Time series photometric spot modelling – V. Phase coherence of spots on UZ Librae

We present spot models for nine years of continuous VI_c photometry of UZ Lib from 1993–2001. The relatively stable double‐humped light curve shape suggests extreme phase coherence. From the spot‐modelling analysis, we found that the major spots or spot groups are always located on the hemisphere facing the secondary star and exactly in the opposite hemisphere anti‐facing the secondary. Several single‐humped light curves and our suggested binary scenario rule out a pure ellipsoidal variability as the cause of the double‐humped light curve shape. We try to explain this preferred spot pattern with a magnetic‐field structure that connects the two components, as suggested earlier for RS CVn stars in general. A possible 4.8 years spot cycle is found from the long‐term brightness variations but needs confirmation. We rediscuss the basic astrophysical data of UZ Lib. The Hipparcos parallax is likely wrong, a possible reason could be that UZ Lib is e.g., a triple system.     

Photoelectric photometry of the RS CVn binary EI Eridani = HD 26337

DifferentialUBV(RI) _KC andUBVRI photometry of the RS CVn binary EI Eridani obtained during December 1987 and January 1988 at fourteen different observatories is presented. A combined visual bandpass light curve, corrected for systematic errors of different observatories, utilizes the photometric period of 1.945 days to produce useful results. Analysis shows the visual light curve to have twin maxima, separated by about 0.4 phase, and a full amplitude of approximately 0.06 mag for the period of observation, a smaller amplitude than reported in the past. The decrease in amplitude may be due to a decrease or homogenization of spot coverage. To fit the asymmetrical light curve, a starspot model would have to employ at least two spotted regions separated in longitude.     

A photometric analysis of the active chromosphere star GT Muscae

GT Mus is a quadruple system containing an RS CVn-type binary and a pair of eclipsing A dwarfs. More than four years of continuous BV(RI)_c photometry of the system has revealed spot-wave variability in the active component of the RS CVn binary. The amplitude and mean level of this spot wave change with time in an activity cycle. An infrared excess was also observed from time to time and this has been interpreted as hydrogen emission from flare events. The system is therefore remarkable for showing four different types of variability, all on different time-scales, and three of these associated with the active star.     

An analysis of close binaries (CB) based on photometric measurements

The subject of the paper is the problem of stellar differntial rotation in close binaries (CB) ofRS CV n type. The differential-rotation parameters we find on the basis of the migration of the depression in the light curves caused by the spot effect over the orbital phase. For that purpose, a simple model (Bussoet al., 1985) and inverse-problem procedure, based on the Marquardt (1963) algorithm, are used. To verify the obtained solutions, the SIMPLEX algorithm (Torczon, 1991) is applied, suitable for the nonlinear parameter optimisation. This algorithm enables a correct solution of the nonlinear equation system describing the differential rotation. The procedure is applied in the determination of the parameters of differential rotation forCV Cam, VV Mon andSS Boo binaries.     

Photoelectric observations of long-period RS CVn binary CQ aurigae

Long-period RS CVn-type binary CQ Aur was observed in 1987 and 1988.B andV light curves for the 1987 and 1988 epochs have been analyzed for the photometric solution by the modified Wilson and Devinney computing code with adjustable spot parameters. One-spot fit is good enough for the 1987 epoch while a wider distribution of spots in longitude is required for the 1988 epoch. The spot covers approximately 3% of total surface area of the cooler component. Absolute dimensions were deduced by combining Popper's spectroscopic results. The volume of the cooler component is approximately 100 times larger than that of the hotter component. Both components are subgiants but the cooler component evolved more than the hotter component.     

Time‐series photometric spot modelling – VI. A new computer code and its application to 23 years of photometry of the active giant IM Pegasi

We present and apply a new computer program named SpotModeL to analyze single and multiple bandpass photometric data of spotted stars. It is based on the standard analytical formulae from Budding and Dorren. The program determines the position, size, and temperature of up to three spots by minimizing the fit residuals with the help of the Marquardt‐Levenberg non‐linear least‐squares algorithm. We also expand this procedure to full time‐series analysis of differential data, just as real observations would deliver. If multi‐bandpass data are available, all bandpasses can be treated simultaneously and thus the spot temperature is solved for implicitly. The program may be downloaded and used by anyone. In this paper, we apply our code to an ≈23 year long photometric dataset of the spotted RS CVn giant IM Peg. We extracted and modelled 33 individual light curves, additionally, we fitted the entire V dataset in one run. The resulting spot parameters reflect the long term light variability and reveal two active longitudes on the substellar point and on the antipode. The radius and longitude of the dominant spot show variations with 29.8 and 10.4 years period, respectively. Our multicolour data suggests that the spot temperature is increasing with the brightening of the star. The average spot temperature from V, I_C is 3550 ± 150 K or approximately 900 K below the effective temperature of the star.     

