Methanol/OH/Water masers and small dishes...

[Steve Olney]

Hi All,

I've been looking at the list of methanol masers (12.178 GHz) from maserdb and it seems to me (from the figures for flux density given there) that for small dishes (< 1.5 m diameter) that there are none strong enough to get a good detection.  And it seems (once again from the maserdb data) that methanol masers are fairly constant - so there is also a low chance of one being detected via a flare event.  This is a pity as the pathway to getting a 12 GHz receiver is relatively easy (one with a 10.75 GHz LO would do the trick).

It seems that a better approach is to aim to go for OH masers (here I could use a 3 m dish) - but the problem here is mechanical - it's a bit of a pain to manhandle it. At least the receiver side of things is not too hard.

As far as interesting maser targets go - the water masers are best IMHO, in that they flare to kJy levels (some to MJy) and even in their 'quiet' times are quite strong.  Trouble is getting a 22 GHz receiver.  The Norsat DRO receiver is about AUD$350 landed here in Oz.  There are no local sources of Ka band LNBFs in Oz as it is not a band used here AFAIK. Therefore there is a risk when sourcing overseas.

Six of one, half-dozen of the other...

Any comments appreciated.

Cheers

Steve O (HawkRAO)

[Steve Olney]

BTW - I should have also mentioned I'm doing calculations for transit mode only.

Steve O

[Michiel Klaassen]

Hi Steve,
I hope you have seen the maser pages and the drift results on the website.

At the moment I am experimenting with below KuKa LNB for SiO.
The horn can be rotated and used separately  also.

Drift only? come on; you can do better.
Michiel

parac.eu

https://www.ebay.com/itm/295195065014?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200818142055%26meid%3Dc9b08f062814498d83ab3f82b8a79a64%26pid%3D101113%26rk%3D1%26rkt%3D12%26sd%3D224057882707%26itm%3D295195065014%26pmt%3D0%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganicWebV9BertRefreshRanker%26brand%3DDIRECTV&_trksid=p2047675.c101113.m2109

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[Eduard Mol]

Hi Steve,

Some of the strongest 12.2GHz methanol maser sources listed in MaserDB are actually quite far south: G351.4170+0.6451 (692- 1210 Jy) at a declination of -35.8 degrees and G39.8842-1.2590 (850 Jy) at -46.1 degrees. I think it should be possible to detect both sources with a 1 metre dish in driftscan mod. In the past I have detected W3(OH), which has a similar flux density, in a single driftscan (see attachment). The SNR was not that good but could be improved by averaging multiple driftscans.

Regards,

Eduard

--

[Eduard Mol]

One more note on 12.2 GHz: you will have to deal with a load of RFI from an ever increasing number of satellites...

[Marcus D. Leech]

On 13/03/2023 13:45, Eduard Mol wrote:

One more note on 12.2 GHz: you will have to deal with a load of RFI from an ever increasing number of satellites...

Indeed, StarLink (and other such constellations, I assume) have their space-to-ground segment in Ku band :(

It's not just a matter of avoiding the Clarke Belt any more.  Such sad.

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[Steve Olney]

Hi Eduard,

Yes - here down-under we have skies with a lot of interesting objects.

For 12 and 22 GHz masers I am making a webpage (unpublished) to try and estimate likelihood of detection with 0.65 and 1.2 m dishes using some assumed figures plugged into the radiometer equation.  For 12 GHz I am assuming a minimum SNR of 5, 150 K Tsys and spectral resolution of 8 kHz. A screenshot of the 12 GHz section of the webpage is included. Those calculations seem to indicate that detection would be unsuccessful - although by tweaking (accepting a lower SNR or wider spectral resolution) might make ithe 1.2 m squeak in - as evidenced by your W3 result.

Please note that the calculations are NOT designed to validate or otherwise anyone else's results - they are solely a guide for me to try and sort out what gear (and associated expenditure) might best be successful here at HawkRAO.

Your drift result is what has motivated me to divert from my obsession with the Vela pulsar into masers :-)

Cheers Steve

[Steve Olney]

Hi Michiel,

Yes - I have looked at the very interesting parac pages - although results for a 9 m dish are way out of my league here.

The KuKa LNB for SiO looks interesting. Look forward to hearing about results there.

Sorry - only driftscan for me. Apart from the extra complexity (and cost) my particular interest lies in daily observations spanning years.  Drift scan is more practical for my resources for long-term observations.  However - using a simple TVRO elevator is a possibility I should look into.

Cheers

Steve O

[Steve Olney]

There's a typo where G351.42+0.64 is left out of the list of unsuccessful masers.

I am looking at getting a 1.5 m dish as this may help to get over the line for G351.42+0.64.

[Eduard Mol]

Hi Steve, 

Two notes on the W3(OH) observation presented above: because W3(OH) is at a relatively high declination (~62 degrees), the transit time was a bit longer. Total integration time was about 15 minutes. Furthermore, the system temperature was ~100 K, as estimated from hot- cold measurement. Finally, the W3(OH) mase feature was quite broad, so I could get away with using 35 KHz bandwidth. If you plug in these numbers in the radiometer equation, you get a minimum detectable flux of 626 Jy (5 sigma). 

By the way, it should be possible to increase the integration time simply by averaging transits from multiple days. Most masers vary on timescales of a few weeks to a few years, so a time resolution of ~1 week is perhaps good enough. 

If we assume a 1.2 metre dish, Tsys of 150 K (maybe a bit pessimistic), 8.2 KHz bandwidth, and 7 days of transits averaged (49 minutes integration time), the detection sensitivity is already brought down from 1970 Jy to 746 Jy... So the strongest methanol masers could be within reach of a 1.2 metre dish in transit mode if you average multiple days of transits.

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[Steve Olney]

Hi Eduard,

I tend to be conservative (pessimistic?) and assumed DEC = 0. Also I figured I would lose detail - especially for the double peak of G351.42+0.64 if I went wider than 8 kHz. I also assumed Tsys would be higher here as I am looking through a gap in the trees - so I assumed sidelobes on the trees would raise Tsys.

Nonetheless I plugged the suggested values into my spreadsheet and it paints a rosier picture...

...where the green shaded boxes are for results for Smin less than the observed minimum flux density.

On this basis I am inclined now to go ahead and order the 1.5 m dish.

I really appreciate your responses. They have been of great assistance.

Steve O