weak HI: high velocity clouds and M31

[Eduard Mol]

Hi all, 

Back in December 2019 I posted my first observation of a high velocity cloud (HVC) on this forum. This was the "H-complex", at galactic coordinates l=131 b=+2. Back then this was a really difficult observation. Last summer I did some upgrades on the dish, now the system temperature is lower and sensitivity better. Tsys is still above 100 K so there is still room for improvement... Detecting the weak HI signals of HVCs is still not an easy task but the results are now much better than they were before.

Since the mount of the dish is not capable of tracking objects I do my observations in driftscan mode. I use the spectra from before and after the target has passed through the beam for bandpass correction. The brighter HVC complexes can be detected with just one driftscan, for  some of the weaker complexes I need to average the results of multiple driftscans to get a good SNR. 

In this post I show some of the results from recent observations

First of all I did some observations of the "Anticentre shell" near the galactic anticentre. Although not a "true" HVC this is still an interesting target for the 3 metre dish.

H- complex:

Complex A IV at l=153 b=38.5:

Complex AC II. This was one of the more difficult targets. The result below is the average of four driftscans.

Finally, inspired by the impressive work of JJ Maintoux F1EHN I decided to try the  Andromeda galaxy (M31) as well. I did 7 driftscans of M31 but I used only 5 of them (the bandpass correction did not go very well for the last two). The signal of M31 is weak and extremely wide (about 3 MHz, nearly half of the airspy mini SDR's bandwidth), so bandpass correction has to be nearly perfect...

My result is of course not as good but the general shape of the spectrum of M31 is still recognisable.

Eduard

[JJM]

Hi Eduard,

Congratulations for all your observations and mainly for the M31 signals.

Very nice report !

In the same order of weak signals, there is also M33.

Best regards.

JJ F1EHN

 

De : sara...@googlegroups.com <sara...@googlegroups.com> De la part de Eduard Mol
Envoyé : dimanche 2 mai 2021 22:15
À : Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Objet : [SARA] weak HI: high velocity clouds and M31

 

Hi all, 

Back in December 2019 I posted my first observation of a high velocity cloud (HVC) on this forum. This was the "H-complex", at galactic coordinates l=131 b=+2. Back then this was a really difficult observation. Last summer I did some upgrades on the dish, now the system temperature is lower and sensitivity better. Tsys is still above 100 K so there is still room for improvement... Detecting the weak HI signals of HVCs is still not an easy task but the results are now much better than they were before.

 

Since the mount of the dish is not capable of tracking objects I do my observations in driftscan mode. I use the spectra from before and after the target has passed through the beam for bandpass correction. The brighter HVC complexes can be detected with just one driftscan, for  some of the weaker complexes I need to average the results of multiple driftscans to get a good SNR. 

In this post I show some of the results from recent observations

 

First of all I did some observations of the "Anticentre shell" near the galactic anticentre. Although not a "true" HVC this is still an interesting target for the 3 metre dish.

 

H- complex:

 

Complex A IV at l=153 b=38.5:

 

Complex AC II. This was one of the more difficult targets. The result below is the average of four driftscans.

 

Finally, inspired by the impressive work of JJ Maintoux F1EHN I decided to try the  Andromeda galaxy (M31) as well. I did 7 driftscans of M31 but I used only 5 of them (the bandpass correction did not go very well for the last two). The signal of M31 is weak and extremely wide (about 3 MHz, nearly half of the airspy mini SDR's bandwidth), so bandpass correction has to be nearly perfect...

My result is of course not as good but the general shape of the spectrum of M31 is still recognisable.

 

Eduard

 

 

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[Michiel Klaassen]

Hi Eduard,

These are very, very nice results; congratulations again. 

The biggest surprise for me was that you did not use a tracking dish; just done with drifting measurements.

I hope that you write down and reveal your methods and basic data results somewhere, so other amateurs can learn from them.

As have mentioned before, our parac website is available.

Regards,

Michiel

parac.eu

Op ma 3 mei 2021 om 12:29 schreef JJM <jjm_...@wanadoo.fr>:

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/005401d74017%24e6ae7f60%24b40b7e20%24%40wanadoo.fr.

[Lamar Owen]

This is very nice work, especially for driftscan.  The spectrum you
received for M31 matches what we've observed here using the AirSpy R2.

On 5/2/21 4:14 PM, Eduard Mol wrote:
> ...

[Eduard Mol]

Hi all

Thanks for the reactions!

Yes M33 is definitely on the list of targets to observe this summer. 

It was indeed surprising that good results can be achieved with a relatively simple setup and driftscans. If I remember correctly Steve Olney also did his observations of the Magellanic clouds and his daily pulsar measurements with fixed antennas. So a tracking mount is not absolutely necessary for detecting weak sources, as long as the beam of the antenna is fairly wide you can gather enough integration time with a relatively small number of transits.

I indeed have to properly document my RA projects. I have already begun writing a page on the methanol maser project for the PARAC website, but it will take some time to finish. Good writing takes time. I also keep a personal logbook and write articles for my local astronomy club but for now I am still not sure how I will make more accessible documentation in the future.

Best regards,

Eduard

Op maandag 3 mei 2021 om 17:09:56 UTC+2 schreef lo...@pari.edu:

[fasleitung3]

Hi Eduard,

This is quite an achievement. Very well done! Congratulations,

Wolfgang

[Jon Wallace]

Eduard,

I also want to congratulate you on your results - amazing data! I would ask that you might share an article (or several) with the SARA journal as well. I would love to read more about how you were able to capture these without tracking.

Thanks for sharing your results!

Take care!

Jon

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