| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Eridanus[1] |
| Right ascension | 04h20m 38.642s[2] |
| Declination | −06° 14′ 45.58″[2] |
| Apparent magnitude (V) | 6.15[1] |
| Characteristics | |
| Spectral type | G8 IV-III[3] or K0 III[4] |
| B−V color index | 0.901±0.002[1] |
| Variable type | BY Dra[5] |
| Astrometry | |
| Radial velocity (Rv) | 6.866±0.0002[6] km/s |
| Proper motion (μ) | RA: +92.020 mas/yr[2] Dec.: −55.192 mas/yr[2] |
| Parallax (π) | 15.6213 ± 0.0236 mas[2] |
| Distance | 208.8 ± 0.3 ly (64.02 ± 0.10 pc) |
| Absolute magnitude (MV) | 2.22[1] |
| Details | |
| Mass | 1.84±0.12[7] M☉ |
| Radius | 4.96±0.14[7] R☉ |
| Luminosity | 15.07±0.35[7] L☉ |
| Surface gravity (log g) | 3.39±0.12[7] cgs |
| Temperature | 5,135±60[7] K |
| Metallicity [Fe/H] | +0.02±0.04[7] dex |
| Rotation | 308.8±2.5 d [7] |
| Rotational velocity (v sin i) | < 1.6±0.4[7] km/s |
| Other designations | |
EK Eri, NSV 1563, BD−06° 875, GC 5264, HD 27536, HIP 20263, HR 1362, SAO 131129, PPM 186813[8] | |
| Database references | |
| SIMBAD | data |
EK Eridani is a single variable star[3] in the equatorial constellationofEridanus.[1] It has the designation HR 1362 from the Bright Star Catalogue; EK Eridani is the variable star designation, abbreviated EK Eri. This star is dimly visible to the naked eye with a brightness that fluctuates around 6.15.[1] Based on parallax measurements, it is located at a distance of 209 light years from the Sun. The star is drifting further away with a heliocentric radial velocity of 6.9 km/s.[6]
From South Africa in 1964, R. Lake reported a variation of 0.7 in the visual magnitude of this star.[9] In 1973, W. P. Bidelman and D. J. MacConnell placed HR 1362 on a list of brighter stars of astrophysical interest because it displayed emission in the H and K lines, although they were uncertain of this finding.[10] F. M. Walter and S. Bowyer detected X-ray emission from this star in 1973, another indicator of magnetic activity in the chromosphere.[11] A series of measurements of the brightness of this star were made from 1979 until 1984, demonstrating it is variable with a 154-day period. At the time, this was the longest period known for a chromospherically active star.[12] By 1990, this period was revised upward to 335 days.[3]
K. G. Strassmeier and associates found the stellar spectrum and color indices to be consistent with a stellar classification of G8 III-IV for HR 1362. They confirmed the moderately strong H and K emission lines as being overactive by over an order of magnitude compared to other cool giant stars.[3] The level of magnetic activity for this star is unusually high for its rotation period, which in 1993 led K. Stępień to suggest it was a strongly magnetic Ap star while on the main sequence.[13] The mean strength of the magnetic field was determined to be 270 Gauss, which is comparable to the typical field strength of RS CVnorFK Com type variable stars.[14]
This is an evolving subgiant star with a very slow rotation period of 308.8 days.[7] It is classified as a BY Draconis variable[5] that changes in luminosity as star spots rotate across the visible surface of the star.[7] The lingering magnetic field may be the result of an interaction between the remnant field from an Ap progenitor star and a deep convection zone. At a 60° axial tilt, the field can be successfully modeled as a simple dipole magnet with a persistent cool spot at the magnetic pole.[15] Asteroseismological measurements show EK Eri has 1.84 times the mass of the Sun and 5 times the Sun's radius. It is radiating 15 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 5,135 K.[7]
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