CFHTLS & MegaPrime News
News from January 2004 and on
[previous 2001-2003 news have been integrated to
the new CFHTLS site in early 2004 and aren't considered updates anymore].
| Feb. 21, 2008 || 0038 || Cosmologists unfold the dark cosmic web || Science |
| Aug. 06, 2007 || 0037 || Notes on 06B&07A semesters - Missing i' filter || General information |
| Jul. 16, 2007 || 0036 || Details of the T0004 release || Data release |
| Jul. 04, 2007 || 0035 || T0004 Official Release available to LS members || Data release |
| Feb. 16, 2007 || 0034 || World wide release: first stacks + catalogs by Terapix || Data release |
| Jan. 02, 2007 || 0033 || CFHTLS and the CFHT at 2007 Users' Meeting || Science |
| Oct. 23, 2006 || 0032 || The CFHTLS continues after strong earthquake || General information |
| Jun. 30, 2006 || 0031 || World wide release: year 1 of CFHTLS public || Data release |
| Apr. 18, 2006 || 0030 || Wide survey: opening of the W4 field || General information |
| Apr. 07, 2006 || 0029 || Statistics: 3 years of scientific operations || Instrument performance |
| Mar. 10, 2006 || 0028 || XMM-LSS/CFHTLS cluster catalogue available || Science |
| Feb. 18, 2006 || 0027 || T0003 Wide+Deep release candidate available || Data release |
| Dec. 13, 2005 || 0026 || Discovery of an exotic Kuiper Belt Object || Science |
| Nov. 22, 2005 || 0025 || SNLS First Scientific Results Announced || Science |
| Sep. 12, 2005 || 0024 || Note on the half-mosaic night in 05BQ03 || Instrument performance |
| Aug. 25, 2005 || 0023 || Semester 05A completed & Semester achievements || General information |
| Aug. 12, 2005 || 0022 || MegaPrime image quality further improved || Instrument performance |
| Jul. 05, 2005 || 0021 || CFHTLS mid-term review: SAC and Board reports || General information |
| Apr. 05, 2005 || 0020 || Dates of CFHTLS releases to the world || Data release |
| Feb. 22, 2005 || 0019 || Semester 2004B completed, 2005A started || General information |
| Jan. 21, 2005 || 0018 || CFHTLS Workshop in Paris - May 2005 || General information |
| Nov. 24, 2004 || 0017 || 04BQ04 brings promising IQ improvement || Instrument performance |
| Nov. 23, 2004 || 0016 || Terapix Data Release T0001 available at CADC || Data release |
| Nov. 04, 2004 || 0015 || 04BQ01 light contaminated data corrected || Data release |
| Oct. 06, 2004 || 0014 || 04BQ02 & 04BQ03 CCDs 27->35 problem || General information |
| Sep. 28, 2004 || 0013 || The CFHTLS and the CFHT 25th anniversary || Public outreach |
| Aug. 25, 2004 || 0012 || 04BQ01 technical misfortunes || General information |
| Aug. 23, 2004 || 0011 || All 2003 Deep data reprocessed || Data release |
| Aug. 04, 2004 || 0010 || Semester 2004A completed || General information |
| Jun. 29, 2004 || 0009 || CFHTLS Elixir data flow || Data release |
| Jun. 13, 2004 || 0008 || CFHTLS 04A (thus far) Elixir data ready || Data release |
| Jun. 02, 2004 || 0007 || Image quality investigation || Instrument performance |
| Mar. 18, 2004 || 0006 || CFHTLS 03B Elixir data ready || Data release |
| Mar. 15, 2004 || 0005 || Terapix CFHTLS performance pages || Data information |
| Mar. 03, 2004 || 0004 || Survey Depth Goals page updated || General information |
| Feb. 11, 2004 || 0003 || CFHTLS Primary Site at CFHT reshaped || General information |
| Feb. 05, 2004 || 0002 || CFHT's CFHTLS Observing Status site opening || Data information |
| Jan. 15, 2004 || 0001 || CFHTLS Elixir data first release || Data release |
Feb. 21, 2008: Cosmologists unfold the dark cosmic web
Based on the Wide survey, the new result probes the dark cosmic web
to unprecedented scales. The press release can be found here.
