Friday, August 25, 2006

H. Hensberge: Modern Techniques for the Analysis of Spectroscopic Binaries (invited talk, Tue, Aug. 22)

This talk within Symposium 240 was about how to extract information from spectroscopic binary (SB) spectra by reconstruction and analysis of the component spectra.

At the beginning, the importance of the line broadening function was discussed. For reconstruction, it is assumed that the observed spectrum is composed of a sum of weighted intrinsic component spectra. The intrinsic component spectra are time-independent (the shape of the spectral lines does not depend on orbital phase), but the weights may be time dependent (light and line strength variability). The reconstruction technique is based on velocity differences between the components and their time-variations. In order to apply this technique successfully, one should aim at observations homogeneously distributed in velocity and not concentrated at extreme line separation.

Historically, SB spectra have been analysed by the following techniques:
  • Cool giant + hotter, less evolved star (very different stars): subtract template for cool giant (Griffin & Griffin 1986)
  • Tomographic separation (Bagnulo & Gies 1991)
  • Disentangling in velocity space (Simon & Sturm 1994)
  • Disentangling in Fourier space (Hadrava 1995)
  • Iteratively correlate - shift - co-add (Marchenko 1998, Gonzalez & Levato 2006)
The application domain of the reconstruction ranges from being a detection tool to detailed analysis of the component spectra. It can be applied over a large range of S/N, from UV to IR, for single lines to large wavelength ranges, and for spectral types from O to G.

As an example, the sharp-lined F8 + close binary (F8 + late-G) system RV Crateris was presented (details in ESO conference proceedings by Hensberge et al.). The disentangling technique revealed 3 components.

The use of the component spectra in astrophysics range from determining fundamental stellar parameters, testing evolutionary models, the spectroscopic detection of eclipses to spectroscopic determination of light ratios. For example, the chemical composition of DG Leo Ab is presented in Fremat, Lampens & Hensberge 2005, MNRAS 356, 545).

One can work in Fourier or velocity space. The options for velocity space are to mask blemishes or unwanted components in the input spectra, weight spectral bins and do an error analysis of the reconstructed components. The options for Fourier space are to analyse the origin and shape of spurious components in the reconstructed component spectra and to weight the Fourier components.

A problem with the technique is that the solutions may not be unique. As a way out one can use external information (photometry, models).

Prospects are:
  • Retrieving astrophysical information by modelling the asymmetrical broadening function
  • Extending the application domain of the spectral disentangling techniques in order to include better physics


At 11:14 PM, Anonymous Anonymous said...

A lovely presentation leaving much to ponder. Does not every set of spectroscopic orbs (such as human eyes) glean unique information by reconstructing and ordering spatial components according to its unique physical wants, needs, and requirements?


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