Improved Orbital Parameters and Transit Monitoring for HD 156846b

TL;DR

This paper refines the orbital parameters of HD 156846b using new radial velocity data, improving transit predictions, and reports photometric monitoring that constrains the planet's transit likelihood and atmospheric dynamics.

Contribution

The study provides improved orbital and transit timing data for HD 156846b, enhancing the accuracy of transit predictions and offering insights into its atmospheric behavior.

Findings

Radial velocity data reduced transit time uncertainty to 20 minutes.

Photometric monitoring showed no transit detection within the predicted window.

Photometry demonstrated millimag stability over rotational timescale.

Abstract

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.