We have analysed a sample of 18 RR Lyrae stars (17 fundamental-mode - RRab - and one first overtone - RRc) and three Population II Cepheids (two BL Her stars and one W Vir star), for which high-resolution (R $\ge$30000), high signal-to-noise (S/N$\ge$30) spectra were obtained with either SARG at the Telescopio Nazionale Galileo (La Palma, Spain) or UVES at the ESO Very Large Telescope (Paranal, Chile). Archival data were also analyzed for a few stars, sampling $\gtrsim$3 phases for each star. We obtained atmospheric parameters (T$_{\rm{eff}}$, log$g$, v$_{\rm{t}}$, and [M/H]) and abundances of several iron-peak and $α$-elements (Fe, Cr, Ni, Mg, Ca, Si, and Ti) for different pulsational phases, obtaining $<$[$α$/Fe]$>$=+0.31$\pm$0.19 dex over the entire sample covering -2.2$<$[Fe/H]$<$-1.1 dex. We find that silicon is indeed extremely sensitive to the phase, as reported by previous authors, and cannot be reliably determined. Apart from this, metallicities and abundance ratios are consistently determined, regardless of the phase, within 0.10-0.15 dex, although caution should be used in the range $0\lesssimϕ\lesssim0.15$. Our results agree with literature determinations for both variable and non-variable field stars, obtained with very different methods, including low and high-resolution spectroscopy. W Vir and BL Her stars, at least in the sampled phases, appear indistinguishable from RRab from the spectroscopic analysis point of view. Our large sample, covering all pulsation phases, confirms that chemical abundances can be obtained for RR Lyrae with the classical EW-based technique and static model atmospheres, even rather close to the shock phases.
The GAIA satellite is likely to observe thousands of RR Lyrae stars within a small spectral window, between 8470A and 8750A, at a resolution of 11,500. In order to derive the metallicity of RR Lyrae stars from Gaia, we have obtained numerous spectra of RR Lyrae stars at a resolution of 35,000 with the Apache Point Observatory 3.5 m echelle spectrograph. We have correlated the Ca II triplet line strengths with metallicity as derived from Fe II abundances, analogous to Preston's (1959) use of the Ca II K line to estimate the metallicity of RR Lyrae stars. The Ca II line at 8498A is the least ble…
We use the data of our extended catalog of spectroscopic determinations of elemental abundances in the atmospheres of Galactic-field RR Lyrae type variables to show that metal-rich RR Lyraes ($\rm{[Fe/H]} > -1.0$) have anomalous abundances of some elements. In particular, the relative abundances of scandium, titanium, and yttrium in metal-rich RR Lyrae type variables are lower than the corresponding abundances in field stars of similar metallicity beyond the errors. We discuss the errors of the determination of the abundances of the above elements and point out the fact that no europium, zirco…
We report the first extensive model atmosphere and detailed chemical abundance study of eight RR Lyrae variable stars of c subclass throughout their pulsation cycles. Atmospheric parameters effective temperature, surface gravity, microturbulent velocity, and metallicity have been derived. Spectra for this abundace analysis have been obtained with the echelle spectrograph of 100-inch du Pont telescope at Las Campanas Observatory. We have found metallicities and element abundance ratios to be constant within observational uncertainties at all phases of all stars. Moreover, the $α$-element and Fe…
This paper sumarizes research on abundances in RR Lyrae stars that one of us (GW) has been engaged in with various astronomers. In addition we report on preliminary analysis of the abundances of C, Si, S and Fe in 24 RR Lyrae stars. Our model atmosphere analysis, including NLTE effects, are based on the spectra of resolving power 30,000 obtained at the Apache Poing Observatory.
