* Astronomy

Title: Improved Orbital Parameters and Transit Monitoring for HD 156846b
Authors: Stephen R. Kane, Andrew W. Howard, Genady Pilyavsky, Suvrath Mahadevan, Gregory W. Henry, Kaspar von Braun, David R. Ciardi, Diana Dragomir, Debra A. Fischer, Eric Jensen, Gregory Laughlin, Solange V. Ramirez, Jason T. Wright

HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a period of 359.55 days. The pericenter passage at a distance of 0.16 AU is nearly aligned to our line of sight, offering an enhanced transit probability of 5.4% and a potentially rich probe of the dynamics of a cool planetary atmosphere impulsively heated during close approach to a bright star (V = 6.5). We present new radial velocity (RV) and photometric measurements of this star as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). The RV measurements from Keck-HIRES reduce the predicted transit time uncertainty to 20 minutes, an order of magnitude improvement over the ephemeris from the discovery paper. We photometrically monitored a predicted transit window under relatively poor photometric conditions, from which our non-detection does not rule out a transiting geometry. We also present photometry that demonstrates stability at the millimag level over its rotational timescale.

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