A B S T R A C TElemental abundances in late-type stars are of interest in several ways: they determine the location of the stars in the HR diagram and therefore their ages, as well as the atmospheric structure in their middle and upper photospheres. Especially in the case of chromospherically active late-type stars the question arises to what degree the upper photosphere is influenced by the nearby chromosphere. Analysing S=N ϳ 200 and Dl=l ϳ 20 000 data, we found a mean metallicity index ½M=Hÿ ¼ ¹0:2 for programme K and M field stars based on an analysis of spectra in the region 5500-9000 Å . We also found that the Ca I 6162-Å transition is a potential surface gravity indicator for K-type stars. For the chromospheric activity interval 4:4 < log F Mg ii < 6:6 we did not find any chromospheric activity impact on photospheric and upper photospheric transitions. With the derived metallicity, we confirmed the Li abundance from our previous paper and thus its dependence on the Mg II chromospheric activity index. The nature of the spectrum for the active M-type star Gl 896A is explained by pure rotation of 14 km s ¹1 . As far as the lithium-rotation relation is concerned, the spectrum of Gl 517 is rotationally broadened as well, by 12 km s ¹1 , and the Li abundance is the second highest in our sample of stars. However, there is no link between very high Li abundance, 2.2 dex, in the K dwarf star Gl 5 and stellar rotation.

Abstract.We report on a photometric study of the flare M4.5 dwarf YZ CMi as based on photoelectric observations from the seasons 1972/73, 1979/80 and 1996/97. We suggest spot activity to explain the light and colour curves. Spots are generally 500K cooler than the surrounding photosphere and there are basically two solutions available for the observations: high latitude spot changing slightly basic properties such as radius and latitude or active near-equatorial (belt-like) centers represented by three spots. However, the activity centers changed in longitudes ( 180 Ó ). The typical spot coverage (inclination i=60 Ó ) is 10-15% and 5% for the season 1996/97 or 25% for the stellar inclination i=75 Ó . As a by-product, V curve and (V-I) and (V-K) indexes turn out to be most promising in modelling of M-type stars as far as present calibrations are concerned.

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We report on BVR precise photometry of active late-type stars EK DRA and 29 DRA in the spring of 2004. The analysis suggests a reasonable fit with single spot model for both cases in the season as far as the V-curve is concerned. The spots are generally cooler than surrounding photosphere and are at high latitudes. The maximal brightness changes for both stars implying a non-rotating component of activity signatures, the spots. We expect that the spot configuration is stable over the period of approximately three months. .

Abstract. We present the results from fitting a semi-empirical atmospheric model including a chromosphere and a transition region to the mean (seasonal) Balmer Hα line profiles of the RS CVn-type K0-giant UZ Librae. As a first step, a static 1D spherical model was applied to the mean component of the Hα-emission core and its profile. The main result of the fitting is that the transition region begins at a log mass depth of −1.8 g cm −2 at a temperature of 7400 K (approximately 3000 K warmer than the photosphere) and then has a steep increase to the peak temperature of ≈10 6 K. A stellar model in plane-parallel mode with "partial-frequency redistribution" option in the line transfer gave roughly the best fit. Subsequently, two-Gaussian fitting of the phase-dependent Hα-line profiles yields a complex velocity field. The radial velocities, from both the absorption reversal and the main emission component, display rotational and/or orbital modulation. The largest differences between consecutive line profiles occur mostly in the red line wings, suggesting the existence of both an inward-pointed velocity field and sporadic radiation events possibly related to flares. The total Hα emission, as derived from the equivalent width, possibly also displays rotational modulation. Indirect evidence is presented for the existence of circumstellar matter in form of an Hα absorption shell. Finally, a preliminary elemental abundance analysis suggests sub-solar metallicity of [M/H] ≈ −0.5 dex based on ATLAS models, or −0.7 dex based on PHOENIX models.