S Coronae Borealis
Star in the constellation Corona Borealis
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S Coronae Borealis (S CrB) is a Mira variable star in the constellation Corona Borealis located about 1,400 light-years away. Its apparent magnitude varies between 5.3 and 13.6, with a period of 360 days, representing about a 2000–fold change in brightness. 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] When it is near its maximum brightness, it can be seen with the naked eye, under good observing conditions.
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Corona Borealis |
| Right ascension | 15h 21m 23.9561s[1] |
| Declination | +31° 22′ 02.573″[1] |
| Apparent magnitude (V) | 5.3 – 13.6[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 mas[5] |
| Distance | 418+21 −18[5] pc |
| Absolute magnitude (MV) | −0.8±0.3[6] |
| Details | |
| Mass | 1.34[7] M☉ |
| Radius | 308[7] (537–664)[8] R☉ |
| Luminosity | 5,897[9] L☉ |
| Temperature | 2,864[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 | |
| SIMBAD | data |
With a typical local maximum magnitude around 7, S Coronae Borealis' is on average brighter than T Coronae Borealis or W Coronae Borealis.
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 5.3 to 13.6 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 mas, which converts to a distance of 1,300±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]