δ Velorum consists of aneclipsing binary, designated Delta Velorum A, and a more distant third companion, Delta Velorum B. δ Velorum A's two components are themselves designated Aa (officially namedAlsephina/ælsɪˈfaɪnə/, the traditional name for the entire system) and Ab.
Delta Velorum bore the traditional nameAlsafinah, which stems from theArabic nameal-safīnah meaning "the ship", referring to theancient Greek constellationArgo Navis, the ship of theArgonauts. It was first used in a 10th-century Arabic translation of theAlmagest, written by the Greek astronomerPtolemy in the second century AD. Although the name originally referred to an entire constellation, it was assigned to this particular bright star at least as early as 1660, when it appeared inAndreas Cellarius's renownedHarmonia Macrocosmica, a magnificently illustrated 17th-centuryDutch book about thecosmos.[12] In 2016, the IAU organized aWorking Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entiremultiple systems.[14] It approved the nameAlsephina for the component δ Velorum Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[15]
InChinese,天社 (Tiān Shè), meaningCelestial Earth God's Temple, refers to an asterism consisting of Delta Velorum,Gamma2 Velorum, Kappa Velorum andb Velorum.[17] Consequently, Delta Velorum itself is known as天社三 (Tiān Shè sān), "the Third Star of Celestial Earth God's Temple".[18] In a different Chinese view, this star appears in an asterism with the given name ofKoo She (Chinese: 弧矢, hú shǐ, "Bow and Arrow"), comprising Delta Velorum,Omega Carinae and stars fromCanis Major.[19]
Relative positions and separations of components A, B, C and D of δ Velorum
Delta Velorum is a triple star system. The outer components, δ Velorum A and B, have a wide orbit with a 143-yearperiod. The primary component A has anapparent magnitude of 2.00, while the secondary B is magnitude 5.54, with a combined magnitude measured at 1.96.[20] As of 2013, the two stars were separated by 0.6", but they have an eccentric orbit and their average separation over the whole orbit is nearly 2".[7]
A white-lightlight curve for Delta Velorum, adapted from Pribullaet al. (2011)[10]
In 2000 it was announced that the inner components Aa and Ab form aneclipsing binary, having an orbital period of 45.15 days and aneccentricity of 0.230.[10] Thesemi-major axis as their orbit corresponds to a mean separation of90.61 R☉.[22] Observations of variability in the Delta Velorum system were made independently by ground-based astronomers and theGalileo spaceprobe atJupiter.[21] The inner pair were resolved usinginterferometry in 2007, and then usingNACOadaptive optics with theVery Large Telescope. Photometry of the components of δ Velorum A gives apparentvisual magnitudes of 2.33 and 3.44.[3] The precise orbits allow adynamical parallax of39.8±0.4 mas to be derived, representing a distance of 25.1 parsecs.[7]
Another binary system is located at anangular separation of 69arcseconds from δ Velorum, sometimes referred to as δ Velorum C and D. The pair is composed of an 11th-magnitude star and a 13th-magnitude star, which are 6 arcseconds apart. The two stars, with approximatespectral types of G8V and K0V, are expected to be more distant than δ Velorum and not physically associated.[23]
HD 76653 is a probable (96% chance) co-moving companion; the two have an estimated physical separation of 2.2 ly (0.6605 pc) with similarproper motions.[24] Both are likely members of theUrsa Major Moving Group.[25]
The brightnesses of the three stars have been measured at visual andinfrared wavelengths using adaptive optics. The physical properties implied by theirsurface brightnesses andcolour indices suggests spectral types of A2IV, A4V and F8V, respectively.[3]
More precise physical properties for the stars can be calculated using accurate orbital parameters. Both members of the spectroscopic binary Delta Velorum A are slightlyevolved stars that are still on themain sequence. Component Aa has 2.5 times themass of the Sun, 2.6 times theSun's radius, and is radiating 56 times theluminosity of the Sun at aneffective temperature of9,470 K. Component Ab is only slightly smaller, with 2.4 times the Sun's mass and radius, with a luminosity of 47 times the Sun and an effective temperature of 9,370 K.[10]
Both stars are rotating rapidly and are significantlyoblate, with polar radii smaller than their equatorial radii.Gravity darkening results in their effective temperatures at the pole being higher. For component Aa, the polar radius and temperature are 2.79 R☉ and 10,100 K, respectively, while the equatorial radius and temperature are 2.97 R☉ and 9,700 K, respectively. For component Ab, the corresponding polar values are 2.37 R☉ and 10,120 K, and the equatorial values are 2.52 R☉ and 9,560 K.[7] This results in the star being brighter when seen along their axes of rotation and less bright when observed at their equators. From Earth, the pair is observed nearly equatorially and the absolute visual magnitude is +0.02; from a different direction the absolute magnitude would be −0.138 or less.[10]
Delta Velorum B is a smallermain-sequence star, with a mass of about 1.4 M☉, a temperature of 6,600 K, a radius of 1.43 R☉, and a bolometric luminosity of 3.5 L☉.[7]
^abJohnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars".Communications of the Lunar and Planetary Laboratory.4 (99): 99.Bibcode:1966CoLPL...4...99J.
^Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)".VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S.1: 02025.Bibcode:2009yCat....102025S.
^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets".arXiv:1012.0707 [astro-ph.SR].
^Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)".VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H.5050: 0.Bibcode:1995yCat.5050....0H.
^abOtero, Fieseler & Lloyd; Fieseler, Paul D.; Lloyd, Christopher (2000). "Delta Velorum is an Eclipsing Binary".Information Bulletin on Variable Stars.4999. IBVS 4999: 1.Bibcode:2000IBVS.4999....1O.
^Eker, Z; Bilir, S; Soydugan, F; Gökçe, E. Yaz; Soydugan, E; Tüysüz, M; Şenyüz, T; Demircan, O (2014). "The Catalogue of Stellar Parameters from the Detached Double-Lined Eclipsing Binaries in the Milky Way".Publications of the Astronomical Society of Australia.31 e024.arXiv:1403.1583.Bibcode:2014PASA...31...24E.doi:10.1017/pasa.2014.17.S2CID119238300.
