Sh2-188 - December 2011

About the image…

Image title – Sh2-188.
Taken at – Observatorio del Teide (Canary Islands – Spain; 16º 30' 35" W, 28º 18' 00" N).
Telescope – IAC80 (82cm diameter).
Instrument– CCD E2V 42-40.
Focal Ratio – Cassegrain f/11.3.
Exposure – Ha: 8 x 1,200s, SII: 6 x 1,200 s, OIII: 8 x 1,200 s.
Image size – 2,048 x 2,048 pixels (10.4 x 10.4 arcmin).
Software – DSS, PhotoShop CS4.
Images taken and reduced by –
Daniel López.
Text – Daniel López and Pablo Rodríguez-Gil.

About the object…

Object type Planetary Nebula.
Equatorial Coordinates J2000.0 – 01h 30m 33s; +58º 24' 50".
Distance – 850 light-years.
Constelation – Cassiopea.

Sh2-188 is a peculiar planetary nebula located in the constellation Cassiopeia, and one of the best examples of interaction between a planetary nebula with the interstellar medium. Discovered in 1951, it was thought to be a supernova remnant, mainly because of its asymmetrical shape. However, later studies found that it is actually a planetary nebula. Sh2-188 doesn't have a symmetrical outer envelope extending from the dying central star. The central star is about 850 light years from Earth and is moving at 125 kilometres per second. This may be the reason for the lack of symmetry in the shell-shaped structure that surrounds it. Since the central star is moving at high speed, most of the material of the ejected shell piles up in the direction of motion, while the material at the back is dragged and eventually dissipates.