Photometric and spectroscopic study of R CMa

UBV light curves and spectrograms of R CMa obtained with the 48-inch telescope of Japal-Rangapur Observatory during 1980–82 have been used for deriving the eclipse and orbital elements as well as the absolute dimensions of the components. The primary is found to be a Main-Sequence F2V star of mass 1.52M and the secondary a subgiant star of spectral type G8 and mass 0.20M which fills its Roche lobe, in agreement with Kopal and Shapley (1956) results, Kopal (1959), or Sahade's (1963) results. From a consideration of the possible evolution of this system it is concluded that a large fraction of the original mass of the secondary is lost from the system. A study of the period changes indicates the possible presence of a third component of mass of about 0.5M which is most likely to be anM dwarf.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Photometric and spectroscopic study of silicon Ap-star HD193722

The period of light variationP=1 _. ^d 13316 has been found for the silicon B9 IVp star HD 193722. Spectroscopic study of this star was based on 35 spectrograms with dispersion 4 Å mm^–1 well distributed in phase. The measurements of radial velocities of spectral line components for SiII, HeI, EuII, FeII and SrII allowed us to localize several regions on the surface of the star with enhanced abundance of these elements. The phase of maximum light inU, B andV was found to be the same as the phase of maximum Eu abundance. The coincidence of the regions with larger abundance of Si and He in HD 193 722 disagree with the hypothesis of diffusion in the presence of a magnetic field developed by Michaud (1971), to explain the peculiar chemical composition of Ap-stars.HD 193722 is a silicon B9 IVp star for which the magnetic field has not been measured. In the list by Palmeret al. (1962) its rotational velocityV sini is given as 250 kms^–1. As will be seen below, this value is too high. Megessier (1971) determined from hydrogen line profiles and continuous spectrumT _eff=13 000° and lgg=3.5.The results of photometric and spectroscopic study of HD193722 are given below.     

Photometric and spectroscopic study of nova Cassiopeiae 1995 (V723 Cas)

We report an 11-year long series of U BV RI observations and the results of our monitoring of the classical slow nova V723 Cas. We analyze the spectra of this star taken using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with a spectral resolution of 3.5–8.5 Å during the nebular stage and at the supersoft X-ray source phase (SSS). This systemhas a large orbital inclination and its orbital period is equal to 0.693265 days. The orbital period increases. We found low-amplitude light variations with the orbital period during the early stages of the outburst and even at the pre-maximum stage. The orbital light curve at the nebular stage is asymmetric and gradually increases its amplitude up to V=2 ^m in 2006. The asymmetry of the light curve of V723 Cas can be explained by the reflection effect, eclipse of the extended accretion disk, and high rate of mass transfer in the system. The light curve of V723 Cas has developed a plateau due to the SSS phase. In the spectrum of V723 Cas the transition to the SSS phase shows up in an order-of-magnitude increase of the flux of the [Fe X] λ 6374 Å emission, which forms in the expanding envelope. In addition, narrow emission lines λ 6466.4 Å (O V) and λ 6500.5 Å (Fe XVII) also emerged in the spectrum.     

Photometric and spectroscopic study of the supergiant with an infrared excess V1027 Cygni

We present the results of our UBV and JHKLM photometry for the semiregular pulsating variable V1027 Cyg, a supergiant with an infrared excess, over the period from 1997 to 2015 (UBV) and in 2009–2015 (JHKLM). Together with the new data, we analyze the photometric observations of V1027 Cyg that we have obtained and published previously. Our search for a periodicity in the UBV brightness variations has led to several periods from P = 212^d to 320^d in different time intervals. We have found the period P = 237^d based on our infrared photometry. The variability amplitude, the lightcurve shape, and themagnitude of V1027 Cyg atmaximum light change noticeably from cycle to cycle. The deepest minimum was observed in 2011, when the amplitudes of brightness variations in the star reached the following values: ΔU = 1 _. ^m 28, ΔB = 1 _. ^m 10, ΔV = 1 _. ^m 05, ΔJ = 0 _. ^m 30, ΔH = 0 _. ^m 35, ΔK = 0 _. ^m 32, ΔL = 0 _. ^m 26, and ΔM = 0 _. ^m 10. An ambiguous correlation of the B ? V and U ? B colors with the brightness has been revealed. For example, a noticeable bluing of the star was observed during the deep 1992, 2008, and 2011 minima, while the variations with smaller amplitudes show an increase in B ? V at the photometric minima. The spectral energy distribution for V1027 Cyg from our photometry in the range 0.36 (U)–5.0 (M) μm corresponds to spectral types from G8I to K3I at different phases of the pulsation cycle. Low-resolution spectra of V1027 Cyg in the range λ4400–9200 ?A were taken during 16 nights over the period 1995–2015. At the 1995 and 2011 photometric minima the star’s spectrum exhibited molecular TiO bands whose intensity corresponded to spectral types M0–M1, while the photometric data point to a considerably earlier spectral type. We hypothesize that the TiO bands are formed in the upper layers of the extended stellar atmosphere. We have measured the equivalent widths of the strongest absorption lines, in particular, the infrared Ca II triplet in the spectrum of V1027 Cyg. The calcium triplet (Ca T) with W _λ(Ca T) = 20.3 ± 1.8 ?A as a luminosity indicator for supergiants places V1027 Cyg in the region of the brightest G–K supergiants. V1027 Cyg has been identified with the infrared source IRAS 20004+2955 and is currently believed to be a candidate for post-AGB stars. The evolutionary status of the star and its difference from other post-AGB objects are discussed.     

