Alpha Trianguli

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Alpha Trianguli
Diagram showing star positions and boundaries of the Triangulum constellation and its surroundings
Cercle rouge 100%.svg

Location of α Trianguli (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Triangulum
Right ascension 01h 53m 04.90710s[1]
Declination +29° 34′ 43.7801″[1]
Apparent magnitude (V) +3.42[2]
Spectral type F5III[3] to F6IV[4] + M[5]
U−B color index +0.06[2]
B−V color index +0.48[2]
Variable type Ellipsoidal variable[4]
Radial velocity (Rv) –12.6[6] km/s
Proper motion (μ) RA: 10.82[1] mas/yr
Dec.: –234.24[1] mas/yr
Parallax (π) 51.50 ± 0.23[1] mas
Distance 63.3 ± 0.3 ly
(19.42 ± 0.09 pc)
Absolute magnitude (MV) 1.98[7]
α Tri A
Mass 1.70[5] M
Radius 3.22[5] R
Surface gravity (log g) 3.91[8] cgs
Temperature 6,288[8] K
Metallicity [Fe/H] –0.09[7] to 0.00[8] dex
Rotational velocity (v sin i) 81.6[9] km/s
Age 1.6[7] Gyr
α Tri B
Mass 0.11[5] M
Other designations
Ras al Muthallah, Caput Trianguli, α Trianguli, α Tri, Alpha Tri, [10] 2 Trianguli, HR 544, HD 11443, BD+28 312, FK5 64, HIP 8796, SAO 74996.[11]

Alpha Trianguli (Alpha Tri, α Trianguli, α Tri) is the Bayer designation for a binary star in the constellation Triangulum. It has the traditional names Ras al Muthallah[10] (or Mothallah) and Caput Trianguli.

Estimates of the combined stellar classification for this system range from F5III[3] to F6IV,[4] with the luminosity class of 'IV' or 'III' indicating the primary component is a subgiant or giant star, respectively. It is a member of a close binary system—a spectroscopic binary—whose components complete an orbit about their center of mass once every 1.736 days. Because the primary star is rotating rapidly, it has assumed the shape of an oblate spheroid. The ellipsoidal profile of the star, as viewed from Earth, varies over the course of an orbit causing the luminosity to vary in magnitude during the same period.[4] Such stars are termed ellipsoidal variables. Within a few million years, as the primary continues to evolve into a red giant star, the system may become a semi-detached binary with the Roche lobe becoming filled to overflowing.[5]

The mean apparent magnitude of +3.42[2] for this pair is bright enough to be readily seen with the naked eye. It forms the second brightest star or star system in this generally faint constellation, following Beta Trianguli. Parallax measurements place this system at a distance of 63.3 light-years (19.4 parsecs) from the Earth. The effective temperature of the primary's outer envelope is 6,288 K,[8] giving it a yellow-white hue typical of F-type stars.[12] It has a mean radius about three times the radius of the Sun.[4] The system is an estimated 1.6 billion years old.[7]

Naming and etymology[edit]

  • The name Ras al Muthallah[10] (or Mothallah) and Caput Trianguli,[10] derived from the Arabic رأس المثلث ra’s al-muθallaθ "the head of the triangle" and its Latin translation.
  • α Tri is listed as UR.BAR.RA "The Wolf", bearing the epithet "the seeder of the plough" in the MUL.APIN, listed after "The Plough", the name for a constellation formed of Triangulum plus Gamma Andromedae.[13]
  • In combination with Beta Trianguli, these stars were called Al Mīzān, which is Arabic for "The Scale Beam".[14]


  1. ^ a b c d e 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. ^ a b c d Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode:1966CoLPL...4...99J 
  3. ^ a b Abt, Helmut A. (January 2009), "MK Classifications of Spectroscopic Binaries", The Astrophysical Journal Supplement 180 (1): 117–118, Bibcode:2009ApJS..180..117A, doi:10.1088/0067-0049/180/1/117 
  4. ^ a b c d e Fekel, Francis C.; Warner, Phillip B.; Kaye, Anthony B. (April 2003), "Spectroscopy of Early F Stars: γ Doradus Candidates and Possible Metallic Shell Stars", The Astronomical Journal 125 (4): 2196–2214, Bibcode:2003AJ....125.2196F, doi:10.1086/368239 
  5. ^ a b c d e Fuhrmann, Klaus (February 2008), "Nearby stars of the Galactic disc and halo - IV", Monthly Notices of the Royal Astronomical Society 384 (1): 173–224, Bibcode:2008MNRAS.384..173F, doi:10.1111/j.1365-2966.2007.12671.x 
  6. ^ Wilson, Ralph Elmer (1953), General catalogue of stellar radial velocities, Carnegie Institution of Washington, Bibcode:1953QB901.W495..... 
  7. ^ a b c d Nordström, B. et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics 418: 989–1019, arXiv:astro-ph/0405198, Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959 
  8. ^ a b c d Balachandran, Suchitra (May 1990), "Lithium depletion and rotation in main-sequence stars", Astrophysical Journal, Part 1 354: 310–332, Bibcode:1990ApJ...354..310B, doi:10.1086/168691 
  9. ^ Schröder, C.; Reiners, J. H. M. M.; Schmitt (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo", Astronomy and Astrophysics 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377 
  10. ^ a b c d Allen, R. H. (1899). Star Names: Their Lore and Meaning. G. E. Stechert. p. 416. 
  11. ^ "V* alf Tri -- Ellipsoidal variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-12 
  12. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  13. ^ Rogers, J. H. (February 1998). "Origins of the ancient constellations: I. The Mesopotamian traditions". Journal of the British Astronomical Association, no.1 108: 9–28. Bibcode:1998JBAA..108....9R. 
  14. ^ Garfinkle, Robert A. (1997), Star-Hopping: Your Visa to Viewing the Universe, Cambridge University Press, p. 238, ISBN 0-521-59889-3 

External links[edit]