Aug. 06, 2007: Notes on 06B&07A semesters - Missing i' filter
The end of the 06B was marred by two serious mechanical issues on the instrument: first
the shutter failed and had to be replaced (run 07Am04), then the filter juke-box failed,
destroying the i' band filter in the process (run 07Am05). The consequence of both of
these failures was shortened observing runs, translating in less data collected for
the CFHTLS (and PIs alike). The nights were however not lost as WIRCAM was immediately
mounted on the telescope.
MegaCam was promptly repaired in both cases by the CFHT staff and a special team from
CEA (who built MegaCam). Note that it was not just a repair: in depth studies and
understanding of the origins of the accidents led to implementation of mechanical, control,
and monitoring improvements. Teams worked around the clock at the summit for four weeks,
and MegaPrime found its way back on the sky, successfully completing a short run under bright Moon
conditions at the end of July.
A new i' band filter is on order from Barr Associates and should be delivered to CFHT mid
to late October. An intense calibration program of the filter will ensue on the sky to
quickly reference this new filter to the previous one (specifications are similar for
both filters of course).
Note that both of these failures had no impact at all on the data, hence the "Normal
Instrumental Setup" flag set for the observing runs.
Jul. 16, 2007: Details on the T0004 release
The Synoptic T0004 Table is now completed and opened to the public
without restriction at TERAPIX. This table provides useful information about the
release and all quality assessment meta-data built during the production
of the release. The table is available
here and the summary of the T0004 can be found
The T0004 release has important new features as compared to T0003:
2 sets of Deep data :
- 25% best seeing images stack (D25: ugriz with seeing down to 0.60" for
some fields and with exposure time up to 15hrs)
- 85% best seeing images stack : the deepest wide field ever produced
with a 4-meter telescope (D85: up to 50 hrs in some fields)
New Wide field: addition of the W4 wide field with 11 deg2 complete in ugriz.
New astrometry: done with 2MASS instead of USNO. It provides more
accurate and more stable astrometric calibration than T0003 for ALL
fields (a gain in rms internal and external error position by a factor
of 2). It also provides a more stable an accurate field-to-field
Number of stacks:
- Deep: 40 [20 D25 (4*ugriz) + 20 D85 (4*ugriz)]
- Wide: 524 (35 u + 133 g + 173 r + 137 i + 46 z)
The following image is a 1% section of one of the Deep85 field gri color image.
This image produced by Terapix comes from the PNG file made available in the Synoptic
Jul. 04, 2007: T0004 Official Release available to LS members
The CFHTLS consortium is pleased to announce that
Release T0004 of the Terapix LS Stack Products is
now available for download from the CADC.
Retrieval instructions are available at:
Information about the content of the T0004 release,
including an explanation of the stacking process,
stack naming conventions and catalog production details,
can be found on the Terapix Summary page at:
These image/catalog stacks are available only to registered
CFHTLS members and all regular CFHTLS data access rules
apply to the use of these data products. To review the
rules regarding data use and access please see the
Data Access Policy pages at:
Feb. 16, 2007: World wide release: first stacks + catalogs by Terapix become public
As announed on the the Worldwide CFHTLS Data Releases page,
the first worlwide release of CFHTLS stacks and catalogs created by Terapix has become public and is available at CADC.
It consist of Terapix' release T0003 which was offered to the French and Canadian communities on Feb, 16 2006.
Jan. 02, 2007: CFHTLS and the CFHT at 2007 Users' Meeting
The CFHT Users' Meeting will be held in Marseille (France), May 9-11, 2007.
The meeting is now open for registration at the following
CFHT Users' Meetings are held every three years. They are a unique opportunity for the
members of the CFHT communities to share their scientific results and discuss their ideas
on the evolution of the Observatory and on the kind of instrumentation and services they
would like the CFHT Corporation to offer in the coming years.
This meeting will be of paramount importance to get a chance to build any ambitious
observing program covering 2008B to the early 2010s, as well as for any new
instrumentation for 2013 and beyond. The CFHTLS is strongly encouraged to come to
share science results, and present its interest in other future surveys with the CFHT.
