Empirical color transformations between SDSS photometry and other photometric systems

Abstract

Aims. We present empirical color transformations between the Sloan Digital Sky Survey (SDSS) ugriz photometry and the JohnsonCousins UBVRI system and Becker's RGU system, respectively. Owing to the magnitude of data that is becoming available in the SDSS photometric system it is particularly important to be able to convert between this new system and traditional photometric systems. Unlike earlier published transformations we based our calculations on stars actually measured by the SDSS with the SDSS 2.5-m telescope. The photometric database of the SDSS provides in a sense a single-epoch set of "tertiary standards" covering more than one quarter of the sky. Our transformations should facilitate their use to easily and reliably derive the corresponding approximate Johnson-Cousins or RGU magnitudes. Methods. The SDSS survey covers a number of areas that were previously established as standard fields in the Johnson-Cousins system, in particular, fields established by Landolt and by Stetson. We used these overlapping fields to create well-photometered star samples on which our calculated transformations are based. For the RGU photometry we used fields observed in the framework of the new Basel high-latitude field star survey. Results. We calculated empirical color transformations between SDSS photometry and Johnson-Cousins UBVRI and Becker's RGU system. For all transformations we found linear relations to be sufficient. Furthermore we showed that the transformations between the Johnson-Cousins and the SDSS system have a slight dependence on metallicity.

Comet 322p/Soho 1: An Asteroid With the Smallest Perihelion Distance?*

“…There was no clear evidence for color variations as a function of rotational phase, although we note that the data are noisy. We converted these to -=  V R 0.41 0.04 and -=  R I 0.24 0.09 using the translations from Jordi et al (2006) for ease of comparison with existing data sets. The V − R color is consistent with the colors found for active and inactive JFCs and long-period comets, but bluer than these comets in R − I (Jewitt 2015 and references therein; Figure 3).…”

“…For each combination of S and η, we let diameter, D, and geometric albedo, A p , vary freely. The model takes the V-band absolute magnitude (converted from r′ using the translations from Jordi et al 2006), the phase function, and the IRAC photometry as input parameters. For each best-fit model, we computed color corrections for the broad IRAC bandpasses (Laine 2015) and re-executed the fitting procedure.…”

The Young Stellar Population of Lynds 1340. An Infrared View

“…The infrared sources lined up along the ∼2 pc long, cold filamentary structure. UBVR C I C magnitudes were tarnsformed from the SDSS data, using the equations published by Ivezić et al (2007) (for BVR C I C ) and Jordi et al (2006) (for U). JHKs magnitudes are from the 2MASS All Sky Catalog of Point Sources (Cutri et al 2003).…”

“…We searched for counterparts of our candidate YSOs in the SDSS Data Release 9 (Ahn et al 2012) within 1″ of the SEIP Source List position. We transformed the SDSS magnitudes of the optical counterparts into the Johnson-Cousins UBVR C I C system, using the equations given in Ivezić et al (2007; for BVR C I C ) and Jordi et al (2006; for U). We found optical counterparts for 149 of the 155 Class II Spitzer sources, and for 8 of the 26 flat spectral energy distribution (SED) sources (see Section 4.1).…”

New Spectroscopic Technique Based on Coaddition of Surface Brightness Fluctuations: NGC 4449 and Its Stellar Tidal Stream

“…The resulting spectra have S/N of 5.2 Å −1 and 6.6 Å −1 , respectively, and mean I-band magnitudes of 23.1 and 23.8, respectively. The i band from our photometry is transformed into the I band following the relation of Jordi et al (2006) and assuming a median r − i color of 0.55 based on the CMD shown in Figure 1.…”