Linear polarization of a group of symbiotic systems

We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin.Facultad de Ciencias Astronómicas y Geofísica

Linear polarization of a group of symbiotic systems

We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin.Facultad de Ciencias Astronómicas y Geofísica

Spectroscopic orbits and variations of RS Ophiuchi

The aims of our study are to improve the orbital elements of the giant, and to derive the spectroscopic orbit for the white dwarf companion. Spectral variations related to the 2006 outburst are also studied. Methods. We performed an analysis of about seventy optical and near infrared spectra of RS Oph that were acquired between 1998 and June 2008. The spectroscopic orbits have been obtained by measuring the radial velocities of the cool component absorption lines and the broad Hα emission wings, which seem to be associated with the hot component. A set of cF-type absorption lines were also analyzed for a possible connection with the hot component motion. Results. A new period of 453.6 days, and a mass ratio, q = Mg/Mh = 0.59 ± 0.05, were determined. Assuming a massive white dwarf as the hot component (Mh = 1.2 − 1.4M⊙) the red giant mass is Mg = 0.68 − 0.80M⊙ and the orbit inclination, i = 49◦ − 52◦. The cF-type lines are not associated with either binary component, and are most likely formed in the material streaming towards the hot component. We also confirm the presence of the Li I doublet in RS Oph and its radial velocities fit very well the M-giant radial velocity curve. Regardless of the mechanism involved to produce lithium, its origin is most likely from within the cool giant rather than material captured by the giant at the time of the nova explosion. The quiescent spectra reveal a correlation of the HI and He I emission line fluxes with the monochromatic magnitudes at 4800 Å indicating that the hot component activity is responsible for those flux variations. We also discuss the spectral characteristics around 54–55 and 240 days after the 2006 outburst. In April 2006 most of the emission lines present a broad pedestal with a strong and narrow component at about -20 kms−1 and two other extended emission components at -200 and +150 kms−1. These components could originate in a bipolar gas outflow supporting the model of a bipolar shock-heated shell expanding through the cool component wind perpendicularly to the binary orbital plane. Our observations also indicate that the cF absorption system was disrupted during the outburst, and restored about 240 days after the outburst, which is consistent with the resumption of accretion.Facultad de Ciencias Astronómicas y Geofísica

Spectroscopic orbits and variations of RS Ophiuchi

The aims of our study are to improve the orbital elements of the giant, and to derive the spectroscopic orbit for the white dwarf companion. Spectral variations related to the 2006 outburst are also studied. Methods. We performed an analysis of about seventy optical and near infrared spectra of RS Oph that were acquired between 1998 and June 2008. The spectroscopic orbits have been obtained by measuring the radial velocities of the cool component absorption lines and the broad Hα emission wings, which seem to be associated with the hot component. A set of cF-type absorption lines were also analyzed for a possible connection with the hot component motion. Results. A new period of 453.6 days, and a mass ratio, q = Mg/Mh = 0.59 ± 0.05, were determined. Assuming a massive white dwarf as the hot component (Mh = 1.2 − 1.4M⊙) the red giant mass is Mg = 0.68 − 0.80M⊙ and the orbit inclination, i = 49◦ − 52◦. The cF-type lines are not associated with either binary component, and are most likely formed in the material streaming towards the hot component. We also confirm the presence of the Li I doublet in RS Oph and its radial velocities fit very well the M-giant radial velocity curve. Regardless of the mechanism involved to produce lithium, its origin is most likely from within the cool giant rather than material captured by the giant at the time of the nova explosion. The quiescent spectra reveal a correlation of the HI and He I emission line fluxes with the monochromatic magnitudes at 4800 Å indicating that the hot component activity is responsible for those flux variations. We also discuss the spectral characteristics around 54–55 and 240 days after the 2006 outburst. In April 2006 most of the emission lines present a broad pedestal with a strong and narrow component at about -20 kms−1 and two other extended emission components at -200 and +150 kms−1. These components could originate in a bipolar gas outflow supporting the model of a bipolar shock-heated shell expanding through the cool component wind perpendicularly to the binary orbital plane. Our observations also indicate that the cF absorption system was disrupted during the outburst, and restored about 240 days after the outburst, which is consistent with the resumption of accretion.Facultad de Ciencias Astronómicas y Geofísica

Line formation regions of the UV spectrum of CI Cygni

Aims. They are the interpretation of the emission line formation regions in CI Cygni. Methods. They involve the examination of radial velocities and fluxes of ultraviolet emission lines at different epochs, deduced from archival IUE and GRHS/HST spectra. Results. The line fluxes give electron densities and were in addition used to calculate emission measures, suggesting line formation in regions rather smaller than the binary separation. Examination of the radial velocities led to us to find a systematic redshift of the high ionization resonance lines with respect to the intercombination, and He ii lines. Possible explanations of the redshift and the high resolution GHRS C iv profile are discussed. We favour that involving resonance line absorption by a circum-binary region most probably in an asymmetric wind interaction shell or in a wind from the accretion disk.Facultad de Ciencias Astronómicas y Geofísica

