Abstract An NUV-optical diagram composed from sources from the second Galaxy Evolution Explorer (GALEX) Ultraviolet Variability (GUVV-2) Catalog provides us with a method to tentatively classify the unknown GUVV-2 sources by their NUV-optical magnitudes. For the purpose of testing the correctness and generality of the method, we carry out a program on the spectroscopic observations of the unidentified GUVV-2 sources. The spectroscopic identification of these 37 sources are 19 type -A to -F stars, 10 type -G to -K stars and 7 M dwarf stars together with an AGN. We also present the light curves in the R-band for two RR Lyrae star candidates selected from the NUV-optical diagram, both of which undergo cyclic variations. Combining their light curves and colors, we classify them as RR Lyrae stars. To confirm the results, we show a color-color diagram for the 37 newly identified spectroscopic objects compared with previously identified ones, which are consistent with our previous results, indicating that the ultraviolet variable sources can initially be classified by their NUV/optical color-color diagram.
Keywords stars: variables: general — galaxies: active — methods: observational — ultraviolet emission
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