Presentation #414.05 in the session Cosmology III.
Gaia’s Early Data Release 3 (EDR3) represents a significant advancement in precision astrometry. The overall accuracy of the parallaxes in this catalog has been further improved by a detailed quantification of the correlation of the parallax bias with the color, magnitude, and ecliptic latitude of individual sources. However, for sources at the extreme ends of the magnitude and color range observed by Gaia, the value of this bias is more uncertain. Further, all EDR3 parallaxes have a minimum systematic error floor of 10 microarcseconds, which prevents distance measurements to most individual sources at the 1% level of accuracy. Given these issues, it is important to cross check independent distance measurements to the stars used in setting the calibration of the extragalactic distance scale. We focus on the Cepheid variable stars. We combine photometry of open clusters from Gaia in the optical with photometry from the Magellan Baade FourStar instrument in the near-infrared. We use main sequence fitting of these data to determine the distances to individual classical Cepheids hosted in these open clusters. We calibrate multi-wavelength period-luminosity relations from the optical to mid-infrared, using existing well-sampled photometry of the Cepheids. A detailed comparison of the precision and accuracy of the parallaxes and main-sequence fitting methods will be presented.