The effect of metallicity on Cepheid Period-Luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds
W. Gieren, J. Storm, P. Konorski, M. Górski, B. Pilecki, I. Thompson, G. Pietrzyński, D. Graczyk, T. G. Barnes, P. Fouqué, N. Nardetto, A. Gallenne, P. Karczmar… 展开作者
W. Gieren, J. Storm, P. Konorski, M. Górski, B. Pilecki, I. Thompson, G. Pietrzyński, D. Graczyk, T. G. Barnes, P. Fouqué, N. Nardetto, A. Gallenne, P. Karczmarek, K. Suchomska, P. Wielgórski, M. Taormina, B. Zgirski
The extragalactic distance scale builds on the Cepheid period-luminosity (PL) relation. In this paper, we want to carry out a strictly differential comparison of the absolute PL relations obeyed by classical Cepheids in the Milky Way (MW), LMC and SMC galaxies. Taking advantage of the substantial metallicity difference among the Cepheid populations in these three galaxies, we want to establish a possible systematic trend of the PL relation absolute zero point as a function of metallicity, and determine the size of such an effect in optical and near-infrared photometric bands. We are using the IRSB Baade-Wesselink type method as calibrated by Storm et al. to determine individual distances to the Cepheids in our samples in MW, LMC and SMC. For our analysis, we use a greatly enhanced sample of Cepheids in the SMC (31 stars) as compared to the small sample (5 stars) available in our previous work. We use the distances to determine absolute Cepheid PL relations in optical and near-infrared bands in each of the three galaxies.} {Our distance analysis of 31 SMC Cepheids with periods from 4-69 days yields tight PL relations in all studied bands, with slopes consistent with the corresponding LMC and MW relations. Adopting the very accurately determined LMC slopes for the optical and near-infrared bands, we determine the zero point offsets between the corresponding absolute PL relations in the 3 galaxies. We find that in all bands the metal-poor SMC Cepheids are intrinsically fainter than their more metal-rich counterparts in the LMC and MW. In the $K$ band the metallicity effect is $-0.23\pm0.06$~mag/dex while in the $V,(V-I)$ Wesenheit index it is slightly stronger, $-0.34\pm0.06$~mag/dex. We find some evidence that the PL relation zero point-metallicity relation might be nonlinear, becoming steeper for lower metallicities.
I report on the recent discovery of modulation in the radial velocity curves in four classical Cepheids. This discovery may enable significant improvements in the accuracy of Baade-Wesselink distances by revealing a not previously considered systematic source of uncertainty.
The projection factor used in the Baade-Wesselink methods of determining the distance of Cepheids makes the link between the stellar physics and the cosmological distance scale. A coherent picture of this physical quantity is now provided based on several approaches. We present the lastest news on the expected projection factor for different kinds of pulsating stars in the Hertzsprung-Russell diagram.
The BBW method remains one of most demanded tool to derive full set of Cepheid astrophysical parameters. Surface brightness version of the BBW technique was preferentially used during last decades to calculate Cepheid radii and to improve PLC relations. Its implementation requires a priory knowledge of Cepheid reddening value. We propose a new version of the Baade--Becker--Wesselink technique, which allows one to independently determine the colour excess and the intrinsic colour of a radially pulsating star, in addition to its radius, luminosity, and distance. It is considered to be a generali…
Aims. The Baade-Wesselink method of distance determination is based on the oscillations of pulsating stars. The key parameter of this method is the projection factor used to convert the radial velocity into the pulsation velocity. Our analysis was aimed at deriving for the first time the projection factor of delta Scuti stars, using high-resolution spectra of the high-amplitude pulsator AI Vel and of the fast rotator beta Cas. Methods. The geometric component of the projection factor (i.e. p0) was calculated using a limb-darkening model of the intensity distribution for AI Vel, and a fast-rota…
We provided accurate estimates of distances, radii and iron abundances for four metal-rich Cepheids, namely V340 Ara, UZ Sct, AV Sgr and VY Sgr. The main aim of this investigation is to constrain their pulsation properties and their location across the Galactic inner disk. We adopted new accurate NIR (J,H,K) light curves and new radial velocity measurements for the target Cepheids to determinate their distances and radii using the Baade-Wesselink technique. In particular, we adopted the most recent calibration of the IR surface brightness relation and of the projection factor. Moreover, we als…
