Extrasolar planets and brown dwarfs around A-F type stars - VII. Theta Cygni radial velocity variations: planets or stellar phenomenon?

Abstract

(abridged) In the frame of the search for extrasolar planets and brown dwarfs around early-type main-sequence stars, we present the results obtained on the early F-type star Theta Cygni. Elodie and Sophie at OHP were used to obtain the spectra. Our dedicated radial-velocity measurement method was used to monitor the star's radial velocities over five years. We also use complementary, high angular resolution and high-contrast images taken with PUEO at CFHT. We show that Theta Cygni radial velocities are quasi-periodically variable, with a ~150-day period. These variations are not due to the ~0.35-Msun stellar companion that we detected in imaging at more than 46 AU from the star. The absence of correlation between the bisector velocity span variations and the radial velocity variations for this 7 km/s vsini star, as well as other criteria indicate that the observed radial velocity variations are not due to stellar spots. The observed amplitude of the bisector velocity span variations also seems to rule out stellar pulsations. However, we observe a peak in the bisector velocity span periodogram at the same period as the one found in the radial velocity periodogram, which indicates a probable link between these radial velocity variations and the low amplitude lineshape variations which are of stellar origin. Long-period variations are not expected from this type of star to our knowledge. If a stellar origin (hence of new type) was to be confirmed for these long-period radial velocity variations, this would have several consequences on the search for planets around main-sequence stars, both in terms of observational strategy and data analysis. An alternative explanation for these variable radial velocities is the presence of at least one planet of a few Jupiter masses orbiting at less than 1 AU. (abridged)

9 pages, accepted in AA

References in corpus (10)

• Validation of the new Hipparcos reduction
• Planet formation around stars of various masses: The snow line and the frequency of giant planets
• Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
• Planets around evolved intermediate-mass stars. I. Two substellar companions in the open clusters NGC 2423 and NGC 4349
• Search for exoplanets with the radial-velocity technique: quantitative diagnostics of stellar activity
• Rapid Formation of Gas Giant Planets around M Dwarf Stars
• An Eccentric Hot Jupiter Orbiting the Subgiant HD 185269
• Extrasolar planets and brown dwarfs around A-F type stars VI. High precision RV survey of early type dwarfs with HARPS
• A Planetary Mass Companion to the K0 Giant HD 17092
• Planetary Companions around Three Intermediate-Mass G and K Giants: 18 Del, xi Aql, and HD 81688

Cited by in corpus (12)

• Limits on Planetary Companions from Doppler Surveys of Nearby Stars
• Interferometric radii of bright Kepler stars with the CHARA Array: θ Cygni and 16 Cygni A and B
• Evidence for the Tidal Destruction of Hot Jupiters by Subgiant Stars
• A new interferometric study of four exoplanet host stars : θ Cygni, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis
• Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample
• Extrasolar planets and brown dwarfs around AF-type stars. X.The SOPHIE northern sample. Combining the SOPHIE and HARPS surveys to compute the close giant planet mass-period distribution around AF-type stars
• Extrasolar planets and brown dwarfs around A--F type stars. VIII. A giant planet orbiting the young star HD113337
• SOPHIE velocimetry of Kepler transit candidates. I. Detection of the low-mass white dwarf KOI-74b
• Three new brown dwarfs and a massive hot Jupiter revealed by TESS around early-type stars
• The Interstellar Medium in the Kepler Search Volume
• Sub-stellar Companions of Intermediate-mass Stars with CoRoT: CoRoT-34b, CoRoT-35b, and CoRoT-36b
• Detection of Solar-Like Oscillations, Observational Constraints, and Stellar Models for $\theta$ Cyg, the Brightest Star Observed by the {\it Kepler} Mission