Harmonizing the RR Lyrae and clump distance scales – stretching the short distance scale to intermediate ranges? |
| |
| Authors: | Piotr Popowski |
| |
| Institution: | Institute of Geophysics and Planetary Physics, L-413, Lawrence Livermore National Laboratory, University of California, PO Box 808, Livermore, CA 94551, USA |
| |
| Abstract: | I explore the consequences of making the RR Lyrae and clump giant distance scales consistent in the solar neighbourhood, Galactic bulge and Large Magellanic Cloud (LMC). I employ two major assumptions: (i) that the absolute magnitude–metallicity, M V (RR)–Fe/H], relation for RR Lyrae stars is universal, and (ii) that absolute I magnitudes of clump giants, M I (RC), in Baade's Window are known (e.g. can be inferred from the local Hipparcos -based calibration or theoretical modelling). A comparison between the solar neighbourhood and Baade's Window sets M V (RR) at Fe/H]=?1.6 in the range (0.59±0.05, 0.70±0.05), somewhat brighter than the statistical parallax solution. More luminous RR Lyrae stars imply younger globular clusters, which would be in better agreement with the conclusions from the currently favoured stellar evolution and cosmological models. A comparison between Baade's Window and the LMC sets M LMC(RC) I in the range (?0.33±0.09,?0.53±0.09). The distance modulus to the LMC is μ LMC∈(18.24±0.08,18.44±0.07). Unlike M LMC(RC) I , this range in μ LMC does not depend on the adopted value of the dereddened LMC clump magnitude, I LMC(RC)0. I argue that the currently available information is insufficient to select the correct distance scale with high confidence. |
| |
| Keywords: | stars: horizontal branch stars: variables: other dust extinction Galaxy: bulge Magellanic Clouds distance scale |
|
|
