Global calibration: method

• Linear drift model: $m^J_{ijk} = m^o_{ik} + a_J + b_Jt^J_j + A_\lambda(X^J_j-1)$
  • i - cal field
  • k - particular star
  • J - observing night
  • j - source detection
  • X - air mass
• n tracer stars in each field
• Linear least squares
  • Self-referential
  • With constraints from calibration standards

• Demand: Minimum variance for individual stars
  Get: Optimal values for nightly offsets and slopes
• Photometry ``cobbled'' together around the sky

 

Figure 1: Calibration strategy