66 Eridani
Star in the constellation Eridanus
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66 Eridani is a binary star in the constellation of Eridanus. The combined apparent magnitude of the system is 5.12 on average.[2] Parallax measurements by Hipparcos put the system at some 309 light-years (95 parsecs) away.[1] It lies half a degree northwest of beta Eridani.[9]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Eridanus |
| Right ascension | 05h 06m 45.65314s[1] |
| Declination | −04° 39′ 18.5939″[1] |
| Apparent magnitude (V) | 5.12[2] |
| Characteristics | |
| Evolutionary stage | main sequence[3] |
| Spectral type | B9V[4] |
| U−B color index | −0.16[5] |
| B−V color index | −0.06[5] |
| Variable type | α2 CVn?[6] |
| Astrometry | |
| Radial velocity (Rv) | 32.28±0.10[7] km/s |
| Proper motion (μ) | RA: +10.70[1] mas/yr Dec.: −0.78[1] mas/yr |
| Parallax (π) | 10.56±0.34 mas[1] |
| Distance | 309 ± 10 ly (95 ± 3 pc) |
| Absolute magnitude (MV) | 0.37[8] |
| Orbit[7] | |
| Period (P) | 5.5226013 ± 0.0000020 d |
| Eccentricity (e) | 0.0844±0.0013 |
| Periastron epoch (T) | 2441356.499±0.017 |
| Argument of periastron (ω) (secondary) | 160.9±1.1° |
| Semi-amplitude (K1) (primary) | 102.83±0.20 km/s |
| Semi-amplitude (K2) (secondary) | 100.35±0.19 km/s |
| Details[7] | |
| 66 Eri A | |
| Mass | 2.629±0.032 M☉ |
| Radius | 1.948±0.063 R☉ |
| Luminosity | 51.3±3.3 L☉ |
| Surface gravity (log g) | 4.28±0.03 cgs |
| Temperature | 11,077 K |
| Rotational velocity (v sin i) | 17.1±0.2 km/s |
| Age | 30 Myr |
| 66 Eri B | |
| Mass | 2.566±0.032 M☉ |
| Radius | 1.919±0.061 R☉ |
| Luminosity | 46.9±3.0 L☉ |
| Surface gravity (log g) | 4.28±0.03 cgs |
| Temperature | 10,914 K |
| Rotational velocity (v sin i) | 16.9±0.2 km/s |
| Other designations | |
| EN Eri, BD−04°1044, HD 32964, HIP 23794, HR 1657, SAO 131777[9] | |
| Database references | |
| SIMBAD | data |
This is a spectroscopic binary: the two stars cannot be individually resolved, but periodic Doppler shifts in its spectrum mean there must be orbital motion. The two stars orbit each other every 5.5 days.[7] Their orbit is fairly circular, with an eccentricity of 0.0844.[7]
The combined spectrum of 66 Eridani matches that of a B-type main-sequence star,[4] and the two stars have similar masses.[7] The spectrum also shows excess of mercury and manganese, as it is a type of chemically peculiar star called a mercury-manganese star.[7] 66 Eridani is an Alpha2 Canum Venaticorum variable. For this reason, it has been given the designation EN Eridani.