Revision of the photometric parameters of BS Cassiopeiae

Seven charge-coupled device(CCD)photometric times of light minimum of the overcontact binary BS Cas which were obtained from 2007 August to November and one CCD light curve in the R band which was observed on 2007 September 24 and October 15,are presented.It is found that the light curve of BS Cas has characteristics like a typical EW-type light variation.The light curve obtained by us is symmetric and shows total eclipses,which is very useful for determining photometric parameters with high precision.Photometric solutions were derived by using the 2003 version of the Wilson-Devinney code.It shows that BS Cas is a W-subtype overcontact binary(f = 27.5% ± 0.4%)with a mass ratio of q = 2.7188 ± 0.0040.The temperature difference between the two components is 190 K.Analysis of the O-C curve suggests that the period of AE Phe shows a long-term continuous decrease at a rate of dP/dt=-2.45 × 10-7 dyr-1.The long-time period decrease can be explained by mass transfer from the primary to the secondary.     

TZ Lyrae： an Algol-type Eclipsing Binary with Mass Transfer

We present a detailed investigation of the Algol-type binary TZ Lyrae, based on 55 light minimum timings spanning 90 years. It is found that the orbital period shows a long-term increase with a cyclic variation superimposed. The rate of the secular increase is dP/dt = 7.18 × 10?8d yr?1, indicating that a mass transfer from the less massive component to the more massive one at a rate of dm = 2.21 × 10-8M⊙yr-1. The cyclic component, with a period of P3 = 45.5 yr and an amplitude of A = 0d.0040, may be interpreted as either the light-time effect in the presence of a third body or magnetic activity cycles in the components. Using the latest version Wilson-Devinney code, a revised photometric solution was deduced from B and V observations. The results show that TZ Lyr is an Algol-type eclipsing binary with a mass ratio of q = 0.297(±0.003). The semidetached configuration with a lobe-filling secondary suggests a mass transfer from the secondary to the primary, which is in agreement with the long-term period increase of the binary system.     

BL Andromedae and GW Tauri: close binary stars in a key evolutionary stage

A photoelectric light curve of BL And is presented along with the first CCD light curve of GW Tau. Both objects are short-period eclipsing binaries and were observed in 2003 or 2004. Photometric elements were computed using the latest version of the Wilson–Van Hamme code. The results reveal that BL And is a semidetached system with the primary component filling its Roche lobe and the secondary one almost filling but still detached, while GW Tau is a marginal-contact binary system with a small degree of contact ( f = 10.9 per cent) and a large temperature difference of about 3100 K. All available eclipse times, including new ones, were analysed for each system. It was found that the orbital period of BL And is decreasing at the rate of  d P /d t =−2.36 × 10⁻⁸ (±0.09) d yr⁻¹  while that of GW Tau may be decreasing or oscillating. We think period decrease is more probable. The derived configuration and secular period decrease for BL And combined with the asymmetry of the light curve indicate that this system may evolve from the present semidetached phase into a contact stage, with mass transfer from the primary component to the secondary one through the L ₁ point, or that it might just undergo the broken stage predicted by the theory of thermal relaxation oscillations. In contrast, GW Tau is a marginal-contact binary in poor thermal contact and may be at the beginning of the contact phase.     

A Photometric Study of the W UMa-Type Contact Binary RZ Corn

We present results of CCD photometric observations of the short-period W UMatype contact binary system, RZ Com. The light curve of the binary has changed from Wsubtype to A-subtype from 1998 to 2003, then back to W-subtype in 2004. An analysis was carried out using the 2003 version of the Wilson-Devinney code. It is confirmed that RZ Com is a low-degree, overcontact f = 20.1% (±7.4%) binary system with a high inclination of i = 81.°40 (±0.°40), and a mass ratio q = 2.351 (±0.031). Combining four newly determined times of light minimum with others in the literature, the variations in orbital period is examined. A small-amplitude oscillation (A=0.0065d), with a period of 41.5 year, is discovered superimposed on a long-term increase at rate dP/dt = +3.97×10-8d yr-1. The period oscillation can be explained either by the light-time effect due to the presence of an unseen third body, or by cycles of magnetic activity on the components. Combining our photometric solution with the spectroscopic elements obtained by Mclean & Hilditch, the absolute dimensions of RZ Com are: M1 = 1.14 (+0.19)Mo, M2 = 0.50 (-4-0.09)Mo, R1= 1.12 (±0.01)R⊙, R2 = 0.78 (±0.01)R⊙ and A = 2.41 (±0.02)R⊙.     

