1,721,001 research outputs found
Photometric Variations and Spot Cycles in RS CVn Stars
No full textThe authors have developed a simple model of spot motions on a stellar
surface, based on what has been observed on the Sun. This model is
applied to RS CVn phenomenology, determining the parameters of the
differential rotation and of the spot motion, in order to obtain group
properties and classification criteria
Rapid time variability in the short-period RS CVn-type binary SV Camelopardalis
No full textThe eclipsing binary SV Cam shows photometric features that suggest its membership to the RS CVn group. The existing light curves (covering the period 1947 - 1986) have been analyzed in order to isolate the contribution of the wave-like distortion; all the observations support the presence of an activity cycle, with a duration of about 10 years
Photometry of southern stars. II - Further evidence of spots in the eclipsing binary BH Virginis
No full textUBVRI photometry of the eclipsing binary BH Virginis at ESO (La Silla,
Chile) in April 1984, is presented. A new determination of the orbital
period confirms its constancy since the discovery of the system. The
light curve out of eclipse shows a moderate curvature, centered around
phases 0.25 and 0.75, and an almost sinusoidal distortion at all five
wavelengths. Comparison with existing observations indicates that this
disturbance is variable in time and apparently migrates through the
light curve. Assuming that the distortion is due to cool starspots, a
temperature difference of about 1300-1400 K between the unperturbed
photosphere and the spotted regions has been derived. However, this
result is very uncertain, due to the small color changes and to the
probable complexity of the spot distributions on both components. No
conclusion about spot cycles and/or differential rotation can be
obtained, since continuous monitoring of the binary does not exist; for
this reason new light curves are needed in the coming years
Differential rotation and activity cycles in RS CVn binaries. II - Model results for short and intermediate period members
No full textThree active binaries of the RS CVn class with short period (SV Cam) and
intermediate period (VV Mon and SS Boo) are studied by applying the
statistical procedure of Busso and Scaltriti (1983) and the analytical
method of Busso et al. (1984; Paper I) to a collection of photometric
light curves extending for some years. The behaviour of the wave
distortion for the studied systems can be reproduced fairly well by the
model and allows to determine relevant parameters, such as the angular
velocity at the equator, the rate of differential rotation, the rate of
latitude shear of spots and the latitude of spots at formation. Though
based on a small sample of objects, the results seem to indicate that
short-period and intermediate-period binaries can behave quite similarly
for what concerns spot cycles
UBV photometry of FK Comae
No full textUBV photometry of the peculiar star FK Comae, obtained during the period
January-June 1983, is presented. The amplitude of the photometric
variation has raised with respect to the previous observations performed
in 1981 and 1982, attaining about 0.18 mag in the V filter. Color curves
indicate that the star is redder at minimum light; this fact is
consistent with both the models presented to explain the properties of
FK Comae. A Fourier analysis of the light curves available in the
literature has been performed; the phases of minimum and maximum light
turn out to be noticeably stable in time. This fact is difficult to be
reconciled with the hypothesis of dark spots that are observed to
migrate in other active stars. Rather, it could be explained by the
model of Walter and Basri (1982a, b), implying an extremely evolved
Algol-type system accreting mass on its primary component
The RS CVn-type binary SV Camelopardalis - Evidence of dark spots from UBV observations and IR fluxes
No full textNew UBV light curves and some infrared JHK observations of the RS
CVn-type binary SV Camelopardalis are presented. New determinations of
primary minimum epochs confirm the presence of a light-time effect, with
a period U = 74.7 yr. The overall shape of the light curve appears to
vary in time by several hundredths of magnitude, due to a distortion
wave whose fast migration causes an inversion in the levels of the
maxima in a few months. IR excesses strongly suggest the presence of
cool regions, in agreement with the common hypothesis that the light
variations are due to starspots. By the method of Vogt (1981) spot
temperatures turn out to be near 3800 K, about 1500 K cooler than the
quiet photosphere. The spot hypothesis is also consistent with the
changes in luminosity observed in the interval 1969-1984, which are
shown to be tightly correlated with the cycles of stellar activity, as
derived by the model of Busso et al. (1984)
Differential rotation and activity cycles in RS CVn binaries. III - UV PISCIUM and UX ARIETIS
No full textNew photoelectric observations of the spotted binaries UX Arietis and UV
Piscium are presented and studied on the basis of a previously
established technique for analyzing unevenly sampled light curves. The
new data, when combined with already published observations, allowed us
to reconstruct the recent evolution of the spot activity in the systems
studied by means of the method described in Busso et al. (1985). The
results confirm the correlations between the differential rotation, the
orbital period, and the duration of spot cycles tentatively established
in that paper
IR excesses of RS CVn-type binaries from IRAS observations
No full textA list of IRAS detections of RS CVn-type binaries, according to the
revised version of the Point Source Catalogue, is presented. Selected
samples of the data are compared to the expected colour sequences for
normal giant stars as well as to the flux ratios typical of black body
emission at various temperatures. In both cases, some (but not all) of
the sources show evidence of an IR excess, indicating that RS CVn
variables do not behave in a unique way at IR wavelengths. The excess,
when present, is not correlated with the activity level nor with the
evolutionary status and its origin still calls for an explanation,
perhaps in terms of mass-loss phenomena near the Main Sequence
Some Comments on the Minima of the RS CVn Type Eclipsing Binaries CQ Aur, RU Cnc, VV Mon and SZ Psc
No full textNot Availabl
A study of the wake-like distortions in the light curves of RS CVN stars by means of time analysis
No full textTime series analysis techniques have been applied to lightcurves of RS
CVn binaries. The procedure consists in (1) reconstitution of uniformly
sampled data by means of a least-square fit in the frequency domain; (2)
application of the cross-correlation technique to find the phase
displacement between lightcurves of different years. In the hypothesis
that the observed variations are due to dark spots, for RU Cnc and CQ
Aur the authors find evidences of the existence of a differential
rotation and of a latitude drift of the spots, similar to the solar
ones; the relative parameters are computed
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