No fundamental-mode pulsation in R Leonis ?

Abstract

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_sun. This far exceeds the range of theoretical predictions for fundamental-mode pulsation (200+50 R_sun), 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.