Coronagraph Observing Modes
Band 1 narrow field imaging with the Hybrid Lyot Coronagraph is formally supported to meet the 10⁻⁷ contrast requirement; all other modes are best-effort and not guaranteed.
Roman CGI Observing Modes
The Coronagraph Instrument has imaging, spectroscopic (R~50), and polarimetric capabilities. The current required and best effort “goal modes” of the Coronagraph are listed in Table 1 below and respective modes, fields of view (to scale). All images and spectra are simulations. The only formal performance requirement for the Coronagraph Instrument is to be able to image a point source with a flux ratio of at least 10⁻⁷ at a separation of 6 − 9 λ/D from a star as faint as V = 5 in a 10% bandpass centered < 600 nm (Band 1). Thus, in order to reach this requirement, only observations in Band 1 with the hybrid Lyot coronagraph are formally supported; all other modes listed in the table below will be supported on a “best effort” basis. Optical elements to enable potential additional “unsupported modes” exist (e.g., Riggs et al. 2022, 2025) but currently there is no guarantee that any of these modes will be commissioned during the baseline observing phase.
| Band | Central wavelength | Bandwidth | Mode | Mask Type | Azimutal Coverage | Support |
|---|---|---|---|---|---|---|
| 1 | 575 nm | 10% | Narrow FoV Imaging | Hybrid Lyot | 360º | Required (Imaging) Best Effort (Polarimetry) |
| 2 | 660 nm | 10% | Wide FoV Imaging | Shaped Pupil | 360º | Best Effort (Imaging & polarimetry) |
| 3 | 730 nm | 15% | Slit + R~50 Prism Spectroscopy | Shaped Pupil | 2x65º | Best Effort |
| 4 | 825 nm | 10% | Wide FoV Imaging | Shaped Pupil | 360º | Best Effort (Imaging & polarimetry) |
Table 1: Summary of the Roman Coronagraph Instrument’s supported observing modes. The Band 1 narrow field imaging mode using the Hybrid Lyot Coronagraph is formally required and supported; all other configurations are offered on a best-effort basis and may be available for use if the operational period is extended. Bandpass, mask type, field geometry, and support level are indicated for each mode.
Figure 1: Simulated fields of view and working angles (to scale) for the supported observing modes of the Coronagraph Instrument. Colored circles represent inner and outer working angles for each mode. Top: Band 1 narrow field imaging (required mode). Middle: Band 3 slit spectroscopy (goal). Bottom: Band 1 and Band 4 wide field imaging (goal).