Fig 1 - uploaded by Lukasz Wyrzykowski
Content may be subject to copyright.
— Color-magnitude diagram (based on mean values) for all 27,258 RRab variables observed in the OGLE fields (upper panel). As bulge variables are considered those inside the three green lines. Other stars are very likely foreground and background objects. The lower sequence is formed by variables from the Sgr dSph galaxy. Binning of the bulge data every 0.1 mag in the V − I color (blue points) shows that the bulge sequence is practically linear for 0 . 7 < V − I < 3 . 1 mag and complete down to I = 18 . 0 mag (lower panel).
Source publication
We have analyzed a sample of 27,258 fundamental-mode RR Lyrae variable stars
(type RRab) detected recently toward the Galactic bulge by the OGLE survey. The
data support our earlier claim that these metal-poor stars trace closely the
barred structure formed of intermediate-age red clump giants. The distance to
the Galactic center (GC) inferred from...
Contexts in source publication
Context 1
... angle of 12 ◦ . 5 ± 0 ◦ . 5. Very recently, Soszyński et al. (2014) presented a collection of 38,257 RR Lyrae variable stars detected in the OGLE fields covering over 182 deg 2 of the central regions of the Galactic bulge. In this set, 21,453 RR Lyrae stars are newly discovered objects in OGLE-IV. The collection consists of 27,258 RRab, 10,825 RRc, and 174 RRd stars. In this paper, we study the spatial structure of the old Galactic bulge based on the whole available sample of the detected RRab type stars from the OGLE survey. Variables of this type are on average brighter, have higher amplitudes, and thanks to their characteristic tooth-shaped light curves are hard to overlook in comparison to first-overtone sinusoidal-like RRc pulsators. We also use the new large sample of RRab type variables to investigate population properties of the Milky Way old bulge. In early studies, classical bulges were as- sumed to be characterized by single stellar populations whose stars formed on short time-scales (e.g. Hernquist 1990; Trager et al. 2000). However, modern spectro- scopic studies have revealed a more complex picture of star formation history via collapse, mergers, and secular processes (e.g. Moorthy & Holtzman 2006; Morelli et al. 2008; Seidel et al. 2015). RR Lyr stars as tracers of old populations may help to answer the question on the dom- inant mechanism responsible for the early formation of our Galaxy. The outline of this paper is as follows. Section 2 de- scribes the cleaning procedure of the sample. In Section 3, we analyze the observed distribution of the bulge RRab stars on the sky. The analysis of the spatial structure is included in Section 4. In Section 5, we investigate the photometric metallicity gradient. In Section 6, we present the discovery of multiple old populations among the bulge RR Lyrae stars. Finally, Section 7 states main conclusions of this work. Prior to the analysis of the bulge RR Lyrae stars the original sample from Soszyński et al. (2014) required several cleaning steps. From the whole sample of 27,258 RRab variables, we rejected 54 stars being bona fide members and very likely members of eight globular clusters (NGC 6441, NGC 6522, NGC 6540, NGC 6553, NGC 6558, NGC 6569, NGC 6642, and NGC 6656). This procedure was based on Clement et al. (2001) catalog of variable stars in Galactic globular clusters and its 2010 update 5 . From the original list, we also rejected ob- ject OGLE-BLG-RRLYR-02792 which was recently confirmed to be a low-mass binary component mimicking an RR Lyrae pulsator (Pietrzyński et al. 2012; Smolec et al. 2013). In the next step, we cleaned the bulge sample from foreground and background RR Lyrae stars by construct- ing the color-magnitude ( V − I , I ) diagram (upper panel in Fig. 1). Due to different reddening toward observed regions the bulge stars form a long sequence in the diagram. By drawing three lines we roughly delimited bulge RR Lyrae variables from background stars (line at I = 1 . 1( V − I ) + 16 . 0), foreground stars (line at I = 1 . 1( V − I ) + 13 . 0), and stars with unreliable color (vertical line at V I = 0 . 3 mag). Most of the back- ground objects are variables from the Sgr dSph galaxy. Other background variables and all foreground variables very likely belong to the Milky Way thick disk and halo. Binning of the bulge data shows that the sequence is clearly linear for 0 . 7 < V − I < 3 . 1 mag (lower panel in Fig. 1) and can be described with the following ...
