Interrelations between Vilnius and Strömgren photometric systems: The luminosity indicator(v – X)

Abstract

Using the largest database of near-IR Ca II Triplet indices currently available (Cenarro et al. [CITE],b), we confirm our finding about the influence of the Ca II stellar lines on the X magnitude of the Vilnius photometric system. This effect is significant for spectral sub-classes from early F until mid K. For this spectral range there is a linear relation between the $v-X$ index and the strength of the infrared Ca II Triplet, which implies that the Ca II H&K lines should influence the difference in a similar way. For the spectral interval studied, $v-X$ repeats the behavior of the Ca II Triplet with respect to gravity, temperature and metallicity. The Ca II Triplet lines are a powerful diagnostic of the stellar populations in galaxies because of their sensitivity to the main stellar atmospheric parameters. Being much easily achievable observationally and virtually reddening free, the $v-X$ index may find similar applications. $v-X$ is log g sensitive but additional means are required to break the dwarf – giant duplicity. For this purpose we have studied the variation of the v (Stromgren)- B (Johnson) index with gravity, temperature and the equivalent width of the Ca II Triplet. Since v (Stromgren)- B (Johnson) have a none overlapping variation with the Ca II Triplet the dwarfs and giants may be separated and T eff and log g may be estimated. The v (Stromgren)- B (Johnson) index has furthermore the advantage that $E(v-B) \approx 0.25E(B-V)$.