SMA OBSERVER CENTER
 

Call for SMA Science Observing Proposals

This site is not currently open for submission of standard proposals. This previous call document is for reference only.

The SMA Time Allocation Committee warmly welcomes submission of proposals for the upcoming 2021B semester. We actively solicit projects of all sizes, and we are particularly interested in increasing the number of smaller proposals that take just a few hours in time, projects that are especially time critical (such as coordinated observing campaigns and ToO triggered event programs) and require data in the coming several months, and in monitoring type proposals.

Information on the array and the submission process are provided below, and we are available to answer questions or point you to any information you may need. Please contact us at sma [hyphen] propose [at] cfa [dot] harvard [dot] edu for questions on proposal preparation, observing techniques and strategies, observing control scripts, and data analysis.


Contents:

Proposal Deadline

Proposal Preparation

Proposal Evaluation

Accepted Proposals and SMA In-Person Observing



Proposal Deadline

The joint SAO-ASIAA SMA Time Allocation Committee (TAC) solicits proposals for observations for the period 2021 Nov 16 - 2022 May 15. Proposals must be submitted by:

Thursday, 16 September 2021, 10:00 HST (Hawaii)
Thursday, 16 September 2021, 16:00 EDT (Cambridge, MA)
Thursday, 16 September 2021, 20:00 GMT
Friday, 17 September 2021, 04:00 CST (Taipei)


SMA Observing Time

The SMA is a joint project funded by the Smithsonian Astrophysical Observatory (SAO), one of two partners in the Center for Astrophysics | Harvard & Smithsonian (CfA), and the Academia Sinica Institute for Astronomy and Astrophysics (ASIAA). The SMA also includes the Institute for Astronomy (IfA) at the University of Hawaii as a partner institution. The time allocation ratios for the three SMA partners, CfA:ASIAA:IfA, are 72:13:15. To promote excellence in scientific research and cooperation in the scientific community, the CfA follows an "open-skies" policy in allocating its share of the SMA time. Proposals from institutions worldwide are accepted for the CfA time and judged solely on scientific merit.

Standard Observing Proposals: Beginning with the 2011B observing semester, the CfA and the ASIAA use the same time allocation committee (TAC). PIs from ASIAA should submit through the ASIAA queue to take advantage of the guaranteed time share of the ASIAA. Astronomers proposing for IfA time should submit proposals directly to the IfA, following their independent procedures. Proposals from outside institutions should be submitted to the CfA/SAO queue. Collaboration between the partner institutions as well as between the partners and other institutions is encouraged.

Large Scale Science and Key Projects: In addition to standard proposal programs, SMA from time to time offers the opportunity for large-scale projects needing observing time in the range of 100 to 1000 hours. As a result, if one or more large scale project proposals is successful, the time available for standard projects will be reduced. Proposers should refer to Observing Time Available for information regarding ongoing large scale projects in the upcoming semester.

DDT Proposals: Several nights of Director's discretionary time are reserved for potential targets of opportunity and other use. Please contact the TAC chair, Mark Gurwell, and the director, Ray Blundell at SMA_DDT [at] cfa [dot] harvard [dot] edu to apply for this time.

Number of Nights Available

On average, between five and six nights per week are allocated for routine science observations. Weather statistics suggest that approximately half of the useable time is suitable for observations in the 230 GHz and the 345 GHz bands each. Taking account of time devoted to testing, reconfigurations, and bad weather, the combined CfA+ASIAA share of the SMA time per semester averages about 50 nights each for the 230 GHz and the 345 GHz bands. The TAC uses these averages to set the approximate number of A-rated tracks.

In 2021B, the fraction of time available may be reduced, depending on safety protocols in place as a response to the coronavirus pandemic, and considering a backlog of repairs and maintenance that needs to be performed. However, we hope to run as close to a normal semester as possible under these constraints.

The oversubscription rate is a function of target RA and DEC. The figure below shows the distribution of target RA proposed in the past, with notable peaks along the inner Galactic Plane, nearby star-forming regions, and extragalactic fields.

Support for New Users

For some basic information on the SMA and its capabilities, as well as more general background information, please see the Technical Information, Tools, and Resources section below. There you will find links to the basic specifications, technical information, useful tools, and several presentations on the SMA and interferometry in general.