Context 2
... angle of 12 ◦ . 5 ± 0 ◦ . 5. Very recently, Soszyński et al. (2014) presented a collection of 38,257 RR Lyrae variable stars detected in the OGLE fields covering over 182 deg 2 of the central regions of the Galactic bulge. In this set, 21,453 RR Lyrae stars are newly discovered objects in OGLE-IV. The collection consists of 27,258 RRab, 10,825 RRc, and 174 RRd stars. In this paper, we study the spatial structure of the old Galactic bulge based on the whole available sample of the detected RRab type stars from the OGLE survey. Variables of this type are on average brighter, have higher amplitudes, and thanks to their characteristic tooth-shaped light curves are hard to overlook in comparison to first-overtone sinusoidal-like RRc pulsators. We also use the new large sample of RRab type variables to investigate population properties of the Milky Way old bulge. In early studies, classical bulges were as- sumed to be characterized by single stellar populations whose stars formed on short time-scales (e.g. Hernquist 1990; Trager et al. 2000). However, modern spectro- scopic studies have revealed a more complex picture of star formation history via collapse, mergers, and secular processes (e.g. Moorthy & Holtzman 2006; Morelli et al. 2008; Seidel et al. 2015). RR Lyr stars as tracers of old populations may help to answer the question on the dom- inant mechanism responsible for the early formation of our Galaxy. The outline of this paper is as follows. Section 2 de- scribes the cleaning procedure of the sample. In Section 3, we analyze the observed distribution of the bulge RRab stars on the sky. The analysis of the spatial structure is included in Section 4. In Section 5, we investigate the photometric metallicity gradient. In Section 6, we present the discovery of multiple old populations among the bulge RR Lyrae stars. Finally, Section 7 states main conclusions of this work. Prior to the analysis of the bulge RR Lyrae stars the original sample from Soszyński et al. (2014) required several cleaning steps. From the whole sample of 27,258 RRab variables, we rejected 54 stars being bona fide members and very likely members of eight globular clusters (NGC 6441, NGC 6522, NGC 6540, NGC 6553, NGC 6558, NGC 6569, NGC 6642, and NGC 6656). This procedure was based on Clement et al. (2001) catalog of variable stars in Galactic globular clusters and its 2010 update 5 . From the original list, we also rejected ob- ject OGLE-BLG-RRLYR-02792 which was recently confirmed to be a low-mass binary component mimicking an RR Lyrae pulsator (Pietrzyński et al. 2012; Smolec et al. 2013). In the next step, we cleaned the bulge sample from foreground and background RR Lyrae stars by construct- ing the color-magnitude ( V − I , I ) diagram (upper panel in Fig. 1). Due to different reddening toward observed regions the bulge stars form a long sequence in the diagram. By drawing three lines we roughly delimited bulge RR Lyrae variables from background stars (line at I = 1 . 1( V − I ) + 16 . 0), foreground stars (line at I = 1 . 1( V − I ) + 13 . 0), and stars with unreliable color (vertical line at V I = 0 . 3 mag). Most of the back- ground objects are variables from the Sgr dSph galaxy. Other background variables and all foreground variables very likely belong to the Milky Way thick disk and halo. Binning of the bulge data shows that the sequence is clearly linear for 0 . 7 < V − I < 3 . 1 mag (lower panel in Fig. 1) and can be described with the following ...
Similar publications
We present in this paper the new study of variable star AM Cnc, a short
period RRab star, in orther to determine, through the light curve and the
physical parameters. The Star were observed for a total of 293 sessions
shooting, and exhibits light curve modulation, the so called Blazhko effect
with the shortest modulation Period=0d.559233 ever obser...
