Precise measurement of the Hubble constant in the era of the Gaia project

NCN Project 2017/26/A/ST9/00446



Type of project: Maestro 9

Funding basis: Agreement number UMO-2017/26/A/ST9/00446 of 17.04.2018 with the National Science Centre

Timeframe: 17.04.2018 – 16.10.2023

Project budget: 3,927,600.00 PLN


1. Project objective/research hypothesis

Precise and accurate determination of the Hubble constant (H0) has always been one of the most important problems in modern astrophysics. The present H0 uncertainty of about 3%, based on Cepheid variables and supernovae type Ia, is too high to definitively resolve pressing cosmology issues, like the nature of dark energy. After about 100 years of intensive work on the determination of H0, we’ve learnt that any significant reduction of its uncertainty can only be achieved by improving the accuracy of the absolute calibration of the Cepheid period-luminosity relation (PLR), which is responsible for about 70% of the entire uncertainty budget. In order to achieve the 1% uncertainty of H0, we need to substantially reduce the systematic error of the zero-point of the PLR by: 1) defining a precise and accurate fiducial PLR to which the observed Cepheid PLRs in distant galaxies can be tied; 2) settling the nagging and unresolved problem of how the metallicity of Cepheids affects their absolute magnitudes in different photometric bands. It will allow us to reduce the uncertainty of the absolute zero-point of the PLR to about 0.7%, and as a result, to determine H0 with an accuracy close to one percent.



2. Methodology

We propose a novel, multi-angled approach based on nearby eclipsing binaries and Cepheid variables, supplemented by parallaxes harvested by the Gaia space mission. The first angle of approach is to refine the surface brightness-color relationship (SBCR), using our photometric and spectroscopic data for 100 Galactic eclipsing binaries (200 stars in total) in tandem with Gaia parallaxes. When applied to eclipsing binaries in the LMC and SMC, the SBCR will allow us to determine distances to individual binary companions and – by averaging the results – achieve 1–2% accuracy.

The second angle of approach is to use already calibrated SBCR together with Gaia parallaxes for 120 Galactic Cepheids, in order to calculate their projection factors (p-factors), with the expected precision of about 1-2%. The p-factor is the crux of the Baade-Wesselink (B-W) method, which allows to calculate distances to individual Cepheids with the precision directly correlated to the precision of the p-factor. Having a large number of very precise determinations of p-factors for the Galactic Cepheids we will calibrate the dependence of the pulsational period on the p-factor, and consequently, solve the main problem of the B-W technique, which will become an excellent tool for measuring 2%-accurate distances to individual Cepheids in the volume of 1 Mpc now, and up to 20 Mpc with the advent of future extremely large telescopes. Next, we will apply the B-W method to measure 2%-accurate individual distances to 40 and 35 Cepheids in the LMC and SMC, respectively.

With much more accurate distances to LMC and SMC Cepheids (thanks to the SBCR and B-W technique) and Galactic Cepheids (thanks to Gaia parallaxes), we will tackle the luminosity-metallicity relation for Cepheids across the wide range of metallicities (–0.8 < [Fe/H] < +0.2) by constructing multiband (BVJK) PLRs and analyzing their residua as a function of metallicity. As a result, we will calibrate the luminosity-metallicity relation for Cepheids 5 times more accurately than ever before.

Finally, we will construct two independent fiducial PLRs for 120 Galactic Cepheids (based on our photometry and Gaia parallaxes) and for ~900 LMC Cepheids (based on already published photometry and our final distances from eclipsing binaries), apply the metallicity correction, and average the zero-points of the two PLRs. As a result, we will deliver the best ever zero-point for the whole extragalactic distance scale (precise to about 0.7%), which will allow us to measure the value of H0 with a precision close to 1%.

In order to collect the vast volume of near-infrared data of bright Galactic Cepheids and eclipsing binaries, we employed a 0.6-m telescope equipped with a professional near-infrared camera in an excellent observing site at Cerro Armazones, in the Atacama Desert, Chile. We further expand and improve this observatory to meet the quality and quantity requirements set on the data we collect, and secure the success of our project.



