Long-term photometry of three active red giants in close binary systems: V2253 Oph, IT Com and IS Vir

We present and analyze long-term optical photometric measurements of the three active stars V2253 Oph, IT Com and IS Vir. All three systems are single-lined spectroscopic binaries with an early K giant as primary component but in different stages of orbital-rotational synchronization. Our photometry is supplemented by 2MASS and WISE near-IR and mid-IR magnitudes and then used to obtain more accurate effective temperatures and extinctions. For V2253 Oph and IT Com, we found their spectral energy distributions consistent with pure photospheric emission. For IS Vir, we detect a marginal mid-IR excess which hints towards a dust disk. The orbital and rotational planes of IT Com appear to be coplanar, contrary to previous findings in the literature. We apply a multiple frequency analysis technique to determine photometric periods, and possibly changes of periods, ranging from days to decades. New rotational periods of 21.55+-0.03d, 65.1+-0.3d, and 23.50+-0.04d were determined for V2253 Oph, IT Com, and IS Vir, respectively. Splitting of these periods led to tentative detections of differential surface rotations of delta P/P ~0.02 for V2253 Oph and 0.07 for IT Com. Using a time-frequency technique based on short-term Fourier transforms we present evidence of cyclic light variations of length ~10yrs for V2253 Oph and 5-6yrs for IS Vir. A single flip-flop event has been observed for IT Com of duration 2-3yrs. Its exchange of the dominant active longitude had happened close to a time of periastron passage, suggesting some response of the magnetic activity from the orbital dynamics. The 21.55-d rotational modulation of V2253 Oph showed phase coherence also with the orbital period, which is 15 times longer than the rotational period, thus also indicating a tidal feedback with the stellar magnetic activity.Comment: 13 pages, 14 figures, accepted to A

Magnitude-range brightness variations of overactive K giants

We study three representative, overactive spotted K giants (IL Hya, XX Tri, and DM UMa) known to exhibit V-band light variations between 0.65-1.05 mags. Our aim is to find the origin of their large brightness variation. We employ long-term phase-resolved multicolor photometry, mostly from automatic telescopes, covering 42 yr for IL Hya, 28 yr for XX Tri, and 34 yr for DM UMa. For one target, IL Hya, we present a new Doppler image from NSO data taken in late 1996. Effective temperatures for our targets are determined from all well-sampled observing epochs and are based on a V-I_C color-index calibration. The effective temperature change between the extrema of the rotational modulation for IL Hya and XX Tri is in the range 50-200 K. The bolometric flux during maximum of the rotational modulation, i.e., the least spotted states, varied by up to 39% in IL Hya and up to 54% in XX Tri over the course of our observations. We emphasize that for IL Hya this is just about half of the total luminosity variation that can be explained by the photospheric temperature (spots/faculae) changes, while for XX Tri it is even about one third. The long-term, 0.6 mag V-band variation of DM UMa is more difficult to explain because little or no B-V color index change is observed on the same timescale. Placing the three stars with their light and color variations into H-R diagrams, we find that their overall luminosities are generally too low compared to predictions from current evolutionary tracks. A change in the stellar radius due to strong and variable magnetic fields during activity cycles likely plays a role in explaining the anomalous brightness and luminosity of our three targets. At least for IL Hya, a radius change of about 9% is suggested from m_bol and T_eff, and is supported by independent vsin(i) measurements.Comment: 13 pages, 8 figures, accepted in A&

Cycle period, differential rotation and meridional flow for early M dwarf stars

Recent observations suggest the existence of two characteristic cycle times for early-type M stars dependent on the rotation period. They are of order one year for the fast rotators ($P_{\rm rot}<1$ day) and of order 4 years for the slower rotators. Additionally, the equator-to-pole differences of the rotation rates with $\delta\Omega$ up to 0.03 rad d$^{-1}$ are known from Kepler data for the fast-rotating stars. These values are well-reproduced by the theory of large-scale flows in rotating convection zones on the basis of the $\Lambda$ effect. The resulting amplitudes $u^{\rm m}$ of the bottom value of the meridional circulation allows the calculation of the travel time from pole to equator at the base of the convection zone of early-type M stars. These travel times strongly increase with rotation period and they always exceed the observed cycle periods. Therefore, the operation of an advection-dominated dynamo in early M dwarfs, where the travel time must always be shorter than the cycle period, is not confirmed by our model nor the data

Az optimális élmény objektív markerei és az optimális élmény megteremtésében szerepet játszó személyiségtényezők = The objective markers of optimal experience and the personality factors which promote flow

