix to have 10000*sqrt(100/10) (or 30000) electrons minimum. For mmag photometry, need even more, plus lamp color match.
Accurate Photometry Transformations Scintillation Differential airmass Signal/noise
Transformations Necessary to place everyone on same system (0.01mag level) Due to differences between standard system and yours (filters) Use set of standard stars and transformation equations, least squares Only good for non-pathological stars
Differential photometry (V-C), (K-C) common Accounts for majority of sky variations Ensemble techniques for higher precision Uses mean comparison: sum(Cmag)/N Reduces error by sqrt(N) (9 comps, 3x less noise contribution from comp star)
Faint stars, bright background Use smallest possible aperture (psf fitting best) Stacking method (average, rejection) makes a difference Compare all methods against average on clean stars
Exoplanets High precision (millimag level) Usually bright stars. Scintillation and finding comp stars important Use ensemble methods where possible High time resolution not important, but transformation important if combining datasets
Gamma-Ray Burst Afterglows Early time observations require cookbook procedure (you cant be thinking about exposure times) Rapid fade, so need to get on it fast Filters highly important (Rc,Ic,Z) Watch stacking techniques to avoid rejecting high/low points