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Antares


Antares, also designated Alpha Scorpii (α Scorpii, abbreviated Alpha Sco, α Sco), is the 15th brightest star in the night sky, and the brightest star in the constellation of Scorpius. Distinctly reddish when viewed with the naked eye, Antares is a slow irregular variable star that ranges in brightness from apparent magnitude +0.6 to +1.6. Despite being often referred to as "the heart of the scorpion", Antares is flanked by Sigma Scorpii and Tau Scorpii in the constellation's center.

Antares
Scorpius IAU.svg
Antares in the constellation Scorpius
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 16h 29m 24.45970s[1]
Declination −26° 25′ 55.2094″[1]
Apparent magnitude (V) 0.6 - 1.6[2] + 5.5[3]
Characteristics
Evolutionary stage Red supergiant
Spectral type M1.5Iab-Ib[4] + B2.5V[5]
U−B color index +1.34[3]
B−V color index +1.83[3]
Variable type Lc[2]
Astrometry
Radial velocity (Rv)−3.4[6] km/s
Proper motion (μ) RA: −12.11[1] mas/yr
Dec.: −23.30[1] mas/yr
Parallax (π)5.89 ± 1.00[1] mas
Distanceapprox. 550 ly
(approx. 170 pc)
Absolute magnitude (MV)−5.28[7] (variable)
Details
A
Mass12±20%[8] M
Radius680[9] - 800[10] R
Diameter680[9] - 800[10] D
Luminosity97700+40300
−28500
[11] L
Surface gravity (log g)−0.1 - −0.2[9] cgs
Temperature3,570[12] K
Rotational velocity (v sin i)20[3] km/s
Age11+3
−1
[11] Myr
B
Mass7.2[13] M
Radius5.2[13] R
Surface gravity (log g)3.9[13] cgs
Temperature18,500[8] K
Rotational velocity (v sin i)250[13] km/s
Other designations
α Scorpii, 21 Sco, Cor Scorpii, Kalb al Akrab, Scorpion's Heart, Vespertilio,[14] HR 6134, CD−26°11359, HIP 80763, SAO 184415, FK5 616, WDS 16294-2626, CCDM J16294-2626
A: HD 148478, AAVSO 1623-26
B: HD 148479
Database references
SIMBADAntares
Antares A
Antares B

Classified as a red supergiant of spectral type M1.5Iab-Ib, Antares is likely among the largest of known stars. It is the brightest, most massive, and most evolved stellar member of the nearest OB association (the Scorpius–Centaurus Association). Antares is a member of the Upper Scorpius subgroup of the Scorpius–Centaurus Association, which contains thousands of stars with mean age 11 million years at a distance of approximately 170 parsecs (550 ly). Its exact size remains uncertain, but if placed at the centre of the solar system it would reach to somewhere between the orbits of Mars and Jupiter. The mass is calculated to be around 12 times that of the Sun. Antares and its fire-like red color have been known since ancient history.

Contents

PropertiesEdit

 
Comparison between the red supergiant Antares and the Sun, shown as the tiny dot toward the upper right. The black circle is the size of the orbit of Mars. Arcturus is also included in the picture for comparison. Like all red giants, the true size of Antares is uncertain based on the uncertainties like the star's distance and luminosity, so the 300 million kilometre radius shown here tends towards minimum of the range of published values. Antares is really much larger.

Antares A is a red supergiant star with a stellar classification of M1.5Iab-Ib, and is indicated to be a spectral standard or prototype for that class.[4] Due to the nature of star, the derived parallax measurements have large errors, so that the true distance of Antares is approximately around 550 light-years (170 parsecs) from the Sun.[1]

Luminosity and massEdit

The brightness in absolute magnitude of Antares at visual wavelengths is about 10,000 times that of the Sun, but because the star radiates a considerable part of its energy in the infrared part of the electromagnetic spectrum, the true bolometric luminosity is actually 10 times greater at around 100,000 times that of the Sun. There is a large margin of error assigned to values for the bolometric luminosity, typically around 30% or more. There is also considerable variation between values published by different authors, for example 75,900 L and 97,700 L published back in 2012 and 2013, respectively.[11][9]

The mass of the star has been calculated to be approximately 12 times greater than the Sun's,[11] or 11 to 14.3 M.[9] Comparison of the effective temperature and luminosity of the star to theoretical evolutionary tracks for massive stars suggest a progenitor mass of 17 M and an age of 12 million years (MYr),[11] or an initial mass 15 times greater and an age of 11 to 15 MYr.[9] Massive stars like Antares are expected to become supernovae.[15]

SizeEdit

 
VLTI reconstructed view of the surface of Antares

Like most cool supergiants, the size of Antares has much uncertainty due to the tenuous and translucent nature of the extended outer regions of the star. Defining an effective temperature is hard due to spectral lines being generated at different depths within the atmosphere, and linear measurements produce different results depending on the wavelength observed.[16] Antares also pulsates, varying its radius by 165 D or around 19%.[11] It also varies in temperature by 150 degrees Kelvin, lagging 70 days behind radial velocity changes which are likely to be caused by the pulsations.[12]

3D possible impression of Antares.

