Periodic Reporting for period 1 - PRESTiGE (Precision stellar astrophysics and the distance scale with pulsating stars in the Gaia era)
Reporting period: 2021-12-01 to 2023-11-30
The "Precision Stellar Astrophysics and the distance scale with pulsating stars in the Gaia era (PRESTiGE)" project aimed to use classical pulsating stars such as Cepheid and RR Lyrae variables as stellar population tracers for stellar astrophysics and cosmic distance scale. Classical Cepheids have traditionally played a crucial role in providing the primary calibration for the extragalactic distance ladder leading to the most precise determination of the Hubble constant, the present expansion rate of the Universe. Despite extensive use of classical Cepheids and other pulsating stars as standard candles, the absolute calibration of their luminosity scales has not reached a desired percent-level precision due to caveats associated with their geometric parallax distances in our Galaxy, impact of composition and ages on their luminosities among other systematic uncertainties. The PRESTiGE project employed both theoretical and observational efforts to quantify residual systematics in the absolute calibration of Cepheid and RR Lyrae luminosity scales and
made a significant progress towards achieving a percent-level precision, which is crucial for the cosmic distance scale studies.
We generated state-of-the-art stellar pulsation models of Cepheid and RR Lyrae variables and obtained observational data from several optical and near-infrared telescopes all over the world to achieve the objectives. The project primarily utilised the Gaia space mission data to calibrate the period-luminosity (PL) and period-luminosity-metallicity (PLZ) relations for Cepheid and RR Lyrae variables that are fundamental tools for the extragalactic distance measurements. The project employed innovative and modern computational methods for analysis of observed and theoretical data related to variable stars analysing their pulsation properties, and providing useful constraints for the input of stellar physics to the stellar evolution and pulsation models.
made a significant progress towards achieving a percent-level precision, which is crucial for the cosmic distance scale studies.
We generated state-of-the-art stellar pulsation models of Cepheid and RR Lyrae variables and obtained observational data from several optical and near-infrared telescopes all over the world to achieve the objectives. The project primarily utilised the Gaia space mission data to calibrate the period-luminosity (PL) and period-luminosity-metallicity (PLZ) relations for Cepheid and RR Lyrae variables that are fundamental tools for the extragalactic distance measurements. The project employed innovative and modern computational methods for analysis of observed and theoretical data related to variable stars analysing their pulsation properties, and providing useful constraints for the input of stellar physics to the stellar evolution and pulsation models.
The project contributed to the computation of a fine grid of pulsation models for Cepheid and RR Lyrae variables for different chemical compositions representative of these variables in the Milky Way, nearby galaxies such as the Large and the Small Magellanic Cloud. These pulsation models were used to derive theoretical PL and PLZ relations for Cepheid and RR Lyrae stars in different bands relevant to space missions such as Gaia, and upcoming ground-based facilities such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (see e.g. De Somma et al. 2024), that were also tested against observations (see e.g. Bhardwaj et al. 2023) . More specifically, these pulsation models were used to gain new insights into the so-called “Hertzsprung progression” in the light and radial velocity curves of Cepheid variables (Marconi et al. 2024). These models were utilised by the students working with the researcher and host to obtain physical parameters of Cepheid and RR Lyrae stars (Kumar et al. 2023), and are currently being used in several projects within the group. All these models are subsequently provided to the community with the publications.
One of the main objectives of the PRESTiGE project was to evaluate the tension in the Hubble constant measurement based on classical Cepheid Supernovae distance ladder and the value that comes from the Planck mission’s observations of the early Universe. One of the systematics in the Cepheid-based Hubble constant determination has been the metallicity effect on their PL relations. The PRESTiGE project obtained high-resolution spectroscopic metallicities of Milky Way Cepheid standards with available Hubble Space Telescope photometry. In a joint publication with the SH0ES project team (Supernovae and H0 for the Equate of State of the Dark Energy led by the Nobel Laureate Adam Riess), the experienced researcher found that there is no significant impact of Cepheid metallicity or the metallicity scale on the local measurement of the Hubble constant. This publication (Bhardwaj, Riess et. al. 2023) further confirmed that Cepheid metallicities are not at the root cause for the Hubble tension.
