Photometric mode identification methods of nonradial pulsations in eclipsing binaries I. -- Dynamic Eclipse Mapping

Abstract

We present the Dynamic Eclipse Mapping (DEM) method designed specifically to reconstruct the surface intensity patterns of non-radial stellar oscillations in eclipsing binaries. The method needs a geometric model of the binary, accepts the light curve and the detected pulsation frequencies on input, and on output yields estimates of the pulsation patterns, in form of images -- thus allowing a direct identification of the surface mode numbers$(\ell ,m)$. Since it has minimal modelling requirements and can operate on photometric observations in arbitrary wavelength bands, DEM is well suited to analyze the wide-band time series collected by space observatories. The method was extensively tested on simulated data, in which almost all photometrically detectable modes with a latitudinal complexity $\ell -|m|\le 4$ were properly restored. Multimode pulsations can be also reconstructed in a natural manner, as well as pulsations on components with tilted rotation axis of known direction. It can also be used in principle to isolate the contribution of hidden modes from the light curve. Sensitivity tests show that moderate errors in the geometric parameters and the assumed limb darkening can be partially tolerated by the inversion, in the sense that the lower degree modes are still recoverable. Tidally induced or mutually resonant pulsations, however, are an obstacle that neither the eclipse mapping, nor any other inversion technique can ever surpass. We conclude that, with reasonable assumptions, Dynamic Eclipse Mapping could be a powerful tool for mode identification, especially in moderately close eclipsing binary systems, where the pulsating component is not seriously affected by tidal interactions so that the pulsations are intrinsic to them, and not a consequence of the binarity.

Accepted for publication in MNRAS. 16 pages, 11 figures and 5 tables

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