S Coronae Borealis
{{Short description|Star in the constellation Corona Borealis}}{{distinguish|Sigma Coronae Borealis}}
{{Starbox begin
| name=S Coronae Borealis
}}
{{Starbox observe
| epoch=J2000
| constell=Corona Borealis
}}
{{Starbox character
| variable=Mira
}}
{{Starbox astrometry
| parallax=2.39
| p_error=0.17
}}
{{Starbox detail
| radius=308 {{nowrap|(537–664)}}
| temperature=2,864 {{nowrap|(2,350–2,600)}}
| metal=
| rotation=
| age=
}}
{{Starbox catalog
| names= S Coronae Borealis, HD 136753, BD+31°2725, HIP 75143, GC 20662, SAO 64652, GSC 02563-01338, DO 15223, AAVSO 1517+31
}}
{{Starbox reference
|Simbad=S+CrB
}}
{{Starbox end}}
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.{{cite book | title=The Night Sky Companion: A Yearly Guide to Sky-Watching 2009 | series=The Patrick Moore Practical Astronomy Series | first1=Tammy | last1=Plotner | first2=Ken | last2=Vogt | publisher=Springer Science & Business Media | year=2009| isbn=978-0387795096 | page=194 | url=https://books.google.com/books?id=bTthlUmBQpAC&pg=PA194 }} 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. It was classified as a long period variable star as other similar objects were discovered, and later as a Mira variable. 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.
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, although a more modern calculation gives a temperature of 2,864 K. Similarly a calculation of the varying radius gives {{solar radius|537 to 664}} although a modern calculation of the radius gives {{solar radius|308}}. The bolometric luminosity varies much less than the visual magnitude and is estimated to be {{solar luminosity|5,623}}. Its parallax has been measured by very-long-baseline interferometry (VLBI), yielding a result of {{val|2.39|0.17|ul=mas}}, which converts to a distance of {{val|fmt=commas|1300|100|u=light-years}}.
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.
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References
{{reflist|refs=
{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=10601 |title=S Coronae Borealis|author=VSX|date=4 January 2010|work=AAVSO Website|publisher=American Association of Variable Star Observers|accessdate=27 June 2014}}
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{{Stars of Corona Borealis}}
{{DEFAULTSORT:S Coronae Borealis}}