Light variations of RT Lac during the last ten years

The RS CVn-type eclipsing binary star RT Lac has been observed inB andV colours, during 1984, 1985, 1986, 1987, and 1988 observing seasons. The orbital period of the system was found to be decreasing with an amount of 62 s century^–1. The brightnesses both at minima and maxima are changing with time. It seems that the variations of the brightnesses at mid-primary and second quarter are similar, but at second first quarters are opposite to each other. We believe that these variations are mainly related with the spots (or spot groups) located on the surface of the component star which is in front during the primary minimum. We also estimate the period of the spot activity cycle to be approximately six years.     

Surface velocity network with anti-solar differential rotation on the activeK-giant σ Geminorum

We demonstrate the power of the local correlation tracking technique on stellar data for the first time. We recover the spot migration pattern of the long-period RS CVn-type binary σ Gem from a set of six Doppler images from 3.6 consecutive rotation cycles. The resulting surface flow map suggests a weak anti-solar differential rotation with α ≈ –0.0022 ± 0.0016, and a coherent poleward spot migration with an average velocity of 220 ± 10ms-1. This result agrees with our recent findings from another study and could also be confirmed theoretically. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of the distortion wave in the RS CVn eclipsing binary SV Camelopardalis

The light outside the eclipses of the totally eclipsing RS CVn binary SV Camelopardalis (SV Cam) is Fourier analysed and the amplitudes of the distortion waves have been derived. The distribution of the percentage contributions of these amplitudes inV, B andU colours with respect to the luminosities of the binary components indicates that the hotter component is the source of the distortion waves. These distortion waves, attributed to star spots, are modelled according to Budding (1977) and spot parameters like longitude, latitude, temperature and size are obtained. From this study it is noticed that while symmetric waves with two minima could be fitted satisfactorily, asymmetric waves with more than two minima could not be fitted well. From the longitudes of the minima of the best fitted curves, migration periods of four spot groups are determined. Assuming synchronism between rotation and orbital periods, the rotation periods of the four spot groups are derived from their migration periods. The period of rotation of one of the spot groups having direct motion is found to be 0^d.5934209 while the periods of the other three spot groups having retrograde motion are 0^d.5926588, 0^d.592607 and 0^d.5924688. As the latitudes of these spots are known from modelling parameters, the latitude having a rotation period equal to that of the orbital period (co-rotating latitude) is found to be about 30°     

Light curves of SZ Piscium for 1977 and 1978

We present a relatively completeV-band light curve of SZ Psc for 1978 and a partial light curve for 1977. From the 1978 light curve we derive a new time of primary minimum, JD2443823.674±0.001, and a Russell-model solution,i=75°.8±0°.1,r _h =0.096±0.003,r _c =0.351±0.001, andL _h =0.253±0.002. The hotter component of this system is a F5-8 main-sequence star, the cooler component a K3-4 star well above the main sequence. The system is detached with the larger component filling only 82% of its Roche lobe. The distortion wave in this RS CVn-type binary seems not to migrate regularly as do those in many other such systems, but rather seems to change phase and amplitude more erratically. Between 1977 and 1978 its phase stayed practically constant while its amplitude decreased by a factor of three. We discuss the implications of this behavior for the spot model of RS CVn-type activity. We find that the traditional comparison star for SZ Psc, HD 219018, is very likely a constant star contrary to a recent suggestion that it is variable. Its brightness and colors,V=7.705, (B-V)=0.628, and (V-I) _c =0.688, are those of a G2V star.Visiting Astronomer, Kitt Peak National Observatory, which is operated by AURA, Inc., under contract with the National Science Foundation, and Visiting Astronomer, Prarie Observatory, University of Illinois.     

CF octantis,an RS CVn-type variable with a prominent activity cycle

Photoelectric photometry has been obtained for CF Octantis on 39 nights. The object is a member of the RS CVn class and has a highly active chromosphere. A 20.15 ±0.06 d period has been found from theB andV magnitudes, which is interpreted as the rotational modulation of the light from a non-uniformly spotted star. The amplitude of this spot wave is observed to vary slowly between ΔV about 0^m.l and 0^m.3, which may be evidence for an activity cycle of 9 ±3 years.     

Photospheric and chromospheric activity on EY Dra

Magnetic activity in the photosphere and chromosphere of the M dwarf EY Dra is studied and possible correlations between the two are investigated using photometric observations in the V and R bands and optical and near infrared spectroscopy. The longitudinal spot configuration in the photosphere is obtained from the V band photometry, and the chromospheric structures are investigated using variations in the Hα line profile and observations of the Paschen β line. The shape of the V band light‐curve indicates two active regions on the stellar surface, about 0.4 in phase apart. The spectroscopic observations show enhanced Hα emission observed close to the phases of the photometrically detected starspots. This could indicate chromospheric plages associated with the photospheric starspots. Some indications of prominence structures are also seen. The chromospheric pressure is limited to log m_TR < –4 based on the non‐detection of emission in the Paschen β wavelength region. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spot activity in the RS CVn binary UX arietis

Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation.     

