Search

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]

New results on the behavior of the double-mode RR Lyrae V338 Boo are presented. The Transiting Exoplanet Survey Satellite (TESS) observed this star again in 2022, and an observing campaign of the American Association of Variable Star Observers (AAVSO) was completed after the TESS observations as a follow-up. We find that the first overtone pulsation mode in this star completely disappears during the TESS observing window. This mode reappears at the end of the TESS observations, and the AAVSO observing campaign shows that in the months that followed, the first overtone mode was not only present but was the dominant mode of pulsation. This star, and potentially others like it, could hold the key to finally solving the mystery of the Blazhko effect in RR Lyrae.

RR Lyrae stars (RRLs) are excellent tracers of stellar populations for old, metal-poor components in the the Milky Way and the Local Group. Their luminosities have a metallicity dependence, but determining spectroscopic [Fe/H] metallicities for RRLs, especially at distances outside the solar neighborhood, is challenging. Using 40 RRLs with metallicities derived from both Fe( ii ) and Fe( i ) abundances, we verify the calibration between the [Fe/H] of RRLs from the calcium triplet. Our calibration is applied to all RRLs with Gaia Radial Velocity Spectrometer (RVS) spectra in Gaia DR3 and to 80 stars in the inner Galaxy from the BRAVA-RR survey. The coadded Gaia RVS RRL spectra provide RRL metallicities with an uncertainty of 0.25 dex, which is a factor of two improvement over the Gaia photometric RRL metallicities. Within our Galactic bulge RRL sample, we find a dominant fraction with low energies without a prominent rotating component. Due to the large fraction of such stars, we interpret these stars as belonging to the in situ metal-poor Galactic bulge component, although we cannot rule out that a fraction of these belong to an ancient accretion event such as Kraken/Heracles.

This work is part of VESTALE, a project initiated within the Legacy Survey of Space and Time (LSST) Cadence Strategy Optimization Process. Its goal is to explore the potential of Rubin-LSST observations aimed at the Galactic bulge (henceforth just “Bulge”) for studying RR Lyrae (RRL) stars. Observation and analysis of RRL stars in the Bulge are crucial for tracing the old population of the central part of our Galaxy and reconstructing its formation. Based on observations conducted with CTIO/DECam by Saha et al. toward Baade’s window, our simulations demonstrate that early Rubin-LSST observations will enable the recovery of RRL light curves (LCs) at Galactic center distances with sufficient precision. This will allow us to utilize theoretical relations from Marconi et al. to determine their distances and/or metallicity, following the REDIME algorithm introduced in Bono et al. We show how reddening and crowding affect our simulations and highlight the importance of considering these effects when deriving pulsation parameters (luminosity amplitudes, mean magnitudes) based on the LCs, especially if the goal is to explore the opposite side of the Bulge through the observation of its RRL. The simulations discussed in this investigation were conducted to support the Survey Cadence Optimization Committee’s decision to observe this important sky region since it has only recently been decided to include part of the Bulge as a target within the LSST main survey.

RRd stars are a subclass of RR Lyrae stars that pulsate simultaneously in the fundamental and the first-overtone radial modes. We report the analysis of 10 RRd stars discovered in the Sloan Digital Sky Survey (SDSS) Stripe 82 region of the Galactic halo using SDSS and Zwicky Transient Facility data. By combining the two data sets, we constructed ∼23 yr long lightcurves in gri bands, and conclude that out of 10, 9 were the classical RRd stars and 1 was the anomalous RRd star. We also observed the long-term variation, the Blazhko effect, in 3 classical RRd stars out of 10 stars, giving an incidence rate of 30%. The shortest Blazhko period observed was 226.4 ± 0.8 days and the longest was 2799 ± 75 days.

Virgo III is a newly discovered ultra-faint-dwarf (UFD) candidate, and finding RR Lyrae associated with this galaxy is important to constrain its distance. In this work, we present a search of RR Lyrae in the vicinity of Virgo III based on the time-series r -band images taken from the Lulin One-meter Telescope (LOT). We have identified three RR Lyrae from our LOT data, including two fundamental mode (ab-type) and a first-overtone (c-type) RR Lyrae. Assuming these three RR Lyrae are members of Virgo III, we derived the distance to this UFD as 154 ± 25 kpc, fully consistent with the independent measurements given in the literature. We have also revisited the relation between absolute V -band magnitude ( M _V ) and the number of RR Lyrae (of all types, N _RRL ) found in local galaxies, demonstrating that the M _V - N _RRL relation is better described with the specific RR Lyrae frequency.

