Analysis of the symbiotic star AG Pegasi

High and low dispersion IUE data are analyzed in conjunction with coincident ground based spectrophotometric scans and supplementary infrared photometry of the symbiotic object AG Pegasi. The IUE observations yield an improved value of E(B-V) = 0.12. The two stellar components are easily recognized in the spectra. The cool component may be an M1.7 III star and the hot component appears to have T (sub eff) of approximately 30000 K. The emission lines observed in the ultraviolet indicate two or three distince emitting regions. Nebular component ultraviolet intercombination lines suggest an electron density of several times 10 billion/cu cm

Simulation and Measurement of Pressure Rise in GIS 145 kV due to nternal Arcing

Internal arc testing of metal-enclosed, SF6 gas insulated switchgear (GIS) is defined by IEC 62271-203 and is not a part of mandatory type tests. However, due to the increasing demands on the safety of personnel, more often the implementation of this test is required in the tender documentation. According to IEC, the duration of the electric arc is related to the performance of the protective system determined by the first and second stage of protection. For the rated short-circuit current equal or higher than 40 kA, during the first stage of protection (0.1 s), no external effects on enclosure other than the operation of pressure relief device is permitted. During the second stage of protection (≤0.3 s) no fragmentation is permitted, but burn-through is acceptable. The test should be carried out on the GIS compartment with the smallest volume at nominal gas pressure. Since a newly developed GIS 145 kV is designed as a three-phase encapsulated, arc initiation is achieved by short connecting of all three phase conductors in the vicinity of a partition by means of a thin metal wire. This ensures that two electric arcs burn simultaneously commutating between the phases, so the possibility of enclosure burn-through in this type of GIS is minimized. In order to prevent the release of SF6 gas in the atmosphere during the testing, a test enclosure should be placed in a protective gastight enclosure filled with air or more often SF6 gas at pressure of 0.1 MPa. This test object configuration significantly complicates the pressure rise calculation and increases the testing cost. In order to prevent enclosure fragmentation, the pressure difference between the test enclosure and the protective enclosure during the test should always be less than the bursting pressure of test enclosure. Also, the protective enclosure should be designed to withstand the maximum pressure rise that may occur after pressure relief device opens. In order to assess the likelihood of passing the upcoming type test for newly developed GIS, a computer program for calculation of pressure and temperature in the test enclosure and protective enclosure was developed. The mathematical model is based on the paper of the working group CIGRE A3.24, published in 2014. The basic model shown in the paper is enhanced by the real properties of the SF6 gas/plasma, evaporation of the electrode material and the insulator ablation. The contribution of exothermic/endothermic reactions between the gas and the electrode material on the pressure and temperature rise was also considered. At the same time, the measurements of pressure rise in GIS enclosure and protective enclosure were carried out in Končar High Power Laboratory. The experiments performed on a copper and aluminum electrodes in SF6 gas confirmed significantly higher contribution of aluminum electrodes to the pressure and temperature rise compared to the copper electrodes. The computer program is verified by measurement results

A study of the interacting binary V 393 Scorpii

We present high resolution J-band spectroscopy of V 393 Sco obtained with the CRIRES at the ESO Paranal Observatory along with a discussion of archival IUE spectra and published broad band magnitudes. The best fit to the spectral energy distribution outside eclipse gives $T_{1}$= 19000 $\pm$ 500 $K$ for the gainer, $T_{2}$= 7250 $\pm$ 300 $K$ for the donor, $E(B-V)$= 0.13 $\pm$ 0.02 mag. and a distance of $d$= 523 $\pm$ 60 pc, although circumstellar material was not considered in the fit. We argue that V 393 Sco is not a member of the open cluster M7. The shape of the He I 1083 nm line shows orbital modulations that can be interpreted in terms of an optically thick pseudo-photosphere mimicking a hot B-type star and relatively large equatorial mass loss through the Lagrangian L3 point during long cycle minimum. IUE spectra show several (usually asymmetric) absorption lines from highly ionized metals and a narrow L$\alpha$ emission core on a broad absorption profile. The overall behavior of these lines suggests the existence of a wind at intermediate latitudes. From the analysis of the radial velocities we find $M_{2}/M_{1}$= 0.24 $\pm$ 0.02 and a mass function of $f$= 4.76 $\pm$ 0.24 M$\odot$. Our observations favor equatorial mass loss rather than high latitude outflows as the cause for the long variability.Comment: 13 pages, 14 figures, 7 tables. Accepted for publication in MNRAS, main journa

