arXiv subjects

Shashi M. Kanbur

Publications and source records attributed to Shashi M. Kanbur.

At least 19 recordsLinked to original sources

arXiv2025

The light curve model fitting of LMC Cepheids: MESA-RSP versus Stellingwerf's code predictions

A major challenge in modeling classical Cepheids is the treatment of convection, particularly its complex interplay with pulsation. This inherently three-dimensional process is typically approximated in one-dimensional hydrocodes using dimensionless turbulent convection (TC) free parameters. Calibrating these parameters is essential for reproducing key observational features such as light-curve amplitudes, secondary bumps, and the red edge of the instability strip. In this work, we calibrate TC parameters adopted in the publicly available MESA-RSP code through comparison with both observational data of classical Cepheids and stellar parameter constraints from the Stellingwerf code. We compute multi-band (V, I, and Ks) MESA-RSP light curves for 18 observed Large Magellanic Cloud Cepheids, using stellar parameters determined from the Stellingwerf code. By fine-tuning the mixing-length and eddy viscosity parameters, we calibrate the TC treatment in MESA-RSP. We then compare the resulting period-luminosity (PL), period-radius (PR), and period-mass-radius (PMR) relations with predictions from the Stellingwerf models. We successfully reproduce multi-band light curves and obtain PL, PR, and PMR relations consistent with Ragosta et al. (2019). While in broad agreement with previous work, we explicitly identify distinct mass-luminosity (ML) relations for fundamental-mode and first-overtone Cepheids for the first time. This suggests that the macroscopic processes affecting the ML relation depend on stellar mass and/or effective temperature range. Although our study focuses on the calibration of TC parameters, we do not find a single set of parameter values that reproduces all light curves. No statistically significant correlation is found between stellar properties and convection parameters, although subtle trends with period and effective temperature may be present.

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arXiv2025

Multiwavelength study of observed and predicted pulsation properties of First overtone Cepheids in the Magellanic Clouds

We present a detailed analysis of the light curves and pulsation properties of First Overtone (FO) Cepheids in the Magellanic Clouds (MCs) obtained using observations and predictions from stellar pulsation models. Multiwavelength observational light curves were compiled from the literature (OGLE-IV, Gaia and VMC). We investigate the period-amplitude (PA), period-colour (PC), period-luminosity (PL), and amplitude-colour (AC) relations for FO Cepheids at multiwavelengths. We find that the PA distribution of FO Cepheids in the MCs modelled using a Gaussian Mixture Model shows that the SMC consists of higher amplitude stars than the LMC. We find multiple break-points in the PC/PL/AC relations for FO/FU Cepheids in the optical and near-infrared bands including the one near to P = 2.5 d in the MCs using piecewise regression analysis and F- test statistics. Similarly, for the LMC FO Cepheids, we find a break-point in the PC/PL/AC relations near P = 0.58 d. The slopes of the PC relations for LMC FO Cepheids are found to be shallow for 0.58 < P(d) < 2.5 but steeper for P < 0.58 d and P > 2.5 d. We complemented the observed relations using theoretical models for FO Cepheids with chemical compositions Z = 0.008 and Z = 0.004, appropriate for the LMC and SMC, respectively computed with MESA-RSP. Our results show that the pulsation properties of FO Cepheids in PC/PL/AC relations and colour-magnitude diagram are strongly correlated and their connections can provide stringent constraints for the theoretical pulsation models.

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arXiv2025

A theoretical framework for BL Her stars IV. New period-luminosity relations in the Rubin-LSST filters