Accurate determination of the stellar atmospheric parameters of RR Lyrae stars (RRLs) requires short individual exposures of the spectra to mitigate pulsation effects. We present improved template-matching methods to determine the stellar atmospheric parameters of RRLs from single-epoch spectra of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, also known as the Guoshoujing Telescope (LAMOST). We determine the radial velocities and stellar atmospheric parameters (effective temperature T _eff , surface gravity $\mathrm{log}\,g$ , and metallicity [M/H]) of 10,486 and 1027 RRLs from 42,729 LAMOST low-resolution spectra (LRS) and 7064 LAMOST medium-resolution spectra (MRS), respectively. Our results are in good agreement with the parameters of other databases, where the external uncertainties of T _eff , $\mathrm{log}\,g$ , and [M/H] for LRS/MRS are estimated to be 207/142 K, 0.21/0.16 dex, and 0.24/0.18 dex, respectively. We conclude with the variation characteristics of the radial velocities (RV) and stellar atmospheric parameters for RRLs during the pulsation phase. There is a significant difference of 28 ± 21 km s ^−1 between the peak-to-peak amplitude ( A _ptp ) of RV from the H α line (RV _H _α ) and from metal lines (RV _metal ) for RRab, whereas it is only 4 ± 17 km s ^−1 for RRc. The A _ptp of T _eff is 930 ± 456 and 409 ± 375 K for RRab and RRc, respectively. The $\mathrm{log}\,g$ of RRab shows a mild variation of approximately 0.22 ± 0.42 dex near the phase of φ = 0.9, while that of RRc almost remains constant. The [M/H] of RRab and RRc show a minor variation of about 0.25 ± 0.50 and 0.28 ± 0.55 dex, respectively, near the phase of φ = 0.9. We expect that the determined stellar atmospheric parameters would shed new light on the study of stellar evolution and pulsation, the structure of the Milky Way, as well as other research fields.

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^{\prime} i^{\prime} z^{\prime} $ 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.

The Draco Dwarf spheroidal (dSph) galaxy is one of the nearest and the most dark-matter-dominated satellites of the Milky Way. We obtained multiepoch near-infrared (NIR, JHK _s ) observations of the central region of Draco dSph covering a sky area of ∼21′ × 21′ using the WIRCam instrument at the 3.6 m Canada–France–Hawaii Telescope. Homogeneous JHK _s time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and five Anomalous Cepheids in Draco dSph are presented and used to derive their period–luminosity relations at NIR wavelengths for the first-time. The small scatter of ∼0.05 mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to ∼0.2 dex, among these centrally located variables. Based on empirically calibrated NIR period–luminosity–metallicity relations for RR Lyrae in globular clusters, we determined a distance modulus to Draco dSph of μ _RRL = 19.557 ± 0.026 mag. The calibrated K _s -band period–luminosity relations for Anomalous Cepheids in the Draco dSph and the Large Magellanic Cloud exhibit statistically consistent slopes but systematically different zero points, hinting at possible metallicity dependence of ∼ − 0.3 mag dex ^−1 . Finally, the apparent magnitudes of the tip of the red-giant branch in I and J bands also agree well with their absolute calibrations with the adopted RR Lyrae distance to Draco. Our recommended ∼1.5% precise RR Lyrae distance, D _Draco = 81.55 ± 0.98(statistical) ± 1.17(systematic) kpc, is the most accurate and precise distance to Draco dSph galaxy.

