S Coronae Borealis

S Coronae Borealis (S CrB) is a Mira variable star in the constellation Corona Borealis. Its apparent magnitude varies between 5.8 and 14.1, 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.[9]

S Coronae Borealis
Observation data
Epoch J2000      Equinox J2000
Constellation Corona Borealis
Right ascension  15h 21m 23.9561s[1]
Declination +31° 22′ 02.573″[1]
Apparent magnitude (V) 5.80 – 14.1[2]
Characteristics
Spectral type M7e[3]
U−B color index 0.36[1]
B−V color index 1.71[1]
Variable type Mira[2]
Astrometry
Radial velocity (Rv)-5.12[4] km/s
Proper motion (μ) RA: -7.73[1] mas/yr
Dec.: -13.03[1] mas/yr
Parallax (π)2.39 ± 0.17[5] mas
Distance418+21
−18[5] pc
Absolute magnitude (MV)-0.8±0.3[6]
Details
Mass1.34[7] M☉
Radius308[7] (537–664)[8] R☉
Luminosity5623+863
−748[7] L☉
Temperature2,864[7] (2,350–2,600)[8] K
Other designations
S Coronae Borealis, HD 136753, BD+31°2725, HIP 75143, GC 20662, SAO 64652, GSC 02563-01338, DO 15223, AAVSO 1517+31
Database references
SIMBADdata
Light curve for the Mira variable S Coronae Borealis over six years

Variability

S Coronae Borealis was discovered to vary in brightness by German amateur astronomer Karl Ludwig Hencke in 1860.[10] It was classified as a long period variable star as other similar objects were discovered,[11] and later as a Mira variable.[2] The maximum range of variation is from magnitude 5.8 to 14.1 although individual maxima and minima can vary in brightness. The period of 360 days is fairly predictable.[12]

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,[8] although a more modern calculation gives a temperature of 2,864 K.[7] Similarly a calculation of the varying radius gives 537 to 664 R☉[8] although a modern calculation of the radius gives 308 R☉.[7] The bolometric luminosity varies much less than the visual magnitude and is estimated to be 5,623 L☉.[7] Its parallax has been measured by very-long-baseline interferometry (VLBI), yielding a result of 2.39 ± 0.17 millarcseconds, which converts to a distance of 1300 ± 100 light-years.[5]

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]

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gollark: Anyway, please answer my three questions.
gollark: Even if it would be preferable if they didn't.
gollark: They might end up doing it anyway, though, yes.
gollark: How are you defining "functionally assist" here, how do they do that, and do you care about intent at all?

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. VSX (4 January 2010). "S Coronae Borealis". AAVSO Website. American Association of Variable Star Observers. Retrieved 27 June 2014.
  3. Bieging, John H.; Schmidt, Gary D.; Smith, Paul S.; Oppenheimer, Benjamin D. (2006). "Optical Spectropolarimetry of Asymptotic Giant Branch and Post–Asymptotic Giant Branch Stars". The Astrophysical Journal. 639 (2): 1053. Bibcode:2006ApJ...639.1053B. doi:10.1086/499772.
  4. Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics. 430: 165. arXiv:astro-ph/0409579. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  5. 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.
  6. Feijth, H. (1977). "The variable S Coronae Borealis". Zenit. 4: 451. Bibcode:1977Zenit...4..451F.
  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. Wallerstein, G. (1977). "Are long-period variables really pulsating". Journal of the Royal Astronomical Society of Canada. 71: 298. Bibcode:1977JRASC..71..298W.
  9. 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 038779509X.
  10. 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.
  11. 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.
  12. 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" (PDF). Astronomy and Astrophysics. 414: 275. Bibcode:2004A&A...414..275C. doi:10.1051/0004-6361:20031597.
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