NGC559 and SNR G127.1+0.5

Star Cluster NGC 559 and Super Nova Remnant (SNR) G127.1+0.5
Published 21 Dec 23

I'm thrilled to announce what could be the first optical amateur detection of SNR G127.1+0.5. So, to provide some evidence of this I've included data and images from several different papers over the years and overlaid them on my Ha image of this region. I think you will be able to see that I most likely detected the shock front of the SNR.

This data was taken with a 152mm f8 refractor and ASI 6200 camera from 8 Sep 23 - 8 Nov 23. It includes 27hrs of Ha, 20 hrs of OIII, and 2hrs each of RGB.

The image below is a RGB image of NGC 559 in Cassiopeia. This wide view taken with a 152mm refractor and ASI 6200 CMOS camera shows the star cluster near image center. NGC 559 is approximately mag 9.6 and near 9 arcmin in diameter. The estimated distance (2006) is approximately .9-1.3 kpc or 2900-4240 light years. NGC 559 contains stars on the order of 11-12th mag and many fainter. The 2nd image below also shows a huge amount of emission nebulosity within this area. Within this nebulosity is the Super Nova Remnant (SNR) G127.1+0.5. I believe this is the first amateur optical image of this Super Nova remnant. While NGC 559 is beautiful in itself you would not even know SNR G127.1+0.5 was visible here. The following images and professional data is the evidence I provide.

The above image shows the region around open cluster NGC 559. To see a larger RGB image click here. This was taken using RGB broadband filters. Just below the star cluster is a dark molecular cloud called LDN 1325. Within this cloud you see very few stars as the dust is too thick to allow much background starlight through. This area is also full of hydrogen emission and also a Super Nova remnant called G127.1+0.5. Below is the RGB image combined with continuum subtracted hydrogen alpha data and further below is where the best stuff is, if you know where to look. We can see the possible shock front from the relatively invisible super nova remnant.

Hydrogen emits light in the wavelength of red. Above you can see the immense area of hydrogen emission that is around NGC 559 intermixed with darker areas of dust.

From what research I could compile, the first mention of this SNR was a paper by Carswell (1977) G127.1 + 0.5 - A remarkable supernova remnant centred on a very compact radio source? Carswell mentioned that no HII was detectable here in Palomar survey plates. 1420 mhz radio continuum data was presented which showed a 45 arc min shell like structure here and also an X-ray point source near the center of the shell. You may ask why 1420 mhz and what is special about this frequency: Probably the single most important frequency in radio astronomy is that detected from atomic hydrogen in the interstellar medium, at 1420.405 MHz. Because of Doppler shift from the motions of interstellar hydrogen the emission can be detected over a range of frequencies. The band 1400 MHz to 1427 MHz is a protected radio astronomy band.

Above is the 1420 mhz radio continuum data from the 1/2 mile Cambridge telescope (Carswell paper)
This central point source, called G127.11+0.54, would later be identified as an Active Galactic Nucleus (AGN). Carswell concluded that this object was probably a SNR.

Xilouris, et al. (1992) produced a paper showing the first optical detection of this SNR Detection of optical emission in the area of G127.1+0.5. Ha data was taken with a 30cm Schmidt Cassegrain telescope with a CCD camera from the island of Crete. The images showed HII emission along the northern edge of the strongest counters in the continuum radio data which matched up will with the shell but no detection was made on the southern side of the shell.

Optical Ha data from the Xilouris et al. (1992) paper overlaid with radio continuum data

The image above shows the Ha data from the Xilouris et al. (1992) paper, overlaid with radio and IR data Xilouiris concluded that the Ha data correlated well with IR and radio data in the northern semicircle of the shell. This data was taken with a cryogenically cooled ccd camera. This was probably very good in its day but its amazing how detectors have changed over the years.

In the paper Leahy et al. (2006) Radio observations and spectrum of the SNR G127.1+0.5 and its central source 0125+628 the authors provided new radio continuum data on the SNR. The distance to the SNR was also updated to 1.15 - 2.9 kpc or 3750 -9469 light years. The distance to NGC 559 ranges between .9 - 1.3 kpc or 2935 - 4240 light years so there is some overlap and the authors mentioned that there may be an association between the star cluster and SNR. Here they also revealed that the point source found near the center of the radio data is actually a AGN and is extragalactic

SNR G127.1+0.5 1420 mhz continuum Emission from the Canadian Galactic Plane Survey Synthesis Telescope of the Dominion Radio Astrophysical Observatory Leahy et al. (2006)

This new radio data showed the outline of the SNR in great detail. The stronger signal is in the northern half. The southern half also has some decent signal. The outline of the brighter blue area is where the signal drops off and its a nice round circle 45 arc min wide.

