The Stellar Abundances and Galactic Evolution Survey:Photonic Passbands and Extinction Coefficients for the u and v Bands

The Stellar Abundances and Galactic Evolution Survey(SAGES)is a multi-band photometric survey focused on estimation of stellar atmospheric parameters and interstellar extinction.In this paper we have derived photonic passbands for the intermediate-band u and v filters of the SAGES photometric system.The derived photonic passbands have been compared with those of the u and v filters of the Stromgren and SkyMapper systems.Synthetic photometry based on the derived photonic passbands could reproduce the observations very well.We have also derived observed,model-free extinction coefficients for the SAGES u and v bands(as well as the Pan-STARRS grizy bands)using the“standard pair”method.The derived reddening coefficients have been compared with those predicted by the extinction laws.Variations of reddening coefficients with effective temperatures and color excesses of B–V given by Schlegel et al.(E(B-V)_(SFD))have been investigated.No obvious trends or significant variations with effective temperatures have been found,but reddening coefficients for all the colors exhibit declining trends with increasing E(B-V)_(SFD),with typical relative variations of twenty-some percent from E(B-V)_(SFD)~0 to 1.