The JWST Advisory Committee (JSTAC): Recommendations for JWST Cycle 1 Proposals
Garth Illingworth, gdi[at]ucolick.org
An overview of the JSTAC's activities and recommendations over the seven years since the JSTAC was formed was in the 2016, Volume 33, Issue 1 of the STScI Newsletter. A core aspect of its charge has guided the JSTAC's deliberations: advising the STScI Director on "maximizing JWST's scientific productivity" during its operational life. While the goal is clear, the issues that JSTAC has wrestled with during its twice-yearly meetings in pursuit of this goal have been numerous and complex.
One of these issues is the framework for the Cycle 1 Call for Proposals. The JSTAC conveyed its recommendations regarding Cycle 1 proposals in its May 2016 letter to the STScI Director. The discussions about the Cycle 1 Call have been interwoven with JSTAC discussions regarding the Early Release Science (ERS) Call for Proposals and Observations. The ERS aspects, to be discussed in a separate letter to the Director, will be reported in a later Newsletter article. This article draws extensively from the May 2016 letter on Cycle 1.
Cycle 1 options
The JSTAC’s discussion spanned a wide range of approaches for Cycle 1 proposals, many of which have been used in the past by NASA’s Great Observatories. This prior experience with doing a call for proposals and executing the selected proposals provides insight as to the effectiveness of the chosen model. Discussed were options for Cycle 1 proposals to:
- consist largely, or even entirely, of Treasury/Legacy programs, as was the Spitzer first year approach;
- have a distributed approach (e.g., for "small, medium, large"), with a community-driven or laissez-faire balance;
- have a distributed approach, as in (2.), but with some explicit encouragement towards particular program size scales;
- include very large science-focused programs akin to the Hubble "Key projects";
- allow the consideration of very large proposals and/or large multi-cycle projects;
- encourage proposers to focus on the four science areas (first light and reionization; assembly of galaxies; birth of stars and protoplanetary systems; planets and origins of life) that have defined the scientific objectives of JWST for policy-makers and the public.
During these discussions, a number of other aspects also played a role in framing the committee's thinking.
Great Observatories experience
The JSTAC heard extensively about the various approaches used by the NASA’s Great Observatories for optimizing the science return from their TAC processes. In particular, these discussions covered the experience from Hubble regarding proposal program size and balance, the evolving approaches used by Chandra, as well as the Legacy program model used by Spitzer for the first cycle. The "real world" experience gained from the different approaches was valuable in helping JSTAC think about the ways to maximize the scientific return in Cycle 1.
Early Release Science (ERS) program
The development of a substantial ERS program was an important consideration (see the JSTAC letters regarding the ERS program—e.g., the 2014 ERS letter). Anticipated to cover a range of science topics that span the expected most-used modes of the instrument suite on JWST, the ERS program will provide insight into the performance of the instruments. This program will be carried out early in Cycle 1 to allow the community to become familiar with the instruments and modes of operation before the Cycle 2 Call for Proposals.
The length and applicability of the proprietary time was also a consideration. As noted in the first Newsletter article in issue 1 of this volume, and in the companion article in the next Newsletter issue, the length of the proprietary period will affect the science productivity of JWST. The JSTAC understands that Large, Treasury, and DD-time programs (e.g., ERS) will be open public datasets, following the current practice for Hubble and the other NASA Great Observatories, and has recommended that all other GO datasets have a six-month proprietary period. The recommendations regarding proposals in Cycle 1 were largely developed with the expectation that JWST will have an approximately six-month proprietary period in Cycle 1 and beyond (see the April 2016 letter/presentation).
The Challenges of Selections in Cycle 1
The JSTAC recognized that Cycle 1 posed a particular challenge for establishing guidelines, since proposals will be selected pre-launch for a mission whose on-orbit performance, as well as the optimal analysis techniques, will still be unknown at the time the TAC meets. In particular, it is realistic to expect that JWST's Cycle 1 on-orbit performance, data quality, and calibrations will not be fully optimized. JWST's performance and data quality will improve with time until it fully meets, or even exceeds, its planned performance, but in the near-term, conservatism is needed in establishing guidelines for the Cycle 1 TAC at its pre-launch meeting.
