[Paper Review] The Araucaria Project: Improving the cosmic distance scale

G. Pietrzyński, W. Gieren+22 more|arXiv (Cornell University)|May 26, 2023

Regional Development and Policy3 citations

TL;DR

This paper presents the 20-year achievements of the Araucaria Project, a collaborative effort to refine the cosmic distance scale using multi-wavelength observations of Cepheid variables and other distance indicators. By combining high-precision photometry and spectroscopy, the project improves the calibration of the extragalactic distance scale, reducing systematic uncertainties and enhancing the accuracy of the Hubble constant determination.

ABSTRACT

The book consists of a number of short articles that present achievements of the Araucaria members, collaborators, and friends, in various aspects of distance determinations and related topics. It celebrates the 20-year anniversary of the Araucaria Project, acknowledges the people who worked for its success, and popularises our methods and results among broader readership. This book is a part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 695099.

Motivation & Objective

• To improve the accuracy of the cosmic distance ladder by refining the calibration of Cepheid and RR Lyrae variables.
• To reduce systematic uncertainties in the Hubble constant by leveraging multi-epoch, multi-wavelength observations of nearby galaxies.
• To celebrate and document two decades of progress in distance scale measurements through a comprehensive synthesis of methods and results.
• To disseminate advanced distance measurement techniques to a broader scientific and public audience.
• To strengthen the foundation of cosmological distance measurements using empirical, multi-method approaches.

Proposed method

• Utilizing high-precision photometry and spectroscopy of Cepheid variables in the Large Magellanic Cloud and nearby galaxies.
• Applying the Baade-Wesselink method to derive distances from pulsation and radial velocity measurements.
• Combining optical and infrared photometry to minimize extinction and metallicity effects in distance calibration.
• Employing interferometric measurements (e.g., from the Very Large Telescope Interferometer) to directly measure stellar angular diameters.
• Integrating results from multiple independent methods (e.g., surface brightness fluctuations, tip of the red giant branch) to cross-validate distances.
• Applying statistical and error-budget modeling to quantify and minimize systematic uncertainties in the distance ladder.

Experimental results

Research questions

• RQ1 How can the precision of Cepheid distance measurements be improved using multi-wavelength and multi-instrument data?
• RQ2 What is the impact of metallicity and extinction on the calibration of the Cepheid period-luminosity relation?
• RQ3 How do interferometric measurements of stellar angular diameters contribute to the absolute calibration of the distance ladder?
• RQ4 To what extent can systematic errors in the Hubble constant be reduced through improved distance scale calibration?
• RQ5 How do combined results from multiple distance indicators (e.g., Cepheids, RR Lyrae, TRGB) enhance the robustness of the cosmic distance scale?

Key findings

• The Araucaria Project achieved a significant reduction in systematic uncertainties in the Cepheid distance scale through multi-epoch, multi-wavelength observations.
• Improved calibration of the period-luminosity relation in the Large Magellanic Cloud led to a more accurate determination of the distance modulus.
• Interferometric measurements of Cepheid angular diameters provided direct constraints on stellar radii and distances, reducing reliance on theoretical models.
• The integration of multiple distance indicators (Cepheids, RR Lyrae, TRGB) yielded consistent results, increasing confidence in the cosmic distance ladder.
• The project's work contributed to a refined estimate of the Hubble constant with reduced systematic error budgets.
• The synthesis of 20 years of data and methods provided a comprehensive, publicly accessible reference for future distance scale studies.