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The Roman Coronagraph Community Participation Program: early calibration plan and pilot observation of a companion

This paper outlines the early calibration plan and a pilot observation of the stellar companion HD 29992 B for the Roman Coronagraph Instrument's Community Participation Program, aiming to generate a canonical dataset to validate the instrument's performance and prepare the community for future direct imaging missions.

Original authors: Julien H. Girard, Eric Cady, Neil T. Zimmerman, Clarissa R. Do Ó, Jingwen Zhang, Guillermo Gonzalez, Bijan Nemati, Vanessa P. Bailey, Alexis Lau, Sophie Noiret, John Krist, Julia Milton, Marie Ygouf

Published 2026-08-19

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CC BY 4.0

Original authors: Julien H. Girard, Eric Cady, Neil T. Zimmerman, Clarissa R. Do Ó, Jingwen Zhang, Guillermo Gonzalez, Bijan Nemati, Vanessa P. Bailey, Alexis Lau, Sophie Noiret, John Krist, Julia Milton, Marie Ygouf, Ramya M. Anche, Schuyler Wolff, Justin Hom, Amanda Chavez, Jason J. Wang, Maxwell A. Millar-Blanchaer, Jessica Gersh-Range, Matthias Samland, Macarena Vega-Pallauta, Wolfgang Brandner, Toshiyuki Mizuki, Masayuki Kuzuhara, Susan Redmond, Kevin Ludwick, Jaren N. Ashcraft, William O. Balmer, Rusland Belikov, Beth Biller, Sarah Blunt, Ellis Bogat, Oscar Carrión-González, Gael Chauvin, Alexandra Z. Greenbaum, Sebastiaan Haffert, Jim Ingalls, Brian Kern, Bertrand Mennesson, Laurent Pueyo, Dmitry Savransky, Dan Sirbu, Peter Williams, Chen Xie

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

For decades, the quest to find other worlds has been a story of light and shadow. Astronomers have successfully spotted young, fiery giant planets that glow with their own heat, but finding mature, Earth-like worlds that reflect the gentle light of their stars has remained a distant dream. These mature planets are incredibly faint compared to the blinding glare of the sun they orbit, creating a contrast so extreme that it is like trying to see a firefly next to a searchlight from miles away. To solve this, scientists are building a new kind of telescope instrument called a coronagraph. Think of it as a specialized mask that blocks the star's light, allowing the faint reflection of a nearby planet to finally become visible. The Nancy Grace Roman Space Telescope, scheduled to launch in late 2026, will carry such an instrument, serving as a crucial testbed for future missions that aim to image truly habitable worlds.

The paper by Julien Girard and his team outlines the careful preparation required to make this first look at the universe a success. Before the telescope can begin its main mission of hunting for planets, the team must prove that the instrument works exactly as predicted. They have designed a specific plan for the first few months after launch, focusing on a "baseline" set of tests to ensure the camera and its light-blocking mask are calibrated correctly. The goal is to verify that the software can take raw data from space and turn it into a clear picture of a planet without the star's light overwhelming the image. This initial phase is not about discovering new worlds immediately, but about building a reliable foundation so that when the real search begins, the community of astronomers knows exactly how to interpret what they see.

To test these systems, the team has selected a specific target for a pilot observation: a known companion star orbiting a bright star named HD 29992. This companion is not a planet, but a smaller, dimmer star that orbits its brighter partner. Because its brightness and position are already well understood, it serves as a perfect practice object. The researchers have calculated that this companion will be at just the right distance from its host star in late 2026 to be seen by the coronagraph's most sensitive setting. By pointing the telescope at this pair, the team can run a complete "end-to-end" test. They will simulate the observation, run the data through their processing software, and check if the companion appears clearly in the final image. If the system works as intended, the companion should be easily recovered without needing complex tricks to remove the star's glare, proving that the instrument is ready for the much harder task of finding faint, Earth-sized worlds.

The paper details a rigorous schedule for these early days, including specific calibration steps to measure how much light the instrument lets through and how accurately it can measure the position of objects in the sky. The team is particularly focused on a mode that operates at a specific shade of green light, which is where mature giant planets are expected to shine brightest. They have refined their plan to be efficient, ensuring that they do not waste precious time in space on unnecessary checks. By using a bright, well-known target like HD 29992, they can quickly validate their tools and train their software. This approach allows them to learn from a relatively easy target first, so they are fully prepared when they turn their gaze toward the more difficult, fainter companions that will define the future of exoplanet science. The ultimate hope is that by 2027, this careful preparation will allow them to capture the first direct image of a mature giant planet reflecting visible light, a milestone that will open a new chapter in our understanding of the cosmos.

