CFHT, QSO



Queued Service Observations with WIRCam

Phase 1 Proposal Submission Instructions

Updated Aug 18, 2016



Table of Contents

A - Introduction

B - 2017A-specific 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]

WIRCam and the QSO mode

WIRCam is a wide field near-infrared camera using a range of narrow and wide band filters. The instrument uses a mosaic of 4 HAWAII-2RG detectors to both guide (on-chip guiding) and acquire science images with a FOV of 21'x21', with gaps of 45''. The pixel scale of 0.3'' slightly undersamples the PSF so a micro-dithering mode is available if the science project requires high spatial resolution. PIs are asked to carefully think about their observing strategy (specifically for sky subtraction) when determining their required integration time.

The filters offered are: Y, J, H, Ks, CH4 (on and off), LowOH-1, LowOH-2, H2, Kcontinuum, BrGamma, CO, and W. Available information about WIRCam filters includes central wavelength, bandwidth, maximum transmission, and transmission curves.

The limitation to at most one filter exchange during the semester remains in force. The SAC will arbitrate filter conflicts between highly ranked proposals, should any occur.

If you propose to use of a narrow band filter which is currently not on the WIRCam filter wheel, please read carefully (list of currently available filters is given below).

To fit a new filter on the WIRCam filter wheel, we have to warm up the detectors, since the filter wheel is inside the cryo-vessel. Each such warm up results in a noticeable degradation of the detector characteristics. To prolong detector life, our policy is to have at most one warm up per semester.

Therefore, to justify your request for a filter change, and to improve the strength of your proposal, please provide a strong case why the requested narrow band filter is essential for your science goals, especially pointing out why you cannot use the filters currently available on the filter wheel.

Importantly, note that even if you are awarded time, there is no guarantee your requested filter change will happen; you may be superseded by a higher ranked program also requesting another filter exchange.

Be assured that within this framework to prolong the life of WIRCam, we will do our best to accommodate your requests. Please contact qsoteam -=at=- cfht.hawaii.edu if you have any questions regarding this.

Narrowband filters in the filter wheel at the start of 2017A will likely be CH4On, H2, W and CO. The broadband Y, J, H and Ks filters are always available. The WIRCam filter wheel can accommodate only 8 filters at any given time.

For other details about the instrument, please see its webpage. For additional questions, please contact Pascal Fouqué (fouque -=at=- cfht.hawaii.edu).

WIRCam 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.]

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 WIRCam, please see the WIRCam page.

B - 2017A-specific information and news [Back to Table of Content]

WIRCam overheads

BASIC OVERHEADS FOR STANDARD DITHERING PATTERNS - If your program simply requires the use of standard dithering patterns, please include 10s of overheads per exposure.

NEW ADDITIONAL OVERHEADS FOR WPD - If you plan to use the "WIRCam Dithering Pattern" (WDP), which puts the object successively on each array of the mosaic, please add 30 seconds of overheads per exposure (instead of 10s).

OVERHEADS FOR LONG SLEWS - If you plan on requesting that we observe 2 targets distant by 15 or more arcmin, consecutively and in the same OG, please include 30s for overheads, for each such pair of 2 targets. Those 2 targets can be a galaxy followed by a sky location more than 15 arcmin away, or one section of a field followed by an adjacent section of that field 15 or more arcmin away. These 30s are in addition to the regular overhead charged for every program (10s per exposure for standard DP, and 30s per exposure for WDP).

Example #1: If your OG will consist of single exposures on 3 fields widely separated on the sky, the overheads will be 3 x 10s, plus 2 x 30s, or 90s total.

Example #2: If your OG will consist of 3 exposures per field (DP3 pattern) on 4 fields widely separated on the sky, the overheads will be 3 x 4 x 10s, plus 3 x 30s, or 210s total.

OVERHEADS FOR NODDING - If you plan to use the PH2-defined nodding mode (i.e. target-sky-target-), an overhead of 60 seconds must be added in your calculations for each slew between the target and the sky position.

WIRCam filters

If you propose to use of a narrow band filter which is currently not on the WIRCam filter wheel, please read carefully (list of currently available filters is given below).

To fit a new filter on the WIRCam filter wheel, we have to warm up the detectors, since the filter wheel is inside the cryo-vessel. Each such warm up results in a noticeable degradation of the detector characteristics. To prolong detector life, our policy is to have at most one warm up per semester.

Therefore, to justify your request for a filter change, and to improve the strength of your proposal, please provide a strong case why the requested narrow band filter is essential for your science goals, especially pointing out why you cannot use the filters currently available on the filter wheel.

Importantly, note that even if you are awarded time, there is no guarantee your requested filter change will happen; you may be superseded by a higher ranked program also requesting another filter exchange.

Be assured that within this framework to prolong the life of WIRCam, we will do our best to accommodate your requests. Please contact qsoteam -=at=- cfht.hawaii.edu if you have any questions regarding this.

Narrowband filters in the filter wheel at the start of 2017A will likely be CH4On, H2, and 2 proprietary filters (W and CO). The broadband Y, J, H and Ks filters are always available. The WIRCam filter wheel can accommodate only 8 filters at any given time.

