Vanessa P. Bailey

Rings are ubiquitous among the giant planets in the solar system, yet their presence around exoplanets remains observationally unconstrained. As direct imaging missions such as the Nancy Grace Roman Space Telescope approach first light, understanding the influence of circumplanetary rings on reflected light photometry is critical for the accurate interpretation and follow-up of direct imaging observations. We present a hybrid forward model for reflected light phase curves of ringed exoplanets, coupling a ray-casting framework for computing mutual planet–ring shadowing with empirical reflectance spectra from Cassini observations of Saturn’s rings. We model Jupiter-like planets with opaque, icy rings spanning 1–10× the radial extent of Saturn’s A, B, and C rings across a grid of inclinations and ring obliquities. Our simulations show that rings enhance the flux ratios at favorable ring geometries. Saturn-equivalent rings increase peak flux by a factor of 3.1 in the visible, while more extended rings produce enhanced contrasts exceeding an order of magnitude. The flux contribution of a ring is highly sensitive to obliquity and orbital location. At certain geometries, rings can suppress total system brightness below that of a ringless planet. We highlight multiband observations as a complementary route for diagnosing the presence of an exoring. We also apply the model to υ Andromedae d as an observational test case and discuss the implications for exoring detectability with the Roman Coronagraph. Exorings have the potential to bias inferred planetary properties from direct images and must be properly accounted for in observation preparation and interpretation.

The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wave front sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference star. High contrast is achieved using wave front sensing and control, also known as “digging a dark hole,” where performance depends on the properties of the reference star, requiring V < 3, a resolved stellar diameter <2 mas, and no stellar multiplicity. The imposed brightness and diameter criteria limit the sample of reference star candidates to high-mass main-sequence and post-main-sequence objects, where multiplicity rates are high. A future HWO coronagraph may have similarly restrictive criteria in reference star selection. From an exhaustive literature review of 95 stars, we identify an initial list of 40 primary and 18 reserve reference star candidates relevant to both the Roman Coronagraph and HWO. We present results from an initial survey of these candidates with high-resolution adaptive optics imaging and speckle interferometry and identify no new companions. We discuss the need for higher-contrast observations to sufficiently vet these reference star candidates prior to Roman Coronagraph observations, along with the implications of reference star criteria on observation planning for Roman and HWO.

We present confirmation of HD 143811 AB b, a substellar companion to spectroscopic binary HD 143811 AB through direct imaging with the Gemini Planet Imager (GPI) and Keck NIRC2. HD 143811 AB was observed as a part of the GPI Exoplanet Survey in 2016 and 2019 and is a member of the Sco-Cen star formation region. The exoplanet is detected ∼430 mas from the host star by GPI. With two GPI epochs and one from Keck/NIRC2 in 2022, we confirm through common proper motion analysis that the object is bound to its host star. We derive an orbit with a semimajor axis of 6 4 − 14 + 32 au and eccentricity 0.23 − 0.16 + 0.24 . Spectral analysis of the GPI H -band spectrum and NIRC2 L′ photometry provides additional proof that this object is a substellar companion. We compare the spectrum of HD 143811 AB b to PHOENIX stellar models and Exo-Radioactive-Convective Equilibrium Model (REM) exoplanet atmosphere models and find that Exo-REM models provide the best fits to the data. From the Exo-REM models, we derive an effective temperature of 104 2 − 132 + 178 K for the planet and translate the derived luminosity of the planet to a mass of 5.6 ± 1.1 M _Jup assuming hot-start evolutionary models. HD 143811 AB b is the first directly imaged planet around a binary that is not on an ultrawide orbit. Future characterization of this object will shed light on the formation of planets around binary star systems.

