In a previous paper, we have shown the important possibility of detecting
extra-solar cometary activity from a photometric survey
(Lecavelier des Etangs et al. 1999, hereafter LVF 99).
Taking the COROT space mission as an example, we consider that
a survey of several tens of thousands of stars with a photometric accuracy
of
during several months will be achievable
in the very near future (Baglin et al. 1997).
We have shown that the occultation of a star by an orbiting extra-solar comet can result in a photometric variation of the star. In most cases the light curve shows a very peculiar "rounded triangular'' shape; but some light curves can mimic planetary occultation. With only a small number of simulations available, it was not possible to accurately determine the proportion of light curves which mimic the planetary occultation.
We also gave the probabilities of detecting comets using a large photometric survey. We found that by the observation of several tens of thousands of stars, it should be possible to detect several hundreds of occultations per year. This last number is larger than the number of expected planetary occultations by Jupiter-like planets, making the cometary occultations a powerful tool to look into the planetary systems' structure and evolution.
However, due to the large computer-time needed by the simulations, only a small set of parameters had been investigated. To better analyze the observations and to determine the specific effects of the parameters, a wide range of input parameters must be considered. We thus decided to compute a large grid of stellar light variations due to the cometary occultations and make the results widely available through an electronic access on the web server http://www.iap.fr/users/lecaveli/grid/
The aim of this work is to provide a large database of simulated cometary occultations which can be used to develop the reduction methods for the photometric surveys and can help for the analysis of future observational results. To accomplish this task, we used the model and code presented in Lecavelier des Etangs et al. (1999) (LVF 99). The database is presented in the form of a list of files. Each file corresponds to different values of the parameters. Six parameters are needed to define the position in the grid: the dust size distribution, the type of the central star, the dust production rate, the periastron distance, the longitude of the periastron, and the inclination of the comet orbit. Each file gives the extinction and scattering of the star light by the cometary cloud as a function of time at three wavelengths: 400 (B), 800 (R) and 2200 nm (K).
In Sect. 2, we describe the model parameters needed to define a cometary occultation. Examples of expected light curves are given in Sect. 3. Estimates of the proportion of light curves which could be mistaken as due to planetary occultation are given in Sect. 4. The conclusion is in Sect. 5.
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