BV photometry of UX Arietis

DifferentialBV photometry of UX Ari obtained on 58 nights during 1984-85, 1985-86, 1986-87, and 1987-88 observing season is presented. We find that (B-V) is phase dependent with the system being reddest at the light maximum and we interpret this as due to the variable fractional contribution by the G5 V component to the total light at shorter wavelengths. An analysis of the available data indicates that at larger amplitudes of the photometric wave the brightness at maximum increases and that at minimum decreases and both converge to δV ≃ −1.0 mag at very low amplitudes. It implies that the low wave amplitudes are essentially due to more homogeneity in the surface distribution of spots rather than due to low levels of spot activity. The variation in wave amplitude is found to be near-sinusoidal with a period around 13–14 years     

Kinematics of the ultracompact helium accretor AM Canum Venaticorum

We report on the results from a five-night campaign of high-speed spectroscopy of the 17-min binary AM Canum Venaticorum (AM CVn), obtained with the 4.2-m William Herschel Telescope on La Palma.
We detect a kinematic feature that appears to be entirely analogous to the 'central spike' known from the long-period, emission-line AM CVn stars GP Com, V396 Hya and SDSS J124058.03−015919.2, which has been attributed to the accreting white dwarf. Assuming that the feature indeed represents the projected velocity amplitude and phase of the accreting white dwarf, we derive a mass ratio   q = 0.18 ± 0.01  for AM CVn. This is significantly higher than the value found in previous, less direct measurements. We discuss the implications for AM CVn's evolutionary history and show that a helium star progenitor scenario is strongly favoured. We further discuss the implications for the interpretation of AM CVn's superhump behaviour, and for the detectability of its gravitational-wave signal with the Laser Interferometer Space Antenna ( LISA ).
In addition, we demonstrate a method for measuring the circularity or eccentricity of AM CVn's accretion disc, using stroboscopic Doppler tomography. We test the predictions of an eccentric, precessing disc that are based on AM CVn's observed superhump behaviour. We limit the effective eccentricity in the outermost part of the disc, where the resonances that drive the eccentricity are thought to occur, to   e = 0.04 ± 0.01  , which is smaller than previous models indicated.     

The multiperiodic δ Scuti star 4 Canum Venaticorum: amplitude variability

Recent multisite campaigns of the Delta Scuti Network have revealed 34 frequencies of pulsation for the star 4 CVn. Our present knowledge of the frequencies makes it possible to reanalyse the shorter data sets in the literature, photometric observations from 1966 to 1997.
4 CVn shows strong amplitude variability with time-scales of ten years or longer, although for neighbouring years the amplitudes usually are similar. Seven of the eight dominant modes show annual variability of ∼12 per cent. The variability increases to ∼40 per cent over a decade. The formally derived time-scale of variation of 30 years can only be a rough estimate, since this is also the length of the available data span. The variability is compared with that of FG Vir, which shows lower amplitude variability.
The cyclic behaviour of the amplitude variations excludes an evolutionary origin. There exists some evidence that a mode at 6.12 d⁻¹, which appeared during 1996 and 1997, may have been present with small amplitudes in the 1976–1978 time period.
The pulsation mode at 7.375 d⁻¹ exhibited the most rapid decrease found so far: the V amplitude dropped from the highest known value of 15 mmag in 1974 to 4 mmag in 1976 and 1 mmag in 1977. After that the mode has been increasing in amplitude. There exists a phase jump between 1976 and 1977, suggesting the growth of a new mode. It is interesting to note that this mode also has the strongest coupling with other modes with combination frequencies, f _i ± f _j . The amplitudes of these combination frequencies are also strongly variable from year to year. We speculate that power is transferred between the modes through mode-coupling.     

Long-Term Study of the Starspot Activity on the Eclipsing Short-Period RS Canum Venaticorum Star UV Piscium

We present optical photometry of the short period eclipsing RS CVn system, UV Piscium for the years 1966–1984. After removing the spot effects from the light curves of Vivekananda Rao and Sarma (1981), we analyzed the cleaned data to obtain system parameters. For each light curve, we model the distortion waves in order to study the behaviour of star spots in this system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Superhumps, magnetic fields and the mass ratio in AM Canum Venaticorum

We show that the observed K velocities and periodicities of AM CVn can be reconciled given a mass ratio   q ≈ 0.22  and a secondary star with a modest magnetic field of surface strength   B ∼ 1 T  . We see that the new mass ratio implies that the secondary is most likely semidegenerate. The effect of the field on the accretion disc structure is examined. The theory of precessing discs and resonant orbits is generalized to encompass higher order resonances than 3 : 2 and shown to retain consistency with the new mass ratio.     

A photometric study of the W UMa-type binary DF Canum Venaticorum

We present new photometric observations for the eclipsing binary DF CVn, and determined five light minimum times. By using the Wilson–Devinney code, two sets of photometric solutions were deduced from our observations in 2009. The asymmetric light curves obtained on 2009 March 5 were modeled by a dark spot on the more massive component. The results indicate that DF CVn is a W-type weak-contact binary, with a mass ratio of q ～ 0.28 and an overcontact degree of f ～ 20%. From the O ? C curve of minimum times, it is found that there exists a cyclic variation, whose period and semi-amplitude are P₃ = 17.2(±0.9) year and A = 0.^d0070(±0.^d0008), respectively. This kind of cyclic oscillation may possibly result from the light-time effect due to the presence of an unseen third body. This kind of additional body may extract angular momentum from the central system. The low-amplitude changes of the light curves on a short-time scale (e.g., half a month) may be attributed to the dark spot activity, which may result in angular momentum loss via magnetic breaking. With angular momentum loss, the weak-contact binary DF CVn will evolve into a deep-contact configuration.     

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.     

Long-term infrared variability of the UX Ori-type star SV Cep

We investigate the long-term optical–infrared variability of SV Cep and explain it in the context of an existing UX Ori (UXOR) model. A 25-month monitoring programme was completed with the Infrared Space Observatory in the 3.3–100 μm wavelength range. Following a careful data reduction, the infrared light curves were correlated with the variations of SV Cep in the V band. A remarkable correlation was found between the optical and the far-infrared light curves. In the mid-infrared regime, the amplitude of variations is lower, with a hint for a weak anti-correlation with the optical changes. In order to interpret the observations, we modelled the spectral energy distribution of SV Cep assuming a self-shadowed disc with a puffed-up inner rim, using a two-dimensional radiative transfer code. We found that modifying the height of the inner rim, the wavelength dependence of the long-term optical–infrared variations is well reproduced, except the mid-infrared domain. The origin of variation of the rim height might be fluctuation in the accretion rate in the outer disc. In order to model the mid-infrared behaviour, we tested adding an optically thin envelope to the system, but this model failed to explain the far-infrared variability. Infrared variability is a powerful tool to discriminate between models of the circumstellar environment. The proposed mechanism of variable rim height may not be restricted to UXOR stars, but might be a general characteristic of intermediate-mass young stars.     

The flare star PP Ori

We give the results of photographic, photoelectric, and spectral observations of the flare star PP Ori. The 109 photographic observations used, which were obtained on the 40 Schmidt telescope of the Byurakan Observatory over a period of about 20 years, and four spectra obtained on the same telescope with a4° objective prism show no variation in brightness. Photoelectric observations in the UBVR bands using the 50cm and 60cm telescopes of the high-altitude Maidanak station of the Tashkent Astronomical Institute in 1987 and 1989 give grounds for suspecting a variation in brightness much larger than observational errors. Spectral observations of the star PP Ori made on the 2.6m telescope of the Byurakan Observatory show weak H emission. The results of all these observations show that PP Ori is an Orion variable of spectral class K7-M0 with absolute visual magnitude7 ^m 5–8 ^m 5.Translated fromAstrofizika, Vol. 38, No. 2, 1995.     

