[daip] Spectral Index maps

[Mercedes Esteves Filho]

yes please!

On Fri, 26 Oct 2007, Amy Mioduszewski wrote:

>  O.K., you've hit on a major pet peeve of mine.  In order to make a realistic
>  spectral index map you should not "taper and convolved the data to the same
>  beam" you should put a model for the image for the lower frequency through the
>  uv coverage of the higher frequency (and then convolve the beam to the lower
>  frequency).  Yes, uv coverage matters and make a big difference.  Simply
>  convolving the data to the same beam misses the fact that you have fewer short
>  spacings at the higher frequency, therefore you miss flux that might be there
>  and *artificially* have a more negative spectral index than is real.  This is
>  particularly important for VLBI arrays that are relatively sparsely populated.
>
>  Anyway, I can give you detailed instructions on how to do this if you want.
>
>  Amy
>
>  Mercedes Esteves Filho wrote:
>  >
>  > Hi. Ive data from the VLBA and would like to construct
>  > spectral index maps. Now Ive tapered and convolved the
>  > data to the same beam. Image size and increment are the
>  > same for both images. So added and divided images using COMB
>  > look ok, but the spectral index maps dont look ok.
>  >
>  > I guess that this will have to do with my choices
>  > for aparm and bparm...But could you help me
>  > out with this?
>  >
>  > Mercedes Filho
>  >
>  > ******************************************************
>  > *                                                    *
>  > *   Mercedes Esteves Filho, Ph.D.                    *
>  > *   Centro de Astrofisica da Universidade do Porto   *
>  > *   Rua das Estrelas                                 *
>  > *   4150 - 762 Porto                                 *
>  > *   Portugal                                         *
>  > *   email: mfilho at astro.up.pt                        *
>  > *   Tel: +351 22 6089 853                            *
>  > *   Fax: +351 22 6089 831                            *
>  > *                                                    *
>  > ******************************************************
>  >
>  > _______________________________________________
>  > Daip mailing list
>  > Daip at listmgr.cv.nrao.edu
>  > http://listmgr.cv.nrao.edu/mailman/listinfo/daip
>  >
>
>

******************************************************
*                                                    *
*   Mercedes Esteves Filho, Ph.D.                    *
*   Centro de Astrofisica da Universidade do Porto   *
*   Rua das Estrelas                                 *
*   4150 - 762 Porto                                 *
*   Portugal                                         *
*   email: mfilho at astro.up.pt                        *
*   Tel: +351 22 6089 853                            *
*   Fax: +351 22 6089 831                            *
*                                                    *
******************************************************