NGC7635 - The Bubble Nebula in Cassiopeia


Copyright 2010 Hap Griffin


Looking like a celestial Christmas tree ornament, this is the beautiful "Bubble Nebula", known officially as NGC7635.  Is is formed by gas being compressed by a strong stellar wind from massive star BD+602522, forty times as massive as our sun and several hundred thousand times more luminous.  As fast moving gas escapes the star, it compresses surrounding sparse gas into a shell.  The shell, consisting of hydrogen, oxygen and sulfur, is ionized by the radiation from BD+602522 causing it to glow.  The bubble is approximately 6 light-years in diameter.  

BD+602522 is a "Wolf-Rayet" star, a star in the end stages of its life which emits fierce stellar winds (charged particles streaming from its surface) rapidly depleting its mass until it finally dies in a supernova.  Wolf-Rayet stars (named for their discoverers) have surface temperatures between 30,000 and 60,000 degrees Kelvin and emit stellar winds with speeds exceeding 1500 kilometers per second.  There are only about 300 Wolf-Rayet stars known in our galaxy.  


Date/Location:    August 7-8, 2010     Griffin/Hunter Observatory    Bethune, SC
Camera: QSI 583wsg
Filters: Astrodon E Series Generation 2 LRGB HA
CCD Temperature: -10 C
Instrument:    Planewave CDK 12.5"  
Focal Ratio:   f/8
Mount: AP-1200
Guiding:    Auto via the QSI camera's built in Off-Axis Guider mirror and an SBIG ST-402 Guider
Conditions:    Hot and humid, clear for summer in SC
Weather:    85-75 F, still
Exposure: 350 minutes total (12 x 10 minutes Luminance, 5 x 10 minutes each RGB binned 2x2, 4 x 20 minutes HA)
Capture: CCDAutopilot 4 w/ Maxim DL Camera Control, focused automatically w/ FocusMax   
Processing:    Frame calibrations, alignment and stacking with ImagesPlus v3.80.  Finishing in Photoshop CS4.  Noise reduction with Noise Ninja.