CAMK
At the present moment (December 2024) all the positions in CAMK are filled.
The team achieved a very important step the calibration of the surface brightness – colour relation based on eclipsing binaries for stars with a wide range of spectral types. This calibration will be extensively used in the following years to measure geometrical distances. We also calibrated P-L relations for several different types of pulsating stars in several passbands. We also dedicated a lot of efforts in writing applications for observing time and preparations for observations with our own telescopes at Rolf Chini Cerro Murphy Observatory (OCM) in Chile (formerly known as the Cerro Armazones Observatory (OCA)). These preparations include new software for planning and executing observations which will significantly improve both the quantity and quality of the data.
OBP PARIS
The research progress has been satisfactory at Paris Observatory over the second reporting period. The recruitment of the PhD student Mrs Garance Bras (working on pulsating RR Lyrae stars and Cepheids) and the post-doctoral researcher Dr Anton Afanasyev (working on distance determination of SN Ia galaxies) went smoothly. This however took slightly more time than initially planned, as they started their contracts in October and November 2022, respectively. Their work has progressed very well. In October 2024, Mrs Wilma Kiviaho joined us for her PhD thesis focused on the precise measurement of the interstellar extinction of Cepheids of the Milky Way, in preparation of the Gaia DR4 publication that will occur in early 2026.. Over the reporting period, the collaboration within the UniverScale project with our Polish and Chilean colleagues has been vibrant, with many shared publications on various topics related to the distance scale. On 2-6 September 2024, we organized the UniverScale/Araucaria collaboration meeting at Paris Observatory, with 30 participants. This meeting was very fruitful, with the launch of several new collaborative projects.
UDEC
Our team at Universidad de Concepcion consisting of Professor Wolfgang Gieren and postdoctoral fellows Paulina Karczmarek, Weronika Narloch and Bartlomiej Zgirski has mainly focused on pulsating stellar distance indicators (classical and Type II Cepheids, RR Lyrae stars) with the goal to improve their usefulness for distance measurement to the sub-percent level as aimed for by the UniverScale project. From synthetic population studies of classical Cepheids we could show that binarity among classical Cepheids has basically a vanishing influence on near-infrared Cepheid period-luminosity relations. Another important achievement was the publication of the first Cepheid period-luminosity relations measured in the Sloan photometric bands. Using the most recent Gaia parallaxes we improved the IRSB (Infrared Surface Brightness) implementation of the Baade-Wesselink method to yield the distances to RR Lyrae stars and Type II Cepheid variables.
CFT & HITS
In the current reporting period, our activity related to the application of Active Galactic Nuclei (AGN) in cosmology has been on developing of the appropriate methodology. This effort is pivotal, addressing the challenge set forth in 1998: using quasar continuum time delays for determining the Hubble constant, a goal not yet achieved. Collaboratively, the CFT and HITS have been engaging in critical modelling and simulations. These are preparatory steps for an upcoming survey at the Cerro Murphy Observatory (OCM). The impact of the stratification of the BLR and dust content has been studied in papers 26,27, and 31. Beyond the traditional time delay estimation methods like the Interpolated Cross-Correlation Function (ICCF) and Chi-squared minimization (Chi2), we've innovated an optimized ICCF approach. This novel method integrates Gaussian processes with a cross-validation technique to estimate delays (paper 14).
We are currently refining our simulation processes and testing a wider range of parameters for different object types to better quantify the uncertainties in our simulations. We tested the prospects of the use of massive data from LSST for line delay measurements (paper 34, 49), and tested the currently available BLR delays for cosmology (paper 41, 47, 48). We also worked on the theoretical aspects of the BLR model, which is essential for the final goal (paper 42, 43, 44, 45, 46). The last few months have brought a significant breakthrough in out attempts to disentangle the accretion disk and DCE. It was achieved so far in the case of an object NGC 5548 which was monitored not by our group, but an international team using the best available spece-based and ground-based instruments (SWIFT, HST, ground telescopes). This allowed us to determine the redshift-independent distance to the source, and subsequently, the value of the Hubble constant based just on this single source. (
https://arxiv.org/pdf/2410.03597(s’ouvre dans une nouvelle fenêtre)). This comprehensive approach is essential to effectively analyse the data that will soon be collected at OCM.