We report estimated carbon-abundance ratios, [C/Fe], for seven newly-discovered carbon-enhanced metal-poor (CEMP) RR Lyrae stars. These are well-studied RRab stars that had previously been selected as CEMP candidates based on low-resolution spectra. For this pilot study, we observed eight of these CEMP RR Lyrae candidates with the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope. Prior to this study, only two CEMP RR Lyrae stars had been discovered: TY Gru and SDSS J1707+58. We compare our abundances to new theoretical models of the evolution of low-mass stars in binary systems. These…
We report the first estimate of the He abundance of the population of RR Lyrae stars in the Galactic bulge. This is done by comparing the recent observational data with the latest models. We use the large samples of ab type RR Lyrae stars found by OGLE IV in the inner bulge and by the VVV survey in the outer bulge. We present the result from the new models computed by Marconi et al. (2017), showing that the minimum Period for fundamental RR Lyrae pulsators depends on the He content. By comparing these models with the observations in a Period versus effective temperature plane, we find that the…
The surface gravities and effective temperatures have been added to a compilative catalog published earlier, which includes the relative abundances of several chemical elements for 100 field RR Lyrae stars. These atmoshperic parameters and evolutionary tracks from the Dartmouth database are used to determine the masses of the stars and perform a comparative analysis of the properties of RR Lyrae stars with different chemical compositions. The masses of metal-rich ($\rm{[Fe/H]}> -0.5$) RR Lyrae stars with thin disk kinematics are in the range $(0.51-0.60)M_{\odot}$. Only stars with initial mass…
Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude delta Scuti star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which 16 exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode. Spectroscopic [Fe/H] values for the 34 stars for which we were able to derive estimates range from -2.54 +/- 0.13 (NR…
Certain carbon-enhanced metal-poor stars likely obtained their composition via pollution from some of the earliest generations of asymptotic giant branch stars and as such provide important clues to early Universe nucleosynthesis. Recently, Kinman et al. discovered that the highly carbon- and barium-enriched metal-poor star SDSS J1707+58 is in fact an RR Lyrae pulsator. This gives us an object in a definite evolutionary state where the effects of dilution of material during the Main Sequence are minimised owing to the object having passed through first dredge-up. We perform detailed stellar mo…
M55 (NGC 6809) and NGC 6362 are among the few globular clusters for which masses and radii have been derived to high precision for member binary stars. They also contain RR Lyrae variables which, together with their non-variable horizontal-branch (HB) populations, provide tight constraints on the cluster reddenings and distance moduli through fits of stellar models to their pulsational and evolutionary properties. Reliable (m-M)_V estimates yield M_V and M_bol values of comparable accuracy for binary stars because the V-band bolometric corrections applicable to them have no more than a weak de…
Up-to-date isochrones, zero-age horizontal branch (ZAHB) loci, and evolutionary tracks for core He-burning stars are applied to the color-magnitude diagrams (CMDs) of M3, M15, and M92, focusing in particular on their RR Lyrae populations. Periods for ab- and c-type variables are calculated using the latest theoretical calibrations of log P_ab and log P_c as a function of luminosity, mass, effective temperature, and metallicity. Our models are generally able to reproduce the measured periods to well within the uncertainties implied by the stellar properties on which pulsation periods depend, as…
We present for the first time a detailed spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the Large and Small Magellanic Cloud (LMC and SMC). Using the MagE echelle spectrograph at the 6.5m Magellan telescopes, we obtain medium resolution (R ~ 2000 - 6000) spectra of six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. These stars were chosen because their previously determined photometric metallicities were among the lowest metallicities found for stars belonging to the old populations in the Magellanic Clouds. We find the spectroscopic metallic…
Space-based photometric missions revealed a surprising abundance of millimagnitude-level additional modes in RR Lyrae stars. The modes that appear in the modulated fundamental-mode (RRab) stars can be ordered into four major categories. Here we present the distribution of these groups in the Petersen diagram, and discuss their characteristics and connections to additional modes observed in other RR Lyrae stars.
