We present new and precise angular diameter measurements of the long-period variable R Leonis at 833 and 903 nm. Our inferred photospheric diameter |(38 ± 2.5\ mas)| and stellar effective temperature |(2459 ± 150 \ K)| are both in good agreement with recent determinations made at the same variability phase in the near-infrared. Assuming a parallax of 8.3 mas, we derive a stellar radius of |495\ R_|. This far exceeds the range of theoretical predictions for fundamental-mode pulsation |(200 ± 50 \ R_)|, and thus requires that R Leonis pulsates in the first- or a higher overtone mode. The expected availability of high-quality parallax measurements from the Hipparcos satellite and state-of-the-art ground-based instruments suggests that similar mode identification will be possible for a dozen or more nearby Mira-type variables.
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Tuthill et al. (1994) studied this question.