A homogeneous set of globular cluster relative distances and reddenings^*,**

¹ Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: [recio;piotto;deangeli;riello]@pd.astro.it
² INAF, Osservatorio Astronomico di Collurania, via M. Maggini, 64100, Teramo, Italy e-mail: cassisi,adriano@te.astro.it
³ Instituto de Astrofísica de Canarias, Via Láctea s/n, 382002 La Laguna Tenerife, Spain e-mail: aaj@ll.iac.es
⁴ ESO, Karl-Schwarschild-Str. 2, 85748 Garching bei Mnchen, Germany
⁵ Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead, CH41 1LD, UK e-mail: ms@astro.livjm.ac.uk
⁶ Departamento de Astronomia, P. Universidad Catolica, Av. Vicuna Mackenna 4860, 7832-0436 Macul, Santiago, Chile e-mail: mzoccali@astro.puc.cl

Received: 7 April 2004
Accepted: 1 July 2004

Abstract

We present distance modulus and reddening determinations for 72 Galactic globular clusters from the homogeneous photometric database of Piotto et al. ([CITE]), calibrated to the HST flight F439W and F555W bands. The distances have been determined by comparison with theoretical absolute magnitudes of the ZAHB. For low and intermediate metallicity clusters, we have estimated the apparent Zero Age Horizontal Branch (ZAHB) magnitude from the RR Lyrae level. For metal rich clusters, the ZAHB magnitude was obtained from the fainter envelope of the red HB. Reddenings have been estimated by comparison of the HST colour-magnitude diagrams (CMD) with ground CMDs of template clusters with low reddening. The homogeneity of both the photometric data and the adopted methodological approach allowed us to obtain highly accurate relative cluster distances and reddenings. Our results are also compared with recent compilations in the literature.