The SMA staff offers support for observers who are not familiar with the SMA. We can provide support at different levels, from help getting started to full collaboration. Please contact us at sma [hyphen] propose [at] cfa [dot] harvard [dot] edu for questions on proposal preparation, observing techniques and strategies, observing control scripts, and data analysis. The SMA also offers a first step data reduction of an observation upon request, for PIs who are not familiar with interferometry and/or the SMA.

"Time Charged" Allocation Rules

Under nominal conditions, 8 antennas are available for scientific observations with the SMA. However, maintenance and operational issues may reduce the number of active antennas available for any given track. In order for a track to be considered passing, the project must a) meet the weather stringency requirements for the track, and b) have a minimum number of elements available in the array, the latter of which is defined as follows:

  • Full-polarization tracks: 7 working antennas with both an operational LCP and RCP receiver
  • Dual-polarization tracks: 14 working receivers (7 tuned to the RxA tuning, 7 tuned to the RxB tuning)

When the array meets the above, the full observing time is charged to the project (i.e., the track is considered "passed"), provided no other significant technical or weather issues. When there are fewer than the above number of elements, but the weather requirements for the project are met, then the project is charged for time/tracks in the following fashion:

  • 6 working antennas/12 working receivers: If the weather is better than requested (e.g., < 2.5 mm PWV during observations, when < 4 mm PWV was requested), then a full track is charged. Otherwise, the project is only charged half-time. I.e., 2 tracks w/ at least 6 antennas/12 receivers are combined to make a single "passing" track).
  • 5 working antennas/10 working receivers: The project is only charged a third of the time. I.e., 3 tracks w/ at least 5 antennas/10 receivers are combined to make a single "passing" track.
  • Fewer than 5 working antennas/10 working receivers: No time charged.

There are two important caveats about the above. First, it does not apply to triggered ToO observations, where the array is accepted "as-is" at the time of trigger. Second, the above does not account for differences in the synthesized beam that may arise from a limited number of elements in the array, and thus may not be suitable for high-SNR projects, where imaging fidelity is primarily limited uv-coverage. PIs with projects that fall into this category may stipulate as much in the "additional instructions" field in the individual time requests, in which case the project will nominally not be run with fewer than 7 antennas.



Proposal Preparation

Checking for Existing SMA data

The SMA has been in operation for nearly 20 years, and has an extensive science data archive. Proposers should query the SMA archive prior to planning new observations to see if existing SMA data suit their scientific goals. Data from past SMA observations are archived by the CfA Radio Telescope Data Center and may be searched. SMA data are publicly available after a proprietary period of 15 months.

If older data exist, the PI should include a short statement in their proposal discussing why new observations are warranted.

Proposal Forms and Submission

Proposals are submitted through each individual PI's SMA Project Account. The project account contains all information about an observer's proposals and projects, and will persist for reuse in future proposal cycles. All SMA project activities begin at the user's My Projects page. Project accounts may be created from the login page if necessary (current SMAOC account holders do not need a separate project account).

Using the proposal submission facility, drafts may be created and edited at any time, but may only be submitted within a few weeks prior to the proposal deadline. Each proposal consists of an on-line cover form and technical information forms, and an attached scientific justification in PDF format. Proposals may be saved and edited on-line as often as needed prior to final submission.

The scientific justification is limited to a maximum of four US-letter sized pages including all text (11pt or larger, with reasonable margins) figures, tables and references. The PI is now free to design their proposal within those boundaries, such as mixing figures within text. The PI should aim for approximately equal space for prose (science justification+technical rationale) vs figures, tables, etc., and text alone should not exceed 3 pages. PLEASE NOTE: typically, a picture is truly worth many words, and proposals that are primarily text will generally not fare well. We strongly urge the PI to consider readability by TAC members; they are experts, but may not be experts in your field.

Proposals should provide clear statements on, and justifications for, the rms flux sensitivities, spectral resolutions, antenna configuration(s), weather conditions, calibration strategies, and (if applicable) any time constraints needed to achieve their science goals.

RA Coverage by Semester and UV Plane Considerations

SMA observations are generally executed at night when the atmospheric phase noise is low and often continued into the early morning. Conditions are rarely suitable for afternoon observations. For 2021 November - 2022 May observing, long tracks will be feasible during at least half the semester for sources in the range of roughly RA=4h to 16h. Sources outside this RA range will also be considered if adequate justification is provided. However, since the array configuration schedule is set to accommodate the most highly ranked approved proposals, such observations may not be possible.

