The stars included in the library have been selected from the sample of lower main sequence stars studied in the Mount Wilson Observatory HK project (Baliunas et al. 1995 and references therein). From this sample the slowly-rotating stars and the stars with the lower Ca II H & K spectrophometric index S (normally lower than 0.2) were chosen.
Several stars not included in the sample of the HK Project have been observed,
because there are known to be inactive and slowly rotating stars and
they were used by other
authors in the application of the spectral subtraction technique
(see Strassmeier et al. 1990; Strassmeier & Fekel 1990; Hall & Ramsey 1992).
Some visual companions of chromospherically active binaries
have been observed simultaneously by locating both components
of the visual par
in the slit when the spectra where taken. Some of these stars are
inactive ADS 1697 B (HD 13480) and some are
little active ADS 16557 A (HD 218739), 
,
and ADS 8119 A (HD 98231) (see Table 3 (click here)).
We have considered as chromospherically inactive stars, those which at our spectral resolution do not present any evidence of emission in the core of Ca II H & K lines. We have found that some stars of the HK project (HD 115417, HD 115383, HD 206860, HD 101501, HD 4628, HD 16160) with relatively low values of S index (0.2-0.3) present a small, but measurable, emission in our Ca II H & K spectra (see Montes et al. 1995c). Hence, they have not been used as reference stars.
Table 3 (click here) presents information about the observed stars.
In this table we give
the HD and HR numbers, name, spectral type and luminosity class (
), from the Bright Star Catalogue
(Hoffleit & Jaschek 1982; Hoffleit & Warren 1991),
the Catalogue of Nearby Stars (Gliese & Jahreiss 1991), and
Kirkpatrick et al. (1995),
metallicity [Fe/H] (from Taylor 1994, 1995),
rotational period (
) and v sini
(from Donahue 1993; Baliunas et al. 1995).
The 
given between brackets are from Hoffleit & Warren (1991)
and the values of v sini marked with "*" are from the
references given in Strassmeier & Fekel (1990).
We also give the Ca II H & K spectrophometric index S
from Baliunas et al. (1995) or from Duncan et al. (1991) (values with "*").
In the columns labeled with
, He I 
, 
, and Ca II
we list information about the observations
for each spectral range, using a code given
in the first column of Tables 1 (click here) and 2 (click here).
In the last column "A" and "R" mean active and reference star respectively,
according with our above mentioned criterion,
and "E" means that the 
line is in emission in our spectra.
In some cases, we have available spectra of several stars that have been
classified with the same spectral type, these spectra present small
differences in the lines that could be attibuted
to differences in metallicities, rotation,
errors in the spectral classification, or even to variations
in the small level of activity that these stars could present.
Figures 1 (click here), 2 (click here), 3 (click here), and 4 (click here) show
representative high-resolution spectra in each spectral range.
In these figures we plot, at the left, the complete wavelength range covered
in each spectrum.
For a better display of the spectral features
an small region of 30 Å centered in the spectral line
of interest in each case is showed at the right.
Figure 5 (click here) presents mid-resolution spectra centered
in the 
line from 6340 to 6740 Å, and
Figure 6 (click here) shows representative mid-resolution spectra
in the wavelength range 5700 to 7600 Å which include the
Na I 
, 
and 
lines.
The stars in these figures are arranged in order of spectral type from F to M.
The HD number and the spectral type of the stars are given in each spectrum.
Table 3: Stellar parameters and spectral region observed
Table 3: continued
Looking at Figs. 1 (click here), 2 (click here), 3 (click here), and 4 (click here) some conclusions concerning the behaviour of different spectral lines present in each spectral region can be obtained.
In the Ca II H & K line region, we can note the effect of the spectral type: the equivalent width of several metallic lines increases with decreasing temperature, in particular the Al I 3961.52 Å line (see Fig. 1 (click here)).
