AAS 203rd Meeting, January 2004
Session 123 Extra Solar Planets I
Oral, Thursday, January 8, 2004, 10:00-11:30am, Centennial I/II

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[123.04] Chromospheric Activity Induced by Short-Period Planets

E. Shkolnik, G.A.H. Walker (University of British Columbia), D.A. Bohlender (HIA/NRC), S. Rucinski (David Dunlap Observatory)

We have detected the first, strong evidence of magnetic interaction between an extrasolar planet and its parent star.

Tidal or magnetic heating of the star by the planet can be detected as stellar chromospheric activity modulated with the orbital period. For magnetic interaction, Pactivity = Porb with an enhancement near the sub-planetary point (\phi = 0). For tidal interaction, Pactivity = Porb/2 with enhancements at both \phi = 0 and 0.5.

We observed the Ca II H & K emission cores of five sun-like stars with short period planets: \tau Boo, HD 179949, HD 209458, 51 Peg and \upsilon And. We acquired 10 nights of high resolution (\approx 110,000), high S/N (~ 500) data at the CFHT over three semesters. The superb quality of the data yielded differential radial velocities to better than 20 m s-1 which yielded updated ephemerides and accurate orbital phases.

Night-to-night modulation of the H & K emission was observed in 4 of the 5 stars. Our two standards, \tau Ceti and the sun, showed no such variability. Three of the `active' stars did not show a clear correlation of activity with orbital phase, however, HD 179949, the star with the tightest planetary orbit (Porb = 3.092 days), repeatedly showed a 4% enhancement near the sub-planetary point and a decrease in activity when the planet was behind the star. The activity persisted for 108 orbits. This is the first detection of magnetic interaction between a star and its giant planet, as well as a first glimpse of an extrasolar planetary magnetosphere.

As an amplified example of enhanced chromospheric activity induced by a companion, we observed ER Vul, an RS CVn binary system with Porb = 17 hours. Ca II H & K spectra show increased activity near the sub-binary longitudes of both components. There is also evidence of Ca II emission from in between the two stars.

The author(s) of this abstract have provided an email address for comments about the abstract: shkolnik@physics.ubc.ca

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