Hot Jupiter - Cold Jupiter: A complex sibling relation

Abstract

A handful of planetary systems hosting a Hot Jupiter have been subsequently found to also host long-period giant planets. These ``cold Jupiters,'' giant planets residing beyond the snow line ($\sim$3\,au), play an important role in the dynamical evolution of the system as a whole. In this work, we investigate the detectability of cold Jupiters around a sample of 28 well-studied Hot Jupiter host stars to estimate the occurrence rate of this distinctive system architecture. We perform extensive simulations using the combination of all publicly available radial velocity (RV) data for those stars with synthetic RV data. The synthetic data test observing strategies along three axes: cadence, duration, and measurement precision. For each scenario, we determine detection limits based on the semi-major axis at which a 1 Jupiter mass planet would be recovered 50\% of the time. We find the following: 1) the existing RV data are remarkably insensitive to these Hot Jupiter/Cold Jupiter pairs; 2) the total baseline over which an observational campaign is carried out is the dominant factor in our ability to detect cold Jupiters; and 3) the results are relatively insensitive to the individual RV measurement precision. We conclude that metre-class telescopes with lower RV precision are ideally suited to surveying Hot Jupiter-cold Jupiter systems.

Figures (11)

• Figure 1: The distribution of RV data used in this work over time for the selected targets (part 1). The instrumental precision of this data, along with additional data, are presented in Table \ref{['tab:observations']}.
• Figure 2: The distribution of RV data used in this work over time for the selected targets (part 2). The instrumental precision of this data, along with additional data, are presented in Table \ref{['tab:observations']}.
• Figure 3: RVSearch completeness contour plot for HD 103720. The large black dot represents the periodic signal identified by RVSearch (i.e., the known planet). The small points denote injected synthetic planets. Blue points correspond to recovered signals, while red points were not recovered. Red contours show the detection probability, averaged over small bins in semi-major axis and $m \sin i$ space. The black line marks the 50% detection probability contour.
• Figure 4: Heat maps showing the detection efficiency for exoplanet candidates injected to the existing observational radial velocity data for 28 known Hot Jupiter host stars. A total of 3,000 unique potential candidate companions were injected, one at a time, for each star considered, with masses and orbital periods each drawn from a log-normal distribution. In both panels, the colour of a square denotes the detection efficiency for a planet in that square -- the mean of the detection efficiencies (number of detections divided by the number of injected planets) across the sample of 28 stars. The left panel shows the data as a function of orbital period, whilst the right shows the same data as a function of log(period). It is clear that planets are most easily detected at short orbital periods, with true Jupiter and Saturn analogues (P$\sim$ 12 and 29 years, respectively) challenging to detect based on current data. The "void" at the top left of the right hand panel is an artefact of the injection-recovery process; the signals injected by RVSearch all had radial velocities of less than 1000 ms$^{-1}$. As a result, no planets were generated in the region of the 'void’, and so recovery of planets in that region was impossible as there were none to recover.
• Figure 5: Comparison of different instruments and observing strategies. It can be noted that the line corresponding to 50% detection shifts downward and to the right as both the cadence and duration increase. Although subtle, differences are also seen between telescopes due to varying measurement precision.