[daip] NH3 Map units question

[Glen Langston]

Hi Eric,

Thanks for your quick response.

The issue is that some sources for which we are
comparing the integrated line intensities of two
molecular lines (in this case NH3 1-1 and 2-2)
We want to do two thinks, look at the effective
transition temperatures and also compare integrated
intensities.   The integrated intensities
are related to the number of atoms by an integral.

Since the spectra are convolved onto a image with
a convolving function represented by a beam shape
(bmin bmaj bpa)  the measure of integrated
intensities should be computed dependent on this.

What we request, in particular, is that
when we execute IMSTAT and have units of

Tmb/Beam in the header, the integrated intensities
are computed _in the same manner_ as Jy/Beam.

Is this difficult to achieve in a program?

It seems to me that drawing a box around two point
sources, even well separated, and asking for the
integrated intensities is a reasonable request,
if the BUNIT is Jy/Beam or Tmb/Beam.

Thanks

Glen

Operationally this issue leads to confusion if we
are forced to always use Jy/Beam in order to
get AIPS to operate in the manner we desire.

> Glen Langston wrote:
>> Hi Wayne
>>
>> The Units are Tmb.  You've reminded me I need to
>> send an email to the AIPS group to get them to fix
>> the programs that are counting on Jy/Beam to make
>> the measurement tools work.
>>
>> We put Jy/beam in to get the measurements that use
>> beam size to work correctly, but the actual units
>> are Tmb/beam.
>>
>> Glen
>>
>> PS Eric, the single dish community often uses T main
>> beam (Tmb) for certain measurements.   Many of the
>> AIPS tools, like imstat  require Jy/Beam to compute
>> the integrated intensities.   Our request is that
>> for any images that have beam sizes provided and
>> have BUNIT = '???/Beam' should have all beam size
>> corrections applied for integrated intensities.
>>
>> I've notices that we have to set NCOMP=1 to get
>> the map to appear to be "cleaned",  This is OK,
>> but does not seem to be logically required.
>>
>> Thanks
>>
>>> Hi Glen,
>>>
>>> We are working on hard on finishing the NH3 paper from our data last
>>> spring and I have a question for you. In the data reduction we
>>> selected TMB as the units for the map yet the headers say Jy/beam.
>>> Which is the correct unit I should be using?
>
> I have written to you before on this subject.  T (degrees K) is itself a
> brightness unit.  Dividing by beam area then does not make sense.  Jy is
> a flux density so it must be divided by an area - beam or pixel - to get
> a brightness unit.  Therefore I have no idea what you mean by Tmb/beam.
>
> Eric Greisen
>