Spica //, designated α Virginis (Latinised to Alpha Virginis, abbreviated Alpha Vir, α Vir), is the brightest object in the constellation of Virgo and one of the 20 brightest stars in the night sky. Analysis of its parallax shows that it is located 250 ± 10 light years from the Sun. It is a spectroscopic binary star and rotating ellipsoidal variable; a system whose two stars are so close together they are egg-shaped rather than spherical, and can only be separated by their spectra. The primary is a blue giant and a variable star of the Beta Cephei type.
Epoch J2000 Equinox J2000
|Pronunciation||// or //|
|Right ascension||13h 25m 11.579s|
|Declination||−11° 09′ 40.75″|
|Apparent magnitude (V)||+0.97 (0.97 - 1.04)|
|Spectral type||B1V (B1III-IV + B2V)|
|U−B color index||−0.94|
|B−V color index||−0.23|
|Variable type||β Cep + Ellipsoidal|
|Radial velocity (Rv)||+1.0 km/s|
|Proper motion (μ)|| RA: −42.35 ± 0.62 mas/yr |
Dec.: −30.67 ± 0.37 mas/yr
|Parallax (π)||13.06 ± 0.70 mas|
|Distance||250 ± 10 ly |
(77 ± 4 pc)
|Absolute magnitude (MV)||−3.55 (−3.5/−1.5)|
|Period (P)||4.0145±0.0001 d|
|Semi-major axis (a)||28.20±0.92 R☉|
|Periastron epoch (T)||2,454,189.4±0.02|
|Argument of periastron (ω)|
|Surface gravity (log g)||3.71±0.10 cgs|
|Rotational velocity (v sin i)||165.3±4.5 km/s|
|Surface gravity (log g)||4.15±0.15 cgs|
|Rotational velocity (v sin i)||58.8±1.5 km/s|
As one of the nearest massive binary star systems to the Sun, Spica has been the subject of many observational studies.
Spica is believed to be the star that gave Hipparchus the data that led him to discover the precession of the equinoxes. 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. Nicolaus Copernicus made many observations of Spica with his home-made triquetrum for his researches on precession.
Spica is 2.06 degrees from the ecliptic and can be occulted by the Moon and sometimes by 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. 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.
A method of finding Spica is to follow the arc of the handle of the Big Dipper (or Plough) 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."
Spica is a close binary star whose components orbit each other every four days. They stay close together enough 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. 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.
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. 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.
Spica is a polarimetric variable, first discovered to be such in 2016. The majority of the polarimetric signal is the result of the reflection of the light from one star off the other (and vice versa). The two stars in Spica were the first ever to have their reflectivity (or geometric albedo) measured. The geometric albedos of Spica A and B are, respectively, 3.61 percent and 1.36 percent, values that are low compared to planets.
The MK spectral classification of Spica is typically considered to be an early B-type main sequence star. Individual spectral types for the two components are difficult to assign accurately, especially for the secondary due to the Struve–Sahade effect. The Bright Star Catalogue derived a spectral class of B1 III-IV for the primary and B2V for the secondary, but later studies have given various different values.
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 main-sequence star. The evolutionary stage has been calculated to be near or slightly past the end of the main sequence phase. This is a massive star with more than 10 times the mass of the Sun and seven times the Sun's radius. The bolometric luminosity of the primary is about 20,500 times that of the Sun, and nine 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.
The primary is classified as a Beta Cephei 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.
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. It may be caused by a strong stellar wind from the primary scattering the light from secondary when it is receding. This star is smaller than the primary, with about 7 times the mass of the Sun and 3.6 times the Sun's radius. Its stellar classification is B2 V, making this a main-sequence star.
Other traditional names are Azimech //, from Arabic السماك الأعزل al-simāk al-ʼaʽzal 'the unarmed simāk' (of unknown meaning,, cf. Eta Boötis); Alarph, Arabic for 'the grape-gatherer' or 'gleaner', and Sumbalet (Sombalet, Sembalet and variants), from Arabic سنبلة sunbulah "ear of grain".
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Spica for this star. It is now so entered in the IAU Catalog of Star Names.
In Chinese, 角宿 (Jiǎo Xiù), meaning Horn (asterism), refers to an asterism consisting of Spica and ζ Virginis. Consequently, the Chinese name for Spica is 角宿一 (Jiǎo Xiù yī, English: the First Star of Horn).
A South Korean Girl Group was named after the star.
In a non-canonical chapter in Re:Zero -Starting Life in Another World-, Subaru had a daughter with Rem named Spica.
