EPRV Research Coordination Network
Welcome!
The EPRV Research Coordination Network (RCN), sponsored by NASA’s Exoplanet Exploration Program, aims to support increased communication and collaboration within the radial velocity community as we work towards the goal of obtaining robust mass measurements for Earth analog planets.
Membership is open to the community and we invite participants from all corners of the RV community and related fields, including but not limited to: observational efforts, instrumentation, data analysis techniques, solar studies, and stellar variability mitigation. Please see the side bar for instructions / links on how to join the RCN.
Note: All members of the EPRV RCN will be required to follow our Code of Conduct
EPRV RCN Colloquium Series
Our next RCN Colloquium will take place on Thursday, May 29th, at 8a Pacific Time and feature Chris Lam [University of Florida] and Hannah Osborne [University College London]
Speaker: Chris Lam
Title: gaspery: Optimized Scheduling of Radial Velocity Follow-Up Observations for Active Host Stars
Abstract: Radial velocity (RV) follow-up is a critical complement of transiting exoplanet surveys like the Transiting Exoplanet Survey Satellite (TESS), both for validating discoveries of exoplanets and measuring their masses. Stellar activity introduces challenges to interpreting these measurements because the noise from the host star, which is often correlated in time, can result in high RV uncertainty. A robust understanding of stellar activity and how its timescales interact with the observing cadence can optimize limited RV resources. For this reason, in the era of over-subscribed, high-precision RV measurements, folding stellar activity timescales into the scheduling of observation campaigns is ideal. We present gaspery, an open-source code implementation to enable the optimization of RV observing strategies. Gaspery employs a generalized formulation of the Fisher Information for RV time series that also incorporates information about stellar correlated noise. We show that the information contained in an observing strategy can be significantly affected by beat frequencies between the orbital period of the planet, the stellar rotation period, and the observation epochs. We investigate how the follow-up observing strategy will affect the resulting radial velocity uncertainty, as a function of stellar properties such as the spot decay timescale and rotation period. We then describe two example use cases for gaspery: 1) calculating the minimum number of observations to reach an uncertainty tolerance in a correlated noise regime and 2) finding an optimal strategy given a fixed observing budget. Finally, we outline a prescription for selecting an observing strategy that is generalizable to different targets.
Speaker: Hannah Osborne
Title: Homogenous analysis of small planet masses
Abstract: Our current view of the mass-radius relationship of small exoplanets, and therefore our understanding of exoplanet compositions and demographics, is not giving the full picture. Planet masses found through precision radial velocity observations are inconsistent; the offsets between different instruments, the data reduction pipelines, and the method used to account for stellar activity varies between studies. The effect of these inconsistencies can cause a significant difference in terms of the extracted planet mass. To combat these issues we have completed a homogenous analysis of 45 systems hosting small exoplanets, using publicly available HARPS data. We asses and compare the impact of different modelling choices on the subsequently measured planet masses. We show that changing one choice in modelling can lead to a difference in planet mass found by up to a factor of four, even for identical datasets. With these new, homogenously derived planet masses we provide an updated mass-radius diagram for small exoplanets and make recommendations for RV teams in the future.
Background on the RCN
The 2018 National Academies’ Exoplanet Science Strategy, which provided input to the Astro 2020 Decadal Survey, acknowledged the importance of the radial velocity method “to provide essential mass, orbit, and census information to support both transiting and directly imaged exoplanet science for the foreseeable future” and recommended that “NASA and NSF should establish a strategic initiative in extremely precise radial velocities (EPRV) to develop methods and facilities for measuring the masses of temperate terrestrial planets orbiting Sun-like stars.” Subsequently, a community Extreme Precision Radial Velocity (EPRV) Working Group was chartered, which developed a roadmap for advancing the radial velocity technique to the point where EPRV detection or exclusion of Earth analogs orbiting nearby target stars of a future direct imaging mission would be feasible.
With the Astro2020 Decadal Survey recommendation for NASA to develop a large infrared/optical/ultraviolet space telescope capable of observing and spectrally characterizing potentially habitable exoplanets orbiting nearby stars, development of EPRV capabilities is critical as they will provide the only method potentially capable of discovering Earth analogs from the ground and measuring their masses. As part of its plan to “break the stellar variability barrier” and work towards enabling EPRV surveys capable of measuring the masses of Earth analogs, the EPRV WG report recommended that NASA establish an EPRV Research Coordination Network (RCN) of scientists across disciplines (solar, stellar, exoplanetary) and instruments.“ Thus, the development of this RCN, which endeavors to support the EPRV community in advancing towards the goal of detecting temperate, terrestrial, planets around Sun-like stars.