Interstellar extinction curves

Each extinction curve k(x) = (A(lambda)-A(V))/(A(B)-A(V)) is given by: k(x) = c1 + c2*x + c3* D(x,x0,y) + c4*F(x) Where x = 1/wavelength (in inverse micron), D is a Drude profile: D(x,x0,y) = x^2^/((x^2^-x0^2^)^2^ + y^2^x^2^) and F is a polynomial of order 3: F(x) = 0.05392(x-5.9)^2^ + 0.0564(x-5.9)^3^ for 5.9<x<8.0 F(x) = 0 for x<5.9 In this scheme the parameters have the following meaning: c1: related directly to c2 because of normalisation k(x) c2: slope of the linear rise ( mag/E(B-V) ) y: width of the bump (inverse micron) c3: c3/y^2^ is bump height, pi*c3/(2.*y) is bump area x0: position of the bump (inverse micron) c4: amount of FUV non-linear rise contribution: at 8 mu^-1^: 2.9c4 (mag/E(B-V)) |

• ^ |
• 2.9c4 | ^
• * k(x)| c3/y^2
• *
• .. v | *< y >* *.. | v
• ..
• * | *.. c2 1 |
• 0 |
• |^
• |Rv
• |v____________________________|_____________________________ V B x0 5.9 8.0 x=1/wavelength (1/micron) Values of Rv, the ratio of total to selective extinction, can be found in Aiello et al. (1988A&AS...73..195A).