- "How to pronounce Spica". Retrieved 2017-02-19.
- "Main definitions of spica in English". Oxford Dictionaries. Retrieved 2018-02-19.
- van Leeuwen, F. (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. Vizier catalog entry
- 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.
- 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.
- Johnson, H. L; Morgan, W. W (1953). "Fundamental stellar photometry for standards of spectral type on the Revised System of the Yerkes Spectral Atlas". The Astrophysical Journal. 117: 313. Bibcode:1953ApJ...117..313J. doi:10.1086/145697.
- Bright Star Catalogue. Yale University Observatory. 1982.
- Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
- 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.
- Tkachenko, A.; et al. (May 2016), "Stellar modelling of Spica, a high-mass spectroscopic binary with a β Cep variable primary component", Monthly Notices of the Royal Astronomical Society, 458 (2): 1964–1976, arXiv:1601.08069, Bibcode:2016MNRAS.458.1964T, doi:10.1093/mnras/stw255
- "V* alf Vir -- Variable Star of beta Cep type". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-04-13.
- 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.
- Evans, James (1998). The History and Practice of Ancient Astronomy. Oxford University Press. p. 259. ISBN 978-0-19-509539-5.
- Allen, Richard Hinckley (2003). Star Names and Their Meanings. Kessinger Publishing. p. 468. ISBN 978-0-7661-4028-8.
- 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.
- Moesgaard, Kristian P. (1973). "Copernican influence on Tycho Brahe". In Jerzy Dobrzycki (ed.). 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.
- "Earth-Sky Tonight, March 26, 2010". Archived from the original on July 7, 2011. Retrieved 2018-08-15.
- Breit, Derek C. (March 12, 2010). "Diary of Astronomical Phenomena 2010". Poyntsource.com. Retrieved 2010-04-13.
- Rao, Joe (June 15, 2007). "Arc to Arcturus, Speed on to Spica". Space.com. Retrieved 14 August 2018.
- "Follow the arc to Arcturus, and drive a spike to Spica | EarthSky.org". earthsky.org. April 8, 2018. Retrieved 14 August 2018.
- 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.
- Morris, S. L. (August 1985). "The ellipsoidal variable stars". Astrophysical Journal, Part 1. 295: 143–152. Bibcode:1985ApJ...295..143M. doi:10.1086/163359.
- 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.
- 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.
- Bailey, Jeremy; Cotton, Daniel V.; Kedziora-Chudczer, Lucyna; De Horta, Ain; Maybour, Darren (2019-04-01). "Polarized reflected light from the Spica binary system". Nature Astronomy. doi:10.1038/s41550-019-0738-7.
- Popper, Daniel M (1980). "Stellar Masses". Annual Review of Astronomy and Astrophysics. 18: 115–164. Bibcode:1980ARA&A..18..115P. doi:10.1146/annurev.aa.18.090180.000555.
- Odell, A. P (1980). "The structure of Alpha Virginis. III - the pulsation characteristics". The Astrophysical Journal. 236: 536. Bibcode:1980ApJ...236..536O. doi:10.1086/157771.
- Schnerr, R. S.; et al. (June 2008). "Magnetic field measurements and wind-line variability of OB-type stars". Astronomy and Astrophysics. 483 (3): 857–867. arXiv:1008.4260. Bibcode:2008A&A...483..857S. doi:10.1051/0004-6361:20077740.
- Kaler, Jim. "Spica". Stars. Retrieved 2010-04-15.
- Firestone, R. B. (July 2014), "Observation of 23 Supernovae That Exploded <300 pc from Earth during the past 300 kyr" (PDF), The Astrophysical Journal, 789 (1): 11, Bibcode:2014ApJ...789...29F, doi:10.1088/0004-637X/789/1/29, 29.
- Gies, Douglas R.; Bagnuolo, William G. Jr.; Penny, Laura R. (April 1997). "Photospheric Heating in Colliding-Wind Binaries". Astrophysical Journal. 479 (1): 408. Bibcode:1997ApJ...479..408G. doi:10.1086/303848.
- Richard Hinckley Allen. "Star Names - Their Lore and Meaning". Retrieved 2018-08-15.
- "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
- "IAU Catalog of Star Names". Retrieved 28 July 2016.
- 陳久金 (2005). 中國星座神話 (in Chinese). 五南圖書出版股份有限公司. ISBN 978-986-7332-25-7.
- "AEEA 天文教育資訊網, Activities of Exhibition and Education in Astronomy" (in Chinese). National Museum of Natural Science, Taiwan. Retrieved 2018-08-15.