Direct measurements of stellar radii regardless of other fundamental properties are a complex issue of observational astrophysics. The number of stars available for these measurements is limited due to small angular sizes of disks and also to technical and methodological difficulties. The radii considerably vary for different types of stars and are unique for objects of a certain type.

The diameter of the M giant IRC+00213 was measured at the 6-m BTA telescope of the Special Astrophysical Observatory of RAS with the method of lunar occultations. Observations were carried out in the night of April 25-26, 2018 with the speckle interferometer at the 6-m BTA telescope in the pseudo-continuum region at a wavelength of 694 nm. This region of the visible spectrum is sparsely populated with titanium-oxide molecular bands typical of such kind of stars. This shows that the obtained value is close to photospheric. The measured angular diameter from a model of a uniformly luminous disk yielded 2,23 ± 0,06 millisecond of arc. It agrees well with an empirical estimate of 2,14 ± 0,13 millisecond of arc based on magnitude and color (van Belle, 1999).

Published:
Dyachenko V., Richichi A., Balega Y., Beskakotov A., Maksimov A., Mitrofanova A., & Rastegaev D. (2018) recently noticed such a dependence. Lunar occultation observations at the SAO RAS 6-m telescope. Monthly Notices of the Royal Astronomical Society, 478(4), pp. 5683-5688