Oct 24, 2006: The CFHTLS continues after an strong earthquake paralizes the CFHT for 4 nights
On Sunday the 15th of October at 7:07AM, a 6.7 magnitude earthquake lasting up to 30 seconds hit
the Big Island. The epicenter was located only 20 miles away from Waimea and gave a good shake
to the CFHT headquarters, as well as the telescope and the dome. Fortunately, no one really
got hurt on the island. It was the strongest earthquake recorded on Mauna Kea since telescopes
have been erected there, but the damages on the CFHT have remained fortunately limited (the
entire telescope jumped up and down by more than an inch!). Thanks to the heroic efforts by the CFHT
staff, the telescope was back on the sky only four days after the earthquake. This
page documents the repair effort on a daily basis, along
with photographs of some of the damages.
Quality assessment on the first sky data show the telescope pointing was off by only one arcsecond,
and MegaPrime's image quality has not been altered by the quake. The CFHTLS data collection
has resumed since.
The main earthquake was followed a few minutes later by a short (5 sec.) independent
(not an aftershock, more of a consequence of the main quake) magnitude 6 earthquake.
Since then, more than a hundred small aftershocks have been felt in the area. The
following map from the Hawaiian Volcano Observatory points the location of the various events:
June 30, 2006: The first year of CFHTLS data becomes public
As planned in the original survey schedule, and following the agreed
calendar, the first year of CFHTLS data (individual frames, the Elixir
ones) is now public and available for download at CADC. Please follow
the link from the CFHTLS world wide release page.
The first worlwide release of Terapix data with happen in February 2007 and will be the
Apr. 18, 2006: Wide survey: opening of the W4 field
To balance the effect of the bad weather during the past winters on the W2
field, following a recommendation by the SAC, and following a consultation
with the Wide community, it has been decided to open a CFHTLS-Wide W4 field
observable during the spring and summer. The field is located in the region
of SA 22, and fully covers the VVDS 22h field and the UKIDSS DXS field. The
W4 field is centered on RA=22:13:18/+01:19:00/2000. The first 16 pointings
are already entered in QSO's PH2 for the semester 06A. The pointings have
been chosen such that linear scales of at least 4 degree are available,
and also to avoid as much as possible high extinction areas where no other
ancillary data are available.
The field is outlined on the following plot: the first set of fields
are plotted with solid green squares (the dashed line represent the
possible new pointings should the data gathering on W2 get even worse over
the next year). The blue square represents the VVDS area, and the red square
represents the UKIDSS DXS coverage.
Apr. 7, 2006: Statistics over three years of scientific operations
The following page presents statistics on 1) Observing efficiency, 2) Image
quality and seeing, 3) Sky transparency and brightness, and 4) Data rate,
over the first three years of operations of the MegaPrime/MegaCam imager.
These statistics aim at showing 1) the dramatic effects from the bad
winters Mauna Kea has been suffering from for 3 years in a row now,
2) the consistent image quality & seeing performance of MegaPrime mounted
on CFHT atop Mauna Kea, 3) the high rate (75%) of photometric conditions (when
the dome is open...) during observations, and 4) the regular increase of
number of images acquired per night through the gradual elimination of
various observing overheads over the first 2 years of operation.
The page, which will be updated regularly, can be found in the "Statistics"
sections of both the MegaPrime/MegaCam and CFHTLS Data sites. The direct
link can be found here.
Mar. 10, 2006: XMM-LSS/CFHTLS cluster catalogue available
The CEA group led by Marguerite Pierre just announced that the
first part of the XMM-LSS cluster catalogue, which includes the W1 region,
is now available on line at the following location: http://l3sdb.in2p3.fr:8080/l3sdb/.
For external users, there are two levels of data access:
- loging as guest: browse the gallery of identified clusters.
- registering as a visitor: retrieve the catalogue of public clusters (both optical and X-ray data).
Feb. 18, 2006: T0003 Wide+Deep release candidate available
At the request of CFHT's Science Advisory Committee, Terapix and CADC
agreed to release "candidate" (pre-release) data products that are
not yet in their final form. This release candidate consists of partial
datasets that concern the Deep and the Wide data obtained between June
1, 2003 and September 5, 2005.
