Epoch J2000.0 Equinox J2000.0
|Right ascension||20h 39m 38.28720s|
|Declination||+15° 54′ 43.4637″|
|Apparent magnitude (V)||+3.777 (3.86 + 6.43)|
|Spectral type||B9 IV|
|U−B color index||−0.205|
|B−V color index||−0.061|
|Radial velocity (Rv)||−3.40 km/s|
|Proper motion (μ)||RA: 53.82 ± 0.43 mas/yr
Dec.: 8.47 ± 0.31 mas/yr
|Parallax (π)||12.85 ± 0.44 mas|
|Distance||254 ± 9 ly
(78 ± 3 pc)
|Absolute magnitude (MV)||−0.4|
|Period (P)||17.0 yr|
|Semi-major axis (a)||0.158″|
|α Del Aa|
|Surface gravity (log g)||3.93 cgs|
|Rotational velocity (v sin i)||144 km/s|
It bore an historical name, Sualocin, which arose as follows: Niccolò Cacciatore was the assistant to Giuseppe Piazzi, and later his successor as Director of the Palermo Observatory. The name first appeared in Piazzi's Palermo Star Catalogue. When the Catalogue was published in 1814, the unfamiliar names Sualocin and Rotanev were attached to Alpha and Beta Delphini, respectively. Eventually the Reverend Thomas Webb, a British astronomer, puzzled out the explanation. Cacciatore's name, Nicholas Hunter in English translation, would be Latinized to Nicolaus Venator. Reversing the letters of this construction produces the two star names. They have endured, the result of Cacciatore's little practical joke of naming the two stars after himself. How Webb arrived at this explanation 45 years after the publication of the catalogue is still a mystery.
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Sualocin for Alpha Delphini on 12 September 2016 and it is now so entered in the IAU Catalog of Star Names.
In Chinese, 瓠瓜 (Hù Guā), meaning Good Gourd, refers to an asterism consisting of Alpha Delphini, Gamma2 Delphini, Delta Delphini, Beta Delphini and Zeta Delphini. Consequently, Alpha Delphini itself is known as 瓠瓜一 (Hù Guā yī, English: the First Star of Good Gourd.).
α Delphini is a spectroscopic binary star which has now been resolved using speckle interferometry. The components are referred to as Aa and Ab, or sometimes as A and G. They are separated by 0.2" and have a 17 year orbit.
In addition, there are five faint listed in multiple star catalogues. They have visual magnitudes around 11th to 13th magnitude and separations of 35" to 72". They all show motion relative to α Delphini A and are likely to be only optical companions.
α Delphini Aa has a spectral type of B9IV. The spectral type of the secondary star cannot be determined as it is too close and too faint compared to the primary, and its other properties are also unknown. The primary is a subgiant that has begun to evolve away from the main sequence. It is 2.82 times as massive as the sun and about twice as hot.
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