[Abridged] I report the discovery of modulations in radial velocity (RV) curves of four Galactic classical Cepheids and investigate their impact as a systematic uncertainty for Baade-Wesselink distances. Highly precise Doppler measurements were obtained using the Coralie high-resolution spectrograph since 2011. Particular care was taken to sample all phase points in order to very accurately trace the RV curve during multiple epochs and to search for differences in linear radius variations derived from observations obtained at different epochs. Different timescales are sampled, ranging from cyc…
Recent progress on Baade-Wesselink (BW)-type techniques to determine the distances to classical Cepheids is reviewed. Particular emphasis is placed on the near-infrared surface-brightness (IRSB) version of the BW method. Its most recent calibration is described and shown to be capable of yielding individual Cepheid distances accurate to 6%, including systematic uncertainties. Cepheid distances from the IRSB method are compared to those determined from open cluster zero-age main-sequence fitting for Cepheids located in Galactic open clusters, yielding excellent agreement between the IRSB and cl…
The Baade-Wesselink (BW) method of distance determination of Cepheids is used to calibrate the distance scale. Various versions of this method are mainly based on interferometry and/or the surface-brightness color relation (SBCR). We quantify the impact of the SBCR, its slope, and its zeropoint on the projection factor. This quantity is used to convert the pulsation velocity into the radial velocity in the BW method. We also study the impact of extinction and of a potential circumstellar environment on the projection factor. We analyzed HARPS-N spectra of eta Aql to derive its radial velocity …
We present a new derivation of the CORS Baade-Wesselink method in the Walraven photometric system. We solved the complete Baade-Wesselink equation by calibrating the surface brightness function with a recent grid of atmosphere models. The new approach was adopted to estimate the mean radii of a sample of Galactic Cepheids for which are available precise light curves in the Walraven bands. Current radii agree, within the errors, quite well with Cepheid radii based on recent optical and near-infrared interferometric measurements. We also tested the impact of the projection factor on the Period-R…
Context. Recent observations of LMC Cepheids bring new constraints on the slope of the period-projection factor relation (hereafter Pp relation) that is currently used in the Baade-Wesselink (hereafter BW) method of distance determination. The discrepancy between observations and theoretical analysis is particularly significant for short period Cepheids Aims. We investigate three physical effects that might possibly explain this discrepancy: (1) the spectroscopic S/N that is systematically lower for LMC Cepheids (around 10) compared to Galactic ones (up to 300), (2) the impact of the metallici…
The simultaneous photometric and spectroscopic observations of the RR Lyrae variables in the globular cluster, M3, published in Jurcsik et al. (2017, Paper I) made it possible to perform Baade-Wesselink (BW) analysis of a large sample of Blazhko stars for the first time. The BW distances of Blazhko stars turned out to be unreliable, as significantly different distances were obtained for the stars of the Blazhko sample and also for the same star in different modulation phases. Even the results of small modulation-amplitude Blazhko stars may be doubtful. This result warns that the application of…
High-resolution spectroscopy of pulsating stars is a powerful tool to study the dynamical structure of their atmosphere. Lines asymmetry is used to derive the center-of-mass velocity of the star, while a direct measurement of the atmospheric velocity gradient helps determine the projection factor used in the Baade-Wesselink method of distance determination. We aim at deriving the center-of-mass velocity and the projection factor of the beta-Cephei star alpha-Lup. We present HARPS high spectral resolution observations of alpha-Lup. We calculate the first-moment radial velocities and fit the spe…