The Pre-Wide and the Very Wide components of the survey will be made
available in the coming weeks. The stacks and catalogues were produced
for the Deep and Wide fields in u,r,g,i,z at Terapix and are available
from the Canadian Astronomy Data Centre (CADC) exclusively to authorized
Location: You can find Terapix stacks and catalogues for the four Deep
fields (all in u,g,r,i,z) and the three Wide fields (some in u,g,r,i,z,
some in g,r,i and some in i only, depending on the progress of the
survey in each filter) at this
In particular the tree*.html files provide user friendly description and
access to the data.
Information: individual u,g,r,i,z stacks and catalogues, chi2
images and catalogues as well as quality assessment data on the Deep
and Wide are available. Various useful information about the Deep and
Wide data sets can be found also.
Validation: These data have been fully validated by Terapix and are
suitable for scientific exploitation. It is expected that the final
full release dataset will be basically identical to these stacks
and catalogues. In case of modifications prior to the full release,
Terapix will make a new announcement. More details about the Deep and
Wide data will be soon available on the terapix pages.
Dec. 13, 2005: Discovery of a Large Kuiper belt object with an Unusual Orbit
A team of astronomers working in Canada, France and the United States have discovered an unusual
small body orbiting the Sun beyond Neptune, in the region astronomers call the Kuiper belt. This
new object is twice as far from the Sun as Neptune and is roughly half the size of Pluto. The body's
highly unusual orbit is difficult to explain using previous theories of the formation of the outer
Currently 58 astronomical units from the Sun (1 astronomical unit, or AU, is the distance between
the Earth and the Sun), the new object never approaches closer than 50 AU, because its orbit is
close to circular. Almost all Kuiper belt objects discovered beyond Neptune are between 30 AU and
50 AU away. Beyond 50 AU, the main Kuiper belt appears to end, and what few objects have been
discovered beyond this distance have all been on very high eccentricity (non-circular) orbits.
Most of these high-eccentricity orbits are the result of Neptune "flinging" the object outward
by a gravitational slingshot. However, because this new object does not approach closer than 50
AU, a different theory is needed to explain its orbit. Complicating the problem, the object's
orbit also has an extreme tilt, being inclined (tilted) at 47 degrees to the rest of the Solar
See the Official Press Release.
Nov. 22, 2005: SNLS First Scientific Results Announced
CFHTLS is a major undertaking from Canada and France, who have joined
a significant fraction (about 50%) of their dark and grey telescope time for a large survey using
the wide field imager MegaPrime equipped with MegaCam.
MegaCam is a mosaic of 36 CCDs, covering a 1 degree x 1 degree field of view. With a PI-less structure
and a data access policy granting equal and immediate access to any member of the two communities
to both processed images and catalogs, the CFHTLS is both exciting and challenging. The CFHTLS is
made of 3 separate surveys, one of which is a deep synoptic survey, the "Deep".
A subset of this Deep survey is used by the SuperNova Legacy Survey
collaboration (SNLS) to measure the distance to far supernovae and the equation of state of Dark Energy.
The first results of the SNLS survey, to be published in Astronomy & Astrophysics,
place strong constraints on cosmological models. Read the full
AAS Press Release.
See also the full
Astronomy & Astrophysics Press Release, and the
press release of the University of Toronto.
The CNRS in France has also issued a press release in collaboration with the CEA.
CNRS Press Release,
CEA Press Release. [In French]
The SNLS relies on spectroscopic follow-up of the SNe candidates detected on the CFHTLS imaging data,
each major telescope involved
Gemini press release
PParc press release
Keck press release
For more information: The SuperNova Legacy Survey
Sep. 12, 2005: Note on the half-mosaic night in 05BQ03
The failure of the CCD controller south (slave) power supply on August
30th 2005 forced the telescope to shut down for the night of the 31st,
and forced QSO to operate the instrument in a half-mosaic mode for the
night of the 1st to the 2nd of September (CCDs 18->35 not active).
