Mamajek, Meyer, & Liebert (2002AJ....124.1670M), appendix C, claim the following equations fit Bessell's relations to 1-2 millimag. The second equation, for the redder B-V colors, is corrected per the erratum in 2006AJ....131.2360M). for -0.25 < (BT-VT) < 2.0: V = VT + 9.7E-04 - 1.334E-01(BT-VT) + 5.486E-02(BT-VT)^2 - 1.998E-02(BT-VT)^3 for 0.5 < (BT-VT) < 2.0: B-V = (BT-VT) - 7.813E-03(BT-VT) - 1.489E-01(BT-VT)^2 + 3.384E-02(BT-VT)^3 for -0.25 < (BT-VT) < 0.5: B-V = (BT-VT) - 0.006 -1.069E-01(BT-VT) + 1.459E-01(BT-VT)^2 ------------------------------------------------------------------------------- Date: Fri, 10 Jan 2003 13:16:03 -1000 (HST) From: Michael Linnolt Subject: Re: Bessell lookup table To: Brian Skiff Brian, While working on loading the Bessel data table into my charting program, I noticed that the (V-Vt) vs. (Bt-Vt) is almost perfectly fit by a single cubic polynomial! V-Vt = -0.02(Bt-Vt)^3 + 0.0549(Bt-Vt)^2 - 0.1334(Bt-Vt) + 0.001 R^2 = 0.99998 Unfortunately the del(B-V) vs. (Bt-Vt) cannot be fit so perfectly by a polynomial, but a 5th order is within R^2=0.99965 with significant departures around (Bt-Vt)~0.4 and (Bt-Vt)~0.15. Clear skies, Mike Linnolt =============================================================================== Corrections to put Hipparcos/Tycho data on the standard V and B system from: 2000PASP..112..961B BESSELL M.S. Publ. Astron. Soc. Pac., 112, 961-965 (2000) [July 2000 issue] The Hipparcos and Tycho photometric system passbands. TABLE 2 RELATION BETWEEN BT-VT AND HIPPARCOS/TYCHO DATA FOR B-G MAIN-SEQUENCE STARS AND K-M GIANTS BT-VT V-VT del(B-V) V-HP -0.250... 0.038 0.031 0.066 -0.200... 0.030 0.021 0.051 -0.150... 0.022 0.011 0.036 -0.100... 0.015 0.005 0.021 -0.050... 0.008 0.002 0.006 -0.000... 0.001 -0.005 -0.011 0.050... -0.005 -0.010 -0.025 0.100... -0.012 -0.017 -0.038 0.150... -0.018 -0.020 -0.048 0.200... -0.024 -0.021 -0.058 0.250... -0.029 -0.023 -0.069 0.300... -0.035 -0.025 -0.079 0.350... -0.040 -0.025 -0.087 0.400... -0.045 -0.026 -0.094 0.450... -0.050 -0.030 -0.101 0.500... -0.054 -0.035 -0.108 0.550... -0.059 -0.045 -0.114 0.600... -0.064 -0.051 -0.120 0.650... -0.068 -0.060 -0.127 0.700... -0.072 -0.068 -0.131 0.750... -0.077 -0.076 -0.134 0.800... -0.081 -0.085 -0.137 0.850... -0.085 -0.094 -0.142 0.900... -0.089 -0.104 -0.147 0.950... -0.093 -0.113 -0.151 1.000... -0.098 -0.122 -0.155 1.050... -0.102 -0.131 -0.158 1.100... -0.106 -0.142 -0.157 1.150... -0.110 -0.154 -0.160 1.200... -0.115 -0.166 -0.162 1.250... -0.119 -0.178 -0.164 1.300... -0.124 -0.189 -0.166 1.350... -0.128 -0.199 -0.166 1.400... -0.133 -0.210 -0.165 1.450... -0.138 -0.222 -0.164 1.500... -0.143 -0.234 -0.161 1.550... -0.148 -0.245 -0.157 1.600... -0.154 -0.256 -0.153 1.650... -0.160 -0.266 -0.148 1.700... -0.165 -0.277 -0.143 1.750... -0.172 -0.288 -0.137 1.800... -0.178 -0.299 -0.131 1.850... -0.185 -0.309 -0.125 1.900... -0.191 -0.320 -0.119 1.950... -0.199 -0.331 -0.112 2.000... -0.206 -0.342 -0.106