Call for nominations for Honorary IAU Members

The International Astronomical Union (IAU) has initiated a relatively  new category of membership called « IAU Honorary Members ».  Details  about this category can be found at and

In brief, Honorary Members would be individuals who are not  professional astronomers and do not qualify as ordinary IAU members,  but they have substantially contributed to the development of  astronomical research in their country.  According to the IAU General  Secretary, these individuals would have « significantly contributed to  the progress of astronomy. This includes training, education,  communication, etc. »

Only **ONE PERSON per year** can be nominated by the Canadian National  Committee (CNC) of the IAU.  The CNC is the CASCA Board of Directors.

This announcement is a call for nominations (or self-nominations) for  Honorary IAU members.

**BY FEBRUARY 1, 2021**, please send (or arrange to have sent):

1. The CV of the nominee.
2. Two letters of recommendation outlining why the nominee should  become the Canadian Honorary Member nominee.

Send this information to:
with the subject line:
IAU Honorary Membership Application (followed by the name of the candidate)

New Page Charges in AAS Journals

As most of you are aware, AAS journals (ApJ, ApJL, ApJS, AJ, etc) switched to Open Access at the start of this year. Several of you have expressed concern to the AAS publications committee that the new resulting page charges are quite high and cannot be easily covered by a typical NSERC Discovery grant.

This was raised during this week’s meeting of the publications committee in Pasadena. Amongst a wide ranging discussion, the main message we’ve been asked to convey back to the CASCA community is that the AAS journals have a substantial budget for full or partial waivers of publication charges, and that it is quite reasonable for a Canadian astronomer to request such waivers given our funding landscape.

You are given the option to request a full or partial waiver during the manuscript submission process. Your request will be confidential to the editor-in-chief, and will not affect how your paper is handled by the associate editor or referee. You are welcomed and encouraged to request a waiver if you cannot easily meet the cost of publication.

If you have any questions or concerns about AAS publication charges or anything else about AAS journals, please reach out to Bryan Gaensler (contact information below) and he will make sure that any concerns you raise are brought to the attention of the publications committee.

Bryan Gaensler

CATAC Update on the Thirty Meter Telescope

par Michael Balogh (CATAC Chair)
(Cassiopeia – été 2022)

TMT Canada Information Session

Just over 50 people attended the CATAC webinar discussion on May 12, 2022. The slides that CATAC presented are available here. Some of the key points of information include:

  • Description of the anticipated steps and milestones in the NSF Major Research Equipment and Facilities Construction (MREFC) process. Once the NSF accepts the project, it enters the MREFC queue and a well-defined process of reviews and studies is initiated. This process hasn’t started yet.
  • The earliest likely first light for TMT is 2032, if the project enters the MREFC queue now. This timeline relative to ELT is still competitive, but further delays will push first light farther into the future, as there is little scope for accelerating construction.
  • We are still awaiting publication of the decision on the appeal to the rescinding of the construction permit on the alternative site, in the Canary Islands.
  • TMT partners are signatories to a Master Agreement, which cannot be changed without unanimous approval from all members. A single member cannot withdraw from the agreement without significant financial compensation to the others.

This was followed by a presentation by the Project Manager, Fengchuan Liu. Highlights include:

  • A summary of the recent full system, PDR-level design review by non-advocate reviewers. The review was successful, with notable identified strengths including the technical readiness of the project and the solid cost estimates and risk assessments. The panel identified the broader impacts program as a major risk – this team has already been rebuilt as recommended by the review.
  • The design is very mature, with 82% of the project in either Final Design or Fabrication stage.
  • A thorough and frank description of dialogue and outreach activities underway in Hawaii. In particular, acknowledgement that past astronomy outreach has mostly been with a subset of the community, typically already well assimilated to western culture. Efforts are underway to also engage much more broadly. Hawaiian communities have appreciated any efforts related to the protection and restoration of the Mauna Kea environment, and to education opportunities that are accessible by all (including K-12 and community colleges).

Recent News

Bob Kirschner is the new Executive Director of TIO, succeeding Ed Stone who retired May 15, 2022. For more information, see here.

Site Update

The Hawaii State Legislature passed a bill which creates a new Authority to manage the Mauna Kea lands. The bill passed with a large majority, and now awaits the Governor’s approval to become law. The full text of the approved bill can be found here. There will be a transition period of up to five years before the new Authority takes over fully from the University of Hawaii; no leases can be renewed or issued during that time. The impact of this new law on TMT and the other observatories on the mountain remains to be seen. However, the bill does include a statement that “the support of astronomy…is a policy of the State”.

