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We are conducting a comprehensive investigation of V815 Her using photometric and spectroscopic data to understand the origin of the activity and what influences it in the short and long term. Using TESS photometry we performed light curve modeling in order to derive astrophysical and orbital parameters for the eclipsing binary subsystem V815 Her B. Using archival photometric data covering a century we carried out a time frequency analysis. Spectral synthesis was applied to determine the basic astrophysical parameters of the rapidly rotating primary using high-resolution STELLA spectra recorded in 2018. Photometric analysis revealed multiple cycles on timescales between ~6.5 and ~26 years. From TESS photometry we obtained orbital solution for the V815 Her B subsystem. The STELLA spectra covering the 200 day-long observing season enabled to create 19 time-series Doppler images, which revealed a constantly changing spotted surface. From the consecutive image pairs we measured a weak solar-type surface differential rotation of the spotted star. We found evidence that the V815 Her B component previously apostrophized as a third body is actually an eclipsing close binary subsystem of two M dwarfs with a period of 0.5 d, i.e., V815 Her is a 2+2 hierarchical quadruple system. The system is apparently young, only a few times ten million years old, consistent with the spotted primary V815 Her Aa being a zero-age main sequence star. Spot activity on the primary was found to be vivid. Fast starspot decay suggests that convective-turbulent erosion plays a more significant role in such a rapidly rotating star. The weak differential rotation of V815 Her Aa is presumably confined by tidal forces of the close companion V815 Her Ab. The slowly increasing photometric cycle of 6.5 years on average is interpreted as a spot cycle of V815 Her Aa, which is probably modulated by the eccentric wide orbit., Comment: 26 pages, to be published in Astronomy and Astrophysics (after final revision)

Changing-look active galactic nuclei (CL-AGN) have been observed to change optical spectral type. Mrk 1018 is unique: first classified as a type 1.9 Seyfert galaxy, it transitioned to a type 1 before returning to its initial classification after approximately 30 years. We present a high-cadence monitoring programme that caught a major outburst in 2020. Due to sunblock, only the decline could be observed. We studied X-ray, UV, optical, and IR before and after the outburst to investigate the responses of the AGN structures. We derived a u'-band light curve of the AGN contribution alone. The flux increased by a factor of the order of 13. We confirmed this in other optical bands and determined the shape and speed of the decline in each waveband. The shapes of H beta and H alpha were analysed before and after the event. Two XMM-Newton observations from before and after the outburst were also exploited. The outburst is asymmetric, with a swifter rise than decline. The decline is best fit by a linear function, ruling out a tidal disruption event. The optical spectrum shows no change approximately 8 months before and 17 months after. The UV flux increased slightly after the outburst but the X-ray primary flux is unchanged. However, the 6.4 keV Iron line has doubled in strength. IR data taken 13 days after the observed optical peak show an increased emission level. Calculating the distance of the broad-line region and inner edge of the torus from the supermassive black hole can explain the multi-wavelength response to the outburst, in particular: i) the unchanged H beta and H alpha lines, ii) the unchanged primary X-ray spectral components, iii) the rapid and extended infrared response, as well as iv) the enhanced emission of the reflected 6.4 keV line. The outburst was due to a dramatic and short-lasting change in the intrinsic accretion rate. We discuss different models as potential causes., Comment: Accepted for publication in A&A

Cool star rotation periods have become an important tool in determining ages of open clusters. We aim to estimate the age of the open cluster NGC 2281 based on the rotational properties of its low-mass members. Previous age estimates for this open cluster range from 275 Myr to 630 Myr. Based on an eight month-long photometric time series obtained at the 1.2 m robotic STELLA telescope in Tenerife, we measured rotation periods for 126 cool star members (70% of the observed members) of NGC 2281. The large set of rotation periods allows us to construct a rich colour-period diagram for NGC 2281 with very few outliers above the slow rotator sequence. We identify an evolved fast rotator sequence which can be used to accurately age date the open cluster relative to other open clusters. Comparisons with M37 and M48 show that all three open clusters are roughly coeval, and we estimate the age of NGC 2281 to be $435\pm50$ Myr. Through comparisons with the younger NGC 3532 and the older Praesepe, we determine the spin down rates of mid-K and early-M fast rotators to be significantly lower than for early-K stars. We suspect that the spin down of early-K fast rotators might be governed by an additional mass dependence. Finally, we show the path towards an empirical description of the evolved fast rotator sequences in open clusters., Comment: Accepted for publication in A&A. 14 pages, 10 figures

We use our photometric time series of more than forty years to analyze the long-term behaviour of EI Eri. Flare activity is investigated using space-borne photometric data obtained with TESS. The MUSICOS campaign aimed to achieve high-resolution spectroscopic observations from many sites around the globe, so that uninterrupted phase coverage of EI Eri became available. We use these data to reconstruct successive surface temperature maps of the star in order to study the changes of starspots on a very short timescale. We use long-term, seasonal period analysis of our photometric time series to study changes in the rotational period. Short-term Fourier-transform is also applied to look for activity cycle-like changes. We also study the phase and frequency distribution of hand-selected flares. We apply our multi-line Doppler imaging code to reconstruct four consecutive Doppler images. These images are also used to measure surface differential rotation by our cross-correlation technique. In addition, we carry out tests to demonstrate how Doppler imaging is affected by the fact that the data came from several different instruments with different spectral resolutions. Seasonal period analysis of the light curve reveals a smooth, significant change in period, possibly indicating the evolution of active latitudes. Temperature curves from $B-V$ and $V-I$ show slight differences, indicating the activity of EI Eri is spot dominated. Short-term Fourier transform reveals smoothly changing cycles between 4.5--5.5 and 8.9--11.6 years. The time-resolved spotted surface of EI Eri from Doppler imaging enabled us to follow the evolution of the different surface features. Cross-correlating the consecutive Doppler maps reveal surface shear of $\alpha=0.036\pm0.007$. Our tests validate our approach and show that the surface temperature distribution is adequately reconstructed by our method., Comment: 14 pages, 13 figures, A&A accepted

