We present K ^ { \prime } -band observations of five Mira stars with the IOTA interferometer .
The interferograms were obtained with the FLUOR fiber optics beam combiner , which provides high-accuracy visibility measurements in spite of time-variable atmospheric conditions .
For the M-type Miras X Oph , R Aql , RU Her , R Ser , and the C-type Mira V CrB we derived the uniform-disk diameters 11.7 mas , 10.9 mas , 8.4 mas , 8.1 mas , and 7.9 mas ( \pm 0.3 mas ) , respectively .
Simultaneous photometric observations yielded the bolometric fluxes .
The derived angular Rosseland radii and the bolometric fluxes allowed the determination of effective temperatures .
For instance , the effective temperature of R Aql was determined to be 2970 \pm 110 K. A linear Rosseland radius for R Aql of 250 ^ { +100 } _ { -60 } R _ { \odot } was derived from the angular Rosseland radius of 5.5 mas \pm 0.2 mas and the HIPPARCOS parallax of 4.73 mas \pm 1.19 mas .
The observations were compared with theoretical Mira star models of Bessel et al .
( 3 ) and Hofmann et al .
( 11 ) .
The effective temperatures of the M-type Miras and the linear radius of R Aql indicate fundamental mode pulsation .