Photometric and spectroscopic observations of the variable star ET And. II

New spectroscopic and photometric observations of the variable Ap star ET And carried out 1982 and 1983 confirm once again the existence of short-time variations. For the radial velocity variations a period of 0.19771 days and for the light variations a period of 0.0989 days was found. Some spectrograms show a velocity progression of the Balmer lines. The gradient is of such a kind that the radial velocity values increase from the line H_γ to H₁₅. Different models for the interpreation of the velocity progression are discussed.     

Polarimetric study of solar flares

The theory of impact polarization is briefly reviewed. Spectropolarimetry provides a tool to derive the nature, the number flux, and the main characteristics of the angular velocity distribution function of energetic particles accelerated in solar flares. As an exemple of application of polarimetry the spatial and temporal characteristics of the linear polarization of the hydrogen H line observed in a solar flare is presented.     

Photometric and spectroscopic investigation of the oscillating Algol type binary: EW Boo

We obtained the physical and geometrical parameters of the EW Boo system, which exhibits short period and small amplitude pulsations as well as brightness variations due to orbital motion of components. Towards this end we carried out photometric observations at Ankara University Kreiken Observatory (AUKO) as well as spectroscopic observations at TUBITAK National Observatory (TNO). The light and radial velocity curves obtained from these observations have been simultaneously analyzed with PHOEBE and the absolute parameters of the system along with the geometric parameters of the components have been determined. Using model light curves of EW Boo, light curve regions in which the pulsations are active have been determined and as a result of analyses performed in the frequency region, characteristic parameters of pulsations have been obtained. We find that the results are compatible with current parameters of similar systems in the literature. The evolutionary status of the components is propounded and discussed.     

Photometric study of VZ hydrae

The photoelectric elements of the system VZ Hydrae have been redetermined inU, B andV colours. Our results are at variance from those given earlier by Walker. The colour of the system has also been given. The system is a detached one.     

Photometric study of MM Cas

TheU, B, andV photometric observations of the eclipsing binary MM Cas have been presented and discussed. The photometric elements have been derived. By use of the colour indicesU-B andB-V, the spectral types of the systemic components are estimated. An examination of all available times of minimum light of MM Cas does not reveal any change in its orbital period.     

Photometric study of BZ Eridani

The 1980–1981U, B, andV observations of the eclipsing binary BZ Eridani have been presented. A new period of BZ Eri comes out to be 0^d.6641703. The colour curves of the system show appreciable variations, and are indicative of intrinsic variability. The secondary minimum falls nearly at phase 0.5. Some interesting features are given. The features of BZ Eri are changing. Some light variations are visible around the phase of the secondary minimum. The discussion reveals that BZ Eri is a complicated system.     

Photometric, spectroscopic and polarimetric variability of the weak-emission T Tauri star HD 288313

Photometric observations over three seasons show HD 288313 to be a light variable with a 2.2636-d period. The observed V amplitudes lie in the range of 0.06–0.15 mag. The star showed appreciable changes in the brightness at maximum and minimum of the light curve from season to season. The (   b − y   ) colour did not show any significant variation during the photometric cycle. The light variation appears to be caused by the rotational modulation of stellar flux by cool starspots distributed asymmetrically across the stellar longitudes. The Hα line strength in HD 288313 varied drastically from completely filled-in emission to almost full absorption, that is typical of a normal star of similar spectral type. The Hα equivalent width is found to show a clear rotational modulation only occasionally. Most of the time, chromospheric active regions are distributed well across the stellar longitudes, thereby suppressing obvious rotational modulations. Broad-band linear polarization measurements show HD 288313 to be a short period, low-amplitude polarization variable. The polarization variation is, apparently, rotationally modulated. Dust grain scattering in a non-spherical circumstellar envelope of a star with inhomogeneities in the surface brightness distribution seems to be the mechanism operating in producing the observed polarization.     

