Galactic Fundamental Mode RR Lyrae Stars: Period-Amplitude Diagram, Metallicities and Distribution

We have analyzed 1455 fundamental mode RR Lyrae of the Galactic field, using the All Sky Automated Survey data. The sample covers 75% of the sky and contains objects in the close neighborhood of the Sun, within 4 kpc distance. Unlike in the previous analysis of the close field RRab, we see a clear manifestation of the Oosterhoff groups on the period amplitude diagram. The relation for Oosterhoff I type variables becomes strongly flattened at large V amplitudes, which was not observed for globular cluster RR Lyrae. We calculate photometric metallicities using methods of Jurcsik & Kovacs (1996) and Sandage (2004) and find significant discrepancies between results from both methods. Comparison with spectroscopic metallicities favors the method of Jurcsik & Kovacs (1996). In addition, we notice that RRab of Oosterhoff II type follow a different metallicity-period-phase relation than Oosterhoff I type variables. The spatial distribution of Galactic field RRab does not show any metallicity gradients with distance from the Galactic Center in either of the Oosterhoff groups. The older, metal poor Oosterhoff II variables are uniformly distributed with the distance from the galactic plane, while the metal rich Oosterhoff I RRab become more concentrated to the Galactic plane with increasing metal content.