Fourier Decomposition Of Light Curves Research Articles

Physical parameters of RR Lyrae stars in NGC 6171

We present an analysis of VI CCD time series photometry of the globular cluster NGC 6171. The main goal is to determine individual physical parameters for single‐mode RR Lyrae stars present in the field of view of our images, by means of light curve Fourier decomposition and well‐established calibrations and zero points. This leads to the estimation of the mean values of the metallicity and distance for the parental cluster. From the RRab stars, we find [Fe/H]ZW = −1.33 ± 0.12 and distance d = 5.3 ± 0.3 kpc, and from the RRc stars we find [Fe/H]ZW = −1.02 ± 0.19 and distance d = 5.3 ± 0.2 kpc. Independent methods such as the P–L (period–luminosity) relations for RRab and SX Phe stars enable the estimation of a weighted average distance to the cluster of 5.4 ± 0.1 kpc. We confirm the amplitude modulations of the Blazhko type of five RRab and the non‐membership of V21 to the cluster. The color–magnitude diagram is consistent with an age of 11 Gyrs. The distribution of RRab and RRc stars seems well segregated around the first overtone red edge of the instability strip. This positions NGC 6171 among OoI‐type clusters where the pulsating modes are neatly separated in the horizontal branch. We report two new irregular variables of the Lb type.

A detailed census of variable stars in the globular cluster NGC 6333 (M9) from CCD differential photometry★

We report CCD $V$ and $I$ time-series photometry of the globular cluster NGC 6333 (M9). The technique of difference image analysis has been used, which enables photometric precision better than 0.05 mag for stars brighter than $V \sim 19.0$ mag, even in the crowded central regions of the cluster. The high photometric precision has resulted in the discovery of two new RRc stars, three eclipsing binaries, seven long-term variables and one field RRab star behind the cluster. A detailed identification chart and equatorial coordinates are given for all the variable stars in the field of our images of the cluster. Our data together with literature $V$-data obtained in 1994 and 1995 allowed us to refine considerably the periods for all RR Lyrae stars. The nature of the new variables is discussed. We argue that variable V12 is a cluster member and an Anomalous Cepheid. Secular period variations, double mode pulsations and/or the Blazhko-like modulations in some RRc variables are addressed. Through the light curve Fourier decomposition of 12 RR Lyrae stars we have calculated a mean metallicity of [Fe/H]$_{\rm ZW}$=$-1.70 \pm 0.01{\rm(statistical)} \pm 0.14{\rm(systematic)}$ or [Fe/H]$_{UVES}=-1.67 \pm 0.01{\rm(statistical)} \pm 0.19{\rm(systematic)}$.Absolute magnitudes, radii and masses are also estimated for the RR Lyrae stars. A detailed search for SX Phe stars in the Blue Straggler region was conducted but none were discovered. If SX Phe exist in the cluster then their amplitudes must be smaller than the detection limit of our photometry. The CMD has been corrected for heavy differential reddening using the detailed extinction map of the cluster of Alonso-Garc\'ia et al. (2012). This has allowed us to set the mean cluster distance from two independent estimates; from the RRab and RRc absolute magnitudes, we find $8.04\pm 0.19$ kpc and $7.88\pm0.30$ kpc respectively.

A Study on W Ursae Majoris-Type Systems Recognised by the ROTSE-IIId Experiment

AbstractWe present a study on characterising the light curves of W UMa-type systems gathered from the archive containing 5 years of data observed with the Robotic Optical Transient Search Experiment Telescope (ROTSE-IIId) located in Turkey. A sample of 45 W UMa-type systems was studied on the basis of Fourier decomposition of light curves and some basic geometrical parameters, namely degree of contact (f), mass ratio (q), and orbital inclination (i), as approximated values for these systems were determined. Moreover, methods based on the Fourier transform technique were applied to the discrete data to determine the orbital periods of those systems. Preliminary estimates for the system parameters were presented and compared with the values available in the literature.

Exploring the variable stars in the globular cluster NGC 5024 (M53): new RR Lyrae and SX Phoenicis stars★

We report CCD V and I time series photometry of the globular cluster NGC 5024 (M53). The technique of difference image analysis has been used which enables photometric precisions better than 10 mmag for stars brighter than V 18.5mag even in the crowded central regions of the cluster. The high photometric precision has resulted in the discovery of two new RR1 stars and thirteen SX Phe stars. A detailed identification chart is given for all the variable stars in the field of our images of the cluster. Periodicities were calculated for all RR Lyraes and SX Phe stars and a critical comparison is made with previous determinations. Out of four probable SX Phe variables reported by Dekany & Kovacs (2009), the SX Phe nature is confirmed only for V80, V81 is an unlikely case while V82 and V83 remain as dubious cases. Previous misidentifications of three variables are corrected. Astrometric positions with an uncertainty of ~ 0.3 arcsec are provided for all variables. The light curve Fourier decomposition of RR0 and RR1 is discussed, we find a mean metallicity of [Fe/H]=-1.92+-0.06 in the scale of Zinn & West from 19 RR0 stars. The true distance moduli 16.36+-0.05 and 16.28+-0.07 and the corresponding distances 18.7+-0.4 and 18.0+-0.5 kpc are found from the RR0 and RR1 stars respectively. These values are in agreement with the theoretical period-luminosity relations for RR Lyrae stars in the I band and with recent luminosity determinations for the RR Lyrae stars in the LMC. The age of 13.25+-0.50 Gyr (Dotter et al. 2010), for NGC 5024, E(B-V)=0.02 and the above physical parameters of the cluster, as indicated from the RR0 stars, produce a good isochrone fitting to the observed CMD. The PL relation for SX Phe stars in NGC 5024 in the V and I bands is discussed in the light of the 13 newly found SX Phe stars and their pulsation mode is identified in most cases.

