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Astron. Astrophys. 346, 897-905 (1999)

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Colour transformations for isochrones in the VI-plane

A. Weiss 1 and M. Salaris 2

1 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85748 Garching, Germany (aweiss@mpa-garching.mpg.de)
2 Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead L41 1LD, UK (ms@staru1.livjm.ac.uk)

Received 12 October 1998 / Accepted 15 April 1999


Reliable temperature-colour transformations are a necessary ingredient for isochrones to be compared with observed colour-magnitude-diagrams of globular clusters. We show that both theoretical and empirical published transformations to [FORMULA] to a large extend exhibit significant differences between them. Based on these comparisons we argue for particular transformations for dwarfs and giants to be preferred. We then show that our selected combination of transformations results in fits of V-[FORMULA]-CMDs of a quality which is comparable to that of our earlier V-[FORMULA] isochrones for a wide range of cluster metallicities. The cluster parameters, such as reddening, are consistent with those derived in [FORMULA]. Therefore, at least in the case of the fit with our own isochrones - based on the particular distance scale provided by our own horizontal branch models, and on the treatment of convection by the mixing-length theory having [FORMULA] calibrated on our solar model - the chosen transformations appear to lead to self-consistent [FORMULA] isochrones. Our isochrones are now well tested and self-consistent for B, V and I photometric data.

Key words: stars: Hertzsprung – Russel (HR) and C-M diagrams – stars: late-type – stars: low-mass, brown dwarfs – stars: Population II – Galaxy: globular clusters: general

Send offprint requests to: A. Weiss

Correspondence to: A. Weiss

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© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999