STScI Newsletter
2021 / Volume 38 / Issue 01

About this Article

M. Mutchler (mutchler[at], R. Ryan (rryan[at], T. Desjardins (desjard[at], and C. Christian (carolc[at]

Roman Telescope in front of nebula next to its logo

Mission Status and Current Highlights

Last year, the Nancy Grace Roman Space Telescope mission advanced to the implementation phase, known as Phase C. This year, flight hardware continues to be built as the mission approaches Critical Design Reviews in the summer and fall of 2021. Primary and secondary mirrors have been refigured, polished, and coated (Fig. 1). An initial set of 18 test Sensor Chip Assemblies (SCAs) have been installed and aligned on the Wide Field Instrument (WFI) Engineering Test Unit (ETU) mosaic plate (Fig. 2). The addition of a K‑band filter (F213) has extended wavelength coverage to the fullest extent possible with Roman's mirrors and detectors (0.5 to 2.3 microns; Fig. 3), and will enable more collaborative research with other observatories (see NASA press release). Roman is planned for launch in 2026, with STScI serving as the Science Operations Center (SOC) in partnership with the Project Office at NASA Goddard and the Science Support Center (SSC) at IPAC. The broad array of science expected with Roman was described in earlier Newsletter articles on community survey results and the Roman2020 conference.

Roman mirror assembly in the clean room
Figure 1: Roman Mirror Assembly.
Roman detectors mounted
Figure 2:  Roman Detectors.
chart of Roman filter suite range
Figure 3: Roman Filter Suite.

How Can You Get Involved?

All of Roman's observing time will be defined by the astronomical community through open processes. A significant opportunity for the community to become engaged with the Roman mission has been announced via the NASA's ROSES-2021 solicitation. Included will be opportunities to help prepare for and contribute to the Roman Space Telescope science goals of studying dark energy and exoplanets, described in the Astro2010 decadal report New Worlds, New Horizons in Astronomy and Astrophysics. These key science topics will be investigated through dedicated telescope time (core surveys), that will account for the majority of Roman observing time during the primary 5‑year mission. The remaining telescope time (about 400 days) will be dedicated to general astrophysics programs. Community calls for general astrophysics proposals as well as funded archival research will be released before launch. These opportunities will be supported with resources familiar to the STScI user community including an online documentation system, Exposure Time Calculator (ETC), the Astronomer's Proposal Tool (APT), and the Mikulski Archive for Space Telescopes (MAST).

All Roman data will be immediately available (no proprietary period) via MAST, with data processing resources available via a state-of-the-art cloud science platform. The SOC will produce and distribute several high-level science products, including rectified mosaics corrected for instrumental signatures and cosmic rays (Fig. 4), homogenous source catalogs with various photometric measurements and value-added fields (such as photometric redshifts), and relevant metadata to trace the history of the data and processing.

Deep Field image showing the small Hubble area and the much larger Roman Field of View
Figure 4: This composite annotated image illustrates the possibility of a Roman Space Telescope "ultra-deep field" observation, centered on the Hubble Ultra Deep Field (outlined in blue). The orange outline shows the field of view of Roman's WFI. Credit NASAESA, and A. Koekemoer (STScI). See the full press release

Resources Available to the Community

The SOC currently provides several Python packages and Jupyter notebooks, based on existing JWST tools, for image simulation and proposal/observation planning. While many user-community resources are still under development, here we highlight some which are available now.

Roman Field of View with Barnad's star and a screenshot showing the archive
Figure 5: The MAST Portal Footprint Service (top layer) can overlay Roman's Wide Field Instrument (WFI) aperture on the sky (bottom layer), and also export a ds9 region file.

The exposure-time calculator (ETC) is built on the Pandeia engine, which provides functionality to script calculations to examine a host of observational settings and configurations, but also offers a streamlined graphical-user interface (GUI).  The current version (1.6) has several updates, including an improved thermal model for instrumental background and point-spread functions (PSFs).  The WebbPSF toolkit can generate oversampled theoretical PSFs with tunable parameters (e.g., wavelength/bandpass, field position, and pixel scale) that can be integrated into other simulation packages.  Additionally, the WebbPSF has several analysis tools for computing radial profiles or encircled energy curves, and the difference between two PSFs.  

The Space Telescope Imaging Product Simulator (STIPS) can generate complex astrophysical scenes, based on user input (e.g., observational set-up and stellar or galactic populations) and the up-to-date models for the instrument and detector performance characteristics. STIPS brings together WebbPSF, along with parametric models for extended sources for the morphological aspects of scene generation, while the Pandeia engine performs the relevant spectral calculations.

This combination of three packages provides a self-consistent, easy-to-use, and fully customizable software suite to simulate Roman images complete with the current understanding of the detector and instrumental effects. At present, STIPS only works with a single SCA, however future releases will transparently model all 18 detectors in the focal plane.  See the simulated Roman image of M31 (NASASTScI, and B. F. Williams, University of Washington) produced with STIPS.





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