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

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 () and to confirm definitely the existence of a Jupiter-like planet. Therefore this planet deserves a particular study. From Charbonneau et al. (1999) data, and days, one obtains , while Henry et al. 2000) data, and days, give . This planet is then found to lie in a precise way at the predicted peak of probability density of the fundamental "orbital" . 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 planet ().

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

Fig. 4. Observed distribution of for exoplanets and brown dwarfs with , 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 expected at ).

Before concluding, note that the observed distribution of small values suggests that there exists a new hierarchy level of structuration based on km/s for 51 Peg types exoplanets (which would imply the possibility of finding exoplanets lying at from their star). This would agree with our result (Nottale et al. 1997) that the 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 km/s and km/s (Nottale & Schumacher in preparation).

© European Southern Observatory (ESO) 2000

Online publication: September 5, 2000
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