Le 30 octobre 2015De 10h30 à 12h00
Eddie SCHLAFLY
MPIA Heidelberg
The dust extinction curve is an important diagnostic of the physics of the interstellar medium, as well as a critical element to many observational programs. Detailed studies of the extinction curve and its variation have so far been limited to samples of hundreds of specially chosen stars. We make new measurements of the dust extinction curve and its variation towards tens of thousands of stars using the APOGEE spectroscopic survey in combination with photometry in ten bands from Pan-STARRS1, 2MASS, and WISE. We find that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves described by R(V), with little need for further parameters. The local curvature of the extinction curve increases with decreasing R(V) throughout the optical and infrared: the extinction curve in the infrared, while less variable than in the optical, is not “universal,” in contrast to several widely-used extinction curve parameterizations. Meanwhile we find that the optical extinction curve is somewhat more uniform than suggested in past works, with σ(R(V)) = 0.2, with less than two percent of sight lines having R(V) > 4. However, significant spatially coherent variations in R(V) do exist. The primary variations are on scales much larger than individual molecular clouds, indicating that grain growth in dense molecular cloud environments is not the primary driver of R(V) variations in dust at large. Indeed, we find no correlation between R(V) and dust column density up to E(B−V) ≈ 2. Finally, we discover a strong correlation between the shape far-infrared dust emission spectrum and the shape of the optical extinction curve, an important new constraint on dust grain models and an avenue to predicting R(V) variations across the entire sky.