Epsilon Cephei

Epsilon Cephei, Latinized from ε Cephei, is a star in the northern constellation of Cepheus. Based upon an annual parallax shift of 38.17 mas as seen from the Earth,[1] it is located about 85 light years from the Sun. The star is visible to the naked eye with an apparent visual magnitude of 4.18.[5]

Epsilon Cephei
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cepheus
Right ascension  22h 15m 02.19530s[1]
Declination +57° 02′ 36.8771″[1]
Apparent magnitude (V) 4.15 - 4.21[2]
Characteristics
Spectral type F0 V (Sr II)[3] or F0 IV[4]
U−B color index +0.073[5]
B−V color index +0.277[5]
Variable type δ Sct[2]
Astrometry
Radial velocity (Rv)−4.7±0.8[6] km/s
Proper motion (μ) RA: +481.53[1] mas/yr
Dec.: +46.04[1] mas/yr
Parallax (π)38.17 ± 0.97[1] mas
Distance85 ± 2 ly
(26.2 ± 0.7 pc)
Absolute magnitude (MV)+2.13[7]
Details
ε Cep Aa
Mass1.64[8] M☉
Radius1.86[9] R☉
Luminosity11.65[7] L☉
Surface gravity (log g)4.11±0.14[8] cgs
Temperature7,514±255[8] K
Metallicity [Fe/H]+0.08[7] dex
Rotational velocity (v sin i)91[10] km/s
Age1.097[8] Gyr
ε Cep Ab
Mass0.57[11] M☉
Other designations
ε Cephei, 23 Cephei, BD+56 2741, HD 211336, HIP 109857, HR 8494, SAO 34227[12]
Database references
SIMBADdata

This is a yellow-white hued, F-type star with a stellar classification of F0 V (Sr II)[3] or F0 IV.[4] Thus it may either be an F-type main sequence star showing an abundance excess of strontium, or it could be a more evolved subgiant star. It is a Delta Scuti variable star that cycles between magnitudes 4.15 and 4.21 every 59.388 minutes.[2] The star displays an infrared excess, indicating the presence of a debris disk with a temperature of 65 K orbiting at a radius of 62 AU. This dust has a combined mass equal to 6.6% of the Earth's mass.[9]

There is a faint companion star at an angular separation of 330±50 mas along a position angle of 90°±10°. This corresponds to a projected physical separation of 8.6±1.4 AU. The probability of a random star being situated this close to Epsilon Cephei is about one in a million, so it is most likely physically associated. If so, then the debris disk is probably circumbinary. The fact that this companion was not detected during the Hipparcos mission may indicate its orbit has a high eccentricity. The companion star has a K-band magnitude of 7.8 and is probably of class K8–M2.[4]

Naming

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of ε Cephei, α Lacertae, 4 Lacertae, π2 Cygni, π1 Cygni, HD 206267, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for ε Cephei itself is 螣蛇九 (Téng Shé jiǔ, English: the Ninth Star of Flying Serpent)[13]

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References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. "eps Cep", AAVSO Website, American Association of Variable Star Observers, retrieved 2017-05-07.
  3. Gray, R. O.; et al. (2001), "The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars", The Astronomical Journal, 121 (4): 2148–2158, Bibcode:2001AJ....121.2148G, doi:10.1086/319956.
  4. Mawet, D.; et al. (September 2011), "A Dim Candidate Companion to epsilon Cephei", The Astrophysical Journal Letters, 738 (1): 5, arXiv:1107.3872, Bibcode:2011ApJ...738L..12M, doi:10.1088/2041-8205/738/1/L12, L12.
  5. Breger, M. (March 1968), "UBV and narrow-band UVBY photometry of bright stars", Astronomical Journal, 73: 84–85, Bibcode:1968AJ.....73...84B, doi:10.1086/110602.
  6. Gontcharov, G. A. (2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065
  7. 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.
  8. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  9. Rhee, Joseph H.; et al. (May 2007), "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs", The Astrophysical Journal, 660 (2): 1556–1571, arXiv:astro-ph/0609555, Bibcode:2007ApJ...660.1556R, doi:10.1086/509912.
  10. Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224.
  11. De Rosa, R. J.; Patience, J.; Wilson, P. A.; Schneider, A.; Wiktorowicz, S. J.; Vigan, A.; Marois, C.; Song, I.; MacIntosh, B.; Graham, J. R.; Doyon, R.; Bessell, M. S.; Thomas, S.; Lai, O. (2013), "The VAST Survey - III. The multiplicity of A-type stars within 75 pc", Monthly Notices of the Royal Astronomical Society, 437 (2): 1216, arXiv:1311.7141, Bibcode:2014MNRAS.437.1216D, doi:10.1093/mnras/stt1932.
  12. "eps Cep -- Variable Star of delta Sct type", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-05-06.
  13. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日
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