Deep/SNLS (sequential): 809995 to 810004
Note that CFHTLS data were obtained that night but are not included
in the CFHTLS data set of this web site as they do not have a legacy
value since they are much altered compared to the normal data (they
were taken only for the SNLS and the Very-Wide real-time needs). The
odometer numbers for these CFHTLS exposures are:
Very Wide: (sequential): 809963 to 809994
After heroic work by the CFHT on the 2nd of September, the origin
of the problem was identified (a weak +5V line in the power supply)
and MegaCam was back on the sky on the evening of the 2nd in full
Aug. 25, 2005: Semester 05A completed & Semester achievements
The 05A semester has been remarkably trouble free on the instrument
side, but badly affected by mediocre weather on Mauna Kea for the
second year in a row. The document prepared by CFHT for the CFHTLS
mid-term review presented clear statistics on the reasons why the CFHTLS
did not get data as fast as initially planned. The main culprits over the
first 3 semesters (03B-04A-04B) were the weather, technical problems (including
the image quality, an issue mainly solved last December), and the observing overheads.
While nothing can done about the weather, CFHT was happy to report
a few months ago, that the instrument failures have dramatically decreased
in 05A as did the observing overheads, specially the focusing which gobbled about
50mn a night. The acquisition time of guide stars was also greatly improved
in May thanks to the speeding of the guide probes (a factor of 10 faster,
allowing exposures to start earlier).
The autofocus currently implemented, a thermal model of the telescope, has been
extensively tested over the past runs to compare it with the time consuming focus
sequences (deriving the focus from the PSF of stars on images taken at different
focus positions). Our confidence level in the autofocus rose quickly, and the
number of focus sequences needed through the night has dramatically decreased,
with many nights free of focus sequences (sometimes the seeing is so unstable
that it confuses the QSO observers, who feel naturally compelled to run some focus
sequences - one again, blame it on the current Mauna Kea poor conditions). After
a few observing runs in this autofocus mode, we estimate the time saved to approximately
50 minutes per night. There is however still a substantial on-going effort to
optimize the thermal model of the telescope to ensure the best focusing: the current
model still exhibits a 50 microns scatter (the depth of field under 0.5 arcsec.
seeing) and we want that scatter to go down to 25 microns at least.
In addition to saving the time previously used for focus sequences, autofocus
is increasing the QSO validation rate! Changes in focus are activated between
each exposure and, as a result, less exposures are lost. For example, the run
05AQ05 has a QSO validation rate of 93%, which is the highest rate ever achieved
in the history of QSO (CFH12K included). Even better, the validation rate on
all CFHTLS in 05AQ06 data is 98%!
The weather, technical problems and engineering time over the runs
since autofocus has become active, amounted to 20 to 27% (mostly weather
and bits of engineering to work on the wide-field corrector tuning), a range
we consider higher than normal for this time of the year. Indeed, 75% of the time
during the first three runs (winter/spring period) of 05A was lost to bad weather.
On the recent spring/summer runs we however achieved 5.2 hours of validated data
(QSO definition) on average for nights of only 8.2 hours. When scaled
to the average night length over the year of 9.5 hours, we end up with 6.0 hours per
night of validation rate. With hopefully better weather conditions in the near future,
expect this number to improve this coming semester.
What does it mean for the CFHTLS and for MegaPrime QSO for the immediate
future? The CFHTLS re-design done after the recent review process
developed a strategy based on an average of 4.5 hours per nights of
validated observations. If 5.5 to 6.0 hours per nights were indeed to be
the average for the coming semesters, the CFHTLS could actually speed up
its planned pace, catching up on some on the time lost over the past two
years, and decrease its load on the Canadian and French time allocation.
What is coming on the instrument side for this semester? After a fruitful
visit at CFHT by the CEA team who built MegaCam, a preventive maintenance plan is
being put in action. This plan should save us from failures related to
the aging of the instrument. After a year of intense work on the image
quality issue, we are very close to the final configuration that
will put the instrument within the design specifications (see news
0022). And since every second counts, CFHT will pursue
its efforts at hunting down and decreasing each and single observing overhead.
And now back to the CFHTLS status as of Aug. 15, 2005 (including the first observing run of 2005B = 05AQ01), the CFHTLS
distribution of validated exposure is (including the 40 seconds overhead per exposure):
Survey Component : Deep Wide Very Wide Pre-Survey
Total integration [validated exp.]: 451.1hr 214.0hr 158.7hr 23.3hr
Number of validated exposures: 3840 1515 3528 381
Current fraction of CFHTLS : 54.8% 26.0% 19.3% n/a
Target(*) fraction of CFHTLS : 44.0% 34.0% 22.0% n/a
(*) These numbers and future figures will be adjusted to reflect the recent
decision of halting the Very Wide component of the CFHTLS as of 2005A.
