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The work of Commission 25 covers a wide range of topics concerning the measurement of magnitude, colour and polarisation of astronomical objects. As such, the area of interest covers virtually every field of astrophysical research in the visual and infrared spectral domain. Our reports cover some aspects of photometry and polarimetry as a technique rather than being an account of research highlights over the last three years.
This review is concerned with the following topics: 1. The occurrence of chemical peculiar stars in binaries; 2. Determination of masses of CP stars; 3. Determination of radii of CP stars; 4. CP stars in clusters. The paper emphasizes the literature from the 23rd Liege Colloquium in 1981 on, and does not refer systematically to earlier papers.
20 Leo is a spectroscopic triple system composed of 3 very similar stars, one of which seems to be a δ Sct star. Observations at high spectral and high time resolution have been obtained at the Observatoire de Haute Provence with the ELODIE spectrograph on the 1.9-m telescope. The spectra were taken during 7 nights in 2003 January and cover the whole optical domain from 3900 to 6800 Å. We used a Fourier transform technique recently developed by P. Hadrava to disentangle the combined spectrum. Application of the method allows the derivation of radial velocities at all orbital phases (even at phases of complete blending), as well as individual spectra for each component. From these computations we deduced more accurate individual radial velocities and improved orbital parameters describing the motion of the inner binary. Model atmospheres were used to analyze each individual spectrum and determine stellar fundamental parameters of the three components such as effective temperature, surface gravity and projected rotation velocity.
Southern bright CP2 stars mentioned in the literature to be constant in light are observed to search for possible variations over months or years. Presently (up to end of April, 1985) four candidate long-period CP2 stars are detected, one of which had already, been noticed in the literature as a slow spectroscopic variable.
V2107 Cyg is located in the direction of Cyg OB1 stellar association. The eclipsing system consists of an early-B primary and a late-B type secondary component contributing about 6% of the total light. Line profile variability and photometry suggest strongly it is a β Cep type non-radial pulsator. A signature of the faint secondary component is for the first time identified through spectra disentangling.
DV Cam is a triple system showing the diversity of the physics of photospheres of B-type stars at a common age: an SPB star in a wide orbit around a close binary consisting of an ultra-slowly rotating helium-weak star and a much faster rotating mid-B star.
In the framework of the EVRENA project, high-resolution spectra of northern eclipsing close binaries in stellar groups are obtained with the HERMES Echelle spectrograph at the Mercator telescope (Roque de los Muchachos Observatory). This contribution gives the first results on DV Camelopardalis.
As we have noted before, the WG-IR was created following a Joint Commission Meeting at the IAU General Assembly in Baltimore in 1988, a meeting that provided both diagnosis and prescription for the perceived ailments of infrared photometry at the time. The results were summarized in Milone (1989). The challenges involve how to explain the failure to systematically achieve the milli-magnitude precision expected of infrared photometry and an apparent 3% limit on system transformability. The proposed solution was to re-define the broadband Johnson system, the passbands of which had proven so unsatisfactory that over time effectively different systems proliferated although bearing the same JHKLMNQ designations; the new system needed to be better positioned and centered in the atmospheric windows of the Earth's atmosphere, and the variable water vapour content of the atmosphere needed to be measured in real time to better correct for atmospheric extinction.
DG Leo is a spectroscopic triple system showing $\delta$ Scuti type photometric and spectroscopic variations. The three components have nearly equal masses but different chemical compositions in the outer layers. All three are potential pulsators. Frequency analyses of the photometric data were carried out using various methods. These global results together with those of the spectroscopic analysis permit us to discuss of the behaviour of each component with respect to pulsation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
Components of multiple systems generally originate from the same protostellar environment. Their similarities or differences in surface chemical composition therefore relates to their individual evolutionary paths (stellar evolution, rotation) and the possible influence of a close companion.
DG Leo is a spectroscopic hierarchical triple system with almost equal-mass late-A type components. Observations with high time and high spectral resolution were used to disentangle the spectrum of each component from the composite spectra. A detailed abundance analysis of the component spectra reveals that the wide companion has a nearly solar-like composition, while both components in the close binary show Am type peculiarities.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
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