Astron. Astrophys. Suppl. Ser.
Volume 130, Number 2, June I 1998
|Page(s)||251 - 265|
|Published online||15 June 1998|
Star formation history of early-type galaxies in low density environments*
I. Nuclear line–strength indices
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
Send offprint request to: M. Longhetti
Accepted: 8 December 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 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 Δ(4000 Å) defined by by Hamilton (1985), H+K(CaII) and Hδ/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 ( 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
Based on observations obtained at ESO, La Silla, Chile. Tables 1-8 are also available in electronic form at CDS and Tables 9-15 are only available in electronic form at CDS: via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsweb.u-strasbg.fr/Abstract.html
© European Southern Observatory (ESO), 1998