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Astron. Astrophys. 361, 379-387 (2000)

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6. The planet around HD 209458 and other 51 Peg-like planets

More recently, a 51 Peg-like planet, initially found from a precision Doppler survey, has been detected in a more direct way by its transit across its parent star, HD 209458 (Charbonneau et al. 1999; Henry et al. 2000; Robichon & Arenou 2000). This photometric detection allows one to determine the inclination of the orbit, then the exact mass ([FORMULA]) and to confirm definitely the existence of a Jupiter-like planet. Therefore this planet deserves a particular study. From Charbonneau et al. (1999) data, [FORMULA] and [FORMULA] days, one obtains [FORMULA], while Henry et al. 2000) data, [FORMULA] and [FORMULA] days, give [FORMULA]. This planet is then found to lie in a precise way at the predicted peak of probability density of the fundamental "orbital" [FORMULA]. This argument is reinforced by the recent probable spectral detection (Cameron et al. 1999), from Doppler-shifted reflected starlight, of the planet orbiting Tau Boo, which is also a fair [FORMULA] planet ([FORMULA]).

Eight 51 Peg like planets with [FORMULA] have now been discovered, and also two brown dwarfs (Mayor et al. 1997), HD 98230 ([FORMULA]) and HD 283750 ([FORMULA]). Except for one object at [FORMULA] (HD 217107), they are all clustered between [FORMULA] and 1.1 (see Fig. 4). The mean orbital velocity of these planets is [FORMULA] km/s, i.e., they constitute a direct and precise achievement of the fundamental constant [FORMULA].

[FIGURE] Fig. 4. Observed distribution of [FORMULA] for exoplanets and brown dwarfs with [FORMULA], where a is the orbital semi-major axis and M the parent star mass, compared with the theoretical prediction (peak of probability density of the orbital [FORMULA] expected at [FORMULA]).

Before concluding, note that the observed distribution of small [FORMULA] values suggests that there exists a new hierarchy level of structuration based on [FORMULA] km/s for 51 Peg types exoplanets (which would imply the possibility of finding exoplanets lying at [FORMULA] from their star). This would agree with our result (Nottale et al. 1997) that the [FORMULA] orbital of the outer solar system is actually sub-structured in terms of the inner solar system itself. Moreover, the distribution of the perihelions of intramercurial comets show peaks at predicted positions corresponding to constants [FORMULA] km/s and [FORMULA] km/s (Nottale & Schumacher in preparation).

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© European Southern Observatory (ESO) 2000

Online publication: September 5, 2000