相接双星金牛座AH

本文给出了金牛座AH的BV两色光电光变曲线。发现该双星的光变曲线从1973年到1986年发生了较大的变化,新观测到的光变曲线是对称的,用Wilson-Devinney方法分析我们的观测求得了AH Tau的测光解。结合该双星的光度视差求出了它的基本参量,并发现它距太阳的距离是昂星团距太阳距离的二倍。因此,AH Tau虽然在昴星团的方向上,但它不是昴星团的成员星。     

The first light curve solutions and period study of two contact binary systems: V1370 Tau and QQ Boo

The first light curve solutions of the binary systems V1370 Tau and QQ Boo are presented. The periodic changes are calculated, and a new ephemeris presented for each of these two binary systems. O-C analysis is performed using the MCMC method in OCFit code. The changing rate of period was measured as dP/dt= 0.2423 days/year for V1370 Tau and dP/dt= -0.1363 days/year for QQ Boo. The light curve solutions suggest that V1370 Tau is a weak-contact eclipsing binary system with a photometric mass ratio q = 0.829, and that the corresponding fillout factor is 11.06%. Furthermore, it is suggested that the QQ Boo binary system is also a weak-contact W UMa eclipsing binary with a photometric mass ratio q = 0.831, and that its fillout factor equals 10.26%. The light curve solutions require cold spots. Utilizing the Wilson-Devinney code the photometric and geometric parameters of the systems are determined. The distance of both V1370 Tau and QQ Boo are calculated according to the estimated absolute parameters as 159.95 ± 23 pc and 309.03 ± 25 pc, respectively, which are in a good agreement with the distance values derived from the Gaia DR2 parallax within one standard deviation. Moreover, the positions of their components on the H-R diagram are represented.     

Physical parameters of some close binaries: ET Boo,V1123 Tau,V1191 Cyg,V1073 Cyg and V357 Peg

With the aim of providing new and up-to-date absolute parameters of some close binary systems, new BVR CCD photometry was carried out at the Ankara University Observatory (AUG) for five eclipsing binaries, ET Boo, V1123 Tau, V1191 Cyg, V1073 Cyg and V357 Peg between April, 2007 and October, 2008. In this paper, we present the orbital solutions for these systems obtained by simultaneous light and radial velocity curve analyses. Extensive orbital solution and absolute parameters for ET Boo system were given for the first time through this study. According to the analyses, ET Boo is a detached binary while the parameters of four remaining systems are consistent with the nature of contact binaries. The evolutionary status of the components of these systems are also discussed by referring to their absolute parameters found in this study.     

Rotational Brightness Modulation and Starspots on the RS CVn-type Stars IN Com, IL Com, UX Ari, and V711 Tau

UBVRI photometric observations and models of spotting are presented for four noneclipsing RS CVn systems: IN Com (G5III/IV), IL Com (F8V+F8V), UX Ari (K01V+G5V), and V711 Tau (K1IV+G5V). A low amplitude variability caused by cold (T=1700K)spots which can occupy up to 19% of the star's surface is confirmed for the little-studied star IL Com. Long-term light curves are constructed and the stellar magnitudes and color indices of the unspotted photospheres are estimated for IN com, UX Ari, and V711 Tau. It is shown that UX Ari becomes bluer with decreasing brightness, so its variability cannot be fully explained in terms of cold spots. Models of spotting on In Com and V711 Tau are constructed from the full set of available photometric observations. The spots on both of these variables lie at middle latitudes and occupy up to 22% (In Com) and 33% (V711 Tau) of the stars' surfaces. Both stars manifest a tendency for the width of the spots to decrease as their area increases. This is a crude analog of the Maunder butterflies. These stars experience cyclical spot activity and have a differential rotation of the type found on the sun.     

BVR photometry of the three RS CVn binary stars: V711 Tau,UX Ari and IM Peg

Differential BVR photometric observations of the three RS CVn binary stars: V711 Tau, UX Ari and IM Peg obtained during the period November 26, 1994–February 24, 1995 using the 0.35 m reflector telescope equipped with photoelectric photometer are presented. Analysis of light curves shows significant changes in shape, amplitude as well as the phases of minimum light of all the three binaries. The amplitude of IM Peg, in particular, is found to have reached a larger value in the present epoch of observation than reported earlier.     

