Calibrator Database

Got a calibration problem? Discuss it here.

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ste616
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Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Calibrator Database

Post by ste616 »

We are aware that the current calibrator database has a number of issues, and hasn't been updated for some time for most sources.

There are several reasons for this:
  • we don't often observe calibrators at cm wavelengths in the calibrator project C007
  • I am holding off calibration of mm observations until the Uranus flux calibration issues are sorted out (which is my main focus now)
  • I am also developing a new calibrator database that will use all available observations of calibrators during normal science projects as well, which should allow the database to be kept up-to-date more reliably and automatically than is currently possible, so I am loathe to spend too much time on the old database before its imminent obsolescence
If anyone requires more up-to-date information on any source in the ATCA calibrator catalogue, please contact me and I will provide it.
cheers
Jamie Stevens
ATCA Senior System Scientist
baerbel
Posts: 6
Joined: Mon Feb 08, 2010 1:27 pm

Re: Calibrator Database

Post by baerbel »

The issue of polarisation calibrators at cm wavelength has come up; maybe this is also an issue at mm-wavelength.

Do we have a set of standard polarisation calibrators ? Are these monitored or do these need to be monitored ?
The source 3C286 is often used as the main polarisation calibrator, but I believe observers are questioning its usefulness.

Can anybody add details, please. This is not my field of expertise.
ste616
Site Admin
Posts: 220
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Re: Calibrator Database

Post by ste616 »

There are some standard polarisation calibrators; they are listed in Dave Rayner's memo regarding ATCA polarisation:

http://www.atnf.csiro.au/observers/memo ... lguide.pdf" onclick="window.open(this.href);return false

They are part of the normal calibrator database, and so would be monitored in the same way as all the other C007 calibrators. However, the standard C007 reduction does not account for polarisation, and the C007 observation method -- one 2 minute observation every couple of months-- would not be enough to properly characterise polarisation properties anyway.

A new monitoring program could be started if a lot of people require polarisation information and we suspect that the polarisation properties of these sources change over time.

I currently have no handle on whether source polarisation does change on short time scales (ie. years).
cheers
Jamie Stevens
ATCA Senior System Scientist
ste616
Site Admin
Posts: 220
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Re: Calibrator Database

Post by ste616 »

The new calibrator database is now available in a preliminary form for users on the internal network only.

To access the web interface, which currently uses the same interface as the old, go to:

http://mentok.atnf.csiro.au:8080/calibrators" onclick="window.open(this.href);return false;

As you can see it is hosted on my own machine. This machine is also being used to reduce all the data that is going into the database so database access through the web interface may take a few seconds for any particular calibrator.

Notable things:
- from the main page of the web interface, all three sections (distance from coordinate, calibrator name and calibrators in an area) all work as expected, but the flux level specification doesn't do anything yet
- only cm observations have been reduced so far as I still don't trust mm flux calibration
- the fluxes are listed now for the recommended CABB frequencies - no old correlator data is in the database yet
- the calibrator tables always list the most recent flux that has been reduced, although currently the reduction is chugging away through June 2009 data, and is proceeding at the rate of a few weeks to a month per day
- the page for each individual calibrator know also includes the uncertainty on its flux, along with the date and time that measurement was made
- clicking on "Flux History" on the individual calibrator pages will bring up an interactive graph of flux vs time that uses Flash; each flux can be moused-over to see the measured flux, uncertainty and observation date/time

I encourage whomever is interested to use the new database. The interface is rudimentary at the moment, and we are looking for someone to improve it; we had employed Tui Britton for this but she is now flat out with her PhD work. We'd welcome suggestions and assistance!
cheers
Jamie Stevens
ATCA Senior System Scientist
mkeith
Posts: 1
Joined: Thu Feb 03, 2011 4:33 pm

17,24 GHz flux of 1253-055/1921-293

Post by mkeith »

Hello,

I have been trying to calibrate 17/24 GHz Parkes data using 1253-055 and/or 1921-293. In the ATCA cal database it seems that the measured flux density varies quite a lot, even over one day... I suspect that this is an artefact of the database, since otherwise the calibrators must not be that useful for gain calibration at ATCA(???)

Does anyone have any idea about if it is sensible for me to try and use the ATCA database to determine the flux density of these sources, or should I investigate other options?

Cheers,
Mike Keith
ste616
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Posts: 220
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW

Re: Calibrator Database

Post by ste616 »

Hi Keith,

Yes, unfortunately the automatically reduced data (which is what you see on those two sources at those two frequencies) is on the scan timescale, and yes, these do vary over the day. The automatic reduction algorithm has not yet been able to stabilise the fluctuations we expect due to changing seeing, different atmospheric thicknesses etc. that occur during a single observing run. However, there are plenty of manually reduced values for these sources and frequencies, which are much more stable since they are taken by averaging over the entire run.

However, the manually reduced data does not cover the entire time CABB time range. If you're after specific times and frequencies, get in touch and we'll try to help you out.
cheers
Jamie Stevens
ATCA Senior System Scientist
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