Site Map
Contacts
Follow us on Facebook Follow us on Twitter YouTube channel
Centro de Astrofísica da Universidade do Porto

Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots

F. Pont, R. L. Gilliland, C. Moutou, F. Bouchy, T. M. Brown, D. Charbonneau, M. Mayor, D. Queloz, N. C. Santos, S. Udry

Abstract
We monitored three transits of the giant gas planet around the nearby K dwarf HD 189733 with the ACS camera on the Hubble Space Telescope. The resulting very-high accuracy lightcurve (signal-to-noise ratio near 15000 on individual measurements, 35000 on 10-minute averages) allows a direct geometric measurement of the orbital inclination, radius ratio and scale of the system: i = 85.68 ± 0.04, Rpl/R∗ = 0.1572 ± 0.0004, a/R∗ = 8.92 ± 0.09. We derive improved values for the stellar and planetary radius, R∗ = 0.755 ± 0.011 R⊙, Rpl = 1.154 ± 0.017 RJ , and the transit ephemerides, Ttr = 2453931.12048 ± 0.00002 + n · 2.218581 ± 0.000002. The HST data also reveal clear evidence of the planet occulting spots on the surface of the star. At least one large spot complex (> 80000 km) is required to explain the observed flux residuals and their colour evolution. This feature is compatible in amplitude and phase with the variability observed simultaneously from the ground. No evidence for satellites or rings around HD 189733b are seen in the HST lightcurve. This allows us to exlude with a high probability the presence of Earth-sized moons and Saturn-type debris rings around this planet. The timing of the three transits sampled is stable to the level of a few seconds, excluding a massive second planet i outer 2:1 resonance.

Astronomy and Astrophysics
Volume 476, Page 1347
December 2007

>> ADS>> DOI

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

Proceed on CAUP's website|Go to IA website