Back to Volume
Paper: Towards Precise and Accurate Cepheid Chemical Abundances for a 1% H0 Measurement: Temperature Determination
Volume: 529, RR Lyrae/Cepheid 2019: Frontiers of Classical Pulsators
Page: 265
Authors: Mancino, S.; Romaniello, M.; Anderson, R. I.; Kudritzki, R.
Abstract: One of the outstanding problems in modern physics is the origin of the accelerated expansion of the Universe. High-precision determinations of the Hubble parameter at different redshifts provide direct insight into the Universe expansion: equation of state of the Dark Energy, geometry and curvature of space, sum of neutrino masses, and isotropy of the Universe. We investigate the effect of chemical composition on the classical distance ladder based on Cepheid stars and supernovae type Ia. Cepheids belonging to Magellanic Clouds (MCs) represent a natural anchor for the ladder, due to their proximity and the very well-known geometric distance. Accordingly, the LACES collaboration collected the largest spectroscopic sample of MC Cepheids, containing more than 300 stars and more than 1200 medium-high resolution spectra. Abundance measurements, performed by equivalent width and curve of growth analysis, have been tested on a wide grid of synthetic spectra to quantify the systematics arising from this procedure. We focus on the errors arising from temperature measurements, using the Line Depth Ratio method. We find that in order to not bias the final results, many aspects (e.g. degeneracy of the atmospheric parameters, instrumental set up, etc.) should be explicitly taken into account. In particular, there is a non-negligible metallicity dependence.
Back to Volume