For a full report on the semester seen from the QSO side, the report has
just been posted
Aug. 12, 2005: MegaPrime image quality further improved
With the knowledge accumulated over the past two years and a half,
since CFHT started tweaking MegaPrime's wide-field corrector, we
predicted an improvement of the image quality over what was produced
by the fortunate flipping of the lens L3 (News 0017)
by applying a change in height of the entire corrector versus the
primary mirror. Shortly before the start of 05AQ07, the corrector was
pushed further up (away) from the mirror by reducing the spacer from
5.5mm to 2.1mm.
The predictions were correct: the upper left corner and the
lower right corner have been recovered and the analysis of the new
data show that we are now only left with a slight tilt of the focal
plane, which we plan to adjust within this coming 05B semester.
The improvement is significant in terms of homogeneity of the image
quality over the entire field of view. It is stable over several nights, and
stable in shape in various telescope configurations in all tested filters.
Most important for the most demanding scientific project in terms of
image quality, gravitational lensing, the optical distortion is now
The following plots (produced by Terapix' QualityFITS pipeline) show the
image quality histogram, as well as the orientation and ellipticity map
on the entire image for the three main configurations encountered so
far: prior the L3 flip, the L3 flip configuration, and the new
configuration (these maps were derived from 30 seconds long, guided
exposures on dense stellar fields). Note that the scale of the histogram
is different from one configuration to the next (the Y scale represents
the number of CCDs having a given FWHM: the highest, the most uniform
the image quality is across the field of view). Note how the histogram
skewness has now significantly decreased compared to the L3 flip
configuration. The individual postscript files can be retrieved here.
New (Spacer) - Jul.05:
Initial - May 03:
L3 flip - Dec. 04:
In terms of quantitative measurements, here is the IQ map for the exposure 807216o:
IQ MAP & CLASS TO MEDIAN 1-9 | *0 |+/-1|+/-2|+/-3|+/-4|+/-5|+/-6|+/-7|+/-8|+/-9|
IQ difference from median: 0.02<0.06<0.11<0.17<0.22<0.28<0.34<0.39<0.41<...
This is truly spectacular: the image quality degradation from center to the edge
does not exceed 0.08 arcsec. on this 0.42 arcsec. seeing exposure! However, when
we look at frames taken slightly in and out of focus from the optimal position,
we clearly see some areas of the focal plane getting worse. This is an indication
of a slight tilt of the focal plane (which can actually be derived using these
exposures). The following diagram proposes the orientation and ellipticity map for
four images: 807216o.fits and 807221o.fits taken at the optimal focus (to prove it is
repeatable), 807218o.fits taken at +90 microns from the optimal focus, and 807224o.fits
taken at -90 microns from the optimal focus. The individual postscript files can be retrieved here:
807218o exhibits a degradation of the image quality in the lower left part, while 807224o
exhibits a degradation of the image quality in the upper right. With no tilt present on the focal plane,
a defocus would bring a uniform degradation of the image quality across the
entire field of view. The current optimal focus shows signs of image degradation
towards the left, but this is minor compared to what we've been facing until now.
The MPIQ project
web site goes in much detail on this latest evolution.
Jul. 15, 2005: CFHTLS mid-term review - SAC and Board reports
Following the reviewing process conducted by the SAC in May 2005, and based on
documents produced by the CFHTLS Steering Group (soon available on this
site), the SAC recommendations and subsequent decisions by the CFHT Board
of Directors are presented on the following page:
Apr. 05, 2005: Dates of CFHTLS releases to the world
Following the CFHTLS data policy defined by the CFHT Board of Directors,
the CFHT Legacy Survey, which officially started on May 30th 2003, will be
open to world access at CADC for the raw FITS and the Elixir data
products (Processed FITS and ancillary data) according to the following time table:
Jun. 30, 2006: All data from May 30, 2003 to May 29, 2004
Dec. 30, 2006: All data data from May 30, 2004 to May 29, 2005
All data taken after May 30, 2005 will become available 13 months later.