We present new theoretical light curves in the Rubin-LSST filters for a fine grid of BL Her models computed using MESA-RSP. We also derive new theoretical period-luminosity (PL) and period-Wesenheit (PW) relations in the Rubin-LSST filters with the goal to study the effect of convection parameters and metallicity on these relations. The grid of BL Her models was computed with the input stellar parameters: metallicity ($-2.0\; \mathrm{dex} \leq \mathrm{[Fe/H]} \leq 0.0\; \mathrm{dex}$), stellar mass ($0.5M_{\odot}-0.8M_{\odot}$), stellar luminosity ($50L_{\odot}-300L_{\odot}$), and effective temperature (across the full extent of the instability strip; in steps of 50K) and using four sets of convection parameters. Bolometric correction tables from MIST were used to transform the theoretical bolometric light curves of the BL Her models into the Rubin-LSST ugrizy filters. The PL relations of the BL Her models exhibit steeper slopes but smaller dispersion with increasing wavelengths in the Rubin-LSST filters. The PL and PW slopes for the complete set of BL Her models computed with radiative cooling (sets B and D) are statistically similar across the grizy filters. The BL Her models exhibit weak or negligible effect of metallicity on the PL relations for wavelengths longer than the g filter for both the cases of the complete set of models as well as the low-mass models. However, we find significant effect of metallicity on the PL relation in the u filter. Strong metallicity effects are observed in the PWZ relations involving the u filter and are found to have significant contribution from the high-metallicity BL Her models. Due to negligible metallicity effect for relations involving the Wesenheit indices $W(i,g-i)$, $W(z,i-z)$ and $W(y,g-y)$, we recommend these filter combinations for BL Her stars when observed with the Rubin-LSST to be used as reliable standard candles.

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arXiv2024

A theoretical framework for BL Her stars III. A case study: Robust light curve optimisation in the LMC

We carry out an extensive light curve comparison of BL Her stars using observations from Gaia DR3 and stellar pulsation models computed using MESA-RSP with the goal to obtain the best-matched modeled-observed pairs for BL Her stars in the LMC. We use the Fourier decomposition technique to analyse the light curves in the G band obtained from Gaia DR3 and from MESA-RSP and use a robust light curve fitting approach to score the modeled-observed pairs with respect to their pulsation periods and over their Fourier parameter space. We obtain the best-fit models for 48 BL Her stars in the LMC and thereby provide the stellar parameter estimates of these stars, 30 of which are labelled as the gold sample with superior light curve fits. We find a relatively flat distribution of stellar masses between 0.5-0.65 Msolar for the gold sample of modeled-observed pairs. An interesting result is that the majority of the best-matched models in the gold sample are computed using the convection parameter sets without radiative cooling. The period-Wesenheit relation for the best-matched gold sample of 30 BL Her models exhibits a slope of $-2.805 \pm 0.164$ while the corresponding period-radius relation exhibits a slope of $0.565 \pm 0.035$, both in good agreement with the empirical PW and PR slopes from BL Her stars in the LMC, respectively. We also used the Wesenheit magnitudes of the 30 best-matched modeled-observed pairs to estimate a distance modulus of $μ_{\rm LMC} = 18.582 \pm 0.067$ to the LMC, which lies within the bounds of previous literature values. We also discuss the degeneracy in the stellar parameters of the BL Her models that result in similar pulsation periods and light curve structure, and highlight that caution must be exercised while using the stellar parameter estimates.

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arXiv2024

Bridging theory and observations in stellar pulsations: The impact of convection and metallicity on the instability strips of Classical and Type-II Cepheids

The effect of metallicity on the theoretical and empirical period-luminosity (PL) relations of Cepheid variables is not well understood and remains a highly debated issue. Here, we examine empirical colour-magnitude diagrams (CMDs) of Classical and Type-II Cepheids in the Magellanic Clouds and compare those with the theoretically predicted instability strip (IS) edges. We explore the effects of incorporating turbulent flux, turbulent pressure, and radiative cooling into the convection theory on the predicted IS at various metallicities using MESA-RSP. We find that the edges become redder with the increasing complexity of convection physics incorporated in the fiducial convection sets, and are similarly shifted to the red with increasing metallicity. The inclusion of turbulent flux and pressure improves the agreement of the red edge of the IS, while their exclusion leads to better agreement with observations of the blue edge. About 90% of observed stars are found to fall within the predicted bluest and reddest edges across the considered variations of turbulent convection parameters. Furthermore, we identify and discuss discrepancies between theoretical and observed CMDs in the low effective temperature and high luminosity regions for stars with periods greater than ~ 20 days. These findings highlight the potential for calibrating the turbulent convection parameters in stellar pulsation models or the prediction of a new class of rare, long-period, 'red Cepheids', thereby improving our understanding of Cepheids and their role in cosmological studies.