A flow képesség mérésére kidolgozásra került a Flow Képesség és Flow Kapacitás Kérdőív felnőtt és serdülőkori változata, majd a 6-18 éves korosztály számára érzelmi intelligencia tesztek is kifejlesztésre kerültek. A flow élmény alapdimenzióinak kérdőíves feltárását is célul tűztük ki. Az elméleti alapokon nyugvó, mégis empirikusan kimunkált mérőeszköz több fázison keresztül, számos vizsgálat mentén került kidolgozásra. A flow élmény fiziológiai markereinek ellenőrzésére 3 vizsgálat került lebonyolításra, a személyiségtényezők vizsgálatával párhuzamosan. Az eredmények szerint, kizárólag a flow helyzetben a spektrális aktivitás növekszik a tevékenység első szakaszában, majd a teljesítmény fenntartása mellett az aktivitásszint csökken. A GBR eredmények megerősítik a szimpatikus aktivációval magyarázott korábbi kutatásokat, mivel a flow helyzetben a megemelkedett GBR az arousal magas szintjét jelzi. A szívfrekvencia szignifikánsan nagyobb flow helyzetben, amely alacsonyabb szívritmus-variabilitást jelezhet. A vizsgálatok során a személyiségtényezőkkel való összefüggést is elemeztük. A flow élmény jellemző arckifejezésének feltárására Ekman rendszerét használtuk, a videóval rögzített arckifejezések elemzésére, a flow és antiflow helyzetekben egyaránt, dinamikus megközelítéssel. Az eredmények alapján összességében elmondható, hogy a flow helyzetben kódolt érzelmek és arckifejezések átlaga a szorongás és unalom helyzetek között található. | The Flow Ability and Flow Capacity Questionnaire was developed for measuring flow ability among adults and adolescents, then several emotional intelligence tests were established for the ages between 6-18. Instead of the establishment of a measuring tool of flow ability we invented a questionnaire of the basic dimensions of flow experience. The new tool is based on the theory but it has an empirical establishment through more phases along the studies. In order to check the physiological markers of flow, 3 studies were conducted. According to the results in the flow situation there is an increasing spectral activity in the first phase of the activity, then align with maintain the performance, this activity level decreases. Aligned with the sympathetic activation, our EDA results are corresponding with the previous research, so during flow and increased EDA can be registered, as the signal of the high arousal level. Heart Frequency is significantly higher in the flow situation, which may sign a decreased heart rate variability. In the studies we analyzed the correspondence with the personality characteristics also. For revealing the special facial patterns of flow experience, Ekman’s FACS was used to analyze the facial patterns took down during flow and antiflow states, following a dynamic approach. According to the results we can summarize that the coded emotions during flow and the mean of the facial patterns can be found between the anxiety and boredom situations

Time-series Doppler images and surface differential rotation of the effectively-single rapidly-rotating K-giant KU Pegasi

According to most stellar dynamo theories, differential rotation (DR) plays a crucial role for the generation of toroidal magnetic fields. Numerical models predict surface differential rotation to be anti-solar for rapidly-rotating giant stars, i.e., their surface angular velocity could increase with stellar latitude. However, surface differential rotation has been derived only for a handful of individual giant stars to date. The spotted surface of the K-giant KU Pegasi is investigated in order to detect its time evolution and quantify surface differential rotation. We present altogether 11 Doppler images from spectroscopic data collected with the robotic telescope STELLA between 2006--2011. All maps are obtained with the surface reconstruction code iMap. Differential rotation is extracted from these images by detecting systematic (latitude-dependent) spot displacements. We apply a cross-correlation technique to find the best differential rotation law. The surface of KU Peg shows cool spots at all latitudes and one persistent warm spot at high latitude. A small cool polar spot exists for most but not all of the epochs. Re-identification of spots in at least two consecutive maps is mostly possible only at mid and high latitudes and thus restricts the differential-rotation determination mainly to these latitudes. Our cross-correlation analysis reveals solar-like differential rotation with a surface shear of $\alpha=+0.040\pm0.006$, i.e., approximately five times weaker than on the Sun. We also derive a more accurate and consistent set of stellar parameters for KU Peg including a small Li abundance of ten times less than solar.Comment: 13 pages, 12 figures, accepted for publication in A&

Multiple and changing cycles of active stars II. Results

We study the time variations of the cycles of 20 active stars based on decades-long photometric or spectroscopic observations. A method of time-frequency analysis, as discussed in a companion paper, is applied to the data. Fifteen stars definitely show multiple cycles; the records of the rest are too short to verify a timescale for a second cycle. The cycles typically show systematic changes. For three stars, we found two cycles in each of them that are not harmonics, and which vary in parallel, indicating that a common physical mechanism arising from a dynamo construct. The positive relation between the rotational and cycle periods is confirmed for the inhomogeneous set of active stars. Stellar activity cycles are generally multiple and variable.Comment: Accepted to Astronomy and Astrophysic