| Author(s): | Wielen, R. |
| Title: | Searching for VIMs: An astrometric method to detect the binary nature of double stars with a variable component |
| Source: | Astron. Astrophys. 314, 679 |
| Year: | 1996 |
| Abstract: | The photo-center of a close double star in which one component has a variable luminosity moves on the sky in the same rhythm as the total luminosity of the system varies in time. This provides an astrometric method to detect the binary nature of the system if more direct methods fail. We propose to call such systems `variability-induced movers', or VIMs. We discuss the required properties of a system for being detected as a VIM, such as separation, light amplitude, and relative brightness of the components. High-precision astrometric instruments like the HIPPARCOS satellite or the proposed mission GAIA should be able to detect a significant number of VIMs among the variables. In a proper astrometric treatment of variables, all the observed variable stars should be tested for beings VIMs and treated as such if necessary. We present a quantitative method to handle VIMs by means of the available astrometric and photometric observations carried out by HIPPARCOS. Different schemes can be applied to various cases, e.g. for binaries with a fixed relative geometry or for astrometric binaries with orbital motions. If a close binary has (constant or variable) components of different colour and if the observations are carried out in at least two photometric pass-bands, then the position (and sometimes also the proper motion) of the photo-center of this double star depends on the wavelength, i.e. on the pass-band. Objects with such `colour-induced displacements' of their photo-centers may be called `CIDs'. A method to detect such binaries and to treat CIDs is outlined. |
| Preprint issued: | December 1995 |
| Remarks: |
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