With the above models and considerations in mind, the JSTAC developed its recommendations for the Cycle 1 TAC program. These are taken directly from the JSTAC letter to ensure conformity:
- JSTAC recommends that programs be "balanced" across the broad categories of small, medium, and large programs, as per recent Great Observatory practice, with procedures to ensure that an appropriate balance is obtained. JSTAC felt that the experience with the Great Observatories has proven that such balanced approaches were scientifically productive and an effective scientific use of resource-intensive, observatory-level space missions.
- JSTAC recommends that very large programs should not be part of the baseline for Cycle 1. Such programs, involving a huge investment of time (broadly discussed as being those requesting ∼500–1000 hours), were seen by the JSTAC as unwise for selection before launch in Cycle 1, when the performance of the telescope and its instruments have not been measured on-orbit.
- JSTAC similarly recommends that large multi-cycle programs should not be part of the baseline for Cycle 1, though well-justified smaller programs that require multi-cycle observations (transient, transit, or proper motion programs) were considered by the JSTAC to be appropriate (possibly with additional review in Cycle 2 to ensure viability once the performance characteristics of JWST are better known).
- JSTAC recommends that "Key projects" should not be established for JWST. While JWST has a number of high-level science objectives, the maturity and sophistication of the science community following many years of NASA's Great Observatory science programs indicated to the JSTAC that such "directed" science was not necessary.
Clarifications and further thoughts
JSTAC recognized that there were broad aspects of Cycle 1 (or the early cycles) that were particularly important for the scientific success of JWST. These were noted by the JSTAC to address questions raised by the recommendations.
Very Large Programs
While the JSTAC recommendations regarding very large programs and large multi-cycle programs are for Cycle 1 where the actual on-orbit performance of JWST and its instruments remains TBD, the situation will change for subsequent Cycles. Such very large programs are expected to play a significant role in subsequent cycles once JWST's on-orbit performance is established, and will contribute significantly to the scientific excellence of JWST, as they have done for Hubble, Spitzer, and Chandra.
Proposal Size—Small Programs in Cycle 1
The JSTAC members and presenters noted a number of times in discussions about proposal size that JWST is so powerful that much unique cutting-edge science can be done with short observations. While encouraging balance across the small-medium-large categories was a clear recommendation from the JSTAC, the committee recognized that an initial modest bias towards smaller programs might be a scientifically beneficial approach.
In addition to their overall scientific merit, the JSTAC recommends that the Cycle 1 TAC include in their assessment the foundational nature of the Cycle 1 programs and the JWST-unique observations and science that they will subsequently enable. For example, imaging programs designed to return significant samples of targets for spectroscopic follow-up could provide a valuable set of objects for later cycles, or programs that demonstrate new science opportunities or observing capabilities could provide the basis for large programs in subsequent cycles (including large multi-cycle programs). In a potentially limited-life mission, JSTAC noted that it is prudent to establish datasets that are stepping-stones for subsequent major scientific investigations.
JWST's Science Themes
The widely espoused four science themes for JWST (first light and reionization; assembly of galaxies; birth of stars and protoplanetary systems; planets and origins of life) have a special role in defining the science mission for JWST for policy-makers and the public. In item (6.), under Cycle 1 options, the JSTAC considered whether proposals in these themes should get special consideration by the TAC. JSTAC decided not to recommend any special guidance since we currently expect that, given the breadth of the four science goals, it is quite likely that the community-selected ERS and Cycle 1 programs will cover those science areas to the satisfaction of all concerned. But, if this is not the case, some guidance could be given by the Institute in subsequent cycles.
The JSTAC deliberations on this topic extended over many meetings, culminating in the JSTAC's May 2016 Cycle 1 letter. The excellent presentations from Institute staff and the very detailed discussions with those at the Institute with extensive experience with the Hubble TAC process, greatly aided JSTAC in developing its recommendations.