Spica

For other uses, see Spica (disambiguation).
Spica


Location of Spica (circled)

Observation data
Epoch J2000      Equinox J2000
Constellation Virgo
Pronunciation /ˈspaɪkə/
Right ascension 13h 25m 11.579s[1]
Declination −11° 09′ 40.75″[1]
Apparent magnitude (V) +0.97[2] (0.97 - 1.04[3])
Characteristics
Spectral type B1 III-IV/B2 V[4]
U−B color index −0.94[2]
B−V color index −0.23[2]
Variable type β Cep + Rotating ellipsoid[3]
Astrometry
Radial velocity (Rv)+1.0[5] km/s
Proper motion (μ) RA: −42.35 ± 0.62[1] mas/yr
Dec.: −30.67 ± 0.37[1] mas/yr
Parallax (π)13.06 ± 0.70[1] mas
Distance250 ± 10 ly
(77 ± 4 pc)
Absolute magnitude (MV)−3.55 (−3.5/−1.5)[6]
Orbit[7]
Period (P)4.0145898 d
Eccentricity (e)0.067 ± 0.014
Inclination (i)54 ± 6°
Periastron epoch (T)2440678.09
Argument of periastron (ω)
(secondary)		140 ± 10°
Details
Primary
Mass10.25 ± 0.68[7] M☉
Radius7.40 ± 0.57[7] R☉
Luminosity12,100[8] L☉
Surface gravity (log g)3.7 ± 0.1[6] cgs
Temperature22,400[6] K
Rotational velocity (v sin i)199 ± 5[7] km/s
Secondary
Mass6.97 ± 0.4[7] M☉
Radius3.64 ± 0.28[7] R☉
Luminosity1,500[8] L☉
Temperature18,500[8] K
Rotational velocity (v sin i)87 ± 6[7] km/s
Other designations
Spica, Azimech, Spica Virginis, Alaraph, Dana, α Virginis, 67 Virginis, HR 5056, BD -10°3672, HD 116658, GCTP 18144, FK5 498, CCDM 13252-1109, SAO 157923, HIP 65474.[9]

Spica (/ˈspaɪkə/; α Vir, α Virginis, Alpha Virginis) is the brightest star in the constellation Virgo, and the 15th brightest star in the night sky. Located 250 ± 10 light years from Earth, it is actually a spectroscopic binary and rotating ellipsoidal variable—a system whose two main stars are so close together they are egg-shaped rather than spherical, and can only be separated by their spectrum. The primary is a blue giant and a variable star of the Beta Cephei type.

Observation history

Spica is believed to be the star that gave Hipparchus the data that led him to discover the precession of the equinoxes.[10] A temple to Menat (an early Hathor) at Thebes was oriented with reference to Spica when it was built in 3200 BC, and, over time, precession slowly but noticeably changed Spica's location relative to the temple.[11] Nicolaus Copernicus made many observations of Spica with his home-made triquetrum for his researches on precession.[12][13]

As one of the nearest massive binary star systems to the Sun, Spica has been the subject of many observational studies.[14]

Analysis of its parallax shows that it is 250 ± 10 light years from Earth.[1]

Visibility

How to locate the star Spica

Spica is 2.05 degrees from the ecliptic and can be occulted by the Moon and sometimes by the planets. The last planetary occultation of Spica occurred when Venus passed in front of the star (as seen from Earth) on November 10, 1783. The next occultation will occur on September 2, 2197, when Venus again passes in front of Spica.[15] The Sun passes a little more than 2° north of Spica around October 16 every year, and the star's heliacal rising occurs about two weeks later. Every 8 years, Venus passes Spica around the time of the star's heliacal rising, as in 2009 when it passed 3.5° north of the star on November 3.[16]

A method of finding Spica is to follow the arc of the handle of the Big Dipper to Arcturus, and then continue on the same angular distance to Spica. This can be recalled by the mnemonic phrase, "arc to Arcturus and spike to Spica."

