Up: Star formation history of environments
The aim of the present work (cf. also Papers II and III) is that of
looking for the presence of recent star formation events connected to
interaction, that can have involved only a few percentages of the total
mass of the galaxies. Both observations and numerical/hydrodynamical
simulations (see for references Barnes & Hernquist 1992) indicate
that induced star formation is a possible effect of the interaction.
Young stellar populations, if present, are made recognizable in a
galaxy by the presence of very hot stars (T > 10000 K).
These kinds of stars are under-represented in the sample from which
W92 derived his fitting functions. Consequently, the
knowledge of the indices behaviour in the range of stellar
temperatures greater than 10000 K
is a necessary step in the construction of suitable
fitting functions.
![\begin{figure}
\includegraphics [width=8cm]{1429f8.eps}\end{figure}](/articles/aas/full/1998/11/ds1429/Timg84.gif) |
Figure 8:
Fitting functions of W92 for gravity g=4.5 and
different metallicities (lines: solid line [Fe/H]=-2, short dash [Fe/H]=-1, medium
dash [Fe/H]=0, long dash [Fe/H]=1). Full squares represent our measures on
a sample of 17 hot stars, listed in Table 14. Note that in the case of the H index, fitting functions from W92 do not match our observations |
We have observed 17 hot stars (whose parameters are listed in Table 14)
in order to test the Lick standard fitting functions in the high
temperature regime. Figure 8
shows a comparison between Lick
fitting functions for some indices and stellar data collected in the
present work. In the case of the H
index, the only classic age
indicator in the "red'' part of the spectrum, it is quite evident that
the standard fitting functions do not match our observations. This
suggests that the extrapolation starting from lower values of stellar
temperatures towards higher ones need to be better investigated on a
larger sample. We have used our new data to construct a tentative
extension of the Lick Group fitting functions for the 16 common "red''
indices. Table 13 lists the coefficients of these new extensions,
obtained through a linear interpolation of the values
starting from log
for the different metallicities and
gravities.
Acknowledgements
ML acknowledges the kind hospitality of the Brera Observatory and
of the Padova Observatory during her PhD
Thesis.
We thank Ginevra Trinchieri for the careful
reading of the manuscript.
ML, AB and CC acknowledge the support by the European Community
under TMR grant ERBFMRX-CT96-0086.
Up: Star formation history of environments
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