arXiv subjects

R. Figuera Jaimes

Publications and source records attributed to R. Figuera Jaimes.

83 records · Page 5Linked to original sources

arXiv2013

EMCCD photometry reveals two new variable stars in the crowded central region of the globular cluster NGC 6981

Two previously unknown variable stars in the crowded central region of the globular cluster NGC 6981 are presented. The observations were made using the Electron Multiplying CCD (EMCCD) camera at the Danish 1.54m Telescope at La Silla, Chile.The two variables were not previously detected by conventional CCD imaging because of their proximity to a bright star. This discovery demonstrates that EMCCDs are a powerful tool for performing high-precision time-series photometry in crowded fields and near bright stars, especially when combined with difference image analysis (DIA).

astro-ph.SR↗

arXiv2013

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-García 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.

astro-ph.SR↗

arXiv2013

Variable stars in the globular cluster NGC 7492. New discoveries and physical parameters determination

We have performed a photometric V, R, I CCD time-series analysis with a baseline of ~8 years of the outer-halo globular cluster NGC 7492 with the aim of searching for new variables and using these (and the previously known variables) to determine the physical parameters of interest for the cluster (e.g. metallicity, absolute magnitude of the horizontal branch, distance, etc.). We use difference image analysis (DIA) to extract precise light curves in the relatively crowded star field, especially towards the densely populated central region. Several approaches are used for variability detection that recover the known variables and lead to new discoveries. We determine the physical parameters of the only RR0 star using light curve Fourier decomposition analysis. We find one new long period variable and two SX Phe stars in the blue straggler region. We also present one candidate SX Phe star which requires follow-up observations. Assuming that the SX Phe stars are cluster members and using the period-luminosity relation for these stars, we estimate their distances as ~25.2+-1.8 and 26.8+-1.8 kpc, and identify their possible modes of oscillation. We refine the periods of the two RR Lyrae stars in our field of view. We find that the RR1 star V2 is undergoing a period change and possibly exhibits the Blazhko effect. Fourier decomposition of the light curve of the RR0 star V1 allows us to estimate the metallicity [Fe/H]_ZW-1.68+-0.10 or [Fe/H]_UVES-1.64+-0.13, log-luminosity ~1.76+-0.02, absolute magnitude ~0.38+-0.04 mag, and true distance modulus of ~16.93+-0.04 mag, which is equivalent to a distance of ~24.3+-0.5 kpc. All of these values are consistent with previous estimates in the literature.

astro-ph.SR↗

arXiv2013

Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry

We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. We used difference image analysis 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. We also derive an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H]_ZW=-2.01 +- 0.04, or [Fe/H]_UVES=-2.11 +- 0.06, and a distance of 8.32 +- 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 +- 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 +- 1.0 Gyr for M 30.

astro-ph.SR↗

arXiv2012

Physical parameters of three field RR Lyrae stars

Strömgren $uvby-β$ photometry of the stars classified as RR Lyrae stars RU Piscium, SS Piscium and TU Ursae Majoris has been used to estimate their iron abundance, temperature, gravity and absolute magnitude. The stability of the pulsating period is discussed. The nature of SS Psc as a RRc or a HADS is addressed. The reddening of each star is estimated from the Strömgren colour indices and reddening sky maps. The results of three approaches to the determination of [Fe/H], $T_{\rm eff}$ and $\log(g)$ are discussed: Fourier light curve decomposition, the Preston $ΔS$ index and the theoretical grids on the $(b-y)_o - c_1{_o}$ plane.

astro-ph.GA↗

arXiv2012

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

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. 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. We also derive an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). 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 \pm 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).

astro-ph.SR↗

arXiv2012

Difference Image Analysis: Extension to a Spatially Varying Photometric Scale Factor and Other Considerations

