Astronomy:Epsilon Cephei

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Short description: Star in the constellation Cepheus
Epsilon Cephei
Location of ε Cephei (circled in red)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cepheus[1]
Right ascension  22h 15m 02.197s[2]
Declination +57° 02′ 36.85″[2]
Apparent magnitude (V) 4.15 to 4.21[3]
Characteristics
Evolutionary stage main sequence[2][4]
Spectral type F0 V (Sr II)[5] or F0 IV[6]
U−B color index +0.073[7]
B−V color index +0.277[7]
Variable type δ Sct[3]
Astrometry
Radial velocity (Rv)−4.7±0.8[8] km/s
Proper motion (μ) RA: +423.159[2] mas/yr
Dec.: +52.691[2] mas/yr
Parallax (π)38.1598 ± 0.2432[2] mas
Distance85.5 ± 0.5 ly
(26.2 ± 0.2 pc)
Absolute magnitude (MV)+2.13[1]
Details
ε Cep Aa
Mass1.64[9] M☉
Radius1.86[10] R☉
Luminosity11.65[1] L☉
Surface gravity (log g)4.11±0.14[9] cgs
Temperature7,514±255[9] K
Metallicity [Fe/H]+0.08[1] dex
Rotational velocity (v sin i)91[11] km/s
Age1.097[9] Gyr
ε Cep Ab
Mass0.57[12] M☉
Other designations
ε Cephei, 23 Cephei, BD+56 2741, HD 211336, HIP 109857, HR 8494, SAO 34227[13]
Database references
SIMBADdata

Epsilon Cephei is a star in the northern constellation of Cepheus. Its name is a Bayer designation that is Latinized from ε Cephei, and abbreviated Epsilon Cep or ε Cep. Based upon an annual parallax shift of 38.16 mas as seen from the Earth,[14] it is located about 85.5 light-years (26.2 pc) from the Sun. The star is visible to the naked eye with an apparent visual magnitude that varies around 4.18.[7]

Properties

Physical characteristics

A visual band light curve for Epsilon Cephei, adapted from Bruntt et al. (2007)[15]

This is a yellow-white hued, F-type star with a stellar classification of F0 V (Sr II)[5] or F0 IV.[6] 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.[3] 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.[10]

Binary

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.[6]

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).[16]

References

  1. ↑ 1.0 1.1 1.2 1.3 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A.  XHIP record for this object at VizieR.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 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 "eps Cep", AAVSO Website (American Association of Variable Star Observers), https://www.aavso.org/vsx/index.php?view=detail.top&oid=9067, retrieved 2017-05-07. 
  4. ↑ Zorec, J.; Royer, F. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy and Astrophysics 537: A120. doi:10.1051/0004-6361/201117691. Bibcode: 2012A&A...537A.120Z. 
  5. ↑ 5.0 5.1 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, doi:10.1086/319956, Bibcode: 2001AJ....121.2148G. 
  6. ↑ 6.0 6.1 6.2 Mawet, D. et al. (September 2011), "A Dim Candidate Companion to epsilon Cephei", The Astrophysical Journal Letters 738 (1): 5, doi:10.1088/2041-8205/738/1/L12, L12, Bibcode: 2011ApJ...738L..12M. 
  7. ↑ 7.0 7.1 7.2 Breger, M. (March 1968), "UBV and narrow-band UVBY photometry of bright stars", Astronomical Journal 73: 84–85, doi:10.1086/110602, Bibcode: 1968AJ.....73...84B. 
  8. ↑ Gontcharov, G. A. (2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters 32 (11): 759–771, doi:10.1134/S1063773706110065, Bibcode: 2006AstL...32..759G 
  9. ↑ 9.0 9.1 9.2 9.3 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, doi:10.1088/0004-637X/804/2/146, Bibcode: 2015ApJ...804..146D. 
  10. ↑ 10.0 10.1 Rhee, Joseph H. et al. (May 2007), "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs", The Astrophysical Journal 660 (2): 1556–1571, doi:10.1086/509912, Bibcode: 2007ApJ...660.1556R. 
  11. ↑ Royer, F. et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics 463 (2): 671–682, doi:10.1051/0004-6361:20065224, Bibcode: 2007A&A...463..671R. 
  12. ↑ De Rosa, R. J. et al. (2013), "The VAST Survey - III. The multiplicity of A-type stars within 75 pc", Monthly Notices of the Royal Astronomical Society 437 (2): 1216, doi:10.1093/mnras/stt1932, Bibcode: 2014MNRAS.437.1216D. 
  13. ↑ "eps Cep". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=eps+Cep. 
  14. ↑ van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V. 
  15. ↑ Bruntt, H. et al. (January 2007), "Asteroseismology with the WIRE satellite I. Combining ground- and space-based photometry of the δ Scuti star ɛ Cephei", Astronomy and Astrophysics 461 (2): 619–630, doi:10.1051/0004-6361:20065766, Bibcode: 2007A&A...461..619B. 
  16. ↑ Script error: The function "in_lang" does not exist. 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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