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arXiv2024

A theoretical framework for BL Her stars -- II. New period-luminosity relations in the Gaia passbands

We present new theoretical period-luminosity (PL) and period-Wesenheit (PW) relations for a fine grid of convective BL Her, the shortest period T2Cs, models computed using MESA-RSP and compare our results with the empirical relations from Gaia DR3. We use the state-of-the-art 1D non-linear radial stellar pulsation tool MESA-RSP to compute models of BL Her stars over a wide range of input parameters - metallicity (-2.0 dex $\leq$ [Fe/H] $\leq$ 0.0 dex), stellar mass (0.5M$_{\odot}$-0.8M$_{\odot}$), stellar luminosity (50L$_{\odot}$-300L$_{\odot}$) and effective temperature (full extent of the instability strip; in steps of 50K). The BL Her stars in the All Sky region exhibit statistically different PL slopes compared to the theoretical PL slopes computed using the four sets of convection parameters. We find the empirical PL and PW slopes from BL Her stars in the Magellanic Clouds to be statistically consistent with the theoretical relations computed using the different convection parameter sets in the Gaia passbands. There is negligible effect of metallicity on the PL relations in the individual Gaia passbands. However, there exists a small but significant negative coefficient of metallicity in the PWZ relations for the BL Her models using the four sets of convection parameters. This could be attributed to the increased sensitivity of bolometric corrections to metallicities at wavelengths shorter than the V band. Our BL Her models also suggest a dependence of the mass-luminosity relation on metallicity. We found the observed Fourier parameter space to be covered well by our models. Higher mass models (> 0.6M$_{\odot}$) may be needed to reliably model the observed light curves of BL Her stars in the All Sky region. We also found the theoretical light curve structures (especially the Fourier amplitude parameters) to be affected by the choice of convection parameters.

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arXiv2023

Geometry of the LMC based on multi-phase analysis of multi-wavelength Cepheid light curves using OGLE-IV and Gaia DR3 data

The period-luminosity (PL) relation of Cepheids in the Large Magellanic Cloud (LMC) plays a pivotal role in extra-galactic distance measurement and the determination of the Hubble constant $(H_{0})$. In this work, we probe the geometry of the LMC through a detailed study of multi-phase PL relations of these Cepheids, leveraging data from the OGLE-IV and Gaia DR3 databases. We analyse the light curves of a combined sample of $\sim$3300 fundamental (FU) and first overtone (FO) mode classical Cepheids. We obtain multi-phase data with $50$ phase points over a complete pulsation cycle from the OGLE $(V, I)$ and Gaia $(G,G_{\rm BP}, G_{\rm RP})$ photometric bands. We determine the distance modulus and reddening values of individual Cepheids by fitting a simultaneous reddening law to the apparent distance modulus values. We calculate the LMC viewing angle parameters: the inclination angle $(i)$ and position angle of line of nodes $(θ_{\rm lon})$ by fitting a plane of the form $z = f(x,y)$ to the three-dimensional distribution of Cepheids in Cartesian coordinates $(x,y,z)$. The values of LMC viewing angles from multi-phase PL relations are found to be: $i = 22\rlap{.}^{\circ}87 \pm 0\rlap{.}^{\circ}43 ~\textrm{(stat.)} \pm 0\rlap{.}^{\circ}53 ~\textrm{(syst.)}$, $θ_{\rm lon} = 154\rlap{.}^{\circ}76 \pm 1\rlap{.}^{\circ}16 ~\textrm{(stat.)} \pm 1\rlap{.}^{\circ}01 ~\textrm{(syst.)}$, respectively. The use of multi-phase PL relations in multiple bands results in lower uncertainties for the LMC viewing angle parameters as compared to those derived from the mean light PL relations. This shows that the use of multi-phase PL relations with multi-wavelength photometry significantly improves the precision of these measurements, allowing better constraints on the morphology and the structure of the LMC.

