Diameters of δ Cephei and η Aquilae Measured with the Navy Prototype Optical Interferometer
Hajian, Arsen R.; Hummel, C. A.; Germain, M. E.; Mozurkewich, D.; Armstrong, J. T.; Thessin, R. N.; Nordgren, Tyler E.; Hindsley, R. B.
United States
Abstract
We have measured the diameters of the Cepheid variables δ Cephei (18 nights) and η Aquilae (11 nights) with the Navy Prototype Optical Interferometer. The primary results of these observations are the mean angular diameters <θLD> of these Cepheids: 1.520+/-0.014 milliseconds of arc (mas) for δ Cep and 1.69+/-0.04 mas for η Aql. We also report limb-darkened diameters for the check stars in this program: for β Lac, θLD=1.909+/-0.011 mas and for 12 Aql, θLD=2.418+/-0.010 mas. When combined with radius estimates from period-radius relations in the literature, the Cepheid angular diameters suggest distances slightly smaller than, but still consistent with, the Hipparcos distances. Pulsations are weakly detected at a level of ~1.5 to 2 σ for both Cepheids.