Equipotential Surfaces and Lagrangian points in Non-synchronous, Eccentric Binary and Planetary Systems

We investigate the existence and properties of equipotential surfaces and Lagrangian points in non-synchronous, eccentric binary star and planetary systems under the assumption of quasi-static equilibrium. We adopt a binary potential that accounts for non-synchronous rotation and eccentric orbits, and calculate the positions of the Lagrangian points as functions of the mass ratio, the degree of asynchronism, the orbital eccentricity, and the position of the stars or planets in their relative orbit. We find that the geometry of the equipotential surfaces may facilitate non-conservative mass transfer in non-synchronous, eccentric binary star and planetary systems, especially if the component stars or planets are rotating super-synchronously at the periastron of their relative orbit. We also calculate the volume-equivalent radius of the Roche lobe as a function of the four parameters mentioned above. Contrary to common practice, we find that replacing the radius of a circular orbit in the fitting formula of Eggleton (1983) with the instantaneous distance between the components of eccentric binary or planetary systems does not always lead to a good approximation to the volume-equivalent radius of the Roche-lobe. We therefore provide generalized analytic fitting formulae for the volume-equivalent Roche lobe radius appropriate for non-synchronous, eccentric binary star and planetary systems. These formulae are accurate to better than 1% throughout the relevant 2-dimensional parameter space that covers a dynamic range of 16 and 6 orders of magnitude in the two dimensions.Comment: 12 pages, 10 figures, 2 Tables, Accepted by the Astrophysical Journa

Fullerenol nanoparticles as a new delivery system for doxorubicin

Doxorubicin is a very potent chemotherapeutic drug, however its side effects limit its clinical use. The aim of this research was to investigate the properties of a fullerenol/doxorubicin nanocomposite, its potentially cytotoxic and genotoxic effects on malignant cell lines, as well as its toxicity towards zebra fish embryos. Chromatographic, NMR and mass spectral analysis of the nanocomposite imply that interactions between doxorubicin and fullerenol are non-covalent bonds. The stability of the nanocomposite was confirmed by the use of atomic force microscopy, dynamic light scattering and transmission electron microscopy. The nanocomposite, compared to the free doxorubicin at equivalent concentrations, significantly decreased the viability of MCF-7 and MDA-MB-231 cells. The flow cytometry results indicated that doxorubicin-loaded fullerenol could remarkably increase the uptake of doxorubicin suggesting that fullerenol might be a promising intracellular targeting carrier for the efficient delivery of antitumor drugs into tumor cells. The nanocomposite also affected cell cycle distribution. A genotoxicity test showed that the nanocomposite at all examined concentrations on MCF-7 and at lower concentrations on MDA-MB-231 cells caused DNA damage. Consequently, cell proliferation was notably reduced when compared with controls. Results of the zebrafish embryotoxicity assay showed a decreased overall toxicity, particularly cardiotoxicity and increased safety of the nanocomposite in comparison to doxorubicin alone, as manifested by a higher survival of embryos and less pericardial edema

Evidence of a Massive Black Hole Companion in the Massive Eclipsing Binary V Puppis

