NGC 3532 is a large, rich open cluster at the prow of Argo. We were strongly motivated by Andy Campbell's recent much
wider field shot, which includes this area, using combined narrowband and RGB, and showing much interesting nebulosity.
Here we have only the Eastern half of the cluster NGC 3532, a small part of Andy's field, with 6 minutes each RGB (2 min subs) and 3 hrs H-alpha in 1 hr subs as luminance.
Full size image
We tried to capture both the nebulosity and the richly varying colours of the stars.
Colours:
We see a very striking range of colours, with many blue-white stars typical of an open cluster, plus a handful of bright orange stars. The background shows many tiny orange-red stars.
An
image and write-up by ESO describes the cluster as containing about 400 members, ranging from lots of obvious brilliant blue-white young stars to a handful of orange giants at the end of their lives, and very many much smaller cooler red dwarfs. That fits with what we see.
The ESO shot is perhaps a little extreme in its saturation. We've tried to be a little more sedate.
The PPM catalogue shows the blue-white stars in our image are spectral class around B5 (scorching) to A2 (merely incandescent), while the handful of bright orange ones (presumably the red giants) are a merely warm K2 or thereabouts.
Nebulosity:
The parent gas that formed the cluster must have largely dissipated. Lots of very soft, gentle H-alpha throughout the field, but perhaps unrelated. No hard edges, no shock fronts, anywhere. These must have all dissipated by now.
This is the first time we've tried using H-alpha as a luminance channel, in order to show the nebulosity but at the same time show star colours. In this particular case we seem to have gotten away with it.
Why only half the cluster? We did do a mosaic of the whole thing, and have RGB for the whole thing, but the serial port controlling the cameras decided to die during the H-alpha for the western part. We'll have another go later.