We conduct an asteroseismological analysis on the non-Blazhko ab-type RR Lyrae star EPIC 248846335, employing the Radial Stellar Pulsations module of the Modules for Experiments in Stellar Astrophysics based on the set of stellar parameters. The atmospheric parameters T _eff = 6933 ± 70 K, log g = 3.35 ± 0.50, and [Fe/H] = −1.18 ± 0.14 are estimated from low-resolution spectra of LAMOST DR9. The luminosity L = ${49.70}_{-1.80}^{+2.99}$ L _⊙ and mass M = 0.56 ± 0.07 M _⊙ are calculated, respectively, using the distance provided by Gaia and the metallicity estimated from the low-resolution spectra. The Fourier parameters of the light curves observed by K2 and radial velocity (RV) curves determined from the medium-resolution spectra of LAMOST DR10 are also calculated in this work. The period of the fundamental mode of the star and the residuals r of the Fourier parameters between the models and observations serve to select an optimal model, whose stellar parameters are T _eff = 6700 ± 220 K, log g = 2.70, [Fe/H] = −1.20 ± 0.2, M = 0.59 ± 0.05 M _⊙ , and L = 56.0 ± 4.2 L _⊙ . The projection factors are constrained as 1.20 ± 0.02 and 1.59 ± 0.13 by the blue- and red-arm observed velocities with their corresponding RV curves derived from the best-fit model, respectively. The precise determination of stellar parameters in ab-type RR Lyrae stars is crucial for understanding the physical processes that occur during pulsation and for providing a deeper understanding of their period–luminosity relationship.

The possible existence of stellar halos in low-mass galaxies is being intensely discussed nowadays after some recent discoveries of stars located in the outskirts of dwarf galaxies of the Local Group. RR Lyrae stars can be used to identify the extent of these structures, taking advantage of the minimization of foreground contamination they provide. In this work we use RR Lyrae stars obtained from Gaia DR3, the Dark Energy Survey, the Zwicky Transient Facility, and Pan-STARRS1 to explore the outskirts of 45 ultrafaint dwarf galaxies. We associate the stars with a host galaxy based on their angular separations, magnitudes, and proper motions. We find a total of 120 RR Lyrae stars that belong to 21 different galaxies in our sample. We report seven new RR Lyrae stars in six ultrafaint dwarf galaxies (Hydrus I, Ursa Major I, Ursa Major II, Grus II, Eridanus II, and Tucana II). We found a large number of new possible members in Bootes I and Bootes III as well, but some of them may actually belong to the nearby Sagittarius stream. Adding to our list of 120 RR Lyrae stars the observations of other ultrafaint dwarf galaxies that were beyond the reach of our search, we find that at least 10 of these galaxies have RR Lyrae stars located at distances greater than four times their respective half-light radius, which implies that at least 33% of the 30 ultrafaint dwarfs with a population of RR Lyrae stars have extended stellar populations.

Multiband light curves of two RR Lyrae variables in Segue II and Ursa Major II ultrafaint dwarf galaxies were collected from near simultaneous observations using the Lulin One-meter Telescope in Vgri bands. Together with Gaia G -band light curves, we determined photometric metallicities using empirical relations involving pulsation period and Fourier parameter as dependent parameters. We demonstrated that the RR Lyrae photometric metallicity can be determined accurately when these empirical relations were employed at multiple wavelengths, which can potentially improve the distance determination based on RR Lyrae stars. The photometric metallicities based on our approach were found to be −2.27 ± 0.13 dex and −1.87 ± 0.16 dex for the RR Lyrae in Segue II and Ursa Major II UFD, respectively, with corresponding distance moduli of 17.69 ± 0.15 mag and 17.58 ± 0.15 mag, in agreement with previous literature determinations. This approach of photometric metallicity of RR Lyrae based on multiband optical light curves will be particularly relevant for distance measurements in the era of the Vera C Rubin’s Legacy Survey of Space and Time.

RR Lyrae (RR Lyr) stars are a well-known and useful distance indicator for old stellar populations such as globular clusters and dwarf galaxies. Fundamental-mode RR Lyr (RRab) stars are commonly used to measure distances, and the accuracy of the determined distance is strongly constrained by metallicity. Here, we investigate the metallicity dependence in the period–luminosity (PL) relation of double-mode RR Lyr (RRd) stars. We find and establish a linear relation between metallicity and period or period ratio for RRd stars. This relation can predict the metallicity as accurately as the low-resolution spectra. Based on this relation, we establish a metallicity-independent PL relation for RRd stars. Combining the distance of the Large Magellanic Cloud and Gaia parallaxes, we calibrate the zero point of the derived PL relation to an error of 0.022 mag. Using RRd stars, we measure the distances of globular clusters and dwarf galaxies with an accuracy of 2-3% and 1-2%, respectively. In the future, RRd stars could anchor galaxy distances to an accuracy of 1.0% and become an independent distance ladder in the Local Group. [ABSTRACT FROM AUTHOR]

