Visual and infrared extinction from Cepheid observations

Accurate visual and infrared photometry of Cepheids in the Galaxy and the Magellanic Clouds is used to determine the visual and infrared extinction laws. The infrared reddening law is derived for the standard system defined by Carter. Two different techniques are used to determine the value of R = Av/E(B – V ). Both give consistent results with a weighted mean of R0 = 3.06 ± 0.09 at (B – V )0 = 0, given the assumption that Av/E(V– K) = 1.1 (Whittet & van Breda). The derived infrared colour excess ratios are E (H – K )/E(B– V) = 0.171 ± 0.007 and E (J – H )/E(B – V) = 0.314 ± 0.020 for (B – V )0 = 0 in the limit E(B – V) goes to zero, implying that E(J – H )/E(H– K ) = 1.83 ± 0.14 The infrared extinction coefficients derived are AJ/E(B – V) = 0.764, AH/E(B – V) = 0.450 and AK/E(B – V) = 0.279.