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R Apodis (HD 131109; HR 5540; 18 G. Apodis) is a solitary star 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. Parallax measurements imply a distance of 413 light-years and it is drifting closer with a heliocentric radial velocity of −31.2 km/s. At its current distance, R Apodis' brightness is diminished by an interstellar extinction of 0.26 magnitudes and it has an absolute magnitude of −0.22.

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. However, observations conducted in a 1952 field star survey revealed that R Apodis was not variable at all. Keenan & Pitts (1980) found that it varied between magnitudes 5.5 and 6.1, but this was never confirmed. Hipparcos photometric data revealed that R Apodis indeed had a constant brightness. It has since been listed as a class CST: in the General Catalog of Variable Stars.

R Apodis has a stellar classification of K4 III:, 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. It radiates 293 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,318 K. R Apodis is metal deficient with an iron abundance roughly half of the Sun's and it spins slowly with a projected rotational velocity lower than 1.3 km/s.

References

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v t e Constellation of Apus
Apus in Chinese astronomy List of stars in Apus
Stars	Bayer α β γ δ ε ζ η θ ι κ κ Variable R (not variable) S Z MY NN NO HR 5240 5279 5306 5327 5389 5520 5547 5555 5628 5757 5786 5955 6135 6357 6373 6635 6646 6731 6751 HD 128294 129899 131664 134606 137366 137388 (Karaka) 141846 152010 Other Godzilla star
Star clusters	NGC 6101 Other IC 4499
Nebulae Hen 2-131
Galaxies Sunburst galaxy
Category

• Henry Draper Catalogue objects
• Apus
• K-type giants
• Objects with variable star designations
• Bright Star Catalogue objects
• Hipparcos objects
• Durchmusterung objects
• 2MASS objects
• IRAS catalogue objects