Queued Service Observations with MegaCam

Phase 1 Proposal Submission Instructions

Updated Feb 17, 2021

Table of Contents

A - Introduction

B - Important information and news

C - NorthStar

D - Applicants

E - Justifications

F - Observing Requests

G - Target list

H - Additional issues

Z - Check list

A - Introduction [Back to Table of Content]

MegaCam, the QSO mode, and the QSO SNR mode

MegaCam is CFHT's optical Wide-Field instrument, offered with a new set of broad-band and narrow-band filters:

The old broad-band filters are not offered anymore.

For details about the filters, please see the new filters page (transmission curves, basic characteristics) and the Technical Considerations page. For other details about the instrument, please see its webpage. If you have additional questions, please contact Heather Flewelling (heather -=at=-

MegaCam is offered under the Queued Service Observing (QSO) mode only. The main concept behind the QSO scheme is to perform observing programs only during sky conditions or time constraints required to meet their science goals, as defined by the investigators. This can only be achieved if the programs are all grouped together in a database and are selected appropriately according to a set of constraints, rules and sky conditions. Programs are then carried out by a well trained, local team of observers in a service mode (i.e. investigators are not present at the observatory).

Before submitting a CFHT proposal, please read the short tutorial How QSO works at CFHT. [Keywords: QSO, Regular/TOO/Snapshot programs, Deadlines, NorthStar, Exposure Time Calculators, Technical Evaluations, TAC, Ranking, QSO grade, C programs, Snapshot programs, PH2, Observations, Sky conditions, Calibrations, Night Reports, Data reduction and distribution, Proprietary period, QSO rules, Contact information.]

Starting in 2017A, the QSO SNR mode (using condition-driven exposure times with a SNR goal rather than fixed exposure times) is used by default for all programs except non-sidereal observations, short exposures (<30s), or observations that require precise timing. To opt out of the SNR mode, include a justification in your proposal.

NorthStar Phase 1 Tool

CFHT is using the NorthStar Phase 1 tool. NorthStar is used by Principal Investigators (PIs) to submit their proposal(s). All new PIs must register as new NorthStar users; the registration page offers a Help file if assistance is needed. The login information from NorthStar is NOT transferred to PH2. After login in, Help on how to use NorthStar is available on each page.

For technical information regarding MegaCam, please see the MegaCam page.

B - Important information and news [Back to Table of Content]

Please consult the generalities regarding the current Call for Proposals.

Extension of the proprietary period for metadata

PIs have the option of requesting a delay in the reporting of the metadata with appropriate justification in their proposals. This can be done via Northstar by checking "Yes" to the "Exception to the Community/World proprietary periods and metadata release" in the Observing request tab and writing your justification in the box that appears. The metadata includes the name and coordinates of the targets. Unless the release date for the metadata is extended, they will become available immediately at CFHT and CADC.

Gender neutrality of Canadians proposals

For Canadian proposals, the name of the PIs will be withheld from the proposals sent to the Canadian TAC to avoid gender bias issues; the top corner of each page will have "(blank)". The proposal will instead list the name of the authors in random order. However, accepted proposals will be created under the PI's name as previously.

Available dark time and pressure from Large Programs

Please consult the table of Approximate RA pressure from Large Programs for this semester. The dark time is split between MegaCam and SITELLE and the bright time between ESPaDOnS, WIRCam and SPIRou.

MegaCam PI programs that overlap in RA with the Large Programs will suffer from the competition with the LP unless they request grey or bright time, and/or a poorer Image Quality.

Following a SAC 2014 recommendation: "Beginning with the proposals submitted in the March 2010 round, when CFHT performs its technical evaluation (which is then communicated to the TACs), CFHT will flag any proposal which has conflicts in RA and observing conditions with an existing LP. During their ranking process, the national TACs which are participating in both the conflicting PI programs and LP(s) will provide information to CFHT on the relation and priority of each of those, although agency balancing will continue to be the first decision point for CFHT" (see SAC recommendation #12 from Nov 2009).

