Sharpless II 155 Cave Nebula

Designations:	Sharpless 155, Caldwell C9, Cave Nebula
Object Type:	Emission Nebula
Constellation:	Cepheus
RA:	22 hr 56.8 min	Dec:	+62° 37 min
Magnitude:	10.0
Discoverer:	Noted by Stewart Sharpless on photographic plates 1953

Sharpless 2-155 "The Cave Nebula", it turns out, is part of an extensive region of ionized hydrogen gas - an HII region - associated with the Cepheus B giant molecular cloud. Part of the cloud is illuminated by a pack of hot, young stars known as the Cepheus OB3 association. Energetic photons from these stars strip the surrounding hydrogen atoms of their electrons, causing the gas in the visible nebula to glow. The now-defunct Rosat satellite has revealed some 40 point sources of X-rays in the association, the majority of which are T Tauri stars - hot young suns still partially swaddled in dusty blankets of gas. Radio and near-infrared observations also have revealed a small near-infrared star cluster coincident with a bright knot of hydrogen-alpha emission near the southern edge of the OB association (itself several degrees across). This cluster's location is tantalizing, for it lies near a sharp spike of ionized gas that delineates the interface between the HII region and the molecular cloud. The cluster may be the result of star formation that was triggered by a front of ionized gas, which pushed out from the OB association into the molecular cloud.

Telescope:	Takahashi TSA102 APO Refractor
Focal Length:	610 mm at f5.98 with dedicated reducer/flattener
Mount:	Mountain Instruments MI-250 mount
Camera	SBIG ST10XME
Guider:	SBIG ST402ME
Exposures:	10 x 10-minute (HA), 8 8-minute (red) 12 x 8-minute (green) 12 x 8-minute (blue)
Location:	Cicero, IN
Software:	CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2
Image Automation: