Astronomy:EK Eridani

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Short description: Star in the constellation Eridanus
EK Eridani
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A visual band light curve for EK Eridani, adapted from Dall et al. (2010)[1]
Observation data
Equinox J2000.0]] (ICRS)
Constellation Eridanus[2]
Right ascension  04h 20m 38.642s[3]
Declination −06° 14′ 45.58″[3]
Apparent magnitude (V) 6.08 to 6.42[4]
Characteristics
Spectral type G8 IV-III[5] or K0 III[6]
B−V color index 0.901±0.002[2]
Variable type BY Dra[7]
Astrometry
Radial velocity (Rv)6.866±0.0002[8] km/s
Proper motion (μ) RA: +92.020[3] mas/yr
Dec.: −55.192[3] mas/yr
Parallax (π)15.6213 ± 0.0236[3] mas
Distance208.8 ± 0.3 ly
(64.02 ± 0.10 pc)
Absolute magnitude (MV)2.22[2]
Details
Mass1.84±0.12[9] M☉
Radius4.96±0.14[9] R☉
Luminosity15.07±0.35[9] L☉
Surface gravity (log g)3.39±0.12[9] cgs
Temperature5,135±60[9] K
Metallicity [Fe/H]+0.02±0.04[9] dex
Rotation308.8±2.5 d [9]
Rotational velocity (v sin i)< 1.6±0.4[9] km/s
Other designations
EK Eri, NSV 1563, BD−06° 875, GC 5264, HD 27536, HIP 20263, HR 1362, SAO 131129, PPM 186813[10]
Database references
SIMBADdata

EK Eridani is a single variable star[5] 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 between 6.1 and 6.4 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.[8]

From South Africa in 1964, R. Lake reported a variation of 0.7 in the visual magnitude of this star.[11] 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.[12] F. M. Walter and S. Bowyer detected X-ray emission from this star in 1973, another indicator of magnetic activity in the chromosphere.[13] 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.[14] By 1990, this period was revised upward to 335 days.[5]

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.[5] 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.[15] 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.[16]

This is an evolving subgiant star with a very slow rotation period of 308.8 days.[9] It is classified as a BY Draconis variable[7] that changes in luminosity as star spots rotate across the visible surface of the star.[9] 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.[17] 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.[9]

See also

References

  1. ↑ Dall, T. H.; Bruntt, H.; Stello, D.; Strassmeier, K. G. (May 2010). "Solar-like oscillations and magnetic activity of the slow rotator EK Eridani". Astronomy and Astrophysics 514: A25. doi:10.1051/0004-6361/200913710. Bibcode: 2010A&A...514A..25D. https://www.aanda.org/articles/aa/pdf/2010/06/aa13710-09.pdf. Retrieved 21 September 2024. 
  2. ↑ 2.0 2.1 2.2 2.3 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  3. ↑ 3.0 3.1 3.2 3.3 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.
  4. ↑ "EK Eri". AAVSO. https://vsx.aavso.org/index.php?view=detail.top&oid=14135. 
  5. ↑ 5.0 5.1 5.2 5.3 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. 
  6. ↑ Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey 5, Bibcode: 1999MSS...C05....0H. 
  7. ↑ 7.0 7.1 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. 
  8. ↑ 8.0 8.1 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. 
  9. ↑ 9.00 9.01 9.02 9.03 9.04 9.05 9.06 9.07 9.08 9.09 9.10 Bonanno, A. et al. (August 2019), "Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani", Astronomy and Astrophysics 628 (A106): A106, doi:10.1051/0004-6361/201935834, Bibcode: 2019A&A...628A.106B. 
  10. ↑ "EK Eri". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=EK+Eri. 
  11. ↑ 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. 
  12. ↑ 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.
  13. ↑ 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. 
  14. ↑ 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): 1, Bibcode: 1985IBVS.2696....1B. 
  15. ↑ 15.0 15.1 Stepien, K. (October 1993), "HR 1362: The Evolved 53 Camelopardalis", Astrophysical Journal 416: 368, doi:10.1086/173240, Bibcode: 1993ApJ...416..368S. 
  16. ↑ 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. 
  17. ↑ 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. (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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