We embarked on a high-resolution optical spectroscopic survey of bright Transiting Exoplanet Survey Satellite (TESS) stars around the Northern Ecliptic Pole (NEP), dubbed the Vatican-Potsdam-NEP (VPNEP) survey. Our NEP coverage comprises 1067 stars, of which 352 are bona fide dwarf stars and 715 are giant stars, all cooler than spectral type F0 and brighter than V=8. m 5. Our aim is to characterize these stars for the benefit of future studies in the community. We analyzed the spectra via comparisons with synthetic spectra. Particular line profiles were analyzed by means of eigen-profiles, equivalent widths, and relative emission-line fluxes (when applicable). Two R=200 000 spectra were obtained for each of the dwarf stars with the Vatican Advanced Technology Telescope (VATT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), with typically three R=55 000 spectra obtained for the giant stars with STELLA and the STELLA Echelle Spectrograph (SES). Combined with V-band magnitudes, Gaia eDR3 parallaxes, and isochrones from the Padova and Trieste Stellar Evolutionary Code, the spectra can be used to obtain radial velocities, effective temperatures, gravities, rotational and turbulence broadenings, stellar masses and ages, and abundances for 27 chemical elements, as well as isotope ratios for lithium and carbon, line bisector spans, convective blue-shifts (when feasible), and levels of magnetic activity from H{\alpha}, H{\beta}, and the Ca ii infrared triplet. In this initial paper, we discuss our analysis tools and biases, presenting our first results from a pilot sub-sample of 54 stars (27 bona-fide dwarf stars observed with VATT+PEPSI and 27 bona-fide giant stars observed with STELLA+SES) and making all reduced spectra available to the community.

Open clusters serve as a useful tool for calibrating models of the relationship between mass, rotation, and age for stars with an outer convection zone due to the homogeneity of the stars within the cluster. Cluster to cluster comparisons are essential to determine whether the universality of spin down relations holds. NGC 6709 is selected as a young open cluster for which no rotation periods of members have previously been obtained. This cluster is at a distance of over 1 kpc and has two red giant members. Isochrones place the age of the cluster at around 150 Myr, or approximately the same age as the Pleiades. Photometry is obtained over a multi-month observing season at the robotic observatory STELLA. After basic processing, PSF photometry was derived using Daophot II, and a suite of related software allowed us to create time series of relative magnitude changes for each star. Four time series analysis methods are then applied to these light curves to obtain rotation periods for members stars. We obtain for the first time rotation periods for 45 FGK cluster members of NGC 6709. We compare our rotation periods to Gaia EDR3 colors and find a slow-rotating sequence with increasing rotation periods towards redder stars and a smaller clump of rapid rotators that have not yet joined this sequence. NGC 6709 has rotation periods very similar to that of another Pleiades-age open cluster, NGC 2516., Comment: 18 pages, 6 figures, 5 tables, 1 appendix with figure

Double-lined eclipsing binaries allow the direct determination of masses and radii, which are key to test stellar models. With the launch of the TESS mission, many well-known eclipsing binaries have been observed at higher photometric precision, permitting the improvement of the absolute dimensions determinations. Using TESS data and newly-obtained spectroscopic observations, we aim at determining the masses and radii of the eccentric eclipsing binary systems V889 Aql and V402 Lac, together with their apsidal motion parameters. We modelled simultaneously radial velocity curves and times of eclipse for each target to precisely determine the orbital parameters of the systems, which we used to analyse the light curves and then obtain their absolute dimensions. We compared the obtained values with those predicted by theoretical models. We determined masses and radii of the components of both systems with relative uncertainties lower than 2%. V889 Aql is composed of two stars with masses $2.17\pm0.02$ M$_{\odot}$ and $2.13\pm0.01$ M$_{\odot}$ and radii $1.87\pm0.04$ R$_{\odot}$ and $1.85\pm0.04$ R$_{\odot}$. We found conclusive evidence of the presence of a third body orbiting V889 Aql with a period of 67 years. Based on the detected third light and the absence of signal in the spectra, we suggest that this third body could in turn be a binary composed by two $\sim$1.4 M$_{\odot}$ stars. V402 Lac is composed by two stars with masses $2.80\pm0.05$ M$_{\odot}$ and $2.78\pm0.05$ M$_{\odot}$ and radii $2.38\pm0.03$ R$_{\odot}$ and $2.36\pm0.03$ R$_{\odot}$. The times of minimum light are compatible with the presence of a third body for this system too, although its period is not yet fully sampled. In both cases we have found a good agreement between the observed apsidal motion rates and the model predictions., Comment: Accepted for publication in A&A

Current theories of planetary evolution predict that infant giant planets have large radii and very low densities before they slowly contract to reach their final size after about several hundred million years. These theoretical expectations remain untested to date, despite the increasing number of exoplanetary discoveries, as the detection and characterisation of very young planets is extremely challenging due to the intense stellar activity of their host stars. However, the recent discoveries of young planetary transiting systems allow to place initial constraints on evolutionary models. With an estimated age of 20 million years, V1298\,Tau is one of the youngest solar-type stars known to host transiting planets: it harbours a multiple system composed of two Neptune-sized, one Saturn-sized, and one Jupiter-sized planets. Here we report the analysis of an intense radial velocity campaign, revealing the presence of two periodic signals compatible with the orbits of two of its planets. We find that planet b, with an orbital period of 24 days, has a mass of 0.64 Jupiter masses and a density similar to the giant planets of the Solar System and other known giant exoplanets with significantly older ages. Planet e, with an orbital period of 40 days, has a mass of 1.16 Jupiter masses and a density larger than most giant exoplanets. This is unexpected for planets at such a young age and suggests that some giant planets might evolve and contract faster than anticipated, thus challenging current models of planetary evolution., Comment: 47 pages, 13 figures, 3 tables, infinite stress

