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Session 40 - The Environment of Stars: From Protostars to the Main Sequence.
Display session, Tuesday, June 11
We report the detection of accelerations in the astrometric motion of Lalande 21185 that indicate the presence of a planetary system. The clearest indication is an excess in the apparent perspective acceleration of the star, detected at two wavelengths in the data gathered with two independent telescopic optical systems and with detectors of two different types. Superimposed upon this multidecade effect are possibly two shorter term perturbations each near the detection sensitivity of the system with which it is espied. Alone, either of the latter effects would simply result in an increased rate of observation, but some evidence of each effect is detected in the signal of the other astrometric instrumentation and neither seems to explain the long term acceleration. An initial pass to the data indicates that the disturbing masses would usually be more than 0.8 arcsec from this frequently observed star. Thus companions of significant luminosity are effectively ruled out. The approximate nature of a relatively short period component is suggested by data obtained, over the last 8.5 years, with the University of Pittsburgh Multichannel Astrometric Photometer (MAP). We find: a low eccentricity orbit, a period of approximately 5.8 yrs, a semimajor axis of 0.0022 arcsec, and a probable mass of 0.9 times that of Jupiter. Residuals from this orbital analysis, and from data obtained from the Allegheny Observatory's plate series, indicate the presence of at least one additional component, but its exact nature is unclear. A possible solution involves a second companion with a period of approximately 30 years, however the period is not well established and the residuals to this solution also indicate a remaining acceleration. The source of the latter may be a substantial underestimation of the period of the second mass or it may indicate the presence of a yet longer period 3rd planetary body.
Program listing for Tuesday