Figures & data
Note: The underlying image comes from the UV space telescope Galaxy Evolution Explorer (GALEX [Citation9])
Note: The underlying image comes from the infrared space telescope Wide-field Infrared Survey Explorer (WISE, [Citation23])
Note: The two boundaries are R[mag] = 25 – 3log and R[mag] = 32.2 – 6log, separating the variables into classical Cepheids (left), population II Cepheids (middle) and LPVs (right) in the period-luminosity plot.
Note: The Cepheids light curve amplitude is relatively small in the infrared than in the optical band, so even random-phased photometry yields very clean PL relation.