A photometric study of BO Canum Venaticorum

Photometric BV light curves of BO CVn obtained in 1992 and new times of minima are presented. The primary minimum shows a transit, whereas the secondary minimum, shows an occultation. The system may be classified as an A‐type W UMa system. A complete study of minima allows one to detect a possibly increasing period by about 0.037 s/yr. This indicates that the conservative mass transfer rate from the less massive component to the more massive one is 1.57 10^—10M_⊙ /yr. Because of the variable period, the new ephemeris is determined for future observations. Using the Wilson‐Devinney code a simultaneous solution of the B and V light curves is also performed. The analysis shows that the system is in a contact configuration with q = 0.205 ± 0.001 and fillout factor (f) = 0.18, T₁ = 7240 K (fixed), T₂ = 7150± 10 K. The high orbital inclination i = 87°.54 ± 0.26 was con firmed by photometric observations of the secondary minimum.     

New photometric investigation of the low-mass-ratio contact binary star V1853 Orionis

Four-color charge-coupled device(CCD) light curves in the B, V, Rc and I c bands of the totaleclipsing binary system V1853 Orionis(V1853 Ori) are presented. By comparing our light curves with those published by previous investigators, it is determined that the O'Connell effect on the light curves has disappeared. By analyzing those multi-color light curves with the Wilson-Devinney code(W-D code),it is discovered that V1853 Ori is an A-type intermediate-contact binary with a degree of contact factor of f = 33.3%(3.7%) and a mass ratio of q = 0.1896(0.0013). Combining our 10 newly determined times of light minima together with others published in the literature, the period changes of the system are investigated. We found that the general trend of the observed minus calculated(O-C) curve shows a downward parabolic variation that corresponds to a long-term decrease in the orbital period with a rate of d P/dt =-1.96(0.46)×10^-7 d yr^-1. The long-term period decrease could be explained by mass transfer from the more-massive component to the less-massive one. By combining our photometric solutions with data from Gaia DR_2, absolute parameters were derived as M_1 = 1.20 M⊙, M_2 = 0.23 M⊙, R_1 = 1.36 R⊙and R_2 = 0.66 R⊙. The long-term period decrease and intermediate-contact configuration suggest that V1853 Ori will evolve into a high fill-out overcontact binary.     

An orbital period investigation of the Algol-type eclipsing binary VW Hydrae

Orbital period variations of the Algol-type eclipsing binary, VW Hydrae, are analyzed based on one newly determined eclipse time and the other times of light minima collected from the literature. It is discovered that the orbital period shows a continuous increase at a rate of dP/dt = +6.34×10-7 d yr-1 while it undergoes a cyclic change with an amplitude of 0.0639 d and a period of 51.5 yr. After the long-term period increase and the large-amphtude period oscillation were subtracted from the O-C curve, the residuals of the photoelectric and CCD data indicate a small-amplitude cyclic variation with a period of 8.75 yr and a small amplitude of 0.0048d. The continuous period increase indicates a conservative mass transfer at a rate of dM2/dt = 7.89×10-8 M⊙ yr-1 from the secondary to the primary. The period increase may be caused by a combination of the mass transfer from the secondary to the primary and the angular momentum transfer from the binary system to the circumbinary disk. The two cyclic period oscillations can be explained by light-travel time effects via the presence of additional bodies. The small-amplitude periodic change indicates the existence of a less massive component with mass M3 > 0.53 M⊙, while the large-amplitude one is caused by the presence of a more massive component with mass M4 > 2.84 M⊙. The ultraviolet source in the system reported by Kviz & Rufener (1987) may be one of the additional components, and it is possible that the more massive one may be an unseen neutron star or black hole. The rapid period increase and the possibility of the presence of two additional components in the binary make it a very interesting system to study. New photometric and high-resolution spectroscopic observations and a detailed investigation of those data are required in the future.     

Flickering in the Magnetic Cv Star Am Herculis

In this study, we present a photometric study of AM Her, a prototype of a class of magnetic CVs. Optical photometry of AM Her was obtained using the Russian–Turkish 1.5 m telescope at TüBİTAK National Observatory (TUG) in August 2003. The R band light curve of the system shows two maxima and two minima during one orbital cycle. In both observing nights the star showed flickering at a significant level. The measured flickering time scale is about 5 min.     