The Coronagraph Instrument on board of the Nancy Grace Roman Space Telescope will demonstrate key technologies that will prepare the ground for the Habitable Worlds Observatory. The current predictions for the Roman Coronagraph's detection limit range from 1e-8 to a few 1e-9, which would allow for groundbreaking science, such as potentially imaging Jupiter-like planets. However, the performance of the instrument depends on many factors. Simulating images with varying optical error sources can help us connect instrument and observatory performance to science yield. Here we present corosims, a tool to simulate observations of astrophysical scenes with the Coronagraph with evolving errors. This tool wraps around the Coronagraph PROPER diffraction model and detector simulator. We use it to investigate the potential degeneracy between jitter-induced speckles and both hot and warm exozodi disk structures. First, we simulate observations of exozodi around Tau Ceti, with varying jitter. We predict that with nominal post-correction pointing jitter performance (~0.3 mas RMS), the Roman Coronagraph should be sensitive to 12x zodis worth of dust, assuming a face-on (worst case scenario) inclination. We further predict that its sensitivity degrades to 35x zodis if jitter on-target is 3x worse than the nominal value. This estimate assumes the best-modeled wavefront control and stability values from the project, including additional model uncertainty factors. We find that, while jitter hinders warm exozodi detection, jitter residuals are unlikely to result in a false positive. However, if a faint hot exozodi falls at small separation, it may not be distinguishable from jitter-induced speckle residuals of comparable brightness. Finally, we discuss the degeneracies induced between flux and separation retrieved near the inner working angle due the sharp edge of the Roman Coronagraph's focal plane mask.

The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference star. High contrast is achieved using wavefront sensing and control, also known as "digging a dark hole", where performance depends on the properties of the reference star, requiring V<3, a resolved stellar diameter <2 mas, and no stellar multiplicity. The imposed brightness and diameter criteria limit the sample of reference star candidates to high-mass main sequence and post-main sequence objects, where multiplicity rates are high. A future HWO coronagraph may have similarly restrictive criteria in reference star selection. From an exhaustive literature review of 95 stars, we identify an initial list of 40 primary and 18 reserve reference star candidates relevant to both the Roman Coronagraph and HWO. We present results from an initial survey of these candidates with high-resolution adaptive optics imaging and speckle interferometry and identify no new companions. We discuss the need for higher-contrast observations to sufficiently vet these reference star candidates prior to Roman Coronagraph observations along with the implications of reference star criteria on observation planning for Roman and HWO.

The Coronagraph Instrument on board of the Nancy Grace Roman Space Telescope will demonstrate key technologies that will prepare the ground for the Habitable Worlds Observatory. The current predictions for the Roman Coronagraph’s detection limit range from ∼10−8 to a few 10−9, which would allow for groundbreaking science, such as potentially imaging Jupiter-like exoplanets around mature stars or imaging exozodi disks in scattered light. However, the performance of the instrument depends on many factors. Simulating images with varying optical error sources can help us connect instrument and observatory performance to potential science yield. We present a tool, corosims, to simulate observations of arbitrary astrophysical scenes with the Roman Coronagraph in the presence of evolving wavefront errors. This tool wraps around the Roman Coronagraph PROPER diffraction model and detector simulator. We use corosims to investigate the potential degeneracy between jitter-induced speckles and both hot and warm exozodi disk structures. First, we simulate observations of warm exozodi around τ Ceti, with varying jitter levels. We predict that with nominal post-correction pointing jitter performance (∼0.3 mas RMS), the Roman Coronagraph should be sensitive to 12× zodis worth of dust, assuming a face-on (worst case scenario) inclination. We further predict that its sensitivity degrades to 35× zodis if jitter on-target is 3× worse than the nominal value. This estimate assumes the best-modeled wavefront control and stability values from the Roman project, including additional “model uncertainty factors” on performance. We find that, although jitter hinders warm exozodi detection by increasing the noise, jitter residuals are unlikely to result in a false positive, particularly if two-color imaging is conducted. However, if a faint, hot exozodi disk falls <λ/D projected separation, it may not be distinguishable from jitter-induced speckle residuals of comparable brightness. Finally, we discuss the degeneracies induced between flux and separation retrieved near the inner working angle due to the sharp edge of the Roman Coronagraph’s focal plane mask.

