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Home > Group > Tim Naylor > tau-squared > Manual
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The basic use of the code involves running the following programs in
this order.
1) monteThis creates the 2D isochrone models required by grid using a Monte-Carlo. You will be asked for a model number and the colour combination you want. The output files consist of the 2D isochrones (e.g. geneva_V_B-V_07.000.00.fit, where the number is the base ten logarithm of the age in years) and a list of the first 10,000 simulated stars. The latter is useful if the isochrone does not stretch as far in the 2D CMD as you think it should. If you sort the file on the third column (mass), and then examine the last column (flag) you can get an idea of if it is (say) the model isochrone which does not stretch to the mass you want, or the conversions from luminosity and temperature to magnitude and colour. 2) grid
This takes a catalogue of observations in
cluster format and fits them
to a model.
It does this by a grid search in the parameter space.
It assumes that the uncertainties you give for say V and B-V are
correlated, unless the uncertainties in colour are smaller than those
in magnitude.
It then creates uncertainties in each magnitude, e.g. V and B.
The final tau-squared it gives you is after removing data points whose
tau-squared lies above the clipping threshold.
The output files are as follows. 3) tau2Calculates the expected value of tau^2 for you. For tau2 to give statistically meaningful answers you must have run grid to obtain a fit which has no datapoints soft clipped. You can achieve this by running grid once with a soft clipping of 20, and then renaming unclipped.cat to something like fitme.cat, and then re-running grid with this as the datafile and with a negative value for the soft clipping parameter (this switches it off). Inputs
The best fitting model (e.g. best_model.fit) Outputs
integ.tau - The cumulative distribution of tau-squared. Search through
this file to find the nearest value of tau-squared to the
one you have, and the number next to it is the
corresponding value of Pr(tau-squared).
This is also given in the output from the program. 4) UncerDerives uncertainty contours in tau-squared space. The 68 percent confidence limit is printed to the screen, as are some one-dimensional parameter limits. Use the latter with the same caution you would in the chi-squared case, i.e. if you have one free parameter they are right, more than that and they do not allow for any correlation in the parameters. There is a brief description of the underlying idea behind uncer. Inputs
grid.fit - From grid. The tau-squared grid from the fitting process.
You are not prompted for this, it is read automatically. Outputs
uncer.out - The values of tau^2 appropriate for each confidence
limit. Read down the confidence limits to find the appropriate value
for a tau-squared contour. SimCreates a simulated catalogue of observations from an isochrone. One possible input is a linear isochrone, such as Sim/linear.iso The isochronesThe isochrones consist of two distinct parts, the model interiors which give effective temperature and luminosity, and the model atmospheres which convert these into colour and magnitude. We provide three sets of conversions. Jeffries/Naylor: The bolometric corrections are derived from fitting observations for cool low-mass stars, and from Bessell, Castelli & Plez (1998) for the the hooter stars. The technique is outlined in Naylor et al (2002). In one case the bolometric correction is from Flower (1996). You can see the polynomials for the bolometric corrections in the code. The conversions from effective temperature are derived from fitting the Pleiades ("Pleiades tuning") and is described in Jeffries et al (2001). The problem this produces is that we have not determined the effective temperature to colour conversion for all models. Making them is not hard, checking that dozens of them are right is. So, if the conversion is not present for the particular isochrone you want (the error message will be from monte, and something like "Error opening file /h/timn/CMDfit/Data/dam97_K_J-K.dat"), let me know, and I can generate it for you; provided you undertake to check its reasonable). Bessell: These are solar metallicity bolometric corrections, effective temperature to colour conversions and colour dependent reddening vectors from Bessell, Castelli & Plez (1998). The model atmospheres folded through the filter responses do not always give the colours of Vega to be zero (the V magnitude is zero). We choose to tweak the colour scale so all the colours are zero (though there is a compilation option to change this). These can give problems when dealing with post-main-sequence isochrones as the higher temperatures do not have the lower gravities required for the giants. Bessell Tycho: Bolometric corrections and effective temperature to colour conversions into the Hipparcos Tycho system from Bessell (2000). Note that we then use the extinctions from Bessell, Castelli & Plez (1998), but in the cases we've done the extinction is so small the error is not important. These can then be applied to the following models. Note, however, that you may want to be careful about combining one metallicity of interior with a different metallicity atmosphere.
dam97: from
D'Antona & Mazzitelli (1997) The following models come ready converted into colour and absolute magnitude, but you can also apply any of the above atmospheres.
padova: z=0.019 (i.e. solar metallicity) from
Girardi et al (2002) Finally, you can supply your own isochrones at fixed ages. The files should be call something like user_V_B-V_06.800.dat. The format us as follows. The code uses the last header line to pick out the columns it wants, and is quite intelligent at doing so. so not all the columns are needed. The mass used is M_ini.
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