CATAC Membership

Kristine Spekkens and David Lafreniere ended their terms on CATAC in May 2022. Their advice to CATAC over the years has been outstanding and essential, and we are very grateful for their service. We are currently awaiting replacements to be nominated by CASCA and ACURA.

Michael Balogh (University of Waterloo), Chair,
Bob Abraham (University of Toronto; TIO SAC)
Stefi Baum (University of Manitoba)
Laura Ferrarese (NRC)
Harvey Richer (UBC)
Kim Venn (University of Victoria)
Luc Simard (Director General of NRC-HAA, non-voting, ex-officio)
Don Brooks (Executive Director of ACURA, non-voting, ex-officio)
Christine Wilson (Acting CASCA President, non-voting, ex-officio)
Stan Metchev (TIO SAC, non-voting, ex-officio)
Tim Davidge (TIO SAC Canadian co-chair; NRC, observer)
Greg Fahlman (NRC, observer)

ALMA Matters


par Brenda Matthews (ALMA)
(Cassiopeia – été 2022)

Cycle 9 Proposal Statistics

Cycle 9 set yet another record for the amount of time requested on ALMA. There were 1769 proposals requesting a whopping 51,370 hours of observing on the 12m-, 7m- and TP-arrays, an overall oversubscription rate of 7.0. Forty Large Program proposals were submitted.

Proposals with PIs/co-PIs from Canadian institutions also requested a record amount of time. There were 46 Canadian-PI proposals, requesting 4,721 hours of time, more than 3.5 times the previous record of 1335 hours set in Cycle 5. This is over 20% of the time requested by the entire North American community in Cycle 9.

For a more complete summary of global Cycle 9 proposal submissions, see here.

Cycle 8 Status

Cycle 8 observations began on September 30, 2021. The array is currently in Configuration 5, and the array configurations will gradually expand over the coming months.

Science Ready Data Products

Not an interferometric expert, or short on time to reduce your own or archival ALMA data? No problem!

The North American ALMA Science Center can produce Science Ready Data Products for you, to your specifications! For ALMA data, this includes a calibrated measurement set (Cycles 5 and later) and via the AUDI (ALMA User-Defined Imaging), continuum or spectral imaging with modified spatial and spectral resolution.

These are great ways to optimize your use of ALMA data!

Visualize Data in the ALMA Archive with CARTA

The ALMA Archive has recently incorporated the Cube Analysis and Rendering Tool for Astronomy (CARTA) into the ALMA archive. With CARTA you can quickly visualize ALMA data products interactively in the archive without spending the time and bandwidth downloading them to your personal computer. In particular, some imaging products are being stored in the ALMA archive, like the ARI-L imaging products from early ALMA cycles. ARI-L images can be explored with CARTA and the downloaded in a science ready form. The successful integration of CARTA is nationally exciting since CARTA was initially developed in Canada using ALMA Development funding based on prototype work from Canada’s CyberSKA project. For more information on using CARTA in the ALMA archive, see here and for more information about the CARTA project in general, see the CARTA page.

Video Tutorials for ALMA Users

At the end of 2021, the NAASC announced a new YouTube channel for the ALMA Primer Series of video tutorials. The platform currently hosts several short video tutorials designed to explain aspects of ALMA and interferometry, such as estimating sensitivities for proposals, understanding the largest angular scale, and the ins and outs of weighting schemes.

The site will be populated as well with short animations from the videos suitable for use in seminars and live training. New videos will be added from time to time.

Check out and subscribe, here!

Report from the LCRIC

par Sharon Morsink (LCRIC chair)
(Cassiopeia – été 2022)

The Long Range Plan Community Recommendations Implementation Committee (LCRIC) has been meeting weekly from March – May this spring and is now taking a summer recess. We thank Chris Wilson (LCRIC Chair June 2021 – May 2022) and LCRIC members Shantanu Basu, Michael Reid, Etienne Artigau, and Hilding Neilson for their work on this committee over the last year. Brenda Matthews, Laurie Rousseau-Nepton, and Sharon Morsink (LCRIC Chair June 2022 – May M023) will be continuing to work on this committee over the next year along with new LCRIC members.

