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We present [Fe/H] values for globular clusters associated with the Fornax, Sagittarius, and Canis Major dwarf spheroidal galaxies based on the light curve properties of their ab-type RR Lyrae variables. Fornax is a classical dwarf spheroidal containing five globular clusters and exhibiting a spheroidal shape in the sky. Sagittarius and Canis Major, possess six and four globular clusters, respectively, and have both been tidally disrupted to a significant degree by the gravitational field of the Milky Way galaxy. Based on an analysis of the periods and light curve amplitudes of 76 globular cluster ab-type RR Lyraes in Fornax, 103 in Sagittarius, and 29 in Canis Major, we find mean metallicities of |$\langle$| [Fe/H] |$\rangle$| = –1.67 ± 0.05, –1.76 ± 0.12, and –1.69 ± 0.25 for the globular clusters in Fornax, Sagittarius, and Canis Major, respectively. Given the similarity of these three values, and coupled with the well-established correlation between the mean metal abundance and total luminosity for dwarf spheroidal galaxies, we conclude that the absolute V -band magnitudes of these three galaxies are indistinguishable to within ∼0.8 mag. [ABSTRACT FROM AUTHOR]

Astronomy is entering an unprecedented era of big-data science, driven by missions like the ESA's Gaia telescope, which aims to map the Milky Way in three dimensions. Gaia's vast dataset presents a monumental challenge for traditional analysis methods. The sheer scale of this data exceeds the capabilities of manual exploration, necessitating the utilization of advanced computational techniques. In response to this challenge, we developed a novel approach leveraging deep learning to estimate the metallicity of fundamental mode (ab-type) RR Lyrae stars from their light curves in the Gaia optical G-band. Our study explores applying deep-learning techniques, particularly advanced neural-network architectures, in predicting photometric metallicity from time-series data. Our deep-learning models demonstrated notable predictive performance, with a low mean absolute error (MAE) of 0.0565, the root mean square error (RMSE) of 0.0765, and a high  R 2  regression performance of 0.9401, measured by cross-validation. The weighted mean absolute error (wMAE) is 0.0563, while the weighted root mean square error (wRMSE) is 0.0763. These results showcase the effectiveness of our approach in accurately estimating metallicity values. Our work underscores the importance of deep learning in astronomical research, particularly with large datasets from missions like Gaia. By harnessing the power of deep-learning methods, we can provide precision in analyzing vast datasets, contributing to more precise and comprehensive insights into complex astronomical phenomena. [ABSTRACT FROM AUTHOR]

We made a survey of the variable stars in a 13.2 × 13.2 arcmin |$^{2}$| centred on the field of the Galactic bulge cluster NGC 6558. A total of 78 variables were found in the field of the cluster. Many of these variables are included in the catalogue of variable stars in Galactic globular clusters (Clement et al. 2001), OGLE or Gaia DR3 data releases. A membership analysis based on the proper motions of Gaia DR3 revealed that many of these variables do not belong to the cluster. We employed the data from the aforementioned surveys and our own data in the VI photometric system to estimate the periods, which along with the light-curves morphology and position in a deferentially dereddened colour–magnitude diagram (CMD), help classifying the variable types. Two new member variables were found; an eclipsing binary (V18) and a semiregular SR/L (V19). In the end, we conclude that only nine variables are likely cluster members. Member variables were used to discuss the mean metallicity and distance of the parental cluster and find the average values. [ABSTRACT FROM AUTHOR]

Context. The photometric observations from the recent decade revolutionized our view on classical pulsators. Low-amplitude signals have been detected photometrically in addition to the dominant high-amplitude radial mode pulsations in many RR Lyrae stars and classical Cepheids. First-overtone pulsators with an additional low-amplitude signal at a period ratio of around 0.61 with the main mode, the so-called 0.61 stars, form the most populous group among these stars. The nature of this signal has been attributed to non-radial pulsations. Another mysterious group are stars in which the additional signal forms a period ratio of around 0.68. These are the 0.68 stars. The origin of the signal remains unknown. Aims. Here, we search for similar phenomena in spectroscopic observations of first-overtone classical Cepheids collected as part of the VELOCE project. Methods. We performed a frequency analysis of several parameters derived from cross-correlation functions (CCFs), including radial velocity, the full width at half maximum, the bisector inverse span, and the CCF depth (contrast). Using standard pre-whitening, we searched for additional low-amplitude signals. We identified the location of these stars in various sequences of the Petersen diagram. Results. We detect additional signals in four first-overtone classical Cepheids: BG Cru, QZ Nor, V0391 Nor, and V0411 Lac. We classified BG Cru, QZ Nor, and V0391 Nor as 0.61 stars based on their period ratios. V0411 Lac, however, exhibits a ratio of 0.68 between the two modes, and the additional signal has a longer period. This type of multi-periodicity remains unexplained. Conclusions.VELOCE CCFs yield the first spectroscopic detections of non-radial pulsation modes in classical Cepheids. This opens an asteroseismic window for pursuing a more detailed understanding of these important stars. While the 0.61 signal of BG Cru, QZ Nor, and V0391 Nor is understood to originate from non-radial modes of moderate degrees, the 0.68 signal of V0411 Lac still lacks a physical explanation. [ABSTRACT FROM AUTHOR]

In order to constrain the evolutionary history of the Milky Way, we hunt for faint RR Lyrae stars (RRLs) using Dark Energy Camera data from the High cadence Transient Survey and the Halo Outskirts With Variable Stars survey. We report the detection of |$\sim$| 500 RRLs, including previously identified stars and |$\sim$| 90 RRLs not yet reported. We identify nine new RRLs beyond 100 kpc from the Sun, most of which are classified as fundamental-mode pulsators. The periods and amplitudes of the distant RRLs do not place them in either one of the two classical Oosterhoff groups, but in the Oosterhoff intermediate region. We detect two groups of clumped distant RRLs with similar distances and equatorial coordinates, which we interpret as an indication of their association with undiscovered bound or unbound satellites. We study the halo density profile using spheroidal and ellipsoidal (⁠|$q=0.7$|⁠) models, following a Markov chain Monte Carlo methodology. For a spheroidal halo, our derived radial profile is consistent with a broken power law with a break at |$18.1^{+2.1}_{-1.1}$| kpc separating the inner and the outer halo, and an outer slope of |$-4.47^{+0.11}_{-0.18}$|⁠. For an ellipsoidal halo, the break is located at |$24.3^{+2.6}_{-3.2}$| kpc and the outer slope is |$-4.57^{+0.17}_{-0.25}$|⁠. The break in the density profile is a feature visible in different directions of the halo. The similarity of these radial distributions with previous values reported in the literature seems to depend on the regions of the sky surveyed (direction and total area) and halo tracer used. Our findings are compatible with simulations and observations that predict that the outer regions of Milky Way-like galaxies are mainly composed of accreted material. [ABSTRACT FROM AUTHOR]