Substructure revealed by RR Lyraes in SDSS Stripe 82

We present an analysis of the substructure revealed by RR Lyraes in Sloan Digital Sky Survey Stripe 82, which covers in declination on the celestial equator over the right ascension range to ⁠. We use the new public archive of light-motion curves in Stripe 82, published by Bramich et al. in 2008, to identify a set of high-quality RR Lyrae candidates. Period estimates are determined to high accuracy using a string-length method. A subset of 178 RR Lyraes with spectrally derived metallicities are employed to derive metallicity–period–amplitude relations, which are then used, together with archive magnitude data and light-curve Fourier decomposition, to estimate metallicities and hence distances for the entire sample. The RR Lyraes lie 5–115 kpc from the Galactic Centre, with distance estimates accurate to ∼8 per cent. The RR Lyraes are further divided into subsets of 316 RRab types and 91 RRc types based on their period, colour and metallicity. We fit a smooth density law to the distribution as a simple representation of the data. For Galactocentric radii 5–25 kpc the number density of RR Lyraes falls as r−2.4, but beyond 25 kpc, the number density falls much more steeply, as r−4.5. However, we stress that in practice the density distribution is not smooth, but dominated by clumps and substructure. Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the Hercules–Aquila Cloud, respectively, are identified. Hence, ∼70 per cent of the RR Lyraes in Stripe 82 belong to known substructure, and the sharp break in the density law reflects the fact that the dominant substructure in Stripe 82 – the Hercules–Aquila Cloud and the Sagittarius Stream – lie within 40 kpc. In fact, almost 60 per cent of all the RR Lyraes in Stripe 82 are associated with the Hercules–Aquila Cloud alone, which emphasizes the cloud's pre-eminence. Additionally, evidence of a new and distant substructure – the Pisces Overdensity– is found, consisting of 28 faint RR Lyraes centred on Galactic coordinates (ℓ≈ 80°, b≈−55°), with distances of ∼80 kpc. The total stellar mass in the Pisces Overdensity is ∼104 M⊙ and its metallicity is [Fe/H]∼−1.5.

The optical gravitational lensing experiment. Variable stars in globular clusters

We present V-band photometry for 141 variable stars from the field of ω Cen. All but one variables are either RR Lyr stars or Pop. II Cepheids. One object is a distant background RR Lyr star from the galactic halo. The presented sample includes 33 newly identified variables, mostly low amplitude RR Lyr stars. We identified also two Pop. II Cepheids with exceptionally low amplitudes of light variations . The presented data may be used to study period changes of ω Cen variables and/or for Fourier decomposition of light curves.

Eclipsing Binaries in the OGLE Variable Star Catalog.I.W Uma-Type Systems as Distance and Population Tracers in Baade's Window

An algorithm, based on Fourier decomposition of light curves, permitted to define a sample of 388 contact binaries with well observed light curves, periods shorter one day and with available V-I colors (the R-sample), from among 933 eclipsing binary systems in the OGLE variable-star catalog for 9 fields of Baade's Window. The sample of such systems which was visually classified by the OGLE project as EW-type binaries (the O-sample) is by 55% larger and consists of 604 stars. The algorithm prevents inclusion of RR Lyr and SX Phe stars which in visual classification might be mistakenly taken for contact binaries with periods equal to twice their pulsation periods. Determinations of distances for the contact systems, utilizing the M_I = M_I(log P, V-I) absolute-magnitude calibration and the map of reddening and extinction of Stanek (1996), indicate an approximately uniform distribution of contact binaries almost all the way to the Galactic Bulge, implying heights up to z = 420 - 450 pc. This distribution, as well as a tendency for the colors to be concentrated in the region normally occupied by old Turn-Off-Point stars, confirm the currently held opinion that contact binary systems belong to the old stellar population of the Galaxy. The apparent frequency estimated in the volume-limited sense, relative to nearby MS dwarfs to the distances of 2 and 3 kpc, is one contact system per about 250 - 300 stars: it is one contact system per 400 MS stars if M-dwarfs are included. The apparent density of contact systems is 7-10x10^-5 pc^-3.

Cepheids in the Magellanic Clouds

AbstractIn the past few years, the Magellanic Clouds have been the targets for several major variable star surveys. The results of these surveys are now becoming available and it is clear that a Renaissance in LMC and SMC variable star research will result. In this review, I will describe the results of such surveys and review the questions that are likely to be answered by further work.With respect to results, I will concentrate on LMC MACHO Project data, including beat Cepheids, discovery statistics, mode identification, Fourier decomposition of lightcurves, and the differences between the LMC and galactic sample.