ON THE RR LYRAE STARS IN GLOBULARS. IV. ω CENTAURI OPTICAL UBVRI PHOTOMETRY

• Published in: The Astronomical journal 2016-12, Vol.152 (6), p.170
• Main Authors: Braga, V. F., Stetson, P. B., Bono, G., Dall’Ora, M., Ferraro, I., Fiorentino, G., Freyhammer, L. M., Iannicola, G., Marengo, M., Neeley, J., Valenti, E., Buonanno, R., Calamida, A., Castellani, M., da Silva, R., Degl’Innocenti, S., Di Cecco, A., Fabrizio, M., Freedman, W. L., Giuffrida, G., Lub, J., Madore, B. F., Marconi, M., Marinoni, S., Matsunaga, N., Monelli, M., Persson, S. E., Piersimoni, A. M., Pietrinferni, A., Prada-Moroni, P., Pulone, L., Stellingwerf, R., Tognelli, E., Walker, A. R.
• Format: Article
• Language: English
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CALIBRATION; CHARGE-COUPLED DEVICES; COLOR; COMPARATIVE EVALUATIONS; DIAGRAMS; DISTANCE; LUMINOSITY; METALLICITY; METALS; MILKY WAY; PHOTOMETRY; PULSATIONS; SKY; STAR CLUSTERS; VARIABLE STARS
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.3847/0004-6256/152/6/170

New accurate and homogeneous optical UBVRI photometry has been obtained for variable stars in the Galactic globular cluster ω Cen (NGC 5139). We secured 8202 CCD images covering a time interval of 24 years and a sky area of 84 × 48 arcmin. The current data were complemented with data available in the literature and provided new, homogeneous pulsation parameters (mean magnitudes, luminosity amplitudes, periods) for 187 candidate ω Cen RR Lyrae (RRLs). Among them we have 101 RRc (first overtone) and 85 RRab (fundamental) variables, and a single candidate RRd (double-mode) variable. Candidate Blazhko RRLs show periods and colors that are intermediate between the RRc and RRab variables, suggesting that they are transitional objects. A comparison of the period distribution and the Bailey diagram indicates that RRLs in ω Cen show a long-period tail not present in typical Oosterhoff II (OoII) globulars. The RRLs in dwarf spheroidals and in ultra-faint dwarfs have properties between Oosterhoff intermediate and OoII clusters. Metallicity plays a key role in shaping the above evidence. These findings do not support the hypothesis that ω Cen is the core remnant of a spoiled dwarf galaxy. Using optical period–Wesenheit relations that are reddening-free and minimally dependent on metallicity we find a mean distance to ω Cen of 13.71 ± 0.08 ± 0.01 mag (semi-empirical and theoretical calibrations). Finally, we invert the I -band period–luminosity–metallicity relation to estimate individual RRLs’ metal abundances. The metallicity distribution agrees quite well with spectroscopic and photometric metallicity estimates available in the literature.