Issue |
Astron. Astrophys. Suppl. Ser.
Volume 130, Number 2, June I 1998
|
|
---|---|---|
Page(s) | 251 - 265 | |
DOI | https://doi.org/10.1051/aas:1998410 | |
Published online | 15 June 1998 |
Star formation history of early-type galaxies in low density environments*
I. Nuclear line–strength indices
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
Send offprint request to: M. Longhetti
Received:
1
July
1997
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
© European Southern Observatory (ESO), 1998