The rules for the Terapix data releases to the world (stacked ressampled FITS
and catalogs) will not follow those for the raw and Elixir data, or
the ones for the Terapix releases to the Canadian & French CFHTLS community
(releases every 6 months).
Terapix data products will be made available to the world through data releases
yet to be defined, happening in various steps: the first one not later than
three years after the beginning of the survey (Jun. 30, 2006), and the last
one not later than one year after the end of the survey.
Feb. 22, 2005: Semester 2004B completed, 2005A started
The 04B semester started with some great weather but ended bad with the
predictable bad winter weather battering the Big Island. This is clearly
reflected in the statistics page for the 3 surveys where it appears that
the winter field for the wide (W2) got affected due to the natural priority
that goes to the deep when the weather affects the operations. Note also
that since the finding of the L3 flipping effect, the wide had been put on
hold in November, then the weather really affected the QSO runs: in the end
the wide got short of its allocated time.
Note that on the top of that statistics page that the blue framed table now
reflects the time as allocated and validated by the CFHT observing process: a 40
seconds overhead is included per exposure. This changes only slightly
the stats based on pure integration time (the following tables remain in that
form), and it matches exactly the statistics published daily by the
QSO team here.
As of Feb. 2005 (including the first observing run of 2005A), the CFHTLS distribution
of validated exposure is (including the 40 seconds overhead per exposure):
Survey Component : Deep Wide Very Wide Pre-Survey
Total integration [validated exp.]: 343.8hr 145.6hr 109.9hr 9.2hr
Number of validated exposures: 2898 959 2484 151
Current fraction of CFHTLS : 57.4% 24.3% 18.3% n/a
Target fraction of CFHTLS : 44.0% 34.0% 22.0% n/a
For more information on the past semester, feel free to browse the
04B QSO report.
The whole instrument MegaPrime/MegaCam has behaved very well this past
semester after the first run which got affected with several problems
(cf News 0012). The most important breakthrough was the finding of
the L3 lens flipping (November News 0017) in the wide field corrector which brings
a spectacular improvement of the image quality. This has been accepted
as the default configuration and won't be changed for another semester
(or more) until CFHT finds a mean to improve even further the image quality
(in the top right and bottom left extreme corners in particular). With this
major step behind, the CFHT staff can now focus on the new top priority
for MegaPrime: the reduction of the observation overheads to gain more open
shutter time per night.
As per the data flow, we have now had for several months a steady
release of Elixir products to CADC within 10 days after the end
of an observing run (and then to the community within minutes
thanks to the highly automated scheme in place at CADC).
Jan. 21, 2005: CFHTLS Workshop in Paris - May 2005
With the first Terapix-processed data released a few months ago and the second
one (T0002) looming, 2005 should see promising preliminary scientific results
based on CFHTLS data, marking the first of many productive years of CFHTLS-related
Spring 2005 will be the time of the first external review of the CFHTLS. The
comments of the reviewers will be evaluated by the CFHT Scientific Advisory
Council (SAC) just before its May 2005 meeting in Paris. To offer to the
CFHTLS users an opportunity to share their experience with the CFHTLS data
and their first scientific analysis, and to provide SAC with an opportunity
to meet CFHTLS users, CFHT will organize a CFHTLS workshop in Paris (IAP)
just before the SAC meeting, on May 26 and 27.
The CFHTLS, with nearly 500 nights allocated over five years, is a major
commitment of the Canadian and French Agencies as well as a major program
for CFHT. HIA and INSU have both agreed to provide a limited support to
those who want to present their CFHTLS experience at this workshop.
Information and a registration form can be found on this dedicated site:
The sooner you register, the better for the organizers! If you have any
question, feel free to ask the organizers at: LSW05@cfht.hawaii.edu
Nov. 24, 2004: 04BQ04 brings promising IQ improvement
As part of the ongoing effort for understanding the issue with
the MegaPrime image quality (IQ), the wide-field corrector was taken
apart one more time between the 04BQ03 and 04BQ04 observing runs and
the lens L3 (third from the bottom) was accidentally mounted back up
side down in the corrector (the mechanical design allows for this mistake
to easily happen, plus this weak lens is almost flat, making it difficult to say
on which side the curvature is). The mounting error was quickly discovered
within the first moments of the first night of the 04BQ04 run because
the focus level (vertical motion) appeared to be shifted down by 5 mm, causing
the system to hit some limit switches, and making it impossible to focus in the
g' and z' filters. However, to our surprise, the image quality in that
configuration in the u*, r' and i' filters (which could be well focused)
appeared to be the best ever achieved on MegaPrime!