Ultraviolet to near-infrared continuum flux distribution in the active binary RS canum venaticorum

We present multifrequency observations of the active binary RS CVn. Ultraviolet observations were obtained from the IUE data bank. Optical observations were made at the Observatorio del Roque de los Muchachos (La Palma), while the infrared observations were obtained at the Observatorio del Teide (Tenerife).The continuum of RS CVn shows that both components behave in good agreement with normal values for their spectral type and luminosity class, when observed data are corrected for small spot effects. No significant circumstellar reddening is detected.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Discovery of cyclic spot activity on the G8 giant HD 208472

We present and analyze 17 consecutive years of UBVRI time‐series photometry of the spotted giant component of the RS CVn binary HD 208472. Our aim is to determine the morphology and the evolution of its starspots by using periodsearch techniques and two‐spot light‐curve modelling. Spots on HD208472 always occur on hemispheres facing the observer during orbital quadrature and flip their location to the opposite hemisphere every approximately six years. The times when the spots change their preferential hemisphere correspond to times when the light curve amplitudes are the smallest and when abrupt changes of the photometric periods are observed. During these times the star is also close to a relative maximum brightness, suggesting a vanishing overall spottedness at each end of the previous cycle and the start of a new one. We find evidence for a 6.28±0.06‐yr brightness cycle, which we interpret to be a stellar analog of the solar 11‐year sunspot cycle. We also present clear evidence for a brightening trend, approximated with a 21.5±0.5‐yr period, possibly due to a stellar analog of the solar Gleissberg cycle. From the two‐spot modelling we also determine an upper limit for the differential‐rotation coefficient of α = ΔP/P of 0.004±0.010, which would be fifty times weaker than on the Sun (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spot activity on HD 89546 (FG UMa) from long‐term photometry

We present the analysis of 20 years of time‐series BV photometry of the SB1 RS CVn binary HD 89546. The system's yearly mean V brightness, the B – V color index, the photometric period, and the light curve amplitude all show clear cyclic variability with an ≈9‐year time scale. We also find some evidence for brightness variability on a time scale longer than the 20‐year time span of our observations, perhaps indicating a longer cycle analogous to the solar Gleissberg cycle. We estimate the unspotted V magnitude of HD 89546 to be 7.^m154, which is ≈0.^m2 brighter than the observed maximum brightness. Spot modelling of the system shows that spot temperature variations affect the observed B – V color as well as the V brightness. Two active longitudes are observed, centered around 180° and 360° longitude on the G9 III primary, each covering a longitude range of 120°. Furthermore, two inactive longitude zones are seen spanning only 60° between the two active longitudes. The longitudinal distribution of the spots exhibits no strong cyclic variability but does show rapid jumps of 120° that look like the flip‐flop phenomenon. We estimate the differential rotation coefficient of the star as k = 0.086 by considering the range of observed photometric period variations and assumed latitudinal spot variations over 45° (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The search for hot spots associated with the Cygnus X-3 relativistic jet

We report and shortly discuss here the observational work carried out in order to test the possibility that two previously detected radio sources, in the vicinity of the well known microquasar Cygnus X-3, could be hot spot tracers of interaction between its relativistic jet and the interstellar medium (ISM). The motivation behind this search is in part justified considering recent theoretical models of high energy γ-ray emission which strongly rely on the interaction sites of galactic relativistic jets with nearby ISM clouds. The results presented in this paper include an improved radio exploration of the several arc-minute field around Cygnus X-3 using the Very Large Array (VLA), as well as deep near infrared (NIR) imaging with the Calar Alto 3.5 m telescope. We anticipate here that our observations do not appear to support the initial hot spot hypothesis. Instead, the resulting images suggest that the two radio sources, originally believed to be hot spot candidates, are most likely background or foreground objects.     

Infrared radiation oF RS CVn systems

We give the results of our J, H, K photometry on 41 RS CVn systems and the data on 40 RS CVn systems identified with IRAS point sources. For those systems in which the components have individual spectral types, we discuss their infrared color excess. We found only very few systems showed infrared excesses. (UX Ari, Z Her and HR 1099 in the near infrared and SZ Psz at 12μm).

For systems having fluxes at 12 and 25μm and K magnitudes, we plotted a color-color diagram and found the majority of points to be lying close to the black body line. These observations are in conflict with Biermann and Hall's statement [1] that infrared excess is a general characteristic of RS CVn systems.     

UBV photometry of ER Vulpeculae

UBV photometry of RS CVn-type eclipsing binary system ER Vulpeculae has been presented. The period comes out to be 0 _. ^d 698093. The average depths of primary and secondary minima are, respectively, 0 _. ^m 21 and 0 _. ^m 12. The colours at various phases have been given. A dip is seen around phase 0 _. ^p 73 as was seen in the observations of Arevaloet al. (1988). Large scatter is present in the observations as noticed earlier, and may be due to activity of the components.     

Cover Picture: Astron. Nachr. 7/2013

The spot activity of the spectroscopic binary V2253 Oph indicates a cyclic variation of about ten years and a phase coherence with the orbital period (see K. Olah et al., this issue, p. 625). (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)