The quantification of the impact of metallicity on Cepheid and RR Lyrae pulsation properties has been a crucial issue for stellar astrophysics and distance scale. In line with the objective of the PRESTiGE project, the researcher and host provided new empirical and theoretical calibrations of RR Lyrae PLZ relations at near-infrared wavelengths. The publication (Bhardwaj, Marconi+2023) provided the most precise PLZ relation using nearly 1000 RR Lyrae stars in 11 Milky Way globular clusters and found an excellent agreement with the theoretical predictions and empirical results. Similarly, the researcher and host also derived empirical PLZ relations for classical Cepheids using parallaxes from the Gaia space mission and photometric data collected through their observing programs (Bhardwaj, Ripepi et al. 2024).
One of the main objectives of the PRESTiGE project was to evaluate the tension in the Hubble constant measurement based on classical Cepheid Supernovae distance ladder and the value that comes from the Planck mission’s observations of the early Universe. One of the systematics in the Cepheid-based Hubble constant determination has been the metallicity effect on their PL relations. The PRESTiGE project obtained high-resolution spectroscopic metallicities of Milky Way Cepheid standards with available Hubble Space Telescope photometry. In a joint publication with the SH0ES project team (Supernovae and H0 for the Equate of State of the Dark Energy led by the Nobel Laureate Adam Riess), the experienced researcher found that there is no significant impact of Cepheid metallicity or the metallicity scale on the local measurement of the Hubble constant. This publication (Bhardwaj, Riess et. al. 2023) further confirmed that Cepheid metallicities are not at the root cause for the Hubble tension.
The quantification of the impact of metallicity on Cepheid and RR Lyrae pulsation properties has been a crucial issue for stellar astrophysics and distance scale. In line with the objective of the PRESTiGE project, the researcher and host provided new empirical and theoretical calibrations of RR Lyrae PLZ relations at near-infrared wavelengths. The publication (Bhardwaj, Marconi+2023) provided the most precise PLZ relation using nearly 1000 RR Lyrae stars in 11 Milky Way globular clusters and found an excellent agreement with the theoretical predictions and empirical results. Similarly, the researcher and host also derived empirical PLZ relations for classical Cepheids using parallaxes from the Gaia space mission and photometric data collected through their observing programs (Bhardwaj, Ripepi et al. 2024).
The PRESTiGE project provided several key scientific results for Cepheid and RR Lyrae variables. The researcher led publications on determining an independent Cepheid-based local value of the Hubble constant, providing most precise empirical determination of the metallicity coefficients for RR Lyrae PLZ relations, probing helium enhancement in RR Lyrae stars in Milky Way bulge globular clusters, to deriving empirical calibration of Cepheid PL relations at multiple bands using Gaia parallaxes. The researcher has so far published 4 first author papers (15 in total) within the PRESTiGE project.
The research carried out within the PRESTiGE project collaborated with international teams such as the SH0ES and VMC survey team. The project employed multidisciplinary aspects by utilising innovative machine-learning algorithms for comparing predicted and observed properties of Cepheid and RR Lyrae variables, and published a new RRL interpolator to generate predicted light curves. The state-of-the-art interpolator is provided to the community through a web-page that is publicly accessible (Kumar et al. 2023). The scientific results also provide new challenges and constraints for the most-widely used stellar evolutionary and pulsation models by the astronomical community.
The research carried out as part of the PRESTiGE project has contributed to one of the key problems in modern cosmology, that is the tension in the expansion rate in the early and late Universe. The results of this research are being communicated through talks, seminars in conferences, workshops, and through open-access journal publications. The astronomical community will continue using these results for further science, education and outreach purposes.
The research carried out within the PRESTiGE project collaborated with international teams such as the SH0ES and VMC survey team. The project employed multidisciplinary aspects by utilising innovative machine-learning algorithms for comparing predicted and observed properties of Cepheid and RR Lyrae variables, and published a new RRL interpolator to generate predicted light curves. The state-of-the-art interpolator is provided to the community through a web-page that is publicly accessible (Kumar et al. 2023). The scientific results also provide new challenges and constraints for the most-widely used stellar evolutionary and pulsation models by the astronomical community.
The research carried out as part of the PRESTiGE project has contributed to one of the key problems in modern cosmology, that is the tension in the expansion rate in the early and late Universe. The results of this research are being communicated through talks, seminars in conferences, workshops, and through open-access journal publications. The astronomical community will continue using these results for further science, education and outreach purposes.