Astronomy:Epsilon Cassiopeiae

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Short description: Star in the constellation Cassiopeia
Epsilon Cassiopeiae
Cassiopeia constellation map.png
Red circle.svg
Location of ε Cas (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cassiopeia
Right ascension  01h 54m 23.73409s[1]
Declination +63° 40′ 12.3602″[1]
Apparent magnitude (V) 3.37[2]
Characteristics
Spectral type B3 V[3]
U−B color index −0.62[2]
B−V color index −0.15[2]
Variable type Periodic[4]
Astrometry
Radial velocity (Rv)−8.1[5] km/s
Proper motion (μ) RA: +29.587[1] mas/yr
Dec.: −18.387[1] mas/yr
Parallax (π)7.0037 ± 0.1599[1] mas
Distance470 ± 10 ly
(143 ± 3 pc)
Absolute magnitude (MV)−2.19[6]
Details
Mass9.2±0.2[7] M☉
Radius6.10±0.06[1] R☉
Luminosity3,059[1] L☉
Surface gravity (log g)3.5[8] cgs
Temperature15,174[8] K
Metallicity [Fe/H]−0.28[1] dex
Rotational velocity (v sin i)30[9] km/s
Age15.4±3.0[7] Myr
Other designations
Database references
SIMBADdata

Epsilon Cassiopeiae or ε Cassiopeiae, officially named Segin (/ˈsɛɡɪn/),[10][11] is a single[12] star in the northern constellation of Cassiopeia. With an apparent visual magnitude of 3.4, this is one of the brightest stars in the constellation. The distance to this star has been determined directly using parallax measurements, yielding a value of around 460–430 light-years (140–130 parsecs) from the Sun. It is drifting closer with a radial velocity of −8 km/s.[5]

Nomenclature

ε Cassiopeiae, Latinised to Epsilon Cassiopeiae, is the star's Bayer catalog designation.

The star bore the traditional name Segin, which probably originates from an erroneous transcription of Seginus, the traditional name for Gamma Boötis, which itself is of uncertain origin.[13] Different sources report varying pronunciations, with SEG-in the most common but the variants SAY-gin and seg-EEN also appearing.[13][14] In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN approved the name Segin for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[11]

While some published reports incorrectly claim that this star was designated by NASA as Navi ('Ivan', backwards), in honor of astronaut Virgil Ivan "Gus" Grissom, one of the three astronauts who died in the Apollo 1 accident,[16] the actual star so designated is Gamma Cassiopeiae in the center of the constellation.[17][18]

In Chinese, 閣道 (Gé Dào), meaning Flying Corridor, refers to an asterism consisting of Epsilon Cassiopeiae, Iota Cassiopeiae, Delta Cassiopeiae, Theta Cassiopeiae, Nu Cassiopeiae and Omicron Cassiopeiae.[19] Consequently, the Chinese name for Epsilon Cassiopeiae itself is 閣道二 (Gé Dào èr, English: the Second Star of Flying Corridor.)[20]

Properties

A light curve for Epsilon Cassiopeiae, plotted from Hipparcos data[21]

Epsilon Cassiopeiae has a stellar classification of B3 V, indicating that it is a main sequence star fusing hydrogen in its core. Cote et al. (2003) indicate that it displays the spectral properties of a Be star, even though it is not categorized as such.[22] The presence of emission lines in the spectrum indicates the presence of a circumstellar shell of gas that has been thrown off by the star.[23] Epsilon Cassiopeiae has nine[7] times the mass and six times the radius of the Sun. It is radiating 3,000 times the luminosity of the Sun from its photosphere at an effective temperature of 15,174 K (14,901 °C; 26,854 °F),[8] giving it the blue-white hue of a B-type star.[24]

