Stellar Pulsation Research Articles

Asteroseismology of Triple-mode Radial δ Scuti Star: TIC 400562821

Abstract We investigated the pulsating behavior of TIC 400562821 using high-precision observations from TESS. Fourier analysis of time-series data revealed three independent frequencies. The period ratios of F to F1 (0.774) and F to F2 (0.625), along with an amplitude change of approximately 0.1 mag, indicate that TIC 400562821 is a triple-mode High-Amplitude δ Scuti (HADS) star. Using the Best Parent Method and the Γ O functions, we identified that the harmonics and sum combination frequencies of F and F1 are caused by the nonlinear response of the stellar medium to pulsation. We also analyzed the amplitude variations of F, F1, and F2. Observational data over 76 days show stable amplitudes for these modes. However, Radial Stellar Pulsations modeling suggests that, over 10,000 cycles, the amplitude of F remains constant, while F1 gradually decreases and F2 approaches zero. This implies that TIC 400562821 may eventually evolve into a single-mode HADS star. Furthermore, asteroseismic modeling was performed, and several effects, such as the mixing-length parameter α MLT and nonadiabatic, were examined on this star. In view of the results by Daszyńska-Daszkiewicz et al. (i.e., α MLT < ∼1 for δ Scuti stars), TIC 400562821 is suggested to be more likely in the post-main-sequence stage, with mass M = 1.34–1.38 M ⊙ and metallicity Z = 0.007–0.008, but still warrants further study to ascertain its nature.

TIC 435850195: The Second Triaxial Tidally Tilted Pulsator

The Transiting Exoplanet Survey Satellite (TESS) has enabled the discovery of numerous tidally tilted pulsators (TTPs), which are pulsating stars in close binaries where the presence of a tidal bulge has the effect of tilting the primary star’s pulsation axes into the orbital plane. Recently, the modeling framework developed to analyze TTPs has been applied to the emerging class of triaxial pulsators, which exhibit nonradial pulsations about three perpendicular axes. In this work, we report on the identification of the second-ever discovered triaxial pulsator, with 16 robustly detected pulsation multiplets, of which 14 are dipole doublets separated by 2ν orb. We jointly fit the spectral energy distribution and TESS light curve of the star, and find that the primary is slightly evolved off the zero-age main sequence, while the less massive secondary still lies on the zero-age main sequence. Of the 14 doublets, we associate eight with Y 10x modes and six with novel Y 10y modes. We exclude the existence of Y 11x modes in this star and show that the observed pulsation modes must be Y 10y . We also present a toy model for the triaxial pulsation framework in the context of this star. The techniques presented here can be utilized to rapidly analyze and confirm future triaxial pulsator candidates.

Finding The Relationship between Pulsation Motion and Hα Emission Lines on γ Cas using Photometric and Spectroscopic Data

Abstract Pulsating stars show variability in brightness due to changes in their volume. There are two types of pulsation/oscillation: radial and non-radial. Radial oscillation keeps the symmetrical shape of the star, while non-radial oscillation does not. We study a pulsating star: γ Cas, classified as a B0.5 IVe variable star because of its pulsations and also an emission star due to the emission lines in its spectra. When a star pulsates, its atmosphere expands and contracts, potentially leading to the formation of shock waves. Observational features such as discontinuities in the radial velocity curve and emission lines support this phenomenon. In this study, we analyse the relationship between pulsation motion and the H α emission lines of γ Cas using photometric and spectroscopic data. Photometric data is obtained from the BRIght Target Explorer (BRITE) catalog, while spectroscopic data comes from the Be Star Spectra (BeSS) catalog. Both datasets cover the same observational dates: August 28 to October 26, 2015. Confirming the pulsation period of γ Cas at 1.21 days, we also discover an added pulsation period of 10 days from photometric data. To confirm this, we examine spectroscopic data from three specific dates: August 28, September 7, and 27, 2015. Notably, the relative flux of the H α emission lines continue to increase, leading us to conclude that these lines are indeed caused by the pulsation of γ Cas.

