Photometric Zero Points & Color Terms

Updated on June 4, 2021, 9:37 am

Last updated: K. Olsen 27 August 2003

    Chip 1 Chip 2 Chip 3 Chip 4 Chip 5 Chip 6 Chip 7 Chip 8
Zero

Point
U 2.217 (0.007) 2.220 (0.005) 2.231 (0.005) 2.254 (0.008) 2.234 (0.010) 2.215 (0.005) 2.216 (0.005) 2.227 (0.009)
B -0.107 (0.008) -0.120 (0.008) -0.115 (0.008) -0.111 (0.009) -0.111 (0.008) -0.101 (0.008) -0.106 (0.008) -0.104 (0.008)
V -0.448 (0.008) -0.472 (0.004) -0.472 (0.004) -0.476 (0.011) -0.475 (0.004) -0.471 (0.006) -0.472 (0.005) -0.475 (0.007)
R -0.636 (0.004) -0.633 (0.004) -0.648 (0.004) -0.632 (0.004) -0.628 (0.004) -0.616 (0.004) -0.629 (0.005) -0.624 (0.006)
I 0.089 (0.010) 0.118 (0.008) 0.076 (0.010) 0.094 (0.008) 0.094 (0.004) 0.123 (0.007) 0.113 (0.011) 0.088 (0.010)
Color

Term
U 0.027 (0.019) 0.028 (0.015) 0.021 (0.015) 0.018 (0.019) -0.025 (0.024) 0.019 (0.016) 0.015 (0.016) -0.002 (0.021)
B -0.069 (0.010) -0.062 (0.010) -0.058 (0.010) -0.055 (0.011) -0.056 (0.010) -0.079 (0.011) -0.081 (0.010) -0.068 (0.010)
V 0.038 (0.009) 0.044 (0.005) 0.042 (0.005) 0.060 (0.012) 0.063 (0.005) 0.041 (0.007) 0.039 (0.006) 0.056 (0.008)
R -0.025 (0.008) -0.037 (0.008) -0.022 (0.008) -0.032 (0.008) -0.028 (0.008) -0.045 (0.008) -0.035 (0.010) -0.029 (0.011)
I 0.009 (0.009) -0.002 (0.007) 0.008 (0.009) 0.006 (0.007) 0.003 (0.004) -0.002 (0.006) 0.003 (0.011) 0.011 (0.010)

The equations used to fit the standard star photometry are of the form:

u = U + A0 + A1X + A2(U-B)

b = B + B0 + B1X + B2(B-V)

v = V + C0 + C1X + C2(B-V)

r = R + D0 + D1X + D2(V-R)

i = I + E0 + E1X + E2(V-I
)

where lowercase letters are the instrumental magnitudes (-2.5log(ADU sec-1)+25), X is the airmass, and capital letters are the standard magnitudes.