Meter-sized ground-based telescopes are frequently used today for the follow-up of extrasolar planet candidates. While the transit signal of a Jupiter-sized object can typically be detected to a high level of confidence with small telescope apertures as well, the shallow transit dips of planets with the size of Neptune and smaller are more challenging to reveal. We employ new observational data to illustrate the photometric follow-up capabilities of meter-sized telescopes for shallow exoplanet transits. We describe in detail the capability of distinguishing the photometric signal of an exoplanet transit from an underlying trend in the light curve. The transit depths of the six targets we observed, Kepler-94b, Kepler-63b, K2-100b, K2-138b, K2-138c, and K2-138e, range from 3.9 ppt down to 0.3 ppt. For five targets of this sample, we provide the first ground-based photometric follow-up. We detect or rule out the transit features significantly in single observations for the targets that show transits of 1.3 ppt or deeper. The shallower transit depths of two targets of 0.6 and 0.8 ppt were detected tentatively in single light curves, and were detected significantly by repeated observations. Only for the target of the shallowest transit depth of 0.3 ppt were we unable to draw a significant conclusion despite combining five individual light curves. An injection-recovery test on our real data shows that we detect transits of 1.3 ppt depth significantly in single light curves if the transit is fully covered, including out-of-transit data toward both sides, in some cases down to 0.7 ppt depth. For Kepler-94b, Kepler-63b, and K2-100b, we were able to verify the ephemeris. In the case of K2-138c with a 0.6 ppt deep transit, we were able to refine it, and in the case of K2-138e, we ruled out the transit in the time interval of more than +-1.5 sigma of its current literature ephemeris., Comment: accepted for publication in Astronomy & Astrophysics

Continuous photometry with up to three BRITE satellites was obtained for 12 targets and subjected to a period search. Contemporaneous high-resolution optical spectroscopy with STELLA was used to obtain radial velocities through cross correlation with template spectra as well as to determine astrophysical parameters through a comparison with model spectra. The Capella red light curve was found to be constant over 176 days with a root mean square of 1 mmag, but the blue light curve showed a period of 10.1$\pm$0.6 d, which we interpret to be the rotation period of the G0 component. The BRITE light curve of the F0 supergiant $\varepsilon$Aur suggests 152 d as its main pulsation period, while the STELLA radial velocities reveal a clear 68 d period. An ingress of an eclipse of the $\zeta$Aur binary system was covered with BRITE and a precise timing for its eclipse onset derived. $\eta$Aur is identified as a slowly pulsating B (SPB) star with a main period of 1.29 d and is among the brightest SPB stars discovered so far. The rotation period of the magnetic Ap star $\theta$Aur is detected from photometry and spectroscopy with a period of 3.6189 d and 3.6177 d, respectively, likely the same within the errors. Photometric rotation periods are also confirmed for the magnetic Ap star $\tau$Aur of 2.463 d and for the solar-type star $\kappa^1$Cet of 9.065 d, and also for the B7 HgMn giant $\beta$Tau of 2.74 d. Revised orbital solutions are derived for the eclipsing SB2 binary $\beta$Aur, for the 27 year eclipsing SB1 $\varepsilon$Aur, and for the RS CVn binary HR 1099. The two stars $\nu$ Aur and $\iota$Aur are found to be long-term, low-amplitude RV and brightness variables, but provisional orbital elements based on a period of 20 yr and an eccentricity of 0.7 could only be extracted for $\nu$Aur. The variations of $\iota$Aur are due to oscillations with a period of $\approx$4 yr.

The properties of inhomogeneities on the surface of active stars (i.e. dark spots and bright faculae) significantly influence the determination of the parameters of an exoplanet. The chromatic effect they have on transmission spectroscopy could affect the analysis of data from future space missions such as JWST and Ariel. To quantify and mitigate the effects of those surface phenomena, we developed a modelling approach to derive the surface distribution and properties of active regions by modelling simultaneous multi-wavelength time-series observables. By using the StarSim code, now featuring the capability to solve the inverse problem, we analysed $\sim$ 600 days of BVRI multiband photometry from TJO and STELLA telescopes exoplanet host star WASP-52. From the results, we simulated the chromatic contribution of surface phenomena on the observables of its transits. We are able to determine the relevant activity parameters of WASP-52 and reconstruct the time-evolving longitudinal map of active regions. The star shows a heterogeneous surface composed of dark spots with a mean temperature contrast of $575\pm150$ K with filling factors ranging from 3 to 14 %. We studied the chromatic effects on the depths of transits obtained at different epochs with different stellar spot distributions. For WASP-52, with peak-to-peak photometric variations of $\sim$7 % in the visible, the residual effects of dark spots on the measured transit depth, after applying the calculated corrections, are about $10^{-4}$ at 550 nm and $3\times10^{-5}$ at 6$\mu$m. We demonstrate that by using contemporaneous ground-based multiband photometry of an active star, it is possible to reconstruct the parameters and distribution of active regions over time, and thus, quantify the chromatic effects on the planetary radii measured with transit spectroscopy and mitigate them by about an order of magnitude., Comment: 17 pages, 12 figures

Young, fast rotating single stars can show dramatically different magnetic signatures and levels of magnetic activity as compared with the Sun. While losing angular momentum due to magnetic breaking and mass loss through stellar winds, the stars gradually spin down resulting in decreasing levels of activity. Studying magnetic activity on such solar analogues plays a key role in understanding the evolution of solar-like stars and allows a glimpse into the past of the Sun as well. In order to widen our knowledge of the magnetic evolution of the Sun and solar-like stars, magnetic activity of the young solar analogue V1358 Ori is investigated. Fourier analysis of long-term photometric data is used to derive rotational period and activity cycle length, while spectral synthesis is applied on high resolution spectroscopic data in order to derive precise astrophysical parameters. Doppler imaging is performed to recover surface temperature maps for two subsequent intervals. Cross-correlation of the consecutive Doppler maps is used to derive surface differential rotation. The rotational modulation of the chromospheric activity indicators is also investigated. An activity cycle of $\approx 1600$ days is detected for V1358 Ori. Doppler imaging revealed a surface temperature distribution dominated by a large polar cap with a few weaker features around the equator. This spot configuration is similar to other maps of young solar analogues from the literature, and supports recent model predictions. We detected solar-like surface differential rotation with a surface shear parameter of $\alpha = 0.016 \pm 0.010$ which fits pretty well to our recently proposed empirical relation between rotation and differential rotation. The chromospheric activity indicators showed a rotational modulation., Comment: 9 pages, 10 figures, A&A accepted