3. Significance of the results on science development

The empirical determination of the Hubble constant with 1% accuracy will be extremely important for cosmology, as it will allow us to refine the rate of expansion of the Universe (Nobel Prize awarded in 2011) and investigate the nature of dark energy, which causes it. In the process of pursuing more accurate determination of H0, we will develop two unique tools for precise and accurate distance measurements to nearby galaxies – the perfect laboratories to study an enormous variety of objects and processes. We will determine very precise stellar parameters (mass, radius, etc) for some 200 stars, which will constrain theoretical models of stellar evolution. The scientific results will be published in about 40 refereed publications in prestigious astronomical journals. The results will also be presented at ~10 international conferences and ~20 seminars. Our project will have a very significant impact on the early stages of the careers of several young astronomers (we expect 3 master, 2 PhD, and 3 habilitation degrees). The most important and spectacular discoveries will be submitted to Nature or Science journals, and will obtain adequate coverage in the media (newspapers, radio, TV, etc). We plan to publish a series of outreach articles (in Urania, Sky and Telescope, etc.) presenting our results in the framework of the distance scale studies. We will establish an interactive web page for our project where we will share with the astronomical community all the data and results obtained in the course of our project.


4. Determination the extent and scope of the project which involves pioneering research, including interdisciplinary research, important for the advancement of science beyond the current state of knowledge

Two recent, famous determinations of H0 (the classical approach involving Cepheids and supernovae Ia, and the cosmological approach based on the microwave background radiation) differ by about 4σ. This so-called Hubble tension may hint to the incomplete understanding of the underlying physics and prelude a breakthrough across numerous fields of modern astrophysics and cosmology. Our results will answer if new physics beyond the standard cosmological model is required. They will also be crucial for our understanding of the physical nature of dark energy, which constitutes about 72% of the total mass/energy density of the Universe and is responsible for the accelerated expansion of the Universe (Nobel prize awarded in 2011). The project may produce interdisciplinary results beyond the current state of knowledge.




Principal investigator: prof. Grzegorz Pietrzyński

Co-investigator: dr Ksenia Suchomska

Co-investigator: dr Megan Lewis

Co-investigator: dr Bogumił Pilecki

Co-investigator: mgr Gonzalo Rojas



Other collaborators (in alphabetical order):

S. Blex

S. Borgniet

L. Breuval

R. Chini

A. Gallenne

C. Gałan

Z. Ghaffari

B. Ghazinouri

M. Gładkowski

D. Graczyk

M. Górski

G. Hajdu

G. Hazinouri

V. Hocde

M. Kałuszyński


P. Karczmarek

P. Kołaczek-Szymański

K. Kotysz

T. Lisow

P. Mikołajczyk

D. Moździerski

W. Narloch

S. Noroozi

F. Pozo-Nunez

W. Pych

C. Sobrino Figaredo

F. Symietz

B. Trahin

P. Wielgórski

B. Zgirski




Publications in the order of the most recent


Long-period maser-bearing Miras in the Galactic center. Period-luminosity relations and extinction estimates

M. O. Lewis, R. Bhattacharya, L. O. Sjouwerman, Y. M. Pihlström, G. Pietrzynski, R. Sahai, P. Karczmarek and M. Górski

Publication: Astronomy & Astrophysics, Volume 677, id.A153, 14 pp.

 Pub Date: September 2023

 DOI: 10.1051/0004-6361/202346568 


Period-Luminosity Relations for Galactic Classical Cepheids in the Sloan Bands

Weronika Narloch, Gergely Hajdu, Grzegorz Pietrzyński, Wolfgang Gieren, Piotr Wielgórski, Bartłomiej Zgirski, Paulina Karczmarek, Marek Górski, and Dariusz Graczyk

Publication: The Astrophysical Journal, Volume 953, Issue 1, id.14, 15 pp.

