Theta Tucanae

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θ Tucanae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Tucana
Right ascension 00h 33m 23.3s
Declination −71° 15' 58"
Apparent magnitude (V) +6.11
Distance 490 ± 38 ly
(150 ± 12 pc)
Spectral type A7IV
Other designations
HR 139, HD 3112, CP-71 20, FK5 2035, HIP 2629, SAO 255679.

Theta Tucanae (θ Tuc, θ Tucanae) is a star in the constellation Tucana.

Like other stars in Tucana, it was given its Bayer designation by French explorer and astronomer Nicolas Louis de Lacaille in 1756.[1] It was found to be variable in 1971.[2]

Theta Tucanae is a white A-type subgiant of spectral type A7IV with a mean apparent magnitude of +6.11, located approximately 423 light years from Earth.[3] It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +6.06 to +6.15 with periods of around 70 to 80 minutes.[2][4] These Delta Scuti variables are a class of short-period (six hours at most) pulsating stars that have been used as standard candles and as subjects to study astroseismology.[5]

Observations over the decades have shown that its colour slightly changes and it exhibits variation in light that indicate the star is actually an ellipsoidal binary with a period of seven days.[6] The system is more luminous than expected, given the spectrum and distance of the primary star, indicating that the companion star must be contributing a good proportion of its light. Stellar evolution modelling has concluded that the system likely begun as a binary system, with one star about double the Sun's mass and the other roughly equivalent to that of the sun. The larger star eventually aged and expanded as it used up its core hydrogen, and begun having its mass siphoned off by the smaller star; the system is likely to have been an Algol-type eclipsing binary at this stage. This star appears now to be an aged star composed mostly of helium with very little hydrogen and with a mass of 0.2 solar masses and around 37 times the luminosity of our Sun and surface temperature of 7000 K, while the once-smaller star is the Delta Scuti variable that is now around two solar masses.[7] Around 0.8 solar masses has been lost from the system over time.[7]


  1. ^ Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, VA: The McDonald & Woodward Publishing Company. pp. 305–07. ISBN 978-0-939923-78-6. 
  2. ^ a b Stobie, R. S.; Shobbrook, R. R. (1976). "Frequency Analysis of the Delta Scuti star, Theta Tucanae". Monthly Notices of the Royal Astronomical Society 174: 401–09. Bibcode:1976MNRAS.174..401S. doi:10.1093/mnras/174.2.401. 
  3. ^ "Theta Tucanae - Variable Star of Delta Scuti type". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 2 February 2014. 
  4. ^ Watson, Christopher (4 January 2010). "Theta Tucanae". AAVSO Website. American Association of Variable Star Observers. Retrieved 2 February 2014. 
  5. ^ Templeton, Matthew (16 July 2010). "Delta Scuti and the Delta Scuti Variables". Variable Star of the Season. AAVSO (American Association of Variable Star Observers). Retrieved 2 February 2014. 
  6. ^ Sterken, C. (1997). "The δ Scuti star &thetas; Tucanae. II. UVBY colour variations and pulsational/orbital properties". Astronomy and Astrophysics 325: 563–68. Bibcode:1997A&A...325..563S. 
  7. ^ a b Templeton, Matthew R.; Bradley, Paul A.; Guzik, Joyce A. (2000). "Asteroseismology of the Multiply Periodic δ Scuti Star Theta Tucanae". The Astrophysical Journal 528: 979–88. Bibcode:2000ApJ...528..979T. doi:10.1086/308191.