In the case of the line, we note the increasing line wings with hotter spectral type. At spectral type F the line exhibits extended wings that decrease with decreasing temperature. The line becomes sharper at spectral type K (see Fig. 2 (click here)). Some strong absorption lines in this spectral region, that could be used for radial and rotational velocity determinations are: the Fe I 6495 Å, 6546.25 Å, 6663.4 Å, and 6677.9 Å lines and the Ca I 6718 Å line. The intensity of these lines increases toward later spectral types, in particular the , Fe I 6495 Å ratio has been used as a spectral classification criterion (Danks & Dennefeld 1994).
The line presents a marked temperature effect in the wings (see Fig. 3 (click here)) in the same way as the line. The Fe I 4878.08 Å line is an isolated and strong absorption line in this spectral region that could be used for radial and rotational velocity determinations.
The He I line region also includes the Na I and lines, which are well known temperature and luminosity discriminants among late-type stars, and they show the expected trend of metallic-line intensity increasing with decreasing temperature (O'Connell 1973; Torres-Dodgen & Weaver 1993; Danks & Dennefeld 1994; Serote Roos et al. 1996). The effect is more important in the later spectral types and especially in the wing of the lines (see Fig. 4 (click here)). The behaviour of these lines confirms the spectral classification of the star HD 22072 as G7V (Baliunas et al. 1995) rather than the K1V given by Hoffleit & Jaschek (1982). These Na I resonance lines are collisionally-controlled in the atmospheres of late-type stars and have been observed in emission or filled-in in very active red dwarf flare stars (Pettersen et al. 1984; Pettersen 1989), so the spectra of the inactive stars presented here can be used to apply the spectral subtraction technique to other active stars and obtain information about chromospheric emission in these lines (see Montes et al. 1996b).
In the mid-resolution spectra (Figs. 5 (click here) and 6 (click here)) in addition to the Na I , , and the other lines above described, we can also see other interesting features such as Fe I 6411.66 Å, Fe I 6430.85 Å, and Ca I 6439.08 Å normally used for the application of the Doppler imaging technique (see Fig. 5 (click here)) and the Ca I (6122 and 6162 Å) lines which are very weak at spectral type F and increase in strength with decreasing temperature (see Fig. 6 (click here)). From mid K through M stars we can also see absorption molecular bands of TiO in the following regions (5847-6058), (6090-6390), (6651-6852), (7053-7270) and of CaH in (6346, 6482, 6389) and (6750-7050) (see the K and M stars in Fig. 6 (click here)). These molecular bands become very strong at the later M spectral types, and dominate the spectrum of these stars. For spectral type M7 or later the VO absorption band (7400-7510) is also present. This feature can be used as an additional spectral classifier in the later spectral types, because it is strongly dependent on temperature (Kirkpatrick et al. 1995). Finally, we note in Fig. 6 (click here) the strong telluric line O (6867 Å), and the very deep atmospheric B-band absorption feature at 7600 Å.
In order to enable other investigators to make use of the spectra of this library, all the spectra of the stars listed in Table 3 (click here) are available as FITS and ASCII format files at the CDS in Strasbourg, France, via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5). They are also available via the World Wide Web at:
http://www.ucm.es/OTROS/Astrof/fgkmsl/fgkmsl.html
Acknowledgements
This research has made use of the SIMBAD data base, operated at CDS, Strasbourg, France. We wish to thank the staff of Calar Alto and La Palma observatories for their efficient assistance. We have made use of the La Palma ING data archive for retrieving some spectra. This work has been supported by the Universidad Complutense de Madrid and the Spanish Dirección General de Investigación Científica y Técnica (DGICYT) under grant PB94-0263.
Figure 1: High-resolution spectra in the
Ca II H & K line region
Figure 2: High-resolution spectra in the line region
Figure 3: High-resolution spectra in the line region
Figure 4: High-resolution spectra in the
Na I , , and He I line region
Figure 5: Mid-resolution spectra in the line region
in the wavelength range 6340 to 6740 Å
Figure 6: Mid-resolution spectra in the
Na I , , and line region,
in the wavelength range 5650 to 7640 Å
Figure 6: continued