Characteristics

Spica is a close binary star whose components orbit about each other every four days. They stay close enough together that they cannot be resolved as two stars through a telescope. The changes in the orbital motion of this pair results in a Doppler shift in the absorption lines of their respective spectra, making them a double-lined spectroscopic binary.[7] Initially, the orbital parameters for this system were inferred using spectroscopic measurements. Between 1966 and 1970, the Narrabri Stellar Intensity Interferometer was used to observe the pair and to directly measure the orbital characteristics and the angular diameter of the primary, which was found to be (0.90 ± 0.04) × 10−3 arcseconds, and the angular size of the semi-major axis of the orbit was found to be only slightly larger at (1.54 ± 0.05) × 10−3 arcseconds.[6]

The primary star has a stellar classification of B1 III–IV. The luminosity class matches the spectrum of a star that is midway between a subgiant and a giant star, and it is no longer a B-type main-sequence star.[4] This is a massive star with more than 10 times the mass of the Sun and seven times the Sun's radius. The total luminosity of this star is about 12,100 times that of the Sun, and eight times the luminosity of its companion. The primary is one of the nearest stars to the Sun that has enough mass to end its life in a Type II supernova explosion.[8]

The primary is classified as a Beta Cephei-type variable star that varies in brightness over a 0.1738-day period. The spectrum shows a radial velocity variation with the same period, indicating that the surface of the star is regularly pulsating outward and then contracting. This star is rotating rapidly, with a rotational velocity of 199 km/s along the equator.[7]

The secondary member of this system is one of the few stars whose spectrum is affected by the Struve–Sahade effect. This is an anomalous change in the strength of the spectral lines over the course of an orbit, where the lines become weaker as the star is moving away from the observer.[14] It may be caused by a strong stellar wind from the primary scattering the light from secondary when it is receding.[17] This star is smaller than the primary, with about 7 times the mass of the Sun and 3.6 times the Sun's radius.[7] Its stellar classification is B2 V, making this a main-sequence star.[4]

Spica is a rotating ellipsoidal variable, which is a non-eclipsing close binary star system where the stars are mutually distorted through their gravitational interaction. This effect causes the apparent magnitude of the star system to vary by 0.03 over an interval that matches the orbital period. This slight dip in magnitude is barely noticeable visually.[18] Both stars rotate faster than their mutual orbital period. This lack of synchronization and the high ellipticity of their orbit may indicate that this is a young star system. Over time, the mutual tidal interaction of the pair may lead to rotational synchronization and orbit circularization.[19]

Spica is an polarimetric variable, which suggests that protostellar material is entrained between the two stars.[20]

Names

The name Spica derives from Latin spīca virginis "the virgin's ear of [wheat] grain". It was also anglicized as Virgin's Spike. Johann Bayer cited the name Arista. Another alternative name is Azimech, from Arabic السماك الأعزل al-simāk al-a‘zal 'the Undefended', and Alarph, Arabic for 'the Grape Gatherer'. Sumbalet (Sombalet, Sembalet and variants) is from an Arabic sunbulah "corn ear". [21]

In his Three Books of Occult Philosophy, Cornelius Agrippa attributes its kabbalistic symbol to Hermes Trismegistus.

In Chinese astronomy, the star is known as Jiao Xiu 1 (角宿一), i.e. the first star of the Jiao Xiu asterism.

In Hindu astronomy, Spica corresponds to the Nakshatra Chitra.

A blue star represents Spica on the flag of the Brazilian state of Pará. Spica is also the star representing Pará on the Brazilian flag.

Namesakes

Both USS Spica (AK-16) and USNS Spica (T-AFS-9) were named after this star whilst USS Azimech (AK-124), a Crater-class cargo ship, was given one of the star's medieval names. A South Korean Girl Group was named after the star. Spica is a Vocaloid song sung by Hatsune Miku

Spring Triangle and Great Diamond asterisms

Spica, along with Denebola or Regulus depending on the source and Arcturus, is part of the Spring Triangle asterism, and by extension, also of the Great Diamond together with Cor Caroli.