We analyzed 151 variables previously classified as fundamental mode RR Lyrae stars from Campaigns 01-04 of the Kepler two wheel (K2) archive. By employing a method based on the application of systematics filtering with the aid of co-trending light curves in the presence of the large amplitude signal component, we searched for additional Fourier signals in the close neighborhood of the fundamental period. We found only 13 stars without such components, yielding the highest rate of 91% of modulated (Blazhko) stars detected so far. A detection efficiency test suggests that this occurrence rate li…
Low-mass, variable, high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high- or hyper-velocity stars were young stars thought to originate from the Galactic centre. Wide-area surveys like APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities larger than 350 km/s. In this study we present the first abundance analysis of a low-mass, RR Lyrae star, located close to the Galactic bulge, with a space motion of ~ -400 km/s. Using medium-resolution spectra, we derive abundanc…
Spectroscopic metallicities and first α-element abundances of RR Lyrae stars in Baade's Window
Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学）；Universidad de Santiago de Chile（智利圣地亚哥大学）；Center for Interdisciplinary Research in Astrophysics and Space Exploration (CIRAS)（天体物理与空间探索跨学科研究中心）；Università degli Studi di Bologna（博洛尼亚大学）；INAF（意大利国家天体物理研究所）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Universität Heidelberg（海德堡大学）；IAC – Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉帕尔马大学）；European Southern Observatory（欧洲南方天文台）
We present a detailed abundance study of 11 RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic.High resolution and high S/N echelle spectra of these variables were obtained with 2.5 m du Pont telescope at the Las Campanas Observatory. We obtained more than 2300 spectra, roughly 200 spectra per star, distributed more or less uniformly throughout the pulsational cycles. A new method has been developed to obtain initial effective temperature of our sample stars at a specific pulsational phase. We find that the abundance ratios …
Metal-deficient stars are important tracers for understanding the early formation of the Galaxy. Recent large-scale surveys with both photometric and spectroscopic data have reported an increasing number of metal-deficient stars whose kinematic features are consistent with those of the disk stellar populations. We report the discovery of an RR~Lyrae variable (hereafter RRL) that is located within the thick disk and has an orbit consistent with the thick-disk kinematics. Our target RRL (HD 331986) is located at around 1 kpc from the Sun and, with V=11.3, is among the 130 brightest RRLs known so…
The chemical composition of extremely metal-poor stars (EMP stars; [Fe/H]<~ -3) is a unique tracer of early nucleosynthesis in the Galaxy. As such stars are rare, we wish to find classes of luminous stars which can be studied at high resolution. We aim to determine the detailed chemical composition of the two EMP stars CS30317-056 and CS22881-039, originally thought to be red horizontal-branch (RHB) stars, and compare it to earlier results for EMP stars as well as to nucleosynthesis yields from various supernova (SN) models. In the analysis, we discovered that our targets are in fact the two m…
For the first time, a direct NLTE analysis of carbon and nitrogen lines in the spectra of nine RR Lyrae stars was carried out. We have determined the abundances of these elements together with oxygen, and have shown that the nitrogen content is increased in metallicity deficient program stars. We conclude that this is a sign of the first dredge up, which occurred at the previous stage of the red giant branch, and brought material processed in an incomplete CNO cycle to the surface of the star. This effect is significantly enhanced by thermohaline (extra-) mixing, which is more effective for me…
We present time-series photometry of two fields near M32 using archival observations from ACS/WFC onboard HST. One field is centered about 2 arcmin from M32 while the other is located 15 arcmin to the southeast of M31. We identify a total of 1139 RR Lyrae variables of which 821 are ab-type and 318 are c-type. In the field near M32, we find a radial gradient in the density of RR Lyraes relative to the center of M32. This gradient is consistent with the surface brightness profile of M32 suggesting that a significant number of the RR Lyraes in this region belong to M32. This provides further conf…
Continuous, high-precision photometry from space revolutionized many fields of stellar astrophysics, and that extends to the well-studied families of RR Lyrae and Cepheid variable stars as well. After the pioneering work of MOST, the CoRoT and Kepler missions released an avalanche of discoveries. We found signals that needed exquisite precision, such as an abundance of additional modes and granulation. Other discoveries, like period doubling, simply needed us to break away from the day-night cycle of the Earth. And the future holds more possibilities, with the BRITE, K2, and Gaia missions at f…