We present a comprehensive photometric study of RR Lyrae stars in the M3 globular cluster, utilizing a vast data set of 3140 optical (UBVRI) CCD images spanning 35 yr from astronomical data archives. We have successfully identified previously known 238 RR Lyrae stars from the photometric data, comprising 178 RRab, 49 RRc, and 11 RRd stars. Multiband periodogram was used to significantly improve the long-term periods of 65 per cent of RR Lyrae stars in our sample, thanks to the unprecedentedly long temporal coverage of the observations. The light curve templates were used to obtain accurate and precise mean magnitudes and amplitudes of all RR Lyrae variables. We combined optical (UBVRI) and near-infrared (NIR, JHKs) photometry of RR Lyrae variables to investigate their location in the colour-magnitude diagrams as well as the pulsation properties such as period distributions, Bailey diagrams and amplitude ratios. The period–luminosity relations in R and I bands and Period–Wesenheit relations were derived after excluding outliers identified in CMDs. The Period–Wesenheit relations calibrated via the theoretically predicted relations were used to determine a distance modulus of |$\mu = 15.04 \pm 0.04 \, {\rm (stats)} \pm 0.19 \, {\rm {(syst.)}}$|  mag (using metal-independent WBV Wesenheit) and |$\mu = 15.03 \pm 0.04 \, {\rm (stats)} \pm 0.17 \, {\rm {(syst.)}}$|  mag (using metal-dependent WVI Wesenheit). Our distance measurements are in excellent agreement with published distances to M3 in the literature. We also employed an artificial neural network based comparison of theoretical and observed light curves to determine physical parameters (mass, luminosity, and effective temperature) for 79 non-Blazhko RRab stars that agree with limited literature measurements. [ABSTRACT FROM AUTHOR]

Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterized using red giants and main-sequence stars. RR Lyrae (RRL) variables can play a crucial role in tracing the early formation of the MW since they are ubiquitous, old (t ≥ 10 Gyr) low-mass stars and accurate distance indicators. We exploited Data Release 3 of the GALAH survey to identify 78 field RRLs suitable for chemical analysis. Using synthetic spectra calculations, we determined atmospheric parameters and abundances of Fe, Mg, Ca, Y, and Ba. Most of our stars exhibit halo-like chemical compositions, with an iron peak around [Fe/H] ≈ −1.40, and enhanced Ca and Mg content. Notably, we discovered a metal-rich tail, with [Fe/H] values ranging from −1 to approximately solar metallicity. This sub-group includes almost 1/4 of the sample, it is characterized by thin disc kinematics and displays sub-solar α-element abundances, marginally consistent with the majority of the MW stars. Surprisingly, they differ distinctly from typical MW disc stars in terms of the s-process elements Y and Ba. We took advantage of similar data available in the literature and built a total sample of 535 field RRLs for which we estimated kinematical and dynamical properties. We found that metal-rich RRLs (1/3 of the sample) likely represent an old component of the MW thin disc. We also detected RRLs with retrograde orbits and provided preliminary associations with the Gaia–Sausage–Enceladus, Helmi, Sequoia, Sagittarius, and Thamnos stellar streams. [ABSTRACT FROM AUTHOR]

RR Lyrae stars are standard candles with characteristic photometric variability and serve as powerful tracers of Galactic structure, substructure, accretion history, and dark matter content. Here we report the discovery of distant RR Lyrae stars, including some of the most distant stars known in the Milky Way halo, with Galactocentric distances of ∼300 kpc. We use time-series u * g ′ i ′ z ′ Canada–France–Hawaii Telescope/MegaCam photometry from the Next Generation Virgo Cluster Survey (NGVS). We use a template light-curve fitting method based on empirical Sloan Digital Sky Survey Stripe 82 RR Lyrae data to identify RR Lyrae candidates in the NGVS data set. We eliminate several hundred suspected quasars and identify 180 RR Lyrae candidates with heliocentric distances of ∼20–300 kpc. The halo stellar density distribution is consistent with an r −4.09±0.10 power-law radial profile over most of this distance range with no signs of a break. The distribution of ab-type RR Lyrae in a period–amplitude plot (Bailey diagram) suggests that the mean metallicity of the halo decreases outward. Compared to other recent RR Lyrae surveys, like Pan-STARRS1, the High Cadence Transient Survey, and the Dark Energy Survey, our NGVS study has better single-epoch photometric precision and a comparable number of epochs but smaller sky coverage. At large distances, our RR Lyrae sample appears to be relatively pure and complete, with well-measured periods and amplitudes. These newly discovered distant RR Lyrae stars are important additions to the few secure stellar tracers beyond 150 kpc in the Milky Way halo. [ABSTRACT FROM AUTHOR]

Context. Type II Cepheids (T2Cs) are the less frequently used counterparts of classical or type I Cepheids (CCs) which provide the primary calibration of the distance ladder for measuring the Hubble constant in the local Universe. In the era of the "Hubble tension", T2C variables together with the RR Lyrae stars and the tip of the red giant branch (TRGB) can potentially provide non-CC-dependent calibration of the cosmic distance ladder. Aims. Our goal is to provide an absolute calibration of the period–luminosity, period–luminosity–colour, and period–Wesenheit relations (PL, PLC, and PW, respectively) of T2Cs in the Large Magellanic Cloud (LMC), which traditionally serves as a crucial first anchor of the extragalactic distance ladder. Methods. We exploited time-series photometry in the near-infrared (NIR) Y,  J, and Ks bands for a sample of approximately 320 T2Cs in the Magellanic Clouds (MCs). These observations were acquired during 2009–2018 in the context of the VISTA survey of the Magellanic Clouds system (VMC), an ESO public survey. We supplemented the NIR photometry from the VMC survey with well-sampled optical light curves and accurate pulsation periods from the Optical Gravitational Lensing Experiment (OGLE) IV survey and the Gaia mission. We used the best-quality NIR light curves to generate custom templates for modelling sparsely sampled light curves in YJKs bands. Results. The best-fitting YJKs template light curves were used to derive accurate and precise intensity-averaged mean magnitudes and pulsation amplitudes of 277 and 62 T2Cs in the LMC and SMC, respectively. We used optical and NIR mean magnitudes for different T2C subclasses (BLHer, WVir, and RVTau) to derive PL/PLC/PW relations in multiple bands, which were calibrated with the geometric distance to the LMC as derived from eclipsing binaries and with the Gaia parallaxes. We used our new empirical calibrations of PL and PW relations to obtain distances to 22 T2C-host Galactic globular clusters, which were found to be systematically smaller by ∼0.1 mag and 0.03−0.06 mag than in the literature when the zero points are calibrated with the distance of the LMC or Gaia parallaxes, respectively. Better agreement is found between our distances and those based on RR Lyrae stars in globular clusters, providing strong support for using these population II stars together with the TRGB for future distance scale studies. [ABSTRACT FROM AUTHOR]

