AAS 196th Meeting, June 2000
Session 46. Binary and Variable Stars
Display, Wednesday, June 7, 2000, 10:00am-7:00pm, Empire Hall South

## [46.06] Direct Measurement of Polaris' Diameter and its Position in the Cepheid Period-Radius Plane

T. Nordgren (USNO-NPOI)

Mean angular diameters are presented for four cepheid variables measured with the Navy Prototype Optical Interferometer (NPOI). Trigonometric parallaxes measured by Hipparcos and the USNO Flagstaff Station are used to derive linear radii for \alpha Ursae Minoris (Polaris), \zeta Geminorum, \delta Cephei and \eta Aquilae. These radii are compared to those found from theoretical and empirical period-radius relations in the literature. The observed diameter of Polaris is in excellent agreement with these relations only if it is a first overtone pulsator.