RCW89 in Circinus

RCW89 in Circinus

Filamentary HII Region Powered by Pulsar Jet

Constellation: Circinus
Ra: 15hr 13m 35s
Dec: -58d 59m 30s
Distance: 17,000 ly
Image Size: 31.5 x 31.5'
North: Up; East left



RCW89 is a faint 4 arcmin HII emission nebula in the southern Constellation of Circinus (Latin for compass, as in the drafting instrument to make circles). North is up and East is to the left and the image is 31.5 x 31.5 arcmin. RCW89 has a filamentary structure consisting primarily of H-a along with weaker OIII emissions. This is where it gets interesting because it is thought to be related to a large 20-30 arcmin supernova remnant, G320.4-01.2 (MSH15-52, Kes23) that is centered about halfway between RCW89 and the lower left corner of my image (southeast), which contains the bright open cluster, Pismis 20 toward the west (left) edge of the image. Yatsu et al. (Chandra Observation of the Interaction between the Hot Plasma Nebula RCW89 and the Pulsar Jet of PSR B1509-58 arXiv:astro-ph/0507049v1, 2 July 2005) suggest that RCW89 is energized by the pulsar, PSR 1509-58 from the SNR. Yatsu et al. consider RCW89 to be at the terminus of the northern relativistic jet from the pulsar where there is interaction with the interstellar medium (ISM). The SNR has bilateral radio shells with a diameter of ~ 30 arcmin. The pulsar is a 150 ms, X-Ray, radio and gamma-ray pulsar which is located at the center of the SNR. The age of the SNR is estimated to be 6-20,000 years at a distance of 17,000 light years, whereas the pulsar is estimated to be much younger at 1,700 years, but at the same distance. The brightest part of RCW89 corresponds to the brightest radio emissions of the SNR. This arrangement and energetics are likely to be similar to the pulsars and surrounding filamentary structures in the Crab Nebula and Vela SNR. This image contains 9 hours of 5 nm H-a color-mapped to red/magenta and 9.5 hours of 3 nm OIII, mapped to blue-green to achieve a natural color while takingadvantage of the high contrast of the narrowband filters to bring out the filamentary detail in RCW89. 1.5 hours of RGB data were added for star colors. Total exposure time was 20 hours.
Exposure: 20hrs Total: 9 hrs H-a, 9.5hrs OIII, 1.5hrs RGB
Telescope: PlaneWave CDK20 0.5m f/6.8
Mount: PlaneWave Ascension 200h
Oag: Astrodon MonsterMOAG
Acquisition: ACP-8 Expert
Calibration: CCDStackv2
Observatory Site: iTelescope.net, Siding Spring, NSW, Australia
Camera: SBIG STX16803
Filters: Astrodon 5nm H-a, 3nm OIII, Gen 2 E-Series RGB
Guider: SX Lodestar
Camera Operation: MaximDL5.24
Processing: Photoshop CC 2017
Image Date: 03/27/2017 - 04/22/2017


  1. Josep Drudis

    Amazing! How beautiful is this object and how masterfully processed! I like it. It’s a “Celestial Lace”…

  2. Sakib

    This looks amazing! I love filamentary structures and you really get the impression a star blew up! However I thought RCW 89 is a supernova remnant and not a HII region according to SIMBAD and other sources?

    • astrodon

      Thanks. It does indeed look like a SNR, but the article referenced in the Description characterized it as an HII region illuminated by the pulsar jet in the actual SNR. However, to me, the filamentary structure looks very much like a shock front at the expanding edge of a SN explosion. I guess we leave it in the hands of the professionals who can make the measurements that we cannot.

      • Sakib

        You’re right is confusingly describes it as a HII region but you’ve got to consider the overall body of evidence. It can all get confusing sometimes. 🙂
        Well we can all agree it is a beautiful image with lots of colour!

  3. John Gleason

    Hi Don, i just completed a 12 segment mosaic of this area in Halpha with the FSQ and 16803. This object and many others make this a facinating and overlooked piece of sky. Cheers, jg

    • astrodon

      Hey, John, good to hear from you again. Yes, this region is filled with little gems like this, many of which have not been hi-res imaged. Great region for H-a. Have you posted your mosaic?


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