• Proposal 549 Cordiner Total Power with the 12-m Array: Unlocking ALMA's Potential for Astrochemistry in Extended Sources

  • Reviewer 2

Grade: 2.5

Title Total Power with the 12-m Array: Unlocking ALMA's Potential for Astrochemistry in Extended Sources (PI: Cordiner)

1. Alignment with NA ALMA Partnership strategic goals;

The proposed Study is well aligned with at least two of the ALMA strategic goals, namely improving the technical capability and strengthening the NA radio astronomy community.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the "ALMA 2030" development documents.

The focus of this Study is on total power measurements, which are most applicable for extended sources, potentially including sources much larger than the primary beam of an individual ALMA antenna.

Total power measurements are not identified as one of the highest priority efforts in the ALMA 2030 Roadmap. The apparently highest priority science case described is for cometary comae, yet the number of sufficient comets is also described as only one every 1 to 3 years. Some of the other science cases described are only qualitative in nature, though a mitigating factor is that the topic of astrochemistry is often more observational and data driven. In sum, while interesting, the science cases described do not appear to be of the highest priority.

3. Quality of the upgrade conceptual design;

The proposed Study is of high quality. The proposing team has already done substantial foundational work, and they describe a Study that appears capable of leveraging both their own past work and existing Archive data.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

This proposed work is likely a combination of rapid and longer term development. Some of the calibration strategies and observing scripts might be possible to be implemented relatively rapidly. Any changes to CASA or other software might be straightforward, but still require a longer term effort for development.

5. Strength of the consortium organization (if applicable);

The consortium is quite strong. It involves researchers at a range of institutions, with considerable background in the field. The involvement of researchers at a NASA Center is particularly notable for the possibility of ALMA work being tied to future space missions.

6. Qualifications of the key personnel of the Study;

The key personnel include researchers who have led some of the first ALMA observations of objects such as comets and researchers with considerable experience with ALMA from an institutional perspective (affiliated with the NA ALMA Science Center). The team is well positioned to conduct the Study.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Largely covered by the comments in #5 and #6. The primary resources required would be computer equipment, phone access, and office space for mining the ALMA Archive, analyzing data within CASA, and developing new scripts and software.

8. Assessment of the level of risk inherent in the design;

Low to Modest.

The team is experienced, and there is likely to be data available to guide their development efforts. The reason that this Study is not rated Low risk is that it could identify more intensive development of CASA or other software than is currently estimated. If so, it would take longer for the results of this Study to be incorporated into ALMA.

9. Strength of the Scientific Team supporting the Study;

Largely covered by comments in #6. The key personnel involved have the advantage of having both a scientific interest in the Study and having much of the technical expertise to execute it.

10. Level of support guaranteed by the Institutes;

No in-kind support is identified, but only modest resources are required from the institutes involved.

11. Budgeted cost of the Study;

The cost of the Study appears reasonable, potentially even slightly low. However, the team already has significant experience, potentially with scripts partially written, so it is plausible that they will be able to make rapid progress.

  • *Reviewer*5
Grade: 7

Total Power with the 12-m Array: Unlocking ALMA's Potential for Astrochemistry in Extended Sources

1. Alignment with NA ALMA Partnership strategic goals;

While ALMA currently has a dedicated total power array, it consists of just 4 dishes, and the proposed study aims to utilize the full ALMA array in total power mode to gain increased sensitivity to extended sources. This study will aim to determine if total power mode can be implemented on the current array with only software modifications and additional data reduction procedures. This possibly makes such a mode highly beneficial with little overall cost.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

This program aims to leverage the spectral line sensitivity of ALMA.

3. Quality of the upgrade conceptual design;

The scientific motivation for the study is strong, many sources are simply too big to be observed by ALMA and single-dish telescopes have senstivity limitations that ALMA in total power mode can easily surpass.

A weakness I found in the study was that the authors compared with facilities such as APEX, JCMT, and IRAM, but I could not find a comparison to the 4 current total power antennas. If sensitivity increases as N^0.5, where N is the number of antennas. 4 total power antennas are 2x more sensitive than a single 12m dish, but 45 antennas are then 6.7x more sensitive than a single 12m dish. The improvement over the 4 TPA antennas is then only a factor of 3.3x, not as dramatic as the 10x improvement that the study authors are claiming with respect to the other observatories.

It is unclear if the testing using APEX archival data for weather conditions will be applicable to ALMA or not since the receivers are different as is the IF and correlator system.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

The proposed methodology looks ready for additional testing in a proper total power mode where the array switches to off-source positions. They have already demonstrated proof-of-concept from existing autocorrelation

5. Strength of the consortium organization (if applicable);

N/A

6. Qualifications of the key personnel of the Study;

The personnel in the program are experts in molecular astronomy and there are a number ALMA experts from NRAO on the proposal. However, their level of commitment to the proposal is small. I was also surprised that no one from the CARMA consortium was part of this proposal. They had successfully implemented total power using autocorrelations had may have had valuable experience that would be relevant to an ALMA implementation of total power.