In the last five years, the number of periodic variable stars has increased by two million. We used the ZTF DR2 data to find and build a catalog that includes 780,000 periodic variable stars. These periodic variable stars were classified into 11 types, which greatly complemented the variable stars in Galactic disk. Based on the latest ZTF DR16 data, we found 2 million variable candidates. We trained a machine learner to classify variable stars, and the learner had a prediction accuracy of 94%. Using millions of variable stars, we carried out studies to optimize the period–luminosity relations and the Galactic structure and the extinction law. With the future China Space Station Telescope, millions of variable stars in the Local Group will be discovered. They help to study the structure of our Local Group and also to cross-check the distance ladders based on different variable stars. [ABSTRACT FROM AUTHOR]

RR Lyrae variables are excellent Population II distance indicators thanks to their well-defined period–luminosity relations (PLRs) at infrared wavelengths. We present results of near-infrared (NIR) monitoring of Galactic globular clusters to empirically quantify the metallicity dependence of NIR PLRs for RR Lyrae variables. Our sample includes homogeneous, accurate, and precise photometric data for 964 RR Lyrae variables in 11 globular clusters covering a large metallicity range (Δ[Fe/H] ∼ 2 dex). We derive JHK _s -band period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations anchored using 346 Milky Way field RR Lyrae stars with Gaia parallaxes, and simultaneously solved for independent distances to globular clusters. We find a significant metallicity dependence of ∼0.2 mag dex ^−1 in the JHK _s -band PLZ and PWZ relations for RR Lyrae stars independent of the adopted metallicity scale. The metallicity coefficients and the zero-points of the empirical PLZ and PWZ relations are in excellent agreement with the predictions from the horizontal branch evolution and pulsation models. Furthermore, RR Lyrae–based distances to our sample of globular clusters are also statistically consistent with other independent measurements in the literature. Our recommended empirical JHK _s -band PLZ relations for RR Lyrae stars with periods of fundamental mode pulsation ( P _f ) are: \begin{eqnarray*}\begin{array}{rcl}{M}_{J} & = & -0.44\,(\pm 0.03)-1.83\,(\pm 0.02)\mathrm{log}({P}_{{\rm{f}}})+0.20\,(\pm 0.02)\,[\mathrm{Fe}/{\rm{H}}]\,(\sigma =0.05\,\mathrm{mag})\\ {M}_{H} & = & -0.74\,(\pm 0.02)-2.29\,(\pm 0.02)\mathrm{log}({P}_{{\rm{f}}})+0.19\,(\pm 0.01)[\mathrm{Fe}/{\rm{H}}]\,(\sigma =0.05\,\mathrm{mag})\\ {M}_{{K}_{s}} & = & -0.80\,(\pm 0.02)-2.37\,(\pm 0.02)\mathrm{log}({P}_{{\rm{f}}})+0.18\,(\pm 0.01)\,[\mathrm{Fe}/{\rm{H}}]\,(\sigma =0.05\,\mathrm{mag}).\end{array}\end{eqnarray*}

RR Lyrae stars (RRLs) are pulsating stars, many of which also show a long-term variation called the Blazhko effect which is a modulation of amplitude and phase of the lightcurve. In this work, we searched for the incidence rate of the Blazhko effect in the first-overtone pulsating RR Lyrae (RRc) stars of the Galactic halo. The focus was on the Stripe 82 region in the Galactic halo which was studied by Sesar et al. using the Sloan Digital Sky Survey (SDSS) data. In their work, 104 RRLs were classified as RRc type. We combined their SDSS light curves with Zwicky Transient Facility (ZTF) data, and used them to document the Blazhko properties of these RRc stars. Our analysis showed that among the 104 RRc stars, eight were rather RRd stars, and were excluded from the study. Out of the remaining 96, 34 were Blazhko type, 62 were non-Blazhko type, giving the incidence rate of 35.42% for Blazhko RRc stars. The shortest Blazhko period found was 12.808 ± 0.001 days for SDSS 747380, while the longest was 3088 ± 126 days for SDSS 3585856. Combining SDSS and ZTF data sets increased the probability of detecting the small variations due to the Blazhko effect, and thus provided a unique opportunity to find longer Blazhko periods. We found that 85% of RRc stars had the Blazhko period longer than 200 days.

