Beta Delphini

Beta Delphini

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Beta Delphini

Diagram showing star positions and boundaries of the Delphinus constellation and its surroundings

Cercle rouge 100%.svg

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]
Spectral type F5 III + F5 IV[4]
B−V color index A: 0.43 ± 0.14
B: 0.56 ± 0.25[1]
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]
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)
Semi-amplitude (K1)
7.6[5] km/s
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
Rotanev, Rotanen, Venator, β Del, Beta Delphini, Beta Del, 6 Delphini, 6 Del, BD+14 4369, HD 196524, HIP 101769, HR 7882, SAO 106316, WDS 20375+1436AB.[8][9][10]

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]

See also