The diameter of Antares can be measured accurately using interferometry, or by alternatively observing lunar occultations events. An apparent diameter from occultations 41.3 ± 0.1 milliarcseconds have been published.[17] Interferometry allows synthesis of a view of the stellar disc, which is then represented as a limb-darkened disk surrounded by an extended photosphere. The angular diameter of the limb-darkened disk was measured as 37.38±0.06 milliarcseconds in 2009 and 37.31±0.09 milliarcseconds in 2010. The linear radius of the star can be calculated from its angular diameter and distance. However, the distance to Antares is not known with the same accuracies as modern measurements of its diameter. Using the Hipparcos satellite's trigonometric parallax of 5.40″±1.68″[18]) leads to a radius of about 680 D.[9] A diameter of 890 D was derived from older measurements of the diameter,[12] but those measurements are likely to have been affected by asymmetry of the atmosphere and the narrow range of infrared wavelengths observed. Antares has an extended shell which radiates strongly at those particular wavelengths.[9] A reasonable estimate of the star's upper limit size is near 800 D.[10]

ReferencesEdit

  1. 1.0 1.1 1.2 1.3 1.4 1.5 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.
  2. 2.0 2.1 Kiss, L. L.; Szabo, G. M.; Bedding, T. R. (2006). "Variability in red supergiant stars: pulsations, long secondary periods and convection noise". Monthly Notices of the Royal Astronomical Society 372 (4): 1721–1734. arXiv:astro-ph/0608438. Bibcode 2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x. ISSN 0035-8711.
  3. 3.0 3.1 3.2 3.3 Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally published in: 1964BS....C......0H 5050. Bibcode 1995yCat.5050....0H. Vizier database entry CDS. Accessed on line September 07, 2012
  4. 4.0 4.1 Keenan, Philip C; McNeil, Raymond C (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series 71: 245. Bibcode 1989ApJS...71..245K. doi:10.1086/191373.
  5. Baade, R.; Reimers, D. (October 2007). "Multi-component absorption lines in the HST spectra of α Scorpii B". Astronomy and Astrophysics 474 (1): 229–237. Bibcode 2007A&A...474..229B. doi:10.1051/0004-6361:20077308.
  6. Lua error in Module:Citation/CS1 at line 637: attempt to concatenate local 'chapter' (a table value).
  7. Lua error in Module:Citation/CS1 at line 637: attempt to concatenate local 'chapter' (a table value).
  8. 8.0 8.1 Schröder, K.-P.; Cuntz, M. (April 2007), "A critical test of empirical mass loss formulas applied to individual giants and supergiants", Astronomy and Astrophysics 465 (2): 593–601, arXiv:astro-ph/0702172, Bibcode 2007A&A...465..593S, doi:10.1051/0004-6361:20066633
  9. 9.0 9.1 9.2 9.3 9.4 9.5 9.6 Ohnaka, K; Hofmann, K.-H; Schertl, D; Weigelt, G; Baffa, C; Chelli, A; Petrov, R; Robbe-Dubois, S (2013). "High spectral resolution imaging of the dynamical atmosphere of the red supergiant Antares in the CO first overtone lines with VLTI/AMBER". Astronomy & Astrophysics 555: A24. arXiv:1304.4800. Bibcode 2013A&A...555A..24O. doi:10.1051/0004-6361/201321063.
  10. 10.0 10.1 https://www.aavso.org/vsots_alphasco
  11. 11.0 11.1 11.2 11.3 11.4 11.5 Mark J. Pecaut; Eric E. Mamajek; Eric J. Bubar (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association". Astrophysical Journal 746 (2): 154. arXiv:1112.1695. Bibcode 2012ApJ...746..154P. doi:10.1088/0004-637X/746/2/154.
  12. 12.0 12.1 12.2 Pugh, T.; Gray, D.F. (2013). "On the Six-year Period in the Radial Velocity of Antares A". The Astronomical Journal 145 (2): 4. Bibcode 2013AJ....145...38P. doi:10.1088/0004-6256/145/2/38. 38.
  13. 13.0 13.1 13.2 13.3 Kudritzki, R. P.; Reimers, D. (1978). "On the absolute scale of mass-loss in red giants. II. Circumstellar absorption lines in the spectrum of alpha Sco B and mass-loss of alpha Sco A". Astronomy and Astrophysics 70: 227. Bibcode 1978A&A....70..227K.
  14. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  15. Hockey, T.; Trimble, V. (2010). "Public reaction to a V = -12.5 supernova". The Observatory 130: 167. Bibcode 2010Obs...130..167H.
  16. Ireland, M. J. et al. (May 2004). "Multiwavelength diameters of nearby Miras and semiregular variables". Monthly Notices of the Royal Astronomical Society 350 (1): 365–374. arXiv:astro-ph/0402326. Bibcode 2004MNRAS.350..365I. doi:10.1111/j.1365-2966.2004.07651.x.
  17. A. Richichi (April 1990). "A new accurate determination of the angular diameter of Antares". Astronomy and Astrophysics 230 (2): 355–362. Bibcode 1990A&A...230..355R.
  18. Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; Bastian, U.; Bernacca, P. L.; Crézé, M.; Donati, F. et al. (July 1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics 323: L49–L52. Bibcode 1997A&A...323L..49P.

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