AAS 206th Meeting, 29 May - 2 June 2005
Session 23 Stars and Observing Them
Oral, Monday, 2:00-3:30pm, May 30, 2005, 102 B

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[23.06] The Effect of Stellar Meridional Motions on Extrasolar Planet Detection

J.M. Beckers (University of Chicago)

Most Extrasolar Planet detections use periodic Doppler velocity variations of the parent star to infer the presence of a planet. Refinements of this technique have reached precisions of 1 m/sec and better. At these precisions periodic flows on the stellar surface may well lead to false detections. The most likely flows of concern are meridional motions.

Solar surface meridional motions have unambiguously been observed. They move towards the pole and have an approximate shape of the second Legendre Polynomial of order m=1 reaching a maximum surface velocity of about 30 m/sec. Depending on the inclination of the rotation axis to the line of sight this would cause a red shift in the spectrum of integrated sunlight of 8 m/sec when viewed perpendicular to this axis [sin(i)=1] and a blue shift of 15 m/sec when viewed along this axis [sin(i)=0]. The Sun is a relatively slow rotator among G and earlier type stars, so that many of the stellar effects are likely to be larger.

Of interest is, of course, the temporal variation of this motion. Observations of solar surface meridional flows go back to 1967. They appear to show variations but my search for periodic meridional motion changes is so far inconclusive. This search is complicated by possible changing instrumental effects and latitudinal change in convective blue shift ("limb effect"). The latter is also of interest for false Extrasolar Planet detection techniques. It can be evaluated by observing the Doppler shifts for different line strengths and excitation potential. The former requires a long time sequence of solar observations of surface meridional flows using the same, unchanging instrument. The GONG and SOHO/MDI helioseismology observatories, now in operation for about one solar cycle, might provide the necessary data.

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Bulletin of the American Astronomical Society, 37 #2
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