Image credit: Karen Teramura, IfA/UH

Why SPI?

Evgenya Shkolnik (IfA/UH), David A. Bohlender (HIA/NRC), Gordon A. Walker (UBC), Andrew C. Cameron (St. Andrews)

Star-planet interactions (SPI) offer an indirect way to detect and measure planetary magnetic fields, providing the unique opportunity to explore the interiors of planets and set constraints on the rapid hydrodynamic escape of hot Jupiter atmospheres. Our work over the past 6 years reveals evidence suggesting an observable magnetic interaction between a star and its hot Jupiter, which appears as a cyclic variation of stellar activity synchronized to the planet's orbit. Both HD 179949 and upsilon And display synchronicity of the Ca II emission with the planet's orbit during several observational epochs while during other seasons rotational modulation is observed. This on/off nature of star-planet interaction in the two systems is likely a function of the changing stellar magnetic field structure throughout its activity cycle. The complete sample of 13 targets exhibits a tentative correlation between this activity and the ratio of the planet's minimum mass to its rotation period, a quantity proportional to the hot Jupiter's magnetic moment, thereby improving SPI's potential as a probe of extrasolar planetary magnetic fields.

Realistic SPI Light Curves from Solar-type Magnetic Fields

Steven Cranmer (CfA)

There is growing observational evidence that the planet-phased chromospheric activity seen on some stars with extrasolar giant planets does not repeat exactly from orbit to orbit. Indeed, this is expected for a planet plowing through a slowly varying stellar magnetic field. At the 14th Cool Stars meeting, Cranmer and Saar (astro-ph/0702530) presented example models that used the complex solar magnetic field to simulate both orbit-to-orbit variability of SPI light curves, as well as longer-term trends using the 11-year solar cycle. These models will be reviewed briefly, and some new statistical results from the models will be presented that give some indication for how often one should expect the light curves to repeat. Considering more complex magnetic fields introduces new difficulties in the interpretation of observations, but it may also lead to valuable new diagnostics of exoplanet magnetospheres.

ESPaDOnS and NARVAL observations of hot Jupiter systems

Rim Fares (LATT), Claire Moutou (LAM)

In the last decade, tens of giant planets orbiting close to their host stars (hot Jupiters) have been discovered - many of them are so close to their host star (a<0.1AU) that interactions between the star and the planet are expected (and observed) to occur. Studying these interactions helps understanding the formation, evolution and migration of hot jupiters. Using spectropolarimetry (e.g. ESPaDOnS at CFHT & NARVAL at TBL), one can reconstruct the large-scale magnetic topologies of hot-Jupiter hosting stars and thus quantitatively study such interactions. We will present the work on 3 such hot Jupiters (tau Boo, HD 189733 and HD 179949) and the kind of constraints we can obtain from such observations on the physical nature of the star/planet magnetic interactions.

Properties of planet-hosting CoRoT stars

Malcolm Fridlund (ESA), Magali Deluil (OAMP), Claire Moutou (LAM), Eike Guenther (TLT), Oleg Kuchukov and the CoRoT team

Several of the first stars found by CoRoT to host planets show signs of active behavior. Since these planets orbit in very short period orbits (less than 2 days), they are within there host stars Alvenic radius. Some signs of peculiar flare activity is obvious and is being investigated. It is also very important to carry out detailed spectroscopic characterisation, and modeling, of the hosting stars in order to properly determine the physical properties of the planets themselves. This process and some results is presented.

Magnetic Reconnections in Planet Magnetosphere and Chromospheric/Coronal Activities of a Central Star

Takeru Suzuki (U.Tokyo), Pin-gao Gu (ASIAA)

We have studied the effect of magnetic reconnections in the magnetosphere of hot Jupiter-type planets on the chromosphere and wind of central stars. A fraction of reconnection jets propagate to a central star along stellar magnetic filed. The jets, or the beam of charged particles, interact with stellar wind and corona where the density becomes high for sufficient Coulomb coupling. We have investigated this process by 1D MHD simulation. We have found that if the beam density is sufficiently high the emission from chromosphere and corona is intermittently enhanced related to thermal instability of radiative cooling. We finally discuss this process in terms of observed chromospheric activities of planet-hosting stars.

Empirical evidence for tidal evolution in transiting planetary systems

Frederic Pont (Exeter)

In this talk, we would review the observational evidence for tidal orbital alignment, circularisation and synchronisation, in light of the new results from transit surveys.

The CoRoT planets as probes of star-planet interaction

Suzanne Aigrain (Exeter), C. Moutou (LAM), R. Alonso (LAM), A. Cameron (St. Andrews), T. Mazeh (Tel Aviv), F. Pont (Exeter), and the CoRoT Exoplanet Science Team

CoRoT's long baseline and continuous sampling allow us to study the variability of the host star as well as the transits of the planets it detects. Among the new planets recently discovered by CoRoT, two are particularly interesting from the point of view of star-planet interactions. CoRoT-exo-2b is an inflated giant planet in a very short period (1.75d) orbit around a very active G-star. CoRoT-exo-4b is a giant planet of normal density longer period (9.2d) around a late F-star whose rotation period coincides with the orbital period of the planet. I will briefly discuss the search for evidence of spot-related activity at the period of the planet in both systems, and discuss possible explanations for the apparent synchronicity in the CoRoT-exo-4 system.

A new upper limit to the radio flux from the transiting planet HD 189733b

Alexis Smith (St. Andrews)

We present results from an attempt to detect electron-cycloton maser emission from the interaction between an extra-solar and its host star. Our observations are informed by a new theoretical model which predicts the flux from individual systems, including systems where the planet is predicted to lie within the stellar magnetosphere (Jardine & Cameron, in prep.). We monitored the transiting extra-solar planet HD 189733b during secondary eclipse using the Robert C. Byrd Green Bank Telescope (GBT) to observe over a 40 MHz bandpass centered on 327 MHz. During the eclipse, the observed flux is expected to decrease to zero as the source of the radiation passes behind the star. We present a new upper limit to the radio flux from HD 189733b and compare it to the predictions made by models.

The Jupiter-Io system as a model for star-planet interaction? (Poster)

J. Schmitt (Hamburger Sternwarte)

Since the 1960s surface phenomena on Jupiter have been connected with its moon Io, culminating with the detections of Io's (and the other Galilean moons') footprints in the UV on Jupiter. In situ measurements of particles and magnetic fields near Io with the Voyager and Galileo spacecraft have led to a reasonably detailed understanding of the important physical processes. The most relevant elements of these are: (1) The strong magnetic field of Jupiter, leading to co-rotation of Jupiter's magnetosphere far beyond Io. (2) The rapid rotation of Jupiter, leading to super-Keplerian magnetospheric rotation at Io's orbit. (3) The mass loading due to Io's volcanic activity, leading to the creation of the Io plasma torus and ensuing low Alfven speeds. These properties make Io a MHD generator of currents in excess of 1 million amp producing the observed emissions. I will show that for extrasolar planets around young stars conditions (1)-(3) are met and consequently similar processes are expected to occur on far larger scales. Further, MHD forces might provide a torque to halt planet migration.