All available CCD observation of RV UMa have been analyzed to obtain an
accurate mathematical description of the ligh variation. We discuss in this
paper a new study of variable star RV UMa, a short period RRab star, in orther
to determine through the light curve and the physical parameters, the presence
of "Blazhko effect". The Star were observed...
![Table 2 . Parameters of the empirical fit, W = α + β · log P [mag],...](profile/Clara-Martinez-Vazquez/publication/281312243/figure/tbl1/AS:654795291492360@1533126771307/Parameters-of-the-empirical-fit-W-a-b-log-P-mag-performed-on-each-group-of_Q320.jpg)
We identified and characterized the largest (536) RR Lyrae (RRL) sample in a Milky Way dSph satellite (Sculptor) based on
optical photometry data collected over ∼24 years. The RRLs display a spread in V-magnitude (∼0.35 mag) which appears larger than photometric errors and the horizontal branch (HB) luminosity evolution of
a mono-metallic populatio...
We present a collection of 250 anomalous Cepheids (ACs) discovered in the
OGLE-IV fields toward the Large (LMC) and Small Magellanic Cloud (SMC). The LMC
sample is an extension of the OGLE-III Catalog of ACs published in 2008, while
the SMC sample contains the first known bona fide ACs in this galaxy. The total
sample is composed of 141 ACs in the...
Citations
... As lower-mass counterparts to Cepheid variables, RR Lyrae stars have a long history of use as standard candles for mapping the structure, kinematics, and formation history of the Milky Way (e.g. Vi v as et al. 2008 ;Braga et al. 2015 ;Pietrukowicz et al. 2015 ;Minniti et al. 2016 ;Dong et al. 2017 ;Mateu, Read & Kawata 2017 ). They include the subtype ab, which pulsates in the fundamental mode; subtype c, which pulsates in the first o v ertone mode; and subtype d, which pulsates in both modes. ...
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, disk, 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 Hγ and Hδ 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 datasets in the future.
... We use the optical (V, I)-band light curves of δ Scuti stars in the Galactic bulge and the Large Magellanic Cloud (LMC) from OGLE-IV (Soszyński et al. 2021) and OGLE-III (Poleski et al. 2010), respectively. The Galactic sample was cleaned from foreground and background stars following the procedure described by Pietrukowicz et al. (2015) and Deka et al. (2022a). Outliers from the phased light curves were removed using the median absolute deviation (MAD) Leys et al. (2013); Deka et al. (2022b) criterion, ...
Pulsating variable $\delta$ Scuti stars are intermediate-mass stars with masses in the range of $1-3$ $M_{\odot}$ and spectral types between $A2$ and $F2$. They can be found at the intersection of the Cepheid instability strip with the main sequence. They can be used as astrophysical laboratories to test theories of stellar evolution and pulsation. In this contribution, we investigate the observed period-colour and amplitude-colour (PCAC) relations at maximum/mean/minimum light of Galactic bulge and Large Magellanic Cloud $\delta$ Scuti stars for the first time and test the hydrogen ionization front (HIF)-photosphere interaction theory using the MESA- RSP code. The PCAC relations, as a function of pulsation phase, are crucial probes of the structure of the outer stellar envelope and provide insight into the physics of stellar pulsation and evolution. The observed behaviour of the $\delta$ Scuti PCAC relations is consistent with the theory of the interaction between the HIF and the stellar photosphere.
... One interpretation of this result is that at low , stars at a given are less susceptible to radial migration than at larger . Another possible interpretation is that at low , the age-metallicity relation does not vary much with radius, so it is conserved under radial migration; studies have shown that the observed [Fe/H](R) profile is flatter in the inner disk (e.g., Pietrukowicz et al. 2015;Kovtyukh et al. 2022). Given that the inner and outer disk stars generally represent different populations, it is unclear how this quantifies the effects of radial migration. ...