On the AGB, low to intermediate mass stars blow away their outer envelopes, forming planetary nebulae. Interaction between the planetary nebula and its central progenitor is poorly understood and even more complex when the central object is a binary star with a magnetically active component, like it is the case for IN Com. We aim to quantify the surface activity of the cool binary component of IN Com and aim to explain its origin. We need a better understanding of how central binary stars in planetary nebulae evolve and how this evolution could develop such magnetically active stars like IN Com. We present 13 Doppler images covering six months in 2017 and use them to measure the surface differential rotation. Hitherto unpublished photometric data from between 1989-2017 are presented. We apply Fourier-transformation to both photometry and spectra. Very high resolution spectra are used to update IN Com's astrophysical parameters by means of spectral synthesis. Doppler images show cool and warm spots coexisting with an average surface temperature contrast of -1000K and +300K with respect to the effective temperature. Approximately 8% of the surface is covered with cool spots and 3% with warm spots. A cool polar spot is seen in all images. We found anti-solar surface differential rotation with a shear coefficient of -0.026+/-0.005 and an equatorial rotation period of 5.973+/-0.008 d. We reconfirm the 5.9-day rotation period of the cool star from photometry, radial velocities, and H alpha line-profile variations. A long-term V-brightness variation with a likely period of 7.2yr is found. It appears in phase with the orbital radial velocity of the binary system in the sense brightest at highest velocity and faintest at lowest velocity. We redetermine [Ba/Fe], [Y/Fe] and [Sr/Fe] ratios and confirm the overabundance of these s-process elements in the atmosphere of IN Com., Comment: accepted for publication in Astronomy & Astrophysics

The depth of a secondary eclipse contains information of both the thermally emitted light component of a hot Jupiter and the reflected light component. If the dayside atmosphere of the planet is assumed to be isothermal, it is possible to disentangle both. In this work, we analyze 11 eclipse light curves of the hot Jupiter HAT-P-32b obtained at 0.89 $\mu$m in the z' band. We obtain a null detection for the eclipse depth with state-of-the-art precision, -0.01 +- 0.10 ppt. We confirm previous studies showing that a non-inverted atmosphere model is in disagreement to the measured emission spectrum of HAT-P-32b. We derive an upper limit on the reflected light component, and thus, on the planetary geometric albedo $A_g$. The 97.5%-confidence upper limit is $A_g$ < 0.2. This is the first albedo constraint for HAT-P-32b, and the first z' band albedo value for any exoplanet. It disfavors the influence of large-sized silicate condensates on the planetary day side. We inferred z' band geometric albedo limits from published eclipse measurements also for the ultra-hot Jupiters WASP-12b, WASP-19b, WASP-103b, and WASP-121b, applying the same method. These values consistently point to a low reflectivity in the optical to near-infrared transition regime for hot to ultra-hot Jupiters., Comment: accepted for publication in A&A

Transit events of extrasolar planets offer a wealth of information for planetary characterization. However, for many known targets, the uncertainty of their predicted transit windows prohibits an accurate scheduling of follow-up observations. In this work, we refine the ephemerides of 21 Hot Jupiter exoplanets with the largest timing uncertainty. We collected 120 professional and amateur transit light curves of the targets of interest, observed with 0.3m to 2.2m telescopes, and analyzed them including the timing information of the planets discovery papers. In the case of WASP-117b, we measured a timing deviation compared to the known ephemeris of about 3.5 hours, for HAT-P-29b and HAT-P-31b the deviation amounted to about 2 hours and more. For all targets, the new ephemeris predicts transit timings with uncertainties of less than 6 minutes in the year 2018 and less than 13 minutes until 2025. Thus, our results allow for an accurate scheduling of follow-up observations in the next decade., Comment: accepted for publication in Astronomy & Astrophysics

Two independent investigations of the atmosphere of the hot Jupiter HAT-P-12b by two different groups resulted in discrepant solutions. Using broad-band photometry from the ground, one study found a flat and featureless transmission spectrum which was interpreted as a gray absorption by dense cloud coverage. The second study made use of the Hubble Space Telescope (HST) observations and found Rayleigh scattering at optical wavelengths caused by haze. The main purpose of this work is to find the source of this inconsistency and provide feedback to prevent similar discrepancies in future analyses of other exoplanetary atmospheres. We studied the observed discrepancy via two methods. With further broad-band observations in the optical wavelength regions, we strengthened the previous measurements in precision and with a homogeneous reanalysis of the published data, we managed to assess the systematic errors and the independent analyses of the two different groups. Repeating the analysis steps of both works, we found that deviating values for the orbital parameters are the reason for the aforementioned discrepancy. Our work showed a degeneracy of the planetary spectral slope with these parameters. In a homogeneous reanalysis of all data, the two literature data sets and the new observations converge to a consistent transmission spectrum, showing a low-amplitude spectral slope and a tentative detection of potassium absorption., Comment: Accepted for publication in A&A

Brightness inhomogeneities in the stellar photosphere (dark spots or bright regions) affect the measurements of the planetary transmission spectrum. To investigate the star spots of the M dwarf GJ 1214, we conducted a multicolor photometric monitoring from 2012 to 2016. The measured variability shows a periodicity of 125 +- 5 days, which we interpret as the signature of the stellar rotation period. This value overrules previous suggestions of a significantly shorter stellar rotation period. A light curve inversion of the monitoring data yields an estimation of the flux dimming of a permanent spot filling factor not contributing to the photometric variability, a temperature contrast of the spots of about 370 K and persistent active longitudes. The derived surface maps over all five seasons were used to estimate the influence of the star spots on the transmission spectrum of the planet from 400 nm to 2000 nm. The monitoring data presented here do not support a recent interpretation of a measured transmission spectrum of GJ 1214b as to be caused by bright regions in the stellar photosphere. Instead, we list arguments as to why the effect of dark spots likely dominated over bright regions in the period of our monitoring. Furthermore, our photometry proves an increase in variability over at least four years, indicative for a cyclic activity behavior. The age of GJ 1214 is likely between 6 and 10 Gyr. The long-term photometry allows for a correction of unocculted spots. For an active star such as GJ 1214, there remains a degeneracy between occulted spots and the transit parameters used to build the transmission spectrum. This degeneracy can only be broken by high-precision transit photometry resolving the spot crossing signature in the transit light curve., Comment: 11 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