I also found it strange that Bill Shillue is listed in the labor estimate, but not a co-investigator, I was not able to evaluate his qualificaitons.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

As noted in item 6, the scientific expertise is present in the team and they have already demonstrated some proof of concept tests. However, I was surprised that no one with experience in the CARMA total power effor was included in this project.

The amount of effort required by this project as outlined in the work plan (4.3) is fairly ambitious to carry out on the outlined time scale. There was no discussion of the amount of effort and troubleshooting that will need to go into designing ALMA observing scripts to do total power and whether or not this is a simple implementation or will require more effor than anticipated.

8. Assessment of the level of risk inherent in the design;

The risk assessment level seems reasonable, but there was also no discussion of whether there might be additional technical limitations that may preclude total power on the 12m array. But, this study aims to determine if total power is feasible or not with the current hardware.

9. Strength of the Scientific Team supporting the Study;

The science team supporting the study is excellent, no weaknesses.

10. Level of support guaranteed by the Institutes;

The level of support by the non-NRAO members is reasonable; however, additional NRAO support beyond what is specified in the labor estimate may be required for success.

11. Budgeted cost of the Study;

The budget is reasonable, but this study might have benefitted from more personnel dedicating more time to the effort in order to complete it within the allotted time.

  • *Reviewer*7

Grade: 7

Total Power with the 12-m Array: Unlocking ALMA's Potential for Astrochemistry in Extended Sources

1. Alignment with NA ALMA Partnership strategic goals;

While ALMA currently has a dedicate total power array, it consists of just 4 dishes, and the proposed study aims to utilize the full ALMA array in total power mode to gain increased sensitivity to extended sources. This study will aim to determine if total power mode can be implemented on the current array with only software modifications and additional data reduction procedures. This possibly makes such a mode highly beneficial with little overall cost.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

This program aims to leverage the spectral line sensitivity of ALMA.

3. Quality of the upgrade conceptual design;

The scientific motivation for the study is strong, many sources are simply too big to be observed by ALMA and single-dish telescopes have senstivity limitations that ALMA in total power mode can easily surpass.

A weakness I found in the study was that the authors compared with facilities such as APEX, JCMT, and IRAM, but I could not find a comparison to the 4 current total power antennas. If sensitivity increases as N^0.5, where N is the number of antennas. 4 total power antennas are 2x more sensitive than a single 12m dish, but 45 antennas are then 6.7x more sensitive than a single 12m dish. The improvement over the 4 TPA antennas is then only a factor of 3.3x, not as dramatic as the 10x improvement that the study authors are claiming with respect to the other observatories.

It is unclear if the testing using APEX archival data for weather conditions will be applicable to ALMA or not since the receivers are different as is the IF and correlator system.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

The proposed methodology looks ready for additional testing in a proper total power mode where the array switches to off-source positions. They have already demonstrated proof-of-concept from existing autocorrelation

5. Strength of the consortium organization (if applicable);

N/A

6. Qualifications of the key personnel of the Study;

The personnel in the program are experts in molecular astronomy and there are a number ALMA experts from NRAO on the proposal. However, their level of commitment to the proposal is small. I was also surprised that no one from the CARMA consortium was part of this proposal. They had successfully implemented total power using autocorrelations had may have had valuable experience that would be relevant to an ALMA implementation of total power.

I also found it strange that Bill Shillue is listed in the labor estimate, but not a co-investigator, I was not able to evaluate his qualificaitons.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

As noted in item 6, the scientific expertise is present in the team and they have already demonstrated some proof of concept tests. However, I was surprised that no one with experience in the CARMA total power effor was included in this project.

The amount of effort required by this project as outlined in the work plan (4.3) is fairly ambitious to carry out on the outlined time scale. There was no discussion of the amount of effort and troubleshooting that will need to go into designing ALMA observing scripts to do total power and whether or not this is a simple implementation or will require more effor than anticipated.

8. Assessment of the level of risk inherent in the design;

The risk assessment level seems reasonable, but there was also no discussion of whether there might be additional technical limitations that may preclude total power on the 12m array. But, this study aims to determine if total power is feasible or not with the current hardware.

9. Strength of the Scientific Team supporting the Study;

The science team supporting the study is excellent, no weaknesses.

10. Level of support guaranteed by the Institutes;

The level of support by the non-NRAO members is reasonable; however, additional NRAO support beyond what is specified in the labor estimate may be required for success.

11. Budgeted cost of the Study;

The budget is reasonable, but this study might have benefitted from more personnel dedicating more time to the effort in order to complete it within the allotted time.

  • *Reviewer*10

Grade: 4.5

Title: Total Power with the 12-m Array: Unlocking ALMA’s Potential for Astrochemistry in Extended Sources (PI: Cordiner)

Summary: The authors propose to implement a technical capability to support summed single-dish observations using 45 x 12m ALMA antennas, using frequency- or position-switching as well as ALMA hot/cold load calibration, to reach a net single-dish sensitivity of ~0.2 mK per 1.5 km/s at 230 GHz in 5 hours of observation and 0.25 mK at 350 GHz. This would be an order-of-magnitude improvement over the APEX telescope. The supporting science goals include the study of cometary coma chemistry, AGB circumstellar chemistry, astrochemistry of the ISM at larger angular scale, and planetary chemistry.

