Star of the Month
R Leporis (Hind’s Crimson Star)
Position: 04 hrs 59.6 min -14 deg 48 min.
Due south at 21:22 (GMT) on 15 January 2020
Taken from the Simbad website
Having already met three variable stars over the last few months, we now have a fourth variable star, R Leporis, which is a Mira-type variable, or a carbon star. These intensely red stars fascinated nineteenth century observers including the Danish astronomer Hans Schjellerup (1827-1887), Irish astronomer John Birmingham (1816-1884), John Russell Hind (1823-1895) and Rev. Thomas Espin (1858-1934), who took over the editing of Celestial Objects for Common Telescopes from Rev. Thomas Webb. R Leporis was discovered by Hind in 1845 and is sometimes called Hind’s crimson star. These carbon stars contain more carbon than oxygen and also have a low temperature so the carbon atoms can exist as molecules such as carbon monoxide and even methane and Buckminsterfullerene. Clouds of soot float across the star dimming it as they pass over. The red colour is a result of the absorption of blue light by the carbon compounds and probably also diffraction by the soot particles. These stars are very red and in contrast to red giants such as Betelgeuse are actually seen as red rather than orange-red. The B-V value for R Leporis is a remarkable 5.7 compared with 1.9 for Betelgeuse or 1.8 for Antares; there are only a few carbon stars which have a higher value. To find R Leporis, find an irregular quadrilateral of third magnitude stars underneath Orion roughly on the same level as Sirius. The left-hand (or eastern) stars are Alpha and Beta Leporis (Arneb and Nihal) and the right-hand pair are Mu and Epsilon Leporis. Follow the line between Alpha and Mu Leporis (the top of the quadrilateral) and go about a quarter as far again and R Leporis should be found as a red star of maximum magnitude 5.5. In Havering you will always need binoculars or a telescope to see it. R Leporis has a period of 14.5 months; over the last century its period has varied between 418 days and 441 days. It is rarely as bright as its stated maximum of 5.5. Recent maxima have been between 6.5 and 7 and the star spends much of its time around 8 to 9. Recent minima have been consistently about 10 rather than the stated minimum of 11.7. Its red colour tends to be more pronounced when it is at its dimmest, perhaps partly because of these clouds of soot.