1 Introduction

$\delta$ Sct stars are regularly pulsating variables located in the lower part of the Cepheids instability strip showing short periods (<0 $\hbox{$.\!\!^{\rm d}$ }$3) and visual amplitudes ranging from a few thousandths of a magnitude to several tenths, with typical amplitude of about $0\hbox{$.\!\!^{\rm m}$ }02$. The majority of these stars belong to Population I, however a few variables show low metallicities and high spatial motions typical of Population II. This second small group may be astrophysically different from the normal Population I $\delta$ Sct variables. They are called SX Phe stars and very few are known in the field. Recently, a large number of these variables are being discovered in globular clusters. A number of reviews on $\delta$ Sct variables are available in the literature, e.g. Breger ([1979], [1995], [1999], [2000]), Eggen ([1979]), Wolff ([1983]), Tsvetkov ([1990]), López de Coca et al. ([1990]), Kurtz ([1994], [1996]), Rodríguez et al. ([1994]; hereafter R94), García et al. ([1995]), Garrido ([2000]), Jiang et al. ([2000]).

During the last few years the number of new variables is enormously increasing. Additionally to the immense effort developed by individual groups, a number of long-term monitoring projects are being carried out leading to the discovery of a lot of new variables including $\delta$ Sct pulsating stars. Several of these projects are still in progress as, e.g., EROS (Aubourg et al. [1995]), DUO (Alard [1996]), PLANET (Albrow [2000]), etc., and their results will be available in the next future. In other cases, MACHO (Alcock et al. [2000]) and OGLE (Udalski et al. [1994], 1995a,b, [1996], [1997]) projects, a large number of $\delta$ Sct stars have been discovered already and probably more new variables will be still found. Contributions from OGLE side-projects are being also very important, especially for SX Phe-type variables in globular clusters. Furthermore, a lot of $\delta$ Sct variables have been detected by the Hipparcos mission (ESA [1997]) and more new members are expected from the Tycho mission (Annex B; ESA [1997]).

Additionally to new variables, new catalogues on different parameters have been recently published. This information has been used to up-date each variable in our list, using the most recent catalogues available in the bibliography on photometry (Strömgren and Johnson systems), spectral types, rotational and radial velocities, multiplicity and parallaxes.

The aim of this work is to present an extensive and up-dated list of $\delta$ Sct stars. This catalogue is intended to be a comprehensive review on the observational characteristics of all known $\delta$ Sct stars, including stars contained in earlier catalogues together with other new discovered variables, covering information published until January 2000. Field SX Phe stars have been also included in our list. A catalogue on SX Phe variables in globular clusters will be the subject of another work (Rodríguez & López-González in preparation).