We compile spectroscopic abundance data from 84 literature sources for 50 elements across 3058 stars in the solar neighborhood, within 150 pc of the Sun, to produce the Hypatia Catalog. We evaluate the variability of the spread in abundance measurements reported for the same star by different surveys. We also explore the likely association of the star within the Galactic disk, the corresponding observation and abundance determination methods for all catalogs in Hypatia, the influence of specific catalogs on the overall abundance trends, and the effect of normalizing all abundances to the same …
We present an analysis of the period-$V$-amplitude plane for RR0 Lyrae stars (fundamental mode pulsators) with "normal" light curves in the bulge using the MACHO bulge fields. Although bulge globular clusters have RR Lyraes that divide into two reasonable distinct groups according to the average period of the RR0 Lyraes (Oosterhoff 1939), there is no evidence of a gap between Oosterhoff I and II stars in the bulge field star sample. The majority of the bulge RR0 Lyrae field star population have a difference in period compared to the Oosterhoff I cluster M3 (Delta log P) that is shifted by abou…
We provide the largest and most homogeneous sample of $α$-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs, 162 variables) by using high-resolution spectra. The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (t$\ge$ 10 Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, 1 mixed mode) covering three dex in iron abundance (-3.00$\le$[Fe/H]$\le$0.24). We found that field RRLs are $\sim$0.3 dex more $α$-poor than typical Halo tr…
We present results from a study of ab-type RR Lyrae variables in the Large Magellanic Cloud using the extensive dataset from phase III of the Optical Gravitational Lensing Experiment (OGLE). The metallicities of the RR Lyraes, determined from the periods and amplitudes of their light curves, reveal a statistically significant radial abundance gradient that is approximately one-half of what is seen in the disks of the Milky Way and M33. The RR Lyrae abundance gradient agrees with that of the old and metal-poor LMC globular clusters. The reddenings of the OGLE RR Lyraes have been calculated usin…
We discuss the largest and most homogeneous spectroscopic dataset of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution ({ΔS} method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7,941 RRLs were supplemented with similar literature estimates available, ending up with 9,015 RRLs (6,150 RRab, 2,865 RRc). The metallicity distribution shows a mean value of <[Fe/H]> = -1.51\pm0.01, and σ(standard deviation)= 0.41 dex with a long metal-poor tail approaching [Fe/H] = -3 and a sharp metal-ric…
We report the discovery of high velocity candidates among RR~Lyrae stars found in the Milky Way halo. We identified 9 RR~Lyrae stars with Galactocentric velocities exceeding the local escape velocity based on the assumed Galaxy potential. Based on close examination of their orbits', we ruled out their ejection location in the Milky Way disk and bulge. The spatial distribution revealed that seven out of 9 pulsators overlap with the position of the Sagittarius stellar stream. Two out of these seven RR~Lyrae stars can be tentatively linked to the Sagittarius dwarf spheroidal galaxy on the basis o…
We describe and employ a stacking procedure to investigate abundances derived from the low S/N spectra obtained in the Carnegie RR Lyrae Survey (CARRS; Kollmeier et al. 2013). We find iron metallicities that extend from [Fe/H] ~ -2.5 to values at least as large as [Fe/H] ~ -0.5 in the 274-spectrum CARRS RRc data set. We consider RRc sample contamination by high amplitude solar metallicity delta Scuti stars (HADS) at periods less than 0.3 days, where photometric discrimination between RRc and delta Scuti stars has proven to be problematic. We offer a spectroscopic discriminant, the well-marked …
We present new theoretical period-luminosity-metallicity (PLZ) relations for RR Lyrae stars (RRL) at Spitzer and WISE wavelengths. The PLZ relations were derived using nonlinear, time-dependent convective hydrodynamical models for a broad range in metal abundances (Z=0.0001 to 0.0198). In deriving the light curves, we tested two sets of atmospheric models (Brott & Hauschildt 2005, Castelli & Kurucz 2003) and found no significant difference between the resulting mean magnitudes. We also compare our theoretical relations to empirical relations derived from RRL in both the field and in the globul…
Photospheric abundances of C, N, O, and Na were determined by applying the synthetic spectrum-fitting technique to 34 snap-shot high-dispersion spectra of 22 RR Lyr stars covering a metallicity range of -1.8 <[Fe/H] < 0.0, with an aim of investigating the mixing mechanism in the interior of low-mass giant stars by examining the abundance anomalies of these elements possibly affected by the evolution-induced dredge-up of nuclear burning products. Special attention was paid to check the recent theoretical stellar evolution simulations indicating the importance of thermohaline mixing in low-mass …
