Effective airmass for combined image: IMCOMBINE
Frank Valdes wrote on May 14, 1998
Q: I am currently combining 4 exposures of the same image. I have used geomap to obtain the transformations relative to a reference frame, and I then used register to perform the registration. I then performed an average imcombine to combine the images. My problem is, how do I determine the proper airmass of the combined image (since imcombine simply uses the image header of the first image in the list) ? A: If the airmass is varying between exposures then you probably need to apply a multiplicative scaling to your exposures when combining. If you let IMCOMBINE compute this then you would use the image which has a scale factor nearest one as the basis for the airmass. You can also set the scaling values from a file or from a header keywords. In this case you can adjust things so that one of your images has unit scaling. Use this as the first one in the list of input images to IMCOMBINE and then the appropriate airmass will be that for the first image which is, as you said, the header that is used as the basis for the output header. Alternatively to having IMCOMBINE do the scaling you could scale your images to one of the image separately (say with IMARITH) and then use IMCOMBINE with no scaling. The best detailed way to determine the scaling is to use photometry of the common stars, using any of the photometry tasks in IRAF, and determine how to scale the images to make the photometry agree to one of the images as reference. This would then be the airmass reference image. Of course if the images were taken consecutively and you combine by averaging (without scaling) you could just treat this as a single long exposure and compute the airmass at the middle of the total exposure (maybe using SETAIRMASS after setting the the starting exposure time and total exposure time appropriately). I hope this helps. This questions has not come up much before so this is the best answer I currently have.
Indrajit Chakrabarty AKK wrote on Jun 17, 1998
Dear Friends, I am interested in finding out the higher order (a5,b5,a6,b6,a7,b7,a8,and b8) coefficients in the ELLIPSE task. How do I do it and what is the maximum number of such coefficients that I can get from ELLIPSE? Sincerely, Indrajit Chakrabarty , Snail mail :- IUCAA , Post Bag No.4, Ganeshkhind , PUNE . INDIA . ZIP - 411 007 e-mail :- indrajit@iucaa.ernet.in _____________________________________________________________________
Ivo Busko wrote on Jun 17, 1998
> From adass-iraf-applications@noao.edu Wed Jun 17 00:19 EDT 1998 > Date: Tue, 16 Jun 98 21:17:05 MST > Reply-To: adass-iraf-applications@noao.edu > Originator: adass-iraf-applications@iraf.noao.edu > Sender: adass-iraf-applications@noao.edu > From: irafmail-gateway@noao.edu (Indrajit Chakrabarty AKK) > To: busko@stsci.edu > Subject: Increasing the harmonic components in ELLIPSE task > X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas > Content-Type: text > Content-Length: 482 > > Dear Friends, > > I am interested in finding out the higher order > (a5,b5,a6,b6,a7,b7,a8,and b8) coefficients in the ELLIPSE task. How do I > do it and what is the maximum number of such coefficients that I can get > from ELLIPSE? > > Sincerely, > > Indrajit Chakrabarty , > > Snail mail :- IUCAA , Post Bag No.4, > Ganeshkhind , PUNE . > INDIA . ZIP - 411 007 > > e-mail :- indrajit@iucaa.ernet.in > _____________________________________________________________________ > > Just set the samplepar.harmonics parameter to "5 6 7 8". The task will create additional columns in the output table with the harmonic amplitudes and their errors. Note that these amplitudes are NOT converted into deviations from a perfect ellipse. Instead, they are written in raw intensity units. They can be converted into deviations from an ellipse by using task 'ttools.tcalc'. Just divide the respective columns by columns labeled 'SMA' and 'GRAD'. -Ivo ********************************************************************* * Ivo C. Busko e-mail: busko@stsci.edu * * Science Software Group * * Science Support Division Voice: (410)338-4472 * * Space Telescope Science Institute FAX: (410)338-4767 * * 3700 San Martin Drive * * Baltimore MD 21218-2410 USA * *********************************************************************
Indrajit Chakrabarty AKK wrote on Jun 19, 1998
Dear Sir, Thanks for clarifying the method of getting the higher order harmonics in the task ELLIPSE. I have since employed the method and 've been successful. I would like to know whether the latest (or the olderone) version of IRAF can fit isophotes along the minor axis of an elliptical galaxy. This is particularly necessary for identifying a "disky" component in an elliptical as was done by Scorza and Bender ( Ref. Astronomy and Astrophysics, Vol. 235, pp. 49-54; figure 9). Thanking you, Sincerely, Indrajit Chakrabarty , Snail mail :- IUCAA , Post Bag No.4, Ganeshkhind , PUNE . INDIA . ZIP - 411 007 e-mail :- indrajit@iucaa.ernet.in _____________________________________________________________________
Last post on Jun 19, 1998