We present a new set of tools to derive systemic velocities for single-mode RR Lyrae stars from visual and near-infrared spectra. We derived scaling relations and line-of-sight velocity templates using both APOGEE and Gaia spectroscopic products combined with photometric G-band amplitudes. We provide a means to estimate systemic velocities for the RR Lyrae subclasses, RRab and RRc. Our analysis indicates that the scaling relation between the photometric and line-of-sight velocity amplitudes is nonlinear, with a break in a linear relation occurring around ≈0.4 mag in both the V-band and G-band amplitudes. We did not observe such a break in the relation for the first-overtone pulsators. Using stellar pulsation models, we further confirm and examine the nonlinearity in scaling relation for the RRab subclass. We observed little to no variation with stellar parameters (mass, metallicity, and luminosity) in the scaling relation between the photometric and line-of-sight velocity amplitudes for fundamental-mode pulsators. We observed an offset in the scaling relation between the observations and stellar pulsation models, mainly in the low-amplitude RR Lyrae regime. This offset disappears when different sets of convective parameters are used. Thus, the Fourier amplitudes obtained from the photometry and line-of-sight velocity measurements can be utilized to constrain convective parameters of stellar pulsation models. The scaling relations and templates for APOGEE and Gaia data accurately predict systemic velocities compared to literature values. In addition, our tools derived from the Gaia spectra improve the precision of the derived systemic velocities by approximately 50 percent and provide a better description of the uncertainty distribution in comparison with previous studies. Our newly derived tools will be used for RR Lyrae variables observed toward the Galactic bulge. [ABSTRACT FROM AUTHOR]

We present the first internally consistent set of [Fe/H] values for 14 of the 15 old globular clusters in the Large Magellanic Cloud (LMC). We make use of periods and amplitudes of fundamental mode (ab-type) RR Lyrae stars in the vicinity of these LMC clusters, mostly taken from the Optical Gravitational Lensing Experiment (OGLE) data base, in order to calculate metallicities for the clusters. Our data set contains a total of 417 ab-type cluster RR Lyrae stars (289 from OGLE and the rest from the literature) and yields a set of homogeneous metallicities for 14 old LMC globular clusters all on the Zinn and West scale. No previously published work contains metallicities for as many of the old LMC globular clusters as presented herein. An analysis of a subset of our abundances compared with seven other metallicity studies in the peer-reviewed literature indicates very little overall agreement between these [Fe/H] values suggesting that significantly more effort needs to be devoted to measuring internally consistent [Fe/H]s for the old LMC globular clusters. [ABSTRACT FROM AUTHOR]

Thanks to the precise astrometric measurements of proper motions by the Gaia mission, a new tidal stellar stream has been discovered in the northern hemisphere. The distribution of star count shows that the stream is approximately 80° long and 1.°70 wide. Observations of 21 member stars, including 14 RR Lyrae stars, indicate that the stream has an eccentric and retrograde orbit with e = 0.58. The low metallicity, high total energy, and large angular momentum suggest that it is associated with the merging event Sequoia. This discovery suggests the possibility of finding more substructures with high eccentricity orbits, even in the inner halo. [ABSTRACT FROM AUTHOR]

The results of a Fourier analysis of high-precision Kepler photometry of 75 double-mode RR Lyrae (RRd) stars observed during NASA's K2 Mission (2014-18) are presented. Seventy-two of the stars are 'classical' RRd (cRRd) stars lying along a well-defined curve in the Petersen diagram and showing no evidence of Blazhko modulations. The remaining three stars are 'anomalous' RRd (aRRd) stars that lie well below the cRRd curve in the Petersen diagram. These stars have larger fundamental-mode amplitudes than first-overtone amplitudes and exhibit Blazhko variations. Period-amplitude relations for the individual pulsation components of the cRRd stars are examined, as well as correlations involving Fourier phase-difference and amplitude-ratio parameters that characterize the light curves for the two radial modes. A simple statistical model relating the fundamental (P 0) and first-overtone (P 1) periods to [Fe/H] provides insight into the functional form of the Petersen diagram. A calibration equation for estimating [Fe/H]phot abundances of 'classical' RRd stars is derived by inverting the model and using 211 field and 57 globular cluster cRRd stars with spectroscopic metallicities to estimate the model coefficients. The equation is used to obtain [Fe/H]phot for the full sample of 72 K2 cRRd stars and for 2130 cRRd stars observed by the ESA Gaia Mission. Of the 49 K2 cRRd stars that are in the Gaia DR3 catalogue only five were found to be correctly classified, the remainder having been misclassified 'RRc' or 'RRab'. [ABSTRACT FROM AUTHOR]

RR Lyrae are a well-known class of pulsating horizontal branch stars widely used as tracers of old, metal-poor stellar populations. However, mounting observational evidence shows that a significant fraction of these stars may be young and metal-rich. Here, through detailed binary stellar evolution modelling, we show that all such metal-rich RR Lyrae can be naturally produced through binary interactions. Binary companions of these RR Lyrae stars formed through binary interactions partly strip their progenitor's envelopes during a preceding red giant phase. As a result, stripped horizontal branch stars become bluer than their isolated stellar evolution counterparts and thus end up in the instability strip. In contrast, in the single evolution scenario, the stars can attain such colours only at large age and low metallicity. While binary-made RR Lyrae can possess any ages and metallicities, their Galactic population is relatively young (1 – |$9\, {\rm Gyr}$|⁠) and dominated by the thin disc and the bulge. We show that Galactic RR Lyrae from binary evolution are produced at rates compatible with the observed metal-rich population and have consistent G -band magnitudes, Galactic kinematics, and pulsation properties. Furthermore, these systems dominate the RR Lyrae population in the solar neighbourhood. We predict that all metal-rich RR Lyrae have an A, F, G, or K-type companion with a long orbital period (⁠|$P \gtrsim 1000\, {\rm d}$|⁠). Observationally characterizing the orbital periods and masses of such stellar companions will provide valuable new constraints on mass and angular momentum-loss efficiency for Sun-like accretors and the nature of RR Lyrae populations. [ABSTRACT FROM AUTHOR]

We present a sample of 56 RR Lyrae variable stars (48 ab-type and 8 c-type) measured from a set of F475W (≈ B filter) and F814W (≈ I filter) archival images taken with the Hubble Space Telescope /Advanced Camera for Surveys of one field in the Local Group dwarf galaxy LGS-3 (also known as the Pisces Dwarf or Pisces I). The ab-type variables exhibit a mean period of =0.623 ± 0.007 d. Applying a relationship between [Fe/H] and period, we calculate a mean metallicity of 〈[Fe/H]〉 = −1.81 ± 0.04 on the Zinn & West scale. Finally, we conclude that the mean metal abundance of the RR Lyraes in LGS-3 is consistent with that of the LGS-3 field stellar population at an age of >10 Gyr. [ABSTRACT FROM AUTHOR]

