Who decides what and how to observe with the James Webb Space Telescope?


The James Webb Space Telescope. Note the hexagonal structure of its mirror mounted on an array of solar panels that shield it from the Sun and power it electrically.
Sergio Messina Sergio Messina 10 minutes

Each year there are many proposals for observations using the James Webb Space Telescope (JWST).. Consider that it would take approx. to implement these proposals in the last year 36,000 hours when the telescope is capable of it 5000.

So, the requirement is a factor of 7.2 larger than the actual options. The need to make a choice arises so that only the best proposals are accepted, i.e. those that make it possible to do the best science.

Why observe with JWST

With a primary mirror of more than 6 meters and a set of 4 different instruments, jewels of technology, capable of observing in the near-infrared region, JWST is a unique telescope. It is able to observe both the nearby universe (our solar system) as far as space with high spatial resolution, creates images and spectra of objects that would otherwise remain hidden by dust.

The list of absolutely beautiful images and scientific discoveries obtained by this telescope in just over a year of observation is already long.

Image of the planet Uranus with rings and moons recently observed by JWST. Credit: NASA, ESA, CSA, STScI

Scholars greatly benefited from his abilities exoplanetsOf star-forming regionsscholars from Solar System and extragalactic objectsto mention a few areas of observation.

How telescope time is divided

The total time that JWST can observe is divided between three types of observation programs.

Granted Time Observer (GTO) programs.

Scientists who have contributed in various capacities to the creation of the hardware and software components of the telescope and its instrumentation are entitled to be guaranteed a fraction of the time to observe objects of interest to them as recognition for the work done.

However, GTO programs are only operational for the first three years of the telescope’s life, after which scientists who have been guaranteed observing time will be able to continue to propose observations, but under another program type.

GO (General Observer) programs

The General Observer Program is a general telescope time allocation program for all scientists in the international community.

Gravitational lens
A recent image of the giant galaxy cluster MACS0416 with gravitational lensing observed by JWST. Acknowledgments: NASA, ESA, CSA, STScI, Jose M. Diego (IFCA), Jordan CJ D’Silva (UWA), Anton M. Koekemoer (STScI), Jake Summers (ASU), Rogier Windhorst (ASU), Haojing Yan ( University of Missouri)

Scientists (who were not involved in the construction of the telescope and its instruments) can submit three types of observation proposals: small (if they propose to use JWST for less than 25 hours of observation); medium (for applications between 25 and 75 hours); big (for observation programs that require more than 75 hours). They are here too long-term program in case the observation must be made in a time interval longer than 1 year.

There is also an opportunity to present joint programs for the observation of astronomical objects, which will be carried out simultaneously with JWST and the Hubble Space Telescope (HST).

Who selects the proposals

Due to the uniqueness of the JWST telescopewith its very high spatial resolution and near-infrared spectroscopy and imaging capabilities, there are many astronomical objects for which his observations would be invaluable. Consequently there are many scientists and their teams asking to observe with JWST.

The time available is not enough to satisfy all observation proposals a selection must be made and admit only the best proposals.

There is a special committee called the Time Allocation Committee to make this selection (Telescope time allocation fee) composed of eminent scientists. They are tasked with carefully reading numerous sighting proposals to select the best ones.

Selection criteria

There are term(s) in which scientists submit their observations proposals for the following year, or more technically, a Cycle (which in the case of JWST lasts one year). 1st observation cycle ended in June 2023; Observations of the 2nd cycle began in July 2023 and will end in June 2024, when the 3rd cycle of observations will begin.

For the ongoing cycle 2, 5000 hours of observations have been made available for the GO program. From them 2900 hours have been assigned to programs small, 1250 to the programs medium, 850 for the programs big.

by the deadline TAC therefore receives thousands of proposals for observations.

The main purpose of the TAC is to ensure that the entire scientific community has equal access to the use of the telescope while maximizing the scientific performance of the telescope.

To achieve these two goals a special selection process called the “Dual Anonymous Review of Proposals Process” was developed.thus a twice-anonymous proposal review process.

All telescopes to which the international community has access (e.g. Hubble, ALMA, …) have similar procedures for selecting observation designs.

All draft observations are read one at a time and studied by TAC members.

First stage

In the first step, all links to the team that proposed the observation are hidden so that the commission focuses exclusively on the quality of the scientific proposal, without the possibility of being influenced by the gender, nationality and knowledge of the proposing team.

A specific character is present during the selection process, “Leveler” or comparator, whose sole function is to ensure that the discussion remains focused solely on scientific merit and not the design team if indirectly identified.

All suggestionsso rated anonymously, they are ranked according to meritalso based on their feasibility and compliance with the number of hours required.

The second phase

In the second phase, the committee has access to information about the proposing team and its experience and scientific strengths (one of the information that needs to be provided when preparing the observation proposal is precisely that about the composition of the team and its experience).

JWST image of the Cassiopeia A supernova remnant. Acknowledgments: NASA, ESA, CSA, STScI, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (Ghent University)

At this point, based on the personal information of the team members associated with each proposal, the committee cannot change the assigned score, but add a “downgrade” flag with a majority vote and a written reason why the proposal is rejected (these are the rare cases where it seems that the team is not at all qualified to carry out the submitted proposal).

Starting with the highest scorers, gradually the proscontributions are approved until the available hours are exhausted.

Once the observations requested in one of the accepted proposals have been made, the team has exclusivity on those images or spectra for one year, after which the observations become public and placed in public archives for any scientist to use for their own research.

Spectacular images obtained with JWST which we often find on the web, including those also advertised by Meteored, thus, they are not obtained by random item selection or for pleasure, rather, they are those obtained in various TAC-approved sighting designs and then analyzed, interpreted and finally published by the team that designed them.


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