D. M. Skowron, I. Soszyński, A. Udalski, M. K. Szymański, P. Pietrukowicz, J. Skowron, R. Poleski,

Ł. Wyrzykowski, K. Ulaczyk, S. Kozłowski, P. Mróz, M. Pawlak

2016, Acta. Astron, 66, 269 (arXiv:1608.00013)

Ł. Wyrzykowski, K. Ulaczyk, S. Kozłowski, P. Mróz, M. Pawlak

2016, Acta. Astron, 66, 269 (arXiv:1608.00013)

In an era of extensive photometric observations, the catalogs of RR Lyrae type variable stars number tens of thousands of objects. The relation between the iron abundance [Fe/H] and the Fourier parameters of the stars light curve allows us to investigate mean metallicities and metallicity gradients in various stellar environments, independently of time-consuming spectroscopic observations. In this paper we use almost 6500 V- and I-band light curves of fundamental mode RR Lyrae stars from the OGLE-IV survey to provide a precise relation between the V- and I-band phase parameter phi_31 used to estimate [Fe/H]. The relation depends on metallicity, which limits its applicability.

We show that the metallicity dependent (I->V) phi_31 transformation formula is only slightly less accurate than the metallicity independent one, so we apply the latter to photometric metallicity formulae developed for the Johnson V- and the Kepler Kp-band to obtain the relation between [Fe/H] and phi_31 for the I-band photometry.

We apply the new relation of Nemec et al. (2013) to the OGLE-IV fundamental mode RR Lyrae stars data and construct a metallicity map of the Magellanic Clouds. Median [Fe/H] is -1.39 +- 0.44 dex for the LMC and -1.77 +- 0.48 dex for the SMC, on the Jurcsik (1995) metallicity scale.

We also find a metallicity gradient within the LMC with a slope of -0.029 +- 0.002 dex/kpc in the inner 5 kpc and -0.030 +- 0.003 dex/kpc beyond 8 kpc, and no gradient in-between (−0.019 +- 0.002 dex/kpc integrally). We do not observe a metallicity gradient in the SMC, although we show that the metal-rich RRab stars are moreconcentrated toward the SMC center than the metal-poor.

Computer readable **Table 3** from the Paper is available for download here: table3.dat

ID | R.A. | Dec | Dist | [Fe/H]_J95 | [Fe/H]_ZW84 | ||
---|---|---|---|---|---|---|---|

[deg] | [deg] | [kpc] | |||||

lmc502_08_6887 | 81.655250 | -70.702472 | 51.65 | -1.510 | 0.087 | -1.670 | 0.061 |

lmc563_28_7986 | 88.958750 | -65.657083 | 46.75 | -1.470 | 0.039 | -1.642 | 0.027 |

lmc556_21_903 | 85.632917 | -65.586028 | 48.58 | -0.601 | 0.451 | -1.035 | 0.315 |

lmc551_14_16904 | 86.225667 | -71.925306 | 49.26 | -2.419 | 0.087 | -2.306 | 0.061 |

lmc520_13_1187 | 82.357042 | -65.215250 | 48.92 | -1.628 | 0.051 | -1.753 | 0.036 |

lmc531_02_18976 | 74.110208 | -69.658528 | 54.35 | -1.367 | 0.075 | -1.570 | 0.052 |

see whole Table |

- Dist - distance from the observer
- [Fe/H]_J95 - photometric metallicity on the scale of Jurcsik (1995)
- [Fe/H]_ZW84 - photometric metallicity on the scale of Zinn and West (1984)

**PLEASE cite the following paper when using the data or referring to these OGLE results:**

Skowron *et al.*, 2016,
Acta. Astron, 66, 269
(arXiv:1608.00013)

Any comments about the data and the form of their presentation are welcome as they can improve the future releases of OGLE analysis. Send your messages to this address.