In the Milky Way, the distribution of stars in the $[\alpha/\mathrm{Fe}]$ vs. $[\mathrm{Fe/H}]$ and $[\mathrm{Fe/H}]$ vs. age planes holds essential information about the history of star formation, accretion, and dynamical evolution of the Galactic disk. We investigate these planes by applying novel statistical methods called copulas and elicitable maps to the ages and abundances of red giants in the APOGEE survey. We find that the low- and high-$\alpha$ disk stars have a clean separation in copula space and use this to provide an automated separation of the $\alpha$ sequences using a purely statistical approach. This separation reveals that the high-$\alpha$ disk ends at the same [$\alpha$/Fe] and age at high $[\mathrm{Fe/H}]$ as the low-$[\mathrm{Fe/H}]$ start of the low-$\alpha$ disk, thus supporting a sequential formation scenario for the high- and low-$\alpha$ disks. We then combine copulas with elicitable maps to precisely obtain the correlation between stellar age $\tau$ and metallicity $[\mathrm{Fe/H}]$ conditional on Galactocentric radius $R$ and height $z$ in the range $0 < R < 20$ kpc and $|z| < 2$ kpc. The resulting trends in the age-metallicity correlation with radius, height, and [$\alpha$/Fe] demonstrate a $\approx 0$ correlation wherever kinematically-cold orbits dominate, while the naively-expected negative correlation is present where kinematically-hot orbits dominate. This is consistent with the effects of spiral-driven radial migration, which must be strong enough to completely flatten the age-metallicity structure of the low-$\alpha$ disk.
... Marconi et al. 2015;Das et al. 2018;Marconi et al. 2018). RRLs are excellent tracers of the old stellar populations due to their age and have been detected in different ★ E-mail: niteshchandra039@gmail.com galactic (Vivas & Zinn 2006;Drake et al. 2013;Zinn et al. 2014;Pietrukowicz et al. 2015) and extra-galactic (Moretti et al. 2009;Soszyński et al. 2009;Fiorentino et al. 2010;Cusano et al. 2013) environments. They have also been identified in several globular clusters (Coppola et al. 2011;Di Criscienzo et al. 2011;Kuehn et al. 2013;Kunder et al. 2013). ...
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 LMC and SMC 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.
... The rich sample of RR Lyrae-type stars is commonly used to study the Galactic bulge (BLG; Pietrukowicz et al. 2015Pietrukowicz et al. , 2020Kunder et al. 2020;Savino et al. 2020;Semczuk et al. 2022a), while spiral arms and GD are studied using young starsclassical Cepheids Mróz et al. 2019;Skowron et al. 2019aSkowron et al. , 2019b. Past research showed that Mira variables, thanks to their wide range of ages, abundance throughout the Milky Way, and relatively easy detection, can be used to study the structure of the BLG, as well as the spiral arms (Feast et al. 1980;Glass & Feast 1982;Groenewegen & Blommaert 2005;Matsunaga et al. 2005Matsunaga et al. , 2009Catchpole et al. 2016;López-Corredoira 2017;Grady et al. 2020;Urago et al. 2020;Sanders et al. 2022;Semczuk et al. 2022b). ...
... Stars located inside the mask were assigned a value of 0 in the column "mask" in Table 1, while stars located outside the mask (so the ones used in further analyses) were assigned a value of 1. A similar cut was made by Pietrukowicz et al. (2015) during their analysis of the three-dimensional structure of the BLG using RR Lyrae stars. ...
... The only parameter with the informative prior defined by the normal distribution was θ, i.e., the inclination of the bar to the line of sight. As a θ prior, we used ( ) ( ) p ; 20, 3 q q = , where the mean and standard deviation values were taken from Pietrukowicz et al. (2015). Priors for all parameters that we used during model fitting are presented in Table 2. ...