In this paper we present new photometric and radial velocity data for the PMS $δ$ Sct star H254, member of the young cluster IC 348. Photometric V,R$_C$,I$_C$ light curves were obtained at the Loiano and Asiago telescopes. The radial velocity data was acquired by means of the SARG@TNG spectrograph. High-resolution spectroscopy allowed us to derive precise stellar parameters and the chemical composition of the star, obtaining: T$_{\rm eff}$\,=\,6750\,$\pm$\,150 K; $\log g$\,=\,4.1\,$\pm$\,0.4 dex; [Fe/H]=-0.07$\pm$0.12 dex. Photometric and spectroscopic data were used to estimate the total abso…
The projection factor p is the key quantity used in the Baade-Wesselink (BW) method for distance determination; it converts radial velocities into pulsation velocities. Several methods are used to determine p, such as geometrical and hydrodynamical models or the inverse BW approach when the distance is known. We analyze new HARPS-N spectra of delta Cep to measure its cycle-averaged atmospheric velocity gradient in order to better constrain the projection factor. We first apply the inverse BW method to derive p directly from observations. The projection factor can be divided into three subconce…
Pulsation modelling of the Cepheid Y Ophiuchi with RSP/MESA. Impact of the circumstellar envelope and a high projection factor on Baade-Wesselink method
The Milky Way Cepheid RS Puppis is a particularly important calibrator for the Leavitt law (the Period-Luminosity relation). It is a rare, long period pulsator (P=41.5 days), and a good analog of the Cepheids observed in distant galaxies. It is the only known Cepheid to be embedded in a large (~0.5 pc) dusty nebula, that scatters the light from the pulsating star. Due to the light travel time delay introduced by the scattering on the dust, the brightness and color variations of the Cepheid imprint spectacular light echoes on the nebula. I here present a brief overview of the studies of this ph…
One of the largest uncertainties for using the Baade-Wesselink method to measure Cepheid distances is the value of the projection factor (p-factor). However, p-factors measured using the IRSB technique and from hydrodynamic models disagree. In this work, we compute spherically-symmetric static model stellar atmospheres and predict a period p-factor relation.
In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observat…
We present the analysis of multiband time-series data for a sample of 24 Cepheids in the field of the Large Magellanic Cloud cluster NGC1866. Very accurate BVI VLT photometry is combined with archival UBVI data, covering a large temporal window, to obtain precise mean magnitudes and periods with typical errors of 1-2% and of 1 ppm, respectively. These results represent the first accurate and homogeneous dataset for a substantial sample of Cepheid variables belonging to a cluster and hence sharing common distance, age and original chemical composition. Comparisons of the resulting multiband Per…
Galactic Cepheids are necessary tools for calibrating the period-luminosity relation, but distances to individual Galactic Cepheids are difficult to precisely measure and are limited to a small number of techniques such as direct parallax, main-sequence fitting to open clusters that host Cepheids and Baade-Wesselink (BW) methods. In this work, we re-examine the application of Wesenheit function in determining distances to more than 300 Galactic Cepheids, by taking advantage of the fact that the Wesenheit function is extinction free by definition. The Wesenheit distances were used to calibrate …
We present a revised distance to the nearby galaxy NGC6822 using a new multi-band fit to both previously published and new optical, near- and mid-infrared data for Cepheid variables. The new data presented in this study include multi-epoch observations obtained in 3.6\um and 4.5\um with the \emph{Spitzer Space Telescope} taken for the Carnegie Hubble Program. We also present new observations in J, H and \kswith FourStar on the Magellan Baade telescope at Las Campanas Observatory. We determine mean magnitudes and present new period-luminosity relations in V, I, J, H, \ks, IRAC 3.6\um and 4.5\um…
Hydrodynamic computations of nonlinear Cepheid pulsation models with periods from 20 to 100 day on the evolutionary stage of core helium burning were carried out. Equations of radiation hydrodynamics and time--dependent convection were solved with initial conditions obtained from selected models of evolutionary sequences of population I stars with initial masses from $8M_\odot$ to $12.5M_\odot$. For each crossing of the instability strip the pulsation period $Π$ and the rate of period change $\dotΠ$ were derived as a function of evolutionary time. Comparing results of our computations with obs…
