R Aquilae is a variable star in the equatorial constellation of Aquila. It is located approximately 780 light years distant from the Sun based on parallax,[1] 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.
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Aquila |
Right ascension | 19h 06m 22.25105s[1] |
Declination | +08° 13′ 48.0004″[1] |
Apparent magnitude (V) | 5.3 to 12.0[2] |
Characteristics | |
Evolutionary stage | AGB[3] |
Spectral type | M5-9IIIe[2] |
U−B color index | 0.37[4] |
B−V color index | 1.60[4] |
Variable type | Mira[2] |
Astrometry | |
Radial velocity (Rv) | 34.6±0.6[5] km/s |
Proper motion (μ) | RA: +4.404[1] mas/yr Dec.: −68.042[1] mas/yr |
Parallax (π) | 4.2030 ± 0.4306 mas[1] |
Distance | approx. 780 ly (approx. 240 pc) |
Details | |
Mass | 1.0[3] M☉ |
Radius | 259±67[6] R☉ |
Luminosity | 3,470±50[3] L☉ |
Temperature | 3,000±300[3] K |
Other designations | |
Database references | |
SIMBAD | data |
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.[6] It is oxygen-rich in abundance with the same mass as the Sun but has expanded to 259[6] times the Sun's radius. On average, the star is radiating 3,470 K[3] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 3000 K or so. It is losing mass at the rate of (6 – 35) × 10−7 M☉ yr−1, forming a dusty silicate shell.[3]