No evidence of a hot Jupiter around HD 188753 A

Abstract

Context. The discovery of a short-period giant planet (a hot Jupiter) around the primary component of the triple star system HD 188753 has often been considered as an important observational evidence and as a serious challenge to planet-formation theories. Aims. Following this discovery, we monitored HD 188753 during one year to better characterize the planetary orbit and the feasibility of planet searches in close binaries and multiple star systems. Methods. We obtained Doppler measurements of HD 188753 with the ELODIE spectrograph at the Observatoire de Haute-Provence. We then extracted radial velocities for the two brightest components of the system using our multi-order, two-dimensional correlation algorithm, TODCOR. Results. Our observations and analysis do not confirm the existence of the short-period giant planet previously reported around HD 188753 A. Monte Carlo simulations show that we had both the precision and the temporal sampling required to detect a planetary signal like the one quoted. Conclusions. From our failure to detect the presumed planet around HD 188753 A and from the available data on HD 188753, we conclude that there is currently no convincing evidence of a close-in giant planet around HD 188753 A.

Precise radial velocities of giant stars

“…The only unsaturated photometry for HD 59686 A was acquired by the Hipparcos mission (ESA 1997) between March 16, 1990 andMarch 10, 1993 (2447966.9 -2449057.2 JD), more than six years before first RV observations of HD 59686 A. The Hipparcos data set consists of 96 measurements with 5.6 mmag mean error, 5.6 mag mean value, and a standard deviation of 5.5 mmag, similar to the mean error of the measurements.…”

“…This scenario has been invoked in the past to explain the origin of a giant planet in the system HD 188753 (Pfahl 2005;Portegies Zwart & McMillan 2005). However, the existence of this planet was recently proved false by Eggenberger et al (2007). Pfahl & Muterspaugh (2006) estimated that dynamical interaction in the parent star clusters would deposit giant planets in roughly 0.1% of binary systems with semi-major axis of a < 50 au.…”

Stellar wobble caused by a nearby binary system: eccentric and inclined orbits

“…A hot Jupiter with a 3.35 day period orbit around the A star was announced by Konacki (2005) but this was later challenged by Eggenberger et al (2007) who claimed they could not find evidence for this planet. This shows the difficulty in identifying planets of stars with a nearby binary system.…”

“…As noted previously, when observing the target star to obtain its spectrum we are likely to also detect light from the nearby stars. In the case of HD 188753, the contribution of Bb is modest since this star is faint but we cannot ignore the contribution of Ba, which is blended within the target star A's spectrum (Eggenberger et al 2007). The parameters of this triple system are M = 1.06 M , M 1 = 0.96 M , M 2 = 0.67 M , a = 12.3 AU, a b = 0.67 AU, e = 0.5, e b = 0.1, and I = 34 • (Konacki 2005).…”

Exoplanet Observations

“…On the basis of these methods [56], a planet was claimed to have been detected around the primary of a close triple star system (HD 188753A), but this is controversial because with the other [57] method the planet was not detected. This further illustrates the difficulty of reliably detecting planets around close multiples.…”