Beta Delphini
|
 Location of β Delphini (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Delphinus |
| Right ascension | 20h 37m 32.94130s[1] |
| Declination | +14° 35′ 42.3195″[1] |
| Apparent magnitude (V) | 3.617 ± 0.016[2] (4.11 + 5.01)[3] |
| Characteristics | |
| Spectral type | F5 III + F5 IV[4] |
| B−V color index | A: 0.43 ± 0.14 B: 0.56 ± 0.25[1] |
| Astrometry | |
| Beta Delphini A | |
| Proper motion (μ) | RA: +118.09[1] mas/yr Dec.: -48.06[1] mas/yr |
| Parallax (π) | 32.33 ± 0.47[1] mas |
| Distance | 101 ± 1 ly (30.9 ± 0.4 pc) |
| Absolute magnitude (MV) | 1.58 ± 0.12[2] |
| Beta Delphini B | |
| Absolute magnitude (MV) | 2.79 ± 0.14[2] |
| Orbit[3] | |
| Period (P) | 26.660 yr |
| Semimajor axis (a) | 0.440″ |
| Eccentricity (e) | 0.36 |
| Inclination (i) | 61° |
| Longitude of the node (Ω) | 177° |
| Periastron epoch (T) | 1989.50 yr |
| Argument of periastron (ω) (secondary) |
349° |
| Semi-amplitude (K1) (primary) |
7.6[5] km/s |
| Details | |
| Beta Delphini A | |
| Mass | 1.75 ± 0.002[2] M☉ |
| Luminosity | 24[6] L☉ |
| Surface gravity (log g) | 3.50[6] |
| Temperature | 6,587[6] K |
| Metallicity [Fe/H] | –0.05[2] dex |
| Rotational velocity (v sin i) | 49.8[6] km/s |
| Age | 1.79+0.17 −0.72[2] Gyr |
| Beta Delphini B | |
| Mass | 1.47 ± 0.04[2] M☉ |
| Luminosity | 8[7] L☉ |
| Other designations | |
Beta Delphini (Beta Del, β Delphini, β Del) is a binary star in the constellation of Delphinus. As a practical joke, the astronomer Niccolò Cacciatore gave it the name Rotanev, which is a reversal of his Latinized family name, Venator.[10] The name first appeared in Giuseppe Piazzi‘s Palermo Catalogue, published in 1814. Beta Delphini was found to be a binary star system in 1873 by the American astronomer S. W. Burnham.[11]
In Chinese, 瓠瓜 (Hù Guā), meaning Good Gourd, refers to an asterism consisting of β Delphini, α Delphini, γ2 Delphini, δ Delphini, and ζ Delphini.[12] Consequently, β Delphini itself is known as 瓠瓜四 (Hù Guā yī, English: the Second Star of Good Gourd.)[13].
This system consists of a pair of F-type stars stars that orbit each other with a period of 26.66 years and an eccentricity of 0.36. The plane of the orbit is inclined by an angle of 61° to the line of sight from the Earth. The two stars have an angular separation of about 0.44 arcseconds, making them a challenge to resolve with a telescope. The larger member of the pair is a giant star with 1.75 times the mass[2] and 24 times the luminosity of the Sun,[6] while the secondary component is a subgiant star that has 1.47 times the Sun’s mass[2] and around 8 times the Sun’s luminosity.[7] The system is around 1.8 billion years old.[2]