Double Star of the Month:
Lambda Orionis
AKA: Meissa, STF 738
Position: 05 hr 35.1 min +09 degrees 56 min 03 sec
Due south at 23:57 (GMT) on 15 December 2021
Image credit: Jeremy Perez (http://www.perezmedia.net/beltofvenus)
Used with permission
I have not hitherto mentioned any multiple stars, mainly because it is boring for the reader to have to plough through a detailed description of the various members of the multiple and it is sometimes tricky to find the fainter members in the telescope. However Lambda Orionis, better known as Meissa, is such a pretty sight that I feel obliged to mention it. It has no less than six members all told, but all but the main pair are below magnitude 9, so we can more or less treat it as a double. The main star is magnitude 3.5 so it can easily be seen from Havering. The main companion is magnitude 5.5 and easily seen in the telescope. With a separation of 4.3 arcseconds, it is fairly tight so you will need to use a reasonably high magnification. The two stars are more or less white, but you may see slight differences between them. William Herschel who discovered the multiplicity of the star on 7 October 1779 described them as white and pale rose. Herschel also mentioned two other stars which are magnitude 9.6 and 78.5 arcseconds distant which is to the right of the main star and the other one is slightly brighter at 9.2 and is 151 arcseconds distant in roughly the same direction. The main star is a giant star of type O8 which is about 27 times the mass of our Sun. The three companions mentioned here are all Be type stars, the nearest one being B0 and the others being B9. Hence all of these stars are massive and hot. Perhaps surprisingly they are not physically connected but are part of the star cluster Collinder 69 which provides a beautiful background to this star.
As the presence of these O and B stars indicates, it is a young cluster but it also contains a number of low mass stars including T Tauri stars (see Star of the Month for December 2020) and brown dwarfs. There is a good deal of nebulosity in this region and there is a ring, not visible in amateur telescopes, which is the relic of a supernova a million years ago. It is easy to find Meissa, which lies above Betelgeuse on one side and Bellatrix on the other, but higher up. It is sometimes considered to be the “head” of Orion. The Arabic name Al-Maisan from which Meissa is derived means the shining one which seems hardly appropriate for a star of magnitude 3.5, but the name was originally applied to Gamma Geminorum which is magnitude 1.9. For some unknown reason the name migrated to the star discussed here.