Alpha Camelopardalis

Alpha Camelopardalis (Alpha Cam, α Camelopardalis, α Cam) is a star in the constellation Camelopardalis, with an apparent visual magnitude of 4.3. It is the third-brightest star in this not-very-prominent circumpolar constellation, the first and second-brightest stars being β Camelopardalis and CS Camelopardalis, respectively. It is the farthest constellational star, with a distance of 6,000 light-years from Earth.

α Camelopardalis
Location of α Camelopardalis (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Camelopardalis
Right ascension 04h 54m 03.01040s[1]
Declination +66° 20′ 33.6365″[1]
Apparent magnitude (V) 4.29[2]
Characteristics
Spectral type O9Ia[3]
U−B color index −0.87[2]
B−V color index +0.05[2]
R−I color index 0.00[2]
Astrometry
Radial velocity (Rv)+6.1[4] km/s
Proper motion (μ) RA: –0.13[1] mas/yr
Dec.: +6.89[1] mas/yr
Parallax (π)0.52 ± 0.19[1] mas
Distanceapprox. 6,000 ly
(approx. 1,900 pc)
Absolute magnitude (MV)–7.1[5]
Details[5]
Mass30.9 M☉
Radius29 R☉
Luminosity620,000 L☉
Surface gravity (log g)3.00 cgs
Temperature30,000 K
Rotational velocity (v sin i)80 km/s
Age~2 million[6] years
Other designations
α Cam, Alpha Camelopardalis, Alpha Cam, 9 Camelopardalis, 9 Cam, BD+66 358, FK5 178, GC 5924, HD 30614, HIP 22783, HR 1542, IRAS 04490+6615, PPM 15047, SAO 13298, WDS J04541+6621
Database references
SIMBADdata

Description

Alpha Camelopardalis has a stellar classification of O9 Ia, with the 'Ia' indicating that it is an O-type luminous supergiant. It is a massive star with 31 times the mass of the Sun and 37 times the Sun's radius. The effective temperature of the outer envelope is 30,000 K; much hotter than the Sun's effective temperature of 5,778 K, giving it the characteristic blue hue of an O-type star.[7] It is emitting 620,000 times the luminosity of the Sun and is a weak X-ray emitter.[8]

Variations in the profiles of Alpha Camelopardalis' spectral lines are caused by fluctuations in the photosphere and stellar wind. This may be caused by non-radial pulsations. The absorption lines in the optical spectrum show radial velocity variations, although there is significant uncertainty about the period. Estimates range from a period as low as 0.36 days up to 2.93 days. The stellar wind from this star is not smooth and continuous, but instead shows a behavior indicating clumping at both large and small scales.[9] This star is losing mass rapidly through its stellar wind at a rate of approximately 6.3 × 10−6 solar masses per year,[5] or the equivalent of the mass of the Sun every 160,000 years.

In 1968, this star was classified as a spectroscopic binary, indicating that it has an orbiting stellar companion with a period of 3.68 days and an orbital eccentricity of 0.45. Subsequent studies refined the period to 3.24 days. However, in 2006 it was recognized that the changes in the spectrum were probably the result of changes in the atmosphere or stellar wind, so it is more likely a single star.[10] Speckle interferometry observations with the 3.67 m Advanced Electro Optical System Telescope at the Haleakala Observatory failed to detect a secondary component.[11]

In 1961, based on the criteria that the proper motion of this star indicates a space velocity of greater than 30 km/s,[12] Alpha Camelopardalis was suggested as a candidate runaway star that had been ejected from the cluster NGC 1502. This was based upon the kinematic properties of the star and cluster, as well as the location of this star at a high galactic latitude in an area otherwise lacking in stellar associations. Over the course of a million years, this star should have moved only 1.4° across the sky, while it was estimated as being only two million years old.[6]

Runaway stars such as this with a stellar wind that is moving at supersonic velocity through the interstellar medium have their wind confined by a bow shock due to ram pressure. The dust in this bow shock can be detected using an infrared telescope.[13] Just such a bow shock was observed with NASA's Wide-field Infrared Survey Explorer, or WISE. The star is traveling at a rate of somewhere between 680 and 4,200 kilometers per second: between 1.5 and 9.4 million mph.[14]