References

  1. 1 2 3 4 5 6 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction" (PDF). Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  2. 1 2 3 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: 0. Bibcode:2002yCat.2237....0D.
  3. 1 2 Ruban, E. V.; Alekseeva, G. A.; Arkharov, A. A.; Hagen-Thorn, E. I.; Galkin, V. D.; Nikanorova, I. N.; Novikov, V. V.; Pakhomov, V. P.; Puzakova, T. Yu. (2006). "Spectrophotometric observations of variable stars". Astronomy Letters 32 (9): 604. Bibcode:2006AstL...32..604R. doi:10.1134/S1063773706090052.
  4. 1 2 3 Schnerr, R. S.; et al. (June 2008). "Magnetic field measurements and wind-line variability of OB-type stars" (PDF). Astronomy and Astrophysics 483 (3): 857–867. arXiv:1008.4260. Bibcode:2008A&A...483..857S. doi:10.1051/0004-6361:20077740. Retrieved 2010-04-16.
  5. ↑ Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953QB901.W495.....
  6. 1 2 3 4 Herbison-Evans, D.; Hanbury Brown, R.; Davis, J.; Allen, L. R. (1971). "A study of alpha Virginis with an intensity interferometer". Monthly Notices of the Royal Astronomical Society 151 (2): 161–176. Bibcode:1971MNRAS.151..161H. doi:10.1093/mnras/151.2.161.
  7. 1 2 3 4 5 6 7 8 9 10 Harrington, David; Koenigsberger, Gloria; Moreno, Edmundo; Kuhn, Jeffrey (October 2009). "Line-profile Variability from Tidal Flows in Alpha Virginis (Spica)". The Astrophysical Journal 704 (1): 813–830. arXiv:0908.3336. Bibcode:2009ApJ...704..813H. doi:10.1088/0004-637X/704/1/813.
  8. 1 2 3 4 Kaler, Jim. "Spica". Stars. Retrieved 2010-04-15.
  9. ↑ "V* alf Vir -- Variable Star of beta Cep type". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-04-13.
  10. ↑ Evans, James (1998). The History and Practice of Ancient Astronomy. Oxford University Press. p. 259. ISBN 0-19-509539-1.
  11. ↑ Allen, Richard Hinckley (2003). Star Names and Their Meanings. Kessinger Publishing. p. 468. ISBN 0-7661-4028-8.
  12. ↑ Rufus, W. Carl (April 1943). "Copernicus, Polish Astronomer, 1473–1543". Journal of the Royal Astronomical Society of Canada 37 (4): 134. Bibcode:1943JRASC..37..129R.
  13. ↑ Moesgaard, Kristian P. (1973). "Copernican influence on Tycho Brahe". In Jerzy Dobrzycki. The reception of Copernicus' heliocentric theory: proceedings of a symposium organized by the Nicolas Copernicus Committee of the International Union of the History and Philosophy of Science. Toruń, Poland: Studia Copernicana, Springer. ISBN 90-277-0311-6.
  14. 1 2 Riddle, R. L.; Bagnuolo, W. G.; Gies, D. R. (December 2001). "Spectroscopy of the temporal variations of α Vir". Bulletin of the American Astronomical Society 33: 1312. Bibcode:2001AAS...199.0613R.
  15. ↑ Earth-Sky Tonight, March 26, 2010
  16. ↑ Breit, Derek C. (March 12, 2010). "Diary of Astronomical Phenomena 2010". Poyntsource.com. Retrieved 2010-04-13.
  17. ↑ Gies, Douglas R.; Bagnuolo, William G., Jr.; Penny, Laura R. (April 1997). "Photospheric Heating in Colliding-Wind Binaries". Astrophysical Journal 479: 408. Bibcode:1997ApJ...479..408G. doi:10.1086/303848.
  18. ↑ Morris, S. L. (August 1985). "The ellipsoidal variable stars". Astrophysical Journal, Part 1 295: 143–152. Bibcode:1985ApJ...295..143M. doi:10.1086/163359.
  19. ↑ Beech, M. (August 1986). "The ellipsoidal variables. III - Circularization and synchronization". Astrophysics and Space Science 125 (1): 69–75. Bibcode:1986Ap&SS.125...69B. doi:10.1007/BF00643972.
  20. ↑ Cotton, D. V.; et al. (January 2016). "The linear polarization of Southern bright stars measured at the parts-per-million level". Monthly Notices of the Royal Astronomical Society 455 (2): 1607–1628. arXiv:1509.07221. Bibcode:2016MNRAS.455.1607C. doi:10.1093/mnras/stv2185.
  21. ↑ Star Names - Their Lore and Meaning, by Richard Hinckley Allen

External links

Coordinates: 13h 25m 11.5793s, −11° 09′ 40.759″

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