Fourier decomposition of RR Lyrae ligth curves and the SX Phe population in the central region of NGC 3201

 

A. Arellano Ferro,^1,2 J. A. Ahumada,³ J. H. Calderón,^1,3,4 and N. Kains⁵

 

¹ Visiting Astronomer, Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, and the National Universities of La Plata, Córdoba, and San Juan, Argentina.

² Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, México, D. F., C.P. 04510, México (armando@astro.unam.mx).

³ Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina (javier@oac.uncor.edu, jehumcal@gmail.com).

⁴ Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.

⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA (nkains@stsci.edu).

 

Received April 23 2014.
Accepted June 10 2014.

 

RESUMEN

Presentamos el análisis de una serie temporal de imágenes CCD de la región central del cúmulo globular NGC 3201. El objetivo principal de este trabajo es la descomposición de Fourier de las curvas de luz de las estrellas RR Lyrae y su empleo en la determinación de la metalicidad del cúmulo y de su distancia. De esta manera hemos obtenido, para la metalicidad, el valor medio [Fe/H]_zw = −1.483 ±0.006 (estadístico) ±0.090 (sistemático), y para la distancia, 5.000 ± 0.001 kpc (estadístico) ±0.220 (sistemático). La metalicidad y la distancia estimados a partir de dos estrellas RRc son congruentes con los anteriores. Debido a la presencia de enrojecimiento diferencial, derivamos valores individuales de E(B − V) para las estrellas RR Lyrae analizando sus curvas de color V − I. El valor promedio encontrado es E(B − V) = 0.23±0.02. Una exploración de las curvas de luz de las estrellas en la región de las blue stragglers condujo al descubrimiento de tres nuevas variables SX Phe. La relación periodo-luminosidad de las estrellas SX Phe se empleó para obtener una determinación independiente de la distancia al cúmulo y de los enrojecimientos individuales. La distancia calculada fue de 5.0 kpc.

 

ABSTRACT

CCD time-series observations of the central region of the globular cluster NGC 3201 were obtained with the aim of performing the Fourier decomposition of the light curves of the RR Lyrae stars present in that field. This procedure gave the mean values, for the metallicity, of [Fe/H]_zw = −1.483 ± 0.006 (statistical) ±0.090 (systematic), and for the distance, 5.000 ± 0.001 kpc (statistical) ±0.220 (systematic). The values found from two RRc stars are consistent with those derived previously. The differential reddening of the cluster was investigated and individual reddenings for the RR Lyrae stars were estimated from their V − I curves. We found an average value of E(B − V) = 0.23 ± 0.02. An investigation of the light curves of stars in the blue straggler region led to the discovery of three new SX Phe stars. The period-luminosity relation of the SX Phe stars was used for an independent determination of the distance to the cluster and of the individual reddenings. We found a distance of 5.0 kpc.

Key Words: globular clusters: individual: (NGC 3201) — stars: variables: RR Lyrae.

 

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ACKNOWLEDGMENTS

We warmly thank Dr. Daniel Bramich for allowing us the use DanDIA and for guiding our reduction process, as well as for useful and opportune comments. We are thankful to our referee Christine Clement for her constructive suggestions and comments. AAF acknowledges Roberto Figuera Jaimes for his valuable help in the first stages of the data reduction. We are indebted to the CONACyT (México) and MINCyT (Argentina) for financial support through the interchange project 188769 (MX/12/09). AAF acknowledges the support from DGAPA-UNAM grant through project IN104612, and is thankful to the European Southern Observatory (Garching), and to the Observatorio Astronómico of the Universidad Nacional de Córdoba (Argentina) for warm hospitality during different stages of this work. We have made an extensive use of the SIMBAD and ADS services, for which we are thankful.

 

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