Variable Stars in M31 Stellar Clusters from the Panchromatic Hubble Andromeda Treasury

Variable stars in stellar clusters can offer key constraints on stellar evolution and pulsation models, utilizing estimates of host cluster properties to constrain stellar physical parameters. We present a catalog of 86 luminous (F814W < 19) variable stars in M31 clusters identified by mining the archival Panchromatic Hubble Andromeda Treasury (PHAT) survey using a combination of statistical analysis of sparse PHAT light curves and difference imaging. We determine the evolutionary phases and initial masses of these variable stars by matching them with theoretical isochrones generated using host cluster properties from the literature. We calculate the probability of PHAT photometry being blended due to the highly crowded nature of cluster environments for each cluster-variable star, using these probabilities to inform our level of confidence in the derived properties of each star. Our 86 cluster-variable stars have initial masses between 0.8 and 67 M ⊙. Their evolutionary phases span the main sequence, more evolved hydrogen- and helium-burning phases, and the post–asymptotic giant branch. We identify numerous candidate variable star types: RV Tauri variables, red supergiants, and slowly pulsating B-type supergiants, along with Wolf–Rayet stars, α Cygni and Mira variables, a classical Cepheid, and a possible superasymptotic giant. We characterize 12 cluster-variable stars at higher confidence based on their difference image quality and lower blending probability. Ours is the first systematic study of variable stars in extragalactic stellar clusters leveraging the superior resolution of the Hubble Space Telescope and demonstrating the unique power of stellar clusters in constraining the fundamental properties of variable stars.

Variability and stellar pulsation incidence in Am and Fm stars using TESS and Gaia data

Aims. We aim to study chemically peculiar Am and Fm stars, distinguished by their unique abundance patterns, which are crucial for studying mixing processes in intermediate-mass stars. These stars provide a window into the atomic diffusion in their stellar envelopes, the evolution-dependent changes in mixing, and the resulting effects on pulsation mechanisms. Methods. This study examines the pulsation characteristics of the Am and Fm star group. Our analysis encompasses 1276 stars (available as catalogues on GitHub), utilising data from TESS and Gaia and focussing on stars from the Renson catalogue. Results. In our sample, 51% of stars (649) display no variability, and are thus categorised as constant stars. Among those that remain, 25% (318 stars) are pulsating Am, Fm, and ρ Puppis stars, including 20% (261 stars) that are exclusively Am and Fm stars. Additionally, 17% of stars (210) show variability indicative of binarity and/or rotational modulation and 7% (93 stars) are eclipsing binaries. Of the pulsating stars, 10% (32 stars) are γ Doradus type, 54% (172 stars) δ Scuti type, and 36% (114 stars) are hybrids, underlining a diverse pulsational behaviour of Am and Fm stars. Conclusions. Our findings indicate that pulsating stars predominantly occupy positions near the red edge of the classical instability strip, allowing us to ascertain the incidence of pulsations in this stellar population.

The coevolution of migrating planets and their pulsating stars through episodic resonance locking

The coevolution of migrating planets and their pulsating stars through episodic resonance locking

The compact circumstellar material of SN 2024ggi: another supernova with a pre-explosion effervescent zone and jet-driven explosion

I examine recent theoretical studies and observations of the recent core-collapse supernova (CCSN) SN~20224ggi and find that the likely explanation for its dense, compact circumstellar material is an effervescent model, where parcels or streams of gas are uplifted by stellar convection and pulsation and fall back. The effervescent zone exists alongside the regular wind from the red supergiant (RSG) progenitor of SN~2024ggi. I find that an extended wind-acceleration zone encounters some difficulties in accounting for the required CSM mass. Recent modelling finds the explosion energy of SN~2024ggi to be erg, and up to erg. I examine this explosion energy against a recent study of the delayed neutrino explosion mechanism and find that this mechanism might have some difficulties in accounting for the required energy. This might suggest that the explosion was caused by the jittering jets explosion mechanism (JJEM). This adds to other recent pieces of evidence supporting the JJEM, particularly point-symmetric CCSN remnants.

