Red-wavelength spectroscopic and photometric follow-up observations of the stars with H&K emission are used to additionally determine the absolute H_alpha-core flux the lithium abundance from the Li I 6707 A equivalent width the rotational velocity v*sin(i) the radial velocity and the light variation and its periodicity. The latter is interpreted as the stellar rotation period due to an inhomogeneous surface brightness distribution. The photometric part of the survey is still ongoing.

Scientific motivation for a Ca II H&K survey

Recently Solanki et al. (1997) and Strassmeier et al. (1998) suggested that magnetic fields concentrated in polar starspots could be the reason for the lack of angular-momentum loss as observed in cluster stars and very active field stars. Solanki et al. presented numerical simulations that show that the effect would be quantitatively the same as with a dynamo saturation process. The only way to find conclusive observational evidence for or against the polar-spot hypothesis is to Doppler image these stars and to search for polar starspots. That however needs a larger target sample.

Data acquisition

Figure 1.

Fig.1 shows the sky coverage and galactic distribution of all target stars observed. Colored dots denote the stars that were found to exhibit H&K emission while white dots denote those without emission. Fig.2 are four plots that show the distribution of V, B-V, T_eff and M_V in the input sample.

Figure 2. V [mag] Mv [mag] B-V Teff [K]

Results

Figure 3.

Out of the total of 371 H&K emission-line stars 46 have Halpha-emission or are significantly filled-in by emission. The panels in Fig.4 show the distribution of the quantities measured. Lithium abundances are determined from non-LTE curves of growth and effective temperatures from B-V. Abundances are uncertain by only 0.05-0.1 dex when we propogate the uncertainties from the equivalent-width measurement. If we further assume an error of ± 100 K for the effective stellar temperatures the uncertainties are 0.15-0.16 dex. The largest lithium equivalent widths in our sample were obtained for HD140637 (420 mA) HD6665 (398 mA) HD217352 (331 mA) and HD109703 (300 mA) which basically amount to the primordial lithium abundance. Our detection limit is around 2-3 mA. Out of the 385 stars in the red sample 102 had undetectable Li 119 had Li below 10 mA 128 between 10-99 mA and 36 more than 100 mA (detections in SB2s and SB3s are counted only once). Radial velocities were derived from both the blue-wavelength and the red-wavelength spectra by cross-correlating them with spectra of velocity standard stars. Altogether 19 double-lined spectroscopic binaries (SB2) and two triple-lined spectroscopic binaries (SB3) are in our sample. The latter are HD86590 (DH Leo) and HD237944A. Out of the 19 SB2 systems 10 are new detections. The A-component of the close visual binary HD197913 turned out to be a SB2 with components Aa and Ab. Space motions are computed for all targets using the Hipparcos data (positions distances and proper motions; ESA 1997) and our new radial velocities and will be made available in tabular form. Rotational velocities v*sin(i) for the stars with Ca II H and K emission were determined from the widths of selected lines in the red-wavelength spectra. Errors are estimated to be 2-4 km/s for stars with v*sin(i) < 50 km/s and ~5 km/s for stars with higher rotation rates. For stars without a red spectrum i.e. the stars without Ca II H and K emission v*sin(i) was estimated from the blue spectra. Altogether we present v*sin(i) measurements for well over 1000 stars. Light curves and rotation periods Out of the 371 stars with Ca II H&K emission only 172 could be observed because of telescope-time limitations but 168, i.e. 97.7%, were found to be variable. A photometric period was determined for 134 of them, i.e. for 78% for the original 172 H&K emission-line stars. Lower limits for the period are found for further 11 targets. Additionally, a total of 32 of our comparison or check stars turned out to be variables and for 22 of them a possible period, or a lower limit for the period, was obtained. Except for a few eclipsing binaries (e.g. HD 553, HD 105575), we interpret the photometric periods found in this paper to be the stellar rotation period. Four of our target stars were recently discovered to be variables by Cutispoto et al. (1999). For two of these stars, we obtained a first period and confirmed the periods for the other two targets. Altogether, 170 new variables were discovered. References Cutispoto G., Pastori L., Tagliaferri G., Messina S., Pallavicini R., 1999, A&AS 138, 87 ESA 1997, The Hipparcos and Tycho catalogue SP-1200 Solanki S., Motamen S., Keppens R., 1997, A&A 324, 943 Strassmeier K. G., Bartus J., Kovari Zs., Weber M., Washuettl A., 1998, A&A 336, 587 Download   Download Area

Figure 4. Intensity K-line [0-5] log F'(K) [erg/cm2/s] log F(Halpha) [erg/cm2/s] EW Lithium [mA] log n(Li) [log n(H)=12] I_Sr [rel. I_H] v sin(i) [km/s] EW Strontium [mA] R_HK [sigma Teff4] delta y [mag] P_phot [days]