Empirical extinction coefficients for the Swift-UVOT optical-through-ultraviolet passbands

Abstract

ABSTRACT We calculated empirical reddening and extinction coefficients with respect to the dust reddening map of Schlegel et al. (1998) for the Swift-UVOT passbands, using the ‘star pair’ method and photometric data from the UVOT Serendipitous Source Catalogue and 2MASS as well as spectroscopic data from LAMOST Data Release 7. The reddening coefficients for the UVW2 − UVM2, UVM2 − UVW1, UVW1 − U, U − B, and B − V colours are −1.39, 2.08, 0.78, 0.72, and 0.84, respectively. The extinction coefficients for the UVW2, UVM2, UVW1, U, B, and V bands are 5.60, 6.99, 4.91, 4.13, 3.41, and 2.57, respectively. The numbers are consistent with predictions by the Fitzpatrick’s extinction law of R(V) = 3.0. Temperature-dependent variations of the coefficients are found and discussed, particularly for the ultraviolet passbands. We recommend using the new reddening and extinction coefficients in future when dereddening the Swift-UVOT data.