Up to now, most stellar-mass black holes were discovered in X-ray emitting binaries, in which the black holes are formed through a common-envelope evolu tion. Here we give evidence for the presence of a massive black hole candidate as a tertiary companion in the massive eclipsing binary V Puppis. We found that the orbital period of this short-period binary (P=1.45 days) shows a periodic variation while it undergoes a long-term increase. The cyclic period oscillation can be interpreted by the light-travel time effect via the presence of a third body with a mass no less than 10.4 solar mass. However, no spectral lines of the third body were discovered indicating that it is a massive black hole candidate. The black hole candidate may correspond to the weak X-ray source close to V Puppis discovered by Uhuru, Copernicus, and ROSAT satellites produced by accreting materials from the massive binary via stellar wind. The circumstellar matter with many heavy elements around this binary may be formed by the supernova explosion of the progenitor of the massive black hole. All of the observations suggest that a massive black hole is orbiting the massive close binary V Puppis with a period of 5.47 years. Meanwhile, we found the central close binary is undergoing slow mass transfer from the secondary to the primary star on a nuclear time scale of the secondary component, revealing that the system has passed through a rapid mass-transfer stage.Comment: Accepted for publication in ApJ

Episodic mass loss in binary evolution to the Wolf-Rayet phase: Keck and HST proper motions of RY Scuti's nebula

Binary mass transfer via Roche-lobe overflow (RLOF) is a key channel for producing stripped-envelope Wolf-Rayet (WR) stars and may be critical to account for SN Ib/c progenitors. RY Scuti is an extremely rare example of a massive binary star caught in this brief but important phase. Its toroidal nebula indicates equatorial mass loss during RLOF, while the mass-gaining star is apparently embedded in an opaque accretion disk. RY Scuti's toroidal nebula has two components: an inner ionised double-ring system, and an outer dust torus that is twice the size of the ionised rings. We present two epochs of Lband Keck NGS-AO images of the dust torus, plus three epochs of HST images of the ionised gas rings. Proper motions show that the inner ionised rings and the outer dust torus came from two separate ejection events roughly 130 and 250 yr ago. This suggests that RLOF in massive contact binaries can be accompanied by eruptive and episodic burst of mass loss, reminiscent of LBVs. We speculate that the repeating outbursts may arise in the mass gainer from instabilities associated with a high accretion rate. If discrete mass-loss episodes in other RLOF binaries are accompanied by luminous outbursts, they might contribute to the population of extragalactic optical transients. When RLOF ends for RY Scuti, the overluminous mass gainer, currently surrounded by an accretion disk, will probably become a B[e] supergiant and may outshine the hotter mass-donor star that should die as a Type Ib/c supernova.Comment: 15 pages, 7 figures, submitted to MNRA

Mass Transfer by Stellar Wind

I review the process of mass transfer in a binary system through a stellar wind, with an emphasis on systems containing a red giant. I show how wind accretion in a binary system is different from the usually assumed Bondi-Hoyle approximation, first as far as the flow's structure is concerned, but most importantly, also for the mass accretion and specific angular momentum loss. This has important implications on the evolution of the orbital parameters. I also discuss the impact of wind accretion, on the chemical pollution and change in spin of the accreting star. The last section deals with observations and covers systems that most likely went through wind mass transfer: barium and related stars, symbiotic stars and central stars of planetary nebulae (CSPN). The most recent observations of cool CSPN progenitors of barium stars, as well as of carbon-rich post-common envelope systems, are providing unique constraints on the mass transfer processes.Comment: Chapter 7, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe

UX Monocerotis as a W Serpentis binary

Using our new photometric and spectroscopic observations as well as all available published data, we present a new interpretation of the properties of the peculiar emission-line binary UX Mon. We conclude that this binary is in a rare phase of fast mass transfer between the binary components prior to the mass ratio reversal. We firmly establish that the orbital period is secularly decreasing at a rate of $\dot{P}=-0.260$ seconds per year. From several lines of reasoning, we show that the mass ratio of the component losing mass to the mass-gaining component $q$ must be larger than 1 and find our most probable value to be $q=1.15\pm0.1$. The BINSYN suite of programs and the steepest descent method were used to perform the final modeling. We modeled the star as a W Ser star with a thick disk around its primary. Although the remaining uncertainties in some of the basic physical elements describing the system in our model are not negligible, the model is in fair agreement with available observations. Only the nature of the light variations outside the primary eclipse remains unexplained