AN EXAMINATION OF RECENT TRANSFORMATIONS TO THE BV(RI){sub C} PHOTOMETRIC SYSTEM FROM THE PERSPECTIVE OF STELLAR MODELS FOR OLD STARS
- Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6 (Canada)
- Max Planck Institute for Astrophysics, Postfach 1317, 85741 Garching (Germany)
Isochrones for ages {approx}>4 Gyr and metallicities in the range -2.5{approx}< [Fe/H] {approx}<+0.3 that take the diffusion of helium and recent advances in stellar physics into account are compared with observations in the Johnson-Cousins BV(RI){sub C} photometric system for several open and globular star clusters. The adopted color-T{sub eff} relations include those which we have derived from the latest MARCS model atmospheres and the empirical transformations for dwarf and subgiant stars given by Casagrande et al. (CRMBA). Those reported by VandenBerg and Clem have also been considered, mainly to resolve some outstanding questions concerning them. Indeed, for the latter, V - I{sub C} colors should be corrected by {approx}-0.02 mag, for all metal abundances, in order to obtain consistent interpretations of the observed (B - V, V), (V - R{sub C} , V), and (V - I{sub C} , V) diagrams for M 67 and the Hyades as well as for local subdwarfs. Remarkably, when the subdwarfs in the CRMBA data set that have {sigma}{sub {pi}/{pi}} {<=} 0.15 are superimposed on a set of 12 Gyr isochrones spanning a wide range in [Fe/H], the inferred metallicities and effective temperatures agree, in the mean, with those given by CRMBA to within {+-}0.05 dex and {+-}10 K, respectively. Thus, the hot T{sub eff} scale derived by CRMBA is nearly identical with that predicted by stellar models; and consequently, there is excellent consistency between theory and observations on the Hertzsprung-Russell diagram and the different color-magnitude diagrams considered in this investigation. To obtain similar consistency, the colors obtained from the MARCS and VandenBerg and Clem (B - V)-T{sub eff} relations for metal-poor dwarf stars should be adjusted to the red by 0.02-0.03 mag. In general, isochrones that employ the CRMBA transformations provide reasonably consistent fits to our BV(RI){sub C} photometry for main-sequence stars in the globular clusters 47 Tuc, M 3, M 5, M 92, and NGC 1851-but not the cluster giants (when adopting the synthetic MARCS colors). We speculate that differences between the actual heavy-element mixtures and those assumed in the theoretical models may be the primary cause of this difficulty.
- OSTI ID:
- 21443224
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 140, Issue 4; Other Information: DOI: 10.1088/0004-6256/140/4/1020; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ABUNDANCE
COLOR
DWARF STARS
HELIUM
HERTZSPRUNG-RUSSELL DIAGRAM
MAIN SEQUENCE STARS
METALS
PHOTOMETRY
STAR CLUSTERS
STAR EVOLUTION
DIAGRAMS
ELEMENTS
EVOLUTION
FLUIDS
GASES
INFORMATION
NONMETALS
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHYSICAL PROPERTIES
RARE GASES
STARS