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تسجيل مستخدم جديدBridging the Ultraviolet and Optical Regions: Transformation Equations between {it GALEX} and {it UBV} Photometric Systems
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We derive transformation equations between GALEX and UBV colours by using the reliable data of 556 stars. We present two sets of equations; as a function of (only) luminosity class, and as a function of both luminosity class and metallicity. The metallicities are provided from the literature, while the luminosity classes are determined by using the PARSEC mass tracks in this study. Small colour residuals and high squared correlation coefficients promise accurate derived colours. The application of the transformation equations to 70 stars with reliable data shows that the metallicity plays an important role in estimation of more accurate colours.
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Although core helium-burning red clump (RC) stars are faint at ultraviolet wavelengths, their ultraviolet-optical color is a unique and accessible probe of their physical properties. Using data from the GALEX All Sky Imaging Survey, Gaia Data Release
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Interstellar extinction in ultraviolet is the most severe in comparison with optical and infrared wavebands and a precise determination plays an important role in correctly recovering the ultraviolet brightness and colors of objects. By finding the o
bserved bluest colors at given effective temperature and metallicity range of dwarf stars, stellar intrinsic colors, $C^0_{rm B,V}$, $C^0_{rm NUV,B}$, $C^0_{rm FUV,B}$ and $C^0_{rm FUV,NUV}$, are derived according to the stellar parameters from the LAMOST spectroscopic survey and photometric results from the $GALEX$ and APASS surveys. With the derived intrinsic colors, the ultraviolet color excesses are calculated for about 25,000 A- and F-type dwarf stars. Analysis of the color excess ratios yields the extinction law related to the $GALEX$ UV bands: $E_{{rm NUV,B}}$/$E_{{rm B,V}} = 3.77$, $E_{{rm FUV,B}}$/$E_{{rm B,V}} = 3.39$, $E_{{rm FUV,NUV}}$/$E_{{rm B,V}} = -0.38$. The results agree very well with previous works in the $NUV$ band and in general with the extinction curve derived by Fitzpatrick (1999) for $R_{rm V}=3.35$.
We present colour transformations for the conversion of the {em 2MASS} photometric system to the Johnson-Cousins $UBVRI$ system and further into the {em SDSS} $ugriz$ system. We have taken {em SDSS} $gri$ magnitudes of stars measured with the 2.5-m t
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