In the months since the vernal equinox, LCRIC has written and released to the CASCA community a document on Land and Consent, in response to Recommendation #1 of the Long Range Plan (LRP2020). We thank the CASCA members who gave us thoughtful comments and feedback at the CASCA AGM or privately. We will release a final revision of this document in Autumn 2022 and look forward to working with the CASCA Board on issues related to Land and Consent in astronomy.

We have made excellent progress on developing terms for the creation of an Indigenous Engagement Committee, in response to Recommendation #46 of LRP2020. We are interested in consulting with the new President’s Indigenous Advisory Circle to get their input before presenting plans for a new committee to the CASCA Board.

On March 31, 2022, we hosted a webinar titled « Including Indigenous Voices in Astronomy Education ». This webinar included panelists Jason Bazylack (Professor of Engineering at University of Toronto), Samantha Lawler (Assistant Professor of Physics at University of Regina), Ismael Moumen (Researcher at Universite Laval/CFHT), and Laurie Rousseau-Nepton (Resident Astronomer at CFHT). The panelists discussed their work on bringing Indigenous perspectives to their classrooms, outreach with Indigenous communities, and facilitating an inclusive environment. We hope that the CASCA community who were able to attend this webinar found it educational!

Over the last 3 months, we have met with the Sustainability Committee and the Graduate Student Committee to discuss their concerns and LRP2020 recommendations related to these specific committees. In the coming months, we plan to meet again with the Postdoc, Equity and Inclusivity, and Education and Public Outreach Committees to discuss progress on LRP2020 recommendations.

Over the next few months, we will be carefully examining progress on the LRP2020 recommendations in collaboration with the Ground-based Astronomy Committee, the Joint Committee on Space Astronomy, and the CASCA Board to make sure that all recommendations receive attention, and that we have a detailed plan and timeline for acting on the LRP2020 recommendations.

The LCRIC recognizes that transparency and consultation are very important as our community moves forward to implement the recommendations of the LRP. We will be seeking input from a diversity of perspectives, recognizing that astronomy and astronomers exist in a broader societal context. We welcome feedback and comments at any time, via email to the LCRIC chair. Communications will be kept confidential if requested.

President’s Message

par Chris Wilson (CASCA Acting President)
(Cassiopeia – été 2022)

I would like to start this President’s report by welcoming the new members of the CASCA Board: Adam Muzzin as Vice President, Rob Cockcroft as Secretary, and Renee Hlozek and Karun Thanjavur as new Directors. Lewis Knee has been acclaimed to a second term as CASCA Treasurer, while Laura Parker and Julie Hlavacek-Larrondo are continuing in their third year as Directors. Thanks to all of you for being willing to serve! Thank you also to the outgoing Board members: Judith Irwin (Secretary), Ivana Damjanov (Director), and Etienne Artigau (Director). A special thank you to Erik Rosolowsky (Acting Vice-President) and Rob Thacker (Acting President) for stepping up to serve in these important CASCA roles last summer.

As those of you who attended the CASCA Business Meeting in May will know, I have agreed to step in to serve as CASCA Acting President for 2022-2023. Like Rob Thacker this past year, I am in this position under Bylaw 9.1, and will not be continuing in this position beyond the 2023 AGM. Thus, in 2023 we will look to elect a new President, as well as two new Directors. More information about the elections, including how to nominate someone or be nominated yourself, will be circulated later this year.

As I have been in the Acting President position for just over a month, this message will provide a short update on a few key areas. I plan to provide a more extensive discussion in my fall message, once I have had more time to review what the CASCA Board has on its “to do” list.

Coalition activities continue to focus on the Square Kilometre Array (SKA), where things appear to be progressing well. The SKA is now one year into construction of SKA Phase 1 and continues to evolve rapidly. Canada’s scientists and engineers are participating in SKA through March 2023 via a co-operation agreement between NRC and the SKAO. To continue our leading role in SKA construction deliverables such as the SKA1-mid correlator will require the Canadian government to commit to construction and operations funding quite soon. Please refer to the excellent article by Kristine Spekkens for more information on the SKA.

Another important initiative that is gaining significant momentum is CASTOR, a Canadian-led optical-UV space telescope and the highest priority in space astronomy in the 2020 Long Range Plan (LRP2020). The Canadian Space Agency (CSA) held a virtual Canadian Space Exploration Workshop June 14-16, 2022, which I am sure many of you attended. The workshop provided an opportunity to discuss ideas for Canadian space exploration over the next 30 years and will serve as input to CSA’s planning process.

