Astron. Astrophys. Suppl. Ser. 130, 251-265
M. Longhetti1 - R. Rampazzo1 - A. Bressan2 - C. Chiosi3
Send offprint request: M. Longhetti
1 - Osservatorio Astronomico di Brera, Via Brera 28, I-20121, Milano, Italy
2 - Osservatorio Astronomico di Padova, Vic. dell'Osservatorio, 5, I-35122 Padova, Italy
3 - Dip. di Astronomia, Univ. di Padova, Vic. dell'Osservatorio, 5, I-35122 Padova, Italy
Received July 1; accepted December 8, 1997
This paper is the first of a series (Longhetti et al. 1997a,b) dedicated to the study of the star formation history in early-type galaxies which show fine structures and/or signatures of interaction. It presents nuclear line-strength indices for a sample composed of 21 shell galaxies, from the Malin & Carter (1983) southern survey, and 30 members of isolated interacting pairs, from the Reduzzi & Rampazzo (1995) catalogue, located in low density environments.
The spectral range covers 3700 Å 5700 Å at 2.1 Å FWHM resolution. We measure 16 red ( 4200 Å) indices defined by the Lick Group. Measures have been transformed into the Lick-IDS "standard'' system. The procedure has been tested on a set of 5 elliptical galaxies selected from the Gonzalez (1993) sample.
We derive also three blue ( 4200) indices, namely (4000 Å) defined by Hamilton (1985), H+K(CaII) and H/FeI defined by Rose (1984, 1985). Blue indices are correlated to the age of the last starburst occurred in a galaxy (Leonardi & Rose 1996).
The determination of these indices, the estimate of the measurement errors and the correction for the galaxies velocity dispersions are discussed in detail.
In the Appendix A we present the indices for a set of hot stars (T> 10000 K) which may be used for extending W92 fitting functions toward high temperatures.
Key words: galaxies: fundamental parameters -- galaxies: elliptical and lenticular -- galaxies: interactions -- galaxies: evolution
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