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CFHT Legacy Survey Science Query Help


General Description

This form can be used by registered CFHTLS users to browse the catalog of CFHTLS science images. This catalog is a subset of the larger and broader MegaPrime image catalog created by selecting only MegaPrime observations with run ID's containing the letter "L" for the agency code. Queries can be executed based upon object and/or observational constraints.

Retrieval Options

Field Name Description
Order_by Use this selection box to list the results of your query in the desired order. The default is to list most recent exposures first.
Return Maximum number of rows to be returned by query.

Object and Coordinate Constraints

Field Name Description
Object Name The object name. Note that object names are defined by the observers according to a soft set of target naming conventions. When searching on this field you can either search on the CFHT object name (liberal use of wildcards is recommended. The match is not case sensitive) or query the CADC resolver (which uses NED and SIMBAD) for the coordinates of the given object.
Name Resolver The user can specify the source of the target name to use. We strongly recommend using the SIMBAD target name. In this case, we transparently interrogate SIMBAD to resolve the target name in searching coordinate with a box size.
RA The right ascension of the target. The search box specifies the search range.
DEC The declination of the target. The search box specifies the search range.
Equinox Equinox for object equatorial coordinates. Possible choices are B1950.0 or J2000.0 (default).
Galactic Latitude Galactic Latitude (bii) of object.
Galactic Longitude Galactic longitude (lii) of object.
Search Box The search box can be used as an easy way to specify a range on RA and Dec. The range given here is applied to the coordinates returned from a RESOLVER search, or if you type in coordinates in the RA and Dec fields below. Default value is 40 arcminutes.

Observation Constraints

Field Name Description
Exposure Number The unique identifying "odometer" number for a CFHT exposure.
Survey Type The CFHTLS is sub-divided into three different surveys: Very Wide (Kuiper Belt objects), Wide Synoptic (weak lensing), and Deep Synoptic (supernovae). The "PI Follow-ups" survey type consists of PI CFHTLS follow-up programs that have been kindly made available to the entire CFHTLS community by their respective PI.
Run ID Identification code for observing run during which observation was taken. Example: 2003AL01. All CFHTLS science observations are uniquely identified by the letter "L" as the agency code in their run ID.
Camera Run ID Identification code for camera run during which observation was taken. The camera run ID uniquely identifies a given period of time during which MegaPrime is mounted on the telescope. Example: 01Ak01 denotes the period between 2001/01/27 to 2001/02/06. A camera run can therefore encompass many observing runs. The full list of camera run IDs can obtained from the MegaPrime camera run ID page at CFHT.
Creation Date The UT time and date when the observation was begun, e.g. 12 Dec 2003
Release Date The UT time and date when a CFHTLS observation (and any available previews) becomes public data. Prior to this date only registered members of the CFHTLS community can request the data.
MJ Date The Modified Julian Date of the observation.
Sidereal Time Sidereal time of the observation.
Observer Last name(s) of the observer(s).
PI Name Last name of Principal Investigator. In the case of CFHTLS data, this is the last name of the Survey Coordinator for the program under which the observation was taken.
Exposure Time Exposure time of the observation in seconds
Filter Filter used for the observation.
Airmass Airmass at which the observation was taken.
Observed Image Quality Observed image quality (FWHM in arcsec) of the observation. For raw science images, the image quality was computed using the quick Elixir processing pipeline at the summit. The IQ statistics are derived from the Elixir processing based on SExtractor analysis of each of the MegaPrime CCDs. The five IQ statistics provide several views of the global image quality in a MegaPrime image.
  1. IQ_REFCCD gives the image quality measured for the single reference CCD (currently ccd13). This measurement is used by the QSO team during the observations and the validation stage to assess if the image meets the requested image quality.
  2. IQ_CENTER is derived from the central 10 detectors. The 10 values are clipped for > 3 sigma outliers before the remaining detector IQ values are averaged.
  3. IQ_R_RATIO provides the ratio between the central 10 detectors and the outer 26 detectors. Both lists are clipped by 3 sigma as above.
  4. IQ_X_RATIO provides the ratio between the left (east) 8 detectors and the right (west) 8 detectors. Both lists are clipped by 3 sigma as above.
  5. IQ_Y_RATIO provides the ratio between the top (north) 9 detectors and the bottom (south) 9 detectors. Both lists are clipped by 3 sigma as above.
Observed Image Background Observed image background the observation in counts per second.
Limiting Magnitude Limiting magnitude of the observation. Available only for processed science images as it is determined by Elixir.
QSO Eval Service Observing Rating. This flag ranges from 1 to 4 and is set in real-time during the night by the observer at the telescope. The meanings of the flags are:
  1. Taken within, or better than, the conditions defined by the Principal Investigator (the Survey Coordinator for the CFHTLS) in terms of seeing, sky background, and sky transparency.
  2. Taken almost within the conditions defined by the Principal Investigator (the Survey Coordinator for the CFHTLS): one of the three parameters (seeing, sky background, sky transparency) is slightly out of boundaries.
  3. Taken outside the conditions defined by the Principal Investigator (the Survey Coordinator for the CFHTLS): one of the parameters (seeing, sky background, sky transparency) is way out of boundaries, or two, or all of the parameters are out of bound.
  4. Horrible observing conditions which most likely prevent any science to be done.
  5. A lost cause, nothing to be done with that exposure.
QSO Status QSO Coordinator validation. This flag can be set to "VALIDATED" or "OBSERVED". The day following the night when that exposure was obtained, the QSO coordinator checks the service observer rating and other comments to define if that exposure fits within the specifications defined by coordinator. The fact that an exposure is validated does not however necessarely means that its integration time will be accounted for in the time balance allocated to the observing program: this depends on the observing group validation described as follows:

- VALIDATED: the exposure qualifies for the science goals defined by the Principal Investigator. An exposure can be validated even if the Service Observer rating is equal to 2 since a degradation on of the parameters won't most likely affect the science dramatically.

- OBSERVED: the exposure does not qualify for the science goals defined by the Principal Investigator (the Survey Coordinator for the CFHTLS). The exposure will be processed and distributed anyway but the time used to acquire it is not deducted from the time allocated to the observing program.

QSO Comment Comment written by the Service Observer at the time of image acquisition. Mainly used to describe telescope status and weather conditions.

Processing Constraints

Field Name Description
Processing Level This field can be used to select science images with different levels of processing. There are three possible options:
  1. "Processed" will show only images that have been processed by the Elixir system.
  2. "Raw" will show only images that have not been processed by the Elixir system.
  3. "Either" will show current image processing levels (raw or processed).
MasterBias Master detrend bias calibration image used if bias correction was applied.
MasterDark Master detrend dark calibration image used if dark correction was applied.
MasterFlat Master detrend flat calibration image used if flat-field correction was applied.
MasterFringe Master detrend fringe calibration image used if fringe correction was applied.
MasterScatter Master detrend scattered light calibration image used if scattered light correction was applied.
MasterMask Master bad pixel mask if bad pixel masking was applied.
PhotCal This field can be used to select science images with or without photometric calibrations. There are three possible options:
  1. "Status" will show the current status of the photometric calibrations of the images returned by the query.
  2. "Calibrated" will show only images that have been photometrically calibrated.
  3. "Uncalibrated" will show only images that have not been photometrically calibrated.


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