 Pub Date: August 2023

 DOI: 10.3847/1538-4357/acdd01 


New Near-infrared Period-Luminosity-Metallicity Relations for Galactic RR Lyrae Stars Based on Gaia EDR3 Parallaxes

Bartłomiej Zgirski, Grzegorz Pietrzyński, Marek Górski, Wolfgang Gieren, Piotr Wielgórski, Paulina Karczmarek, Gergely Hajdu, Megan Lewis, Rolf Chini, Dariusz Graczyk, Mikołaj Kałuszyński, Weronika Narloch, Bogumił Pilecki, Gonzalo Rojas García, Ksenia Suchomska, and Mónica Taormina

Publication: The Astrophysical Journal, Volume 951, Issue 2, id.114, 22 pp.

 Pub Date: July 2023

 DOI: 10.3847/1538-4357/acd63a 


Synthetic Population of Binary Cepheids. II. The Effect of Companion Light on the Extragalactic Distance Scale

Paulina Karczmarek, Gergely Hajdu, Grzegorz Pietrzyński, Wolfgang Gieren, Weronika Narloch, Radosław Smolec, Grzegorz Wiktorowicz, and Krzysztof Belczynski

Publication: The Astrophysical Journal, Volume 950, Issue 2, id.182, 13 pp.

 Pub Date: June 2023

 DOI: 10.3847/1538-4357/acc845 


The Araucaria project: High-precision orbital parallaxes and masses of binary stars. I. VLTI/GRAVITY observations of ten double-lined spectroscopic binaries

A. Gallenne, A. Mérand, P. Kervella, D. Graczyk, G. Pietrzynski, W. Gieren and B. Pilecki

Publication: Astronomy & Astrophysics, Volume 672, id.A119, 30 pp.

 Pub Date: April 2023

 DOI: 10.1051/0004-6361/202245712 


HARPS-N high spectral resolution observations of Cepheids. II. The impact of the surface-brightness color relation on the Baade-Wesselink projection factor of η Aql

N. Nardetto, W. Gieren, J. Storm, V. Hocdé, G. Pietrzynski, P. Kervella, A. Mérand, A. Gallenne, D. Graczyk, B. Pilecki, E. Poretti, M. Rainer, B. Zgirski, P. Wielgórski, G. Hajdu, M. Górski, P. Karczmarek, W. Narloch and M. Taormina

Astronomy & Astrophysics, Volume 671, id.A14

Pub Date: March 2023

 DOI:  10.1051/0004-6361/202245298 


An Absolute Calibration of the Near-infrared Period–Luminosity Relations of Type II Cepheids in the Milky Way and in the Large Magellanic Cloud

Piotr Wielgórski , Grzegorz Pietrzyński, Bogumił Pilecki, Wolfgang Gieren Bartłomiej Zgirski, Marek Górski, Gergely Hajdu, Weronika Narloch, Paulina Karczmarek, Radosław Smolec, Pierre Kervella, Jesper Storm, Alexandre Gallenne, Louise Breuval, Megan Lewis, Mikołaj Kałuszyński, Dariusz Graczyk, Wojciech Pych, Ksenia Suchomska, Mónica Taormina, Gonzalo Rojas Garcia, Aleksandra Kotek, Rolf Chini, Francisco Pozo Nũnez, Sadegh Noroozi, Catalina Sobrino Figaredo, Martin Haas, Klaus Hodapp, Przemysław Mikołajczyk, Krzysztof Kotysz, Dawid Moździersk and Piotr Kołaczek-Szymański

Publication:  The Astrophysical Journal, Volume 927, Issue 1, id.89, 23 pp.

 Pub Date:  March 2022

 DOI:  10.3847/1538-4357/ac470c 


Metallicities and ages for star clusters and their surrounding fields in the Large Magellanic Cloud

W. Narloch , G. Pietrzynski, W. Gieren, A. E. Piatti, P. Karczmarek, M. Górski, D. Graczyk, R. Smolec, G. Hajdu, K. Suchomska, B. Zgirski, P. Wielgórski, B. Pilecki, M. Taormina, M. Kałuszynski, W. Pych, G. Rojas García and M. O. Lewis

Publication:  Astronomy & Astrophysics, Volume 666, id.A80, 39 pp.

