(Image: NASA\/JPL-Caltech)<\/small><\/p>\r\n
<\/span><\/p>\r\n Welcome to the EXPANDING Universe<\/em> International Team webpage!<\/span><\/span><\/p>\r\n Abstract<\/span><\/span><\/strong><\/p>\r\n The fundamental method for determining distances to astrophysical objects is through the measurement of their geometric parallaxes. Distance determinations beyond these geometric methods rely on standard candles, which have known intrinsic luminosities. The absolute calibration of the luminosities of stellar standard candles forms the first rung of the cosmic distance ladder used to determine the Hubble constant – the expansion rate of the Universe. Currently, the Hubble constant values based on a variety of standard candles observed with the Hubble\/James Webb space telescopes, are in an intriguing discord with the measurement from the Planck space mission. This Hubble Tension points to new physics in the cosmological model and must be evaluated against all sources of measurement errors. One of the main systematic uncertainties is the absolute luminosity scales of stellar standard candles, which have not yet reached 1% accuracy despite unprecedented geometric distances of ~1.5 billion sources in the Gaia space mission data. This is mainly due to caveats associated with Gaia parallax offsets, lack of complementary multiband photometry and high-resolution spectroscopy, and highly debated effects of composition and age on the luminosities, among other uncertainties. Project Summary<\/strong><\/span><\/p>\r\n The EXPANDING Universe ISSI-IT made significant progress toward establishing a highly precise and internally consistent calibration of the first rung of cosmic distance ladder that is used to determine the present expansion rate of the Universe \u2013 the Hubble constant. The published results collectively focus on improving the absolute luminosity calibration of stellar standard candles\u2014including Cepheids, RR Lyrae stars, Mira variables, the Tip of the Red Giant Branch (TRGB), using precise parallaxes from the <\/span>Gaia<\/span><\/i> mission together with multi-wavelength photometry, spectroscopy, and theoretical pulsation and stellar-evolution models.<\/span><\/span><\/p>\r\n A major outcome of these studies has been an independent determination of the Hubble constant that is anchored to the Mira variable stars in the Milky Way star clusters. This new Mira-based calibration complemented previously available anchors, the Large Magellanic Cloud and NGC 4248, providing a 3.7% measurement of the Hubble constant based on cool stars. This study led by the team leader (including 2 team members) also showed that the metallicity effects on Mira luminosities are substantially smaller compared to Cepheid stars. At the same time, several team members attempted to quantify the metallicity effects on Cepheid stars more precisely within the C-MetaLL survey and these results are published in a series of papers.\u00a0<\/span><\/p>\r\n The team\u2019s work also advanced theoretical understanding of stellar pulsation physics through improved nonlinear pulsation models of Cepheids and RR Lyrae, and machine-learning approaches for classification and parameter inference. The early career researchers in the team have led publications comparing results and underlying physical and numerical assumptions in the state-of-the-art stellar pulsation models, MESA-rsp and Stellingwerf\u2019s code for the first time. Theoretical models of variable stellar standard candles have been published by team members providing luminosity calibrations in filters and wavelengths specific to ongoing and upcoming large time domain surveys and space telescopes. The team leader was also a member of the Distance Network collaboration that led a community effort reporting a measurement of the local Hubble constant approaching ~1% precision. These efforts further reinforce the possibility that the Hubble tension likely reflects new physics in the standard cosmological model rather than unaccounted measurement errors.<\/span><\/p>\r\n <\/span><\/p>","protected":false},"excerpt":{"rendered":" (Image: NASA\/JPL-Caltech) Welcome to the EXPANDING Universe International Team webpage! Abstract The fundamental method for determining distances to astrophysical objects is through the measurement of their geometric parallaxes. Distance determinations beyond these geometric methods rely on standard candles, which have known intrinsic luminosities. The absolute calibration of the luminosities of stellar standard candles forms the […]<\/p>\n","protected":false},"author":141,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/pages\/2","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/users\/141"}],"replies":[{"embeddable":true,"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/comments?post=2"}],"version-history":[{"count":7,"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/pages\/2\/revisions"}],"predecessor-version":[{"id":70,"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/pages\/2\/revisions\/70"}],"wp:attachment":[{"href":"https:\/\/teams.issibern.ch\/expanding\/wp-json\/wp\/v2\/media?parent=2"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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Our International Team aims to strategically address these shortcomings before the nominal five-year Gaia mission data release to achieve 1% calibration of stellar distance indicators. For this purpose, we are using\u00a0 state-of-the-art stellar evolution and pulsation models, multi-wavelength datasets from space and ground-based facilities together with machine-learning approaches, leveraging our team’s competences and expertise in a multidisciplinary context. The projects led by team members will provide cross-investigation of 1% precise luminosity scales of a variety of stellar standard candles with high accuracy and fidelity to firmly rule out (or confirm) measurement uncertainties as the origin of the Hubble tension. These precise luminosity calibrations will be the primary resource for the astronomical distance determination in the era of space and ground-based large observational facilities in the next-decade.<\/span><\/span><\/p>\r\n