Wednesday, 20 September 2017

Cr401: What is it?

Per Collinder was a Swedish astronomy student who, in 1931, compiled a list of open clusters as part of his paper "On structural properties of open galactic clusters and their spatial distribution". Strangely enough, he didn't grab a telescope and browsed the night's sky but studied photographs in search for clusters. Most of the 471 clusters on his list are not original and already appeared in the much older Messier and NGC catalogues. Number 401, however, is. Actually, it's so original that no-one seems to know for sure what good old Per had in mind when adding it to his list. 

Some sources claim that Cr401 refers to the bright double star HD185297, which is surrounded by an asterism of seven or eight stars. This seventh magnitude star is actually a very interesting double, with a smaller companion only 0.8 arc-seconds apart. Other sources state that Cr401 is the loose cluster just south of it (up on my sketch). Not even Stellarium, Sky Safari or my telescope's Argo Navis seem to agree! So in order to content all, I've sketched them both in the same field of view. Enjoy!


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