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J. Posson-Brown (Smith College), D. W. Latham, R. P. Stefanik, G. Torres (Harvard-Smithsonian Center for Astrophysics), W. J. Borucki, D. A. Caldwell (NASA Ames Research Center), J. M. Jenkins (SETI Institute)
The discovery of close-in extrasolar giant planets raised the possibility that planetary transits might be observable using ground-based photometry. This was confirmed by the detection of transits for HD 209458. We analyze echelle spectra for ten planetary transit candidates identified by the photometric project Vulcan, all of which show periodic dimming of a few percent, and periods of up to a few days. Our goal is to look for orbital motion and to derive estimates for the astrophysical characteristics of the parent stars, especially the radius and mass, to see if the light curves can be explained by stellar rather than planetary companions. Five of the transit candidates are spectroscopic binaries with stellar companions. In three cases the orbits have the same period as the light curve, so the dimming is due to a grazing eclipse by a stellar companion. The periods for the other two are longer than a year, so the stellar companions are not responsible for the dimming. However, for both of these systems, we conclude that dimming due to a planetary companion is unlikely, because the primary stars appear to be giants, and are therefore too large for a planetary transit to be detected by Vulcan. Three more of the candidates are very hot and/or rapidly rotating, making it difficult to determine precise radial velocities. The two remaining candidates may be giants, but we are unsure of their luminosity classification. They may warrant further study, such as highly precise velocity measurements and dedicated photometric observations designed to produce better light curves. Part of this work was done as a Research Experience for Undergraduates at the Harvard-Smithsonian Center for Astrophysics, funded by the National Science Foundation. Funding for the Vulcan photometric search for extrasolar planets was provided by the NASA Origins and Astrobiology Programs.
The author(s) of this abstract have provided an email address for comments about the abstract: jposson@smith.edu