Context. Transit events of extrasolar planets offer the opportunity to study the composition of their atmospheres. Previous work on transmission spectroscopy of the close-in gas giant TrES-3 b revealed an increase in absorption towards blue wavelengths of very large amplitude in terms of atmospheric pressure scale heights, too large to be explained by Rayleigh-scattering in the planetary atmosphere. Aims. We present a follow-up study of the optical transmission spectrum of the hot Jupiter TrES-3 b to investigate the strong increase in opacity towards short wavelengths found by a previous study. Furthermore, we aim to estimate the effect of stellar spots on the transmission spectrum. Methods. This work uses previously published long slit spectroscopy transit data of the Gran Telescopio Canarias (GTC) and published broad band observations as well as new observations in different bands from the near-UV to the near-IR, for a homogeneous transit light curve analysis. Additionally, a long-term photometric monitoring of the TrES-3 host star was performed. Results. Our newly analysed GTC spectroscopic transit observations show a slope of much lower amplitude than previous studies. We conclude from our results the previously reported increasing signal towards short wavelengths is not intrinsic to the TrES-3 system. Furthermore, the broad band spectrum favours a flat spectrum. Long-term photometric monitoring rules out a significant modification of the transmission spectrum by unocculted star spots., Comment: 12 pages, 9 Figures, accepted for publication in Astronomy & Astrophysics

Context: Stars with about 1$-$2 solar masses at the red giant branch (RGB) represent an intriguing period of stellar evolution, i.e. when the convective envelope interacts with the fast-rotating core. During these mixing episodes freshly synthesized lithium can come up to the stellar surface along with high angular momentum material. This high angular momentum may alter the surface rotation pattern. Aims: The single rapidly rotating K-giant V1192 Ori is revisited to determine its surface differential rotation, lithium abundance, and basic stellar properties such as a precise rotation period. The aim is to independently verify the antisolar differential rotation of the star and possibly find a connection to the surface lithium abundance. Methods: We applied time-series Doppler imaging to a new multi-epoch data set. Altogether we reconstructed 11 Doppler images from spectroscopic data collected with the STELLA robotic telescope between 2007--2016. We used our inversion code iMap to reconstruct all stellar surface maps. We extracted the differential rotation from these images by tracing systematic spot migration as a function of stellar latitude from consecutive image cross-correlations. Results: The position of V1192 Ori in the Hertzsprung-Russell diagram suggests that the star is in the helium core-burning phase just leaving the RGB bump. We measure $A({\rm Li})_{\rm NLTE}=1.27$, i.e. a value close to the anticipated transition value of 1.5 from Li-normal to Li-rich giants. Doppler images reveal extended dark areas arranged quasi-evenly along an equatorial belt. No cool polar spot is found during the investigated epoch. Spot displacements clearly suggest antisolar surface differential rotation with $\alpha=-0.11\pm0.02$ shear coefficient. Conclusions: The surface Li enrichment and the peculiar surface rotation pattern may indicate a common origin., Comment: Accepted for publication in Astronomy and Astrophysics

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&A

Multi-colour broad-band transit observations offer the opportunity to characterise the atmosphere of an extrasolar planet with small- to medium-sized telescopes. One of the most favourable targets is the hot Jupiter HAT-P-32 b. We combined 21 new transit observations of this planet with 36 previously published light curves for a homogeneous analysis of the broad-band transmission spectrum from the Sloan u' band to the Sloan z' band. Our results rule out cloud-free planetary atmosphere models of solar metallicity. Furthermore, a discrepancy at reddest wavelengths to previously published results makes a recent tentative detection of a scattering feature less likely. Instead, the available spectral measurements of HAT-P-32 b favour a completely flat spectrum from the near-UV to the near-IR. A plausible interpretation is a thick cloud cover at high altitudes., Comment: 12 pages, 6 figures, accepted for publication in MNRAS

HD 208472 is among the most active RS~CVn binaries with cool starspots. Decade-long photometry has shown that the spots seem to change their longitudinal appearance with a period of about six years, coherent with brightness variations. Our aim is to spatially resolve the stellar surface of HD 208472 and relate the photometric results to the true longitudinal and latitudinal spot appearance. Furthermore, we investigate the surface differential rotation pattern of the star. We employed three years of high-resolution spectroscopic data with a high signal-to-noise ratio (S/N) from the STELLA robotic observatory and determined new and more precise stellar physical parameters. Precalculated synthetic spectra were fit to each of these spectra, and we provide new spot-corrected orbital elements. A sample of 34 absorption lines per spectrum was used to calculate mean line profiles with a S/N of several hundred. A total of 13 temperature Doppler images were reconstructed from these line profiles with the inversion code iMap. Differential rotation was investigated by cross-correlating successive Doppler images in each observing season. Spots on HD 208472 are distributed preferably at high latitudes and less frequently around mid-to-low latitudes. No polar-cap like structure is seen at any epoch. We observed a flip-flop event between 2009 and 2010, manifested as a flip of the spot activity from phase 0.0 to phase 0.5, while the overall brightness of the star continued to increase and reached an all-time maximum in 2014. Cross-correlation of successive Doppler images suggests a solar-like differential rotation that is ~15 times weaker than that of the Sun., Comment: 12 pages, 11 figures

We aim to study the temporal and spectral behaviour of four polar CVs from the infrared to X-ray regimes, refine our knowledge of the physical parameters of these systems at different accretion rates, and to search for a possible excess of soft X-ray photons. We analysed four XMM X-ray observations of three of the sources, two of them discovered in SDSS, one in RASS. The X-ray data were complemented by optical photometry and spectroscopy and, for two sources, archival Swift observations. SDSSJ0328 was X-ray bright in two XMM and two Swift observations, and shows transitions from high and low accretion states over a few months. It has no strong soft excess. We measured the magnetic field strength at the main pole to be 39 MG, the inclination to be 45

COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast spinning, heavily spotted, yellow giant FK Com (HD117555; G4 III). This single star is thought to be a recent binary merger, and is exceptionally active by measure of its intense ultraviolet and X-ray emissions, and proclivity to flare. COCOA-PUFS was carried out with Hubble Space Telescope in the UV (120-300 nm), using mainly its high-performance Cosmic Origins Spectrograph, but also high-precision Space Telescope Imaging Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy Transmission Grating Spectrometer; together with supporting photometry and spectropolarimetry in the visible from the ground. This is an introductory report on the project. FK Com displayed variability on a wide range of time scales, over all wavelengths, during the week-long main campaign, including a large X-ray flare; "super-rotational broadening" of the far-ultraviolet "hot-lines" (e.g., Si IV 139 nm (T~80,000 K) together with chromospheric Mg II 280 nm and C II 133 nm (10,000-30,000 K); large Doppler swings suggestive of bright regions alternately on advancing and retreating limbs of the star; and substantial redshifts of the epoch-average emission profiles. These behaviors paint a picture of a highly extended, dynamic, hot (10 MK) coronal magnetosphere around the star, threaded by cooler structures perhaps analogous to solar prominences, and replenished continually by surface activity and flares. Suppression of angular momentum loss by the confining magnetosphere could temporarily postpone the inevitable stellar spindown, thereby lengthening this highly volatile stage of coronal evolution., Comment: to be published in ApJS

The detection of trends or gradients in the transmission spectrum of extrasolar planets is possible with observations at very low spectral resolution. Transit measurements of sufficient accuracy using selected broad-band filters allow for an initial characterization of the atmosphere of the planet. We obtained time series photometry of 20 transit events and analyzed them homogeneously, along with eight light curves obtained from the literature. In total, the light curves span a range from 0.35 to 1.25 microns. During two observing seasons over four months each, we monitored the host star to constrain the potential influence of starspots on the derived transit parameters. We rule out the presence of a Rayleigh slope extending over the entire optical wavelength range, a flat spectrum is favored for HAT-P-12b with respect to a cloud-free atmosphere model spectrum. A potential cause of such gray absorption is the presence of a cloud layer at the probed latitudes. Furthermore, in this work we refine the transit parameters, the ephemeris and perform a TTV analysis in which we found no indication for an unseen companion. The host star showed a mild non-periodic variability of up to 1%. However, no stellar rotation period could be detected to high confidence., Comment: 13 pages, 6 figures, Accepted for publication in A&A

We observed the Saturn-mass and Jupiter-sized exoplanet HAT-P-19b to refine its transit parameters and ephemeris as well as to shed first light on its transmission spectrum. We monitored the host star over one year to quantify its flux variability and to correct the transmission spectrum for a slope caused by starspots. A transit of HAT-P-19b was observed spectroscopically with OSIRIS at the Gran Telescopio Canarias in January 2012. The spectra of the target and the comparison star covered the wavelength range from 5600 to 7600 AA. One high-precision differential light curve was created by integrating the entire spectral flux. This white-light curve was used to derive absolute transit parameters. Furthermore, a set of light curves over wavelength was formed by a flux integration in 41 wavelength channels of 50 AA width. We analyzed these spectral light curves for chromatic variations of transit depth. The transit fit of the combined white-light curve yields a refined value of the planet-to-star radius ratio of 0.1390 pm 0.0012 and an inclination of 88.89 pm 0.32 degrees. After a re-analysis of published data, we refine the orbital period to 4.0087844 pm 0.0000015 days. We obtain a flat transmission spectrum without significant additional absorption at any wavelength or any slope. However, our accuracy is not sufficient to significantly rule out the presence of a pressure-broadened sodium feature. Our photometric monitoring campaign allowed for an estimate of the stellar rotation period of 35.5 pm 2.5 days and an improved age estimate of 5.5^+1.8_-1.3 Gyr by gyrochronology., Comment: 14 pages, 9 figures, Accepted for publication in A&A

PEPSI is the bench-mounted, two-arm, fibre-fed and stabilized Potsdam Echelle Polarimetric and Spectroscopic Instrument for the 2x8.4 m Large Binocular Telescope (LBT). Three spectral resolutions of either 43 000, 120 000 or 270 000 can cover the entire optical/red wavelength range from 383 to 907 nm in three exposures. Two 10.3kx10.3k CCDs with 9-{\mu}m pixels and peak quantum efficiencies of 96 % record a total of 92 echelle orders. We introduce a new variant of a wave-guide image slicer with 3, 5, and 7 slices and peak efficiencies between 96 %. A total of six cross dispersers cover the six wavelength settings of the spectrograph, two of them always simultaneously. These are made of a VPH-grating sandwiched by two prisms. The peak efficiency of the system, including the telescope, is 15% at 650 nm, and still 11% and 10% at 390 nm and 900 nm, respectively. In combination with the 110 m2 light-collecting capability of the LBT, we expect a limiting magnitude of 20th mag in V in the low-resolution mode. The R=120 000 mode can also be used with two, dual-beam Stokes IQUV polarimeters. The 270 000-mode is made possible with the 7-slice image slicer and a 100- {\mu}m fibre through a projected sky aperture of 0.74", comparable to the median seeing of the LBT site. The 43000-mode with 12-pixel sampling per resolution element is our bad seeing or faint-object mode. Any of the three resolution modes can either be used with sky fibers for simultaneous sky exposures or with light from a stabilized Fabry-Perot etalon for ultra-precise radial velocities. CCD-image processing is performed with the dedicated data-reduction and analysis package PEPSI-S4S. A solar feed makes use of PEPSI during day time and a 500-m feed from the 1.8 m VATT can be used when the LBT is busy otherwise. In this paper, we present the basic instrument design, its realization, and its characteristics.