The LRP Community Recommendations Implementation Committee (LCRIC) has continued their hard work over the past three months. They hosted a well-attended webinar on “Including Indigenous voices in astronomy education” at the end of March. They have drafted a very important policy paper on land and consent (LRP2020 Recommendation #1) as it relates to new astronomical facilities that has been circulated to the community and was presented and discussed in a special session at the CASCA AGM. Sharon Morsink has taken over as chair of LCRIC for 2022-23 and I look forward to working closely with her and the rest of the LCRIC as they work to move the societal recommendations from LRP2020 forward.

I hope everyone has a healthy and productive summer,


Square Kilometre Array (SKA) Update

par Kristine Spekkens (Canadian SKA Science Director) and the AACS
(Cassiopeia – été 2022)

Artist’s impression of the SKA, combining elements from South Africa and Australia from left to right in the image. Photos of real hardware have been blended with realizations of the future SKA antennas. Image credit: SKA Observatory.

We are now a year into the construction phase of SKA Phase 1 (= SKA1), and the project continues to evolve rapidly. Major milestones of the staged construction plan include the first correlated SKA1-Low stations and SKA1-Mid dishes in 2024, the first data from scientifically competitive arrays in 2026, and science readiness reviews of completed arrays underway by late 2028. The SKA Construction Proposal and Observatory Delivery Plans detail SKA1 science drivers, technical requirements and anticipated broader impacts, with the latter structured around the UN Sustainable Development Goals. In particular, the project is committed to building partnerships with Indigenous and local communities at the remote sites where the dishes and antennas will be located.

There are 16 partner countries of the SKA Observatory (SKAO) that is building and will operate SKA1: 8 are Full Members (Australia; China; Italy; the Netherlands; Portugal; South Africa; Switzerland; the United Kingdom) with voting rights on the SKAO Council which governs the project, and 8 are Observers (Canada; France; Germany; India; Japan; South Korea; Spain; Sweden) that witness SKAO Council meetings where governance decisions are made. In April, France signed an accession agreement to transition from SKAO Observer to Full Member once it ratifies the Observatory Convention, formalizing its long-term commitment to the project. Other Observers are completing their internal processes to become Full Members as well.

A cooperation agreement between NRC and the SKAO allows Canada’s scientific and engineering communities to continue participating in the SKA through March 2023, while longer-term SKAO membership is given full consideration by the federal government. Work under the cooperation agreement is fully funded and proceeding on schedule, with the Canadian correlator team from NRC and industry partner MDA on track to provide the backends to support the initial four-dish Array Assembly (= AA0.5) and the subsequent 16-dish Array Assembly (= AA1) for SKA1-Mid. In addition, the NRC digitizer team has delivered a qualification model system to South Africa for dish testing and is currently working towards the Critical Design Review for the SKA1-Mid Single-Pixel Feed and Receiver in July.

In order to maintain our leading role in SKA1-Mid correlator work, a Canadian commitment to construction and operations beyond the cooperation agreement will soon be required from our government. In this context, bilateral meetings between NRC and SKAO are underway to discuss topics including the accession process, the valuation of Canadian financial contributions in terms of observing time and fair work return, and the funding schedule for a 6% participation in SKA1 recommended by LRP2020. The goal of the meetings is to bring the most up-to-date information to our government as it decides on long-term participation in the SKA.

There has also been significant recent activity to develop the SKA Regional Centres (SRCs), a network of ~five data centres around the world managed through a partnership between SKAO and participating countries that will handle the global science processing (~20 PFlop/s), science archive (~700 PB/yr) and related user support needs. The SRC Steering Committee (SRCSC) is initiating a round of trilateral discussions between the SKAO Council, the SKAO Project Office and the SRCSC national representatives in the different partner countries to develop a common understanding of the SRC Network concept, along with the planning and decisions required to deploy it at scale by the onset of full SKA1 operations at the end of this decade.

Preparatory SRC Network activities are ramping up significantly, with all partner countries contributing personnel to develop an SRC Network Implementation Plan to present to the SKAO Council in mid-2023. The requirements phase is nearly complete, and an architecture phase is now ramping up in parallel with a major prototyping effort. In Canada, the CADC is contributing 1 full-time equivalent (FTE) of effort as well as software to the prototyping activity, with in-kind support from the Digital Research Alliance (the successor organisation to Compute Canada). The costing presented to the federal government for long-term Canadian participation in SKA1 includes a Canadian SRC to leverage our digital research infrastructure expertise and support Canadian science using SKA1.

