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R Aquilae

R Aquilae is a variable star in the equatorial constellationofAquila. It is located approximately 760 light years distant from the Sun^[6] and is drifting further away with a radial velocity of 35 km/s.^[5] This is a thermally-pulsating Mira variable that ranges in brightness from 5.3 down to 12.0 with a period of 269.84 days.^[2][7] The period was over 300 days when first observed, and has declined steadily since – decreasing from 320 in 1915 down to 264 in 2010, at an average rate of 0.4 days per year. The amplitude of the variation has also decreased by about a magnitude since discovery.^[8] The peak magnitude is bright enough for the star to be visible to the naked eye as a dim, red-hued star.

R Aquilae is an aging red giant on the asymptotic giant branch^[3] with a stellar classification that varies over time, between M5e and M9e,^[2] where the 'e' suffix indicates emission features in the spectrum. The cooler spectral types occur near the minimum visual magnitude, and the hottest near maximum.^[9] The star may have recently undergone a helium flash.^[10] It is oxygen-rich in abundance with the same mass as the Sun but has expanded to 275^[6] times the Sun's radius. On average, the star is radiating 3,470^[3] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 2,800 K or so.^[6] It is losing mass at the rate of (6 – 35) × 10⁻⁷ M_☉yr⁻¹, forming a dusty silicate shell.^[3]