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Recent works have challenged our canonical view of RR Lyrae (RRL) stars as tracers of exclusively old populations ($\gtrsim10$~Gyr) by proposing a fraction of these stars to be of intermediate ages ($\sim$2-5~Gyr). Since it is currently not possible to infer stellar ages directly for individual RRL stars, our goal in this work is to search for these in association to intermediate-age clusters whose reliable ages can then be safely be attributed to the RRL. We used the Gaia DR3 Specific Object Study and OGLE IV public catalogues to search for RRL stars around stellar clusters older than 1~Gyr in the Large and Small Magellanic Clouds. Modelling membership probabilities based on proper motion and photometric distance we obtained a list of 302 RRL stars associated with Magellanic clusters. Of these, 23 RRL are likely members of 10 intermediate-age clusters: 3 and 7 in the Small and Large Magellanic Clouds, respectively. By modelling the inferred expectation values of the number of RRL stars per cluster, we inferred the delay time distribution of the RRL in three age ranges. For the old population ($>8$~Gyr) we find $2.6^{+0.4}_{-0.3}$ RRL$/10^5 M_\odot$. For the young (1-2 Gyr) and intermediate age (2-8 Gyr) populations we find rates of $0.9^{+0.3}_{-0.2}$ and $0.27^{+0.1}_{-0.09}$ RRL$/10^5 M_\odot$, respectively. While radial velocities are necessary for definitively confirming cluster memberships, the high-probability list of intermediate-age RRL stars presented here offers a promising opportunity for the first direct confirmation of these enigmatic stars., Comment: 14 pages, 8 figures, submitted to MNRAS

RR Lyrae stars (RRLs) are easy to identify thanks to their large photometric variation and short periods. All stars in the RRL instability strip are pulsators is often a hidden assumption in most stellar population studies using RRLs. Non-variable stars in the instability strip have been discovered for Cepheids and $\delta$ Scuti, and in this paper, we report the discovery of non-variable filed stars in the RRL instability strip. Using a high-quality sample selected from Gaia DR3, we find at least 15% of the stars in the empirical instability strip where the variable fraction is > 0.7 have near-zero photometric variations or variations that are significantly smaller than typical RRLs. The non-variable stars are mostly bright and close by, on cold orbits in the Galactic plane. Metallicity from Gaia BP/RP spectra suggests the non-variable stars have an average metallicity is ~ -0.5 dex, with a peak at 0. The discovery of these non-variable stars in the RRL instability strip challenges our understanding of stellar physics and further investigation is needed to understand the origin of these stars., Comment: submitted

The outskirts of the Milky Way disc have been known to be warped since the late 1950s. Although various stellar populations have shown an underlying warped distribution, the relation between the age of the population and the warp they trace remains an open question. Our goal in this work is to detect the presence of the warp in the RR Lyrae (RRL) population of the Galactic disc. We use a compilation of public catalogues of RRL stars, precise photometric distances ($\sim 5\%$) and Gaia DR3 proper motions to kinematically select a sample of thin disc RRL in the Galactic anticentre, where the tangential velocity best approximates the azimuthal velocity to differentiate between disc and halo. For disc-like RRL we analyse their mean vertical height and mean vertical velocity. We show, for the first time, that RRL stars with thin disc-like kinematics trace the warp. In the anticentre direction, the RRL population reaches a minimum in mean vertical height of $\approx 0.4$ kpc, with a trend systematically lower than the one found with Classical Cepheids. The kinematical signal of the RRL warp starts at $R\approx 10$ kpc and, rather than resembling the Cepheid's, shows a similar trend to the Red Clump population from previous works, reaching a maximum value of $\approx 7$ km/s in vertical velocity. We also obtain an estimation of the pattern speed of the RRL warp with a prograde rotation of $\approx 13 \pm 2 $ km/s/kpc, compatible with results obtained from Cepheids. Finally, we obtain a vertical velocity dispersion $\approx 17 $km/s, inconsistent with the kinematics of a canonical old age ($> 10$ Gyr) disc population and, instead, favouring a population dominated by intermediate-age ($3-4$ Gyr). Our results indicate that the thin disc RRL stars are a dynamical intermediate-age tracer of the warp, opening a new window to study the dependency of the warp with stellar age., Comment: 6 pages, 5 figures. 2 pages with 2 figures in the appendices. Submitted to A&A

The warp is a well-known undulation of the Milky Way disc. Its structure has been widely studied, but only since Gaia DR2 has it been possible to reveal its kinematic signature beyond the solar neighbourhood. In this work we present an analysis of the warp traced by Classical Cepheids by means of a Fourier decomposition of their height ($Z$) and, for the first time, of their vertical velocity ($V_z$). We find a clear but complex signal that in both variables reveals an asymmetrical warp. In $Z$ we find the warp to be almost symmetric in amplitude at the disc's outskirts, with the two extremes never being diametrically opposed at any radius and the line of nodes presenting a twist in the direction of stellar rotation for $R>11$ kpc. For $V_z$, in addition to the usual $m=1$ mode, an $m=2$ mode is needed to represent the kinematic signal of the warp, reflecting its azimuthal asymmetry. The line of maximum vertical velocity is similarly twisted as the line of nodes and trails behind by $\approx 25^\circ$. We develop a new formalism to derive the pattern speed and change in amplitude with time $\dot{A}$ of each Fourier mode at each radius, via a joint analysis of the Fourier decomposition in $Z$ and $V_z$. By applying it to the Cepheids we find, for the $m=1$ mode, a constant pattern speed in the direction of stellar rotation of $9.2\pm3.1$ km/s/kpc, a negligible $\dot{A}$ up to $R\approx 14$ kpc and a slight increase at larger radii, in agreement with previous works., Comment: Accepted for publication in MNRAS. 15 pages, 10 figures, 4 tables (+ Appendices). Full version of tables 1 and 2 included

Nearly a hundred stellar streams have been found to date around the Milky Way and the number keeps growing at an ever faster pace. Here we present the galstreams library, a compendium of angular position, distance, proper motion and radial velocity track data for nearly a hundred (95) Galactic stellar streams. The information published in the literature has been collated and homogenised in a consistent format and used to provide a set of features uniformly computed throughout the library: e.g. stream length, end points, mean pole, stream's coordinate frame, polygon footprint, and pole and angular momentum tracks. We also use the information compiled to analyse the distribution of several observables across the library and to assess where the main deficiencies are found in the characterisation of individual stellar streams, as a resource for future follow-up efforts. The library is intended to facilitate keeping track of new discoveries and to encourage the use of automated methods to characterise and study the ensemble of known stellar streams by serving as a starting point. The library is publicly available as a Python package and served at the galstreams GitHub repository., Comment: Accepted for publication at MNRAS. 29 pages, 19 figures, 2 tables, updated to match final version (new figures added! conclusions unchanged). The library of stellar stream tracks is publicly available at https://github.com/cmateu/galstreams