In Search of Decay: An Analysis of Transit Times of Hot Jupiters in Main-sequence and Post-main-sequence Systems

Abstract Tidal interactions are one of the primary drivers of orbital evolution for massive planets with short orbital periods. Tidal dissipation within host stars can cause the orbits of such planets to decay. However, the mechanisms of tidal dissipation are difficult to probe. Generally, tidal dissipation is parameterized by the modified stellar tidal quality factor, or <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>Q</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> , but the lack of observational evidence of orbital decay to confirm dissipation theories has resulted in orders of magnitude of uncertainty in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>Q</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> . We present a new transit timing analysis of 54 systems with varying stellar evolutionary states in an attempt to search for orbital decay across multiple stages of stellar evolution. For each system, we obtained mid-transit times from new TESS data and evaluated potential departures from a linear ephemeris using the Bayesian information criterion. We then determined tidal quality factors using widely tested theoretical relations. Of the systems studied, 25 showed evidence of a decrease in orbital period over time and eight showed evidence of a decrease that was inconsistent with zero by three standard deviations: CoRoT-2, TrES-5, WASP-4, WASP-12, WASP-19, WASP-45, WASP-99, and XO-3. However, the significance of some of these detections may be influenced by unreliable transit time measurements. Similarly, we see that the lower limit on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>Q</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> for evolved systems is marginally lower than it is for the sample of all systems, though both limits are orders of magnitude below the expected theoretical values for both samples. These new constraints on transit times and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>Q</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> values will help to narrow the search for orbital decay in the future and place important constraints on current theories of star–planet interactions.