Template K Light Curves for RR Lyrae Stars

Abstract

We discuss a technique to compute (K) using templates developed by fitting a Fourier series to existing high-quality K light curves of field RR Lyraes. We find that a series of order 2 is sufficient to model the light curves of first-overtone RRc variables, but four different sixth-order templates are needed for the fundamental RRab stars due to changes in the light curves that appear to correlate with the B amplitude. Applying the appropriate template to single-phase observations yield estimated (K) values whose deviation from the true (K) is randomly distributed over phase, and is of the same order of magnitude as the observational uncertainty, as long as the ephemeris phase is accurate. The addition of a second point, separated by at least 0.2 in phase from the first, allows the use of template shifting to remove deviations that may arise from uncertainties in the ephemeris phase, and template and scaling factor selection, with final systematic errors reduced to less than 0.03 mag. We find that the use of templates yield superior results to those derived using other techniques, which can produce (K) values that show systematic deviations over phase.

Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud

“…In most cases we have five K s measurements per star. To improve the intrinsic precision of the RR Lyrae mean magnitudes, we performed a fit of the individual phase points with template curves taken from Jones et al (1996). These authors have determined different template shapes depending on the type of variability (RRab or RRc type, standing for fundamental and first overtone pulsators, respectively) and on the B-amplitude of the variable, and described each of these templates in terms of a Fourier series.…”

“…Then we computed the average magnitude value for each variable star, which are listed in Table 4. According to Jones et al (1996), the use of templates to determine mean K s values is precise to within 0.03 mag.…”

Near-Infrared photometry of the LMC cluster Reticulum

“…With this relation we obtained a distance modulus to the LMC cluster Reticulum that is in good agreement with the LMC Cepheid distance. The accuracy of the result could be further improved by fitting the light curves with suitable templates (Jones et al, 1996). Finally, as a preliminary result, we also estimated the Reticulum distance modulus with a period-luminosity-metallicity relation for the J-band, and we obtained a value in good agreement with the P LZ K distance.…”

Improving the cosmic distance ladder. Distance and structure of the Large Magellanic Cloud

“…Longmore et al (1986) pioneering work was followed by Liu & Janes (1990), Skillen et al (1993) and Jones et al (1996). A comprehensive analysis of the IR properties of RR Lyrae stars was performed by Nemec et al (1994).…”

“…9 and 10 in Catelan et al (2004) and assuming [α/Fe]∼ 0.3 (e.g., Carney 1996) we transformed Eq. 1.17 into the form: Templates from Jones et al (1996) were used to fit the light curves of the RR Lyrae stars and derive mean K magnitudes. The zero-point of the relation was calculated using 22 CHAPTER 1.…”