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Are the Ultra Long Period Cepheids cosmological standard candles?
Musella I., Marconi M., De Somma G., Molinaro R., Leccia S., Ripepi V., Fiorentino G.
Ultra Long Period Cepheids are becoming a very interesting and important topic thanks to the contribution they can give to understanding the current tension existing between the early-universe and local Hubble constant measurements. These bright pulsating variables are hypothesized to be the counterparts at higher luminosity and mass of the Classical Cepheids. They are observable up to cosmological distances (larger than 100 Mpc) allowing us, in principle, to measure the Hubble constant without the need for secondary indicators, thus reducing the possible systematic errors in the calibration of the extragalactic distance scale. In this paper, the largest known ULP sample, including new possible candidates, is analyzed to give an observational and theoretical overview of their role as distance indicators and of their evolutionary properties.