Spectral study of the flare star EV Lac

Spectral observations of the flare star EV Lac made on the 2.6-m telescope at the Byurakan Observatory in 2000–2002 are reported. A powerful flare was detected and it was possible to follow the variation in the equivalent widths of the Hα and Hβ lines, both during the flare and during the quiescent phase of the star. It is shown that the profiles and equivalent widths of the lines underwent substantial changes. The equivalent widths of these emission lines reached a maximum roughly 40 min after the flare maximum. __________ Translated from Astrofizika, Vol. 49, No. 4, pp. 573–583 (November 2006).     

Discovery of a flare star near Sirius

The discovery of a flare star (R.A. (1950)=6^h43^m6^s.07, Decl.(1950)=?16°45′24″) located about 6 arc min south of Sirius is reported. During photometric observations on the night of 13 January, 1982, using the 102 cm telescope at Kavalur, India, the star was seen to brighten by 2.55 mag. inV band over a duration of about 200 s. Observations on this object for a duration of about 10.5 hr spread over seven more nights indicate the star to be variable. The results of these observations are presented.     

Very short-term behaviour of the flare star EV Lac

Sinusoidal variations in Johnson'sB-band of the flare star EV Lac have been confirmed at its quiet state luminosity. The cycle lengths are more than one hour and less than two hours with amplitudes varying from 0 _. ^m 105 to 0 _. ^m 306. These registered cycles have agreed with cycles detected by Mavridis and Varvoglis (1990) and Mavridis (1990). In the same time, the cycles have confirmed the light variation detection in Johnson'sV-band in the same flare star by Pettersen (1980) with a cyclic period equals about 4 _. ^d 378 and an amplitude of about 0 _. ^m 07. Our net results confirm, to some extent, the presence of active region(s) as an origin of stellar flare phenomenon of UV Ceti type flare stars. We can cautiously say that the solar and stellar flare phenomenon have a similar origin.     

Variation in the flare activity of the star UV Ceti

This is an analysis of the dependence of the flare activity of the well known flare star UV Ceti on the linear distance between the components of this binary system. It is shown that its flaring activity clearly depends on the mutual distance of the components, while this kind of variability is not seen in isolated flare stars.     

A new flare star member candidate in the Pleiades cluster

We present a new flare star, which was discovered during our survey on a selected field at the edge of the Pleiades cluster. The field was observed in the period 2007–2010 with three different CCD‐cameras at the University Observatory Jena with telescopes from 25 to 90 cm. The flare duration is almost one hour with an amplitude in the R‐band of about 1.08 mag. The location of the flare star in a color‐magnitude diagram is consistent with age and distance of the Pleiades. In the optical PSF of the flare star there are two 2MASS objects (unresolved in most images in the optical Jena PSF), so it is not yet known which one of them is responsible for this flare. The BVRIJHK colors yield spectral types of M1 and M2 with extinction being A_v = 0.231 ± 0.024 mag and A_v = 0.266 ± 0.020 for those two stars, consistent with the Pleiades cluster (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoelectric observations of the flare star BD + 55° 1823

A light variation in Johnson'sV-band of flare star EV Lac has been registered by Pettersen (1980). The cycle length was 4 _. ^d 378 with amplitude about 0 _. ^m 07. A Fourier analysis programme has been applied on our measured data of the flare star BD+55°1823 in Johnson'sV andB bands. A period of 16^d and amplitude of 0 _. ^m 14 have been detected in theV-band.     

A short period trial detection of the flare star AD Leo

A Fourier analysis programme was applied on observational data taken in Stephanion Observatory, Greece, for flare star AD Leo. The purpose of this task is to try to register a short period variation in Johnson'sB-band in the star's brightness at quiet-state to confirm a result obtained by Pettersen (1980) inV-band of the flare star EV Lac. A negative result has been obtained.