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.

We use the distant outer halo globular cluster Palomar 14 as a test case for classical versus modified Newtonian dynamics (MOND). Previous theoretical calculations have shown that the line-of-sight velocity dispersion predicted by these theories can differ by up to a factor of 3 for such sparse, remote clusters like Pal 14. We determine the line-of-sight velocity dispersion of Palomar 14 by measuring radial velocities of 17 red giant cluster members obtained using the Very Large Telescope and Keck telescope. The systemic velocity of Palomar 14 is (72.28 ± 0.12) km s −1 . The derived velocity dispersion of (0.38 ± 0.12) km s −1 of the 16 definite member stars is in agreement with the theoretical prediction for the classical Newtonian case according to Baumgardt et al. In order to exclude the possibility that a peculiar mass function might have influenced our measurements, we derived the cluster's main-sequence mass function down to 0.53 M using archival images obtained with the Hubble Space Telescope. We found a mass function slope of α = 1.27 ± 0.44, which is, compared to the canonical mass function, a significantly shallower slope. The derived lower limit on the cluster's mass is higher than the theoretically predicted mass in the case of MOND. Our data are consistent with a central density of ρ 0 = 0.1 M pc −3 . We need no dark matter in Palomar 14. If the cluster is on a circular orbit, our spectroscopic and photometric results argue against MOND, unless the cluster experienced significant mass loss.

Context. The dynamical evolution of a single globular cluster and also of the entire Galactic globular cluster system has been studied theoretically in detail. In particular, simulations show how the "lost" stars are distributed in tidal tails emerging from the clusters. Aims. We investigate the distribution of Galactic globular cluster stars on the sky to identify such features as tidal tails. The Sloan Digital Sky Survey provides consistent photometry of a large part of the sky to study the projected two-dimensional structure of the 17 globular clusters in its survey area. Methods. We used a color-magnitude weighted counting algorithm to map (potential) cluster member stars on the sky. Results. We recover the already known tidal tails of Pal 5 and NGC 5466. For NGC 4147 we find a two-arm morphology. Possible indications of tidal tails are also seen around NGC 5053 and NGC 7078, confirming earlier suggestions. Moreover, we find potential tails around NGC 5904 and Pal 14. Especially for Palomar clusters other than Pal 5, deeper data are needed to confirm or to rule out the existence of tails. For many of the remaining clusters in our sample we observe a pronounced extratidal halo, which is particularly large for NGC 7006 and Pal 1. In some cases, the extratidal halos may be associated with the stream of the Sagittarius dwarf spheroidal galaxy (e.g., NGC 4147, NGC 5024, NGC 5053).