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Type II Cepheids as stellar tracers and distance indicators

Type II Cepheids are both useful distance indicators and tracers of old age stellar populations in their host galaxy. We summarize near-infrared observations of type II Cepheids in the Large Magellanic Cloud and discuss the absolute calibration of their Period-Luminosity relations. Combining with the near-infrared data for type II Cepheids in the Galactic bulge from the VISTA VVV survey, we estimated a robust distance to the Galactic center. We found that type II Cepheids trace the spherically symmetric spatial distribution with possible evidence of ellipsoidal structure, similar to RR Lyrae stars. Together with Gaia and VVV proper motions, type II Cepheids were found to trace the old, metal-poor, kinematically hot stellar populations in the Galactic bulge.