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.[10]

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☉
Luminosity5,897[9] 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.[11] It was classified as a long period variable star as other similar objects were discovered,[12] 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.[13]

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]

References
  1. Van Leeuwen, F. (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. S2CID 18759600.
  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. S2CID 17804304.
  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. S2CID 18816871.
  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. McDonald, I.; De Beck, E.; Zijlstra, A. A.; Lagadec, E. (2018). "Pulsation-triggered dust production by asymptotic giant branch stars". Monthly Notices of the Royal Astronomical Society. 481 (4): 4984. arXiv:1809.07965. Bibcode:2018MNRAS.481.4984M. doi:10.1093/mnras/sty2607. S2CID 118969263.
  10. 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.
  11. 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.
  12. 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.
  13. 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: 275–288. Bibcode:2004A&A...414..275C. doi:10.1051/0004-6361:20031597.
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