EK Eridani

EK Eridani

A visual band light curve for EK Eridani, adapted from Dall et al. (2010)[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Eridanus[2]
Right ascension 04h 20m 38.642s[3]
Declination −06° 14′ 45.58″[3]
Apparent magnitude (V) 6.15[2]
Characteristics
Spectral type G8 IV-III[4] or K0 III[5]
B−V color index 0.901±0.002[2]
Variable type BY Dra[6]
Astrometry
Radial velocity (Rv)6.866±0.0002[7] km/s
Proper motion (μ) RA: +92.020 mas/yr[3]
Dec.: −55.192 mas/yr[3]
Parallax (π)15.6213 ± 0.0236 mas[3]
Distance208.8 ± 0.3 ly
(64.02 ± 0.10 pc)
Absolute magnitude (MV)2.22[2]
Details
Mass1.84±0.12[8] M☉
Radius4.96±0.14[8] R☉
Luminosity15.07±0.35[8] L☉
Surface gravity (log g)3.39±0.12[8] cgs
Temperature5,135±60[8] K
Metallicity [Fe/H]+0.02±0.04[8] dex
Rotation308.8±2.5 d [8]
Rotational velocity (v sin i)< 1.6±0.4[8] km/s
Other designations
EK Eri, NSV 1563, BD−06° 875, GC 5264, HD 27536, HIP 20263, HR 1362, SAO 131129, PPM 186813[9]
Database references
SIMBADdata

EK Eridani is a single variable star[4] in the equatorial constellation of Eridanus.[2] 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.[2] 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.[7]

From South Africa in 1964, R. Lake reported a variation of 0.7 in the visual magnitude of this star.[10] 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.[11] F. M. Walter and S. Bowyer detected X-ray emission from this star in 1973, another indicator of magnetic activity in the chromosphere.[12] 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.[13] By 1990, this period was revised upward to 335 days.[4]

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.[4] 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.[14] The mean strength of the magnetic field was determined to be 270 Gauss, which is comparable to the typical field strength of RS CVn or FK Com type variable stars.[15]

This is an evolving subgiant star with a very slow rotation period of 308.8 days.[8] It is classified as a BY Draconis variable[6] that changes in luminosity as star spots rotate across the visible surface of the star.[8] 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.[16] 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.[8]

  1. ^ Cite error: The named reference Dall was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference Anderson_Francis_2012 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference GaiaDR3 was invoked but never defined (see the help page).
  4. ^ a b c d Cite error: The named reference Strassmeier_et_al_1990 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Houk_Swift_1999 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Samus_et_al_2017 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Soubiran_et_al_2018 was invoked but never defined (see the help page).
  8. ^ a b c d e f g h i j k Cite error: The named reference Bonanno_et_al_2019 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Lake_1964 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Bidelman_MacConnell_1973 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Walter_Bowyer_1981 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Boyd_et_al_1985 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Stepien_1993 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Aurière_et_al_2008 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Aurière_et_al_2011 was invoked but never defined (see the help page).