PEXO: A Global Modeling Framework for Nanosecond Timing, Microarcsecond Astrometry, and μm s⁻¹ Radial Velocities

Abstract

The ability to make independent detections of the signatures of exoplanets with complementary telescopes and instruments brings a new potential for robust identification of exoplanets and precision characterization. We introduce PEXO, a package for Precise EXOplanetology to facilitate the efficient modeling of timing, astrometry, and radial velocity data, which will benefit not only exoplanet science but also various astrophysical studies in general. PEXO is general enough to account for binary motion and stellar reflex motions induced by planetary companions and is precise enough to treat various relativistic effects both in the solar system and in the target system. We also model the post-Newtonian barycentric motion for future tests of general relativity in extrasolar systems. We benchmark PEXO with the pulsar timing package TEMPO2 and find that PEXO produces numerically similar results with timing precision of about 1 ns, space-based astrometry to a precision of 1 μas, and radial velocity of 1 μm s−1 and improves on TEMPO2 for decade-long timing data of nearby targets, due to its consideration of third-order terms of Roemer delay. PEXO is able to avoid the bias introduced by decoupling the target system and the solar system and to account for the atmospheric effects that set a practical limit for ground-based radial velocities close to 1 cm s−1. Considering the various caveats in barycentric correction and ancillary data Required to realize cm s−1 modeling, we recommend the preservation of original observational data. The PEXO modeling package is available at GitHub (https://github.com/phillippro/pexo) and Zenodo (Feng et al. 2019).

Optimized modelling of Gaia–Hipparcos astrometry for the detection of the smallest cold Jupiter and confirmation of seven low-mass companions

“…The discrepancy in the estimation of inclination is probably due to the use of a different convention used by Sozzetti & Desidera (2010). We use the astrometric convention, which is the only consistent convention according to Feng et al (2019b). Sozzetti & Desidera (2010) probably used the so-called "observer-independent ascending node" (Feng et al 2019b) to define inclination.…”

“…We use the astrometric convention, which is the only consistent convention according to Feng et al (2019b). Sozzetti & Desidera (2010) probably used the so-called "observer-independent ascending node" (Feng et al 2019b) to define inclination. These two inclination angles 1 and 2 are related by 1 = − 2 .…”

A surprise in the updated list of stellar perturbers of long-period comet motion

“…comm.) we have been given an access to the new, unpublished right ascension, declination, parallax, proper motions, and the radial velocity of the centre of mass of Kruger 60 which were calculated using the PEXO package (Feng et al 2019) based on data from Hipparcos (van Leeuwen 2007), the WDS catalogue (Mason et al 2001), and the recent LCES HIRES/Keck survey (Butler et al 2017).…”

A Small Actively Controlled High-resolution Spectrograph Based on Off-the-shelf Components

“…One of the key issues for high precision spectrographs is that they must be stable on all timescales which might be of interest for astronomical phenomena. When considering exoplanets this might be from hours to hundreds of years (e.g., Feng et al 2019). Both simultaneously calibrated spectrographs such as HARPS and Iodine stabilized spectrographs such as HIRES work on the premise that the optical arrangement should be as stable as possible.…”