The mode switching in Cepheids is studied using the methods of the nonlinear theory of stellar pulsation, depending on the main sequence mass $M_0$ and the abundance of elements heavier than helium $Z$. The grid of evolutionary and hydrodynamic models of core--helium burning Cepheids is represented by 30 evolutionary sequences of stars with initial masses $5.7M_\odot\le M_0\le 7.2M_\odot$ and $Z=0.014$, 0.018, 0.022. For considered values of $Z$ the periods of the fundamental mode and the first overtone at the oscillation mode switching are shown to depend on the mean density of the stellar ma…
The projection factor (p), which converts the radial velocity to pulsational velocity, is an important parameter in the Baade-Wesselink (BW) type analysis and distance scale work. The p-factor is either adopted as a constant or linearly depending on the logarithmic of pulsating periods. The aim of this work is to calibrate the p-factor if a Cepheid has both the BW distance and an independent distance measurement, and examine the p-factor for delta Cephei -- the prototype of classical Cepheids. We calibrated the p-factor for several Galactic Cepheids that have both the latest BW distances and i…
We present a realization of the maximum-likelihood (ML) technique, which is one of the latest modifications of the Baade--Becker--Wesselink (BBW) method. Our approach is based on non-linear calibrations of the effective temperature and bolometric correction which take into account metallicity and surface gravity. It allows one to estimate the key Cepheid parameters, the distance modulus, and the interstellar reddening, combining photometric and spectroscopic data (including the effective temperature data). This method is applied to a sample of 44 Galactic Cepheids, for which multiphase tempera…
The projection factor (p-factor) is an essential component of the classical Baade-Wesselink (BW) technique, that is commonly used to determine the distances to pulsating stars. It is a multiplicative parameter used to convert radial velocities into pulsational velocities. As the BW distances are linearly proportional to the p-factor, its accurate calibration for Cepheids is of critical importance for the reliability of their distance scale. We focus on the observational determination of the p-factor of the long-period Cepheid RS Pup (P = 41.5 days). This star is particularly important as this …
Period-Luminosity Relations, projection factor and radii of Anomalous Cepheids
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文中心）；Universidad de Concepción, Departamento de Astronomía（康塞普西翁大学天文学系）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学、蔚蓝海岸天文台、法国国家科学研究中心拉格朗日实验室）；LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台观测天体物理学和宇宙学实验室、巴黎文理研究大学、法国国家科学研究中心、索邦大学、巴黎西岱大学）
We have obtained extensive high-quality spectroscopic observations of the OGLE-LMC-CEP-1718 eclipsing binary system in the Large Magellanic Cloud which Soszynski et al. (2008) had identified as a candidate system for containing two classical Cepheids in orbit. Our spectroscopic data clearly demonstrate binary motion of the Cepheids in a 413-day eccentric orbit, rendering this eclipsing binary system the first ever known to consist of two classical Cepheid variables. After disentangling the four different radial velocity variations in the system we present the orbital solution and the individua…
Context. One challenge for measuring the Hubble constant using Classical Cepheids is the calibration of the Leavitt Law or period-luminosity relationship. The Baade-Wesselink method for distance determination to Cepheids relies on the ratio of the measured radial velocity and pulsation velocity, the so-called projection factor and the ability to measure the stellar angular diameters. Aims. We use spherically-symmetric model stellar atmospheres to explore the dependence of the p-factor and angular diameter corrections as a function of pulsation period. Methods. Intensity profiles are computed f…
Based on new observations and improved modeling techniques, we have reanalyzed seven Cepheids in the Large Magellanic Cloud. Improved physical parameters have been determined for the exotic system OGLE LMC-CEP-1718 composed of two first-overtone Cepheids and a completely new model was obtained for the OGLE LMC-CEP-1812 classical Cepheid. This is now the shortest period Cepheid for which the projection factor is measured. The typical accuracy of our dynamical masses and radii determinations is 1%. The radii of the six classical Cepheids follow period--radius relations in the literature. Our ver…
