Periodic Reporting for period 2 - H1PStars (Measuring Hubble's Constant to 1% with Pulsating Stars)
Período documentado: 2022-10-01 hasta 2024-03-31
The H1PStars project addresses this need by investigating the astrophysics of pulsating stars as well as their use as "standard candles" to measure astronomical distances. Pulsating stars are fascinating objects whose brightness varies periodically due to self-excited oscillations that provide important insights for stellar astrophysics. Even more importantly, the intrinsic brightnesses of such stars are related to their pulsations via Leavitt laws, which can be calibrated using geometrically measured distances. Thus, pulsating stars are the backbone of the distance ladder used to measure the Hubble constant and also dominate its uncertainties. The H1PStars project pursues a three-pronged approach to push towards a 1% measurement of H0 by a) reinforcing the calibration of Leavitt laws based on geometric distances; b) improving the standardization of distances measured using Leavitt laws; c) developing new insights into the astrophysics of pulsating stars to ensure that the claimed accuracy of our distance measurements is supported by a solid understanding of the stars upon which they are based.
For a) we have extensively studied data from the ESA mission Gaia, whose third data release published an unprecedented dataset of positions, parallaxes (distances), motions, light curves, and other information for 1.8 billion stars. We worked to obtain the best Leavitt law calibrations using this data set, which required much work to understand the data and to understand how to deal with the flaws that appear at the limits of Gaia's capabilities. Additionally, we measured how the chemical composition of pulsating stars affects their distance measurements.
For b) we collected new observations with the Hubble Space Telescope (HST) and the brand-new James Webb Space Telescope. We analyzed these data along with existing HST images to quantify systematic uncertainties related to the brightness measurements of pulsating stars many tens of millions of light years distant. We also developed methods to correct for changes in the measured light that are caused by effects explained by Einstein's special relativity. Last, but not least, we measured the distance of the Whirlpool galaxy using classical Cepheids and a type-IIp supernova.
For c) we collected a very large number of observations from telescopes in Chile and the island of La Palma for the VELOCE project. These observations have allowed us to describe the pulsations (periodic expansions and contractions) measured along the line of sight in unprecedented detail. We developed novel methods to search for periodic signals in these observations and prepared the first data release of the VELOCE project.
Last, but not least, we used large computer simulations to investigate how stellar dynamics influence the properties and evolution of pulsating stars.
We provided the first comprehensive investigation of relativistic effects on distance measurements based on pulsations stars. We showed that the so-called K-corrections can significantly bias distance measurements planned by other teams, requiring solutions for mitigation.
Observations collected with the Hubble and James Webb Space Telescopes have significantly improved our understanding of systematic uncertainties in the brightness measurements of Cepheids. Specifically, the JWST observations showcased the significant improvement in brightness measurements thanks to JWST's unparalleled spatial resolution and sensitivity. We expect that JWST will play a vital role in further improving the accuracy of the Hubble constant measurement.
Our dynamical simulations have drawn the first detailed picture of how the dynamics of large groups of stars affect the evolution of classical Cepheid stars. These results show that interactions among stars in binary and higher-order multiple star systems, as well as clusters, have a significant influence over the observed properties of these crucial stars.
Last, but not least, the new observations collected from Chile and La Palma have been used to develop an unprecedented reference of line-of-sight velocity curves of classical Cepheids. Thanks to a unique combination of extreme precision, temporal baseline, and phase sampling, we have identified previously unknown features of Cepheid pulsations and are able to obtain the most detailed study of Cepheid multiplicity to date.