Now that the construction phase has begun a significant ramp-up in staffing across the project is also underway, and many scientists, engineers, software designers, and support and administrative personnel are being hired. Individuals from all nationalities are welcome to apply. Those interested should keep an eye on the SKAO Recruitment Portal, which includes a “job alert” tool to set up personalized emails filtered by field of expertise, location, duration, and employment type.

For more information and updates on Canada and the SKA:

Update on CASTOR

par Patrick Côté, John Hutchings (NRC Herzberg Astronomy & Astrophysics Research Centre)
(Cassiopeia – été 2022)

CASTOR continues to make progress on several fronts. The following list summarizes activities since the last e-CASS report in March.

  1. The technical risk-retirement (STDP) contract has developed the detector work plan, involving the supplier T-e2v, the JPL doping and coating process, readout electronics from NRC-HAA, and lab testing at Honeywell, the Open University in the UK, and the University of Calgary UV vacuum lab.
  2. The Phase 0 Science Working Groups (SWGs) and full science team are meeting monthly for science development work. Under NRC-HAA contracts, specific work is continuing at several Canadian universities.
  3. The Industrial Phase 0 Mission Concept Review (MCR) is due later this month, where the mission requirements will be outlined and agreed on. The CASTOR science team has been closely engaged in preparing for this important milestone.
  4. Partnership discussions have included a town-hall meeting in the UK, attended by the UK Space Agency to advise on funding opportunities later this year. Other individuals in Europe, United States and Asia have expressed interest and are contributing specific studies.
  5. The FORECASTOR tools for exposure time calculations and data simulations continues development on several fronts with contributions from a number of students, postdocs and faculty members. SWGs will be using these tools to raise the science readiness levels of CASTOR’s planned surveys to a minimum of SRL=4 by conclusion of the Phase 0 study.
  6. The mission business case is now in development by CSA, and will be completed later this year. ACURA and the Coalition have been briefed as part of their regular activities and CASTOR has been mentioned favourably in several of the CSA Topical Team meetings, and the recent Canadian Space Exploration Workshop.
  7. Detailed education and public outreach plans are being developed by the science team. Those who are interested in being involved in these efforts are encouraged to contact Nathalie Ouellette.

BRITE-Constellation Mission Update

par Gregg Wade (on behalf of the Canadian BRITE team)
(Cassiopeia – été 2022)

BRITE-Constellation is an international space astronomy mission consisting of a fleet of 20x20x20 cm nanosatellites dedicated to precision optical photometry of bright stars in two photometric colours. The mission continues in full science operations, with 38 datasets available in the public domain from the BRITE public archive. As of April of 2020, all data is made public as soon as decorrelation is complete, with no proprietary period.

The BRITE mission is a collaboration between Canadian, Austrian and Polish astronomers and space scientists. The Canadian partners represent University of Toronto, Université de Montréal, Mount Allison University, and Royal Military College of Canada. The mission was built, and the Canadian satellites operated by, the University of Toronto Institute for Aerospace Studies Space Flight Lab (UTIAS-SFL). The Canadian Space Agency funded the construction of the Canadian satellites, and continues to support their day-to-day operations.


There are five BRITE satellites in the Constellation, which work together to obtain well-sampled, long term continuous (~6 months) light curves in both red and blue band passes across a variety of sky fields.

As this issue of Cassiopeia went to press, the assignments of the BRITE nanosats were:

  • BRITE Toronto (Canada): This satellite observes with a red filter. It is currently observing the Cyg V field. (As indicated by the roman numeral, Cygnus is a BRITE legacy field being observed for the 5th time.) The pointing performance of the satellites on this field has been poor, and an alternative field may be considered.
  • BRITE Lem (Poland): Lem observes with a blue filter, but is currently idle due to unresolved stability issues.
  • BRITE Heweliusz (Poland): Heweliusz observes with a red filter. It is currently observing the Cru-Car IV field with good performance.
  • BRITE Austria (Austria): BRITE Austria observes with a blue filter. It is currently observing the Sgr VIII field.
  • UniBRITE (Austria): Currently out of order.

The BRITE Constellation observing program is currently set through mid-2022. Details of the observing plan will be available on the BRITE photometry Wiki page.

