Delta Aquilae
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Star δ Aquilae |
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| Aquila constellation | |||||||||||||||||
| AladinLite | |||||||||||||||||
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| Constellation | Eagle | ||||||||||||||||
| Right ascension | 19 h 25 m 29.9 s | ||||||||||||||||
| declination | + 03 ° 06 ′ 53.2 ″ | ||||||||||||||||
| Apparent brightness | 3.36 mag | ||||||||||||||||
| Typing | |||||||||||||||||
| B − V color index | +0.32 | ||||||||||||||||
| U − B color index | +0.04 | ||||||||||||||||
| R − I index | +0.16 | ||||||||||||||||
| Spectral class | F0 IV | ||||||||||||||||
| Astrometry | |||||||||||||||||
| Radial velocity | (−34.0 ± 0.2) km / s | ||||||||||||||||
| parallax | (64.41 ± 1.00) mas | ||||||||||||||||
| distance | (50.64 ± 0.79) ly (15.53 ± 0.24) pc |
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| Visual absolute brightness M vis | +2.40 mag | ||||||||||||||||
| Proper movement | |||||||||||||||||
| Rec. Share: | (254.54 ± 1.19) mas / a | ||||||||||||||||
| Dec. portion: | (82.51 ± 0.77) mas / a | ||||||||||||||||
| Physical Properties | |||||||||||||||||
| Dimensions | 1.65 M ☉ | ||||||||||||||||
| radius | 1.5 R ☉ | ||||||||||||||||
| Luminosity |
8.2 L ☉ |
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| Effective temperature | 7600 K | ||||||||||||||||
| Rotation time | <0.9 days | ||||||||||||||||
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Other names and catalog entries |
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Delta Aquilae (δ Aql) is the fifth brightest star in the constellation Eagle . Together with Eta Aquilae and Theta Aquilae , it forms a chain of stars , which the Arabs called al-Mizān . Delta Aquilae used to belong to the constellation Antinous , which was abolished in 1800 and which was introduced in ancient times to honor the Roman emperor Hadrian 's favorite of the same name, who died young .
Delta Aquilae has an apparent magnitude of 3.40 mag and is a relatively close star at a distance of 50 light years . It is classified as a sub-giant of the spectral class F0, but in contradiction to this, calculations using stellar evolution models show that it has only spent a little more than half of its lifespan on the main sequence and will therefore be a dwarf star for a long time .
More changeable with little companions?
Delta Aquilae may be a multiple star . Variations in its spectrum suggested that it was a spectroscopic binary star with a period of only 3.77 hours. However, according to recent research, these variations seem to be caused by minor pulsations. According to this, Delta Aquilae could be a pulsation variable of the Delta Scuti type , which, however, has only very small fluctuations in brightness of 0.003 mag.
In addition, Delta Aquilae was thought to be an astrometric binary star ; ie the companion is not visible in telescopes, but its existence can only be inferred from regular oscillations of the main star's own motion . The companion is expected to orbit Delta Aquilae in 3.422 years and a distance of 0.9 AU . However, since these figures cannot be reconciled with the calculated mass of Delta Aquilae, the existence of this small companion is doubtful.
Finally, star catalogs show another faint companion of 10.9 mag at an angular distance of 108.9 "to Delta Aquilae. But since it was observed that the two stars diverged another 14 "from each other within 81 years and this value is far too high for a gravitational bond, it is only an optical double star : both stars are only seen from Earth coincidentally close together, but in reality far behind each other.