An Application of Asymptotic Analysis in Linear Stellar Pulsation: a Case of Non-distinct Characteristic Roots

An Application of Asymptotic Analysis in Linear Stellar Pulsation: a Case of Non-distinct Characteristic Roots

The phase curve of the ultra-hot Jupiter WASP-167b as seen by TESS

Context. Ultra-hot Jupiters (UHJs) orbiting pulsating A/F stars represent an important subset of the exoplanetary demographic. They are excellent candidates for the study of exoplanetary atmospheres, and are astrophysical laboratories for the investigation of planet-to- star interactions. Aims. We analysed the TESS light curve of the WASP-167 system, consisting of an F1V star and a substellar companion on a ~2.02 day orbit. Methods. We modelled the combination of the ellipsoidal variability and the Doppler beaming to measure the mass of WASP-167b, and the reflection effect to obtain constraints on the geometric albedo, while placing a special emphasis on noise separation. We implemented a basic model to determine the dayside (TDay), nightside (TNight), and intrinsic (TInternal) temperatures of WASP-167b, and put a constraint on its Bond albedo. Results. We confirm the transit parameters of the planet seen in the literature. We find that a resonant ~2P−1 stellar signal (which may originate from planet-to-star interactions) interferes with the phase curve analysis. After careful and thought-out treatment of this signal, we find Mp = 0.34 ± 0.22 MJ. We measure a dayside temperature of 2790 ± 100 K, classifying WASP-167b as an UHJ. We find a 2σ upper limit of 0.51 on its Bond albedo, and determine the geometric albedo at 0.34 ± 0.11 (1σ uncertainty). Conclusions. With an occultation depth of 106.8 ± 27.3 ppm in the TESS passband, the UHJ WASP-167b is an excellent target for atmospheric studies, especially those at thermal wavelength ranges, where the stellar pulsations are expected to be less influential.

Buoyancy glitches in pulsating stars revisited

Sharp structural variations induce specific signatures on stellar pulsations that can be studied to infer localised information on the stratification of the star. This information is key to improve our understanding of the physical processes that lead to the structural variations and how to model them. Here we revisit and extend the analysis of the signature of different types of buoyancy glitches in gravity-mode and mixed-mode pulsators presented in earlier works, including glitches with step-like, Gaussian-like, and Dirac-δ-like shapes. In particular, we provide analytical expressions for the perturbations to the periods and show that these can be reliably used in place of the expressions provided for the period spacings, with the advantage that the use of the new expressions does not require modes with consecutive radial orders to be observed. Based on a comparison with two limit cases and on simulated data, we further tested the accuracy of the expression for the Gaussian-like glitch signature whose derivation in an earlier work involved a significant approximation. We find that the least reliable glitch parameter inferred from fitting that expression is the amplitude, which can be up to a factor of two larger than the true amplitude, reaching this limit when the glitch is small. We further discuss the impact on the glitch signature of considering a glitch in the inner and outer half of the g-mode cavity, emphasising the break of symmetry that takes place in the case of mixed-mode pulsators.

Exploring the unexpected: Disharmonized harmonic pulsation modes in high-amplitude δ Scuti stars

Harmonics are a ubiquitous feature across various pulsating stars. They are traditionally viewed as mere replicas of the independent primary pulsation modes and have thus been excluded from asteroseismological models. Recent research, however, has uncovered a significant discrepancy: in high-amplitude δ Scuti (HADS) stars, harmonics exhibit uncorrelated variations in amplitude and frequency relative to their independent primary pulsation modes. The nature of these disharmonized harmonics is a question of critical importance. In our study we analysed five triple-mode HADS stars observed by the Transiting Exoplanet Survey Satellite (TESS) and discovered some pervasive patterns of disharmonized harmonics in both the fundamental (f0) and first overtone (f1) pulsation modes. Intriguingly, through an in-depth frequency interaction analysis of V1393 Cen, we identified 2f1 as an independent pulsation mode, distinct from f1, and identified it as the progenitor of the frequency variations observed in 3f1, 4f1, 5f1, and 6f1. Similar behaviour can be found in DO CMi and GSC 06047-00749, in which 2f1 and 3f1 are the independent pulsation modes, respectively. Notably, we found an interesting pattern when decomposing the harmonics that might suggest a generation process of harmonics. These findings serve as a new window on the research of harmonics, which remains a hidden corner of contemporary asteroseismology.

