RVFC: Radial Velocity Follow-up Calculator

The RVFC is a web-based tool used to calculate the number of radial velocity measurements required to detect the semi-amplitude of a transiting exoplanet at a desired detection significance. These calculations can be performed in the general case of correlated RV noise and in the white noise limit which is less computationally expensive but is often not an accurate approximation to real empirical RV time-series. Calculations of the number of RV measurements―and total observing time―are useful for planning RV follow-up observations and how to distribute observing time among a set of targeted transiting planetary systems. The inherent assumptions in the RVFC and instructions on its use are provided below. Additionally, the model and calculator are described in detail in this paper.

The python-based backend of the RVFC is also available here for those who prefer to run their calculations locally.

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Inherent assumptions in the RVFC
● When calculating the number of RV measurements with the RVFC, we always assume that:

● When calculating the number of RV measurements with the RVFC―when the RV noise model is white―we further assume that:

To begin, select one of the two options at the bottom of this page. The applicability of each option is described below along with instructions on their usage.

Option 1: to-be used when the photon-noise limited RV precision and the effective RV rms are unknown for the target of interest.

Option 2: to-be used when the photon-noise limited RV precision or the effective RV rms is known a-priori for the target of interest (often from previous runs of the RVFC or from independent calculations).

● Acknowledgement: if you make use of the RVFC please cite this paper

● The various sources of additive RV noise included in the RVFC calculations include the photon-noise limited RV precision, stellar activity, RV rms from additional planets in the system, and a systematic uncertainty from the RV noise floor. These parameters can be set explicitly by the user or sampled from empirical distributions depending on which RVFC suboption is selected.

● If the RVFC is run in the presence of correlated RV noise, it is recommended that the number of Gaussian process (GP) trials be set to ≳ 10 as these results are sensitive to the window function of the observations which are not fixed and should be sampled. Note however that more GP trials will result in a longer wall time for the calculation. When more than one GP trial is submitted the median and median absolute deviation of the results over the multiple GP trials are returned. Alternatively, the number of GP trials can be set to zero to only consider the white noise calculation.

● The window functions adopted when using the RVFC in the presence of correlated noise (i.e. number of GP trials > 0) are uniformly sampled in time. The ability to upload custom window functions is intended for future versions of the RVFC.

● Questions and comments about the RVFC (including any bug encounters) should be sent to cloutier@astro.utoronto.ca.