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arXiv2023

A study of the stellar photosphere-hydrogen ionization front interaction in $δ$ Scuti stars

Pulsating variable $δ$ 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 $δ$ 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 $δ$ Scuti PCAC relations is consistent with the theory of the interaction between the HIF and the stellar photosphere.

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arXiv2023

A multiphase study of classical Cepheids in the Magellanic Clouds- Models and Observations

This work presents the study of multiphase relations of classical Cepheids in the Magellanic Clouds for short periods (log P < 1) and long periods (log P > 1). From the analysis, it has been found that the multiphase relations obtained using the models as well as observations are highly dynamic with pulsational phase. The multiphase relations for short and long periods are found to display contrasting behaviour for both LMC and SMC. It has been observed that the multiphase relations obtained using the models agree better with the observations in the PC plane in most phases in comparison to the PL plane. Multiphase relations obtained using the models display a clear distinction among different convection sets in most phases. Comparison of models and observations in the multiphase plane is one way to test the models with the observations and to constrain the theory of stellar pulsation.

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arXiv2023

High-resolution Spectroscopic Metallicities of Milky Way Cepheid Standards and their impact on the Leavitt Law and the Hubble constant

Milky Way Cepheid variables with accurate {\it Hubble Space Telescope} photometry have been established as standards for primary calibration of the cosmic distance ladder to achieve a percent-level determination of the Hubble constant ($H_0$). These 75 Cepheid standards are the fundamental sample for investigation of possible residual systematics in the local $H_0$ determination due to metallicity effects on their period-luminosity relations. We obtained new high-resolution ($R\sim81,000$), high signal-to-noise ($S/N\sim50-150$) multi-epoch spectra of 42 out of 75 Cepheid standards using ESPaDOnS instrument at the 3.6-m Canada-France-Hawaii Telescope. Our spectroscopic metallicity measurements are in good agreement with the literature values with systematic differences up to $0.1$ dex due to different metallicity scales. We homogenized and updated the spectroscopic metallicities of all 75 Milky Way Cepheid standards and derived their multiwavelength ($GVIJHK_s$) period-luminosity-metallicity and period-Wesenheit-metallicity relations using the latest {\it Gaia} parallaxes. The metallicity coefficients of these empirically calibrated relations exhibit large uncertainties due to low statistics and a narrow metallicity range ($Δ\textrm{[Fe/H]}=0.6$~dex). These metallicity coefficients are up to three times better constrained if we include Cepheids in the Large Magellanic Cloud and range between $-0.21\pm0.07$ and $-0.43\pm0.06$ mag/dex. The updated spectroscopic metallicities of these Milky Way Cepheid standards were used in the Cepheid-Supernovae distance ladder formalism to determine $H_0=72.9~\pm 1.0$\textrm{~km~s$^{-1}$~Mpc$^{-1}$}, suggesting little variation ($\sim 0.1$ ~km~s$^{-1}$~Mpc$^{-1}$) in the local $H_0$ measurements due to different Cepheid metallicity scales.

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arXiv2023

Predicting light curves of RR Lyrae variables using artificial neural network based interpolation of a grid of pulsation models

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.

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arXiv2023

Predicting Physical Parameters of Cepheid and RR Lyrae variables in an Instant with Machine Learning

We present a machine learning method to estimate the physical parameters of classical pulsating stars such as RR Lyrae and Cepheid variables based on an automated comparison of their theoretical and observed light curve parameters at multiple wavelengths. We train artificial neural networks (ANNs) on theoretical pulsation models to predict the fundamental parameters (mass, radius, luminosity, and effective temperature) of Cepheid and RR Lyrae stars based on their period and light curve parameters. The fundamental parameters of these stars can be estimated up to 60 percent more accurately when the light curve parameters are taken into consideration. This method was applied to the observations of hundreds of Cepheids and thousands of RR Lyrae in the Magellanic Clouds to produce catalogs of estimated masses, radii, luminosities, and other parameters of these stars.

