Enhanced emission cores in the Ca II
H & K, are the primary optical indicators of chromospheric activity
in late-type stars, but also the emission or the
filling-in of the central core of other lines such as
, 
, Na I 
, 
, and He I 
indicate the existence of an active chromosphere in these stars.
Actually, the later mentioned lines are only in emission in a few
very active stars, whereas in a large number of moderately active stars only
a filling-in of the photospheric absorption is present.
To infer the chromospheric activity level a comparison with non-active
stars is needed, for example by means of the spectral subtraction technique.
This technique provides reliable measurements of the
the active-chromosphere contribution to these lines
(see Montes et al. 1995a,c; and references therein).
To apply this technique a large number of spectra of inactive stars
(i.e., stars with negligible Ca II H & K emission) with different
spectral types and luminosity classes taken
with the same spectral resolution that of the stars under consideration
is needed.
Previously published stellar libraries
cover the optical range and extend to
the near infrared, however they are of poor spectral resolution.
The more widely used have the following wavelength ranges and spectral
resolutions:
Gunn & Stryker (1983) (
, 20 and 40 Å);
Jacoby et al. (1984) (
, 4.5 Å);
Pickles (1985) (
, 15 Å);
Kirkpatrick et al. (1991) (
, 8 and 18 Å);
Silva & Cornell (1992) (
, 11 Å);
Torres-Dodgen & Weaver (1993) (
, 15 Å);
Danks & Dennefeld (1994) (
, 4.3 Å);
Allen & Strong (1995) (
, 6 Å) and
Serote Roos et al. (1996) (
, 1.25 and 8.5 Å).
As can be seen the higher spectral
resolution is only 1.25 Å (Serote Roos et al. 1996)
and 4.5 Å (Jacoby et al. 1984) that is
much lower than needed in detailed spectroscopic studies of
chromospheric activity.
Table 1: Summary of high-resolution observations
Table 2: Summary of mid-resolution observations
Our intent in this paper is to provide
a library of higher resolution spectra
(
) of F, G, and K chromospherically inactive stars
to be used in the application of the spectral subtraction technique
in chromospherically active single and binary stars.
These spectra can also be used for spectral classification purposes
(see Jaschek & Jaschek 1990)
and specially for the spectral classification of chromospherically active
binary stars with composite spectra (see Strassmeier & Fekel 1990).
In addition, we provide spectra of M-type
stars with resolution significantly higher
than in previous databases (Jacoby et al. 1984;
Kirkpatrick et al. 1991, 1995).
We present a total of 170 spectra centered in the spectral lines most widely used as optical indicators of chromospheric activity in a sample of 116 F, G, K and M field stars.
In Sect. 2 we report the details of our observations and data reduction. The library is presented in Sect. 3 with comments on the behaviour of some interesting spectral lines.