We present a detailed study of the classical Cepheid in the double-lined, highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a fundamental mode pulsator with a period of 2.988 days. The orbital period of the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes and photometry spanning 22 years, we were able to derive the dynamical masses and radii of both stars with exquisite accuracy. Both stars in the system are very similar in mass, radius and color, but the companion is a stable, non-pulsating star. The Cepheid is slightly more massive and bigg…
This work reports the discovery of cycle-to-cycle modulated spectral line and atmospheric velocity gradient variability in long-period Cepheids based on 925 high-resolution optical spectra of $\ell$ Carinae (P $\sim$ 35.5 d) recorded during three heavy duty-cycle monitoring campaigns (in 2014, 2015, and 2016). Spectral line variability is investigated via cross-correlation functions (CCFs) computed using three sets of spectral lines (weak, solar, strong). A metallic line velocity gradient, δv$_r$ (t), is computed as the difference between weak and strong-line RVs. CCF shape indicators BIS (asy…
As one of the most luminous Cepheids in the Milky Way, the 41.5-day RS Puppis is an analog of the long-period Cepheids used to measure extragalactic distances. An accurate distance to this star would therefore help anchor the zero-point of the bright end of the period-luminosity relation. But, at a distance of about 2 kpc, RS Pup is too far away for measuring a direct trigonometric parallax with a precision of a few percent with existing instrumentation. RS Pup is unique in being surrounded by a reflection nebula, whose brightness varies as pulses of light from the Cepheid propagate outwards. …
The extragalactic distance scale builds directly on the Cepheid Period-Luminosity (PL) relation as delineated by the sample of Cepheids in the Large Magellanic Cloud (LMC). However, the LMC is a dwarf irregular galaxy, quite different from the massive spiral galaxies used for calibrating the extragalactic distance scale. Recent investigations suggest that not only the zero-point but also the slope of the Milky Way PL relation differ significantly from that of the LMC, casting doubts on the universality of the Cepheid PL relation. We want to make a differential comparison of the PL relations in…
We present a modern ephemeris and modern light curve of the first-discovered Cepheid variable in M31, Edwin Hubble's M31-V1. Observers of the American Association of Variable Star Observers undertook these observations during the latter half of 2010. The observations were in support of an outreach program by the Space Telescope Science Institute's Hubble Heritage project, but the resulting data are the first concentrated observations of M31-V1 made in modern times. AAVSO observers obtained 214 V-band, Rc-band, and unfiltered observations from which a current ephemeris was derived. The ephemeri…
Determining the expansion of the universe, i.e. the Hubble constant (H0) to better than 2% is required in order to understand the nature of dark energy. However, the two most accurate methods to do it, the cosmic microwave background and the distance scale ladder are inconsistent today, which is refereed as the "tension". One of the key to resolve this tension is related to the calibration of the period-luminosity (PL) of Cepheids : what is its zero-point ? Is it metallicity dependent ? Can we reduce the dispersion of the PL relation ? The eclipsing binaries method was recently used to determi…
The cross correlation method (hereafter CC) is widely used to derive the radial velocity curve of Cepheids when the signal to noise of the spectra is low. However, if it is used with the wrong projection factor, it might introduce some biases in the Baade-Wesselink (hereafter BW) methods of determining the distance of Cepheids. In addition, it might affect the average value of the radial velocity curve (or gamma-velocity) important for Galactic structure studies. We aim to derive a period-projection factor relation (hereafter Pp) appropriate to be used together with the CC method. Moreover, we…
Surface brightness-colour relations of Milky Way and Magellanic Clouds classical Cepheids based on Gaia magnitudes
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS（蔚蓝海岸大学，蔚蓝海岸天文台，法国国家科学研究中心）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台 LIRA 实验室，巴黎文理研究大学，索邦大学，巴黎西岱大学，CY 塞尔吉巴黎大学，法国国家科学研究中心）；French-Chilean Laboratory for Astronomy, IRL 3386, CNRS（中智天文学联合实验室，法国国家科学研究中心）；Universidad de Concepción（康塞普西翁大学）；Leibniz Institute for Astrophysics（波茨坦莱布尼茨天体物理研究所）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文中心）；Instituto de Alta Investigación, Universidad de Tarapacá（塔拉帕卡大学高等研究院）
