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

TL;DR

This paper empirically derives reddening and extinction coefficients for Swift-UVOT passbands using observational data, providing updated values that account for temperature variations and align with established extinction laws.

Contribution

It presents new empirical reddening and extinction coefficients for Swift-UVOT passbands, validated against the Fitzpatrick law and considering temperature-dependent effects.

Findings

Reddening coefficients for UVOT colors are quantified.

Extinction coefficients for UVOT bands are provided.

Coefficients are consistent with Fitzpatrick's extinction law.

Abstract

We calculated empirical reddening and extinction coefficients with respect to the dust reddening map of Schlegel et al. for the Swift-UVOT passbands, using the 'star pair' method and photometric data from the UVOT Serendipitous Source Catalogue and spectroscopic data from LAMOST Data Release 7 and 2MASS. The reddening coefficients for the UVW2-UVM2, UVM2-UVW1, UVW1-U, U-B, and B-V colors 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.