We employ a sample of 135 873 RR Lyrae stars (RRLs) with precise photometric-metallicity and distance estimates from the newly calibrated P –ϕ31– R 21–[Fe/H] and Gaia G band P – R 21–[Fe/H] absolute magnitude–metallicity relations of Li et al. combined with available proper motions from Gaia EDR3, and 6955 systemic radial velocities from Gaia DR3 and other sources, in order to explore the chemistry and kinematics of the halo of the Milky Way (MW). This sample is ideally suited for characterization of the inner- and outer-halo populations of the stellar halo, free from the bias associated with spectroscopically selected probes, and for estimation of their relative contributions as a function of Galactocentric distance. The results of a Gaussian mixture model analysis of these contributions are broadly consistent with other observational studies of the halo, and with expectations from recent MW simulation studies. We apply the hdbscan clustering method to the specific energies and cylindrical actions (E , Jr, Jϕ, J z ), identifying 97 dynamically tagged groups (DTGs) of RRLs, and explore their associations with recognized substructures of the MW. The precise photometric-distance determinations (relative distance errors on the order of 5 per cent or better), and the resulting high-quality determination of dynamical parameters, yield highly statistically significant (low) dispersions of [Fe/H] for the stellar members of the DTGs compared to random draws from the full sample, indicating that they share common star-formation and chemical histories, influenced by their birth environments. [ABSTRACT FROM AUTHOR]

RR Lyrae stars play a central role in tracing phase-space structures within the Milky Way because they are easy to identify, are relatively luminous, and are found in large numbers in the Galactic bulge, disc, and halo. In this work, we present a new set of spectroscopic metallicity calibrations that use the equivalent widths of the Ca  ii  K and Balmer H γ and H δ lines to calculate metallicity values from low-resolution spectra. This builds on an earlier calibration from Layden by extending the range of equivalent widths which map between Ca  ii  K and the Balmer lines. We have developed the software rrlfe to apply this calibration to spectra in a consistent, reproducible, and extensible manner. This software is open-source and available to the community. The calibration can be updated with additional data sets in the future. [ABSTRACT FROM AUTHOR]

Non-linear pulsation modelling of classical variable stars is among the first topics that were developed at the beginning of the computational era. Various developments were made, and many questions were answered in the past 60 yr, and the models became more complex, describing the genuinely 3D convection in a single dimension. Despite its successes, the recent public availability of the mesa radial stellar pulsations (mesa rsp) module and the emerging results from multidimensional codes made clear that the eight free convective parameters, unique to these models, together with the underlying physical models need calibration. This could be done by comparing them against multidimensional codes, but before that, it is important to scrutinize the free parameters of the 1D codes using observations. This is a follow-up work of our previous calibration on the convective parameters of the budapest-florida and mesa rsp pulsation codes for RRab stars. In this letter, we extend the previous calibration to the RRc stars and the RR Lyrae stars in general. We found that correlations of some of the parameters are present in RRc stars as well but have a different nature, while high-temperature RRc stars' pulsation properties are very sensitive to the chosen parameter sets. [ABSTRACT FROM AUTHOR]

We report seven newly identified high-amplitude δ Scuti (HADS) stars. Among them, two stars (TIC 30977864 and TIC 387379145) exhibit pure radial pulsation without the excitation of non-radial modes. TIC 30977864 is classified as a double-mode HADS star, while the other four stars potentially show triple-mode HADS behavior. TIC 112682462 and TIC 255603395 closely resemble RR Lyrae stars based on their light curves, position in the period–luminosity diagram, and the period ratio diagram. However, without spectral observations, it is challenging to ascertain whether these two stars are HADS or RR Lyrae stars. TIC 281695001 exhibits a fundamental frequency amplitude smaller than that of the first overtone, suggesting the presence of intriguing phenomena that necessitate further analysis. We analyzed the relationship between metallicity and period using data provided by Netzel & Smolec. The metallicities of the 176 stars display a broad distribution ranging from −2.0 dex to 0.5 dex, with periods spanning 0.05 to 0.20 days. This random distribution of metallicities may contribute to the dispersion observed in the P1/P0 ratio. To derive more accurate conclusions, future spectroscopic observations of a larger sample of HADS stars are crucial. These observations will provide precise rotational velocities and more accurate determinations of metallicities. [ABSTRACT FROM AUTHOR]

We use 3653 (2661 RRab, 992 RRc) RR Lyrae stars (RRLs) with 7D (3D position, 3D velocity, and metallicity) information selected from Sloan Digital Sky Survey, Large Sky Area Multi-Object Fiber Spectroscopic Telescope, and Gaia EDR3, and divide the sample into two Oosterhoff groups (Oo I and Oo II) according to their amplitude–period behaviour in the Bailey diagram. We present a comparative study of these two groups based on chemistry, kinematics, and dynamics. We find that Oo I RRLs are relatively more metal-rich, with predominately radially dominated orbits and large eccentricities, while Oo II RRLs are relatively more metal-poor, and have mildly radially dominated orbits. The Oosterhoff dichotomy of the Milky Way's halo is more apparent for the inner-halo region than for the outer-halo region. Additionally, we also search for this phenomenon in the haloes of the two largest satellite galaxies, the Large and Small Magellanic clouds, and compare over different bins in metallicity. We find that the Oosterhoff dichotomy is not immutable, and varies based on position in the Galaxy and from galaxy to galaxy. We conclude that the Oosterhoff dichotomy is the result of a combination of stellar and galactic evolution, and that it is much more complex than the dichotomy originally identified in Galactic globular clusters. [ABSTRACT FROM AUTHOR]

Photometric observations from the last decade have revealed additional low-amplitude periodicities in many classical pulsators that are likely due to pulsations in non-radial modes. One group of multimode RR Lyrae stars, the so-called 0.61 stars, is particularly interesting. In these stars, the radial first overtone is accompanied by additional signals with period ratios around 0.61. The most promising explanation for these signals is pulsation in non-radial modes of degrees 8 and 9. If the theory behind the additional signals in the 0.61 stars is substantiated, it would allow us to use non-radial modes to study classical pulsators. We aim to perform asteroseismic modelling of selected 0.61 stars with independently determined physical parameters to test whether this assumption behind the modelling leads to correct results. Namely, we test whether the additional signals are indeed due to non-radial modes of the proposed moderate degrees. We selected a number of RR Lyrae stars that are also 0.61 stars and have good observational constraints on their other physical parameters. We assume that the nature of those modes is correctly explained with non-radial modes of degrees 8 or 9. Using this assumption and observational constraints on physical parameters, we performed asteroseismic modelling to test whether the observed periods and period ratios can be reproduced. For the majority of selected targets, we obtained a good match between observed and calculated periods and period ratios. For a few targets however, the results obtained are ambiguous and not straightforward to interpret. [ABSTRACT FROM AUTHOR]

Photometric metallicity formulae of fundamental-mode RR Lyr (RRab) stars are presented using globular-cluster data exclusively. The aim is to check whether this selection may help increasing the overall accuracy of the fits and eliminating the systematic bias of the photometric results, namely that they tend to overestimate [Fe/H] of the most metal-poor variables. The G band time-series data available in the Gaia DR3 archive and a new compilation of the published spectroscopic globular cluster [Fe/H] values on a uniform solar reference metallicity scale are utilized. We have derived a new [Fe/H]phot − P , φ31 formula, and have diagnosed that no significant increase in the accuracy of the fit can be achieved using non-linear or multiparameter formulae. The best result is obtained when different formulae are applied for variables with Oosterhoff (Oo)-type I and II properties. However, even this solution cannot eliminate the systematic bias of the results completely. This separation of the variables has also led to the conclusion that the photometric estimates of the [Fe/H] are less reliable for the Oo-type II variables than for the Oo-type I sample. Published [Fe/H]phot values and the results of the available photometric formulae in the Gaia G band are compared with the present results. It is found that each of the solutions yields very similar results, with similar accuracy and systematic biases. Major differences are detected only in the zero-points of the [Fe/H] scales, and these offsets are larger than differences in the accepted solar reference values would explain. [ABSTRACT FROM AUTHOR]