The last paper I would like to comment on is the paper by Zhou et al. (2014). DISCOVERY OF A PRE-EXISTING MOLECULAR FILAMENT ASSOCIATED WITH SUPERNOVA REMNANT G127.1+0.5 The authors discovered a curved molecular filament which shows evidence of being fully engulfed by the remnant's forward shock. The image is a integrated map of Carbon Monoxide (CO) emission overlaid with the 1420 mhz radio data.

CO integrated image showing a curved portion of a molecular cloud (in Red) which was bent by the shock of the SN explosion. Zhou et al. (2014)

So what does all this have to do with the image I took of NGC 599? Well if you overlay these images from these different papers you can see that the radio data, which outlines the SNR clearly matches a faint nearly circular boundary in my HII image which I think is the reflection of the shock boundary in Ha. The curved molecular cloud from the Zhou paper also closely matches a curved darker cloud in the Ha image. So below is an animation of my data overlaid with the image data from these papers.

You can see in the animation that when the stars are removed from the Ha image, its much easier to see the eastern and southern ring of faint Ha emission which matches nearly perfectly with the boundaries of the radio continuum data.

I sent this data and animation to Dr. Knox Long, a emeritus astronomer at the Space Telescope Science Institute and Dr Robert Fesen at Dartmouth College. Both specialize in supernovae and their remnants.

Here is a quote from Dr Long, "I also think it is likely that you have detected the shock in Ha (on the side where the SNR looks to be running into a molecular cloud according to https://ui.adsabs.harvard.edu/abs/2014ApJ...791..109Z/abstract. Your images certainly look a lot more convincing than the images that Xilouris obtained in the 90’s."

Dr. Fesen, from Dartmouth, also mentioned that this is the probable answer, "Your Halpha image(s) appear likely to have detected emission from the G127 SNR. Yay. But they appear pretty faint so getting confirming spectra will take a bit of doing. But their match to the edges of the WENSS radio map is strongly suggestive.
Your images are far better and more useful that those taken by Xilouris et al. (1993) so I think you should post them on Astrobin. The G127 SNR has not gotten much attention
from optical SNR researchers so far but maybe that will change with your new images."

Lastly I would like to show the 20hr starless and continuum subtracted OIII image of this area. The OIII image does not show any faint wispy features like the SNR G126.1+1.2 just to the north of this area. It does show very faint OIII emission around this entire area

Above is the 20hr OIII image which has been continuum subtracted and the stars removed

So, I think its pretty suggestive that, indeed, we can see this shock front in Ha data. The imaging equipment we have now is so much better than what professional astronomers had to use in the 90's when this was discovered. I hope this set of images and data will convince some professional researchers to take new spectra on this object and solve this question.

Lastly above is an annotated image showing where the star cluster NGC 559 is and the dark nebula LDN 1325 along with a few faint background galaxies. The yellow circle is what I believe is the boundary of the super nova remnant G127.1+0.5. The yellow hatch marks show where the center of the SNR is believed to be. Click on the image above to get a full resolution view

My many thanks go out to Sakib Rasool for suggesting this region of the sky and to Dr's Long and Fesen for giving me a bit of guidance as to what I was probably seeing in my Ha image.

Image Details

Optics : Stellarvue SVX 152T refractor @f8 1200mm FL
Mount: Paramount MYT
Camera: ZWO ASI6200
Filters: Chroma 50mm RGB, 5nm OIII and Astrodon 5nm Ha
Exposure (min): RGBHaOIII 120:120:120: 1620:1200 53hrs, 2x2 binning
Automation Control: The Sky X, Voyager, PrimaluceLab Eagle 4
Guiding: StarlightXpress Lodestar X2
Processing Software: PixInsight, PS CC
Location: Stark Bayou Observatory, Ocean Springs, MS
Sky: Typical SQM 19.6-20.1, Bortle 5, Suburban
Date: 8 Sep - 8 Nov 2023

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