Analysis of spectra of V471 Tau and HD 115404

We analyze the chemical composition of the atmospheres of a single K-type star HD 115404 and the secondary component of the V471 Tau variable. We use the technique of modeling of synthetic spectra to analyze the high-resolution spectra of these stars, taken with the RTT 150 Russian-Turkish telescope and find the abundances of 23 and 17 elements in the atmospheres of HD 115404 and V471 Tau, respectively. We demonstrate the lack of composition anomalies in the HD 115404 and show it to be consistent with the published data, inferred from equivalent widths of spectral lines. We find the abundances of 15 elements from Na to Ba to be consistent with the metallicity of the atmosphere of V471 Tau ([Fe/H] = −0.22 ± 0.12dex), which differs significantly from the average metallicity of the Hyades cluster. We show the existence of strong carbon and oxygen overabundances (by more than 1dex) due to the enrichment of the secondary by the nucleosynthesis products during the common-envelope stage of the system. On the whole, we demonstrate that V471 Tau and the other precataclysmic variables share similar composition anomalies.     

Infrared photometry for two RV Tau stars and V1027 Cyg

We present and discuss the results of our long-term JHKLM photometry for two RV Tau stars (R Sge and RV Tau) and the yellow supergiant V1027 Cyg, a candidate for protoplanetary nebulae. The amplitude of the infrared brightness variations in R Sge and RV Tau over fourteen years of observations was 0 _. ^m 9?1 ^m ; the infrared brightness variations in V1027 Cyg over eighteen years did not exceed 0 _. ^m 25. The infrared brightness and color of R Sge fluctuated about their gradually changing mean values; the infrared brightness variations agree with a period of 70.77 days. The periodic J brightness and J-H color variations in R Sge can be explained by temperature pulsations with ΔT ≤ 200 K and radial pulsations with [ΔR/R] ≤ 0.2. From 1995 to 2008, the mean J brightness of RV Tau increased, while its mean J-H color index decreased; the variations in the mean J brightness can be associated mainly with stellar temperature variations; a periodic component with P = 78.73 days is observed in the infrared brightness and color fluctuations. The variations in the mean J brightness and J-H color index of the supergiant V1027 Cyg over eighteen years of observations did not exceed a few hundredths of a magnitude; both temperature and radial pulsations may be present in the observed J brightness variations. The most probable period of the infrared brightness fluctuations in V1027 Cyg is 237 ± 2 days. The dust shell of R Sge may consist of two layers with grain temperatures of ～1000 and ～700 K; the optical depth at 1.25 µm is ～0.02 and ～0.24, respectively. The grain temperatures in the circumstellar dust shells of the supergiants RV Tau and V1027 Cyg are ～600 K (RV Tau) and ～700 K (V1027 Cyg). Their optical depths at 1.25 µm are ～0.24 (RV Tau) and ～0.008 (V1027 Cyg).     

Discovery of a cyclic period change in the contact binary system V1128 Tau

We obtained several epochs of light minima and a complete R light curve of the W-type contact binary V1128 Tau in 2009. Two cool spots on the massive component are used to model the photometric light curve. Using all available data we find evidence for a long-term period variation with an amplitude of 0.0050±0.0012 days and a period of 16.7±0.9 years. Using parameters derived from a photometric model of the 2009 light curve we show that this period change could be explained by the Applegate mechanism on one of the components.     

On the nature of the photometric activity of the T Tauri star V1184 Tau

We present our 2-year-long photometric (V, R _c, I _c) observations of the T Tauri star V1184 Tau. They show that the relatively quiet “photometric life” of this object, which ended in 2004 with a sharp brightness decline by four magnitudes, was succeeded by a qualitatively new (in nature) period of activity characterized by high-amplitude irregular photometric variability. Judging by its color variations, the object belongs to the class of UX Ori stars and, hence, variable circumstellar extinction is responsible for its brightness variations. Moreover, the (V?I _c)/V color-magnitude diagram for the object is identical to that for UX Ori itself, suggesting that the optical properties of dust grains in the circumstellar space of these stars are similar. At the same time, V1184 Tau is quite dissimilar to UX Ori stars in its light curve, variability amplitude (reaching 4.5 magnitudes in the V band), and some other parameters.     