The eclipsing polar CSS081231 turned bright (V_max ~ 14.5) in late 2008 and was subsequently observed intensively with small and medium-sized telescopes. A homogeneous analysis of this comprehensive dataset comprising 109 eclipse epochs is presented and a linear ephemeris covering the five years of observations, about 24000 orbital cycles, is derived. Formally this sets rather tight constraints on the mass of a hypothetical circumbinary planet, M_pl <= 2 M_Jup. This preliminary result needs consolidation by long-term monitoring of the source. The eclipse lasts 433.08 +- 0.65 s, and the orbital inclination is found to be i=79.3 - 83.7 degrees. The centre of the bright phase displays accretion-rate dependent azimuthal shifts. No accretion geometry is found that explains all observational constraints, suggesting a complex accretion geometry with possible pole switches and a likely non-dipolar field geometry., Comment: 11 pages, 11 figures, accepted for publication in AN

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&A

We investigate the surface spot activity of the rapidly rotating, lithium-rich active single K-giant DI Psc to measure the surface differential rotation and understand the mechanisms behind the Li-enrichment. Doppler imaging was applied to recover the surface temperature distribution of DI Psc in two subsequent rotational cycles using the individual mapping lines Ca I 6439, Fe I 6430, Fe I 6421 and Li I 6708. Surface differential rotation was derived by cross-correlation of the subsequent maps. Difference maps are produced to study the uniformity of Li-enrichment on the surface. These maps are compared with the rotational modulation of the Li I 6708 line equivalent width. Doppler images obtained for the Ca and Fe mapping lines agree well and reveal strong polar spottedness, as well as cool features at lower latitudes. Cross-correlating the consecutive maps yields antisolar differential rotation with shear coefficient -0.083 +- 0.021. The difference of the average and the Li maps indicates that the lithium abundance is non-activity related. There is also a significant rotational modulation of the Li equivalent width., Comment: 8 pages, 7 figures, accepted in A&A

V405 Peg is a low-luminosity cataclysmic variable (CV) that was identified as the optical counterpart of the bright, high-latitude ROSAT all-sky survey source RBS1955. The system was suspected to belong to a largely undiscovered population of hibernating CVs. Despite intensive optical follow-up its subclass however remained undetermined. We want to further classify V405 Peg and understand its role in the CV zoo via its long-term behaviour, spectral properties, energy distribution and accretion luminosity. We perform a spectral and timing analysis of \textit{XMM-Newton} X-ray and ultra-violet data. Archival WISE, HST, and Swift observations are used to determine the spectral energy distribution and characterize the long-term variability. The X-ray spectrum is characterized by emission from a multi-temperature plasma. No evidence for a luminous soft X-ray component was found. Orbital phase-dependent X-ray photometric variability by $\sim50\%$ occurred without significant spectral changes. No further periodicity was significant in our X-ray data. The average X-ray luminosity during the XMM-Newton observations was L_X, bol simeq 5e30 erg/s but, based on the Swift observations, the corresponding luminosity varied between 5e29 erg/s and 2e31 erg/son timescales of years. The CV subclass of this object remains elusive. The spectral and timing properties show commonalities with both classes of magnetic and non-magnetic CVs. The accretion luminosity is far below than that expected for a standard accreting CV at the given orbital period. Objects like V405 Peg might represent the tip of an iceberg and thus may be important contributors to the Galactic Ridge X-ray Emission. If so they will be uncovered by future X-ray surveys, e.g. with eROSITA., Comment: A&A, in press

The visual A component of the Gliese 586AB system is a double-lined spectroscopic binary consisting of two cool stars with the exceptional orbital eccentricity of 0.976. Such an extremely eccentric system may be important for our understanding of low-mass binary formation. We present a total of 598 high-resolution echelle spectra from our robotic facility STELLA from 2006-2012 which we used to compute orbital elements of unprecedented accuracy. The orbit constrains the eccentricity to 0.97608+/-0.00004 and the orbital period to 889.8195+/-0.0003d. The masses of the two components are 0.87+/-0.05 Msun and 0.58+/-0.03 Msun if the inclination is 5+/-1.5degr as determined from adaptive-optics images, that is good to only 6% due to the error of the inclination although the minimum masses reached a precision of 0.3%. The flux ratio Aa:Ab in the optical is betwee n 30:1 in Johnson-B and 11:1 in I. Radial velocities of the visual B-component (K0-1V) appear constant to within 130 m/s over six years. Sinusoidal modulations of Teff of Aa with an amplitude of apprx 55 K are seen with the orbital period. Component Aa appears warmest at periastron and coolest at apastron, indicating atmospheric changes induced by the high orbital eccentricity. No light variations larger than approximately 4 mmag are detected for A, while a photometric period of 8.5+/-0.2 d with an amplitude of 7 mmag is discovered for the active star B, which we interpret to be its rotation period. We estimate an orbital period of approx 50,000 yr for the AB system. The most likely age of the AB system is >=2 Gyr, while the activity of the B component, if it were a single star, would imply 0.5 Gyr. Both Aa and B are matched with single-star evolutionary tracks of their respective mass.

PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 sec readout cadence and 2 with 2.5 sec candence) providing a wide field-of-view (2232 deg2) and a large photometric magnitude range (4-16 mag). It focusses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2%, 4-10% and 10% for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50% of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0., Comment: 63 pages, 17 figures, submitted to Experimental Astronomy (ExA)

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 AN

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the "historical" context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes., Comment: 6 pages, 2 color figures, this is the pre-peer reviewed version of Denker et al. 2012, Astron. Nachr. 333, 810

We have used two robotic telescopes to obtain time-series high-resolution spectroscopy and V I and/or by photometry for a sample of 60 active stars. Orbital solutions are presented for 26 SB2 and 19 SB1 systems with unprecedented phase coverage and accuracy. The total of 6,609 R=55,000 echelle spectra are also used to systematically determine effective temperatures, gravities, metallicities, rotational velocities, lithium abundances and absolute H{\alpha}-core fluxes as a function of time. The photometry is used to infer unspotted brightness, V - I and/or b - y colors, spot-induced brightness amplitudes and precise rotation periods. Our data are complemented by literature data and are used to determine rotation-temperature-activity relations for active binary components. We also relate lithium abundance to rotation and surface temperature. We find that 74% of all known rapidly-rotating active binary stars are synchronized and in circular orbits but 26% are rotating asynchronously of which half have Prot > Porb and e > 0. Because rotational synchronization is predicted to occur before orbital circularization active binaries should undergo an extra spin-down besides tidal dissipation. We suspect this to be due to a magnetically channeled wind with its subsequent braking torque. We find a steep increase of rotation period with decreasing effective temperature for active stars. For inactive, single giants with Prot > 100 d, the relation is much weaker. Our data also indicate a period-activity relation for H{\alpha} of the form RH{\alpha} \propto P - 0.24 for binaries and RH{\alpha} \propto P -0.14 for singles. Lithium abundances in our sample increase with effective temperature. On average, binaries of comparable effective temperature appear to exhibit 0.25 dex less surface lithium than singles. We also find a trend of increased Li abundance with rotational period of form log n(Li) \propto - 0.6 log Prot.