Technical Summary: The Roman Coronagraph Community Participation Program: Early Calibration Plan and Pilot Observation of a Companion

Problem and Context
The Nancy Grace Roman Space Telescope, scheduled for launch in August 2026, carries the Coronagraph Instrument (CGI), a technology pathfinder designed to demonstrate critical capabilities for future Habitable Worlds Observatory (HWO) missions. The CGI aims to achieve contrast ratios of $\sim 10^{-8}$ to $10^{-9}$ to directly image mature, giant exoplanets in visible reflected light. However, the instrument faces significant operational challenges, including a complex entrance aperture with a large central obscuration, low throughput (a few percent), and the need for precise wavefront control in space. To maximize scientific return and prepare the broader community for these unprecedented capabilities, the Community Participation Program (CPP) was established. The primary challenge addressed in this paper is the development of a robust "baseline" calibration strategy for the instrument's initial months of operation and the design of a pilot observation to validate the end-to-end observing and data reduction pipeline before attempting more difficult science targets.

Methodology
The paper outlines a two-pronged approach: the refinement of the on-sky calibration plan and the preparation of a specific pilot observation.

Calibration Strategy Update:
The authors updated the initial calibration plan (previously defined in Zellem et al. 2022) based on more accurate estimates of clock time and error budgets. The strategy prioritizes "completeness first," ensuring a full set of baseline calibrations is acquired early to validate the Data Reduction Pipeline (DRP) and analysis software. Key calibration activities include:
- Absolute Flux (AF) Calibration: Observing CALSPEC standard stars with and without neutral density (ND) filters. The plan was optimized to use fewer stars (1 bright, 3 faint) while still achieving a ~2.9% Contrast Budget Estimate (CBE), reducing clock time to allow for repetition.
- Core Throughput (CT) Calibration: Utilizing a sparser, azimuthal dithering pattern (2.8 to $9 \lambda/D$ ) rather than the previously dense arc pattern. This adjustment accommodates targets closer to the Inner Working Angle (IWA) and checks for asymmetries, keeping the activity under 3 hours.
- Astrometric, Flat Field, and Detector Calibrations: These include mapping distortion using the Large Magellanic Cloud, creating flat fields using Neptune or Uranus, and characterizing detector noise (CTI, cosmic rays, dark current, and nonlinearity).
- Goal Modes: While the Hybrid Lyot Coronagraph Narrow Field Band 1 (HLC NF B1) is the required "Technology Demonstration Requirement Level 1" (TTR5) mode, calibrations for polarimetry and spectroscopy are planned on a "Best Effort" basis with lower cadence.
Pilot Observation Design:
The authors propose a pilot program to observe the stellar companion HD 29992 B. The selection criteria required a host star with $V < 6$ (to test low-order wavefront sensing), a flux ratio between $10^{-5}$ and $10^{-6}$ in Band 1 (575 nm), and a separation within the HLC B1 field of view (150–450 mas).
- Target Refinement: HD 29992 B, an M-dwarf companion, was selected. Its orbital parameters were refined using a new astrometric point from MagAO-X (March 2026), which revealed the companion was further away than previously predicted. The new fit predicts a separation of $\sim 324$ –$345$ mas in late 2026, placing it near the $6 \lambda/D$ mark.
- Simulation and Planning: Using the CorgiSim tool, the team simulated 1.6 ks integrations (2 rolls) with a reference star (V=1.8). The simulations tested raw contrast levels of $3 \times 10^{-8}$ (nominal) and $1 \times 10^{-7}$ (pessimistic) to assess the necessity of Post-Processing (PSF subtraction).

Key Contributions and Results

Optimized Calibration Plan: The paper presents a revised Table 2 detailing the clock time and target requirements for each calibration item. The authors demonstrate that by adjusting the number of standard stars and the dithering pattern, they can maintain scientific rigor while significantly reducing the time required for calibration, thereby freeing up more time for challenging science targets.
Orbital Refinement of HD 29992 B: Through the integration of new MagAO-X data, the authors resolved degeneracies in the companion's orbit. The updated prediction places the companion at a favorable separation ( $\sim 6 \lambda/D$ ) and a flux ratio ( $\sim 3 \times 10^{-6}$ to $3 \times 10^{-5}$ ) that makes it an ideal "training" target.
Pipeline Validation Simulation: Simulations indicate that for HD 29992 B, the companion should be easily recoverable even with pessimistic raw contrast ( $10^{-7}$ ) and minimal post-processing. In the nominal case ( $3 \times 10^{-8}$ ), the companion is recoverable without PSF subtraction. This confirms the feasibility of using this target as a functional checkout to validate headers, orientation, and the DRP.

Significance and Claims
The paper positions this work as a critical step in transitioning the Roman Coronagraph from commissioning to science verification. The authors claim that the proposed "completeness first" calibration approach and the HD 29992 B pilot observation are designed to:

Mitigate Risk: By securing a "moderate contrast" detection early, the team can validate the entire observing pipeline and data reduction tools before attempting more difficult targets (such as brown dwarfs or fainter planets).
Community Training: The pilot program serves as a "training" dataset to familiarize the community with the instrument's performance and the DRP in a regime where the signal is robust.
Operational Readiness: The activity will provide immediate feedback on contrast performance, wavefront sensing stability, and the efficacy of various PSF subtraction strategies (e.g., roll subtraction vs. reference star subtraction).

The authors modestly conclude that while the system still requires testing for photon-counting modes and various frame configurations, this pilot program is essential to ensure that the community is prepared to image at least one mature giant planet in visible reflected light during the 2027 observing phase.

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