Symbiotic stars as possible progenitors of SNe Ia: binary parameters and overall outlook

Symbiotic stars are interacting binaries in which the first-formed white dwarf accretes and burns material from a red giant companion. This paper aims at presenting physical characteristics of these objects and discussing their possible link with progenitors of type Ia supernovae.Comment: 4 pages. Invited rewiev at "Binary Paths to Type Ia Supernovae", IAU Symposium No. 281, R. Di Stefano & M. Orio, eds., Cambridge University Pres

Mm/submm observations of symbiotic binary stars: implications for the mass loss and mass exchange

We discuss mm/submm spectra of a sample of symbiotic binary systems, and compare them with popular models proposed to account for their radio emission. We find that radio emission from quiescent S-type systems originates from a conical region of the red giant wind ionized by the hot companion (the STB model), whereas more complicated models involving winds from both components and their interaction are required to account for radio emission of active systems. We also find that the giant mass-loss rates derived from our observations are systematically higher than those for single cool giants. This result is in agreement with conclusions derived from IRAS observations and with requirements of models for the hot component.Comment: 7 pages, 8 figures. Paper presented at COSPAR 2000 "New results in FIR and Submm Astronomy", to be published in Advances in Space Researc

The secondary minimum in YY Her: Evidence for a tidally distorted giant

We present and analyze quiescent UBVRI light curves of the classical symbiotic binary YY Her. We show that the secondary minimum, which is clearly visible only in the quiescent VRI light curves, is due to ellipsoidal variability of the red giant component. Our simple light curve analysis, by fitting of the Fourier cosine series, resulted in a self-consistent phenomenological model of YY Her, in which the periodic changes can be described by a combination of the ellipsoidal changes and a sinusoidal changes of the nebular continuum and line emission.Comment: 5 pages, 2 figures, to appear in Astronomy & Astrophysic

Line formation regions of the UV spectrum of CI Cygni

We have examined radial velocities and fluxes of ultraviolet emission lines at different epochs, deduced from archival IUE and GRHS/HST spectra. 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 HeII lines. Possible explanations of the redshift and the high resolution GHRS CIV 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.Comment: 8 pages, 4 figures, A&A accepte

Optical spectroscopy and X-ray observations of the D-type symbiotic star EF Aql

We performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with SALT, we determine the temperature ($\sim$55 000 K) and the luminosity ($\sim$ 5.3 $L_\odot$) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements. We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$, which means that EF Aql is consistent with the faintest X-ray systems detected so far. Otherwise we detected it with the UVOT instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4$\pm$0.3 d caused by the pulsations of the Mira-type donor star. The spectra are available upon request from the authors.Comment: Accepted for publication in MNRA

Eyes on the enterprise: problematising the concept of a teaching-research nexus in UK higher education

Existing research into the relationship between teaching and research in higher education is mainly normative and atheoretical, resulting in assumptions of a close and beneficial connection between them. We problematise the idea of a nexus by undertaking a critical examination of the concept through the lens of educational ideologies to theorise the changes over time that shape the ways teaching and research are practised. Two hundred seven academic staff in the Humanities and Social Sciences were surveyed in 10 universities in England and Wales; the universities were identified as having strength in teaching, research, or in both. Along with analysis of interviews with senior managers at these universities, findings suggest that systemic forces which separate teaching and research are evident in institutional contexts with implications for the idea of a nexus. While the nexus may exist in theory, in practice, we argue that teaching and research can be pulled in different directions by institutional priorities. Furthermore, in institutions which adopt an enterprise ideology, there are signs of a nascent nexus emerging between research and innovation

On the nature of the cool component of MWC 560

Context.MWC 560 (V694 Mon) is one of the most enigmatic symbiotic system with a very active accretion-powered hot component. Such activity can be supported only by a luminous asymptotic giant branch star, i.e. a Mira or SR variable, with a high mass-loss rate. It is also a very unusual jet source because the jet axis lies practically parallel to the line of sight. Aims. The aims of our study are the determination of the evolutionary status of the cool component of MWC 560. Methods. Our methods involve analysis of near-IR JHKL and optical light curves. Results. The cool component of MWC 560 pulsates with a period of ∼340 days, and it is probably a red SR variable on the thermally pulsing AGB. The high mass-loss rate expected for such a star is sufficient to power the observed activity of the hot companion