Talk:Atmospheric parameters of VSOP B-A stars

Overview
Team: Cedric, Thomas (lead)

Goal: obtain Teff, logg, [Fe/H], plus radial velocity and vsini for all B-A stars to be treated in VSOP Paper1.

Methods: Calculate atmospheric models (ATLAS9) and corresponding synthetic spectra using MOOG. Matching of observed profiles of H-gamma, and possibly H-delta, using chi^2 minimization following Catanzaro et al. 2004 (A&A 425, 641)

Deadlines:
 * 1) Define fitting regions for atm.params and for vsini and [Fe/H]
 * 2) Procedures for iterative analysis defined
 * 3) Vsini found
 * 4) Atmospheric parameters found

Remember that the team leader should organize the work, and make sure dates are assigned to the deadlines. These should be published on this Team-page before May 24 (for Paper1)

Categories:
 * B stars
 * A stars

Update 2006-06-03
I have finalized the 'tools' side of it: The (semi-)NLTE treatment of Balmer lines using SYNTHE and ATLAS 9 models. I have these tools installed now, and am downloading a grid of models to use with it. The fitting regions are pretty obvious, namely around H-delta and H-gamma (4070-4130 and 4310-4370 respectively). Next I need to find some regions with (FeI and) FeII lines to estimate the metallicity and vsini. What is missing is a nice way to do chi^2 comparison of the spectrum with the synthetic one... -- Tdall 03:33, 3 June 2006 (CLT)

Update 2006-06-19
I have checked the available python resources for chi-square minimization. Plenty of things, of course, but no clue how to use them... I found two at least, for cross-checking the results. The most obvious way to proceed, which is the most computation-consuming of course, is to construct a chi-square map in N dimensions, and locate the minimum. How many dimensions we have?... If this is too big, as I suspect, we should simply provide a model function with N parameters to be minimized. And this, I have no clue. I mean, you have an observed spectrum, an synthetic one, what is the minimization function looks like? A gaussian? For CC I use sometimes parabolas. I am bit lost. -- C édric T alk  06:27, 19 June 2006 (CLT)

Check Chi-square minimization procedure. -- C édric T alk  16:41, 1 September 2006 (CLT)