Merge d7a1b7a into dd752c8

dust_extinction/dust_extinction.py

@@ -33,7 +33,7 @@ class CCM89(Model):
 
     Returns
     -------
-    elvebv: float
+    elvebv: np.array(dtype=float)
         E(x-V)/E(B-V) extinction curve [mag]
 
     Raises
@@ -50,8 +50,6 @@ class CCM89(Model):
     F99 should be used instead as it is based on 10x more observations 
     and a better treatment of the optical/NIR photometry based portion 
     of the curves.
-
-    CCM89 is mainly for historical puposes
     """
     inputs = ('x',)
     outputs = ('elvebv',)
@@ -146,6 +144,47 @@ def evaluate(in_x, Rv):
         a[fuv_indxs] = np.polyval((-.070, .137, -.628, -1.073), y)
         b[fuv_indxs] = np.polyval((.374, -.42, 4.257, 13.67), y)
 
-        # return Al/Av
+        # return E(lambda-V)/E(B-V)
         return a + b/Rv
+
+    def extinguish(self, x, Av=None, Ebv=None):
+        """
+        Calculate the extinction as a fraction
+
+        Parameters
+        ----------
+        x: float
+           expects either x in units of wavelengths or frequency
+           or assumes wavelengths in wavenumbers [1/micron]
+           internally wavenumbers are used
+
+        Av: float
+           A(V) value of dust column
+           Av or Ebv must be set
+
+        Ebv: float
+           E(B-V) value of dust column
+           Av or Ebv must be set
+
+        Returns
+        -------
+        frac_ext: np.array(dtype=float)
+           extinction as a function of x 
+        """
+        # get the extinction curve
+        elvebv = self(x)
+
+        # check that av or ebv is set
+        if (Av is None) and (Ebv is None):
+            raise ValueError('neither Av or Ebv passed, one is required')
+
+        # if Av is not set and Ebv set, convert to Av
+        if Av is None:
+            Av = self.Rv*Ebv
+
+        # convert to A(lambda)/A(V)
+        alav = elvebv/self.Rv + 1
+
+        # return fractional extinction
+        return np.power(10.0,-0.4*alav*Av)