# Extinction and reddening dataset

Where can I find a dataset containing the interstellar reddening and extinction values for all globular clusters, preferably in the HST/WFC3 system.

Note that they are related via the reddening law, i.e. $$\begin{equation*}R_\lambda = \frac{A_\lambda}{E(B-V)}\end{equation*}$$ where $$A_\lambda$$ is the extinction at wavelenght $$\lambda$$, and $$E(B-V)$$ is the color excess for $$B-V$$. In literature is commonly used $$E(B-V)$$, while in practice is usually needed $$A_\lambda$$, to switch back and forth from apparent magnitude $$m_\lambda$$ to absolute magnitude $$M_\lambda$$ with $$\begin{equation*}m_\lambda=M_\lambda+A_\lambda+(m-M)_0\end{equation*}$$ using the absolute distance modulus $$(m-M)_0$$.
Finding $$R_\lambda$$ is more tricky. You can search in the literature for tabulated values (e.g. Tables 14 and 15 in Sirianni et al. 2005), otherwise a rough-but-still-working approach is to take a $$R_\lambda$$ vs. $$\lambda$$ plot (e.g. the one in Fitzpatrick 1999) and to extrapolate by-hand $$R_\lambda$$ at the effective wavelength of your filter. Note that usually are presented several reddening laws, distinguished by $$R_V$$. This is because they're not universal and depends on the environment; a reasonable choice for GGCs is $$R_V=3.1$$ .