Based on the Gaia DR3 RR Lyrae catalogue, we use two methods to fit the density profiles with an improved broken power law, and find that there are two break radii coinciding with the two apocentre pile-ups of high-eccentricity Gaia -Sausage-Enceladus (GSE) merger. Also, there is a break caused by the Sagittarius (Sgr) stream. Combining the positions of all breaks, we briefly analyse the metallicity and its dispersion as a function of r as well as its distribution in cylindrical coordinates. For the clean sample, the z − x ellipsoid axial ratio q in |$36\, {\rm kpc}\, \lt \, r\, \lt \, 96\, {\rm kpc}$| becomes much smaller than that of the inner halo |$(r\, \lt \, 36\, {\rm kpc})$|⁠ , while the major axis has a large uncertainty in the region of |$36-66\, {\rm kpc}$| and the one in the region of |$66-96\, {\rm kpc}$| is obviously different from that dominated by the Hercules–Aquila Cloud (HAC) and the Virgo Overdensity (VOD) in the inner halo, which indicates that there is an over-density structure distributed at low-zenithal angles. Finally, we found that the over-density structure in the outer halo (⁠|$r\, \gt \, 50\, {\rm kpc}$|⁠) is shell-shaped and relatively metal-rich compared to the outer background halo. We conclude that the shells could be the apocentre pile-ups of the high-eccentricity GSE merger, which is supported by previous numerical simulations. [ABSTRACT FROM AUTHOR]

We present a comprehensive analysis of the variable stars projected on the field of the Galactic bulge globular cluster NGC 6522, offering valuable insights into their characteristics. Using proper motions from Gaia-DR3, we aim to distinguish between field stars and true cluster members. For an accurate color-magnitude diagram of the member stars, we produced a differential reddening map. We detect and discuss the peculiarities of variable stars of the types RR Lyrae, type II Cepheids, Long Period Variables (LPV) and eclipsing binaries, whose light curves are available through the OGLE III and IV databases. Notably, we explore the variable V24, which shows a prominent phase modulation resulting from period changes in a time scale of 1100 days. The variable stars among the cluster members serve as indicators of the cluster metallicity and distance; these determinations are based on their light curves. With the Fourier light curve decomposition of three RRc stars, we have derived the following cluster parameters: the metallicity in the spectroscopic scale [Fe/H] UVES = − 1.16 ± 0.09 ; and the mean distance D = 8.77 ± 0.16 kpc. [ABSTRACT FROM AUTHOR]

We present a CCD VI time-series analysis of the globular cluster NGC 6139 and its variable star population. Using the astrometric data available in Gaia -DR3, we performed a membership analysis that enabled the construction of a clean colour–magnitude diagram (CMD). Variable stars in the field of the cluster reported by Gaia -DR3 and newly discovered ones in this paper are classified and their membership is critically evaluated. We report two cluster members RRc (V12, V15) and four SR (V13, V14, V17, V18) not previously detected and assign variable names to V11 and V16 detected by Gaia as they proof to be cluster members. Light curves and periods for non-member Gaia eclipsing binaries, semiregular variables, and newly detected RR Lyrae stars are provided. Fourier decomposition of the light curves of the cluster member RRab and RRc stars leads to the values [Fe/H] = −1.63 dex, and distance of 9.63 ± 0.68 kpc. The Oosterhoff type II nature of the cluster is confirmed. We adopted the mean reddening E (B − V) = 0.786 mag and performed a differential reddening analysis based on the dispersion of the red giant branch. The differential map allowed a mild correction of the CMD. [ABSTRACT FROM AUTHOR]

In this concluding work of the series, a sample of selected ∼ 20 , 000 type-ab RR Lyrae stars from a total of 39,617 sources of the old bulge at distances r < 3.5 kpc from the Galactic Centre (GC) identified in the Vista Variables in the Vía Láctea survey (VVV) via the latest sample of the VIrac VAriable Classification Ensemble (VIVACE) pipeline is leveraged. As a model of the bulge, an oblate spheroid of stars with two major perpendicular axes a and b situated in the Galactic plane and a minor axis c perpendicular to this plane is adopted. The spatial distribution of stars is approximated by a standard power law with constant flattening and truncations at the lower and upper limits while allowing for the Sun's distance from the GC r 0 , the power-law index α , and the oblateness q = c / a to be free parameters. Our estimate of the distance is r 0 = 8.15 ± 0.04 kpc. The implied r 0 is almost the same for 1.5 < r max < 3.5 kpc, while the | α | and q values are varying systematically with increasing truncation radius r max in the ranges 1.56 − 2.66 and 1.0 − 0.76 . A weighted average and weighted uncertainty associated with all our measurements of r 0 in the series is also taken, r 0 = 8.2 ± 0.1 kpc. We argue that the ensuing result may be among the most robust indirect estimates that exist, as certain of the findings are tied to passbands of the Optical Gravitational Lensing Experiment (OGLE) RR Lyraes and globular clusters, and to near-infrared passbands of the VVV Type II Cepheids and VIVACE-VVV RR Lyraes. The distribution of stars within ≈ 3 kpc from the GC is spherical-like, q ≈ 1 . The average power-law indexes derived from the distribution of bulge RRab and inner halo globular clusters are nearly identical. This pertinent result demonstrates that the old bulge and inner halo form a continuous subsystem, and the bulk of the bulge objects represents the inner extension of a centrally concentrated, almost axisymmetric halo in the Galaxy. [ABSTRACT FROM AUTHOR]