QSO SNR mode

Starting in 2017A, the QSO SNR mode (using condition-driven exposure times with a SNR goal rather than fixed exposure times) is used by default for all programs except non-sidereal observations, short exposures (<30s), or observations that require precise timing. To opt out of the SNR mode, include a justification in your proposal.

Mandatory ETC calculations

PH1 mandatory field
The PH1 system has been changed to have users include the values of the exposure time calculators into their proposals. Proposals cannot be submitted if this field is not filled. This is not counted toward the page charge.

Snapshot programs

All agencies are invited to encourage their community to submit snapshot programs. These programs must be able to accept an Image Quality worse than 1.2" or significant levels of extinction. Snapshot programs are used not only during bad weather conditions but also to fill gaps in the queues when no A, B or C program are available or suitable. Snapshot programs are not counted toward an agency's allocation.

Non-sidereal observations

Non-sidereal guiding is now offered. The non sidereal tracking option is still available (following a target with non-sidereal rates, but without guiding on stars), but the telescope shows drifts on exposures of 2-3min or longer. If you have questions or concerns related to this option for your proposal, please do not hesitate to contact the QSO Team (qsoteam -=at=-

Updated Exposure Time Calculator DIET

The exposure time calculators for MegaCam and WIRCam, DIET, have been merged together. The ETC was also updated to include a galaxy profile mode. Please read the updated information about the new modes for point sources and extended sources. Note that between the most convervative (large aperture) and most aggressive (PSF photometry) modes, the exposure times for the same SNR vary by more than a factor of 3. Be sure to know what type of SNR you are requesting! Please present in your Technical justification the details of your exposure time calculations.

The new galaxy profile mode was added to the previous point-source and extended source modes. This new mode corresponds to galaxies more extended than a point-source, but where the seeing still matters. The galaxy profile itself is based on Sersic profiles with indices varying from 1 (exponential disks) to 5 (4 corresponds to de Vaucouleurs. profiles, typical of elliptical galaxies). The width of this profile is settled by the half-light radius, given in arcsec. The galaxy profile is then convolved with the seeing profile to make the exposure time or signal-to-noise ratio computations. This new feature is intended to replace the .galaxy" choice in the previous ETC. For larger galaxies where the seeing does not matter, you can either use the galaxy mode with a large half-light radius, or the extended source mode if you plan to reach a given surface brightness in the outskirts of the galaxy.

The primary mirror was recoated in September 2020.

Page limit for Canadian proposals

For Canadian proposals: the Science justification is now limited to 2 pages, and the Technical justification to 1 page. For all other agencies, the page limits are 3 pages and 2 pages respectively.

For more information about the submission of your QSO proposal(s), contact the QSO Team qsoteam -=at=-

C - NorthStar [Back to Table of Content]

NorthStar is the Phase 1 tool to submit proposals. This tool is not Latex-based. The scientific and technical justifications, along with references and figures, are uploaded as PDF files, which may be prepared by the PIs on any software they may wish to use. Figures and references may be included with the Scientific and/or the Technical justifications.

Also note the following regarding the list of targets:

D - Applicants [Back to Table of Content]

For each proposal, there can only be one submitter. However, co-I may be invited to view and edit the proposal too. The PI may also be different than the proposer (contact author). Note that if a proposal is accepted, it will get registered in PH2 under the PI's name, not the name of the contact author or the submitter! Each program belongs to its PI and requires the PI's login information in PH2.

E - Justifications [Back to Table of Content]

The Scientific and Technical justifications must be uploaded as PDF files, and have a limit of 2 and 1 page respectively for Canadian proposals, and 3 and 2 pages respectively for all other agencies.

Please use the MegaCam Direct Imaging Exposure Time Calculator (DIET) to calculate the exposure time for each of your target and justify the total integration time requested. The justification must mention the SNR needed per exposure and/or to obtain the required final depth, and this number must be reflected in the ETC examples provided.

Starting in 2017A, the QSO SNR mode (using condition-driven exposure times with a SNR goal rather than fixed exposure times) is used by default for all programs except non-sidereal observations, short exposures (<30s), or observations that require precise timing. To opt out of the SNR mode, include a justification in your proposal.