The SMA operates in 4 configurations with maximum baselines of 30m (the six antennas on the inner ring of "subcompact"), 70m ("compact"), 220m ("extended"), and 508m ("very extended"); see Technical Information, Tools, and Resources section below for more infomation. The configuration schedule is determined after the TAC process to best fit the highest ranked approved projects.

Many projects do not need full tracks (a full rise to set observation)for adequate uv coverage and/or sensitivity, and the TAC strongly encourages requests for snapshots, partial tracks, and tracks sharing several targets in a field to enhance efficiency.

Technical Information, Tools, and Resources

For Semester 2021B we are offering as a standard capability our expanded processed bandwidth of 12 GHz per sideband per polarization, equal to 48 GHz of total processed dual reciever bandwidth, all at 140 kHz resolution. All receivers and IF chains offer full bandwidth (4-16 GHz IF range), allowing each receiver to covering 12 GHz in each sideband. In much of the SMA tuning range (~200 - 275 GHz and ~328 - 365 GHz), where receivers with orthogonal polarization have overlapping coverage, the receivers can be tuned with the same LO frequency, providing dual polarization observations for increased line sensitivity. In the case of equal LOs for the two selected receivers, it is also possible to obtain full polarization observations near 1.3mm and 870 micron.

The receivers are also independently tunable. Around the regions of tuning overlap for the dual recievers, a continuous 44 GHz coverage is possible (with 4 GHz of 'overlap'). See Array Status and Technical Information for more details, where up-to-date technical information about the SMA, including antenna configurations, correlator setups, receiver status, and new or updated SMA capabilities are always available.

The SMA maintains several online tools for planning SMA observations, available on the Tools page.

The Beam Calculator / Sensitivity Estimator is a particularly useful tool to estimate angular resolution, UV coverage and nominal sensitivities for different configurations and weather conditions (precipitable water vapor). Variations in weather may considerably impact actual sensitivities.

Generally, observations at lower frequencies can be done in atmospheric conditions of higher precipitable water vapor. Standard values are < 4.0 and < 2.5mm of water vapor for observations in the frequency ranges <300 and 300-420 GHz, respectively. Proposers must indicate and justify the atmospheric conditions required for their scientific goals. The SMA is more oversubscribed in the weather conditions suitable for the 350 GHz band (< 2.5mm water vapor).

The Passband Visualizer Tool provides interactive information on spectral line coverage and tuning.

SMA observations require calibrator sources for bandpass, gain, and flux calibration. Quasars are generally used for bandpass and gain calibration; however, suitable calibrators may not be available for all parts of the sky particularly at the higher frequencies. See The Submillimeter Calibrator List. Solar system bodies are generally used for flux calibration but may not be available at all times of the year. Observers should show that their proposed observations can be adequately calibrated.

Resources:

SMA Basic Specifications

Array Status and Technical Information

SMA Introduction and Proposal Information (2021A) PDF of 19 Feb 2021 presentation

SMA Proposal Planning Tools

Presentations from the 2021 SMA Interferometry School


Proposal Evaluation

Proposal selection is based on clearly demonstrated scientific merit, alignment with SMA uniqueness and capabilities, and technical feasibility.

The TAC assigns each proposal a numerical score and recommends an amount of time to be allocated. The proposals are ranked and grouped into three categories: A (best effort to execute), B (may be executed as conditions permit), and C (will not be executed). Proposers are notified of their proposal rating by e-mail shortly after the TAC completes its work, typically within about 7-8 weeks of the proposal deadline. Please see the TAC Procedures for more details of the TAC review process.


Accepted Proposals and SMA In-Person Observing

All accepted proposals are shared-risk, with no guarantee of success. Standard proposals accepted but not observed due to time constraints will generally not be carried over and must be resubmitted in response to a future call for proposals.

Usually, principal investigators of successful proposals should be prepared to provide an observer on Mauna Kea. Most proposals are queue scheduled to maximize return based on the prevailing weather conditions and instrument status. The SMA scheduler decides which project will be observed each night. It is unlikely that visiting observers will execute their own project when present on Mauna Kea. Due to the ongoing pandemic, we are currently not hosting any visitors, including SMA staff not stationed in Hawaii, and it is uncertain when this will change. Therefore, at this time we do not know if observing support by PIs will be required for successful 2021B proposers.


Questions?

Please e-mail any questions about preparing and submitting proposals to sma [hyphen] propose [at] cfa [dot] harvard [dot] edu.

Last updated: 2021-Aug-14 by Mark Gurwell