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered by the Optical Gravitational Lensing Experiment survey. The spatial distribution of the Mira stars is analyzed with a model containing three barred components that include the X-shaped boxy component in the Galactic center (GC) and an axisymmetric disk. We take into account the distance uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is R 0 = 7.66 ± 0.01(stat.) ± 0.39(sys.) kpc, while the inclination of the major axis of the bulge to the Sun–GC line of sight is θ = 20.°2 ± 0.°6(stat.) ± 0.°7(sys.). We present, for the first time, a detailed three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations. Our analysis provides independent evidence for both the X-shaped bulge component and the flaring disk (being plausibly warped). We provide the complete data set of properties of Miras that were used for calculations in this work. The table includes mean brightness and amplitudes in nine photometric bands (covering a range of wavelengths from 0.5 to 12 μ m), photometric chemical type, estimated extinction, and calculated distance with its uncertainty for each Mira variable. The median distance accuracy to a Mira star is at the level of 6.6%.
... The rich sample of RR Lyrae-type stars is commonly used to study the Galactic bulge (BLG; Pietrukowicz et al. 2015Pietrukowicz et al. , 2020Kunder et al. 2020;Savino et al. 2020;Semczuk et al. 2022b), while spiral arms and GD are studied using young stars -classical Cepheids (Skowron et al. 2019a,b;Chen et al. 2019;Mróz et al. 2019). Past research showed that Mira variables, thanks to their wide range of ages, abundance throughout the Milky Way, and relatively easy detection, can be used to study the structure of the BLG, as well as the spiral arms (Feast et al. 1980;Glass & Feast 1982;Groenewegen & Blommaert 2005;Matsunaga et al. 2005Matsunaga et al. , 2009Catchpole et al. 2016;López-Corredoira 2017;Grady et al. 2020;Urago et al. 2020;Semczuk et al. 2022a;Sanders et al. 2022). ...
... Stars located inside the mask were assigned the value of 0 in the column "mask" in Table 1, while stars located outside the mask (so the ones used in further analyses) were assigned the value of 1. A similar cut was made by Pietrukowicz et al. (2015) during their analysis of the three-dimensional structure of the BLG using RR Lyrae stars. ...
... The only parameter with the informative prior defined by the normal distribution was θ, i.e, the inclination of the bar to the line of sight. As a θ prior, we used p(θ) = N (θ; 20, 3), where the mean and standard deviation values were taken from Pietrukowicz et al. (2015). Priors for all parameters that we used during model fitting are presented in Table 2. ...
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered by the Optical Gravitational Lensing Experiment (OGLE) survey. The spatial distribution of the Mira stars is analyzed with a model containing three barred components that include the X-shaped boxy component in the Galactic center (GC), and an axisymmetric disk. We take into account the distance uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is $R_0 = 7.66 \pm 0.01 \mathrm{(stat.)} \pm 0.39 \mathrm{(sys.)}$ kpc, while the inclination of the major axis of the bulge to the Sun-GC line-of-sight is $\theta = 20.2^\circ \pm 0.6^\circ \mathrm{(stat.)} \pm 0.7^\circ \mathrm{(sys.)} $. We present, for the first time, a detailed three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations. Our analysis provides independent evidence for both the X-shaped bulge component and the flaring disk (being plausibly warped). We provide the complete dataset of properties of Miras that were used for calculations in this work. The table includes: mean brightness and amplitudes in nine photometric bands (covering a range of wavelength from 0.5 to 12 $\mu$m), photometric chemical type, estimated extinction, and calculated distance with its uncertainty for each Mira variable. The median distance accuracy to a Mira star is at the level of $6.6\%$.
... Nonetheless, to extract new knowledge in the time-domain era, the physical nature of the variability must be inferred. Retrospective classification (e.g., after each observing season or after survey completion) has shown great utility for the study of variable stars (e.g., Smolec 2005;Drake et al. 2013;Pietrukowicz et al. 2015). However, the scientific impact for ongoing time-domain surveys such as the Zwicky Transient Factory (ZTF, Bellm et al. 2018), the Vera Rubin Observatory (VRO-LSST, Ivezić et al. 2019), and the Wide Field Infrared Survey Telescope (WFIRST, Spergel et al. 2015) can only be maximized if additional follow-up resources are appropriately marshaled on scientifically relevant sources. ...