Pressure from Large Prorams

Please note that during the semester 2017A, Large Programs are using the following RA ranges:

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).

Mandatory field for 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

The non sidereal tracking option (i.e., following a target with non-sidereal rates, but without guiding on stars) is offered, 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=- cfht.hawaii.edu).

Staring Mode

CFHT offers the Staring mode, which is useful for high accuracy relative photometry (better than 1%). Typical science goals are the study of exoplanet eclipses/transits or stellar variability of bright targets (~16 or brighter). It consists of full mosaic science exposures taken over long time sequences at a fixed telescope position (no dithering). Additionally, the telescope can be defocussed to spread the light of a bright object over many pixels, thus averaging individual pixel response errors.

Be advised that systematics are present that limit the achievable accuracy using differential photometry. RMS values <= 0.1% are possible but reaching 0.01% is challenging. See Croll et al. (AJ, 141:30, 2011) for details. Also, experiments using two filters should be considered risky.

If you would like to use that mode, please clearly state so in your proposal. If you have have any question about his mode, please contact Pascal Fouqué (fouque -=at=- cfht.hawaii.edu).

Exposure Time Calculator DIET

The exposure time calculator for MegaCam and WIRCam, DIET, have been merged together and now use a different interface, and different options. 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 exposure time calculator for MegaCam and WIRCam, DIET, have been merged together and now use a different interface, and different options. The ETC was also updated to include a galaxy profile mode.

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.

Page limits 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=- cfht.hawaii.edu.

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 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 WIRCam 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.

F - Observing Requests [Back to Table of Content]

For WIRCam, 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 WIRCam 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 K 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 JHK 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 getting data for a specific program depends strongly on the image quality requested versus the statistics of the site. The chance that your program is performed might be less if you request an exceptional image quality. 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 approximately the seeing statistics on Mauna Kea, in K band. Statistics reveal that seeing is highly variable during a night and globally better during the summer months (Seigar et al., 2002, SPIE, 4844, 366).


Image Quality in K Band (IQ) (airmass=1) Frequency
IQ 0.55" 20%
0.55" < IQ 0.65" 25%
0.65" < IQ 0.80" 20%
0.80" < IQ 1.0" 15%
1.0" < IQ 1.2" 15%

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% or more.

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

Important note on micro-dithering: The pixel scale in WIRCam is 0.3"/pixel so the best image quality which is adequately sampled is ~0.7". To make good use of better seeing, WIRCam uses micro-stepping (or micro-dithering): 4 individual exposures, shifted by 0.15" on a square grid, provide Nyquist sampling of the recombined image for all conditions (several groups of 4 micro-dithered exposures can be done sequentially on one dithering pattern position). In some cases this may require additional detectors readouts, and therefore introduce overheads. Note that micro-dithering is not expected to yield much improvement when the natural seeing is ~ > 0.8". NOTE: Micro-dithering is NOT offered for the narrow-band filters.

In queue mode, the time requested is in HOURS. The numbers of hours to request must take into account the following information:

  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, four types of possible overheads must be considered. The overheads that apply to your observational strategy will be charged at the phase 2 level, and therefore must be requested now:
    1. A 10s overhead (reset + readout time, plus other general overheads) must be included for every exposure of a standard dithering pattern.
    2. A 30s overhead (reset + readout time, plus other general overheads) must be included for every exposure of a WIRCam dithering pattern (WDP).
    3. If you plan to use the PH2-defined nodding mode (i.e. target-sky-target-), an overhead of 60 seconds must be added in your calculations for each slew between the target and the sky position.
    4. If you plan on requesting that we observe 2 targets distant by 15 or more arcmin, consecutively and in the same OG, please add another 30s for overheads, for each such pair of 2 targets. Those 2 targets can be a galaxy followed by a sky location more than 15 arcmin away, or one section of a field followed by an adjacent section of that field 15 or more arcmin away. These 30s are in addition to the regular overhead charged for every program (10s per exposure).
  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.

Important Note on Maximum Exposure times: To limit the sky background and avoid severe non-linearity effects and saturation, exposure times for the filters have an upper limit. This limit is applied automatically in the Phase 2 tool. However, for purpose of correctly calculated the time needed for your observations, the maximum exposure times are given in the following table:

Filter Maximum Exposure Time
Y 150 sec
J 60 sec
H 15 sec
K 25 sec
LowOH1,2 3000sec
CH4on/Off 50 sec
H2/Kcont/BrGamma 200 sec

Important Note on Nodding: Infra-red astronomy differs from visible observations mostly because the sky background is a strong contributor and is much more variable. The near-IR sky on Mauna Kea can change by up to 10-20% in a few minutes. This is why exposure times and observing strategy must be able to frequently sample the sky. If the object is not very extended, the sky can be derived in regions of the mosaic without scientific signal for each dithering pattern position. However, when the object is extended (e.g. > 40% of the field of view of the mosaic), another technique must be used to sample the sky: nodding. The idea is simple: during the observations on the target, the telescope is slewed to a position away from the object in order to frequently established the sky background. For WIRCam, this is possible by applying regular offsets to the telescope. When calculating the time needed for your program, please take into consideration how much time will be needed to sample the sky background, if needed.

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, WIRCam 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=- cfht.hawaii.edu