Context. The unparalleled characteristics of Gaia photometry in terms of calibration, stability, time span, dynamic range, full-sky coverage, and complementary information make it an excellent choice to study stellar variability. Aims. We aim to measure the photometric dispersion in the G, GBP, and GRP bands of the 145 677 450 third Gaia data release (DR3) five-parameter sources with G ≤ 17 mag and GBP – GRP between −1.0 and 8.0 mag. We will use that unbiased sample to analyze stellar variability in the Milky Way (MW), Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC). Methods. For each band we convert from magnitude uncertainties to observed photometric dispersions, calculate the instrumental component as a function of apparent magnitude and color, and use it to transform the observed dispersions into the astrophysical ones: sG, SGBP, and SGRP. We give variability indices in the three bands for the whole sample indicating whether the objects are non-variable, marginally variable, or clearly so. We use the subsample established by Rimoldini and collaborators with light curves and variability types to calibrate our results and establish their limitations. Results. The position of an object in the dispersion-dispersion planes can be used to constrain its variability type, a direct application of these results. We use information from the MW, LMC, and SMC color-absolute magnitude diagrams (CAMDs) to discuss variability across the Hertzsprung-Russell diagram. White dwarfs and B-type subdwarfs are more variable than main sequence (MS) or red clump (RC) stars, with a flat distribution in sG up to 10 mmag and with variability decreasing for the former with age. The MS region in the Gaia CAMD includes a mixture of populations from the MS itself and from other evolutionary phases. Its sG distribution peaks at low values (~1–2 mmag) but it has a large tail dominated by eclipsing binaries, RR Lyrae stars, and young stellar objects. RC stars are characterized by little variability, with their sG distribution peaking at 1 mmag or less. The stars in the pre-main-sequence (PMS) region are highly variable, with a power law distribution in sG with slope 2.75 and a cutoff for values lower than 7 mmag. The luminous red stars region of the Gaia CAMD has the highest variability, with its extreme dominated by AGB stars and with a power law in sG with slope ~2.2 that extends from there to a cutoff of 7 mmag. We show that our method can be used to search for LMC Cepheids. We analyze four stellar clusters with O stars (Villafranca O-016, O-021, O-024, and O-026) and detect a strong difference in sG between stars that are already in the MS and those that are still in the PMS. [ABSTRACT FROM AUTHOR]

Context. Additional low-amplitude signals have been observed in many RR Lyrae stars separate from pulsations in radial modes. The most common of these are short-period signals forming a period ratio of around 0.60–0.65 with the first overtone and long-period signals forming a period ratio of around 0.68. The RR Lyrae stars may also exhibit quasi-periodic modulation in their light curves, the so-called Blazhko effect. Aims. We used the extensive sample of the first-overtone RR Lyrae stars observed by the Kepler telescope during the K2 mission to search for and characterize additional low-amplitude signals. The K2 data provides space-based photometry for a statistically significant sample. Hence, this data is excellent for studying the pulsation properties of RR Lyrae stars in detail. Methods. We used K2 space-based photometry for RR Lyrae candidates from Campaigns 0–19. We selected RR Lyrae stars pulsating in the first overtone and performed a frequency analysis for each star to characterize their frequency contents. Results. We classified 452 stars as first-overtone RR Lyrae. From that sample, we selected 281 RR0.61 stars, 67 RR0.68 stars, and 68 Blazhko stars. We found particularly interesting stars that show all of the above phenomena simultaneously. We detected signals in RR0.61 stars that form period ratios lower than those observed for the majority of stars of this type. These signals likely form a new sequence in the Petersen diagram, around a period ratio of 0.60. In 32 stars, we detected additional signals that form a period ratio close to that expected in RRd stars, but the classification of these stars as RRd is uncertain. We also report a discovery of additional signals in eight stars that form a new group in the Petersen diagram around the period ratio of 0.465–0.490. The nature of this periodicity remains unknown. [ABSTRACT FROM AUTHOR]

We present a new technique to generate the light curves of RRab stars in different photometric bands (I and V bands) using artificial neural networks (ANN). A pre-computed grid of models was used to train the ANN, and the architecture was tuned using the I -band light curves. The best-performing network was adopted to make the final interpolators in the I and V bands. The trained interpolators were used to predict the light curve of RRab stars in the Magellanic Clouds, and the distances to the Large Magellanic Cloud and Small Magellanic Cloud were determined based on the reddening independent Wesenheit index. The estimated distances are in good agreement with the literature. The comparison of the predicted and observed amplitudes, and Fourier amplitude ratios showed good agreement, but the Fourier phase parameters displayed a few discrepancies. To showcase the utility of the interpolators, the light curve of the RRab star EZ Cnc was generated and compared with the observed light curve from the Kepler mission. The reported distance to EZ Cnc was found to be in excellent agreement with the updated parallax measurement from Gaia EDR3. Our ANN interpolator provides a fast and efficient technique to generate a smooth grid of model light curves for a wide range of physical parameters, which is computationally expensive and time-consuming using stellar pulsation codes. [ABSTRACT FROM AUTHOR]

There are primarily two relations currently being used in the literature to calculate the metal abundance of ab-type RR Lyrae variables from their periods and V -band amplitudes. They are the one from Alcock et al. which utilizes both the stars' period and amplitude and the one from Sarajedini et al. which makes use of solely the stars' period of modulation. In this work, we are seeking to test which of these relations is most accurate in reproducing the spectroscopic metal abundances of Galactic globular clusters containing ab-type RR Lyraes to which we can apply these relations. For our sample of 600 ab-type RR Lyrae variables in 33 Galactic globular clusters, we find very similar results for both equations as regards the accuracy of the mean metallicity calculated for each globular cluster as compared with spectroscopic abundance measurements for these clusters. This implies that knowledge of only the periods of ab-type RR Lyrae variables in a globular cluster is sufficient to allow a determination of the mean metallicity of that cluster. In particular, once corrected for the adopted metallicity scale, both of these equations are able to reproduce the spectroscopic metal abundance of each cluster with an accuracy of ±0.28 dex. [ABSTRACT FROM AUTHOR]

Despite the appearance of two- and three-dimensional models thanks to the rapid growth of computing performance, numerical hydrocodes used to model radial stellar pulsations (RSPs) still apply a one-dimensional stellar envelope model without any realistic atmosphere, in which a significant improvement was the inclusion of turbulent convection. However, turbulent convection is an inherently multidimensional physical process in the vicinity of the ionization zones that generate pulsation. The description of these processes in one dimension can only be approximated based on simplified theoretical considerations involving several undetermined dimensionless parameters. In this work, we confront two one-dimensional numerical codes, namely the Budapest–Florida code and the MESA RSPs module, with radial-velocity observations of several non-modulated RRab stars of the M3 globular cluster and specified the undetermined convective parameters by the measured data for both codes independently. Our determination shows that some of the parameters depend on the effective temperature, which dependence is established for the first time in this work, and we also found some degeneracy between the parameters. This procedure gives as by-product suggestions for parameters of the publicly available RSP code extensively used recently by researchers through the MESA package. This work is part of the preparatory work to establish a theoretical framework required to make progress based on the results of one-dimensional models to couple them with multidimensional ones for further detailed analysis of physical processes. [ABSTRACT FROM AUTHOR]

We present an analysis of 50 F 475 W (≈ B filter) and F 814 W (≈ I filter) archival images taken with the Hubble Space Telescope (HST)/Advanced Camera for Surveys of one field in the isolated Local Group dwarf galaxy Wolf–Lundmark–Melotte (WLM). From point spread function fitting photometry of these images, we construct a colour–magnitude diagram and identify and characterize 90 RR Lyrae variables (76 ab-type and 14 c-type) determining their mean magnitudes, colours, periods, and amplitudes in the HST passbands. We have also uncovered 79 Cepheid-type variables, but because of the short time window of our observations (1.85 d), we are not confident in their period determinations. The mean period of the ab-type RR Lyraes is found to be 〈 P ab〉 = 0.609 ± 0.058 (ran) corresponding to a mean metallicity of 〈[Fe/H]〉 = −1.74 ± 0.02 (ran) on the Carretta et al. scale. We also present a re-analysis of the Hodge et al. colour–magnitude diagram of the WLM globular cluster and conclude that it is much more metal-poor than Hodge et al. quote. Based on a comparison of the WLM RR Lyraes with those in the other seven 'isolated' dwarf galaxies of the Local Group (i.e. Leo A, LGS 3, Cetus, IC 1613, Aquarius, Tucana, and Phoenix), we conclude that there was one unique epoch of early star formation common to all of these isolated dwarfs. [ABSTRACT FROM AUTHOR]

