40 Eridani
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Eridanus |
| 40 Eridani A | |
| Right ascension | 04h 15m 16.320s |
| Declination | −07° 39′ 10.34″ |
| Apparent magnitude (V) | 4.43 |
| 40 Eridani B | |
| Right ascension | 04h 15m 21.786s |
| Declination | −07° 39′ 29.22″ |
| Apparent magnitude (V) | 9.52 |
| 40 Eridani C | |
| Right ascension | 04h 15m 21.50s |
| Declination | −07° 39′ 22.3″ |
| Apparent magnitude (V) | 11.17 |
| Characteristics | |
| Spectral type | K1V / DA4 / M4.5eV |
| U−B color index | 0.45 / -0.68 / 0.83 |
| B−V color index | 0.82 / 0.03 / 1.67 |
| Astrometry | |
| Radial velocity (Rv) | -43.0 / ? / -46 km/s |
| Proper motion (μ) |
RA: -2239.72 / -2228.3 / -2237 mas/yr Dec.: -3420.35 / -3377.1 / -3411 mas/yr |
| Parallax (π) | 198.26±0.84mas |
| Distance | 16.45±0.07 ly (5.04±0.02 pc) |
| Absolute magnitude (MV) | 5.92 / 11.01 / 12.66 |
| Orbit | |
| Companion | 40 Eridani BC |
| Period (P) | ~8,000yr |
| Semi-major axis (a) | ~400AU |
| Orbit | |
| Companion | 40 Eridani C |
| Period (P) | 252.1yr |
| Semi-major axis (a) | ~35AU |
| Eccentricity (e) | 0.410 |
| Inclination (i) | 108.9° |
| Longitude of the node (Ω) | 150.9° |
| Periastron epoch (T) | 1849.6 |
|
Argument of periastron (ω) (secondary) |
327.8° |
| Details | |
| A | |
| Mass | 0.84 M☉ |
| Radius | 0.81 R☉ |
| Luminosity | 0.46 L☉ |
| Temperature | 5,300 K |
| Metallicity [Fe/H] | −0.19 dex |
| B | |
| Mass | 0.50 M☉ |
| Radius | 0.014 R☉ |
| Luminosity | 0.013 L☉ |
| Temperature | 16,500 K |
| C | |
| Mass | 0.20 M☉ |
| Radius | 0.31 R☉ |
| Luminosity | 0.008 L☉ |
| Temperature | 3,100 K |
| Age | 5.6 Gyr |
| Other designations | |
| A: HD 26965, HIP 19849, HR 1325, LHS 23, LTT 1907, SAO 131063, BD-07° 780 | |
| B: BD-07° 781, G 160-060, HD 26976, LHS 24, LTT 1908, SAO 131065 | |
| C: DY Eri, BD-07°781 C, LHS 25, LTT 1909 | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
| C | |
40 Eridani (abbreviated 40 Eri), also designated Omicron² Eridani (ο² Eridani, abbreviated Omicron² Eri, ο² Eri) is a triple star system less than 16.5 light years away from Earth, in the constellation of Eridanus.
The primary star of the system, designated 40 Eridani A, also named Keid, is easily visible to the naked eye. It is orbited by a binary system whose two components are designated 40 Eridani B and C, and which were discovered on January 31, 1783, by William Herschel., p. 73 It was again observed by Friedrich Struve in 1825 and by Otto Struve in 1851.
In 1910, it was discovered that although component B was a faint star, it was white in color. This meant that it had to be a small star; in fact it was a white dwarf, the first discovered. Although it is neither the closest white dwarf, nor the brightest in the night sky, it is by far the easiest to observe; it is nearly three magnitudes brighter than Van Maanen's Star (the nearest solitary white dwarf), and unlike the companions of Procyon and Sirius it is not swamped in the glare of a much brighter primary.
40 Eridani is the system's Flamsteed designation and ο² Eridani (Latinised to Omicron² Eridani) its Bayer designation. The designations of the sub-components - 40 Eridani A, B and C - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).40 Eridani C also bears the variable star designation DY Eridani.
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