The GAPS Programme at TNG

Context. HAT-P-67 b is one of the lowest-density gas giants known to date, making it an excellent target for atmospheric characterisation through the transmission spectroscopy technique. Aims. In the framework of the GAPS large programme, we collected four transit events of HAT-P-67 b with the aim of studying the exoplanet atmosphere and deriving the orbital projected obliquity. Methods. We exploited the high-precision GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio Nazionale Galileo (TNG) along with additional archival TESS photometry to explore the activity level of the host star. We performed transmission spec-troscopy, both in the visible (VIS) and in the near-infrared (NIR) wavelength range, and we analysed the Rossiter–McLaughlin (RML) effect when fitting both the radial velocities and the Doppler shadow. Based on the TESS photometry, we redetermined the transit parameters of HAT-P-67 b. Results. By modelling the RML effect, we derived a sky-projected obliquity of (2.2 ± 0.4)°, indicating an aligned planetary orbit. The chromospheric activity index log R′HK, the CCF profile, and the variability in the transmission spectrum of the Hα line suggest that the host star shows signatures of stellar activity and/or pulsation. We found no evidence of atomic or molecular species in the optical transmission spectra, with the exception of pseudo-signals corresponding to Cr I, Fe I, Ha, Na I, and Ti I. In the NIR range, we found an absorption signal of the He I triplet of 5.56−0.30+0.29% (19.0σ), corresponding to an effective planetary radius of ~3 Rp (where Rp ~ 2 RJ), which extends beyond the planet’s Roche lobe radius. Conclusions. Owing to the stellar variability and the high uncertainty of the model, we could not confirm the planetary origin of the signals found in the optical transmission spectrum. On the other hand, we were able to confirm previous detections of the infrared He I triplet, providing a 19.0σ detection. Our finding indicates that the planet’s atmosphere is evaporating.

The β Pictoris b Hill sphere transit campaign

The β Pictoris system is the closest known stellar system with directly detected gas giant planets, an edge-on circumstellar disc, and evidence of falling sublimating bodies and transiting exocomets. The inner planet, β Pictoris c, has also been indirectly detected with radial velocity (RV) measurements. The star is a known δ Scuti pulsator, and the long-term stability of these pulsations opens up the possibility of indirectly detecting the gas giant planets through time delays of the pulsations due to a varying light travel time. We search for phase shifts in the δ Scuti pulsations consistent with the known planets β Pictoris b and c and carry out an analysis of the stellar pulsations of β Pictoris over a multi-year timescale. We used photometric data collected by the BRITE-Constellation, bRing, ASTEP, and TESS to derive a list of the strongest and most significant δ Scuti pulsations. We carried out an analysis with the open-source python package maelstrom to study the stability of the pulsation modes of β Pictoris in order to determine the long-term trends in the observed pulsations. We did not detect the expected signal for β Pictoris b or β Pictoris c. The expected time delay is 6 s for β Pictoris c and 24 s for β Pictoris b. With simulations, we determined that the photometric noise in all the combined data sets cannot reach the sensitivity needed to detect the expected timing drifts. An analysis of the pulsational modes of β Pictoris using maelstrom showed that the modes themselves drift on the timescale of a year, fundamentally limiting our ability to detect exoplanets around β Pictoris via pulsation timing.

