OH masers: NML Cygni and OH 26.5+0.6

[Eduard]

Hi all,

Last week I tried to detect two OH masers, NML Cygni and OH 26.5+0.6, at 1612 MHz with my 3 metre dish.

I had already detected NML Cyg in october 2019, but it took me more than 3 hours of observations to detect it. Since then, I have made some improvements to my setup, and now I can detect NML Cyg with one hour of integration time. (see my previous post). On september 7 I observed NML Cygni for another 3 hours. The stronger blueshifted peak is clearly visible in the spectrum, but the weaker redshifted peak was not detected. It is probably just too weak for detection with my radio telescope.

OH 26.5+0.6 was observed for two hours on the evening of september 8. The spectrum shows two peaks at 13 km/s and 40 km/s. The published values from maserdb

(https://hsweb.hs.uni-hamburg.de/projects/maserdb//) of the velocity range from 13.2 to 13.8 km/s for the blueshifted peak and 40.9 to 41.7 km/s for the redshifted peak. 

Best regards,

Eduard

[Coto]

Hi Eduard,

Very nice work! Can you share the averaged spectrum for a 1-hour observation of NML Cyg? I would also be curious to know of your exact block diagram (what LNAs do you use, filters, amplifiers, SDR etc.?). The minimum integration time I’ve seen NML Cyg be detected with a 3m is 3 hours, so I’m impressed!

Apostolos

[Eduard]

Hi Apostolos,

The spectrum with one hour integration time can be found in my previous post ("improving my radio telescope")

The SNR is not that good but at least the general shape of the blueshifted peak was recognisable.

I use a G8FEK SBA1300-1700 LNA, and a homemade amplifier. The apmlifier does not have that much gain at 1612MHz, but it is enough to overcome cable losses. The SDR is an airspy mini. At the moment I have no suitable filter for 1612 MHz. 

Best regards,

Eduard

Op vr 11 sep. 2020 13:16 schreef Coto <cototh...@gmail.com>:

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[Eduard]

Hi all, 

Here an update on this project:

I have done more observations at 1612 MHz. First of all, I repeated my measurement of OH26.5+0.6 on september 9 and 10. I got the same result, two peaks in the spectrum at 13 and 40 km/s. I also averaged the two new results with the previous one to get a spectrum with a better SNR. 

Next I tried to detect V669 Cassiopeia (OH 127.8+0.0). Maserdb reports peak flux densities between 33 and 318 Jy and velocities from 65.1 to 66 km/s for the blueshifted peak. The light curve at the website of the NRT/stockert maser monitoring program

( https://hsweb.hs.uni-hamburg.de/projects/nrt_monitoring/stockert.html) suggested that this maser is currently near maximum brightness. I hoped that the peak flux density would be in the 200-300 Jy range. However, detecting this maser was much more difficult than expected. My first two observations failed because of a pointing error and RFI. On 19, 21 and 22 september I observed V669 Cas again for 2, 3 and 1.5 hours respectively. I averaged all the spectra collected during these three observing sessions, just like I did with the results of OH 26.5+0.6. There are two peaks in the averaged spectrum, a stronger signal at -84 km/s and a much smaller peak at -67.6 km/s. The stronger peak was ruled out as OH emission from V669 Cas, because it does not match the published velocity, and was only present in the spectra from 21 and 22 september. I am not sure about the weaker signal though. It is close to the expected velocity, but still at least 1,6 km/s off. It is also much weaker than I expected. 

Anyway, detecting OH masers is a very interesting and challenging project. 

Best regards,

Eduard

Op vr 11 sep. 2020 11:06 schreef Eduard <eddiem...@gmail.com>:

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[Michiel Klaassen]

Hi Eduard,
You have obtained very nice results again; so, congratulations again.
Do you still use the wooden dish construction?
I think that the supporting ribs, and more, could also be printed by a 3D printer
Some time ago there was a discussion about that.
Regards,
Michiel
parac.eu

Op wo 23 sep. 2020 om 19:26 schreef Eduard <eddiem...@gmail.com>:

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[Eduard]

Hi Michiel,

Thank you for your comment

Yes this is still the same dish with the wooden construction

Printing the ribs would indeed be possible I guess, but for L band a stressed dish or wooden or aluminium support ribs work just fine. However, I can imagine that bending the ribs in shape or sawing them out of a plate of material is not easy if you are making a dish for microwave frequencies and everything needs to be accurately shaped to whithin millimetres. That is where 3d printing would probably really come in handy.

Best regards,

Eduard

Op wo 23 sep. 2020 21:32 schreef Michiel Klaassen <vmin...@gmail.com>:

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[Marcus D. Leech]

On 09/23/2020 04:21 PM, Eduard wrote:
> Hi Michiel,
>
> Thank you for your comment
>
> Yes this is still the same dish with the wooden construction
>
> Printing the ribs would indeed be possible I guess, but for L band a
> stressed dish or wooden or aluminium support ribs work just fine.
> However, I can imagine that bending the ribs in shape or sawing them
> out of a plate of material is not easy if you are making a dish for
> microwave frequencies and everything needs to be accurately shaped to
> whithin millimetres. That is where 3d printing would probably really
> come in handy.
>
> Best regards,
>
> Eduard
>

CNC plasma-cut or laser-cut of aluminum thin plate stock is probably
fairly cheap

[fasleitung3]

Hi Eduard,

Our most recent observation of OH 127.9+0.0 dates from Aug 28th. The peak flux density then was about 210 Jy. But please note that this is a very sharp peak so the peak intensity may be somewhat dependent on the spectral resolution. The integrated flux density 282 Jy*km/s for this measurement. So indeed we are likely at or near the peak of the present light curve cycle.

Please find attached the plot from the measurement.

Best regards,

Wolfgang

[Eduard]

Hi Wolfgang,

Thank you very much for sharing your observation.

The airspy mini has a bandwidth of 6 MHz. With 1024 FFT bins I get a spectral resolution of 5,86 KHz, or 1,036 km/s at 1612 MHz. As you noted, the peak of V669 Cas is very sharp. From your spectrum it seems that the line width is much less than the spectral resolution. This could explain why V669 Cas was so hard to detect.

Best regards,

Eduard

Op do 24 sep. 2020 21:05 schreef 'fasleitung3' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>:

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[fasleitung3]

Eduard,

Yes indeed. We have used an eight times higher resolution, 732 Hz. Even then the peak is in just one bin, so it may be even sharper. I have re-binned our observation to match your resolution. The apparent drop in peak intensity is very obvious, see attached plot. You lose about a factor of 2.9 as per this test. But then, if you go to higher resolution, a factor of 8 in resolution gives yor a factor 2.8 worse SNR. So you are back at square one :-(

Wolfgang

[Eduard]

Hi Wolfgang,

Your graph clearly demonstrates the problem with detecting such narrow spectral lines. 

Next time I look for masers I will check their line width. Although there are not many OH masers with peak flux densities comparable to that of V669 Cas...

VY Canis Majoris is also around 200 Jy and has a much broader spectral line, so I should lose less. Unfortunately it only comes about 11 degrees above the horizon at my location. OH31.0-0.2 is also a candidate for detection, although it is somewhat weaker at around 140 Jy but it comes much higher above the horizon.

Best regards,

Eduard

 

 

Op vr 25 sep. 2020 09:15 schreef 'fasleitung3' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>:

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