Observation during the Hipparcos mission suggest that the star may undergo weak periodic variability. The amplitude of this variation is 0.0025 in magnitude with a frequency of 11.17797 times per day, or one cycle every 2.15 hours. The signal-to-noise ratio for this measured variation is 4.978.[4] Hipparcos measurements of the space velocity components for this star suggest that it is a member of the Cas-Tau group of co-moving stars, with a 93% likelihood. This group may be kinematically associated with the alpha Persei Cluster, indicating that the Cas-Tau group, including Epsilon Cassiopeiae, may have been separated from the cluster through tidal interactions.[25]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 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.
  2. ↑ 2.0 2.1 2.2 Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99): 99, Bibcode: 1966CoLPL...4...99J 
  3. ↑ Slettebak, A. (1982). "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars". Astrophysical Journal Supplement Series 50: 55. doi:10.1086/190820. Bibcode: 1982ApJS...50...55S. 
  4. ↑ 4.0 4.1 Koen, Chris; Eyer, Laurent (March 2002), "New periodic variables from the Hipparcos epoch photometry", Monthly Notices of the Royal Astronomical Society 331 (1): 45–59, doi:10.1046/j.1365-8711.2002.05150.x, Bibcode: 2002MNRAS.331...45K 
  5. ↑ 5.0 5.1 Wielen, R. et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode: 1999VeARI..35....1W 
  6. ↑ Huang, W. et al. (2012), "A catalogue of Paschen-line profiles in standard stars", Astronomy & Astrophysics 547: A62, doi:10.1051/0004-6361/201219804, Bibcode: 2012A&A...547A..62H. 
  7. ↑ 7.0 7.1 7.2 Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T 
  8. ↑ 8.0 8.1 8.2 Takeda, Yoichi et al. (October 2010), "Oxygen and Neon Abundances of B-Type Stars in Comparison with the Sun", Publications of the Astronomical Society of Japan 62 (5): 1239–1248, doi:10.1093/pasj/62.5.1239, Bibcode: 2010PASJ...62.1239T 
  9. ↑ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, doi:10.1086/340590, Bibcode: 2002ApJ...573..359A 
  10. ↑ starrynighteducation.com, Audio Pronunciation Guide
  11. ↑ 11.0 11.1 "Naming Stars". IAU.org. https://www.iau.org/public/themes/naming_stars/. 
  12. ↑ Hutter, D. J.; Tycner, C.; Zavala, R. T.; Benson, J. A.; Hummel, C. A.; Zirm, H. (2021). "Surveying the Bright Stars by Optical Interferometry. III. A Magnitude-limited Multiplicity Survey of Classical Be Stars". The Astrophysical Journal Supplement Series 257 (2): 69. doi:10.3847/1538-4365/ac23cb. Bibcode: 2021ApJS..257...69H. 
  13. ↑ 13.0 13.1 Simpson, Phil (2012). "3". Guidebook to the constellations. New York: Springer. ISBN 9781441969408. 
  14. ↑ "Audio Pronunciation Guide". http://www.starrynighteducation.com/resources_pronunciation.html. 
  15. ↑ "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/. 
  16. ↑ Rao, Joe (August 29, 2003). "NightSky Friday: Rotanev, Derf, Navi, and other Backward Star Names". Space.com. http://www.space.com/spacewatch/star_names_030829.html. 
  17. ↑ "Post-landing Activities". Apollo 15 Lunar Surface Journal. NASA. https://history.nasa.gov/alsj/a15/a15.postland.html.  commentary at 105:11:33
  18. ↑ "Apollo 10 Flown CSM Star Chart Directly from the Personal Collection of Mission Command Module Pilot John Young". Heritage Auction Galleries. http://historical.ha.com/common/view_item.php?Sale_No=6037&Lot_No=0&LotIdNo=12016&ts=off#Photo. 
  19. ↑ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN:978-986-7332-25-7.
  20. ↑ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 , Hong Kong Space Museum. Accessed on line November 23, 2010.
  21. ↑ Light Curve, ESA, https://www.cosmos.esa.int/web/hipparcos/java-tools/light-curve, retrieved 10 October 2022. 
  22. ↑ Cote, J.; van Kerkwijk, M. H. (July 1993), "New Bright Be-Stars and the Be-Star Frequency", Astronomy and Astrophysics 274 (3): 870, Bibcode: 1993A&A...274..870C 
  23. ↑ Andrillat, A.; Jaschek, M.; Jaschek, C. (July 1990), "A survey of Be stars in the infrared. II - Determination of envelope dimensions", Astronomy and Astrophysics Supplement Series 84 (1): 11–28, Bibcode: 1990A&AS...84...11A 
  24. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16 
  25. ↑ de Zeeuw, P. T. et al. (January 1999), "A HIPPARCOS Census of the Nearby OB Associations", The Astronomical Journal 117 (1): 354–399, doi:10.1086/300682, Bibcode: 1999AJ....117..354D 

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