Evolution of the symbiotic nova RX Puppis

We present and discuss a hundred year history of activity of the hot component of RX Pup based on optical photometry and spectroscopy. The outburst evolution of RX Pup resembles that of other symbiotic novae whereas at quiescence the hot component shows activity (high and low activity states) resembling that of symbiotic recurrent novae T CrB and RS Oph.Facultad de Ciencias Astronómicas y Geofísica

Evolution of the symbiotic nova RX Puppis

We present and discuss a hundred year history of activity of the hot component of RX Pup based on optical photometry and spectroscopy. The outburst evolution of RX Pup resembles that of other symbiotic novae whereas at quiescence the hot component shows activity (high and low activity states) resembling that of symbiotic recurrent novae T CrB and RS Oph.Facultad de Ciencias Astronómicas y Geofísica

The chemically peculiar double-lined spectroscopic binary HD 90264

Context. HD 90264 is a chemically peculiar (CP) double-lined spectroscopic binary system of the type He-weak. Double-lined binaries are unique sources of data for stellar masses, physical properties, and evolutionary aspects of stars. Therefore, the determination of orbital elements is of great importance to study how the physical characteristics of CP stars are affected by a companion. Aims. We carried out a detailed spectral and polarimetric study of the spectroscopic binary system HD 90264 to characterize its orbit, determine the stellar masses, and investigate the spectral variability and possible polarization of the binary components. Methods. We employed medium-resolution echelle spectra and polarimetric data obtained at the 2.15-m telescope at CASLEO Observatory, Argentina. We measured radial velocities and line equivalent widths with IRAF packages. The radial velocity curves of both binary components were obtained combining radial velocity data derived from the single line of Hg ii λ3984 Å and the double lines of Mg ii λ4481 Å. Polarimetric data were studied by means of the statistical method of Clarke & Stewart and the Welch test. Results. We found that both components of the binary system are chemically peculiar stars, deficient in helium, where the primary is a He variable and the secondary is a Hg-Mn star. We derived for the first time the orbital parameters of the binary system. We found that the system has a quasi-circular orbit (e ∼ 0.04) with an orbital period of 15.727 days. Taking into account the circular orbit solution, we derived a mass ratio of q = MHe−w/MHg−Mn = 1.22. We also found a rotational period of around 15−16 days, suggesting a spin-orbit synchronization. Possible signs of intrinsic polarization have also been detected. Conclusions. HD 90264 is the first known binary system comprised of a He variable star as the primary component and a Hg-Mn star as the secondary one.Facultad de Ciencias Astronómicas y Geofísica

The spectroscopic orbits and physical parameters of GG car

GG Car is a peculiar B type star with emission lines classified as a B[e] supergiant star. In this work we present a spectral analysis of this system based on spectra obtained at Casleo. We fit the spectral energy distribution adopting a model for the gas and dust circumstellar components and thus we obtain the physical parameters of the star and its environment.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Pseudomonas Aeruginosa Pilin Glycosylation: The Role of the Pilin Glycan in Pilus Solubility, Function, and Assembly Blank

Pseudomonas aeruginosa strains producing group I type IVa pili comprise over 50% of the clinical isolate population. The pilus lateral surface of these strains is characterized by the attachment of an O-antigen repeating unit to each pilin monomer. O-antigen (glycan) structural analysis provided information on two possible characteristics, charge and size. Solubility experiments of fully, partially, and non-glycosylated P. aeruginosa 1244 pili showed that a full length glycan was required for maximum pilus solubility. Reduced solubility suggested an increased pilus surface hydrophobicity which was supported by protein modeling. While having no effect on the wild type strain, ionic strengths found at many host infection sites inhibited surface and subsurface twitching motility of strain 1244G7, an isogenic mutant unable to glycosylate pilin. This effect was reversed by mutant complementation. A PCR method for assigning R-type (glycan) was developed and conducted for 206 clinical isolates. It was expected that the R-types would be evenly distributed across all isolates, but there was a significant prevalence for the R5 type which encodes the O6 serotype. Verification of the R5 strains was conducted with O6 specific antibodies confirming the genetic classification of these isolates. Results suggest that the increased prevalence of the R5-type as the pilin glycan could potentially lead to its use in a multi-component vaccine or therapeutic for P. aeruginosa infections. Clinical isolates were screened for group I pilin producing strains. Unexpectedly, strains producing non-glycosylated group I pilin were found, prompting the characterization of this altered phenotype. Sequencing and complementation results indicated that non-glycosylation was caused by defects in the main components of glycosylation: pilA, pilO, and the O-antigen biosynthesis pathway. Only one co-phenotype was found among these strains, reduced piliation. Additional characterization of the cause for reduced piliation showed that the presence of non-glycosylated pilin alone was enough to reduce surface pili in these mutant clinical isolates. A pilO knockout was engineered which also showed a loss of glycosylation and a marked reduction in piliation. Providing this mutant with a functional pilO complemented both phenotypes. Overall, these results show that the presence of glycan is important for pilus function, solubility and piliation