The ability to generate physically plausible ensembles of variable sources is critical to the optimization of time domain survey cadences and the training of classification models on data sets with few to no labels. Traditional data augmentation techniques expand training sets by reenvisioning observed exemplars, seeking to simulate observations of specific training sources under different (exogenous) conditions. Unlike fully theory-driven models, these approaches do not typically allow principled interpolation nor extrapolation. Moreover, the principal drawback of theory-driven models lies in the prohibitive computational cost of simulating source observables from ab initio parameters. In this work, we propose a computationally tractable machine learning approach to generate realistic light curves of periodic variables capable of integrating physical parameters and variability classes as inputs. Our deep generative model, inspired by the transparent latent space generative adversarial networks, uses a variational autoencoder (VAE) architecture with temporal convolutional network layers, trained using the OGLE-III optical light curves and physical characteristics (e.g., effective temperature and absolute magnitude) from Gaia DR2. A test using the temperature–shape relationship of RR Lyrae demonstrates the efficacy of our generative “physics-enhanced latent space VAE” (PELS-VAE) model. Such deep generative models, serving as nonlinear nonparametric emulators, present a novel tool for astronomers to create synthetic time series over arbitrary cadences.
... A large number of studies using direct and indirect methods in the recent past have been carried out to determine the Galactic center (GC) distance R0. All these studies lead to a wide range of values as reported in the literature: R0 = 7.5 − 8.9 kpc (Majaess et al. 2009;Minniti et al. 2010;Saito et al. 2012;Pietrukowicz et al. 2012;Dékány et al. 2013;Pietrukowicz et al. 2015;Bhardwaj et al. 2017;Camarillo et al. 2018;Majaess et al. 2018;Reid et al. 2019;Griv et al. 2019Griv et al. , 2020Griv et al. , 2021Bobylev & Bajkova 2021). One of the most recent and direct geometrical estimates of R0 obtained by the GRAVITY team is R0[kpc] = 8.178 ± 0.013stat ± 0.022sys. ...
... However, metal-poor stars like RR Lyrae (RRL) stars show a remarkably different spatial distribution compared to the RC stars (Gonzalez & Gadotti 2016). The RRLs do not trace a prominent Galactic bar but a more spheroidal centrally concentrated distribution with a slight elongation in its center (Majaess 2010;Dékány et al. 2013;Pietrukowicz et al. 2015;Du et al. 2020;Griv et al. 2020). Similarly the old metal-poor Type II Cepheids show a similar spheroidal structure as those of RRL stars (Dékány et al. 2019;Griv et al. 2021). ...
... But there exist considerable differences involving the results of Galactic bar structure as well as the value of inclination angle with respect to the line of sight (Rattenbury et al. 2007;Dékány et al. 2013;Wegg & Gerhard 2013;Cao et al. 2013;Pietrukowicz et al. 2012Pietrukowicz et al. , 2015Simion et al. 2017;Dékány et al. 2019;Du et al. 2020;Grady et al. 2020;Griv et al. 2020Griv et al. , 2021Simion et al. 2021). The matter is still debated and a consensus has yet to be reached. ...