Using two years of data from the TESS space telescope, we have investigated the time series of 633 overtone pulsating field RR Lyrae (RRc) stars. The majority of stars (82.8 per cent) contain additional frequencies beyond the main pulsation. In addition to the frequencies previously explained by the ℓ = 8 and 9 non-radial modes, we have identified a group of stars where the additional frequencies may belong to the ℓ = 10 non-radial modes. We found that stars with no additional frequencies are more common among stars with shorter periods, while stars with longer periods almost always show additional frequencies. The incidence rate and this period distribution both agree well with the predictions of recent theoretical models. The amplitude and phase of additional frequencies are varying in time. The frequencies of different non-radial modes appearing in a given star seem to vary on different time-scales. We have determined a 10.4 per cent incidence rate for the Blazhko effect. For several stars we have detected continuous annual-scale phase change without significant amplitude variation. This type of variation offers a plausible explanation for the 'phase jump' phenomenon reported in many RRc stars. The main pulsation frequency could show quasi-periodic phase and amplitude fluctuations. This fluctuation is clearly related to additional frequencies present in the star: stars with two non-radial modes show the strongest fluctuations, while stars with no such modes show no fluctuations at all. The summation of the phase fluctuation over time may explain the O−C variations that have long been known for many non-Blazhko RRc stars. [ABSTRACT FROM AUTHOR]

We present the results of the UBVI C variability survey in the young open cluster NGC 6611 based on observations obtained during 34 nights spanning one year. In total, we found 95 variable stars. Most of these stars are classified as periodic and irregular pre-main sequence (PMS) stars. The analysis of the JHK S 2MASS photometry and four-colour IRAC photometry revealed 165 Class II young stellar sources, 20 of which are irregular variables and one is an eclipsing binary. These classifications, complemented by JHK UKIDSS photometry and riH α VPHAS photometry, were used to identify 24 candidates for classical T Tauri stars and 30 weak-lined T Tauri stars. In addition to the PMS variables, we discovered eight δ Scuti candidates. None of these were previously known. Furthermore, we detected 17 eclipsing binaries where two were previously known. Based on the proper motions provided by the Gaia EDR3 catalogue, we calculated the cluster membership probabilities for 91 variable stars. For 61 variables, a probability higher than 80 per cent was determined, which makes them cluster members. Only 25 variables with a probability less than 20 per cent were regarded to be non-members. [ABSTRACT FROM AUTHOR]

The author describes the Dominion Astrophysical Observatory during the years when J.S. Plaskett was Director. She makes special reference to the work on galactic rotation by Plaskett and J. A. Pearce and to her own early work on variable stars in globular clusters. [ABSTRACT FROM AUTHOR]

We have conducted a search for open clusters in the vicinity of classical Galactic Cepheids based on high-quality astrometry from the third data release (DR3) of the ESA mission Gaia to improve the calibration of the Leavitt law (LL). Our approach requires no prior knowledge of existing clusters, allowing us to both detect new host clusters and cross-check previously reported associations. Our Gold sample consists of 34 Cepheids residing in 28 open clusters, including 27 fundamental mode and seven overtone Cepheids. Three new bona fide cluster Cepheids are reported (V0378 Cen, ST Tau, and GH Lup) and the host cluster identifications for three others (VW Cru, IQ Nor, and SX Vel) are corrected. The fraction of Cepheids occurring in open clusters within 2 kpc of the Sun is fCC;2 kpc = 0:088+0:029 0:019. Nonvariable cluster members allow us to determine cluster parallaxes to ~7 was in the range 12:5 < G < 17 mag, where recent studies found that parallax corrections by Lindegren et al. (2021, A&A, 649, A4, L21) are accurate and require no further offset corrections. By comparing Cepheids in MW clusters to Cepheids in the LMC, we confirm these independent results and the adequacy of the L21 corrections for the cluster members in this range. By combining cluster and field Cepheids, we calibrate the LL for several individual photometric passbands, together with reddening-free Wesenheit magnitudes based on Gaia and HST photometry, while solving for the residual offset applicable to Cepheid parallaxes, $Cep. The most direct comparison of our results with the SH0ES distance ladder yields excellent (0:3 agreement for both the absolute magnitude of a 10 d solar metallicity Cepheid in the near-IR HST Wesenheit magnitudes, MW H;1 = 5:914 ± 0:017 mag, and the residual parallax offset, $Cep = 13 ± 5 as. Despite the use of a common set of photometry, this is an important cross-check of the recent Hubble constant measurement by Riess et al. (2022a, ApJ, 938, 36) based on independently determined cluster membership and average parallaxes. Using the larger sample of 26 Gold cluster Cepheids and 225MWCepheids with recent Gaia DR3 astrometry and photometry, we determine MW G;1 = 6:051±0:020 mag in the optical Gaia Wesenheit magnitude at the sample average iron abundance of (h[Fe=H]i = 0:069) and $Cep = 22 ± 3 as. Correcting to solar metallicity yields MW G;1 = 6:004 ± 0:019 mag and $Cep = 19 ± 3 as. These results mark the currently most accurate absolute calibrations of the Cepheid luminosity scale based purely on observations of Milky Way Cepheids, and it is also the most precise determination of the residual Cepheid parallax offset at a significance of 67. [ABSTRACT FROM AUTHOR]

The information on Galactic assembly time is imprinted on the chemodynamics of globular clusters. This makes them important probes that help us to understand the formation and evolution of the Milky Way. Discerning between in-situ and ex-situ origin of these objects is difficult when we study the Galactic bulge, which is the most complex and mixed component of the Milky Way. To investigate the early evolution of the Galactic bulge, we analysed the globular cluster NGC 6355. We derived chemical abundances and kinematic and dynamic properties by gathering information from high-resolution spectroscopy with FLAMES-UVES, photometry with the Hubble Space Telescope, and Galactic dynamic calculations applied to the globular cluster NGC 6355. We derive an age of 13.2 ± 1.1 Gyr and a metallicity of [Fe/H]  =   − 1.39 ± 0.08 for NGC 6355, with α-enhancement of [α/Fe]  =   + 0.37 ± 0.11. The abundance pattern of the globular cluster is compatible with bulge field RR Lyrae stars and in-situ well-studied globular clusters. The orbital parameters suggest that the cluster is currently confined within the bulge volume when we consider a heliocentric distance of 8.54 ± 0.19 kpc and an extinction coefficient of RV = 2.84 ± 0.02. NGC 6355 is highly likely to come from the main bulge progenitor. Nevertheless, it still has a low probability of being formed from an accreted event because its age is uncertain and because of the combined [Mg/Mn] [Al/Fe] abundance. Its relatively low metallicity with respect to old and moderately metal-poor inner Galaxy clusters may suggest a low-metallicity floor for globular clusters that formed in-situ in the early Galactic bulge. [ABSTRACT FROM AUTHOR]

