Lambda Aquarii
Lambda Aquarii, informally known as Hydor (/ˈhaɪdɔːr/), is a variable star in the equatorial constellation of Aquarius. The name is Latinized from the Bayer designation λ Aquarii. The apparent visual magnitude of this star ranges from 3.57 down to 3.80, which is bright enough to be visible with the naked eye. It lies just 0.39 degrees south of the ecliptic and so is subject to lunar occultations. The star is eclipsed by the sun from about 1-4 March; thus the star can be viewed the whole night, crossing the sky, in early September, in the current epoch. Lambda Aquarii is located at a distance of approximately 310 light-years (95 pc) from the Sun based on parallax, but is drifting closer with a radial velocity of −10.5 km/s.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 52m 36.87723s |
| Declination | −07° 34′ 46.5830″ |
| Apparent magnitude (V) | 3.722 (3.57 to 3.80) |
| Characteristics | |
| Evolutionary stage | AGB |
| Spectral type | M2.5 IIIa Fe–1 |
| U−B color index | +1.721 |
| B−V color index | +1.641 |
| Variable type | Lb |
| Astrometry | |
| Radial velocity (Rv) | −10.46±0.53 km/s |
| Proper motion (μ) | RA: +11.806 mas/yr Dec.: +34.967 mas/yr |
| Parallax (π) | 8.9360 ± 0.2356 mas |
| Distance | 365 ± 10 ly (112 ± 3 pc) |
| Absolute magnitude (MV) | −1.5 |
| Details | |
| Mass | 3.6 M☉ |
| Radius | 44.10+21.14 −13.20 R☉ |
| Luminosity | 698.5±41.5 L☉ |
| Temperature | 3,835 K |
| Metallicity [Fe/H] | −2.25 dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
The stellar classification of Lambda Aquarii is M2.5 IIIa Fe–1, indicating this is an aging red giant star with an underabundance of iron showing in its spectrum. This star is on the asymptotic giant branch and is generating energy through the nuclear fusion of hydrogen and helium along concentric shells surrounding an inert core of carbon and oxygen. With 3.6 times the mass of the Sun, it has expanded to 44 times the Sun's radius. It is classified as slow irregular variable and pulsation periods of 24.5, 32.0, and 49.5 days have been identified. On average, it is radiating nearly 700 times the luminosity of the Sun from the photosphere at an effective temperature of 3,835 K.