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M. S. Povich (Harvard U.), M. S. Giampapa (NOAO/NSO), J. A. Valenti (NOAO/KPNO), T. Tilleman (NOAO/NSO)
We present the results from a high-resolution, synoptic spectroscopic program of observation of ten F- and G-type stars, seven of which exhibit periodic radial velocity variations attributed to the presence of one or more substellar companions. The observations were obtained from 1998 March to 1999 February using the 1.52-m NSO McMath-Pierce Solar Telescope Facility on Kitt Peak in conjunction with the solar-stellar spectrograph. The spectra were acquired with a resolving power of approximately 1.2 \times 105. The line bisector was then derived from unblended photospheric features. In particular, we define the velocity displacement of the spectral line bisector and determine the bisector amplitude for the Fe I absorption line at 625.26 nm in order to search for variations in the line asymmetry over time. Such variations could mimic Doppler shifts in observations with lower spectral resolution. Examination of the bisector velocity displacement over the time span of our observations reveals no substantial difference between stars with planetary companions and those without reported companions. We find no correlation between the bisector variations and the orbital phase of a substellar companion in any of our target stars. Simulations of a periodic signal with noise levels based on our measurement errors suggest that we can exclude bisector variations with amplitudes greater than about 20 m s-1. These results support the conclusion that extrasolar planets best explain the observed periodic variations in radial velocity.
This work was supported by a NASA grant to the NOAO under the auspices of the Origins of Solar Systems Program. MP gratefully acknowledges support from the NSF-sponsored Research Experience for Undergraduates (REU) program at the NOAO. The NOAO is operated by AURA, Inc., under a cooperative agreement with the NSF.
The author(s) of this abstract have provided an email address for comments about the abstract: povich@fas.harvard.edu