Epsilon Cephei

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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) 4.18[2]
Characteristics
Spectral type F0 V (Sr II)[3] or F0 IV[4]
U−B color index +0.073[2]
B−V color index +0.277[2]
Variable type δ Sct[5]
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
Distance 85 ± 2 ly
(26.2 ± 0.7 pc)
Details
ε Cep Aa
Mass 1.64[7] M
Radius 1.86[8] R
Surface gravity (log g) 4.11±0.14[7] cgs
Temperature 7,514±255[7] K
Rotational velocity (v sin i) 91[9] km/s
Age 1.097[7] Gyr
ε Cep Ab
Mass 0.57[10] M
Radius ~0.7[8] R
Temperature 3650[8] K
Other designations
ε Cep, 23 Cep, BD+56° 2741, HD 211336, HIP 109857, HR 8494, SAO 34227[11]
Database references
SIMBAD data

Epsilon Cephei (ε Cephei, ε Cep) 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.[2]

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.[5] 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.[8]

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[edit]

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, ε Cephei itself is known as 螣蛇九 (Téng Shé jiǔ, English: the Ninth Star of Flying Serpent)[12]

References[edit]

  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d 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. 
  3. ^ a b 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. ^ a b c Mawet, D.; et al. (September 2011), "A Dim Candidate Companion to epsilon Cephei", The Astrophysical Journal Letters, 738 (1): 5, Bibcode:2011ApJ...738L..12M, doi:10.1088/2041-8205/738/1/L12, L12. 
  5. ^ a b "eps Cep", AAVSO Website, American Association of Variable Star Observers, retrieved 2017-05-07. 
  6. ^ Gontcharov, G. A. (2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065 
  7. ^ a b c d 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, Bibcode:2015ApJ...804..146D, arXiv:1501.03154Freely accessible, doi:10.1088/0004-637X/804/2/146. 
  8. ^ a b c d Rhee, Joseph H.; et al. (May 2007), "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs", The Astrophysical Journal, 660 (2): 1556–1571, Bibcode:2007ApJ...660.1556R, arXiv:astro-ph/0609555Freely accessible, doi:10.1086/509912. 
  9. ^ Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, Bibcode:2007A&A...463..671R, arXiv:astro-ph/0610785Freely accessible, doi:10.1051/0004-6361:20065224. 
  10. ^ 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, Bibcode:2014MNRAS.437.1216D, arXiv:1311.7141Freely accessible, doi:10.1093/mnras/stt1932. 
  11. ^ "eps Cep -- Variable Star of delta Sct type", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-05-06. 
  12. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日