R Apodis (HD 131109; HR 5540; 18 G. Apodis) is a solitary star[9] in the constellation Apus. It is faintly visible to the naked eye as an orange-hued point of light with an apparent magnitude of 5.36.[2] Parallax measurements imply a distance of 413 light-years[1] and it is drifting closer with a heliocentric radial velocity of −31.2 km/s.[6] At its current distance, R Apodis' brightness is diminished by an interstellar extinction of 0.26 magnitudes[10] and it has an absolute magnitude of −0.22.[7]
HD 131109 was the first star observed to be variable in the constellation; It was first discovered in 1873 by Benjamin Apthorp Gould. Later, it was hastily given the variable star designation R Apodis in a 1907 variable star catalogue despite it being a suspected variable star at the time.[11] However, observations conducted in a 1952 field star survey revealed that R Apodis was not variable at all.[12] Keenan & Pitts (1980) found that it varied between magnitudes 5.5 and 6.1, but this was never confirmed.[13] Hipparcos photometric data revealed that R Apodis indeed had a constant brightness.[14] It has since been listed as a class CST: in the General Catalog of Variable Stars.[5]
R Apodis has a stellar classification of K4 III:,[3] indicating that it is an evolved K-type giant that has ceased hydrogen fusion at its core and left the main sequence. However, there is uncertainty about the luminosity class. It has a comparable mass to the Sun at 1.1 solar masses but, at the age of 5.68 billion years, it has expanded to 23 times the radius of the Sun.[6] It radiates 293 times the luminosity of the Sun[1] from its enlarged photosphere at an effective temperature of 4,318 K.[6] R Apodis is metal deficient with an iron abundance roughly half of the Sun's[6] and it spins slowly with a projected rotational velocity lower than 1.3 km/s.[15]