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Register a new userOn the variation of light curve parameters of RR Lyrae variables at multiple wavelengths
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We present a detailed light curve analysis of RR Lyrae variables at multiple wavelengths using Fourier decomposition method. The time-series data for RR Lyrae variables in the Galactic bulge and the Magellanic Clouds are taken from the Optical Gravitational Lensing Experiment survey while the infrared light curves are compiled from the literature. We also analyse the multiband theoretical light curves that are generated from the stellar pulsation models of RR Lyrae stars for a wide range of metal-abundances. We find that the theoretical light curve parameters with different metal abundances are consistent with observed parameters in most period bins at both optical and infrared wavelengths. The theoretical and observed Fourier amplitude parameters decrease with increase in wavelength while the Fourier phase parameters increase with wavelength at a given period. We use absolute magnitudes for a subset of theoretical models that fit the observed optical RR Lyrae light curves in the Large Magellanic Cloud to estimate a distance modulus, $mu_textrm{LMC}=18.51pm0.07$, independent of the metallicity. We also use Fourier analysis to study the period-color and amplitude-color relations for RR Lyrae stars in the Magellanic Clouds using optical data and find that the slope of period-color relation at minimum light is very shallow or flat and becomes increasingly significant at the maximum light for RRab stars. We also find that the metallicity dependence of the period-color relations increases as we go from minimum to maximum light, suggesting that the mean light results are indeed an average of the various pulsational phases. We summarize that the average variation in these relations is consistent between theory and observations and supports the theory of the interaction of the stellar photosphere and the hydrogen ionization front.
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We present results from a comparative study of light curves of Cepheid and RR Lyrae stars in the Galaxy and the Magellanic Clouds with their theoretical models generated from the stellar pulsation codes. Fourier decomposition method is used to analyse the theoretical and the observed light curves at multiple wavelengths. In case of RR Lyrae stars, the amplitude and Fourier parameters from the models are consistent with observations in most period bins except for low metal-abundances ($Z<0.004$). In case of Cepheid variables, we observe a greater offset between models and observations for both the amplitude and Fourier parameters. The theoretical amplitude parameters are typically larger than those from observations, except close to the period of $10$ days. We find that these discrepancies between models and observations can be reduced if a higher convective efficiency is adopted in the pulsation codes. Our results suggest that a quantitative comparison of light curve structure is very useful to provide constraints for the input physics to the stellar pulsation models.
We provide homogeneous optical (UBVRI) and near-infrared (JHK) time series photometry for 254 cluster (omega Cen, M4) and field RR Lyrae (RRL) variables. We ended up with more than 551,000 measurements. For 94 fundamental (RRab) and 51 first overtones (RRc) we provide a complete optical/NIR characterization (mean magnitudes, luminosity amplitudes, epoch of the anchor point). The NIR light curves of these variables were adopted to provide new and accurate light-curve templates for both RRc (single period bin) and RRab (three period bins) variables. The templates for the J and the H band are newly introduced, together with the use of the pulsation period to discriminate among the different RRab templates. To overcome subtle uncertainties in the fit of secondary features of the light curves we provide two independent sets of analytical functions (Fourier series, Periodic Gaussian functions). The new templates were validated by using 26 omega Cen and Bulge RRLs covering the four period bins. We found that the difference between the measured mean magnitude along the light curve and the mean magnitude estimated by using the template on a single randomly extracted phase point is better than 0.01 mag (sigma=0.04 mag). We also validated the template on variables for which at least three phase points were available, but without information on the phase of the anchor point. The accuracy of the mean magnitudes is ~0.01 mag (sigma=0.04 mag). The new templates were applied to the Large Magellanic Cloud (LMC) globular Reticulum and by using literature data and predicted PLZ relations we found true distance moduli of 18.47+-0.10+-0.03 mag (J) and 18.49+-0.09+-0.05 mag (K). We also used literature optical and mid-infrared data and we found a mean true distance modulus of 18.47+-0.02+-0.06 mag, suggesting that Reticulum is ~1 kpc closer than the LMC.
