Alpha Fornacis
Star in the constellation Fornax From Wikipedia, the free encyclopedia
Star in the constellation Fornax From Wikipedia, the free encyclopedia
Alpha Fornacis (α Fornacis, abbreviated Alpha For, α For) is a triple star[12] system in the southern constellation of Fornax. It is the brightest star in the constellation and the only one brighter than magnitude 4.0. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 46 light-years (14 parsecs) distant from the Sun.
Location of α Fornacis (upper left). | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Fornax |
| Right ascension | 3h 12m 04.5277s[1] |
| Declination | –28° 59′ 15.425″[1] |
| Apparent magnitude (V) | 3.85[2] (3.98/7.19)[3] |
| Characteristics | |
| Spectral type | F8IV[4] |
| U−B color index | +0.082[5] |
| B−V color index | +0.581[5] |
| Astrometry | |
| Radial velocity (Rv) | –20.5[6] km/s |
| Proper motion (μ) | RA: 371.49[1] mas/yr Dec.: 612.28[1] mas/yr |
| Parallax (π) | 71.4337 ± 0.1320 mas[7] |
| Distance | 45.66 ± 0.08 ly (14.00 ± 0.03 pc) |
| Absolute magnitude (MV) | 3.08[8] |
| Orbit[3] | |
| Period (P) | 269 yr |
| Semi-major axis (a) | 4.0″ |
| Eccentricity (e) | 0.73 |
| Inclination (i) | 81° |
| Longitude of the node (Ω) | 117° |
| Periastron epoch (T) | 1947 |
| Argument of periastron (ω) (secondary) | 43° |
| Details | |
| α For A | |
| Mass | 1.33 ± 0.01[9] M☉ |
| Radius | 2.04 ± 0.06[10] R☉ |
| Luminosity | 4.87 ± 0.16[10] L☉ |
| Surface gravity (log g) | 4.27[9] cgs |
| Temperature | 6,240[9] K |
| Metallicity [Fe/H] | –0.20[9] dex |
| Rotational velocity (v sin i) | 3.9[10] km/s |
| Age | 2.9[11] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Its three components are designated Alpha Fornacis A (officially named Dalim /ˈdeɪlɪm/),[13] Alpha Fornacis Ba and Alpha Fornacis Bb.
α Fornacis (Latinised to Alpha Fornacis) is the system's Bayer designation. The designations of the three components as Alpha Fornacis A, Ba and Bb derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[14] Formerly it was designated as the 12th of Eridanus (12 Eri) by Flamsteed.[15]
Indigenous Arabs had named both Alpha Eridani and Fomalhaut ظَلِيم al-ẓalīm, a local word for 'ostrich'. Later, Arabian astronomer would transfer the appellation to Theta Eridani, as they could not see those other stars from their location.[16] In recent times, Italian astronomer Giuseppe Piazzi applied it with the spelling Dalim to his "III 13" (= α For) in his Palermo Catalogue,[17][18][19] and Elijah Burritt labeled it Fornacis in his Atlas.[20]
In 2016, the IAU organized a Working Group on Star Names (WGSN)[21] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[22] It approved the name Dalim for the component Alpha Fornacis A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[13]
Alpha Fornacis has a high proper motion[2] and the system displays an excess of infrared emission, which may indicate the presence of circumstellar material such as a debris disk.[23] The space velocity components of this star are (U, V, W) = (−35, +20, +30) km/s.[24] Approximately 350,000 years ago, Alpha Fornacis experienced a close encounter with the A-type main-sequence star Nu Horologii. The two came within an estimated 0.265 ly (0.081 pc) of each other, and both stars have debris disks.[25]
Alpha Fornacis A has a stellar classification of F8IV, where the luminosity class IV indicates this is a subgiant star that has just evolved off the main sequence.[26] It has 33% more mass than the Sun and is an estimated 2.9 billion years old.[9][11]
The secondary, Alpha Fornacis B, has been identified as a blue straggler, and has likely accumulated material from a third star in the past. It is a strong source of X-rays and is 78% as massive as the Sun.[27] Such a third star, designated Alpha Fornacis Bb, was detected in 2016. Alpha Fornacis Ba is enriched in barium relative to star A, suggesting that its companion is likely a white dwarf.[12]
