CCD Photometry of the Globular Cluster M15: RR Lyrae Fourier Decomposition and Physical Parameters¹

 

A. Arellano Ferro,² G. García Lugo,³ and P. Rosenzweig³

 

² Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510 México D. F., México (armando@astroscu.unam.mx).

³ Grupo de Astrofísica Teórica, Facultad de Ciencias, Universidad de Los Andes, Mérida, Venezuela (gabysa24@hotmail.com; patricia@ula.ve).

 

Received 2005 October 11
Accepted 2005 December 15

 

RESUMEN

Se reportan los resultados de la fotometría CCD a través de los filtros V y R de 33 estrellas RR Lyrae conocidas en M15. Los períodos de algunas variables han sido recalculados y se dan nuevas efemérides. El efecto Blazhko, reportado previamente para V12 no ha sido detectado. Con la técnica de descomposición de Fourier de las curvas de luz, se han estimado los parámetros físicos de las variables de tipos RRab y RRc. El cúmulo es del tipo Oosterhoff II y los valores determinados para el contenido de hierro y la distancia son: [Fe/H]= —1.98 ± 0.24 y d = 8.67 ± 0.41 kpc, respectivamente. Los valores medios de los parámetros físicos de las estrellas RR Lyrae colocan al cúmulo correctamente en las secuencias tipo de Oosterhoff — metalicidad y metalicidad— temperatura efectiva, válidas para cúmulos globulares. Se han encontrado evidencias de evolución, desde la Rama Horizontal de Edad Cero, de las estrellas RRc pero no de las RRab.

 

ABSTRACT

Results of CCD photometry using V and R filters are reported for 33 RR Lyrae stars in M15. The periodicities of some variables have been revised and new ephemerides are given. The Blazhko effect, previously reported in V12, was not detected. Applying the approach of Fourier decomposition of the light curves, the physical parameters of the type RRab and RRc variables were estimated. The cluster is Oosterhoff type II and the values for the iron content and distance are: [Fe/H]= —1.98 ± 0.24 and d = 8.67 ± 0.41 kpc, respectively. The mean values of the physical parameters determined for the RR Lyrae stars place the cluster precisely into the sequences Oosterhoff type —metallicity and metallicity— effective temperature, valid for globular clusters. Evidences of evolution from the ZAHB are found for the RRc but not for the RRab stars.

Key Words: GLOBULAR CLUSTERS (M15) — STARS: VARIABLES: RR LYRAE — STARS: HORIZONTAL BRANCH.

 

DESCARGAR ARTÍCULO EN FORMATO PDF

 

ACKNOWLEDGEMENTS

We are indebted with the referee, Dr. Ennio Poretti, for his valuable comments and suggestions. AAF acknowledges support from DGAPA-UNAM grant through project IN110102, and to the Universidad de Los Andes for hospitallity. PR is grateful for the financial support provided by C.D.C.H.T.-U.L.A. through Project C-1245-04-05-B. PR and GG wish to express their gratitude for the financial aid given by Sigma Xi Grant-in-Aid 12030111. We thank Enrique Rojo and Aracely Aguilar for assistance with the observations, and Luis O. Porras for some reductions. This work has made extensive use of the SIMBAD and ADS services, for which we are grateful.

 

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Nota

¹ Based on observatios collected at the Observatorio Astronámico Nacional San Pedro Mártir, B.C. México