Shallow Sky Object of the Month: Kappa Cas, SAO11256

Original article appears in GuideStar March, 2014.

Kappa Cas

by Bill Pellerin, editor of the HAS GuideStar

Object: Kappa Cas
Class: Fast moving Star
Constellation: Cassiopeia
Magnitude: 4.17
Speed: 2,500,000 miles/hr = 694 miles/sec
R.A.: 00 h 33m 00 s
Dec: 62 deg 55 min 54 sec
Size/Spectral: B
Distance: ~3500 ly
Optics needed: Unaided eye

Why this is interesting

This star shows up in the GCVS (the General Catalog of Variable Stars), but it isn’t very variable. AAVSO members have reported the star as dim as 4.25 and as bright as 3.8, but that’s not why it’s interesting.

I happened upon an article about the star recently indicating that in infrared images there’s a significant bow shock wave associated with the star. This shock wave occurs because the star is moving so quickly through the interstellar medium. When the magnetic field and stellar wind of the star collides with this medium the medium warms up and glows in the infrared. The picture above was taken with the Spitzer Space Telescope. The star shines mostly in light at the other end of the spectrum, ultraviolet light. If we consider all the energy being given off by the star we find that its energy production is 420,000 times that of our sun.

The mass of Kappa Cas is substantially higher than our sun as well. In fact, Kappa Cas is a late life star mostly fusing helium to carbon and oxygen. Astronomers expect the star to go supernova one day, but not in our lifetimes.

Kappa Cas

The glowing gas in the image is approximately 4 light years ahead of the star, so the distance between the star and the bow shock is about the same as the distance (24 trillion miles) between our sun and Proxima Centauri, the nearest star to us.

I’ve added two dotted lines to associate the star with the familiar W shape of the constellation Cassiopeia. With these two lines, the constellation looks more like a chair (throne) for the queen Cassiopeia.

Visually, you won’t see the bow shock, but you’ll know it’s there and you’ll know that this star is moving very quickly.

Astronomy is as much about what you know about an object as it is about what you see through your telescopes. Every object has at least one story associated with it; some objects have many stories.

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