Relationships among the three sets of equatorial standard stars: McDonald, Landolt, and SAAO. Units are magnitudes. Simple linear relationships (see Figures 1-5) of the form Source_1 = a*(Source_2) + b as reported by the DataGraph plotting routine. No rejections. V: V_SAAO = 1.0015*V_Landolt - 0.0085 V_McDonald = 0.9996*V_Landolt + 0.0048 V_McDonald = 0.9976*V_SAAO + 0.0177 B-V: (B-V)_SAAO = 1.0028*(B-V)_Landolt + 0.0026 (B-V)_McDonald = 1.0003*(B-V)_Landolt - 0.0011 (B-V)_McDonald = 0.9983*(B-V)_SAAO - 0.0038 U-B: (U-B)_SAAO = 0.9779*(U-B)_Landolt + 0.0132 (U-B)_McDonald = 0.9930*(U-B)_Landolt - 0.0008 (U-B)_McDonald = 0.9818*(U-B)_SAAO + 0.0136 V-R: (V-R)_SAAO = 0.9896*(V-R)_Landolt - 0.0007 (V-R)_McDonald = 0.9887*(V-R)_Landolt + 0.0083 (V-R)_McDonald = 0.9982*(V-R)_SAAO + 0.0094 V-I: (V-I)_SAAO = 0.9926*(V-I)_Landolt + 0.0015 (V-I)_McDonald = 0.9994*(V-I)_Landolt + 0.0019 (V-I)_McDonald = 1.0067*(V-I)_SAAO + 0.0007 ***************************************************************** Results of a triangular comparison of standard deviations among McDonald, Landolt, and SAAO standard star lists. Units are magnitudes. No rejections. N.B. "Sigma1" = standard deviation "SigmaN" = mean error in the mean Mean differences and sigmas between McDonald and Landolt: Sigma1 SigmaN N V: 0.0007 0.0089 0.0008 110 B-V: -0.0009 0.0077 0.0007 110 U-B: -0.0045 0.0211 0.0020 110 V-R: 0.0037 0.0082 0.0008 110 V-I: 0.0014 0.0092 0.0009 110 Mean differences and sigmas between Landolt and SAAO: Sigma1 SigmaN N V: 0.0073 0.0058 0.0006 90 B-V: 0.0083 0.0069 0.0007 90 U-B: 0.0165 0.0167 0.0018 90 V-R: 0.0055 0.0046 0.0005 90 V-I: 0.0066 0.0056 0.0006 90 Mean differences and sigmas between McDonald and SAAO: Sigma1 SigmaN N V: -0.0041 0.0086 0.0009 92 B-V: -0.0050 0.0087 0.0009 92 U-B: -0.0035 0.0205 0.0021 92 V-R: 0.0086 0.0062 0.0007 92 V-I: 0.0058 0.0081 0.0008 92 N.B. (Sigma_source1)^2 = (sigma_12^2 - sigma_23^2 + sigma_31^2)/2 (Sigma_source2)^2 = (sigma_12^2 - sigma_31^2 + sigma_23^2)/2 (Sigma_source3)^2 = (sigma_23^2 - sigma_12^2 + sigma_31^2)/2 McDonald photometry (source 1) Landolt standard stars (source 2) SAAO standard stars (source 3) V: The input standard deviations among sources are sigma_12 = 0.0089 sigma_23 = 0.0058 sigma_31 = 0.0086 The calculated standard deviations of the individual sources are sigma_1 = 0.0077 sigma_2 = 0.0044 sigma_3 = 0.0038 B-V: The input standard deviations among sources are sigma_12 = 0.0077 sigma_23 = 0.0069 sigma_31 = 0.0087 The calculated standard deviations of the individual sources are sigma_1 = 0.0066 sigma_2 = 0.0040 sigma_3 = 0.0057 U-B: The input standard deviations among sources are sigma_12 = 0.0211 sigma_23 = 0.0167 sigma_31 = 0.0205 The calculated standard deviations of the individual sources are sigma_1 = 0.0171 sigma_2 = 0.0123 sigma_3 = 0.0113 V-R: The input standard deviations among sources are sigma_12 = 0.0082 sigma_23 = 0.0046 sigma_31 = 0.0062 The calculated standard deviations of the individual sources are sigma_1 = 0.0065 sigma_2 = 0.0050 sigma_3 = 0.0020 (sigma_3^2 is negative; assumed positive for square root) V-I: The input standard deviations among sources are sigma_12 = 0.0092 sigma_23 = 0.0056 sigma_31 = 0.0081 The calculated standard deviations of the individual sources are sigma_1 = 0.0077 sigma_2 = 0.0050 sigma_3 = 0.0025