Approximating RR Lyrae light curves using cubic polynomials

In this paper, we use cubic polynomials to approximate RR Lyrae light curves and apply the method to HST data of RR Lyraes in the halo of M31. We compare our method to the standard method of Fourier decomposition and find that the method of cubic polynomials eliminates virtually all ringing effects and does so with significantly fewer parameters than the Fourier technique. Further, for RRc stars the parameters in the fit are all physical. Our study also reveals a number of additional periodicites in this data not found previously: we find 23 RRc stars, 29 RRab stars and 3 multiperiodic stars.Comment: 6 pages, MNRAS accepte

Large Magellanic Cloud Distance from Cepheid Variables using Least Squares Solutions

Distance to the Large Magellanic Cloud (LMC) is determined using the Cepheid variables in the LMC. We combine the individual LMC Cepheid distances obtained from the infrared surface brightness method and a dataset with a large number of LMC Cepheids. Using the standard least squares method, the LMC distance modulus can be found from the ZP offsets of these two samples. We have adopted both a linear P-L relation and a ``broken'' P-L relation in our calculations. The resulting LMC distance moduli are 18.48+-0.03 mag and 18.49+-0.04 mag (random error only), respectively, which are consistent to the adopted 18.50 mag in the literature.Comment: 2 pages and 1 figure, to appear in proceeding of "Galaxies in the Local Volume" Sydney 8-13 July 200

The Detailed Forms of the LMC Cepheid PL and PLC Relations

Possible deviations from linearity of the LMC Cepheid PL and PLC relations are investigated. Two datasets are studied, respectively from the OGLE and MACHO projects. A nonparametric test, based on linear regression residuals, suggests that neither PL relation is linear. If colour dependence is allowed for then the MACHO PL relation is found to deviate more significantly from the linear, while the OGLE PL relation is consistent with linearity. These finding are confirmed by fitting "Generalised Additive Models" (nonparametric regression functions) to the two datasets. Colour dependence is shown to be nonlinear in both datasets, distinctly so in the case of the MACHO Cepheids. It is also shown that there is interaction between the period and colour functions in the MACHO data.Comment: 20 pages, 20 figures, MNRAS accepte

Period Color and Amplitude Color relations for MACHO project LMC RR Lyraes

In this paper, we analyze period color and amplitude color relations at minimum, mean and maximum $V$ band light for 6391 RRab stars in the Large Magellanic Cloud obtained by the MACHO project. Specifically, we find that color and amplitude are nearly independent of period at minimum light but that there exists a definite relation between period and color and amplitude and color at maximum light. These two properties are easily explained by the application of the Stefan Boltzmann law and the interaction of the photosphere and hydrogen ionization front at minimum light. When we examine the slope of the period color relation as a function of phase, we find that the slope varies significantly with phase and is small for a wide range of phases around minimum light. This suggests that another factor that needs to be considered when trying to understand RR Lyrae observed properties is their behavior at different phases during a pulsation cycle.Comment: Sumitted for publication to MNRAS Letter

Principal Component Analysis of RR Lyrae light curves

In this paper, we analyze the structure of RRab star light curves using Principal Component Analysis. We find this is a very efficient way to describe many aspects of RRab light curve structure: in many cases, a Principal Component fit with 9 parameters can describe a RRab light curve including bumps whereas a 17 parameter Fourier fit is needed. As a consequence we show statistically why the amplitude is also a good summary of the structure of a RR Lyrae light curve. We also use our analysis to derive an empirical relation relating absolute magnitude to light curve structure. In comparing this formula to those derived from exactly the same dataset but using Fourier parameters, we find that the Principal Component Analysis approach has disticnt advantages. These advantages are, firstly, that the errors on the coefficients in such formulae are smaller, and secondly, that the correlation between Principal Components is significantly smaller than the correlation between Fourier amplitudes. These two factors lead to reduced formal errors, in some cases estimated to be a factor of 2, on the eventual fitted value of the absolute magnitude. This technique will prove very useful in the analysis of data from existing large scale survey projects concerning variable stars.Comment: 8 pages, 10 figures, revised version, accepted for publication to MNRA

Testing the nonlinearity of the BVIcJHKs period-luminosity relations for the Large Magellanic Cloud Cepheids

A number of recent works have suggested that the period-luminosity (PL) relation for the Large Magellanic Cloud (LMC) Cepheids exhibits a controversial nonlinear feature with a break period at 10 days. Therefore, the aim of this Research Note is to test the linearity/nonlinearity of the PL relations for the LMC Cepheids in BVIcJHKs band, as well as in the Wesenheit functions. We show that simply comparing the long and short period slopes, together with their associate d standard deviations, leads to a strictly larger error rate than applying rigorous statistical tests such as the F-test. We applied various statistical tests to the current published LMC Cepheid data. These statistical tests include the F-test, the testimator test, and the Schwarz information criterion (SIC) method. The results from these statistical tests strongly suggest that the LMC PL relation is nonlinear in BVIcJH band but linear in the Ks band and in the Wesenheit functions. Using the properties of period-color relations at maximum light and multi-phase relations, we believe that the nonlinear PL relation is not caused by extinction errors.Comment: 6 pages, 5 figures and 2 tables, A&A accepte

International poverty projections

The authors investigate the methodology used in projections of international poverty - particularly those used in many World Bank documents. The methodology, as developed by Ahluwalia, Carter, and Chenery (1979) in an influential paper, is examined critically and subjected to sensitivity analysis. It was found that their projections of poverty are not robust to reasonable changes and improvements in the methodology; in some cases, even the projections'time trend is reversed. Thus, analysts and policymakers should treat such global forecasts of poverty with caution.Economic Theory&Research,Achieving Shared Growth,Economic Conditions and Volatility,Inequality,Environmental Economics&Policies

Poverty Effects of the Minimum Wage: The Role of Household Employment Composition

sector employment, uncovered sector employment, and unemployment. The impact of these labor market adjustments on absolute poverty will depend on how the pattern of employment composition changes within households and on how income is shared within households. An earlier paper (Fields and Kanbur, 2007) focused on the income-sharing dimension of the problem. The present paper focuses on household employment composition. For a particular structure of the labor market— one with good jobs, bad jobs, unemployment, and adult and youth workers— and with a particular model of how the sectoral patterns of employment are translated into household employment composition, we analyze the impact of minimum wages on a class of absolute poverty measures. The precise characterizations demonstrate the need for a nuanced appreciation of the impacts of a minimum wage increase, since they depend intricately on the values of key parameters (the poverty line, poverty aversion, labor demand elasticity, and the starting level of the minimum wage). Moreover, the relationship between poverty and the minimum wage is in general nonmonotonic, so that local effects can be quite different from the effects of large changes in the minimum wage.Minimum wage, poverty, labor market, Financial Economics, Food Security and Poverty, Labor and Human Capital,

Semi-Empirical Cepheid Period-Luminosity Relations in Sloan Magnitudes

In this paper we derive semi-empirical Cepheid period-luminosity (P-L) relations in the Sloan ugriz magnitudes by combining the observed BVI mean magnitudes from the Large Magellanic Cloud Cepheids (LMC) and theoretical bolometric corrections. We also constructed empirical gr band P-L relations, using the publicly available Johnson-Sloan photometric transformations, to be compared with our semi-empirical P-L relations. These two sets of P-L relations are consistent with each other.Comment: 4 pages, 2 tables and 2 figures, ApJ accepte