Tau Scorpii

Alniyat, τ Sco

Alniyat is δ star in one of the Scorpion's claws.
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 16h 35m 52.9537s[1]
Declination -28° 12′ 57.658″[1]
Apparent magnitude (V) 2.814 [1]
Characteristics
Spectral type B0.2V [1]
U−B color index -1.01 [2]
B−V color index -0.25 [2]
Astrometry
Radial velocity (Rv) 2.0[1] km/s
Proper motion (μ) RA: -8.59 [1] mas/yr
Dec.: -22.50 [1] mas/yr
Parallax (π) 7.59 ± 0.78[3] mas
Distance approx. 430 ly
(approx. 130 pc)
Absolute magnitude (MV) -2.78
Details
Mass ~12 [4] M☉
Radius 5 [4] R☉
Luminosity 18,000 [4] L☉
Temperature 30,700 [4] K
Metallicity -0.14 Fe/H[5]
Rotation ~10-24 km/s [6][7]
Age ? years
Other designations
Alniyat, Al Niyat τ Sco, 23 Sco, HR 6165, HD 149438, FK5 620, HIP 81266, SAO 184481, GC 22303
Database references
SIMBAD data

Coordinates: 16h 35m 52.9537s, −28° 12′ 57.658″

Tau Scorpii is a star in the constellation Scorpius. Tau Scorpii also 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".

Tau Scorpii is a blue-white B-type dwarf with an apparent magnitude of +2.82. It is approximately 430 light years from Earth.

Contents

Companion

As yet there is no evidence of a companion in orbit around τ Sco.[8]

Magnetic field

It is a magnetic star whose surface magnetic field was mapped by means of Zeeman–Doppler imaging.[9]

X-ray source

τ Sco is an OB star (B0.2V) that shows O VI superionization caused by X-ray ionization and the Auger ionization effect.[8] ROSAT observed that τ Sco was a star with a harder X-ray spectrum than usual for B0V stars.[8] Over the energy range 0.8-1.2 keV, its X-ray luminosity is Lx = 1.8 x 1031 erg s−1 with a large Lx to Lbol of log Lx/Lbol = -6.53 from ASCA measurements.[8] ROSAT arrived at a log Lx/Lbol ≃ -5.93 for the range 0.1-2.4 keV.[8]

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.[8]

See also

References

  1. ^ a b c d e f g "SIMBAD query result: tau Sco -- Star". Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Tau+Sco&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id. Retrieved 2010-08-01. 
  2. ^ a b Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewski, W. Z. (1966). "UBVRIJKL photometry of the bright stars." (PDF). Comm. Lunar Plan. Lab., 4. Bibcode 1966CoLPL...4...99J. 
  3. ^ Perryman, M. A. C. et al. (1997), "The Hipparcos Catalogue", Astronomy & Astrophysics 323: L49–L52, Bibcode 1997A&A...323L..49P 
  4. ^ a b c d Professor James B. (Jim) Kaler. "Al NIYAT (Tau Scorpii)". University of Illinois. http://stars.astro.illinois.edu/sow/alniyat-t.html. Retrieved 2010-08-01. 
  5. ^ KILIAN J. (February 1994). "Chemical abundances in early B-type stars. V. Metal abundances and LTE/NLTE comparison." (PDF). Astronomy and Astrophysics (ISSN 0004-6361), 282 (3,): pP. 867–873. Bibcode 1994A&A...282..867K. 
  6. ^ Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities.". Contr. Oss. Astrof. Padova in Asiago 239. Bibcode 1970CoAsi.239....1B. 
  7. ^ "Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR. Centre de Données astronomiques de Strasbourg. http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%206165. Retrieved 2010-08-01. 
  8. ^ a b c d e f Mewe R, Raassen AJJ, Cassinelli JP, van der Hucht KA, Miller NA, Güdel M (2003). "High-resolution X-ray spectroscopy of τ Scorpii (B0.2V) with XMM-Newton". Astron Astrophys. 398 (1): 203–11. Bibcode 2003A&A...398..203M. doi:10.1051/0004-6361:20021577. http://dare.uva.nl/document/40494. 
  9. ^ Donati, J.-F.; et al., I.D.; Jardine, M. M.; Petit, P.; Catala, C.; Landstreet, J. D.; Bouret, J.-C.; Alecian, E. et al. (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. 

External links

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