Hemisphere:  Northern  ·  Contains:  NGC 7538  ·  NGC7538  ·  Sh2-158
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NGC 7538 | Home to the Largest Known Protostar, 


            Kevin Morefield
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NGC 7538 | Home to the Largest Known Protostar

Imaging telescopes or lenses: Planewave CDK14

Imaging cameras: QHYCCD QHY600M

Mounts: Planewave L-350

Guiding telescopes or lenses: Planewave CDK14

Guiding cameras: Starlight Express UltraStar Mono

Software: CCDWare CCDAutoPilot 5  ·  Adobe Photoship CC  ·  CCDWare CCDStack 2  ·  PixInsight

Filters: Astrodon SII 3 nm  ·  Astrodon OIII 3 nm  ·  Astrodon Ha 5 nm

Dates:Nov. 4, 2020

Astrodon Ha 5 nm: 67x600" (gain: 56.00) -10C bin 2x2
Astrodon OIII 3 nm: 58x600" (gain: 56.00) -10C bin 2x2
Astrodon SII 3 nm: 53x600" (gain: 56.00) -10C bin 2x2

Integration: 29.7 hours

Darks: ~20

Flats: ~20

Flat darks: ~20

Bias: ~20

Avg. Moon age: 18.26 days

Avg. Moon phase: 86.83%

Bortle Dark-Sky Scale: 3.00

Astrometry.net job: 3983422

RA center: 23h 13' 25"

DEC center: +61° 36' 3"

Pixel scale: 0.608 arcsec/pixel

Orientation: 51.145 degrees

Field radius: 0.354 degrees

Resolution: 3469x2350

Locations: Sierra Remote Observatory, Auberry, California, United States

Data source: Own remote observatory

Remote source: Sierra Remote Observatories


Located near the Bubble nebula, this small, but bright emission/reflection nebula is known for its star formation. The largest known protostar, NGC 7538S, holds ~100 solar masses and has a rotating disc 300 times the size of our solar system.

For this Narrowband image I made use of a dynamic factor in Pixelmath. The OIII data was used as the factor to determine where SII and Ha were used for the Red Channel. Where OIII was strong, SII was used and where OIII was weak, Ha was used. Because the main nebula is a small part of the frame I wanted to highlight the dim Ha field it resides in. Since there is no OIII in that area, I could have that area represented with Ha data and the main nebula with the less powerful SII data.

The Pixelmath statement then was:

R/K = f*S+~f*H (where f = the OIII data with a contrast curve applied)
G = Mean (SII, OIII)

For more detail on this technique, see the excellent write-up here:

After creating this color mix, I applied HDRMT to the bright core on the Ha data and used that for the Luminance channel.

Starnet++ and a difference layer were used in Photoshop to create a star selection. Content aware fill was used to produce a starless layer. Topaz de-noise was used in low light mode to the starless image. Opacity was set at 80%. A large stretch was required to bring out the background nebulosity so noise was quite high.



Kevin Morefield


    NGC 7538 | Home to the Largest Known Protostar, 


            Kevin Morefield
  • Final
    NGC 7538 | Home to the Largest Known Protostar, 


            Kevin Morefield


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Sky plot

Sky plot


NGC 7538 | Home to the Largest Known Protostar, 


            Kevin Morefield