EDP Sciences
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Volume 407, Number 1, August III 2003
Page(s) 377 - 384
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20030781

A&A 407, 377-384 (2003)
DOI: 10.1051/0004-6361:20030781

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

N. Kaltcheva1, J. Knude2 and V. Georgiev3

1  Department of Physics & Astronomy, University of Wisconsin Oshkosh, 800 Algoma Blvd., Oshkosh, WI 54901-8644, USA
2  Niels Bohr Institute for Astronomy, Physics and Geophysics, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
    e-mail: indus@astro.ku.dk
3  Department of Astronomy, University of Sofia, 5 J. Bourchier Ave., 1164 Sofia, Bulgaria
    e-mail: vladimir@phys.uni-sofia.bg

(Received 4 April 2003 / Accepted 18 May 2003 )

Using the largest database of near-IR Ca II Triplet indices currently available (Cenarro et al. 2001a,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(Strömgren)- B(Johnson) index with gravity, temperature and the equivalent width of the Ca II Triplet. Since v(Strömgren)- B(Johnson) have a none overlapping variation with the Ca II Triplet the dwarfs and giants may be separated and $T_{\rm eff}$ and log  g may be estimated. The v(Strömgren)- B(Johnson) index has furthermore the advantage that $E(v-B) \approx
0.25E(B-V)$ .

Key words: methods: observational -- techniques: photometric

Offprint request: N. Kaltcheva, kaltchev@uwosh.edu

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