arXiv subjects

Bastian Lengen

Publications and source records attributed to Bastian Lengen.

4 recordsLinked to original sources

arXiv2026

A 1% distance to the Large Magellanic Cloud measured by population-II pulsating stars using Gaia Data Release 3

Population-II pulsating stars provide a route to extragalactic distances that is independent of the classical Cepheid distance scale and complementary to geometric and tip-of-the-red-giant-branch (TRGB) methods. We apply optical Wesenheit Leavitt laws for RR Lyrae and type II Cepheid stars calibrated with Gaia DR3 data and anchored by homogeneous globular-cluster distances based on trigonometric parallaxes to variable stars in the Large Magellanic Cloud (LMC). We adopt RRab stars as the baseline tracer because they define the absolute zero point of the calibration, dominate the LMC sample, and provide robust classifications. The uncertainty budget propagates the full covariance matrix of the calibration parameters, treating calibration uncertainties as correlated systematics rather than independent star-by-star errors. Using 12,193 RRab stars after outlier rejection, we determine mu_LMC = 18.423 +/- 0.002 (stat) +/- 0.020 (syst) mag. This combines the statistical uncertainty on the mean and the systematic uncertainty of the absolute calibration, which currently limits the total precision. Our result is lower than the detached-eclipsing-binary benchmark by 0.054 mag, corresponding to an approximately 1.7 sigma offset, and agrees with the TRGB distance obtained from the same globular-cluster scale to within 0.024 mag. RRc and T2Cep stars provide useful consistency checks, although the relative RRc-RRab and T2Cep-RRab offsets measured in the LMC differ from those calibrated in globular clusters. Geometric corrections between tracer barycenters and external reference positions are below 0.003 mag. Individual RRab distances map the three-dimensional structure of the LMC across a broad 10-degree-radius field. A planar model reproduces the dominant distance gradient and yields i = 21.3 +/- 0.7 deg and Theta = 145.2 +/- 2.2 deg, in agreement with previous determinations.

astro-ph.GA↗

arXiv2026

Calibrating the Tip of the Red Giant Branch and measuring Magellanic Cloud distances to 2% exclusively with Gaia

We have calibrated the Tip of the Red Giant Branch (TRGB) using our recent catalog of homogeneous, high-accuracy Globular Cluster (GC) distances. The GC distances were determined by a global joint fit to optical period-Wesenheit relations of their member RR Lyrae stars and type-II Cepheids, anchored by trigonometric parallaxes; all data taken from the ESA Gaia mission's (early) third data release (GDR3). Using I-band measurements in 48 GCs from P. Stetson's database, we determined $M_{I,0} = -3.948^{+0.037}_{-0.034}$ mag (1.6% in distance). Calibrating the TRGB using Gaia's homogeneous, space-based RP photometry of 53 GCs, we found $M_{RP,0} = -3.807^{+0.041}_{-0.035}$ mag (1.8%). The stated uncertainties include statistical and systematic effects, including the correlated nature of the GC distances. The robustness of our calibrations is demonstrated via tests against small-number statistics and analysis choices. Specifically, we found no significant metallicity effect for our sample of old, low-metallicity GCs. We measured $\sim 2\%$ distances to the Large (LMC) and Small Magellanic Clouds (SMC), $18.447^{+0.036}_{-0.042}$ mag ($48.9 \pm 0.9$ kpc) and $18.898^{+0.049}_{-0.054}$ mag ($60.2 \pm 1.4$ kpc), respectively, using a single well calibrated photometric system: RP (spectro-)photometry from GDR3. Our new TRGB distances, whose absolute scale derives from Gaia parallaxes, are fully independent of the well-known detached eclipsing binary (DEB) distances and agree with them to within the uncertainties. Combining our new TRGB and existing DEB distances, we illustrate how additional constraints may be incorporated in the Local Distance Network and obtain $H_0 = 73.52 \pm 0.80$ km/s/Mpc. Expected improvements due to the upcoming fourth Gaia data release are discussed.

astro-ph.SR↗

arXiv2025

The Local Distance Network: a community consensus report on the measurement of the Hubble constant at 1% precision

The direct, empirical determination of the local value of the Hubble constant (H0) has markedly advanced thanks to improved instrumentation, measurement techniques, and distance estimators. However, combining determinations from different estimators is non-trivial, due to correlated calibrations and different analysis methodologies. Using covariance weighting and leveraging the broad and comprehensive community of experts, we constructed a rigorous and transparent Distance Network (DN) to find a consensus value and uncertainty for the local H0. All critically reviewed the available data sets, spanning parallaxes, detached eclipsing binaries, masers, Cepheids, the TRGB, Miras, JAGB stars, SN Ia, Surface Brightness Fluctuations, SN II, the Fundamental Plane, and Tully-Fisher relations and voted for indicators to define a `baseline' DN and others to assess robustness and sensitivity of the results. We provide open-source software and data products to support full transparency and future extensions of this effort. Our conclusions: 1) Local H0 is robustly determined, with first-rank indicators internally consistent within their uncertainties; 2) A covariance-weighted combination yields an uncertainty of 1.1% (baseline) or 0.9% (all estimators); 3) The contribution from SNe Ia is consistent across four current compilations of optical magnitudes or using NIR-only magnitudes; 4) Removing either Cepheids or TRGB has minimal effect; 5) Replacing SNe Ia with galaxy-based indicators changes H0 by less than 0.1 km/s/Mpc, while doubling its uncertainty; 6) The baseline result is H0=73.50+/-0.81 km/s/Mpc. Compared to early Universe results, our result differs by 7.1sigma from flat ΛCDM with Planck+SPT+ACT and 5.0 sigma with BBN+BAO (DESI2). A networked approach is invaluable for enabling further progress in accuracy and precision without overreliance on any single method, sample or group.

astro-ph.CO↗

arXiv2025

A joint 1% calibration of the RR Lyrae & type-II Cepheid Leavitt laws yields homogeneous distances to 93 Galactic globular clusters

Recent work has established large samples of astrometrically confirmed RR Lyrae and type-II Cepheid members of Galactic globular clusters (GCs). Any given GC can contain multiple such stars at once, notably RR Lyrae stars pulsating in the fundamental mode (RRab) or the first overtone (RRc), and type-II Cepheids (T2Cep) of BL Her and W Vir types. Here, we present the first joint calibration of the Leavitt laws (LLs) exhibited by 802 RRab, 345 RRc, and 21 T2Cep stars anchored to trigonometric parallaxes. Using the third data release of the ESA Gaia mission (GDR3), we have calibrated the intercepts of the RRab and RRc Leavitt laws in the reddening-free Gaia Wesenheit magnitude to better than 1.0% in distance, and that of T2Cep to 1.3%, using a global fit to all data. The absolute scale is set by 37 nearby GCs with high-accuracy parallaxes while 56 additional GCs provide constraints on LL slopes as well as the LL intercept differences of RRc and T2Cep relative to RRab stars. Our global fit yields homogeneous high-accuracy distances of 93 GCs that show no evidence of bias for Gaia parallaxes of distant GCs. Control of systematics was demonstrated by 31 alternative fit variants, notably involving different treatments of metallicity effects, as well as by Markov Chain Monte Carlo analysis. Our results suggest that photometric metallicities of RR Lyrae stars require further improvements while also exhibiting possible signs of intra-cluster chemical inhomogeneity. This work lays the foundation for exploiting RRab, RRc, and T2Cep stars as high-accuracy standard candles for near-field cosmology and the extragalactic distance scale.

astro-ph.SR↗