[mmaimcal] [Almasci_chile] Some thoughts of ALMA calibrator sources
Harvey Liszt
hliszt at nrao.edu
Fri May 14 11:53:52 EDT 2010
Its very zen. What does it mean to do a flux-limited sample when all
the sources are varying?
H.
------------------------------
On 5/14/10 11:22 AM, Bryan Butler wrote:
>
> the flux densities of all of these sources will be variable, so you're
> never going to be able to get away from that. predictions are probably
> fine. we have provision in our source model for observations over time
> (flux density, structure, etc.).
>
> -bryan
>
>
> Ruediger Kneissl wrote, On 5/10/10 16:57:
>> Hi all,
>>
>> We should obviously discuss this in the meeting Stuartt is going to
>> organise,
>> but here just some thoughts from a conversation with Robert.
>>
>> Right now the catalogue is being used for interferometric pointing,
>> baseline
>> determination, etc. and for these purposes the number of sources is
>> sufficient. The quality of the estimated fluxes is more important in
>> order to
>> optimize the observing efficiency. So simply adding sources with
>> predicted
>> fluxes would not be helpful.
>>
>> When for some early science (verification) projects we need close-by
>> calibrators, we will need to search specifically those areas around the
>> science targets, from all available catalogues. In the longer term,
>> towards
>> early science, we will need the network of sources around the sky to be
>> efficient in our projects.
>>
>> I would suggest that we aim to get the Planck source candidate list
>> around
>> this summer (when the component separation and source extraction has
>> matured),
>> which will give us SEDs in 9 channels from 30 to 900 GHz to pre-select
>> likely
>> candidates. And we can use specifically ATNF and other catalogues to
>> check
>> compactness and improve the positional accuracy, if needed. At this
>> point it
>> would probably be worth spending the time to observe a larger number of
>> sources with ALMA, also with more available antennas, to verify suitable
>> calibrators.
>>
>> Ruediger
>>
>>
>> On Mon, May 10, 2010 4:49 pm, Harvey Liszt wrote:
>>> I of course can give you as many of the predicted-to-be-strong-at-100
>>> GHz
>> ATNF sources as you want, in the format of the existing .py script or
>> whatever.
>>> H.
>>> -----------------------------
>>>
>>> On 5/10/10 4:39 PM, Stuartt Corder wrote:
>>>> Hi all,
>>>> I think we are collecting enough information that we should call
>>>> another
>> amplitude calibration team meeting and discuss some of the details that
>> people have provided along this thread. I think the other thing to start
>> talking about is how to *start* approaching this with ALMA. I have
>> recently developed a script that will do a dip,
>>>> planet/asteroid/moon observation and then start through the list of
>> quasars. The current catalog has some structures (Al mentioned this
>> earlier, sourceCatalog.py) for predicting flux at various bands
>> (basically
>> a spectral slope and 3 mm flux). Of course this is all defaulted to flat
>> spectrum at this point but the structure exists. However, the tools in
>> sourceCat are designed for catalogs with<= a few hundred sources (i.e.,
>> they have rather unintelligent source searching routines..I can say this
>> because I wrote them). If we are really going to start fashioning a
>> catalog of thousands, we need to have a separate catalog that includes
>> some
>> information (like last observed date) so we can add options to observe
>> ones
>> with dates older than X many days. We also need some sorting routines
>> because we will want to do parts of the sky (this isn't hard, someone
>> needs
>> to do it, the most likely candidate for that is me).
>>>> Thanks for all the comments. The ampcal team is supposed to do both
>>>> these
>> sorts of studies and commission the system for accurate
>>>> measurement of the flux scales. Right now I many of you are not on that
>> team. If you would like to be included (specifically Al, Satoki, and
>> Anita
>> since your involvement is both relevant and ALMA-centric) let me know and
>> I'll put you on the team distribution. Rudy, no worries on you, you are
>> already on it.
>>>> Stuartt
>>>>> Dear Al and all,
>>>>> In case of SMA southern calibrator sources (which cannot be
>>>>> observed from
>> NMA, OVRO, BIMA, or PdBI), we first collect the possible calibrator
>> sources
>>>>> from the ATCA& VLA calibrator source catalogs (+ some VLBI calibrator
>> sources). If there are two frequency information, we estimated 230 GHz
>> flux from those, but if not, we used typical spectra index (-0.8? I
>> forgot...), and estimated 230 GHz flux. We then put some lower limit in
>> estimated flux at 230 GHz (> 0.5 Jy? Again I forgot...) and made a
>> survey
>>>>> catalog, and then we actually observed. If it was bright (>0.5
>>>>> Jy?), we
>> put the source in the official SMA catalog. Some sources observed several
>> times, but some only observed once at the survey. So, it is not perfect,
>> but the number of calibrator sources increased.
>>>>> Just my two cents.
>>>>> Cheers,
>>>>> Satoki
>>>>> Al Wootten :
>>>>>> Hi folks
>>>>>> It is a good time to consider this subject again.
>>>>>> As we discussed at the Dec 09 Sci IPT meeting the SPT survey sources
>> presented in:
>>>>>> http://arxiv.org/abs/0912.2338
>>>>>> support the predictions made in the numerous ALMA memos on the
>>>>>> subject.
>>>>>> The area surveyed was very limited but of course this is a dynamic
>>>>>> field with Planck and the SPT still exploring.
>>>>>> I think sourceCatalog.py is a derivative of SMA and other catalogs
>>>>>> but
>> ALMA is reaching the point where it can contribute usefully to compendia.
>> There was a plan at some point for a comprehensive EVLA/VLB/ALMA catalog
>> but I do not know where that stands or whether ALMA needs an independent
>> initiative. Temporal measurements are critical--certain SBs run in March
>> used calibrators which had worked well for the SMA but whose flux had
>> faded to uselessness even for the more sensitive ALMA 3-antenna
>> array.
>>>>>> Clear skies,
>>>>>> Al
>>>>>> Harvey Liszt wrote:
>>>>>>> Something to keep boredom at bay. Attached.
>>>>>>> H
>>>>>>> ------------------------------------------------------------------------
>>>>>>>
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>>> --
>>> Harvey S. Liszt work:+1 434.296.0344 fax 0278
>> Scientist & Spectrum Manager home:+1 434.973.3744
>>> National Radio Astronomy Observatory cell:+1 434.227.6356 (+41792953708)
>> 520 Edgemont Road mailto:hliszt at nrao.edu
>>> Charlottesville, VA 22903-2475 http://www.cv.nrao.edu/~hliszt
>>>
>>> "Be Kind To Radio Astronomy"
>>> http://www.nrao.edu/~hliszt/RFI/
>>>
>>>
>>>
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--
Harvey S. Liszt work:+1 434.296.0344 fax 0278
Scientist & Spectrum Manager home:+1 434.973.3744
National Radio Astronomy Observatory cell:+1 434.227.6356 (+41792953708)
520 Edgemont Road mailto:hliszt at nrao.edu
Charlottesville, VA 22903-2475 http://www.cv.nrao.edu/~hliszt
"Be Kind To Radio Astronomy"
http://www.nrao.edu/~hliszt/RFI/
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