Hemisphere:  Southern  ·  Constellation: Canis Major (CMa)  ·  Contains:  16 omi01 CMa  ·  Sh2-308  ·  The star ο1CMa
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Dolphin Head Nebula (Sh2-308, LBN 1052, RCW 11), 


            Gary Lopez
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Dolphin Head Nebula (Sh2-308, LBN 1052, RCW 11)

Getting plate-solving status, please wait...
Dolphin Head Nebula (Sh2-308, LBN 1052, RCW 11), 


            Gary Lopez
Powered byPixInsight

Dolphin Head Nebula (Sh2-308, LBN 1052, RCW 11)

Imaging telescopes or lenses: William Optics FLT 132 Triplet APO f/7

Imaging cameras: ZWO ASI1600MM Cooled PRO

Mounts: Orion Atlas EQ-G

Guiding telescopes or lenses: Orion 50mm Guide Scope with helical focusing

Focal reducers: William Optics Flattener 68III

Software: Adobe Lightroom CC  ·  Photoshop CC  ·  Main Sequence Software Sequence Generator Pro, v3.0  ·  Pleaides PixInsight Core 1.8

Filters: Astrodon R Gen 2 E-series 31mm  ·  Astrodon G Gen 2 E-series 31mm  ·  Astrodon B Gen 2 E-series 31mm  ·  Astrodon OIII 3nm-31mm  ·  Astrodon SII 3nm-31mm  ·  Astrodon Ha 3nm-31mm

Dates:Dec. 22, 2020Jan. 9, 2021Jan. 13, 2021Jan. 16, 2021Jan. 17, 2021Feb. 4, 2021Feb. 5, 2021Feb. 6, 2021Feb. 9, 2021Feb. 14, 2021Feb. 19, 2021Feb. 22, 2021Feb. 23, 2021March 4, 2021

Astrodon B Gen 2 E-series 31mm: 30x45" (gain: 300.00) -15C bin 1x1
Astrodon G Gen 2 E-series 31mm: 30x45" (gain: 300.00) -15C bin 1x1
Astrodon Ha 3nm-31mm: 49x300" (gain: 300.00) -15C bin 1x1
Astrodon OIII 3nm-31mm: 93x300" (gain: 300.00) -15C bin 1x1
Astrodon R Gen 2 E-series 31mm: 30x45" (gain: 300.00) -15C bin 1x1

Integration: 13.0 hours

Darks: ~30

Bias: ~50

Avg. Moon age: 13.45 days

Avg. Moon phase: 36.84%

Bortle Dark-Sky Scale: 4.00

Astrometry.net job: 4299140

RA center: 6h 54' 15"

DEC center: -23° 54' 3"

Pixel scale: 0.863 arcsec/pixel

Orientation: -121.772 degrees

Field radius: 0.646 degrees

Resolution: 4298x3249

Locations: Monterey Pines Observatory, Monterey, California, United States

Data source: Backyard


In a hydrogen-rich region near the center of the constellation Canis Major is the Dolphin Head Nebula. This object was created by a massive Wolf-Rayet star, EZ Canis Major, whose powerful radiation pushed out the surrounding gas to create an enormous bubble. The current thinking is that this bubble phenomenon is the result of a star that is in the “pre-supernova” phase of stellar evolution.

This has been the most challenging object I have attempted. It is faint, very low on the horizon (rising to a maximum 28 degrees), and visible for only 2 1/2 hours each night. My rule of thumb for astrophotography is to only collect data from about 35-45 degrees above the horizon to the zenith to minimize possible atmospheric degradation. Despite knowing better, I really wanted to create an image of the Dolphin Head (I just finished Bubble Nebula and wanted more bubbles), so I decided to give it a try. Typically, 2.5 has been the maximum HFR value that I will use in an image (for the WO FLT 132 + ZWO ASI1600MM Pro combination). In collecting Sh2-308 data, however, the best HFR I collected was 2.6 and most of the data were >3. One night in late December I had what seemed like very good seeing so I did a test. Aiming the telescope at the zenith the HFR was 1.8. Aimed at Sh2-308 (at 27 degrees above the horizon), the HFR was 2.8. Not surprisingly the low declination of the object was likely putting too much of the moisture-filled Monterey atmosphere between me and the object for consistently good seeing. So, armed with this information, I raised the acceptable HFR to <3.5 for the Sh2-308 data. Even with this low standard, I was still forced to tossed more than 90% of what I collected, with the exposures often eclipsing HFR 5 during the course of the object’s progressing across the sky. As a result of this very slow acquisition pace, more about three months were required to gather about 13 hours of usable data. I am now thinking that when I collect Sh2-308 data again I will use a remote facility in the southern hemisphere. Yes, I am a slow learner.

This image is an HOO/RGB created with PixInsight NBRGB Combination to assemble and adjust the contribution of the channels. Prior to using NBRGB, I applied a synthetic master luminance layer composed of OIII + Ha with HFR <3.0 to the RGB image to enhance its contribution to the nebula. I also used PI multichannel median transform and deconvolution to control the noise of both the OIII and Ha channels prior to assembly. After assembly with NBRGB, I adjusted the color with PS selective color and then reapplied the synthetic luminance to tighten the detail and reduce the color noise.