Photometric and spectroscopic variability of the pre‐main sequence star V1184 Tauri (CB 34V)

We present recent results from optical photometric and spectroscopic observations of the pre‐main sequence star V1184 Tau (CB 34V). The star is associated with the Bok globule CB 34 and was considered as a FUOR candidate in previous studies. Our photometric data obtained from October 2000 to April 2003 show that the stellar brightness varies with an amplitude of about 0.m 5 (I ), but from August 2003 the photometric behavior of the star has changed dramatically. Three deep brightness minima (ΔI ∼ 4^m.2) were observed during the past two years. The analysis of available photometric data suggests that V1184 Tau shows two types of variability produced (1) by rotation of large cool spotted surface and (2) by occultation from circumstellar clouds of dust or from features of a circumstellar disk. The behavior of the V – I index indicates that the star becomes redder towards minimum light, but from a certain turning point (V ∼ 18^m.2) it gets bluer and is fading further. Five medium dispersion optical spectra of V1184 Tau were obtained in the period 2001–2004. Signi.cant changes in the profile and strength of the emission lines in the spectrum of V1184 Tau were found. During minimum light the equivalent width of the Hα emission line increases from 4 Å to 9 Å. The [O I] lines (λλ 6003, 6363 Å) are also seen in emission while the sodium doublet keeps its absorption strength and equivalent width. The possibility to reconstruct the historical light curve of V1184 Tau using photographical plate archives is brie.y discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared photometry of the RS CVn binary HR 1099 (V711 Tau)

Infrared observations inJ, H andK of the RS CVn-type binary HR 1099 (V711 Tau) show apparent light variations similar to those in the visible. The phase shift towards increasing phase is confirmed. There is no conspicuous infrared excess attributable to circumstellar emission. The amplitudes of the infrared variation are compatible with the spot model proposed for RS CVn and enable plausible limits on a characteristic spot temperature and effective spot area to the set.     

Light curve variations in V471 Tauri

The light curves of V471 Tau obtained in four successive years from 1981 to 1984 are presented. The light variations due to the tidally distorted red dwarf have been computed and subtracted out from the light curves obtained so far. A pure shape of the wave-like distortion has therefore been derived. The period of the retrograde migration has been found to be 182.17 days. On the other hand, the mean brightness of the system seems to vary with a period of about 18 years. The amplitude of the variation is greater at longer wavelength. The periodic variation of the mean brightness resembles the solar cycle of about 11.2 years, which depends upon the number of spots or spot groups.     

Light variations and flares on V471 tauri

Two-colour photometric observations of the white-dwarf and K-dwarf eclipsing binary V471 Tau were made during the last four years. The resulting light curves and thirteen timings of mid-eclipse are presented. During the observations two flares were obtained on September 23 and December23, 1992. Both events occurred just after the fourth contact. The increment in the brightness was measured as 0 _. ^m 067. The energy liberated by the flare was computed to be 5.43 × 10³² erg s^–1 in the JohnsonB band, which amounts 1.13 times that of the total radiation of the K-dwarf.     

A photometric study of the neglected eclipsing binaries: V405 Cep,V948 Her,KR Mon and UZ Sge

CCD multi-band light curves of the neglected eclipsing binaries V405 Cep, V948 Her, KR Mon and UZ Sge were obtained and analysed using the Wilson–Devinney code. New geometric and absolute parameters were derived and used to determine their current evolutionary state. V405 Cep, V948 Her and KR Mon are detached systems with their components in almost the same evolutionary stage. UZ Sge is a classical Algol system with a tertiary companion around it. Moreover, since the systems V405 Cep, V948 Her and UZ Sge contain an early type component, their light curves were examined for possible pulsation behaviour.     

