[daip] AIPS TST IMAGR and ISPEC

[Eric Greisen]

On 9/17/2020 5:52 AM, Anna Bartkiewicz via Daip wrote:
>
> Dear All,
>
> I am using the AIPS TST version. Since ca. 13/14 April, the ISPEC task 
> shows too high amplitudes for the spectrum of the image cube generated 
> by IMAGR. That is likely 10 times higher.
>
> The brightest spot is 3.9 Jy and the spectrum from ISPEC shows 70 Jy 
> as you can see in the attached print screen. Can it be related to some 
> changes in IMAGR or calculating the noise in ISPEC?
>
> I would appreciate your help.
>
>
> Greetings,
> Anna Bartkiewicz
>
> ----------------------------------------------------------------
> Dr hab. Anna Bartkiewicz, prof. NCU
> Institute of Astronomy
> Nicolaus Copernicus University
> Gagarina 11
> 87-100 Torun
> Poland         annan at astro.umk.pl    phone: +48 56 6113040
>                                      mobile: +48 885 101 723
>
> ----------------------------------------------------------------
>
> Imstat over the whole cube (201 channels)
>
>> imstat
> AIPS 1: Mean= 3.797E-04 rms= 8.431E-03 JY/BEAM  over    85838256. pixels
> AIPS 1: Maximum= 3.9012E+00 at    312    813    82    1    1 1    1
> AIPS 1: Skypos: RA 18 35 08.1400000  DEC -07 35 04.150000
> AIPS 1: Skypos: 115.3 km/s  IPOL
> AIPS 1: Minimum=-4.4189E-01 at    318    844    79    1    1 1    1
> AIPS 1: Skypos: RA 18 35 08.1395965  DEC -07 35 04.119000
> AIPS 1: Skypos: 115.6 km/s  IPOL
> AIPS 1: Flux density =  1.0627E+03 Jy   Beam area =    30.67 pixels
>
>
> Imstat for one channel image with no emission
>
>> imstat
> AIPS 1: Mean=-9.454E-05 rms= 2.530E-03 JY/BEAM  over      522443. pixels
> AIPS 1: Maximum= 1.2832E-02 at    405    258   201    1    1 1    1
> AIPS 1: Skypos: RA 18 35 08.1337453  DEC -07 35 04.705000
> AIPS 1: Skypos: 104.9 km/s  IPOL
> AIPS 1: Minimum=-1.2264E-02 at    366    843   201    1    1 1    1
> AIPS 1: Skypos: RA 18 35 08.1363682  DEC -07 35 04.120000
> AIPS 1: Skypos: 104.9 km/s  IPOL
> AIPS 1: Flux density = -1.6103E+00 Jy   Beam area =    30.67 pixels
>
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The peaks that you mention are in brightness (Jy/beam) at a single 
pixel.  The plot is the summed brightness over a large area X pixels 
from 254 to 766 and Y pixels from 197 to 926 corrected to Jy by dividing 
by the number of pixels in a Clean beam.  So these are TOTAL fluxes in 
your cube not brightnesses.  OPTYPE in ISPEC controls what is plotted 
and BLC and TRC control the area over which sums or averages are done.  
If you ask for AVER and set BLC=405,258 and set TRC=BLC then you will 
get 12.8 milliJy/beam at channel 201.


Eric Greisen



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