M 103

Open Cluster M103 (NGC 581), type ‘d’,

which Messier included from Mechain’s report, but had not the time to

observe before publication.

This cluster of at least 40 proven members is one of the more remote open

clusters in Messier’s catalog, at about 8,000 light years.

Its appearance is dominated by the non-member binary Sigma 131 (components

A, 7.3 mag, and B, 10.5 mag, separated 13.8″ in position angle 142 deg,

at 1956).

The two brightest cluster members are a B5 Ib supergiant and a B2 III giant,

while the lot of main sequence stars indicate an age of about 9 million

years, according to Cecilia Payne-Gaposhkin’s “Stars and Clusters”, while the

Star Catalog 2000 gives 22 million years. New calculations of the

significantly higher age of 25 million years for M103.

M103 is approaching us at 37 km/sec. Its Trumpler type has been given as

II,3,m (Trumpler, according to Glyn Jones), III,2,p (Sky Catalog 2000)

and II,2,m (Götz).