Photoelectric light and colour variations in V471 Tauri

A new investigation of the variations in the light curves and in the period of the eclipsing binary V471 Tau is presented. The collected observational data have been re-examined and, in addition to old information, it was found that (i) the decrease in the period of the system slows down and (ii) that the mean brightness of the system has been increasing and this is greater at the longer wavelength. For the last seven years the increase in the brightness is estimated to be 0.15 mag inB and 0.18 mag inV bands respectively. Therefore, we conclude that the colour of the system is about 0.03 mag redder in 1980 than in 1973.     

CU Tauri: A W UMa-type system with a small mass ratio

New BV light curves and photometric solutions of the W UMa-type contact binary CU Tau are presented in this paper. From the observations, four times of minimum light were determined and from the present times of minimum light and those collected from the references, a new ephemeris was formed. The O-C diagram of the period change suggests that the orbital period of the system seems to vary. While the B light curve seems to be symmetric, the V light curve appears to exhibit an O'Connell effect, with Maximum I being 0.015 mag. brighter than Maximum II. The light curves are analyzed by means of the latest version of the Wilson-Devinney code. The results show that CU Tau is A-subtype W UMa contact binary with a small mass ratio q = 0.180. The asymmetry of the light curve is explained by star spot models.     

Spot patterns and differential rotation in the eclipsing pre-cataclysmic variable binary, V471 Tau

We present surface spot maps of the K2V primary star in the pre-cataclysmic variable binary system, V471 Tau. The spot maps show the presence of large high-latitude spots located at the sub-white dwarf longitude region. By tracking the relative movement of spot groups over the course of four nights (eight rotation cycles), we measure the surface differential rotation rate of the system. Our results reveal that the star is rotating rigidly with a surface shear rate,  dΩ= 1.6 ± 6 mrad d⁻¹  . The single active star AB Dor has a similar spectral type, rotation period and activity level as the K star in V471 Tau, but displays much stronger surface shear  (46 < dΩ < 58 mrad d⁻¹)  . Our results suggest that tidal locking may inhibit differential rotation; this reduced shear, however, does not affect the overall magnetic activity levels in active K dwarfs.     

New photoelectric observations of four W UMa systems: OO aql,V839 Oph,V566 Oph,and SW Lac

The W UMa-type systems (OO Aql, V839 Oph, V566 Oph, and SW Lac) were observed photoelectrically in two wavebands (B andV) during the years 1982–1983. The light curves of these systems are analysed using Kopal's frequency-domain technique and the optimisation method. New geometrical and physical elements have been determined. The absolute elements and the period variations of these systems are discussed.     

Observations of variable and transient X-ray sources with the Ariel V sky survey experiment

Results obtained during the first six months in orbit of Ariel V with the Leicester Sky Survey are reviewed. Among 80 sources found by a scan of the Milky Way, 16 are new, and 11 UHURU sources in the scanned region are not detected. Some of these sources may be transient. The light curve of Cen X-3 in a binary cycle shows a dip between phase 0.5, and 0.75, and a secondary maximum at the centre of the dip. The dip and the maximum get progressively weaker in the succeeding cycles. These features are interpreted in terms of the stellar wind accretion model. Cyg X-1 observation for 14 days gives a broad minimum around superior conjuction. Four bright transient sources of nova-like light curves have been observed. The light curves and the spectra are given for TrA X-1 (A1524-62) and Tau X-T (A0535+26).Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

A simultaneous spectroscopic and photometric study of two eclipsing binaries: V566 Oph and V972 Her

In this study, we have performed simultaneous solutions of light and radial velocity curves of two eclipsing binary systems, V566 Oph and V972 Her. We observed both systems spectroscopically with a very recently installed spectrograph on the 40 cm telescope, T40, located in Ankara University Kreiken Observatory (AUKR), for the first time. We made use of the photometric data from the Hipparcos satellite for V972 Her, while we obtained the photometric observations of V566 Oph by using the 35 cm telescope, T35, located also in our observatory campus. We derived the absolute parameters for both systems and discussed their evolutionary states. In addition to the simultaneous analysis, we have also analyzed the change in mid-eclipse times for V566 Oph, and found cyclic variations, for which we have discussed light-time effect and magnetic activity as their potential origin, superimposed on a secular change due to a mass transfer between the components of the binary.