Not to be confused with Sigma Coronae Borealis.

S Coronae Borealis (S CrB) is a Mira variable star in the constellation Corona Borealis. Its apparent magnitude varies between 5.3 and 13.6, with a period of 360 days—just under a year. Within the constellation, it lies to the west of Theta Coronae Borealis, and around 1 degree southeast of the eclipsing binary star U Coronae Borealis.[1] When it is near its maximum brightness, it can be seen with the naked eye, under good observing conditions.

Variability

S Coronae Borealis was discovered to vary in brightness by German amateur astronomer Karl Ludwig Hencke in 1860.[2] It was classified as a long period variable star as other similar objects were discovered,[3] and later as a Mira variable.[4] The maximum range of variation is from magnitude 5.3 to 13.6 although individual maxima and minima can vary in brightness. The period of 360 days is fairly predictable.[5]

Properties

S Coronae Borealis is a cool red giant on the asymptotic giant branch (AGB). It pulsates, which causes its radius and temperature to change. One calculation found a temperature range of 2,350 K to 2,600 K,[6] although a more modern calculation gives a temperature of 2,864 K.[7] Similarly a calculation of the varying radius gives [6] although a modern calculation of the radius gives .[7] The bolometric luminosity varies much less than the visual magnitude and is estimated to be .[7] Its parallax has been measured by very-long-baseline interferometry (VLBI), yielding a result of 2.39 ± 0.17 mas, which converts to a distance of 1,300 ± 100 light-years.[8]

The masses of AGB stars are poorly known and cannot be calculated from their physical properties, but they can be estimated using asteroseismology. The pulsations of S Coronae Borealis lead to a mass estimate of 1.34 times that of the Sun.[7]

References

  1. ^ Plotner, Tammy & Vogt, Ken (2009). The Night Sky Companion: A Yearly Guide to Sky-Watching 2009. The Patrick Moore Practical Astronomy Series. Springer Science & Business Media. p. 194. ISBN 978-0387795096.
  2. ^ Hamel, Jürgen (2007). "Hencke, Karl Ludwig". The Biographical Encyclopedia of Astronomers. p. 481. doi:10.1007/978-0-387-30400-7_596. ISBN 978-0-387-31022-0.
  3. ^ Campbell, Leon (1926). "Maxima and minima of two hundred and seventy-two long period variable stars during the years 1900 – 1920". Annals of Harvard College Observatory. 79: 87. Bibcode:1926AnHar..79...87C
  4. ^ VSX (4 January 2010). "S Coronae Borealis". AAVSO Website. American Association of Variable Star Observers. Retrieved 27 June 2014.
  5. ^ Cotton, W. D.; Mennesson, B.; Diamond, P. J.; Perrin, G.; Coudé Du Foresto, V; Chagnon, G.; Van Langevelde, H. J.; Ridgway, S.; Waters, R.; Vlemmings, W.; Morel, S.; Traub, W.; Carleton, N.; Lacasse, M. (2004). "VLBA observations of SiO masers towards Mira variable stars". Astronomy and Astrophysics. 414: 275–288. Bibcode:2004A&A...414..275C. doi:10.1051/0004-6361:20031597
  6. ^ Wallerstein, G. (1977). "Are long-period variables really pulsating". Journal of the Royal Astronomical Society of Canada. 71: 298. Bibcode:1977JRASC..71..298W
  7. ^ Takeuti, Mine; Nakagawa, Akiharu; Kurayama, Tomoharu; Honma, Mareki (2013). "A Method to Estimate the Masses of Asymptotic Giant Branch Variable Stars". Publications of the Astronomical Society of Japan. 65 (3): 60. Bibcode:2013PASJ...65...60T. doi:10.1093/pasj/65.3.60
  8. ^ Vlemmings, W. H. T. & Van Langevelde, H. J. (2007). "Improved VLBI astrometry of OH maser stars". Astronomy and Astrophysics. 472 (2): 547. arXiv:0707.0918. Bibcode:2007A&A...472..547V. doi:10.1051/0004-6361:20077897. S2CID 18816871