IAUS241 Challenge 1

By A. Vazdekis, A.J. Cenarro, A. de Lorenzo-Caceres & M. Beasley (IAC, Tenerife, Spain)



Transformation to the observational plane

The theoretical parameters of the isochrones have been transformed to the observational plane (colours and magnitudes) by using relations inferred on the basis of extensive empirical photometric stellar libraries. We use the metallicity-dependent empirical relations of Alonso, Arribas & Martinez-Roger (1996, 1999), for dwarfs and giants respectively. The empirical (not the theoretical) compilation of Lejeune, Cuisinier & Buser (1997, 1998; and references therein) are used for the coolest dwarfs (Teff < 4000 K) and giants (Teff < 3500 K), respectively, for solar metallicity. A semi-empirical approach was applied to other metallicities on the basis of these relations and the model atmospheres of Bessell et al. (1989, 1991) and the library of Fluks et al. (1994). The empirical compilation of Lejeune et al. was also used for stars with temperatures above ~ 8000 K.

Metal-dependent bolometric correction given by Alonso, Arribas & Martinez-Roger (1995, 1999) for dwarfs and giants have been applied respectively. For the Sun, a bolometric correction BC_sun=-0.12 and a bolometric magnitude of 4.70 has been used according to these authors.


Ages and metallicities of the "best" CMD fits for different sets of isochrones

We have carried out a "by eye" fitting procedure, trying to fit (1) the top main sequence plus the turn-off; (2) the subgiant and red giant branches (the later specially at low magnitudes, as the redder part of the RGB is not very well constrained); and (3) the magnitude of the horizontal branch base. Reddening effects have not been considered; instead, apropriate offsets in both axis have been applied to the isochrones to match the observational CMD.

The Table below lists the "best" ages and metallicities of the program clusters for 4 different isochrone sets. No age/metallicity interpolation between isochrones has been carried out, so the values here derived should be considered as the "closest" solutions. By clicking at the solutions, you will be redirected to the corresponding CMD fits. Notes to the fits: red points are employed to display the observational CMD of the cluster, whilst the white line represents the isochrone whose age and metallicity are labeled within the figure. When the density of stars at a given magnitude bin of the CMD is large enough, green circles indicate the "mode" of the colour distribution (X-axis) within that magnitude bin. It may help to find the "most" populated region of the CMD when many stars are overplotted (note also that it may be wrongly determined at noisy and/or bimodal regions!).


 
CMD type
Padova 1994
Padova 2000
Salasnich 2000
(scaled-solar)

Salasnich 2000
(alpha-enhanced)

47Tuc B-V vs B
Age: 16 Gyr
[Fe/H]: -0.7 dex
Age: 14 Gyr
[Fe/H]: -0.7 dex
Age: 14 Gyr
[Fe/H]: 0.0 dex
Age: 14 Gyr
[Fe/H]: -0.4 dex
M67 B-V vs V
Age: 5 Gyr
[Fe/H]: 0.0 dex

(1)
Age: 4 Gyr
[Fe/H]: 0.0 dex
Age: 3 Gyr
[Fe/H]: 0.3 dex
Age: 4 Gyr
[Fe/H]: 0.0 dex
  V-I vs V
Age: 4 Gyr
[Fe/H]: 0.0 dex

(1)
Age: 4 Gyr
[Fe/H]: -0.4 dex
Age: 4 Gyr
[Fe/H]: 0.0 dex
Age: 4 Gyr
[Fe/H]: 0.0 dex

(1)
NGC1805 V-I vs V
Age: 0.05 Gyr
[Fe/H]: 0.0 dex

(3)
Age: 0.06 Gyr
[Fe/H]: -0.4 dex
Too young for
available isochrones
Too young for
available isochrones
NGC1868 V-I vs V
Age: 0.8 Gyr
[Fe/H]: -0.7 dex

(1,2)
Age: 0.8 Gyr
[Fe/H]: -0.4 dex

(1,2)
Age: 0.6 Gyr
[Fe/H]: -0.4 dex

(1,2)
Age: 0.8 Gyr
[Fe/H]: -0.4 dex

(1,2)
NGC6528 V-I vs V
Age: 13 Gyr
[Fe/H]: 0.0 dex
Age: 13 Gyr
[Fe/H]: 0.0 dex
Age: 13 Gyr
[Fe/H]: 0.3 dex
Age: 13 Gyr
[Fe/H]: 0.0 dex

(1) Not possible to fit both the MSTO and the HB level

(2) MSTO morphology (peak) not reproduced by the observations

(3) Not possible to fit the MSTO