| A broad range of solar-type activity phenomena are seen in the late-type stars,which suggest that there is a similar magnetic dynamo process in the deep convection zone of these stars.We selected three active stars as targets.On the one hand,based on long-term highresolution spectroscopic observations of V711 Tau and UX Ari,we have studied their magnetic activity scale,active region structure and evolution.On the other hand,we have detected and studied prominences of SZ Psc through high time-resolved spectroscopic observations.V711 Tau is a close double-lined RS CVn-type binary consisting of a K1 subgiant star and a G5 main-sequence star in an almost circular orbit with a period of about 2.84 days.Long-term high-resolution spectroscopic observations were carried out with the Coud?e echelle spectrograph mounted on the 2.16-m telescope at Xinglong Station,administered by National Astronomical Observatories,Chinese Academy of Sciences,during eight observing runs from1998 to 2004.Chromospheric activity indicators Ca ii IRT(?8498,?8542,and ?8662),H?,Na i D1,D2 doublet,and He i D3 lines,formed at different atmospheric heights,are analyzed using the spectral subtraction technique.Strong chromospheric emission supports earlier results that indicate V711 Tau is a very active system.The results suggest that the main part of chromospheric emission is attributed to the K1 subgiant star of the system.The G5 mainsequence star also presents weak emission but is less active.Two optical flares were detected during our observations.Moreover,we have found rotational modulation of chromospheric activity in the H? and Ca ii IRT lines,which suggests the presence of the chromospheric activity longitudes over the surface of the K1 subgiant star.Two active longitudes separated by about180?were observed to dominate the activity excluding 2004 February.The chromospheric activity level shows a long-term variation.Finally,by comparing with nearly simultaneous light curves observed by other authors,a close spatial connection between photospheric spots and chromospheric activity regions in both short and long time-scale was found for V711 Tau.UX Ari is a non-eclipsing spectroscopic system,consisting of a K0 subgiant star and a G5main-sequence star,in an almost circular orbit with a period of about 6.44 days.By means of the spectral subtraction technique,chromospheric activity indicators Ca ii IRT(?8498,?8542,and ?8662),H?,Na i D1,D2 doublet,and He i D3 lines obtained with the Coud?e echelle spectrograph of the 2.16-m telescope during five observing runs from 2001 to 2004 were analyzed to study optical flare events and chromospheric activity variability of UX Ari.The results suggest that UX Ari is a very active system and the chromospheric emission is mainly attributed to the K0 subgiant star.Moreover,four large optical flare events were detected during our observations,which show the prominent He i D3 line emission together with the great enhancement in emission of the H? and Ca ii IRT lines and strong filled-in or emission reversal feature in the Na i D1,D2 doublet lines.The new detected flares are much more energetic than the previous discoveries,especially for the flare hunted during 2002 December observing run.Optical flare events on UX Ari are more likely to be observed around two quadratures of the system,except for the optical flares detected during 2004 November observing run.Finally,we have found rotational modulation of chromospheric activity in the H? and Ca ii IRT lines.The chromospheric activity level also shows a long-term variation.SZ Psc is a triple system,in which two main components K1 subgiant star and F8 mainsequence star constitute a RS CVn-type binary with an orbital period of about 3.97 days.To detect stellar prominences,we carried out time-resolved high-resolution spectroscopic observations with the direct echelle mode(DEM)of the Li Jiang Exoplanet Tracker(Li JET)mounted on the 2.4-m telescope of the Lijiang station of Yunnan Observatories during two consecutive observing nights: October 24 and 25,2011.Chromospheric activity indicators Ca ii ?8498,?8542,H?,Na i D1,D2 doublet,He i D3,Mg i b triplet,and H? lines,are analyzed using the spectral subtraction technique,which show the remarkably different behavior between our two observing nights.During the first observing night,the He i D3 line shows absorption feature and there is excess absorption appeared in the subtracted H?,H? and other active lines.According to the gradual blue-shift relative to the K1 subgiant star and the increasing strength of the absorption,it could be understood in terms of a stellar prominence which is rising its height along the line of our sight.We think that this active stellar prominence event was associated with the subsequently occurred optical flare.Part of the flare decay phase was hunted in the second observing night.The flare was characterized by the prominent He i D3 line emission,as well as stronger chromospheric emission in other active lines.The gradual decay of flare was accompanied by an obviously developmental absorption feature in the blue wing of the chromospheric activity indicators(especially for the H? line),which could be explained as cool post-flare loops.Therefore,a series of interesting magnetic activity phenomena,were detected on SZ Psc. |
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