Photometric and spectroscopic evolution of the symbiotic nova V1016 Cygni after its outburst

We have constructed the light curves of the symbiotic nova V1016 Cyg for the period 1971–2007 in a homogeneous photometric system close to UBV using our observations with the Zeiss-600 SAI telescope. Based on the observational data obtained with the 125-cm SAI telescope in 2000–2007, we have performed absolute spectrophotometry of the star in the range λ3700–9300 Å. The derived line intensities are compared with the data of other authors in the preceding years (1965–1988). The behavior of nebular lines showed the variations in electron density and, probably, electron temperature in the [OIII] emission region caused by a variable stellar wind from the hot component. All the available observations of the star confirm the theoretical conclusion that the nova-like outburst of V1016 Cyg was produced by a thermonuclear flash in the accreted envelope of a white dwarf.     

The June 15, 1991 and June 26, 1999 white-light flares

Observational properties of two white-light flares (WLFs), on June 15, 1991, and June 26, 1999, are presented and compared. This is of particular interest, because the former was one of the most intense flares of X-ray class X12, while the latter was a compact flare of class M2.3. Significant differences between some flare parameters (GOES class, H_α classification, the number of WLF kernels and their location in the sunspot group, the size and duration of the WLF emission, and the peak flux density of the microwave emission) have been found. However, both these events had approximately the same powers of the emission per unit area in continuum near 658.0 nm: E = 1.5 × 10⁷ and 1.1. × 10⁷ erg cm^?2 s^?1 nm^?1. There is generally a good temporal coincidence between the microwave and hard X-ray emissions and the WLF emission during the impulsive phase, but the light curve of the WLF emission on June 26, 1999, shows a stronger correlation with the X-ray emission in the energy range 14–23 keV. Both flares can be classified by their spectral characteristics as type I white-light flares.     

Photometric study of 9 doubtful open clusters

We present results of a photometric investigation of 9 poorly studied apparent open clusters. While the aim of our survey was to determine structural and astrophysical parameters for these objects, they were found not to be physical groups of stars. BV wide‐field CCD photometry combined with the near‐infrared JHK_S data from the 2MASS and proper motions were used to study their nature. Detailed analysis of radial density profiles, morphology of decontaminated colourmagnitude diagrams, and proper motion distributions indicate that these stellar ensembles are projective chance alignments of physically unrelated stars. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric study of three contact binary systems

The first complete light curves of two eclipsing binaries in Camelopardalis, NX Cam and V584 Cam, are here presented together with the new observations of the system NSVS 2643686 obtained in 2014. The light curves were modelled using the latest version of the Wilson-Devinney code. Our results show that all the three systems have an extreme mass ratio q < 0.2, two of them, NX Cam and NSVS 2643686, having the fill-out f > 50%, belong to the class of the so called Deep Low Mass Ratio systems (DLMR) but show different physical characteristics. The two above systems are totally eclipsed binaries with the duration of the secondary eclipse of 87 min for NX Cam and 51 min for NSVS 2643686. The other system, V584 Cam, shows a middle fill-out value of f = 33% and low inclination. Using our Times of Minima (ToM) derived from the observations as well as those found in the literature, the ephemerides of the three systems are here revised. The absolute dimensions are estimated and, from statistical diagram, it is found that all the components of the systems follow the general pattern of the well known W UMa contact binaries.     

Photometric study of three ultrashort-period contact binaries

We carried out high-precision photometric observations of three eclipsing ultrashort-period contact binaries (USPCBs). Theoretical models were fitted to the light curves by means of the Wilson-Devinney code. The solutions suggest that the three targets have evolved to a contact phase. The photometric results are as follows: (a) 1SWASP?J030749.87?365201.7, \(q=0.439\pm0.003\), \(f=0.0\pm3.6\%\); (b) 1SWASP?J213252.93?441822.6, \(q=0.560\pm0.003\), \(f=14.2\pm1.9\%\); (c) 1SWASP?J200059.78+054408.9, \(q=0.436\pm0.008\), \(f=58.4\pm1.8\%\). The light curves show O’Connell effects, which can be modeled by the assumed cool spots. The cool spots models are strongly supported by the night-to-night variations in the \(I\)-band light curves of 1SWASP?J030749.87?365201.7. For a comparative study, we collected the whole set of 28 well-studied USPCBs with \(P < 0.24\) day. Thus, we found that most of them (17 of 28) are in shallow contact (i.e. fill-out factors \(f<20\%\)). Only four USPCBs have deep fill-out factors (i.e. \(f>50\%\)). Generally, contact binaries with deep fill-out factors are going to merge, but it is believed that USPCBs have just evolved to a contact phase. Hence, the deep USPCB 1SWASP?J200059.78+054408.9 seems to be a contradiction, making it very interesting. Particularly, 1SWASP?J030749.87?365201.7 is a zero contact binary in thermal equilibrium, implying that it should be a turn-off sample as predicted by the thermal relaxation oscillation (TRO) theory.