NGC 663: A Cluster Known for its “Be” Stars in Cassiopeia

NGC 663, also known as Caldwell 10, is an open star cluster in the constellation of Cassiopeia. It is best viewed in autumn through early winter.

Suburban skygazers with large binoculars may be able to make out NGC 663, but a telescope will be better. The cluster is notable for several reasons: it has several double stars, it sits in front of a molecular cloud so most background stars are blocked, and it contains a high number of “Be” stars. According to Sky Safari pro: “Be stars are formally defined as non-supergiant B-type stars whose spectra have Balmer emission lines. The emission is produced from a flattened disk of gas around the star’s equator. The mystery of the “Be phenomenon” is that the hydrogen emission can come and go episodically on timescales as short as a few days, and as long as several decades. Rapid rotation, nonradial pulsation, radiation-driven winds, flare-like magnetic activity, and binary interaction have all been proposed as factors that may cause the star to shed material from its surface, leading to the formation of the disk.”

My Observations

Even with a quarter moon out tonight, I’m able to view NGC 663 using my 24mm eyepiece. There are 5-6 brighter stars in my view, and I believe some of these may be doubles. Unfortunately, the brightness of the stars drops off considerably. I’m sure on a moonless and dark sky night, my eyepiece would be fuller with brighter stars, but I also wonder if I’m witnessing how the molecular cloud in this region obscures the stars. More research is needed and future observations on my end.

Key Stats

Constellation	Cassiopeia
Best Viewing	Late fall/winter
Visual Magnitude	+7.1
Absolute Magnitude	-4.8
Distance from Earth	8,000 ly
Diameter	32 ly
Apparent Size	14 arcmin
Milky Way Location	Perseus Arm
My Viewing Grade	B

Sources and Notes

Photo of NGC 663 is by Hewholooks and is is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

AKA: Caldwell 10, Lawnmower Cluster