 Pub Date:  October 2022

 DOI:  10.1051/0004-6361/202243378 


Surface brightness-colour relations of dwarf stars from detached eclipsing binaries.

D. Graczyk, G. Pietrzynski, C. Galan, J. Southworth, W. Gieren, M. Kałuszynski, B. Zgirski, A. Gallenne, M. Górski, G. Hajdu, P. Karczmarek, P. Kervella, P. F. L. Maxted, N. Nardetto, W. Narloch, B. Pilecki, W. Pych, G. Rojas Garcia, J. Storm, K. Suchomska, M. Taormina, and P. Wielgórski

Publication:  Astronomy & Astrophysics, Volume 666, id.A128, 17 pp.

 Pub Date:  October 2022

 DOI:  10.1051/0004-6361/202244122 


Evolved eclipsing binary systems in the Galactic bulge: Precise physical and orbital parameters of OGLE-BLG-ECL-305487 and OGLE-BLG-ECL-116218

K. Suchomska, D. Graczyk, C. Gałan, O. Ziółkowska, R. Smolec, G. Pietrzynski, W. Gieren, S. Villanova, M. Górski, I. B. Thompson, P. Wielgórski, B. Zgirski, P. Karczmarek, B. Pilecki, M. Taormina, W. Narloch, G. Hajdu, M. Lewis, M. Kałuszynski and G. Rojas García

Publication:  Astronomy & Astrophysics, Volume 668, id.A30, 11 pp.

 Pub Date:  December 2022

 DOI:  10.1051/0004-6361/202244433 


Cepheids with Giant Companions. I. Revealing a Numerous Population of Double-lined Binary Cepheids

Bogumił Pilecki, Grzegorz Pietrzyński, Richard I. Anderson, Wolfgang Gieren, Mónica Taormina, Weronika Narloch, Nancy R. Evans and Jesper Storm

Publication: The Astrophysical Journal, Volume 910, Issue 2, id.118, 9 pp.

 Pub Date: April 2021



Studies of RR Lyrae Variables in Binary Systems. I. Evidence of a Trimodal Companion Mass Distribution

Gergely Hajdu , Grzegorz Pietrzyński , Johanna Jurcsik, Márcio Catelan, Paulina Karczmarek, Bogumił Pilecki, Igor Soszyński, Andrzej Udalski and Ian B.

Publication:T he Astrophysical Journal, Volume 915, Issue 1, id.50, 16 pp.

 Pub Date: July 2021

 DOI:  10.3847/1538-4357/abff4b 


The Influence of Metallicity on the Leavitt Law from Geometrical Distances of Milky Way and Magellanic Cloud Cepheids

Louise Breuval, Pierre Kervella, Piotr Wielgórski, Wolfgang Gieren, Dariusz Graczyk, Boris Trahin, Grzegorz Pietrzyński, Frédéric Arenou, Behnam Javanmardi and Bartłomiej Zgirski

Publication: The Astrophysical Journal, Volume 913, Issue 1, id.38, 20 pp.

 Pub Date: May 2021



Inspecting the Cepheid Distance Ladder: the Hubble Space Telescope Distance to the SN Ia Host Galaxy NGC 5584

Behnam Javanmardi, Antoine Mérand, Pierre Kervella, Louise Breuval, Alexandre Gallenne, Nicolas Nardetto, Wolfgang Gieren, Grzegorz Pietrzyński, Vincent Hocdé and Simon Borgniet

Publication: The Astrophysical Journal, Volume 911, Issue 1, id.12, 21 pp.

 Pub Date: April 2021

 DOI: 10.3847/1538-4357/abe7e5 


Metallicities and ages for 35 star clusters and their surrounding fields in the Small Magellanic Cloud

W. Narloch, G. Pietrzyński, W. Gieren, A. E. Piatti, M. Górski, P. Karczmarek, D. Graczyk, K. Suchomska, B. Zgirski, P. Wielgórski, B. Pilecki, M. Taormina, M. Kałuszyński, W. Pych, G. Hajdu and G. Rojas García