We have performed the first systematic search of the full Galaxy Evolution Explorer (GALEX) data archive for astrophysical variability on timescales of seconds to minutes by rebinning data across the whole mission to 30 s time resolution. The result is the GALEX Flare Catalog (GFCAT), which describes 1426 ultraviolet variable sources, including stellar flares, eclipsing binaries, δ Scuti and RR Lyrae variables, and active galactic nuclei. Many of these sources have never previously been identified as variable. We have also assembled a table of observations of ultraviolet flares and accompanying statistics and measurements, including energies, and of candidate eclipsing stars. This effort was enabled by a significantly enhanced version of the gPhoton software for analyzing time-domain GALEX data; this “gPhoton2” package is available to support follow-on efforts.

Noting the weakest modulation and relatively high metal abundance of the ab-type RR Lyrae star V838 Cyg, we collected the photometric data of this star from several sky surveys to carry out an in-depth analysis. The O − C diagram shows that the pulsation period of V838 Cyg increases linearly over a long timescale. In a reanalysis of the high-precision Kepler data, we confirmed the modulation with a period of 59.45 ± 0.07 days found by Benkő et al., and also found an additional weak modulation with a longer period (840 ± 21 days). After a series of analyses, we incline to the view that the mechanisms causing the two modulations are different: the former is more similar to the typical Blazhko effect, while the mechanism leading to the latter may be an extrinsic factor. We also collected and compared the modulation and physical parameters of other Blazhko RR Lyrae stars from several works in the literature, and find that there is a potential negative correlation between the modulation amplitude (or upper limit of amplitude) and the metal abundance. We infer that the relatively high metal abundance will promote convection in the outer stellar atmosphere, and then inhibit those factors (turbulence, shock wave, etc.) that may cause Blazhko modulation. Future observations and research work can be carried out with reference to this viewpoint. We also introduce the moiré effects that appear in the Kepler long-cadence light curves and their possible interference in the previous analyses.

We present new period–luminosity and period–luminosity–metallicity relations for Galactic RR Lyrae stars based on a sample of 28 pulsators located at distances of up to 1.5 kpc from the Sun. Near-infrared photometry was obtained at the Cerro Armazones Observatory, and parallaxes were taken from the Gaia Early Data Release 3. Relations were determined for the 2MASS JHK _s bands and the W _JK Wesenheit index. We compare our results with other calibrations available in the literature and obtain very good agreement with the photometry of RR Lyraes from the Large Magellanic Cloud (LMC) anchored using the distance to the Cloud, which is based on detached eclipsing binaries. We find that the dependence of absolute magnitudes on metallicity of 0.070 ± 0.042 ( J band) to 0.087 ± 0.031 ( W _JK index) mag dex ^−1 for the population of fundamental pulsators (RRab) is in agreement with previously published phenomenological works. We perform a refined determination of distance to the LMC based on our new calibration and photometry from Szewczyk et al. We study the dependence of the fitted parameters of the fiducial relations and the LMC distance on the systematic parallax offset.

We report the discovery of Pegasus IV, an ultra-faint dwarf galaxy found in archival data from the Dark Energy Camera processed by the DECam Local Volume Exploration Survey. Pegasus IV is a compact, ultra-faint stellar system ( ${r}_{1/2}={41}_{-6}^{+8}$ pc; M _V = −4.25 ± 0.2 mag) located at a heliocentric distance of ${90}_{-6}^{+4}\,\mathrm{kpc}$ . Based on spectra of seven nonvariable member stars observed with Magellan/IMACS, we confidently resolve Pegasus IV’s velocity dispersion, measuring ${\sigma }_{v}={3.3}_{-1.1}^{+1.7}$ km s ^−1 (after excluding three velocity outliers); this implies a mass-to-light ratio of ${M}_{1/2}/{L}_{V,1/2}={167}_{-99}^{+224}{M}_{\odot }/{L}_{\odot }$ for the system. From the five stars with the highest signal-to-noise spectra, we also measure a systemic metallicity of [Fe/H] = $-{2.63}_{-0.30}^{+0.26}$ dex, making Pegasus IV one of the most metal-poor ultra-faint dwarfs. We tentatively resolve a nonzero metallicity dispersion for the system. These measurements provide strong evidence that Pegasus IV is a dark-matter-dominated dwarf galaxy, rather than a star cluster. We measure Pegasus IV’s proper motion using data from Gaia Early Data Release 3, finding ( μ _α _* , μ _δ ) = (0.33 ± 0.07, −0.21 ± 0.08) mas yr ^−1 . When combined with our measured systemic velocity, this proper motion suggests that Pegasus IV is on an elliptical, retrograde orbit, and is currently near its orbital apocenter. Lastly, we identify three potential RR Lyrae variable stars within Pegasus IV, including one candidate member located more than 10 half-light radii away from the system’s centroid. The discovery of yet another ultra-faint dwarf galaxy strongly suggests that the census of Milky Way satellites is still incomplete, even within 100 kpc.