HR 10 as seen by CHEOPS and TESS. Revealing delta Scuti pulsations, granulation-like signal and hint for transients

HR 10 has only recently been identified as a binary system. Previously thought to be an A-type shell star, it appears that both components are fast-rotating A-type stars, each presenting a circumstellar envelope. Although showing complex photometric variability, spectroscopic observations of the metallic absorption lines reveal variation explained by the binarity, but not indicative of debris-disc inhomogeneities or sublimating exocomets. On the other hand, the properties of the two stars make them potential delta Scuti pulsators. The system has been observed in two sectors by the TESS satellite, and was the target of three observing visits by CHEOPS. Thanks to these new data, we aim to further characterise the stellar properties of the two components. In particular, we aim to decipher the extent to to which the photometric variability can be attributed to a stellar origin. In complement, we searched in the lightcurves for transient-type events that could reveal debris discs or exocomets. We analysed the photometric variability of both the TESS and CHEOPS datasets in detail. We first performed a frequency analysis to identify and list all the periodic signals that may be related to stellar oscillations or surface variability. The signals identified as resulting from the stellar variability were then removed from the lightcurves inorder to search for transient events in the residuals. We report the detection of delta Scuti pulsations in both the TESS and CHEOPS data, but we cannot definitively identify which of the components is the pulsating star. In both datasets, we find flicker noise with the characteristics of a stellar granulation signal. However, it remains difficult to firmly attribute it to actual stellar granulation from convection, given the very thin surface convective zones predicted for both stars. Finally, we report probable detection of transient events in the CHEOPS data, without clear evidence of their origin.

SiO maser polarization and magnetic field in evolved cool stars

Magnetic fields, photospheric and atmospheric dynamics can be involved in triggering the high mass loss observed in evolved cool stars. Previous works have revealed that the magnetic field of these objects extends beyond their surface. The origin of this magnetic field is still debated. The possible mechanisms include a turbulent dynamo, convection, stellar pulsation, and cool spots. Our goal is to estimate the magnetic field strength in the inner circumstellar envelope of six evolved cool stars (five Miras and one red supergiant). Combining this work with previous studies, we tentatively constrain the global magnetic field type and shed light on the mechanisms that cause it. Using the XPOL polarimeter installed at the IRAM-30 m telescope, we observed the $^ SiO $ v = 1, J = 2-1 maser line emission and obtained simultaneous spectroscopic measurements of the four Stokes parameters. Applying a careful calibration method for Stokes $Q$, $U$, and $V$, we derived estimates of the magnetic field strength from the circular and linear polarization fractions considering the saturated and unsaturated maser cases under the Zeeman hypothesis. Magnetic field strengths from several Gauss up to several dozen Gauss are derived. These new and more accurate measurements constrain the field strength in the region of 2-5 stellar radii better than previous studies and appear to exclude a global poloidal magnetic field type. The combination of a toroidal and poloidal field is not excluded, however. A variation in the magnetic field strength over a two-month timescale is observed in one Mira star, which suggests a possible link to the stellar phase, that is, a link with pulsation and photospheric activity.

Analysis of the Impact of the Blazhko Effect Both on the Van Hoof Effect and Radial Velocity Amplitude in the Star RR Lyr

The Van Hoof effect is a phase shift existing between the radial velocity curves of hydrogen and metallic lines within the atmosphere of pulsating stars. In this article, we present a study of this phenomenon through the spectra of the brightest pulsating star RR Lyr of RR Lyrae stars recorded for 22 yr. We based ourselves, on the one hand, on 1268 spectra (41 nights of observation) recorded between the years 1994 and 1997 at the Observatory of Haute Provence (OHP, France) previously observed by Chadid and Gillet, and on the other hand on 1569 spectra (46 nights of observation) recorded at our Oukaimeden Observatory (Morocco) between 2015 and 2016. Through this study, we have detected information on atmospheric dynamics that had not previously been detected. Indeed, the Van Hoof effect which results in a clear correlation between the radial velocities of hydrogen and those of the metallic lines has been observed and analyzed at different Blazhko phases. A correlation between the radial velocities of different metallic lines located in the lower atmosphere has been observed as well. For the first time, we were able to show that the amplitude of the radial velocity curves deduced from the lines of hydrogen and that of Fe ii (λ4923.921 Å) increases toward the minimum of the Blazhko cycle and decreases toward the maximum of the same Blazhko cycle. Furthermore, we found that the Van Hoof effect is also modulated by the Blazhko effect. Thus, toward the minimum of the Blazhko cycle the Van Hoof effect is more visible and at the maximum of the Blazhko cycle, this effect is minimal. We also observed the temporal evolution of the amplitudes of the radial velocities of the lower and upper atmosphere. When observed over a long time, we can interpret it as a function of the Blazhko phases.

