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Alpha Camelopardalis

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Alpha Camelopardalis

α Camelopardalis
Diagram showing star positions and boundaries of the Camelopardalis constellation and its surroundings

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) 4.301[2]
Characteristics
Spectral type O9.5Iae[2]
U−B color index −0.88[3]
B−V color index +0.03[3]
R−I color index 0.00[4]
Astrometry
Radial velocity (Rv) +6.1[5] 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
Distance approx. 6,000 ly
(approx. 1,900 pc)
Absolute magnitude (MV) –7.1[6]
Details
Mass 43.2[6] M
Radius 36.8[6] R
Luminosity 680,000[6] L
Surface gravity (log g) 3.00[6] cgs
Temperature 27,700[6] K
Rotational velocity (v sin i) 80[6] km/s
Age ~2 million[7] 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.[2]
Database references
SIMBAD data

Alpha Camelopardalis (Alpha Cam, α Camelopardalis, α Cam) is a star in the constellation Camelopardalis, with an apparent visual magnitude of 4.301.[2] 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.[8]It is the farthest constellational star, with a distance of 6000 light-years from Earth.

This star has a stellar classification of O9.5Iae, with the 'Ia' indicating that it is an O-type luminous supergiant and the 'e' showing that there are emission lines in its spectrum. It is a massive star with 43 times the mass of the Sun and 37 times the Sun's radius. The effective temperature of the outer envelope is 27,700 K; much hotter than the Sun's effective temperature of 5,778 K, giving it the characteristic blue hue of an O-type star.[9] It is emitting 680,000 times the luminosity of the Sun[6] and is a weak X-ray emitter.[10]

This star shows multiple patterns of variability. It may be a non-radial pulsating variable star, which is causing changes in the spectrum being emitted by the photosphere. 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.[11] This star is losing mass rapidly through its stellar wind at a rate of approximately 6.3 × 10−6 solar masses per year,[6] 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.[12] Speckle interferometery observations with the 3.67 m Advanced Electro Optical System Telescope at the Haleakala Observatory failed to detect a secondary component.[13]

In 1961, based on the criteria that the proper motion of this star indicates a space velocity of greater than 30 km/s,[14] 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.[7] It has been suggested as a runaway star ejected from the OB association Camelopardalis OB1, but subsequent observations cast doubt on this.[8]

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.[15] 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.[16]

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.[17] Consequently, α Camelopardalis itself is known as 紫微右垣六 (Zǐ Wēi Yòu Yuán liù, English: the Sixth Star of Right Wall of Purple Forbidden Enclosure.),[18] representing 少衛 (Shǎowèi), meaning Second Imperial Guard.[19][20] 少衛 (Shǎowèi) is westernized into Shaou Wei by R. H. Allen, the meaning is "Minor Guard", but it is not clearly designated.[20]

References

  1. ^ a b c d e van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664.  
  2. ^ a b c d "alf Cam -- Emission-line Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-24 
  3. ^ a b Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99),  
  4. ^ HR 1542, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line October 19, 2009.
  5. ^ Wilson, Ralph Elmer (1953), General catalogue of stellar radial velocities, Carnegie Institution of Washington,  
  6. ^ a b c d e f g h i Markova, N. (April 2002), "Spectral variability of luminous early type stars . II. Supergiant alpha Camelopardalis", Astronomy and Astrophysics 385: 479–487,   See Table 1.
  7. ^ a b 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,  
  8. ^ a b Kaler, James B., "Alpha Cam", Stars (University of Illinois), retrieved 2009-10-19 
  9. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  10. ^ Aveni, A. F.; Hunter, H. J., Jr. (October 1967), "Observational studies relating to star formation. I.", Astronomical Journal 72: 1019–1027,  
  11. ^ 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,  
  12. ^ McSwain, M. Virginia et al. (January 2007), "A Spectroscopic Study of Field and Runaway OB Stars", The Astrophysical Journal 655 (1): 473–483,  
  13. ^ 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,  
  14. ^ Gies, D. R. (July 1987), "The kinematical and binary properties of association and field O stars", Astrophysical Journal Supplement Series 64: 545–563,  
  15. ^ 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,  
  16. ^ Clavin, Whitney (March 11, 2011), "Speed demon creates a shock", physorg, retrieved 2011-12-24 
  17. ^ (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.
  18. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 11 日
  19. ^ English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010
  20. ^ a b Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 106, retrieved 2011-12-24 

External links

  • HR 1542, entry in the Bright Star Catalogue
  • Alpha Camelopardalis in Aladin
  • Image of the constellational matrix formed by viewing the constellational lines at 16,000 light-years from the sun. Spike at the left is Alpha Camelopardalis.
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