Constraining the parameters of globular cluster NGC 1904 from its variable star population^⋆

¹ European Southern Observatory, Karl-Schwarzschild Straße 2, 85748 Garching bei München, Germany
e-mail: nkains@eso.org
² SUPA School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
³ Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, 04510 Mexico, Mexico
⁴ Indian Institute of Astrophysics, 560034 Koramangala, Bangalore, India

Received: 13 August 2012
Accepted: 24 October 2012

Abstract

Aims. We present the analysis of 11 nights of V and I time-series observations of the globular cluster NGC 1904 (M 79). Using this we searched for variable stars in this cluster and attempted to refine the periods of known variables, making use of a time baseline spanning almost 8 years. We use our data to derive the metallicity and distance of NGC 1904.

Methods. We used difference imaging to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible.

Results. Out of 13 stars previously classified as variables, we confirm that 10 are bona fide variables. We cannot detect variability in one other within the precision of our data, while there are two which are saturated in our data frames, but we do not find sufficient evidence in the literature to confirm their variability. We also detect a new RR Lyrae variable, giving a total number of confirmed variable stars in NGC 1904 of 11. Using the Fourier parameters, we find a cluster metallicity  [Fe/H] _ZW = −1.63 ± 0.14, or  [Fe/H] _UVES = −1.57 ± 0.18, and a distance of 13.3 ± 0.4 kpc (using RR0 variables) or 12.9 kpc (using the one RR1 variable in our sample for which Fourier decomposition was possible).