Magellanic System in OGLE-IV

OGLE-ing the Magellanic System: Photometric Metallicity from Fundamental Mode RR Lyrae Stars

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)

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.

Metallicity dependence of the phi_31 interrelation

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.

Metallicity Map of the Magellanic System       Binned Metallicity Map of the Magellanic System

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.

Metallicity Gradient in the LMC       Metallicity Gradient in the SMC

Metallicity Gradient in the LMC and SMC

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

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.