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arXiv2023

A multiphase study of theoretical and observed light curves of classical Cepheids in the Magellanic Clouds

We present an analysis of the theoretical and observed light curve parameters of the fundamental mode (FU) classical Cepheids in the Magellanic Clouds in $V$- and $I$- photometric bands. The state-of-the-art 1D non-linear radial stellar pulsation (RSP) code in MESA (\textsc{mesa-rsp}) has been utilized to generate the theoretical light curves using four sets of convection parameters. Theoretical light curves with two chemical compositions: $Z=0.008$ and $Z=0.004$ appropriate for the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), respectively, covered a wide range of periods ($3 1$) and all periods. The multiphase relations obtained from theoretical and observed light curves in the PL/PC/AC plane are found to be dynamic in nature, with the effect more pronounced at $Φ\sim 0.75-0.85$. Furthermore, a contrasting behaviour of the theoretical/observed multiphase PL and PC relations between the short and long periods has been found for both LMC and SMC. The analysis shows that multiphase PL relations are more stringent to test the models with observations over the FPs. Distances to the LMC/SMC determined using long period Cepheids are found to be in good agreement with the literature values when the term $R_{21}$ is added to the PL relation.

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arXiv2022

Period-Colour and Amplitude-Colour relations for OGLE-$δ$ Scuti stars in the Galactic Bulge and LMC

We present an analysis on the behaviour of the Galactic bulge and the Large Magellanic Cloud (LMC) $δ$ 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 $δ$ Scuti stars are exploited for the analysis. It has been found that the Galactic bulge $δ$ Scuti stars obey flat PC relations at maximum/mean/minimum light while the LMC $δ$ Scutis have sloped/sloped/flat PC relations at maximum/mean/minimum light. Both the Galactic bulge and the LMC $δ$ Scutis have sloped/flat/sloped AC relations at maximum/mean/minimum. These relations also show that Galactic $δ$ Scutis are hotter as compared to their LMC counterparts. The period-amplitude (PA) relations for $δ$ 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 $δ$ 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 $δ$ 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 $δ$ 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.

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arXiv2020

A theoretical framework of BL Her stars. I. Effect of metallicity and convection parameters on period-luminosity and period-radius relations

We present a new grid of convective BL Herculis models using the state-of-the-art 1D non-linear radial stellar pulsation tool MESA-RSP. We investigate the impact of metallicity and four sets of different convection parameters on multi-wavelength properties. Non-linear models were computed for periods typical for BL Her stars, i.e. $1 \leq \mathrm{P (days)} \leq 4$ covering a wide range of input parameters - metallicity ($-2.0\; \mathrm{dex} \leq \mathrm{[Fe/H]} \leq 0.0\; \mathrm{dex}$), stellar mass (0.5M$_{\odot}$-0.8M$_{\odot}$), luminosity (50L$_{\odot}$-300L$_{\odot}$) and effective temperature (full extent of the instability strip; in steps of 50K). The total number of BL Her models with full-amplitude stable pulsations used in this study is 10280 across the four sets of convection parameters. We obtain their multiband ($UBVRIJHKLL'M$) light curves and derive new theoretical period-luminosity ($PL$), period-Wesenheit ($PW$) and period-radius ($PR$) relations at mean light. We find that the models computed with radiative cooling show statistically similar slopes for $PL$, $PW$ and $PR$ relations. Most empirical relations match well with the theoretical $PL$, $PW$ and $PR$ relations from the BL Her models computed using the four sets of convection parameters. However, $PL$ slopes of the models with radiative cooling provide a better match to empirical relations for BL Her stars in the LMC in the $HK_S$ bands. For each set of convection parameters, the effect of metallicity is significant in $U$ and $B$-bands and negligible in infrared bands, which is consistent with empirical results. No significant metallicity effects are seen in the $PR$ relations.