We present a general framework for matching the point-spread function (PSF), photometric scaling, and sky background between two images, a subject which is commonly referred to as difference image analysis (DIA). We introduce the new concept of a spatially varying photometric scale factor which will be important for DIA applied to wide-field imaging data in order to adapt to transparency and airmass variations across the field-of-view. Furthermore, we demonstrate how to separately control the degree of spatial variation of each kernel basis function, the photometric scale factor, and the differential sky background. We discuss the common choices for kernel basis functions within our framework, and we introduce the mixed-resolution delta basis functions to address the problem of the size of the least-squares problem to be solved when using delta basis functions. We validate and demonstrate our algorithm on simulated and real data. We also describe a number of useful optimisations that may be capitalised on during the construction of the least-squares matrix and which have not been reported previously. We pay special attention to presenting a clear notation for the DIA equations which are set out in a way that will hopefully encourage developers to tackle the implementation of DIA software.

astro-ph.IM↗

arXiv2012

Investigation of variable star candidates in the globular cluster NGC 5024 (M53)

We have performed a careful investigation of the 74 candidate variable stars presented by Safanova & Stalin (2011). For this purpose we used our data base of imaging and light curves from Arellano Ferro et al. (2011) and Arellano Ferro et al. (2012). We find that two candidates are known variable stars, eight candidates were discovered first by Arellano Ferro et al. (2011) but would not have been known to Safanova & Stalin (2011) at the time of their paper submission, while four candidates are new variables. Three of the new variables are SX Phe type and one is a semi-regular red giant variable (SR type). We also tentatively confirm the presence of true variability in two other candidates and we are unable to investigate another four candidates because they are not in our data base. However, we find that the remaining 54 candidate variable stars are spurious detections where systematic trends in the light curves have been mistaken for true variability. We believe that the erroneous detections are caused by the adoption of a very low detection threshold used to identify these candidates.

astro-ph.SR↗

arXiv2011

The unusually large population of Blazhko variables in the globular cluster NGC 5024 (M53)

We report the discovery of amplitude and phase modulations typical of the Blazhko effect in 22 RRc and 9 RRab type RR Lyrae stars in NGC 5024 (M53). This brings the confirmed Blazhko variables in this cluster to 23 RRc and 11 RRab, that represent 66% and 37% of the total population of RRc and RRab stars in the cluster respectively, making NGC 5024 the globular cluster with the largest presently known population of Blazhko RRc stars. We place a lower limit on the overall incidence rate of the Blazhko effect among the RR Lyrae population in this cluster of 52%. New data have allowed us to refine the pulsation periods. The limitations imposed by the time span and sampling of our data prevents reliable estimations of the modulation periods. The amplitudes of the modulations range between 0.02 and 0.39 mag. The RRab and RRc are neatly separated in the CMD, and the RRc Blazhko variables are on averge redder than their stable couterparts; these two facts may support the hypothesis that the HB evolution in this cluster is towards the red and that the Blazhko modulations in the RRc stars are connected with the pulsation mode switch.

astro-ph.SR↗

arXiv2011

Exploring the variable stars in the globular cluster NGC5024 (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.

astro-ph.SR↗

arXiv2010

CCD time-series photometry of the globular cluster NGC 6981: Variable star census and physical parameter estimates

We present the results from 10 nights of observations of the globular cluster NGC 6981 (M72) in the V, R and I Johnson wavebands. We employed the technique of difference image analysis to perform precision differential photometry on the time-series images, which enabled us to carry out a census of the under-studied variable star population of the cluster. We show that 20 suspected variables in the literature are actually non-variable, and we confirm the variable nature of another 29 variables while refining their ephemerides. We also detect 11 new RR Lyrae variables and 3 new SX Phe variables, bringing the total confirmed variable star count in NGC 6981 to 43. We performed Fourier decomposition of the light curves for a subset of RR Lyrae stars and used the Fourier parameters to estimate the fundamental physical parameters of the stars using relations available in the literature. Mean values of these physical parameters have allowed us to estimate the physical parameters of the parent cluster. We derive a metallicity of [Fe/H]_ZW = -1.48+-0.03 on the Zinn & West (1984) scale (or [Fe/H]_UVES = -1.38+-0.03 on the new Carretta et al. (2009) scale) for NGC 6981, and distances of ~16.73+-0.36 kpc and ~16.68+-0.36 kpc from analysis of the RR0 and RR1 stars separately. We also confirm the Oosterhoff type I classification for the cluster, and show that our colour-magnitude data is consistent with the age of ~12.75+-0.75 Gyr derived by Dotter et al (2010).

astro-ph.SR↗