1. Alignment with NA ALMA Partnership strategic goals;

This proposal aligns most closely with the following NA ALMA strategic partnership goal: • (1.1) Improve and extend technical capability: new software and computing technologies that improve and extend capabilities for scientific research.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

This proposal advocates using ALMA as a net single-dish, so improves total sensitivity in this specific region of spatial frequency coverage, but does not overlap strongly otherwise with core priorities noted in ‘ALMA 2030’.

3. Quality of the upgrade conceptual design;

The proposal has specific strengths. It will provide much greater insight into single-dish AC mode for individual (or collective) operation of the 12m ALMA antennas, and will add a new scientific observing mode or niche. I am convinced of the unique scientific value for cometary astrochemistry given the unique angular scales, but less so for AGB or ISM studies, where it is less easy to see this as a highly competitive use of ALMA interferometric time. Even if performed simultaneously there will be scheduling overhead.

The authors propose a full exploration of the feasibility of position- or frequency-switching single-dish calibraiton at these frequencies, at this site, and with the frequency response of the ALMA antennas. The concerns are well-known and the initial results in Figure 4 are not unsurprising. I am cautious about the quality of the residual baselines likely achievable. The project will also certainly require technical exploration of antenna control modes (frequency and position switching) as well as understanding the exact treatment of AC data in the correlator.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

The authors have done initial work and show preliminary results here. The work plan (4.3) can be acted on immediately. However, the data reduction implementation is perhaps being underestimated as it is cited as a task to be delegated to the CASA group and is not an insignificant amount of effort. Fully functional packages that can handle both interferometric and single-dish analysis are notoriously difficult given the assumptions each mode inherits. Much progress has been made, but this is a risk to the schedule.

5. Strength of the consortium organization (if applicable);

This is a very strong consortium.

6. Qualifications of the key personnel of the Study;

The key personnel are highly qualified for this task.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

The institutes have strong experience in this area.

8. Assessment of the level of risk inherent in the design;

I believe there is fundamental risk in the feasibility of single-dish calibration using the proposed calibration modes that will reach the target net sensitivity, however it is certain that this exploration will lead to a greater understanding of this mode at ALMA, and a determination in practice is the only way forward on this question. I believe the requirement to explore aspects of the antenna control system (frequency & position), and the correlator affecting these observations is underestimated, and could present technical roadblocks or significant schedule risks.

9. Strength of the Scientific Team supporting the Study;

The scientific team are very experienced.

10. Level of support guaranteed by the Institutes;

There is no external collaborating institute contribution.

11. Budgeted cost of the Study;

The budget and schedule seem substantially under-estimated relative to the scope of work. Several participants are involved only for weeks on the study.

  • *Reviewer*13

Grade: 2.0

Title: Total Power with the 12-m Array: Unlocking ALMA's Potential for Astrochemistry in Extended Sources

1. Alignment with NA ALMA Partnership strategic goals;

Comment: Alignment with NA ALMA partnership goals is not clear to me, however the science goal seems to be well justified, and well researched, and the technical goals are very well aligned with the science goals.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

Comment: I believe this particular proposal has goals which lie outside of the purview of the ALMA 2030 documents so not really sure how to handle this—I prefer not to penalize. Total power is not listed in the ALMA 2030 ASAC documents, nor are the latter documents referenced in the proposal. Nonetheless, and confessing to a lack of specialization in the specific science targeted, I think the proposals describes and justifies the goal well. I worry just a little about the opportunity cost of using ALMA in a non-interferometric mode.

3. Quality of the upgrade conceptual design; Comment: Very good. The proposers plan to produce scripts and post-processing software, and I think they justify the approach to these goals well.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

Comment: This proposal is quite non intrusive, depending as it does on the development of specialized observing scripts, and observing tools which handle ALMA data, but do not actually touch the ALMA observing system. As such I think the implementation can indeed be completed rapidly and with a minimum of disruption.

5. Strength of the consortium organization (if applicable);

Comment: The PI and team seem to be a good match to the work to be accomplished.

6. Qualifications of the key personnel of the Study;

Comment: Cordiner and collaborators seem to be well qualified.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Comment: Ok or not applicable.

8. Assessment of the level of risk inherent in the design;

Comment: Though it is hard to assess the risk, if any, that the work may not result in the science of quality that is advertised, the risk of other adverse outcomes would seem to be negligible.

9. Strength of the Scientific Team supporting the Study;

Comment: Well matched to the study and well qualified.

10. Level of support guaranteed by the Institutes;

Comment: not applicable.

11. Budgeted cost of the Study;

Comment: My assessment is the study budget is good value for the potential science yielded.

-- AlWootten - 2017-07-19
Topic revision: r1 - 2017-07-19, AlWootten
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