Shock fronts in the symbiotic system BI Crucis

We investigate the symbiotic star BI Crucis (BI Cru) through a comprehensive and self-consistent analysis of the spectra emitted in three different epochs: 1960s, 1970s and late 1980s. In particular, we would like to find out the physical conditions in the shocked nebula and in the dust shells, as well as their location within the symbiotic system, by exploiting both photometric and spectroscopic data from radio to UV. We suggest a model which, on the basis of optical imaging, emission-line ratios and spectral energy distribution profile, is able to account for collision of the winds, formation of lobes and jets by accretion onto the white dwarf (WD), as well as for the interaction of the blast wave from a past, unrecorded outburst with the interstellar medium (ISM). We have found that the spectra observed throughout the years show the marks of the different processes at work within BI Cru, perhaps signatures of a post-outburst evolution. We then call for new infrared and millimeter observations, potentially able to resolve the inner structure of the symbiotic nebula.     

Physical parameters of the O6.5V+B1V eclipsing binary system LS 1135

The 'All Sky Automated Survey' (ASAS) photometric observations of LS 1135, an O-type single-lined binary (SB1) system with an orbital period of 2.7 d, show that the system is also eclipsing performing a numerical model of this binary based on the Wilson–Devinney method. We obtained an orbital inclination     . With this value of the inclination, we deduced masses   M ₁∼ 30 ± 1 M_⊙  and   M ₂∼ 9 ± 1 M_⊙  , and radii   R ₁∼ 12 ± 1 R_⊙  and   R ₂∼ 5 ± 1 R_⊙  for primary and secondary components, respectively. Both the components are well inside their respective Roche lobes. Fixing the T _eff of the primary to the value corresponding to its spectral type (O6.5V), the T _eff obtained for the secondary component corresponds approximately to a spectral type of B1V. The mass ratio   M ₂/ M ₁∼ 0.3  is among the lowest known values for spectroscopic binaries with O-type components.     

A model of AW UMa

The contact binary AW UMa has an extreme mass ratio, with the more-massive component (the current primary) close to the main sequence, while the low-mass star at   q ≈ 0.1  (the current secondary) has a much larger radius than a main-sequence star of a comparable mass. We propose that the current secondary has almost exhausted hydrogen in its centre and is much more advanced in its evolution, as suggested by Stpień. Presumably the current secondary lost most of its mass during its evolution with part of it transferred to the current primary. After losing a large fraction of its angular momentum, the binary may evolve into a system of FK Com type.     

First ground‐based photometry and light‐curve analysis of the eccentric eclipsing binary V744 Cas

The first ground‐based BVR photometric observations of the recently discovered eclipsing binary V744 Cas are presented. From these measurements, timings for two primary and one secondary minima have been calculated. The light curves of the system were analyzed by using the Wilson‐Devinney program. The analysis shows that the system is detached with two similar components of spectral type A2V, and the orbit is eccentric (e = 0.0662 ± 0.0005). The longitude of the periastron (ω) was found significantly different for two different light curves (ours and that of Hipparcos), which is strongly suggestive of an apsidal motion with a period of about 425 ± 68 yr. This makes V744 Cas an important candidate for studies of apsidal motions. The first estimate of the absolute dimensions place the system close to the terminal age of the main sequence (TAMS) in the HR diagram. The distance from the spectroscopic parallax (d = 740 ± 10 pc) was found to be slightly larger than the Hipparcos distance of d = 610 ± 400 pc. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gamma-ray emission from pulsars: strength of the acceleration field in the outer gap

In this study we present and re-analyse the historical, 1889–1998, light curve (LC) of the eclipsing symbiotic binary AR Pav. For the first time, we show that the timing of mid-points of eclipses observed during a quiescent phase obeys a quadratic ephemeris, with an initial orbital period P ₀=605.18 d and a rate of period change     .
We determined a distance to the system of 5.8±1.5 kpc, the mass ratio of the giant to the hot star, M _g M _h=0.4±0.1, the mass of the giant, M _g=1.8+1/−0.5 M_⊙ and its radius, R _g=167±15 R_⊙.
During quiescence, the LC has characteristic features similar to those observed in cataclysmic variables (CVs). It can be well reproduced by a model of a large accretion disc surrounding the hot star. However, it is probable that the geometry of the transferred material in the Roche lobe of the accretor in AR Pav is different from that of CVs.
During active phases the shape of the LC changes considerably. A complex wave-like variation developed as a function of the orbital phase with an amplitude of ∼1 mag. It is interpreted in terms of a collisionally heated emission region located on the giant surface and arising from the hot star eruption.