Water vapour masers in long-period variable stars

Context. Water maser emission is often found in the circumstellar envelopes of evolved stars, that is, asymptotic giant branch stars and red supergiants with oxygen-rich chemistry. The H2O emission shows strong variability in evolved stars of both of these types. Aims. We wish to understand the reasons for the strong variability of water masers emitted at 22 GHz. In this paper, we study U Her and RR Aql as representatives of Mira variable stars. Methods. We monitored U Her and RR Aql in the 22 GHz maser line of water vapour with single-dish telescopes. The monitoring period covered about two decades between 1990 and 2011, with a gap between 1997 and 2000 in the case of RR Aql. Observations were also made in 1987 and 2015 before and after the period of contiguous monitoring. In addition, maps of U Her were obtained in the period 1990–1992 with the Very Large Array. Results. We find that the strongest emission in U Her is located in a shell with boundaries of 11–25 AU. The gas-crossing time is 8.5 yr. We derive lifetimes for individual maser clouds of ≤4 yr based on the absence of detectable line-of-sight velocity drifts of the maser emission. The shell is not evenly filled, and its structure is maintained over much longer timescales than those of individual maser clouds. Both stars show brightness variability on several timescales. The prevalent variation is periodic, following the optical variability of the stars with a lag of 2–3 months. Superposed are irregular fluctuations of a few months in duration, with increased or decreased excitation at particular locations, and long-term systematic variations on timescales of a decade or more. Conclusions. The properties of the maser emission are governed by those of the stellar wind while traversing the H2O maser shell. Inhomogeneities in the wind affecting the excitation conditions and prevalent beaming directions likely cause the variations seen on timescales of longer than the stellar pulsation period. We propose the existence of long-living regions in the shells, which maintain favourable excitation conditions on timescales of the wind-crossing times through the shells or orbital periods of (sub)stellar companions. The H2O maser properties in these two Mira variables are remarkably similar to those in the semiregular variables studied in our previous papers regarding shell location, outflow velocity, and lifetime. The only difference is the regular brightness variations of the Mira variables caused by the periodic pulsation of the stars.

Stellar Atmospheric Parameters of ∼11,000 RR Lyrae Stars from LAMOST Spectra

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 logg , 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, logg , 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 Hα line (RVHα ) and from metal lines (RVmetal) 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 logg 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.

β Cephei Pulsators in Eclipsing Binaries Observed with TESS

The combined strength of asteroseismology and empirical stellar basic parameter determinations for in-depth asteroseismic analysis of massive pulsators in eclipsing binaries shows great potential for treating the challenging and mysterious discrepancies between observations and models of stellar structure and the evolution of massive stars. This paper compiles a comprehensive list of massive pulsators in eclipsing binary systems observed with TESS. The TESS light curves and discrete Fourier transforms of a sample of 8055 stars of spectral type B0–B3 were examined for eclipses and stellar pulsations, and the ephemerides of the resulting subsample of massive pulsators in eclipsing binaries were computed. This subsample was also crossmatched with existing catalogs of massive pulsators. Until now, fewer than 30 β Cephei pulsators in eclipsing binaries have been reported in the literature. Here we announce a total of 78 pulsators of the β Cephei type in eclipsing binaries, 59 of which are new discoveries. Forty-three are recognized as definite, and 35 are candidate pulsators. Our sample of pulsating massive stars in eclipsing binaries allows for future asteroseismic modeling to better understand the internal mixing profile and to resolve the mass discrepancy in massive stars. We have already started follow-up work on some of the most interesting candidates.

The Galactic bulge exploration

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.