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1. RRab variables with identical light-curve shapes at different pulsation periods

   https://doi.org/10.1093/mnras/stac2745  

   Jurcsik, Johanna ; Juhász, Áron ( September 2022 , Monthly Notices of the Royal Astronomical Society)

   In this paper, we report on the detection of RRab stars with quasi-identical-shape light curves but period differences as large as 0.05–0.21 d using the Galactic bulge data of the OGLE-IV survey. We have examined stars with shorter periods than the Oosterhoff I ridge of the bulge. These stars generally have smaller amplitudes and larger Fourier phase-differences than the typical bulge RRab stars have at the same period. Many of these ‘anomalous’ stars have good-quality light curves without any sign of the Blazhko modulation. Examining their Fourier parameters revealed that several of these stars show very similar light curve to the typical bulge RR Lyrae. We found hundreds of quasi-identical-shape light-curve pairs with different periods between the ‘anomalous’- and the ‘normal’-position RRab stars based on the OGLE I-band data. The OGLE V-band, and the archive VVV and MACHO surveys Ks-, b- and r-band data of these stars were also checked for light-curve-shape similarity. Finally, 149 pairs with identical-shape light curves in each available photometric band were identified. Calculating the physical properties of the variables using empirical formulae, on average, −0.5 dex, −0.13 mag, 0.67, and 165 K differences between the [Fe/H], MV, R/R⊙, and Teff values of the members of the pairs are derived, being the short-period stars less metal-poor, fainter, smaller, and hotter than the long-period variables. To explain the existence of variables with different physical properties and pulsation periods but with identical-shape light curves is a challenging task for modelling.

    

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2. Modulation of the Blazhko Cycle in LS Her

   https://doi.org/10.3847/1538-3881/acc4ba  

   Wilhelm, Ronald ; Carrell, Kenneth ; Means, Hannah H. ; Popowicz, Adam ; Bernacki, Krzysztof ; Frąckiewicz, Mariusz ; Szczepański, Marek ; Dustor, Adam ; Lockett, Jaylon ; Taylor, Jill ; et al ( April 2023 , The Astronomical Journal)

   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.

    

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3. The Hubble Space Telescope Survey of M31 Satellite Galaxies. I. RR Lyrae–based Distances and Refined 3D Geometric Structure

   https://doi.org/10.3847/1538-4357/ac91cb  

   Savino, Alessandro ; Weisz, Daniel R. ; Skillman, Evan D. ; Dolphin, Andrew ; Kallivayalil, Nitya ; Wetzel, Andrew ; Anderson, Jay ; Besla, Gurtina ; Boylan-Kolchin, Michael ; Bullock, James S. ; et al ( October 2022 , The Astrophysical Journal)

   Abstract We measure homogeneous distances to M31 and 38 associated stellar systems (−16.8 ≤ M V ≤ −6.0), using time-series observations of RR Lyrae stars taken as part of the Hubble Space Telescope Treasury Survey of M31 Satellites. From >700 orbits of new/archival Advanced Camera for Surveys imaging, we identify >4700 RR Lyrae stars and determine their periods and mean magnitudes to a typical precision of 0.01 day and 0.04 mag. Based on period–Wesenheit–metallicity relationships consistent with the Gaia eDR3 distance scale, we uniformly measure heliocentric and M31-centric distances to a typical precision of ∼20 kpc (3%) and ∼10 kpc (8%), respectively. We revise the 3D structure of the M31 galactic ecosystem and: (i) confirm a highly anisotropic spatial distribution such that ∼80% of M31's satellites reside on the near side of M31; this feature is not easily explained by observational effects; (ii) affirm the thin (rms 7–23 kpc) planar “arc” of satellites that comprises roughly half (15) of the galaxies within 300 kpc from M31; (iii) reassess the physical proximity of notable associations such as the NGC 147/185 pair and M33/AND xxii ; and (iv) illustrate challenges in tip-of-the-red-giant branch distances for galaxies with M V > − 9.5, which can be biased by up to 35%. We emphasize the importance of RR Lyrae for accurate distances to faint galaxies that should be discovered by upcoming facilities (e.g., Rubin Observatory). We provide updated luminosities and sizes for our sample. Our distances will serve as the basis for future investigation of the star formation and orbital histories of the entire known M31 satellite system. 

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4. Zwicky Transient Facility and Globular Clusters: The RR Lyrae gri-band Period–Luminosity–Metallicity and Period–Wesenheit–Metallicity Relations

   https://doi.org/10.3847/1538-3881/ac617e  

   Ngeow, Chow-Choong ; Bhardwaj, Anupam ; Dekany, Richard ; Duev, Dmitry A. ; Graham, Matthew J. ; Groom, Steven L. ; Mahabal, Ashish A. ; Masci, Frank J. ; Medford, Michael S. ; Riddle, Reed ( April 2022 , The Astronomical Journal)

   Based on time-series observations collected from the Zwicky Transient Facility (ZTF), we derived period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations for RR Lyrae located in globular clusters. We have applied various selection criteria to exclude RR Lyrae with problematic or spurious light curves. These selection criteria utilized information on the number of data points per light curve, amplitudes, colors, and residuals on the period–luminosity and/or period–Wesenheit relations. Due to blending, a number of RR Lyrae in globular clusters were found to be anomalously bright and have small amplitudes of their ZTF light curves. We used our final sample of ∼750 RR Lyrae in 46 globular clusters covering a wide metallicity range (−2.36 dex < [Fe/H] < −0.54 dex) to derive PLZ and PWZ relations in thegribands. In addition, we have also derived the period–color–metallicity and, for the first time, the period-Q-index-metallicity relations, where theQ-index is extinction-free by construction. We have compared our various relations to empirical and theoretical relations available in the literature and found a good agreement with most studies. Finally, we applied our derived PLZ relation to a dwarf galaxy, Crater II, and found that its true distance modulus should be larger than the most recent determination.

    

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5. RR Lyrae Mid-infrared Period–Luminosity–Metallicity and Period–Wesenheit–Metallicity Relations Based on Gaia DR3 Parallaxes

   https://doi.org/10.3847/1538-4357/acb20a  

   Mullen, Joseph P. ; Marengo, Massimo ; Martínez-Vázquez, Clara E. ; Chaboyer, Brian ; Bono, Giuseppe ; Braga, Vittorio F. ; Dall’Ora, Massimo ; D’Orazi, Valentina ; Fabrizio, Michele ; Monelli, Matteo ; et al ( March 2023 , The Astrophysical Journal)

   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${\overline{\mu }}_0=19.47\pm 0.06$), the Galactic globular clusters M4 (${\overline{\mu }}_0=11.16\pm 0.05$), and the Reticulum globular cluster in the Large Magellanic Cloud (${\overline{\mu }}_0=18.23\pm 0.06$). The distance moduli determined through all our relations are internally self-consistent (within ≲0.05 mag) but are systematically smaller (by ∼2–3σ) 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.

    

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