Theta Tucanae

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

θ Tucanae
Observation data
Epoch J2000      Equinox J2000
Constellation Tucana
Right ascension  00h 33m 23.35876s[1]
Declination −71° 15′ 58.4904″[1]
Apparent magnitude (V) +6.109[2]
Characteristics
Spectral type A7IV[3]
U−B color index +0.18[4]
B−V color index +0.23[4]
Variable type δ Sct[5]
Astrometry
Radial velocity (Rv)2.3 ± 2[6] km/s
Proper motion (μ) RA: 73.40[1] mas/yr
Dec.: −13.42[1] mas/yr
Parallax (π)7.69 ± 0.22[1] mas
Distance420 ± 10 ly
(130 ± 4 pc)
Absolute magnitude (MV)+0.54[7]
Details[8]
Mass1.9–2.1 M☉
Luminosity20.2–25.1 L☉
Surface gravity (log g)3.818–3.923 cgs
Temperature7500–7685 K
Age0.69–1.04 Gyr
Other designations
CPD−71° 20, HD 3112, HIP 2629, HR 139, SAO 255679[5]
Database references
SIMBADdata

Like other stars in Tucana, it was given its Bayer designation by French explorer and astronomer Nicolas Louis de Lacaille in 1756.[9] It was found to be variable in 1971.[10]

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.[11] 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.[10][12] 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.[8]

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.[13] 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 the Sun and surface temperature of 7000 K, while the once-smaller star is the Delta Scuti variable that is now around two solar masses.[14] Around 0.8 solar masses has been lost from the system over time.[14]

References
  1. van Leeuwen, F.; et al. (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. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  3. Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
  4. Johnson, H. L. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99. Bibcode:1966CoLPL...4...99J.
  5. "tet Tuc". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 18 March 2017.
  6. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
  7. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  8. 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.
  9. 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.
  10. Stobie, R. S.; Shobbrook, R. R. (1976). "Frequency Analysis of the Delta Scuti star, Theta Tucanae". Monthly Notices of the Royal Astronomical Society. 174 (2): 401–09. Bibcode:1976MNRAS.174..401S. doi:10.1093/mnras/174.2.401.
  11. "Theta Tucanae - Variable Star of Delta Scuti type". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 2 February 2014.
  12. Watson, Christopher (4 January 2010). "Theta Tucanae". AAVSO Website. American Association of Variable Star Observers. Retrieved 2 February 2014.
  13. Sterken, C. (1997). "The δ Scuti star θ Tucanae. II. UVBY colour variations and pulsational/orbital properties". Astronomy and Astrophysics. 325: 563–68. Bibcode:1997A&A...325..563S.
  14. Templeton, Matthew R.; Bradley, Paul A.; Guzik, Joyce A. (2000). "Asteroseismology of the Multiply Periodic δ Scuti Star Theta Tucanae". The Astrophysical Journal. 528 (2): 979–88. Bibcode:2000ApJ...528..979T. doi:10.1086/308191.
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