A. Arellano Ferro,2 M. J. Arévalo,3,4 C. Lázaro,3,4 M. Rey,3,4 D. M. Bramich,4,5 and S. Giridhar6
2 Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510 México D. F., México. (armando@astroscu.unam.mx).
3 Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Tenerife.
4 Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain. (mam@ll.iac.es; clh@ll.iac.es; mrey@ll.iac.es).
5 IAC and School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, KY16 9SS, UK. (dmb7@st-andrews.ac.uk).
6 Indian Institute of Astrophysics, Bangalore 500034, India. (giridhar@iiap.ernet.in).
]]>Received 2004 May 27
Accepted 2004 August 9.
ABSTRACT
We report the results of CCD V a nd R photometry of the RR Lyrae stars known in NGC 4147. The periodicities of most variables are revised and new ephemerides are calculated. The Blazhko effect has been detected in V2 and V6. Three previously reported variables; V5, V9, and V15 are found to be non-variable. A new variable V18 was discovered with a period of 0.49205 days and an amplitude of 0.15 mag. Using the approach of Fourier decomposition of the light curves, the physical parameters of the RRab and RRc variables were estimated. The cluster is of the Oosterhoff type I. With the newly values [Fe/H]= -1.22 ±0.31 and 16.8 ± 13 kpc, the cluster fits very well into the Oosterhoff type-metallicity and metallicity-temperature sequence found in globular clusters. A comparison with ZAHB models indicates that the RRab stars have not yet evolved off the horizontal branch, a result consistent with the mean period of the RRab variables and with the metallicity of the cluster derived in this work.
Key Words: Globular clusters: NGC 4147 — Stars: Variables RR Lyrae.
RESUMEN
Reportamos los resultados de la fotometría CCD a través de los filtros V y R de las estrellas RR Lyrae conocidas en NGC 4147. Los períodos de todas las variables han sido recalculados y se dan nuevas efemérides. Se detectó efecto Blazhko en las variables V2 y V6. Las estrellas V5, V9 y V15, reportadas previamente como variables, no muestran variaciones. Se reporta la nueva variable, V18, que muestra un período de 0.49205 días y una amplitud de 0.15 mag. Con la técnica de descomposición de Fourier de las curvas de luz se han estimado los parámetros físicos de las variables RRab y RRc. El cúmulo es del tipo de Oosterhoff I. Los nuevos valores determinados para el contenido de hierro y la distancia; [Fe/H]= -1.22 ± 031 y 16.8 ± 1.3 kpc colocan adecuadamente al cúmulo en las secuencias tipo de Oosterhoff-metalicidad y metalicidad-temperatura efectiva para cúmulos globulares. Una comparación con modelos de la Rama Horizontal indica que las RRab de NGC 4147 no han abandonado esa fase aún, lo que es congruente con su período promedio y la metalicidad del cúmulo.
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ACKNOWLEDGEMENTS
AAF acknowledges support from DGAPA-UNAM grant through project IN110102 and is thankful to the CONACyT (México) and the Department of Science and Technology (India), for the travel support and local hospitality respectively, under Indo-Mexican collaborative project DST/INT/MEXICO/RP001/2001. We thank the staff at IAO and at the remote control station at CREST, Hosakote for assistance during the observations. This work has made a large use of the SIM-BAD and ADS services, for which we are thankful.
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1 Based on observations collected at the San Pedro Mártir Observatory, México, Indian Astronomical Observatory, Hanle, India, and Observatorio del Teide, Tenerife, Spain.
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