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Register a new userBinary-induced magnetic activity? Time-series echelle spectroscopy and photometry of HD123351 = CZ CVn
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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
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{it Kepler} satellite photometry and phase-resolved spectroscopy of the ultracompact AM CVn type binary SDSS J190817.07+394036.4 are presented. The average spectra reveal a variety of weak metal lines of different species, including silicon, sulphur and magnesium as well as many lines of nitrogen, beside the strong absorption lines of neutral helium. The phase-folded spectra and the Doppler tomograms reveal an S-wave in emission in the core of the He I 4471 AA,absorption line at a period of $P_{rm orb}=1085.7pm2.8$,sec identifying this as the orbital period of the system. The Si II, Mg II and the core of some He I lines show an S-wave in absorption with a phase offset of $170pm15^circ$ compared to the S-wave in emission. The N II, Si III and some helium lines do not show any phase variability at all. The spectroscopic orbital period is in excellent agreement with a period at $P_{rm orb}=1085.108(9)$,sec detected in the three year {it Kepler} lightcurve. A Fourier analysis of the Q6 to Q17 short cadence data obtained by {it Kepler} revealed a large number of frequencies above the noise level where the majority shows a large variability in frequency and amplitude. In an O-C analysis we measured a $vertdot{P}vertsim1.0,$x$,10^{-8},$s,s$^{-1}$ for some of the strongest variations and set a limit for the orbital period to be $vertdot{P}vert<10^{-10}$s,s$^{-1}$. The shape of the phase folded lightcurve on the orbital period indicates the motion of the bright spot. Models of the system were constructed to see whether the phases of the radial velocity curves and the lightcurve variation can be combined to a coherent picture. However, from the measured phases neither the absorption nor the emission can be explained to originate in the bright spot.
High-precision time series have recently become available for many stars as a result of data from CoRoT, Kepler, and TESS and have been widely used to study stellar activity. They provide information integrated over the stellar disk, hence many degeneracies between spots and plages or sizes and contrasts. Our aim is to understand how to relate photometric variability to physical parameters in order to help the interpretation of these observations. We computed a large number of synthetic time series of brightness variations for old MS stars within the F6-K4 range, using consistent modeling for radial velocity, astrometry, and LogRHK. We analyzed these time series to study the effect of the star spectral type on brightness variability, the relationship between brightness variability and LogRHK, the interpretation of brightness variability as a function of spot and plage properties, and the spot-dominated or plage-dominated regimes. Within our range of activity levels, the brightness variability increases toward low-mass stars, as suggested by Kepler results. Brightness variability roughly correlates to LogRHK level, but with a large dispersion, caused by spot contrast and inclination. It is also directly related to the number of structures, and we show that it cannot be interpreted solely in terms of spot sizes. In the activity range of old main-sequence stars, we can obtain both spot or plage dominated regimes, as in observation. The same star can be observed in both regimes depending on inclination. Only strong correlations between LogRHK and brightness variability are significant. Our realistic time series proves to be extremely useful when interpreting observations and understanding their limitations, most notably in terms of activity interpretation. Inclination is crucial and affects many properties, such as amplitudes and the respective role of spots and plages.
We present high cadence (1-10 hr^-1) time-series photometry of the eruptive young variable star V1647 Orionis during its 2003-2004 and 2008-2009 outbursts. The 2003 light curve was obtained mid-outburst at the phase of steepest luminosity increase of the system, during which time the accretion rate of the system was presumably continuing to increase toward its maximum rate. The 2009 light curve was obtained after the system luminosity had plateaued, presumably when the rate of accretion had also plateaued. We detect a flicker noise signature in the power spectrum of the lightcurves, which may suggest that the stellar magnetosphere continued to interact with the accretion disk during each outburst event. Only the 2003 power spectrum, however, evinces a significant signal with a period of 0.13 d. While the 0.13 d period cannot be attributed to the stellar rotation period, we show that it may plausibly be due to short-lived radial oscillations of the star, possibly caused by the surge in the accretion rate.
Using a time series of high-resolution spectra and high-quality multi-colour photometry, we reconstruct surface maps of the primary component of the RS CVn type rapidly rotating eclipsing binary, SV Cam (F9V + K4V). We measure a mass ratio, q, of 0.641(2) using our highest quality spectra and obtain surface brightness maps of the primary component, which exhibit predominantly high-latitude spots located between 60-70-degree latitudes with a mean filling factor of about 35%. This is also indicated by the R-band light curve inversion, subjected to rigourous numerical tests. The spectral subtraction of the H-alpha line reveals strong activity of the secondary component. The excess H-alpha absorption detected near the secondary minimum hints to the presence of cool material partially obscuring the primary star. The flux ratios of Ca II IRT excess emission indicate that the contribution of chromospheric plage regions associated with star-spots is dominant, even during the passage of the filament-like absorption feature.
The radial velocity of the Sun as a star is affected by its surface convection and magnetic activity. The moments of the cross-correlation function between the solar spectrum and a binary line mask contain information about the stellar radial velocity and line-profile distortions caused by stellar activity. As additional indicators, we consider the disc-averaged magnetic flux and the filling factor of the magnetic regions. Here we show that the activity-induced radial-velocity fluctuations are reduced when we apply a kernel regression to these activity indicators. The disc-averaged magnetic flux proves to be the best activity proxy over a timescale of one month and gives a standard deviation of the regression residuals of 1.04 m/s, more than a factor of 2.8 smaller than the standard deviation of the original radial velocity fluctuations. This result has been achieved thanks to the high-cadence and time continuity of the observations that simultaneously sample both the radial velocity and the activity proxies.
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