Publication: Astronomy & Astrophysics, volume 647, article no A135

 Pub Date: March 2021

DOI: 10.1051/0004-6361/202039623


The Araucaria Project: Deep Near-infrared Photometric Maps of Local and Sculptor Group Galaxies. I. Carina, Fornax, and Sculptor

Paulina Karczmarek, Grzegorz Pietrzyński, Wolfgang Gieren, Weronika Narloch, Gergely Hajdu, Gonzalo Rojas García, Mikołaj Kałuszyński, Marek Górski, Ksenia Suchomska, Dariusz Graczyk, Bogumił Pilecki, Piotr Wielgórski, Bartłomiej Zgirski, Mónica Taormina and Mradumay Sadh

Publication: The Astrophysical Journal Supplement Series, Volume 253, Issue 2, id.42, 12 pp.

 Pub Date:April 2021

DOI: 10.3847/1538-4365/abdf60 


The surface brightness–colour relations based on eclipsing binary stars and calibrated with Gaia EDR3

D. Graczyk, G. Pietrzynski, C. Galan, W. Gieren, A. Tkachenko, R. I. Anderson, A. Gallenne, M. Górski, G. Hajdu, M. Kałuszynski, P. Karczmarek, P. Kervella, P. F. L. Maxted, N. Nardetto, W. Narloch, K. Pavlovski, B. Pilecki, W. Pych, J. Southworth, J. Storm, K. Suchomska , M. Taormina, S. Villanova, P. Wielgórski, B. Zgirski and P. Konorski

Publication:  Astronomy & Astrophysics, Volume 649, id.A109, 17 pp.

 Pub Date:  May 2021

DOI:  10.1051/0004-6361/202140571 


The Araucaria Project. Distances to Nine Galaxies Based on a Statistical Analysis of their Carbon Stars (JAGB Method

Bartłomiej Zgirski, Grzegorz Pietrzynski, Wolfgang Gieren, Marek Gorski, Piotr Wielgorski, Paulina Karczmarek, Fabio Bresolin, Pierre Kervella, Rolf-Peter Kudritzki, Jesper Storm, Dariusz Graczyk, Gergely Hajdu, Weronika Narloch, Bogumił Pilecki, Ksenia Suchomska and Monica Taormina

Opublikowano w: The Astrophysical Journal, Volume 916, Issue 1, id.19, 11 pp. w lipcu 2021

ublication:  The Astrophysical Journal, Volume 916, Issue 1, id.19, 11 pp.

 Pub Date:  July 2021

 DOI:  10.3847/1538-4357/ac04b2 


Extended envelopes around Galactic Cepheids V. Multi-wavelength and time-dependent analysis of IR excess

A.Gallenne, A. Mérand, P. Kervella, G. Pietrzynski, W. Gieren, V. Hocdé, L. Breuval, N. Nardetto and E. Lagadec

Publication:  Astronomy & Astrophysics, Volume 651, id.A113, 27 pp.

 Pub Date:  July 2021

 DOI:  10.1051/0004-6361/202140350 


G. Pietrzyński, D. Graczyk, A. Gallenne, W. Gieren, I. Thompson, B. Pilecki, P. Karczmarek, M. Górski, K. Suchomska, M. Taormina, B. Zgirski, P. Wielgórski, N. Nardetto, P. Kervella, F. Bresolin, R.-P. Kudritzki, J. Storm, R. Smolec, W. Narloch, M. Kałuszyński, S. Villanova, The Araucaria Project Establishes the Most Precise Benchmark for Cosmic Distances, Msngr, 179, 24 (2020), doi: 10.18727/0722-6691/5189


M. Taormina, R.-P. Kudritzki, J. Puls, B. Pilecki, E. Sextl, G. Pietrzyński, M.A. Urbaneja, W. Gieren, Towards early-type eclipsing binaries as extragalactic milestones: II. NLTE spectral analysis and stellar parameters of the detached O-type system OGLE-LMC-ECL-06782 in the LMC, ApJ, 890, 137 (2020), doi: 10.3847/1538-4357/ab6bd0