We report the spectroscopic analysis of 20 halo ab-type RR Lyrae stars with heliocentric distances between 15 and 165 kpc, conducted using medium-resolution spectra from the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. We obtain the systemic line-of-sight velocities of our targets with typical uncertainties of 5–10 km s−1 and compute orbital parameters for a subsample out to 50 kpc from the Galactic centre, including proper motion data from Gaia DR3. The orientation of our stars' orbits, determined for an isolated Milky Way and for a model perturbed by the Large Magellanic Cloud, appears to suggest an accreted origin for at least half of the sample. In addition, we derive atmospheric parameters and chemical abundance ratios for seven stars beyond 20 kpc. The derived α-abundances of five of these stars follow a Milky Way halo-like trend, while the other two display an underabundance of α-elements for their [Fe/H], indicating an association with accretion events. Furthermore, based on the [Sr/Ba] ratio, we can speculate about the conditions for the formation of a potential chemically peculiar carbon-enhanced metal-poor (CEMP) RR Lyrae star. By analysing the stars' orbital parameters and abundance ratios, we find hints of association of two of our stars with two massive satellites, namely the Large Magellanic Cloud and Sagittarius. Overall, our results are in line with the suggestion that the accretion of sub-haloes largely contributes to the outer halo stellar populations. [ABSTRACT FROM AUTHOR]

We have analysed Optical Gravitational Lensing Experiment photometry for first overtone classical Cepheids in the Large and Small Magellanic Clouds in search for additional periodicities beyond radial modes. We have used standard consecutive pre-whitening technique in some cases followed by time-dependent pre-whitening. We report new candidates for double-mode radial pulsations. However, majority of signals we have detected cannot be interpreted in terms of radial modes. We report 516 double-periodic stars with period ratios, P x/ P 1O, in the range 0.60–0.65. We study the properties of this class and implications for model explaining these periodicities. We also report 28 stars in which additional variability is of longer period, below radial fundamental mode, with median period ratio, P 1O/ P x, of 0.684. This class is an analogue of a class known in RR Lyrae stars. Hundreds of other signals were detected that cannot be attributed to radial modes or the above-mentioned classes. Statistical properties of these signals are analysed. We suggest that majority of these signals correspond to non-radial modes. In particular, a significant fraction can be attributed to non-radial modes of moderate degrees, tightly connected to a class with period ratios in between 0.60 and 0.65. In tens of stars, close to radial mode frequency, relatively large-amplitude and coherent signals are observed, which may represent yet another class. In 27 stars periodic modulation of pulsation was detected. Differences in additional frequency content between the two Clouds are discussed. [ABSTRACT FROM AUTHOR]

Homogeneous metallicities and continuous high-precision light curves play key roles in studying the pulsation properties of RR Lyrae stars. By cross matching LAMOST DR6 with the Kepler and K2 fields, we have determined seven and 50 non-Blazhko RRab stars, respectively, that have homogeneous metallicities determined from low-resolution spectra of the LAMOST–Kepler/K2 survey. The Fourier decomposition method is applied to the light curves of these stars provided by the Kepler space-based telescope to determine the fundamental pulsation periods and parameters. The calculated amplitude ratios of R 21, R 31 and the phase differences of ϕ 21, ϕ 31 are consistent with the parameters of RRab stars in both globular clusters and the Large Magellanic Cloud. We find a linear relationship between the phase differences ϕ 21 and ϕ 31, which is in good agreement with the results in the literature. As far as the amplitude, we find that the amplitude of primary frequency A 1 and the total amplitude A tot follow either a cubic or linear relationship. For the rise time, we do not find its relevance with the period of the fundamental pulsation mode P1, or A tot and ϕ 21. However, it might follow a linear relationship with R 31. Based on the homogeneous metallicities, we have derived a new calibration formula for the period– ϕ 31–[Fe/H] relation, which agrees well with previous studies. [ABSTRACT FROM AUTHOR]

A 5-yr CCD photometric VI time series of NGC 7006 is employed to perform a detailed analysis of the known population of variable stars. In the process, we have corrected inconsistent classifications, sky coordinates and found 10 new cluster member variables. An independent reddening estimate with a value E (B − V) = 0.08 ± 0.05 is made. Using Fourier decompositions of RR Lyrae light curves and well-established calibrations, the cluster mean metallicity and distance [Fe/H]ZW = −1.53 ± 0.15 and 41.2 ± 1.4 kpc are estimated based on an extended sample of cluster member RRab stars. Using the Gaia DR3 data, we performed an extensive membership analysis that leads to a clean colour–magnitude diagram, and hence to the identification of variables that are likely field stars, and to considerations on the variable distribution in the horizontal branch (HB). A double-mode RR Lyrae and three CW stars are discussed. The origin of CW stars from precursors in the blue tail of the HB with very thin (∼0.06 ± 0.01 M⊙) envelopes is argued. Our models indicate that the main-sequence predecessor of RR Lyrae stars had a mass of 0.82–0.85 M⊙ and lost about 25–35 per cent of its mass during the red giant branch events before settling in the HB some 12–13.5 Gyr later. [ABSTRACT FROM AUTHOR]

We investigate the properties of the mixed-mode (RRd) RR Lyrae (RRL) variables in the Fornax dwarf spheroidal (dSph) galaxy by using B - and V -band time series collected over 24 yr. We compare the properties of the RRds in Fornax with those in the Magellanic Clouds and in nearby dSphs, with special focus on Sculptor. We found that the ratio of RRds over the total number of RRLs decreases with metallicity. Typically, dSphs have very few RRds with 0.49≲ P 0 ≲0.53 d, but Fornax fills this period gap in the Petersen diagram (ratio between first overtone over fundamental period versus fundamental period). We also found that the distribution in the Petersen diagram of Fornax RRds is similar to Small Magellanic Cloud (SMC) RRds, thus suggesting that their old stars have a similar metallicity distribution. We introduce the Period–Amplitude RatioS diagram, a new pulsation diagnostics independent of distance and reddening. We found that Large Magellanic Cloud (LMC) RRds in this plane are distributed along a short- and a long-period sequence that we identified as the metal-rich and the metal-poor component. These two groups are also clearly separated in the Petersen and Bailey (luminosity amplitude versus logarithmic period) diagrams. This circumstantial evidence indicates that the two groups have different evolutionary properties. All the pulsation diagnostics adopted in this investigation suggest that old stellar populations in Fornax and Sculptor dSphs underwent different chemical enrichment histories. Fornax RRds are similar to SMC RRds, while Sculptor RRds are more similar to the metal-rich component of the LMC RRds. [ABSTRACT FROM AUTHOR]