We present an analysis of high latitude $\delta$ Scuti stars ($\left|b\right|> 1^{\circ}$) in the Galactic bulge region ($-8^{\circ}.3< l<9^{\circ}.4$) using a clean sample of the photometric data of $7,440$ stars recently released by the OGLE-IV project. The geometrical parameters of the bulge are determined based on Maximum Likelihood (ML) analysis in five-dimensional parameter space. More refined values of these parameters as well as their uncertainties are obtained from a fully Bayesian Markov Chain Monte Carlo (MCMC) analysis. Approximating the bulge as an ellipsoid, the distribution of the number density of stars as a function of Galacto-centric distance has been modelled using three distribution functions: two Exponential ($\rm E_{1},\rm E_{2}$) types and one Gaussian ($\rm G$) type. Based on the AIC and BIC values, the exponential model $\rm E_{1}$ is chosen as the best statistical model for the parameter values obtained from the MCMC analysis. The MCMC analysis yields the following results: the mean distance to the Galactic center (GC) is found to be $R_{0}=8.034\pm0.012_{\rm stat}\pm0.586_{\rm sys}$ kpc; the bulge $\delta$ Scuti distribution has a triaxial shape with normalized ($a\equiv1$) axes ratios ($a:b:c$) as $1.000\pm 0.005:0.348\pm0.002:0.421\pm0.002$. Here $a$ is the semi-major axis lying in the Galactic plane and pointing towards us; $b$ and $c$ are the two semi-minor axes, the former lying in the Galactic plane and the later perpendicular to it. Smaller values of $b$ as compared to $a$ obtained for Galacto-centric distances $R\ge 2.0$~kpc indicate the presence of a bar-like structure of the bulge with a bar angle of $22^{\circ}.006\pm2^{\circ}.078$.
... At first, possible contaminant sources (foreground and background stars) are separated from the Galactic bulge stars and then removed using a colour-magnitude diagram (CMD). The CMD is constructed using the mean appar-ent ( , )-band magnitudes as given in the database by closely following Pietrukowicz et al. (2015). Secondly, the uncertain stars as listed in the 'remarks.txt' ...
We present an analysis on the behaviour of the Galactic bulge and the Large Magellanic Cloud (LMC) $\delta$ Scuti stars in terms of period-colour and amplitude-colour (PCAC) relations at maximum, mean and minimum light. The publicly available Optical Gravitational Lensing Experiment-IV (OGLE-IV) light curves for Galactic bulge and OGLE-III light curves for LMC $\delta$ Scuti stars are exploited for the analysis. It has been found that the Galactic bulge $\delta$ Scuti stars obey flat PC relations at maximum/mean/minimum light while the LMC $\delta$ Scutis have sloped/sloped/flat PC relations at maximum/mean/minimum light. Both the Galactic bulge and the LMC $\delta$ Scutis have sloped/flat/sloped AC relations at maximum/mean/minimum. These relations also show that Galactic $\delta$ Scutis are hotter as compared to their LMC counterparts. The period-amplitude (PA) relations for $\delta$ Scutis exhibit different behaviour in the Galactic bulge and the LMC. The LMC variables are found to have higher amplitudes at a given period. The amplitude of the Galactic bulge $\delta$ Scuti shows a bimodal distribution which can be modelled using a two-component Gaussian Mixture Model: one component with a lower amplitude and another with a higher amplitude. The observed behaviour of the $\delta$ Scuti PCAC relations can be explained using the theory of the interaction of hydrogen ionization front (HIF) and stellar photosphere as well as the PA diagram. We use MESA-RSP to calculate theoretical non-linear hydrodynamical pulsation models for $\delta$ Scuti stars with input metallicities of $Z=0.02$ and $Z=0.008$ appropriate for the Galactic bulge and LMC, respectively. The observed PCAC relations and theoretical calculations support the HIF-photosphere interaction theory.
... Finally, RR Lyrae pulsators have provided a wealth of information on the structures and formation histories of the Galactic Thick Disc, Bulge, Magellanic Clouds, dwarf spheroidals and other galaxies in the local group, e.g. Feast et al. (2008); Pietrukowicz et al. (2015); Gran et al. (2015); Monelli et al. (2018); Muraveva et al. (2018aMuraveva et al. ( , 2020; Cusano et al. (2021); Iorio & Belokurov (2021). ...
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 such RR Lyrae partly strip their progenitor's envelopes during a preceding red giant phase. As a result, stripped horizontal branch stars become bluer compared to 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 RR Lyrae from binary evolution generally can have any ages and metallicities, the Galactic population is relatively young (1 - 9 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 a long-period (P > 1000 d) A, F, G or K-type companion. Observationally characterising 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.
