NGC7822 - "In the Maw of the Monster"
Description: (Credit to APOD and Rob Gendler)
See [url]http://www.flemingastrophotography.com/ngc7822.html[/url] for more sizes.
Pillars of gas, dust, and young, hot stars seem to fill the gaping maw of NGC 7822, a.k.a Sharpless 2-171, and Cederblad 214 in Cepheus. (This nebular region can be found right at the Cepheus/Cassiopeia border.) This star forming region lies about 3,000 light-years away. This image includes data from both broadband and narrowband filters, mapping emission from atomic oxygen, hydrogen, and sulfur into blue, green, and red hues. RGB data was used to give a better true color image of the stars.
The Molecular cloud complex which gives rise to the visible nebula is known as the radio source W1 (Westerhout 1), one of the largest molecular cloud complexes in the Milky Way. The atomic emission is powered by the energetic radiation from the hot stars, whose powerful winds and radiation also sculpt and erode the denser pillar shapes. Stars could still be forming inside the pillars by gravitational collapse, but as the pillars are eroded away, any forming stars will ultimately be cutoff from their reservoir of star stuff. This field spans around 60 light-years at the estimated distance of NGC 7822.
The ionizing radiation field and stellar winds of young massive stars tend to evaporate and destroy the parent molecular cloud from which they formed over a time scale of about 10 million years. During this process triggering of further star formation may occur as the molecular cloud becomes compressed and altered. The lower density gas in the cloud is swept away or ionized, however higher density clumps of gas and dust will resist being boiled away and will emerge as dark globules protruding into adjacent HII regions where they are subject to the ultraviolet radiation of nearby OB stars. The surface of the dense globules becomes ionized, forming the characteristic bright rim of the globule. The expansion of the higher density ionized gas into the lower density HII region causes a persistent mass loss from the globule termed, "photoevaporation". The contents of a globule may be accelerated away from the UV source as it evaporates, forming a comet shaped structure known as a "cometary globule". Ultimately a new generation of low mass stars can form within the globule as it becomes compressed by the radiation and winds of the nearby stars. This process is known as, "radiative implosion". The lifetime of the globule is relatively short as they tend to evaporate away within 500,000 years.
Many of the bright stars are obscured and reddened by the foreground dust clouds of W1. The most prominent cluster is Berkeley 59 (Be59) located in the center of the nebulosity. Be59 is likely a second generation cluster whose formation was triggered by the expanding shell of gas, and has some young components aged no more than a few million years. The complex also includes one of the hottest stars discovered within 1 kpc of the Sun, namely BD+66 1673, which is an eclipsing binary system consisting of an O5V that exhibits a surface temperature of nearly 45000 K and a luminosity ~100000 times that of the Sun. The star is one of the primary sources illuminating the nebula and shaping the complex's famed pillars of creation-type formations, the elephant trunks.
Dates Taken:
- 9/18/2010 through 10/15/2010
Equipment Used:
- TMB 203 F/7
- SBIG STL-6303
- Paramount ME
- Optec 3" rotator
- Starlight Instrument's Digital Feather Touch Focuser, (with electronic focusing)
- Astrodon 6nm narrowband filters, Gen2 RGB filters
Exposures:
This is a two-panel mosaic including the following data:
- Ha: 32x30m (16 hours)
- OIII: 52x30m (26 hours)
- SII: 30x30m (15 hours)
- R: 36x180s (1.8 hours)
- G: 44x180s (2.2 hours)
- R: 54x180s (2.7 hours)
Total of 63.7 hours
Processing:
CCDStack:
1) Calibration with darks, flats, and bias frames
2) Bloom rejection
3) Impute (minor) bloomed pixels
4) Image registration
5) Normalization
6) Data rejection (Clip Min/Max)
7) Mean combine
8) Hot/Cold Pixel rejection
9) Impute hot/cold pixels
10) Deconvolution, Positive Constraint, 25 iterations
11) Produce scaled TIFs
Photoshop CS2:
1) Color combine
2) Color adjustment layers, including "Selective Color", "Hue/Saturation", curves
3) Noel Carboni’s Photoshop action for “local contrast enhancement”
4) Shadow-highlight to bring up the background data
5) Noise removal (NeatImage)
6) Additional deconvolution and sharpening with FocusMagic