Chinese name

In Chinese, 紫微右垣 (Zǐ Wēi Yòu Yuán), meaning Right Wall of Purple Forbidden Enclosure, refers to an asterism consisting of α Camelopardalis, α Draconis, κ Draconis, λ Draconis, 24 Ursae Majoris, 43 Camelopardalis and BK Camelopardalis.[15] Consequently, the Chinese name for α Camelopardalis itself is 紫微右垣六 (Zǐ Wēi Yòu Yuán liù, English: the Sixth Star of Right Wall of Purple Forbidden Enclosure.),[16] representing 少衛 (Shǎowèi), meaning Second Imperial Guard.[17][18] 少衛 (Shǎowèi) is westernized into Shaou Wei by R. H. Allen, the meaning is "Minor Guard", but it is not clearly designated.[18]

References
  1. van Leeuwen, F. (November 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. S2CID 18759600.
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. Sota, A.; Maíz Apellániz, J.; Walborn, N. R.; Alfaro, E. J.; Barbá, R. H.; Morrell, N. I.; Gamen, R. C.; Arias, J. I. (2011). "The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ~ 2500". The Astrophysical Journal Supplement. 193 (2): 24. arXiv:1101.4002. Bibcode:2011ApJS..193...24S. doi:10.1088/0067-0049/193/2/24. S2CID 119248206.
  4. Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington, Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W
  5. Markova, N. (April 2002), "Spectral variability of luminous early type stars . II. Supergiant alpha Camelopardalis", Astronomy and Astrophysics, 385 (2): 479–487, Bibcode:2002A&A...385..479M, doi:10.1051/0004-6361:20020153 See Table 1.
  6. Blaauw, A. (May 1961), "On the origin of the O- and B-type stars with high velocities (the "run-away" stars), and some related problems", Bulletin of the Astronomical Institutes of the Netherlands, 15: 265, Bibcode:1961BAN....15..265B
  7. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 10, 2012, retrieved 2012-01-16
  8. Aveni, A. F.; Hunter, H. J., Jr. (October 1967), "Observational studies relating to star formation. I.", Astronomical Journal, 72: 1019–1027, Bibcode:1967AJ.....72.1019A, doi:10.1086/110378
  9. Prinja, R. K.; et al. (October 2006), "The superimposed photospheric and stellar wind variability of the O-type supergiant α Camelopardalis", Astronomy and Astrophysics, 457 (3): 987–994, arXiv:astro-ph/0606720, Bibcode:2006A&A...457..987P, doi:10.1051/0004-6361:20065114, S2CID 14180933
  10. McSwain, M. Virginia; et al. (January 2007), "A Spectroscopic Study of Field and Runaway OB Stars", The Astrophysical Journal, 655 (1): 473–483, arXiv:astro-ph/0608270, Bibcode:2007ApJ...655..473M, doi:10.1086/509914, S2CID 18121243
  11. Turner, Nils H.; et al. (August 2008), "Adaptive Optics Photometry and Astrometry of Binary Stars. III. a Faint Companion Search of O-Star Systems", The Astronomical Journal, 136 (2): 554–565, arXiv:0805.3162, Bibcode:2008AJ....136..554T, doi:10.1088/0004-6256/136/2/554, S2CID 15819352
  12. Gies, D. R. (July 1987), "The kinematical and binary properties of association and field O stars", Astrophysical Journal Supplement Series, 64: 545–563, Bibcode:1987ApJS...64..545G, doi:10.1086/191208
  13. Noriega-Crespo, Alberto; van Buren, Dave; Dgani, Ruth (February 1997), "Bow Shocks Around Runaway Stars.III.The High Resolution Maps", Astronomical Journal, 113: 780–786, Bibcode:1997AJ....113..780N, doi:10.1086/118298
  14. Clavin, Whitney (March 11, 2011), "Speed demon creates a shock", physorg, retrieved 2011-12-24
  15. (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.
  16. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 11 日
  17. English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived 2008-09-24 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010
  18. Allen, Richard Hinckley (1899), "Star-names and their meanings", New York, G. E. Stechert: 106, Bibcode:1899sntm.book.....A, retrieved 2011-12-24
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