We present a sample of 135,873 RR Lyrae stars (RRLs) with precise photometric metallicity and distance estimates from our newly calibrated P – ϕ _31 – R _21 –[Fe/H]/ P – R _21 –[Fe/H] and G -band absolute magnitude–metallicity relations. The P – ϕ _31 – R _21 –[Fe/H] and P – R _21 –[Fe/H] relations for type RRab and type RRc stars are obtained from nearly 2700 Gaia-identified RRLs, with precise ϕ _31 and R _21 measurements from light curves and metallicity estimates from spectroscopy. Using a few hundreds of nearby RRLs, with accurate distances estimated from the parallax measurements in Gaia Early Data Release 3, new G -band absolute magnitude–metallicity relations and near-IR period–absolute magnitude–metallicity relations are constructed. External checks, using other high-resolution spectroscopic samples of field RRLs and RRL members of globular clusters, show that the typical uncertainties in our photometric metallicity estimates are about 0.24 and 0.16 dex for type RRab and type RRc stars, respectively, without significant systematic bias with respect to the high-resolution spectroscopic metallicity measurements. The accuracies of these metallicity estimates are much improved, especially for type RRab stars, when compared to those provided by Gaia Data Release 3. Validations of our distance estimates, again using members of globular clusters, show that the typical distance errors are only 3%–4%. The distance moduli μ _0 = 18.503 ± 0.001 (stat) ± 0.040 (syst) mag for the Large Magellanic Cloud (LMC) and μ _0 = 19.030 ± 0.003 (stat) ± 0.043 (syst) mag for the Small Magellanic Cloud (SMC) are estimated from our type RRab star sample and are in excellent agreement with previous measurements. The mean metallicities of the LMC and SMC derived in this work are also consistent with previous determinations. Using our sample, a steep metallicity gradient of −0.024 ± 0.001 dex kpc ^−1 is found for the LMC, while a negligible metallicity gradient is obtained for the SMC.

We present new empirical infrared period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations for RR Lyae based on the latest Gaia Early Data Release 3 (EDR3) parallaxes. The relations are provided in the Wide-field Infrared Survey Explorer (WISE) W1 and W2 bands, as well as in the W(W1, V − W1) and W(W2, V − W2) Wesenheit magnitudes. The relations are calibrated using a very large sample of Galactic halo field RR Lyrae stars with homogeneous spectroscopic [Fe/H] abundances (over 1000 stars in the W1 band), covering a broad range of metallicities (−2.5 ≲ [Fe/H] ≲ 0.0). We test the performance of our PLZ and PWZ relations by determining the distance moduli of both galactic and extragalactic stellar associations: the Sculptor dwarf spheroidal galaxy in the Local Group (finding ${\bar{\mu }}_{0}=19.47\pm 0.06$ ), the Galactic globular clusters M4 ( ${\bar{\mu }}_{0}=11.16\pm 0.05$ ), and the Reticulum globular cluster in the Large Magellanic Cloud ( ${\bar{\mu }}_{0}=18.23\pm 0.06$ ). The distance moduli determined through all our relations are internally self-consistent (within ≲0.05 mag) but are systematically smaller (by ∼2–3 σ ) than previous literature measurements taken from a variety of methods/anchors. However, a comparison with similar recent RR Lyrae empirical relations anchored with EDR3 likewise shows, to varying extents, a systematically smaller distance modulus for PLZ/PWZ RR Lyrae relations.