We present a detailed spectroscopic analysis of horizontal branch stars in the globular cluster NGC 3201. We collected optical (4580-5330 A), high resolution (~34,000), high signal-to-noise ratio (~200) spectra for eleven RR Lyrae stars and one red horizontal branch star with the multifiber spectrograph M2FS at the 6.5m Magellan telescope at the Las Campanas Observatory. From measured equivalent widths we derived atmospheric parameters and abundance ratios for α (Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn) and s-process (Y) elements. We found that NGC 3201 is a homogeneous, mono-metallic ([Fe/H]=-…
Accurate metallicities of RR Lyrae are extremely important in constraining period-luminosity-metallicity relationships (PLZ), particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope (SALT). We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.13 dex. All but one RR Lyrae in this sample has accurate (σ_parallax ~ 10%) parallax from Gaia. Combining these new high resolution spectroscopic abundances with similar determinations from the literature for 93 stars, we present new PLZ…
We constructed new sets of He-enhanced (Y = 0.30, Y = 0.40) nonlinear, time-dependent convective hydrodynamical models of RR Lyrae (RRL) stars covering a broad range in metal abundances (Z from 0.0001 to 0.02). The increase in He content from the canonical value (Y = 0.245) to Y = 0.30 and 0.40 causes a simultaneous increase in stellar luminosity and in pulsation period. To investigate the dependence of the RRL distance scale on the He abundance, we computed new optical (RI) and near-infrared (JHK ) period luminosity metallicity helium relations. Interestingly enough, the increase in He conten…
We present a new set of horizontal-branch (HB) models computed with the MESA stellar evolution code. The models adopt $α$-enhanced \cite{ags09} metals mixtures and include the gravitational settling of He. They are used in our HB population synthesis tool to generate theoretical distributions of HB stars in order to describe the multiple stellar populations in the globular clusters 47Tuc, M3, and M13. The observed HB in 47Tuc is reproduced very well by our simulations for [Fe/H] $= -0.70$ and [$α$/Fe] $= +0.4$ if the initial helium mass fraction varies by $ΔY_0 \sim 0.03$ and approximately 21%…
We present a detailed spectroscopic analysis of RR Lyrae (RRL) variables in the globular cluster NGC 5139 (omega Cen). We collected optical (4580-5330 A), high resolution (R = 34,000), high signal-to-noise ratio (200) spectra for 113 RRLs with the multi-fiber spectrograph M2FS at the Magellan/Clay Telescope at Las Campanas Observatory. We also analysed high resolution (R = 26,000) spectra for 122 RRLs collected with FLAMES/GIRAFFE at the VLT, available in the ESO archive. The current sample doubles the literature abundances of cluster and field RRLs in the Milky Way based on high resolution sp…
We report the results of CCD $V$, $r$ and $I$ time-series photometry of the globular cluster NGC 5053. New times of maximum light are given for the eight known RR Lyrae stars in the field of our images and their periods are revised. Their $V$ light curves were Fourier decomposed to estimate their physical parameters. A discussion on the accuracy of the Fourier-based iron abundances, temperatures, masses and radii is given. New periods are found for the 5 known SX Phe stars and a critical discussion of their secular period changes is offered. The mean iron abundance for the RR Lyrae stars is fo…
Two distinct halo populations were found in the solar neighborhood by a series of works. They can be clearly separated by [alpha\Fe] and several other elemental abundance ratios including [Cu/Fe]. Very recently, a non-local thermodynamic equilibrium (non-LTE) study revealed that relatively large departures exist between LTE and non-LTE results in copper abundance analysis. We aim to derive the copper abundances for the stars from the sample of Nissen et al (2010) with both LTE and non-LTE calculations. Based on our results, we study the non-LTE effects of copper and investigate whether the hig…
We constructed a comprehensive model atom for NeI -- NeII using the most up-to-date atomic data available and evaluated the non-local thermodynamic equilibrium (NLTE) line formation for NeI and NeII in classical 1D models representing the atmospheres of B-type stars. We find that the large NLTE strengthening of the NeI lines corresponding to the 2p$^5$3p $-$ 2p$^5$3s transitions array occurs due to extremely small photoionization cross-sections of 2p$^5$3s levels that leads to strong overpopulation of these levels relative to their LTE populations. The deviations from LTE for the most NeII lin…
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 gr…
A probabilistic approach has been used in combination with the parallax data from Gaia (e)DR3 to calibrate Period-Luminosity-(Abundance) (PLZ) Relations covering a wide range of visual to Infrared observations of RR Lyrae stars. Absolute Magnitude Relations are given, derived from the same selection of stars, for $V$, $G$, $I$, $K_\mathrm{s}$ and WISE $W1$ as well as for for the reddening free pseudo-magnitudes $WBV$, $WVI$ and finally also Gaia $WG$. The classical relation between $M_V$ and [Fe/H] is redetermined and as an illustration distances are given to a few selected objects.