NASA’s Nancy Grace Roman Space Telescope includes the coronagraph instrument (CGI): a technology demonstrator for active coronagraphy that uses deformable mirrors for deep starlight suppression, which enables imaging and spectroscopy of nearby faint companions. We provide an overview of the instrument-level test campaign of the CGI that took place at the Jet Propulsion Laboratory prior to the delivery of this instrument for the Roman payload and observatory integration. This test campaign served to expose the instrument to the environments associated with the Roman launch and space operations and to verify the CGI functional and performance requirements in the most comprehensive way possible prior to launch. An overview of the coronagraph requirements and key results of the test campaign is presented.

The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will be the first high-contrast imager in space with active wavefront control, advancing several key technologies for future missions such as the Habitable Worlds Observatory (HWO).^1,2 Future mission concepts have baselined a lenslet-based integral field spectrograph (IFS) for their spectroscopy modes,^3,4 which provides data that simultaneously span two spatial dimensions and one spectral dimension. There are many operational, calibration, and post-processing advantages to such a design, but for cost, mass, and power reasons, a simplified Amici prism and slit are implemented in the primary CGI imaging path. CGI did advance the IFS maturity to a preliminary design review (PDR)-level design; the details of which and comparison to the Amici prism can be found in Groff et al.⁵ Although imaging spectroscopy will continue to be a priority for the HWO coronagraph instrument, we have focused on enabling spectroscopic capability in CGI so that Roman can support both technology and science-related demonstrations related to spectroscopy. Here, we describe the design, assembly, testing, and calibration of the spectroscopic and polarization imaging modes up through instrument integration and test (I&T). Both modes are included in the primary imaging path to the Exoplanet Imaging Camera (ExCam) because they are designed to have a zero angular deviation optical axis. We refer to the polarization and spectroscopy modes as the Wollaston and Zero Optical Deviation (ZOD) spectroscopy modes, respectively. The effort was quite expansive, with the ZOD concept first presented in August 2019, approved to proceed at CGI PDR in September 2019, combined ZOD+Wollaston System Requirements Review (SRR) and PDR in March 2020, tabletop critical design review (CDR) (with preliminary instrument environments) in January 2021, bond qualification in April 2021, combined final CDR and manufacturing readiness review (MRR) in August 2021, pre-ship review (PSR) and delivery to CGI in January 2022. The calibration test program and supporting algorithms for ground and on-orbit spectral calibration followed using the flight spare units. Final ground calibration of the flight units took place during the CGI thermal vacuum (TVAC) test campaign in April 2024.

The HR 2562 system is a rare case where a brown dwarf companion resides in a cleared inner hole of a debris disk, offering invaluable opportunities to study the dynamical interaction between a substellar companion and a dusty disk. We present the first ALMA observation of the system as well as the continued Gemini Planet Imager monitoring of the companion’s orbit with six new epochs from 2016 to 2018. We update the orbital fit, and in combination with absolute astrometry from GAIA, place a 3σ upper limit of 18.5 M _J on the companion’s mass. To interpret the ALMA observations, we used radiative transfer modeling to determine the disk properties. We find that the disk is well resolved and nearly edge-on. While the misalignment angle between the disk and the orbit is weakly constrained, due to the short orbital arc available, the data strongly support a (near) coplanar geometry for the system. Furthermore, we find that the models that describe the ALMA data best have inner radii that are close to the companion’s semimajor axis. Including a posteriori knowledge of the system’s SED further narrows the constraints on the disk’s inner radius and places it at a location that is in reasonable agreement with (possibly interior to) predictions from existing dynamical models of disk truncation by an interior substellar companion. HR 2562 has the potential over the next few years to become a new test bed for dynamical interaction between a debris disk and a substellar companion.