We present analysis of the RR Lyrae star, LS Her, and confirm the previously reported modulation to its Blazhko cycles. We performed Fourier analysis on two sectors (Sector 24 and 25) of data from the Transiting Exoplanet Survey Satellite (TESS) spanning 53 days. We find LS Her to have a primary pulsation period of 0.2308 day and a Blazhko period of 12.7 days in keeping with previously reported results. We also identified sideband frequencies around the Blazhko multiplets suggesting the Blazhko cycle is modulated on a timescale of 112 days. Analysis of the Blazhko effect using the TESS data clearly shows a changing amplitude and phase throughout the four Blazhko cycles. We compared our modeled results, which were based on our TESS frequency analysis, to TESS data (Sector 51) taken ∼700 days later and found our modulation model was not a good representation of the data. We then coupled our TESS analysis with the modulation frequency results from Wils et al. and found excellent agreement with the Sector 51 data. To further test this result we obtained ground-based, V -magnitude observations of LS Her in the summer of 2022. This data also showed excellent agreement with our coupled modulation model. We have verified that LS Her is a Blazhko star with a modulated Blazhko period of 109 days, stability over the 862 days of observations, and possible stability lasting over 15 yr. We discuss the ramifications of the modulation for other Blazhko stars that show Blazhko effect changes over time.

Globular clusters are both primary fossils of galactic evolution and formation and are ideal laboratories for constraining the evolution of low-mass and metal-poor stars. RR Lyrae and type II Cepheid variables are low-mass, radially pulsating stars that trace old-age stellar populations. These stellar standard candles in globular clusters are crucial for measuring their precise distances and, in turn, absolute ages, and for the calibration of the extragalactic distance scale. Herein, the evolutionary stages of RR Lyrae and type II Cepheids are discussed, and their pulsation properties, including the light curves, color–magnitude and period–amplitude diagrams, and period–luminosity relations in globular clusters at optical and infrared wavelengths are presented. The RR Lyrae visual magnitude–metallicity relation and the multiband period–luminosity–metallicity relations in globular clusters covering a wide metallicity range are also discussed in detail for their application to the RR Lyrae-based distance scale.

Based on published parameters of their atmospheres, the masses of 100 RR Lyrae variables (lyrids) in the field are determined using evolutionary tracks from the Dartmouth data base and the properties of lyrids with different metallicities are compared. It was found that the masses of the metal-rich ([Fe/H] > –0.5) lyrids with thin-disk kinematics lie within an interval of (0.51-0.60) Mʘ. According to modern concepts, the initial masses of these stars should be no more than (0.7-0.8) Mʘ. The long evolution time of these low-mass stars conflicts with the significantly lower age of even the oldest stars in the thin-disk subsystem of the Galaxy. A possible explanation is proposed for the nature of these comparatively young and metal-rich variables. [ABSTRACT FROM AUTHOR]

We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including ≈20,000 high-, medium-, and low-resolution spectra for ≈10,000 RRLs. We provide the analytical forms of radial velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental—split into three period bins—and five first-overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H _α , H _β , H _γ , H _δ ). We tackled the long-standing problem of the reference epoch to anchor light-curve and RVC templates. For the V -band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are ∼35% to ∼45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC 3201 collected with MUSE at VLT. We found the cluster barycentric RV of V _γ = 496.89 ± 8.37(error) ± 3.43 (standard deviation) km s ^−1 , which agrees well with literature estimates.

Globular clusters are both primary fossils of galactic evolution and formation and are ideal laboratories for constraining the evolution of low-mass and metal-poor stars. RR Lyrae and type II Cepheid variables are low-mass, radially pulsating stars that trace old-age stellar populations. These stellar standard candles in globular clusters are crucial for measuring their precise distances and, in turn, absolute ages, and for the calibration of the extragalactic distance scale. Herein, the evolutionary stages of RR Lyrae and type II Cepheids are discussed, and their pulsation properties, including the light curves, color–magnitude and period–amplitude diagrams, and period–luminosity relations in globular clusters at optical and infrared wavelengths are presented. The RR Lyrae visual magnitude–metallicity relation and the multiband period–luminosity–metallicity relations in globular clusters covering a wide metallicity range are also discussed in detail for their application to the RR Lyrae-based distance scale. [ABSTRACT FROM AUTHOR]