The history of the observations of RR Lyr variables started in the XIXth century, more than 120 years ago. The very long time baseline of available data combined with the short period of RR Lyrae variables offer an unique opportunity to look at their past as a treasure of valuable information. At this purpose, the amateur/professional association Groupe Europeen dObservations Stellaires (GEOS) has built a database aimed to gather all the published maxima. We could study the period changes due to stellar evolution. Most of the 123 scrutinized RRab stars does not show any significant period variation. This reflects the fact that the rapid evolution is confined in short evolutionary phases. Notwithstanding this, we could put in evidence period increases in 27 stars and decreases in 21 ones. We also used the GEOS database to study the Blazhko effect of galactic RRab stars. The closed curves representing the Blazhko effect are constructed by plotting the magnitudes at maximum vs. the O-C values. We obtained a variegate family of Blazhko potatoes. We could also reconstruct the changes in the pulsational and Blazhko periods of RR Lyr itself, resulted to be completely decoupled. Moreover, the amplitude of the Blazhko effect decreased so much to be hardly detectable by looking at the maxima collected in 2014 only. The effect seems to start again in the 2015 data.
The wide-field synoptic sky surveys, known as the Palomar Transient Factory (PTF) and the intermediate Palomar Transient Factory (iPTF), will accumulate a large number of known and new RR Lyrae. These RR Lyrae are good tracers to study the substructure of the Galactic halo if their distance, metallicity, and galactocentric velocity can be measured. Candidates of halo RR Lyrae can be identified from their distance and metallicity before requesting spectroscopic observations for confirmation. This is because both quantities can be obtained via their photometric light curves, because the absolute V-band magnitude for RR Lyrae is correlated with metallicity, and the metallicity can be estimated using a metallicity-light curve relation. To fully utilize the PTF and iPTF light-curve data in related future work, it is necessary to derive the metallicity-light curve relation in the native PTF/iPTF R-band photometric system. In this work, we derived such a relation using the known ab-type RR Lyrae located in the Kepler field, and it is found to be $[Fe/H]_{PTF} = -4.089 - 7.346 P + 1.280 phi_{31}$ (where $P$ is pulsational period and $phi_{31}$ is one of the Fourier parameters describing the shape of the light curve), with a dispersion of 0.118 dex. We tested our metallicity-light curve relation with new spectroscopic observations of a few RR Lyrae in the Kepler field, as well as several data sets available in the literature. Our tests demonstrated that the derived metallicity-light curve relation could be used to estimate metallicities for the majority of the RR Lyrae, which are in agreement with the published values.
We present a new complete Near-Infrared (NIR, $JHK_s$) census of RR Lyrae stars (RRLs) in the globular $omega$ Cen (NGC 5139). We collected 15,472 $JHK_s$ images with 4-8m class telescopes over 15 years (2000-2015) covering a sky area around the cluster center of 60x34 arcmin$^2$. These images provided calibrated photometry for 182 out of the 198 cluster RRL candidates with ten to sixty measurements per band. We also provide new homogeneous estimates of the photometric amplitude for 180 ($J$), 176 ($H$) and 174 ($K_s$) RRLs. These data were supplemented with single-epoch $JK_s$ magnitudes from VHS and with single-epoch $H$ magnitudes from 2MASS. Using proprietary optical and NIR data together with new optical light curves (ASAS-SN) we also updated pulsation periods for 59 candidate RRLs. As a whole, we provide $JHK_s$ magnitudes for 90 RRab (fundamentals), 103 RRc (first overtones) and one RRd (mixed--mode pulsator). We found that NIR/optical photometric amplitude ratios increase when moving from first overtone to fundamental and to long-period (P>0.7 days) fundamental RRLs. Using predicted Period-Luminosity-Metallicity relations, we derive a true distance modulus of 13.674$pm$0.008$pm$0.038 mag (statistical error and standard deviation of the median)---based on spectroscopic iron abundances---and of 13.698$pm$0.004$pm$0.048 mag---based on photometric iron abundances. We also found evidence of possible systematics at the 5-10% level in the zero-point of the PLs based on the five calibrating RRLs whose parallaxes had been determined with HST
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