F - Observing Requests [Back to Table of Content]

For MegaCam, you may select QSO Regular programs or QSO Snapshot program. QSO Regular programs include all of the normal QSO programs, with fixed or Solar System objects. Target-of-opportunity (TOO) programs submitted at the same time as all other CFHT proposals may simply be submitted as a QSO regular program. Snapshot Programs must request bad sky conditions and accept a low completion level.

The definition of a snapshot program for MegaCam is the following:

  1. A snapshot program describes valuable science to be obtained on targets observed only in the worse sky conditions (seeing larger than 1.2" in r band, and preferably during non-photometric conditions)
  2. A snapshot program will be scientifically useful even of the completion is low
  3. A snapshot program requests simple observations, preferably with the standard ugriz filters (narrow-band filters are possible too but are not always available), sidereal tracking, no monitoring
  4. A snapshot program should preferably include short blocks of observations
  5. The time allocated for such programs is not accounted for in the statistics of time spent for the different Agencies
  6. The proprietary time for the data is 3 months following the end of the semester.
Note that the chance of such programs to be executed, even partially, during a semester can be quite high.

The probability of observing a specific program depends strongly on the image quality requested versus the statistics of the site. The chance that your program is performed is less if you request an IQ of 0.55" than if 0.8" is required. Of course, science should be the priority in your selection of IQ but beware that it cannot be the only criterion in your choice. So, do not request a better image quality than what is really needed for your program. For guidance, the table below describes the seeing statistics on Mauna Kea. These data are for the R-band and were taken with FOCAM at CFHT between 1993-1995 (more recent statistics confirm these values). Note that with MegaPrime we globally achieve about the same IQ distribution than with CFH12K, but not much better.

Image Quality (IQ) Frequency
IQ 0.55" 5%
0.55" < IQ 0.65" 25%
0.65" < IQ 0.80" 30%
0.80" < IQ 1.0" 25%
1.0" < IQ 1.2" 15%
IQ > 1.2" 5%

For your information, the table below gives the average weather statistics for Mauna Kea. Note that the "A" semester is usually more affected by bad weather; time lost during the first few months of the winter can be as high as 50% and even more.

Sky Conditions Frequency
Usable Nights ~70%
Lost to Weather ~20-30%
Usable Photometric Nights ~50%

In queue mode, the time requested is in HOURS.

  1. If the total time of your program is fractional (e.g. 32.4 hr.), please indicate so (.4 hr in a queue mode is possible).
  2. In your calculation of integration time, only add 40s of overheads for each exposure (for readout).
  3. Slewing and acquisition of a guide star SHOULD NOT be accounted for in your calculations.
  4. CFHT provides instrumental calibrations (e.g. flats) and photometric standard stars for the broad band filters only. Photometric standard stars for narrow-band filters, and any other on-sky calibration MUST be included in the proposal and in the time requested. The "Calibration Requirements" box may be used to present those calibrations.

Any time constraint or scheduling constraint must be indicated in the proposal: the need for a certain number of consecutive nights, the need for long blocks of time (for example, 8 hours) per night, the need to coordinate CFHT observations with observations taken by another telescope, etc.

By default, the proprietary period of QSO data extends to 1 year + 1 month starting at the end of the QSO semester. If an extension is requested and approved by TAC, a new date will be set for this program through the QSO system. The release date for the data is indicated in the fits headers by the keyword REL_DATE. For snapshot programs, the proprietary time is 3 months following the end of the semester.

G - Target list [Back to Table of Content]

Besides a list of targets with coordinates, MegaCam proposals may include the magnitude of each target or the diameter of the field. This information will be used to evaluate the technical feasibility of each proposal.

H - Additional issues [Back to Table of Content]

The Additional issues tab is used to link various proposals together, if need be.

Z - Check list [Back to Table of Content]

Before submitting your proposal, please make sure that:

Need More Information?
Contact the QSO Team at
qsoteam -=at=-