Comments on: Fitting surface brightness profiles

By: Eric Peng

Eric Peng — Thu, 17 Dec 2009 06:28:40 +0000

For the ACS Virgo Cluster Survey, we used both the IRAF isophote package and the VISTA “elliprof” package. The latter was used for the Tonry et al SBF survey of nearby early-type galaxies. It works well, but unfortunately the documentation is pretty much nil, and has become impossible to find on the internet with Windows Vista and the VISTA telescope out there. If I can find a link, I will post it here.

I’m intrigued about Archangel, which I hadn’t heard of before now. Anyone use it and have an opinion? The high level stuff being in Python seems like a big plus for today’s user (i.e. the beginning student).

By: Peter Erwin

Peter Erwin — Tue, 15 Dec 2009 22:29:27 +0000

Jane: the Bender et al. code is not, that I'm aware of, available on the web. If you're curious, I could ask around as to its availability (I'd ask Ralf Bender himself, but he's currently out of town). It's written in Fortran, and is not connected to any IRAF package. Hmm... there's another isophote-fitting package called galphot, which I've heard of but never used. (It's originally by Marijn Franx; Franx et al. 1989 is the relevant reference [1]). There is a version of it here, including (it says) both standalone Fortran code and an IRAF version; but it's not clear whether or not the latter works on anything other than Suns. There's a version of galphot built into Astro-WISE, apparently, though that's not any use unless you happen to be at one of the institutes taking part in Astro-WISE. [1] Most of these fitting-ellipses-to-isophotes code seem to date from the same two or three years; for example, the stsdas.isophote.ellipse algorithm is based on Jedrzejewski (1987).

By: Jane

Jane — Tue, 15 Dec 2009 16:48:46 +0000

Peter, yup that’s a tad pedantic. Perhaps I should have written the long-winded: “for a specific example, to measure the asymptotic total magnitude of an inclined disk galaxy”.

The B&M refs are great, thanks. Is what you refer to a version of stsdas.analysis.isophote, or a separate package? Can you provide a URL?

There’s danger, in writing these, “How do you do task X?” posts, of me sounding like an idiot. When asking, “How?”, I’m really asking, “So, I have a cobbled-together solution to problem X. You may, too. Is there a more efficient, more powerful solution out there? What solution should we recommend to a new grad student?”

By: Tom Aldcroft

Tom Aldcroft — Tue, 15 Dec 2009 11:29:07 +0000

Sherpa is well-suited for fitting 1-D radial profiles and 2-D image data. The threads below describe in detail how to do this. These examples are for X-ray data but the same methods would apply for any image data. Radial and elliptical profiles of Image Data Accounting for PSF Effects in 2D Image Fitting Radial and elliptical profiles of Image Data

By: Peter Erwin

Peter Erwin — Tue, 15 Dec 2009 09:09:57 +0000

You mean “generating surface brightness profiles by fitting isophotes in images”, yes? (“Fitting surface brightness profiles” sounds, to me, like modeling surface-brightness profiles with 1-D analytic functions, as in “we fit the surface brightness profile with a Sersic function”, in which case you could be talking about any minimization code.)

OK, enough pedantic nitpicking: isophote, mainly because of inertia (it’s what was and still is widely available, and I’ve learned to work around its idiosyncrasies). I work with people who use the (updated) code from Bender & Moellenhoff (1987); I’m not sure I’ve ever heard of “Archangel.”