Astronomy:EK Eridani

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Short description: Star in the constellation Eridanus
EK Eridani
Observation data
Equinox J2000.0]] (ICRS)
Constellation Eridanus[1]
Right ascension  04h 20m 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[2] mas/yr
Dec.: −55.192[2] mas/yr
Parallax (π)15.6213 ± 0.0236[2] mas
Distance208.8 ± 0.3 ly
(64.02 ± 0.10 pc)
Absolute magnitude (MV)2.22[1]
Details
Mass1.84±0.12[7] M☉
Radius4.96±0.14[7] R☉
Luminosity15.07±0.35[7] L☉
Surface gravity (log g)3.39±0.12[7] cgs
Temperature5,135±60[7] K
Metallicity [Fe/H]+0.02±0.04[7] dex
Rotation308.8±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
SIMBADdata

EK Eridani is a single variable star[3] in the equatorial constellation of Eridanus.[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 CVn or FK 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]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  2. ↑ 2.0 2.1 2.2 2.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  3. ↑ 3.0 3.1 3.2 3.3 Strassmeier, Klaus G. et al. (February 1990), "HR 1362: A Test Case for Stellar Dynamo Theories", Astrophysical Journal 350: 367, doi:10.1086/168390, Bibcode: 1990ApJ...350..367S. 
  4. ↑ Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey 5, Bibcode: 1999MSS...C05....0H. 
  5. ↑ 5.0 5.1 Samus', N. N et al. (2017), "General catalogue of variable stars", Astronomy Reports, GCVS 5.1 61 (1): 80, doi:10.1134/S1063772917010085, Bibcode: 2017ARep...61...80S. 
  6. ↑ 6.0 6.1 Soubiran, C. et al. (2018), "Gaia Data Release 2. The catalogue of radial velocity standard stars", Astronomy and Astrophysics 616: A7, doi:10.1051/0004-6361/201832795, Bibcode: 2018A&A...616A...7S. 
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 Bonanno, A. et al. (August 2019), "Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani", Astronomy and Astrophysics 628 (A106), doi:10.1051/0004-6361/201935834, Bibcode: 2019A&A...628A.106B. 
  8. ↑ "EK Eri". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=EK+Eri. 
  9. ↑ Lake, R. (1964), "Photoelectric Magnitudes and Colours for 100 Southern Stars (Fifth List)", Monthly Notes of the Astronomy Society of Southern Africa 23: 136, Bibcode: 1964MNSSA..23..136L. 
  10. ↑ Bidelman, W. P.; MacConnell, D. J. (October 1973), "The brighter stars astrophysical interest in the southern sky", Astronomical Journal 78: 687–733, doi:10.1086/111475, Bibcode: 1973AJ.....78..687B.  See table VII.
  11. ↑ Walter, F. M.; Bowyer, S. (April 1981), "On the coronae of rapidly rotating stars. I. The relation between rotation and coronal activity in RS CVn systems", Astrophysical Journal 245: 671–676, doi:10.1086/158842, Bibcode: 1981ApJ...245..671W. 
  12. ↑ Boyd, L. J. et al. (March 1985), "HR 1362: a Chromospherically Active Variable with a 5-month Period", Information Bulletin on Variable Stars 2696 (1), Bibcode: 1985IBVS.2696....1B. 
  13. ↑ 13.0 13.1 Stepien, K. (October 1993), "HR 1362: The Evolved 53 Camelopardalis", Astrophysical Journal 416: 368, doi:10.1086/173240, Bibcode: 1993ApJ...416..368S. 
  14. ↑ Aurière, M. et al. (November 2008), "EK Eridani: the tip of the iceberg of giants which have evolved from magnetic Ap stars", Astronomy and Astrophysics 491 (2): 499–505, doi:10.1051/0004-6361:200810502, Bibcode: 2008A&A...491..499A. 
  15. ↑ Aurière, M. et al. (October 2011), "A dominant magnetic dipole for the evolved Ap star candidate EK Eridani", Astronomy & Astrophysics 534: id. A139, doi:10.1051/0004-6361/201117502, Bibcode: 2011A&A...534A.139A. 

Further reading

  • Dall, T. H. et al. (May 2010), "Solar-like oscillations and magnetic activity of the slow rotator EK Eridani", Astronomy and Astrophysics 514: id. A25, doi:10.1051/0004-6361/200913710, Bibcode: 2010A&A...514A..25D. 
  • Dall, T. H. et al. (December 2005), "Binarity, activity and metallicity among late-type stars. I. Methodology and application to HD 27536 and HD 216803", Astronomy and Astrophysics 444 (2): 573–583, doi:10.1051/0004-6361:20053539, Bibcode: 2005A&A...444..573D. 
  • Strassmeier, K. G. et al. (March 1999), "Evolved, single, slowly rotating ... but magnetically active. The G8-giant HR 1362 = EK Eridani revisited", Astronomy and Astrophysics 343: 175–182, Bibcode: 1999A&A...343..175S. 




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