 A visual band light curve for EK Eridani, adapted from Dall et al. (2010) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Eridanus |
| Right ascension | 04 20 38.642 |
| Declination | −06° 14′ 45.58″ |
| Apparent magnitude (V) | 6.15 |
| Characteristics | |
| Spectral type | G8 IV-III or K0 III |
| B−V color index | 0.901±0.002 |
| Variable type | BY Dra |
| Astrometry | |
| Radial velocity (Rv) | 6.866±0.0002 km/s |
| Proper motion (μ) | RA: +92.020 mas/yr Dec.: −55.192 mas/yr |
| Parallax (π) | 15.6213 ± 0.0236 mas |
| Distance | 208.8 ± 0.3 ly (64.02 ± 0.10 pc) |
| Absolute magnitude (MV) | 2.22 |
| Details | |
| Mass | 1.84±0.12 M☉ |
| Radius | 4.96±0.14 R☉ |
| Luminosity | 15.07±0.35 L☉ |
| Surface gravity (log g) | 3.39±0.12 cgs |
| Temperature | 5,135±60 K |
| Metallicity | +0.02±0.04 dex |
| Rotation | 308.8±2.5 d |
| Rotational velocity (v sin i) | < 1.6±0.4 km/s |
| Other designations | |
| EK Eri, NSV 1563, BD−06° 875, GC 5264, HD 27536, HIP 20263, HR 1362, SAO 131129, PPM 186813 | |
| Database references | |
| SIMBAD | data |
EK Eridani is a single variable star in the equatorial constellation of Eridanus. 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. 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.
From South Africa in 1964, R. Lake reported a variation of 0.7 in the visual magnitude of this star. 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. F. M. Walter and S. Bowyer detected X-ray emission from this star in 1973, another indicator of magnetic activity in the chromosphere. 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. By 1990, this period was revised upward to 335 days.
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. 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. 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.
This is an evolving subgiant star with a very slow rotation period of 308.8 days. It is classified as a BY Draconis variable that changes in luminosity as star spots rotate across the visible surface of the star. 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. 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.
See also
- 53 Camelopardalis – a star with properties similar to the EK Eri progenitor.
References
- Dall, T. H.; Bruntt, H.; Stello, D.; Strassmeier, K. G. (May 2010). "Solar-like oscillations and magnetic activity of the slow rotator EK Eridani" (PDF). Astronomy and Astrophysics. 514: A25. Bibcode:2010A&A...514A..25D. doi:10.1051/0004-6361/200913710. Retrieved 21 September 2024.
- ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
- ^ Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ Strassmeier, Klaus G.; et al. (February 1990), "HR 1362: A Test Case for Stellar Dynamo Theories", Astrophysical Journal, 350: 367, Bibcode:1990ApJ...350..367S, doi:10.1086/168390.
- Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
- ^ Samus', N. N; et al. (2017), "General catalogue of variable stars", Astronomy Reports, GCVS 5.1, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
- ^ Soubiran, C.; et al. (2018), "Gaia Data Release 2. The catalogue of radial velocity standard stars", Astronomy and Astrophysics, 616: A7, arXiv:1804.09370, Bibcode:2018A&A...616A...7S, doi:10.1051/0004-6361/201832795, S2CID 52952408.
- ^ Bonanno, A.; et al. (August 2019), "Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani", Astronomy and Astrophysics, 628 (A106), arXiv:1907.01338, Bibcode:2019A&A...628A.106B, doi:10.1051/0004-6361/201935834.
- "EK Eri", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2024-01-15.
- 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.
- Bidelman, W. P.; MacConnell, D. J. (October 1973), "The brighter stars astrophysical interest in the southern sky", Astronomical Journal, 78: 687–733, Bibcode:1973AJ.....78..687B, doi:10.1086/111475. See table VII.
- 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, Bibcode:1981ApJ...245..671W, doi:10.1086/158842.
- 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.
- ^ Stepien, K. (October 1993), "HR 1362: The Evolved 53 Camelopardalis", Astrophysical Journal, 416: 368, Bibcode:1993ApJ...416..368S, doi:10.1086/173240.
- 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, arXiv:0810.2228, Bibcode:2008A&A...491..499A, doi:10.1051/0004-6361:200810502.
- Aurière, M.; et al. (October 2011), "A dominant magnetic dipole for the evolved Ap star candidate EK Eridani", Astronomy & Astrophysics, 534, id. A139, arXiv:1109.5570, Bibcode:2011A&A...534A.139A, doi:10.1051/0004-6361/201117502.
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, arXiv:astro-ph/0508577, Bibcode:2005A&A...444..573D, doi:10.1051/0004-6361:20053539.
- 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.