We determine Period-Luminosity relations for Milky Way Cepheids in the optical and near-IR bands. These relations can be used directly as reference for extra-galactic distance determination to Cepheid populations with solar metallicity, and they form the basis for a direct comparison with relations obtained in exactly the same manner for stars in the Magellanic Clouds, presented in an accompanying paper. In that paper we show that the metallicity effect is very small and consistent with a null effect, particularly in the near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC and SMC to form a best relation. We employ the near-IR surface brightness (IRSB) method to determine direct distances to the individual Cepheids after we have recalibrated the projection factor using the recent parallax measurements to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC should be independent of pulsation period. We confirm our earlier finding that the projection factor for converting radial velocity to pulsational velocity depends quite steeply on pulsation period, p=1.550-0.186*log(P) in disagrement with recent theoretical predictions. We delineate the Cepheid PL relation using 111 Cepheids with direct distances from the IRSB analysis. The relations are by construction in agreement with the recent HST parallax distances to Cepheids and slopes are in excellent agreement with the slopes of apparent magnitudes versus period observed in the LMC., Comment: Accepted for publication by Astronomy and Astrophysics. 15 pages, 11 figures

We present a first and detailed study of the bright and active K0IV-III star HD 123351. The star is found to be a single-lined spectroscopic binary with a period of 147.8919+-0.0003 days and a large eccentricity of e=0.8086+-0.0001. The rms of the orbital solution is just 47 m/s, making it the most precise orbit ever obtained for an active binary system. The rotation period is constrained from long-term photometry to be 58.32+-0.01 days. It shows that HD 123351 is a very asynchronous rotator, rotating five times slower than the expected pseudo-synchronous value. Two spotted regions persisted throughout the 12 years of our observations. Four years of Halpha, CaII H&K and HeI D3 monitoring identifies the same main periodicity as the photometry but dynamic spectra also indicate that there is an intermittent dependence on the orbital period, in particular for Ca ii H&K in 2008. Line-profile inversions of a pair of Zeeman sensitive/insensitive iron lines yield an average surface magnetic-flux density of 542+-72 G. The time series for 2008 is modulated by the stellar rotation as well as the orbital motion, such that the magnetic flux is generally weaker during times of periastron and that the chromospheric emissions vary in anti-phase with the magnetic flux. We also identify a broad and asymmetric lithium line profile and measure an abundance of log n(Li) = 1.70+-0.05. The star's position in the H-R diagram indicates a mass of 1.2+-0.1 Msun and an age of 6-7 Gyr. We interpret the anti-phase relation of the magnetic flux with the chromospheric emissions as evidence that there are two magnetic fields present at the same time, a localized surface magnetic field associated with spots and a global field that is oriented towards the (low-mass) secondary component.

ICE-T (International Concordia Explorer Telescope) is a double 60 cm f/1.1 photometric robotic telescope, on a parallactic mount, which will operate at Dome C, in the long Antarctic night, aiming to investigate exoplanets and activity of the hosting stars. Antarctic Plateau site is well known to be one of the best in the world for observations because of sky transparency in all wavelengths and low scintillation noise. Due to the extremely harsh environmental conditions (the lowest average temperature is -80$^\circ$C) the criteria adopted for an optimal design are really challenging. Here we present the strategies we have adopted so far to fulfill the mechanical and optical requirements., Comment: 7 pages, 2 figures, contributed talk at 'An astronomical Observatory at Concordia (Dome C, Antarctica) for the next decade', 11-15 May, Rome (Italy)

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 Astrophysics

We present a detailed determination of the astrophysical parameters of the chromospherically active binary star EI Eridani. Our new radial velocities allow to improve the set of orbital elements and reveal long-term variations of the barycentric velocity. A possible third-body orbit with a period of approximately 19 years is presented. Absolute parameters are determined in combination with the Hipparcos parallax. EI Eri's inclination angle of the rotational axis is confined to 56.0 plus/minus 4.5 degrees, its luminosity class IV is confirmed by its radius of 2.37 plus/minus 0.12 R_Sun. A comparison to theoretical stellar evolutionary tracks suggests a mass of 1.09 plus/minus 0.05 M_Sun and an age of approximately 6.15 Gyr. The present investigation is the basis of our long-term Doppler imaging study of its stellar surface.

Beating the Earth's day-night cycle is mandatory for long and continuous time-series photometry and had been achieved with either large ground-based networks of observatories at different geographic longitudes or when conducted from space. A third possibility is offered by a polar location with astronomically-qualified site characteristics. Aims. In this paper, we present the first scientific stellar time-series optical photometry from Dome C in Antarctica and analyze approximately 13,000 CCD frames taken in July 2007. We conclude that high-precision CCD photometry with exceptional time coverage and cadence can be obtained at Dome C in Antarctica and be successfully used for time-series astrophysics., Comment: accepted for A&A

Robotic telescopes and grid technology have made significant progress in recent years. Both innovations offer important advantages over conventional technologies, particularly in combination with one another. Here, we introduce robotic telescopes used by the Astrophysical Institute Potsdam as ideal instruments for building a robotic telescope network. We also discuss the grid architecture and protocols facilitating the network integration that is being developed by the German AstroGrid-D project. Finally, we present three user interfaces employed for this purpose., Comment: 4 pages, 5 Figures, refereed proceedings of "Hot-wiring the Transient Universe", June 2007 (Tucson); version 2 including latex geometry package as recommended by arXiv and minor changes as requested by AN except removal of two figures