N. Nardetto, A. Salsi, D. Mourard, V. Hocdé, K. Perraut, A. Gallenne, A. Mérand, D. Graczyk, G. Pietrzynski, W. Gieren, P. Kervella, R. Ligi, A. Meilland, F. Morand, P. Stee, I. Tallon-Bosc, T. ten Brummelaar, Calibrating the surface brightness – color relation for late-type red giants stars in the visible domain using VEGA/CHARA interferometric observations, A&A, 639, A67 (2020), doi: 10.1051/0004-6361/202037679


L. Breuval, P. Kervella, R.I. Anderson, A.G. Riess, F. Arenou, B. Trahin, A. Mérand, A. Gallenne, W. Gieren, G. Pietrzyński, N. Nardetto, B. Javanmardi, V. Hocdé, The Milky Way Cepheid Leavitt law based on Gaia DR2 parallaxes of companion stars and host open cluster populations, A&A, 643, A115 (2020), doi: 10.1051/0004-6361/202038633


D. Graczyk, G. Pietrzyński, I.B. Thompson, W. Gieren, B. Zgirski, S. Villanova, M. Górski, P. Wielgórski, P. Karczmarek, W. Narloch, B. Pilecki, M. Taormina, R. Smolec, K. Suchomska, A. Gallenne, N. Nardetto, J. Storm, R.-P. Kudritzki, M. Kałuszyński, W. Pych, A Distance Determination to the Small Magellanic Cloud with an Accuracy of Better than Two Percent Based on Late-type Eclipsing Binary Stars, ApJ, 904, 13 (2020): doi: 10.3847/1538-4357/abbb2b


A. Gallenne, P. Kervella, S. Borgniet, A. Mérand, G. Pietrzyński, W. Gieren, J.D. Monnier, G.H. Schaefer, N.R. Evans, R.I. Anderson, F. Baron, R.M. Roettenbacher, P. Karczmarek, Multiplicity of Galactic Cepheids from long-baseline interferometry. IV. New detected companions from MIRC and PIONIER observations, A&A, 622A, 164 (2019), doi: 10.1051/0004-6361/201834614


M. Taormina, G. Pietrzyński, B. Pilecki, R.-P. Kudritzki, I. B. Thompson, D. Graczyk, W. Gieren, N. Nardetto, M. Górski, K. Suchomska, B. Zgirski, P. Wielgórski, P. Karczmarek, W. Narloch, Towards early-type eclipsing binaries as extragalactic milestones: I. Physical parameters of OGLE-LMC-ECL-22270 and OGLE-LMC-ECL-06782, ApJ, 886, 111 (2019), doi: 10.3847/1538-4357/ab4b57


W. Narloch, G. Pietrzyński, Z. Kołaczkowski, R. Smolec, M. Górski, K. Kubiak, A. Udalski, I. Soszyński, D. Graczyk, W. Gieren, P. Karczmarek, B. Zgirski, P. Wielgórski, K. Suchomska, B. Pilecki, M. Taormina, M. Kałuszyński, Candidates for non-pulsating stars located in the Cepheid instability strip in the Large Magellanic Cloud based on Strömgren photometry, MNRAS, 489, 3285 (2019), doi: 10.1093/mnras/stz2112


A. Gallenne, G. Pietrzyński, D. Graczyk, B. Pilecki, J. Storm, N. Nardetto, M. Taormina, W. Gieren, A. Tkachenko, P. Kervella, A. Mérand, M. Weber, The Araucaria Project: High-precision orbital parallax and masses of eclipsing binaries from infrared interferometry, A&A, 632, 31 (2019), doi: 10.1051/0004-6361/201935837


A. Gallenne, P. Kervella, N.R. Evans, C.R. Proffitt, J.D. Monnier, A. Mérand, E. Nelan, E. Winston, G. Pietrzyński, G. Schaefer, W. Gieren, R.I. Anderson, S. Borgniet, S. Kraus, R.M. Roettenbacher, F. Baron, B. Pilecki, M. Taormina, D. Graczyk, N. Mowlavi, et al., A Geometrical 1% Distance to the Short-period Binary Cepheid V1334 Cygni, ApJ, 876, 121 (2018), doi: 10.3847/1538-4357/aae373