We have revisited the problem of metallicity prediction of RR Lyrae stars from their near-infrared light curves in the Cousins I waveband. Our study is based on high-quality time-series photometry and state-of-the-art high-resolution spectroscopic abundance measurements of 80 fundamental-mode (RRab) and 24 first-overtone (RRc) stars, spanning $\sim$[$-2.7$,$+0.18$] dex and $\sim$[$-3$,$-0.5$] dex ranges, respectively. Employing machine-learning methods, we investigated various light-curve representations and regression models to identify their optimal form for our objective. Accurate new empir…
We report the discovery of a new subclass of double-mode RR Lyrae stars in the Large and Small Magellanic Clouds. The sample of 22 pulsating stars have been extracted from the latest edition of the OGLE collection of RR Lyrae variables in the Magellanic System. The stars pulsating simultaneously in the fundamental (F) and first-overtone (1O) modes have distinctly different properties than regular double-mode RR Lyrae variables (RRd stars). The $P_{1O}/P_F$ period ratios of our anomalous RRd stars are within a range 0.725-0.738, while "classical" double-mode RR Lyrae variables have period ratio…
We present a new detailed abundance study of field red horizontal branch (RHB) and blue horizontal branch (BHB) non-variable stars. High resolution and high S/N echelle spectra of 11 RHB and 12 BHB were obtained with the McDonald 2.7 m telescope, and the RHB sample was augmented by reanalysis of spectra of 25 stars from a recent survey. We derived stellar atmospheric parameters based on spectroscopic constraints, and computed relative abundance ratios for 24 species of 19 elements. The species include Si II and Ca II, which have not been previously studied in RHB and BHB (Teff < 9000 K) stars.…
We present new sets of nonlinear, time-dependent convective hydrodynamical models of RR Lyrae stars assuming two metal (Z=0.0005, Z=0.001) and three helium abundances (Y=0.24, 0.30, 0.38). For each chemical composition we constructed a grid of fundamental (FU) and first overtone (FO) models covering a broad range of stellar masses and luminosities. To constrain the impact of the helium content on RR Lyrae properties, we adopted two observables --period distribution, luminosity amplitudes-- that are independent of distance and reddening. The current predictions confirm that the helium content h…
We present a new complete Near-Infrared (NIR, $JHK_s$) census of RR Lyrae stars (RRLs) in the globular $ω$ 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…
Distance to the Globular Cluster M 3 from the Infrared Surface Brightness Technique applied to RR Lyrae stars
Universidad de Concepción（孔塞普西翁大学）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天体物理中心）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；Université Côte d’Azur（蔚蓝海岸大学）；Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸天文台，法国国家科学研究中心，拉格朗日实验室）；Instituto de Alta Investigación, Universidad de Tarapacá（塔拉帕卡大学高等研究院）；LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台低层大气研究、星体和宇宙学实验室，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）
Terzan 5 is a complex stellar system in the Galactic bulge, harboring stellar populations with very different iron content (Δ[Fe/H] ~1 dex) and with ages differing by several Gyrs. Here we present an investigation of its variable stars. We report on the discovery and characterization of three RR Lyrae stars. For these newly discovered RR Lyrae and for six Miras of known periods we provide radial velocity and chemical abundances from spectra acquired with X-SHOOTER at the VLT. We find that the three RR Lyrae and the three short period Miras (P<300 d) have radial velocity consistent with being T…
We present new nonlinear, time-dependent convective hydrodynamical models of RR Lyrae stars computed assuming a constant helium-to-metal enrichment ratio and a broad range in metal abundances (Z=0.0001--0.02). The stellar masses and luminosities adopted to construct the pulsation models were fixed according to detailed central He burning Horizontal Branch evolutionary models. The pulsation models cover a broad range in stellar luminosity and effective temperatures and the modal stability is investigated for both fundamental and first overtones. We predict the topology of the instability strip …
We present our analysis of a large sample (over 150k) of candidate Galactic RR Lyrae (RRL) stars for which we derived high quality photometry at UV, optical and infrared wavelengths, using data from publicly available surveys. For a sub-sample of these stars (~2,400 fundamental mode field RRLs) we have measured their individual metallicity using the Delta S method, resulting in the largest and most homogeneous spectroscopic data set collected for RRLs. We use this sample to study the metallicity distribution in the Galactic Halo, including the long-standing problem of the Oosterhoff dichotomy …
