Tau Scorpii
 Location of τ Scorpii (circled) |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Scorpius |
| Right ascension | 16h 35m 52.95285s[1] |
| Declination | -28° 12′ 57.6615″[1] |
| Apparent magnitude (V) | +2.82[2] |
| Characteristics | |
| Spectral type | B0.2 V[3] |
| U−B color index | –1.039[2] |
| B−V color index | –0.252[2] |
| Astrometry | |
| Radial velocity (Rv) | +2.0[4] km/s |
| Proper motion (μ) | RA: –9.89[1] mas/yr Dec.: –22.83[1] mas/yr |
| Parallax (π) | 6.88 ± 0.53[1] mas |
| Distance | 470 ± 40 ly (150 ± 10 pc) |
| Details | |
| Mass | 15[3] M☉ |
| Radius | 6.5[3] R☉ |
| Surface gravity (log g) | 4.24[5] |
| Luminosity | 18,000[6] L☉ |
| Temperature | 31,440[7] K |
| Metallicity [Fe/H] | –0.14[5] dex |
| Rotation | 41 days[8] |
| Rotational velocity (v sin i) | 10[9] km/s |
| Other designations | |
Tau Scorpii is a star in the southern zodiac constellation of Scorpius. It has the traditional name Alniyat or Al Niyat, which it shares with σ Scorpii. The name derives from the Arabic النياط an-niyāţ meaning "the arteries". The apparent visual magnitude of Tau Scorpii is +2.8,[2] while parallax measurements yield a distance estimate of roughly 470 light-years (150 parsecs) from Earth.[1]
Compared to the Sun, Tau Scorpii is a massive OB star with 15 times the Sun's mass and more than six times the radius of the Sun.[3] It is radiating about 18,000[6] times the Sun's luminosity from its outer envelope at an effective temperature of 31,440 K.[7] This gives it the blue-white hue characteristic of B-type stars.[11] As yet there is no evidence of a companion in orbit around τ Sco.[12] It is a magnetic star whose surface magnetic field was mapped by means of Zeeman–Doppler imaging.[13] Tau Scorpii is rotating relatively slowly with a period of 41 days.[8]
The spectrum of this star shows triply-ionized oxygen (O IV) that is being generated by X-rays and the Auger ionization effect. Observations with the ROSAT space telescope showed it has a higher energy (harder) X-ray spectrum than is usual for B0 V stars. Over the energy range 0.8–1.2 keV, its X-ray luminosity is Lx = 1.8 × 1031 erg s–1 with a large Lx to Lbol of log Lx/Lbol = –6.53 from ASCA measurements. ROSAT measurements showed a log Lx/Lbol ≃ –5.93 for the range 0.1-2.4 keV.[12]
The hard component of the X-ray spectrum from τ Sco as studied with XMM-Newton supports the presence of in-falling clumps of plasma in τ Sco.[12]
[edit] See also
[edit] References
- ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ a b c d Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A Photometric Investigation of the Scorpio-Centaurus Association", Astrophysical Journal Supplement 15: 459, Bibcode 1968ApJS...15..459G, doi:10.1086/190168
- ^ a b c d Howk, J. Christopher et al. (May 2000), "Stagnation and Infall of Dense Clumps in the Stellar Wind of τ Scorpii", The Astrophysical Journal 534 (1): 348–358, Bibcode 2000ApJ...534..348H, doi:10.1086/308730
- ^ Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode 1999VeARI..35....1W
- ^ a b Kilian, J. (February 1994), "Chemical abundances in early B-type stars. 5: Metal abundances and LTE/NLTE comparison", Astronomy and Astrophysics 282 (3): 867–873, Bibcode 1994A&A...282..867K
- ^ a b Kaler, James B., Al NIYAT (Tau Scorpii), University of Illinois, http://stars.astro.illinois.edu/sow/alniyat-t.html, retrieved 2010-08-01
- ^ a b Zorec, J. et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics 501 (1): 297–320, Bibcode 2009A&A...501..297Z, doi:10.1051/0004-6361/200811147
- ^ a b Strassmeier, Klaus G. (September 2009), "Starspots", The Astronomy and Astrophysics Review 17 (3): 251–308, Bibcode 2009A&ARv..17..251S, doi:10.1007/s00159-009-0020-6
- ^ Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago 239 (1), Bibcode 1970CoAsi.239....1B
- ^ "tau Sco -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Tau+Sco, retrieved 2010-08-01
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16
- ^ a b c Mewe, R. et al. (2003), "High-resolution X-ray spectroscopy of τ Scorpii (B0.2V) with XMM-Newton", Astronomy & Astrophysics 398 (1): 203–11, Bibcode 2003A&A...398..203M, doi:10.1051/0004-6361:20021577, http://dare.uva.nl/document/40494
- ^ Donati, J.-F. (2006), "The surprising magnetic topology of τ Sco: fossil remnant or dynamo output?", Monthly Notices of the Royal Astronomical Society 370 (2): 629–644, arXiv:astro-ph/0606156, Bibcode 2006MNRAS.370..629D, doi:10.1111/j.1365-2966.2006.10558.x
Coordinates: 
16h 35m 52.9537s, −28° 12′ 57.658″
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