The VISTA survey of the Magellanic Clouds System (VMC) is collecting deep $K_\mathrm{s}$--band time--series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper we have analysed a sample of 130 Large Magellanic Cloud (LMC) Type II Cepheids (T2CEPs) found in tiles with complete or near complete VMC observations for which identification and optical magnitudes were obtained from the OGLE III survey. We present $J$ and $K_\mathrm{s}$ light curves for all 130 pulsators, including 41 BL Her, 62 W Vir (12 pW …
Baade-Wesselink-type (BW) techniques enable geometric distance measurements of Cepheid variable stars in the Galaxy and the Magellanic clouds. The leading uncertainties involved concern projection factors required to translate observed radial velocities (RVs) to pulsational velocities and recently discovered modulated variability. We carried out an unprecedented observational campaign involving long-baseline interferometry (VLTI/PIONIER) and spectroscopy (Euler/Coralie) to search for modulated variability in the long-period (P $\sim$ 35.5 d) Cepheid Carinae. We determine highly precise angular…
Multi-chromatic observations of classical Cepheids using the CHARA Array interferometer: Surface brightness-colour relation, projection factor, and limb-darkening
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台）；European Southern Observatory（欧洲南方天文台）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台 LIRA 实验室，巴黎文理研究大学，索邦大学，巴黎西岱大学，CY 塞尔吉巴黎大学）；French-Chilean Laboratory for Astronomy, IRL 3386, CNRS（中智天文学联合实验室）；Instituto de Alta Investigación, Universidad de Tarapacá（塔拉帕卡大学高等研究院）；Astronomy Department, University of Michigan（密歇根大学天文学系）
The parallax of pulsation, and its implementations such as the Baade-Wesselink method and the infrared surface bright- ness technique, is an elegant method to determine distances of pulsating stars in a quasi-geometrical way. However, these classical implementations in general only use a subset of the available observational data. Freedman & Madore (2010) suggested a more physical approach in the implementation of the parallax of pulsation in order to treat all available data. We present a global and model-based parallax-of-pulsation method that enables including any type of observational data…
GIARPS simultaneous optical and infrared high-spectral-resolution observations of Cepheids I. Limb darkening from cross-correlated radial velocities
Université Côte d’Azur（蔚蓝海岸大学）；Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université（巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，塞吉-蓬图瓦兹大学）；French-Chilean Laboratory for Astronomy, IRL 3386, CNRS and U. de Chile（中法天文学联合实验室）；Universidad de Concepción（康塞普西翁大学）；Leibniz Institute for Astrophysics（莱布尼茨天体物理研究所）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；European Southern Observatory（欧洲南方天文台）
We determine the fundamental stellar parameters of altogether 20 double-mode RR Lyrae (RRd) stars from the Galactic Field and the Large Magellanic Cloud, following our approach employed on the field RRd star BS Comae. The stars were selected to cover wide ranges of periods and period ratios, implying diverse stellar parameters. From the possible observed quantities we use only the periods and determine stellar parameter combinations that satisfy both current helium-burning evolutionary models and grids of linear non-adiabatic purely radiative pulsational models. Thus, the periods of an object …
We study the variable star content of the globular cluster M53 to compute the physical parameters of the constituting stars and the distance of the cluster. Covering two adjacent seasons in 2007 and 2008, new photometric data are gathered for 3048 objects in the field of M53. By using the OIS method and subsequently TFA, we search for variables in the full sample by using DFT and BLS methods. We select variables based on the statistics related to these methods combined with visual inspections. We identified 12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars…
We present results of the analysis of 70 RR Lyrae stars located in the bar of the Large Magellanic Cloud (LMC). Combining spectroscopically determined metallicity of these stars from the literature with precise periods from the OGLE III catalogue and multi-epoch $K_{\rm s}$ photometry from the VISTA survey of the Magellanic Clouds system (VMC), we derive a new near-infrared period-luminosity-metallicity (${\rm PL_{K_{\rm s}}Z}$) relation for RR Lyrae variables. In order to fit the relation we use a fitting method developed specifically for this study. The zero-point of the relation is estimate…