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arXiv2020

A study of the stellar photosphere-hydrogen ionisation front interaction in pulsating variables using period-color relations

Period-color (PC) relations may be used to study the interaction of the stellar photosphere and the hydrogen ionization front (HIF). RR Lyraes (RRLs) and long period classical Cepheids (P > 10d) have been found to exhibit different PC behavior at minimum and maximum light which can be explained by the HIF-photosphere interaction based on their location on the HR diagram. In this work, we extend the study to include type II Cepheids (T2Cs) with an aim to test the HIF-photosphere interaction theory across a broad spectrum of variable star types. We find W Vir stars and BL Her stars to have similar PC relations as those from long period and short period classical Cepheids, respectively. We also use MESA to compute RRL, BL Her and classical Cepheid models to study the theoretical HIF-photosphere distance and find the results to be fairly consistent with the HIF-photosphere interaction theory.

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arXiv2020

The stellar photosphere-hydrogen ionization front interaction in Classical Pulsators: a theoretical explanation for observed period-colour relations

Period-colour and amplitude-colour (PCAC) relations can be used to probe both the hydrodynamics of outer envelope structure and evolutionary status of Cepheids and RR Lyraes. In this work, we incorporate the PCAC relations for RR Lyraes, BL Her, W Vir and classical Cepheids in a single unifying theory that involves the interaction of the hydrogen ionization front (HIF) and stellar photosphere and the theory of stellar evolution. PC relations for RR Lyraes and classical Cepheids using OGLE-IV data are found to be consistent with this theory: RR Lyraes have shallow/sloped relations at minimum/maximum light whilst long-period ($P>10$ days) Cepheids exhibit sloped/flat PC relations at minimum/maximum light. The differences in the PC relations for Cepheids and RR Lyraes can be explained based on the relative location of the HIF and stellar photosphere which changes depending on their position on the HR diagram. We also extend our analysis of PCAC relations for type II Cepheids in the Galactic bulge, LMC and SMC using OGLE-IV data. We find that BL Her stars have sloped PC relations at maximum and minimum light similar to short-period ($P<10$ days) classical Cepheids. W Vir stars exhibit sloped/flat PC relation at minimum/maximum light similar to long-period classical Cepheids. We also compute state-of-the-art 1D radiation hydrodynamic models of RR Lyraes, BL Her and classical Cepheids using the radial stellar pulsation code in MESA to further test these ideas theoretically and find that the models are generally consistent with this picture. We are thus able to explain PC relations at maximum and minimum light across a broad spectrum of variable star types.

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arXiv2019

When a Period Is Not a Full Stop: Light Curve Structure Reveals Fundamental Parameters of Cepheid and RR Lyrae Stars

The period of pulsation and the structure of the light curve for Cepheid and RR Lyrae variables depend on the fundamental parameters of the star: mass, radius, luminosity, and effective temperature. Here we train artificial neural networks on theoretical pulsation models to predict the fundamental parameters of these stars based on their period and light curve structure. We find significant improvements to estimates of these parameters made using light curve structure and period over estimates made using only the period. Given that the models are able to reproduce most observables, we find that the fundamental parameters of these stars can be estimated up to 60% more accurately when light curve structure is taken into consideration. We quantify which aspects of light curve structure are most important in determining fundamental parameters, and find for example that the second Fourier amplitude component of RR Lyrae light curves is even more important than period in determining the effective temperature of the star. We apply this analysis to observations of hundreds Cepheids in the Large Magellanic Cloud and thousands of RR Lyrae in the Magellanic Clouds and Galactic bulge to produce catalogs of estimated masses, radii, luminosities, and other parameters of these stars. As an example application, we estimate Wesenheit indices and use those to derive distance moduli to the Magellanic Clouds of $μ_{\text{LMC},\text{CEP}} = 18.688 \pm 0.093$, $μ_{\text{LMC},\text{RRL}} = 18.52 \pm 0.14$, and $μ_{\text{SMC},\text{RRL}} = 18.88 \pm 0.17$ mag.

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