Jake D. Turner, Brianna M. Smart, Kevin K. Hardegree-Ullman, Timothy M. Carleton, Amanda M. Walker-LaFollette, Benjamin E. Crawford, Carter-Thaxton W. Smith, Allison M. McGraw, Lindsay C. Small, Marco Rocchetto, Kathryn I. Cunningham, Allison P. M. Towner, Robert Zellem, Amy N. Robertson, Blythe C. Guvenen, Kamber R. Schwarz, Emily E. Hardegree-Ullman, Daniel Collura, Triana N. Henz, Cassandra Lejoly, Logan L. Richardson, Michael A. Weinand, Joanna M. Taylor, Michael J. Daugherty, Ashley A. Wilson, Carmen L. Austin
We observed nine primary transits of the hot Jupiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jupiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B_star of 100 G, the Vidotto et al. method predicts a timing difference of 5-11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES-3b's magnetic field strength to range between 0.013 and 1.3 G (for a 1-100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist-Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of Rp = 1.386+0.248-0.144 RJup is consistent with the planet's optical radius.
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http://arxiv.org/abs/1211.4895
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