Recent Science Results

“5 yr of BRITE-Constellation photometry of the luminous blue variable P Cygni: properties of the stochastic low-frequency variability” (Elliot et al. 2022, MNRAS 509, 4246)

The BRITE flux of P Cyg, after subtracting off the global mean, with units of parts per thousand (ppt) (left) and the Fourier amplitude spectrum (right) for the 2015 data. Each peak used in the analysis is highlighted with a different color in the Fourier spectrum, and then the fit is overplotted on the photometry with the corresponding colour for that term and all previous terms. The final multi-frequency fit is then used to calculate the (? − ?) that is shown on the bottom panel of the photometry.

Luminous Blue Variables (LBVs) are massive stars that are likely to be a transitionary phase between O stars and hydrogen-free classical Wolf-Rayet stars. The variability of these stars has been an area of study for both professional and amateur astronomers for more than a century. In this paper, we present 5 yr of precision photometry of the classical LBV P Cygni taken with the BRITE-Constellation nanosatellites. We have analyzed these data with Fourier analysis to search for periodicities that could elucidate the drivers of variability for these stars. These data show some long-time-scale variability over the course of all six calendar years of observations, but the frequencies needed to reproduce the individual light curves are not consistent from 1 yr to the next. These results likely show that there is no periodic phenomenon present for P Cygni, meaning that the variability is largely stochastic. We interpret the data as being caused by internal gravity waves similar to those seen in other massive stars, with P Cygni exhibiting a larger amplitude and lower characteristic frequency than the main-sequence or blue supergiant stars previously studied. These results show evidence that LBVs may be an extrapolation of the blue supergiants, which have previously been shown to be an extension of main-sequence stars in the context of the stochastic low-frequency photometric variability.

Conferences, Resources, and Social Media


The BRITE team will be holding their annual face-to-face strategic planning meeting during the TASC6/KASC13 meeting in Leuven in early July.

Resources and Social Media

The BRITE Public Data Archive, based in Warsaw, Poland, at the Nikolaus Copernicus Astronomical Centre, can be accessed here.

The mission Wiki (including information on past, current and future fields) can be accessed here.

BRITE Constellation is on Facebook, at @briteconstellation.

The BRITE International Advisory Science Team

The BRITE International Advisory Science Team (BIAST), which consists of BRITE scientific PIs, technical authorities, amateur astronomers, and mission fans, advises the mission executive on scientific and outreach aspects of the mission. If you’re interested in joining BIAST, contact Catherine Lovekin, the chair of BEST.

Dissertation: Star-forming Protoclusters

(Cassiopeia – Summer / été 2022)

par Dr. Ryley Hill
Thesis defended on March 15, 2022
Department of Physics and Astronomy, University of British Columbia
Thesis advisor: Prof. Douglas Scott


The Lambda cold dark matter (Lambda CDM) model accurately reproduces many notable observations of our Universe, such as the existence of galaxy clusters embedded in a cosmic web. However, there remain many open questions about the physics governing baryons on galaxy cluster scales that the Lambda CDM model cannot address, such as how star-formation is triggered and quenched, and how feedback processes regulate structure growth. In order to investigate these questions we study SPT2349-56, a star-forming protocluster discovered at redshift 4.3, corresponding to a period when large-scale structure was actively forming. We use submillimetre observations to search for protocluster members, identifying 29 galaxies at z = 4.3. These galaxies are distributed into a central core 300 kpc in diameter, and a northern extension offset from the core by 400 kpc. We find three additional galaxies 1.5 Mpc from the main structure, suggesting the existence of other halos at the same redshift that are not covered by our data. An analysis of the velocity distribution of the central galaxies indicates that this region may be virialized with a mass of (9 ± 5)x1012 solar masses, while the two separated galaxy groups show significant velocity offsets from the central group. We estimate the average star-formation rate density of SPT2349-56 to be roughly 40,000 solar masses per year per cubic Megaparsec; this may be an order of magnitude greater than the most extreme examples seen in simulations. We carry out a suite of optical and near-infrared observations in order to characterize the stellar content of SPT2349-56. Using the submillimetre positions of the protocluster members, we identify counterparts and perform detailed source deblending, allowing us to fit spectral energy distributions and estimate stellar masses. We show that the galaxies in SPT2349-56 have stellar masses proportional to their star-formation rates, consistent with other protocluster galaxies and field submillimetre galaxies (SMGs) around redshift 4. However, the galaxies in SPT2349-56 have on average lower molecular gas-to-stellar mass fractions and depletion timescales than field SMGs, although with considerable scatter. Hydrodynamical simulations predict that the core galaxies will quickly merge into a brightest cluster galaxy, thus our observations provide a direct view of the early formation mechanisms of this class of object.