The Q observing run could however not be completed in such circumstances (no
access to the g' and z' filter), hence the lens was flipped back on the 4th of
November and observations started again on the 5th in the optical configuration
adopted since June 2003.
Investigations show that the L3 flipped mode is not the way the design
calls for that lens to be mounted, and the reasons for the improved
image quality are not currently understood but have provided useful clues
on the behavior of the wide-field corrector.
However, the improvement is so significant (and stable over several nights, and
stable in shape in various telescope configurations) in all tested filters (u*, r', and i')
that CFHT, in consultation with the CFHT Astronomy Group, the SAC, and the CFHTLS Steering Group,
has decided to mount the lens L3 flipped and shift down the limit switch
(within safe limits) such that it'll be possible to focus in all filters.
The image quality will be thoroughly investigated in that new configuration
during the first hours of the coming run (04BQ05) to confirm that we have
indeed gotten back to the best IQ configuration.
Note however that this is still not what the specifications called for,
in particular the top left and bottom right corner exhibit a sharp
degradation of the image quality. Yet, not only is the the PSF better
across the field, it is also a lot more uniform in shape, as shown
by the orientation and ellipticity maps. In that respect, the Wide
Survey coordinator has preferred to put on hold the observations on
the Wide for the duration of this past 04BQ04 run (except for the Pre-Survey
which is about astrometric calibration and is not impacted by the IQ
issue), in order to benefit from the planned significant IQ improvement
coming this December run. Hence no surprise seeing the fraction of
the Deep increase versus the Wide and Very Wide in this month's global
This new optical configuration will be adopted as the new standard until
further investigations (the
MPIQ project) show we can move even further
in terms of image quality improvement.
The following plots (courtesy of Terapix) show it all about the before
and the after of the L3 flip. The two images are low galactic latitude
fields with plenty of stars. 761016o.fits was taken with the June 2003
adopted configuration, and 767523o.fits was taken during the first night
of 04AQ04. Elixir reports the same image quality at the center of the
field, and they're both taken in the i' filter, and are fairly long exposures
(more than 60 seconds). With L3 flipped, the seeing histogram over the field
of view gets nicely tightened by a factor of two at least (note that the Y scale
on the histogram is different for these two diagrams) and the orientation
and ellipticity map show only strong trends in two extreme corners (note that
the sticks size has no absolute length value, it's relative within each image,
these plots aim at showing the fact that the PSF is a LOT more homegeneous with
the new configuration). High resolution postscripts files can be obtained here:
Nov. 23, 2004: Terapix Data Release T0001 available at CADC
From Yannick Mellier (Terapix) & David Schade (CADC):
We are pleased to announce the first CFHTLS release, T0001,
now available to all CFHTLS registered users at CADC. The release
includes the CFHTLS deep data D1, D2, D3 and D4 in u,g,r,i and z bands.
You can retrieve these data from CADC using your CFHTLS login and password
at the following URL:
Details on the data content and data quality are available
at the terapix web site : http://terapix.iap.fr.
under the section "CFHTLS Release T0001". These public pages contain a simple
summary table and an explanatory table.
Comments/suggestions regarding the detail of the data processing
can be addressed to Terapix at the following adress : terapix at iap.fr
We remind you that the CFHTLS release must not be propagated outside
the CFHTLS community, and is only for scientific usage by its registered
users. If in doubt please consult again the CFHT Legacy Survey Data
Access Policy on the official CFHTLS web site at CFHT:
The next release scheduled for late December will include the W1,2,3
and VW data sets.
Nov. 04, 2004: 04BQ01 light contaminated data corrected
The CFHTLS data taken from the 6th (PM) to the 10th (AM) of August covering
the odometer range 756829 to 757179, have been corrected using a dark map
correction, much like a dark current correction since the contamination
was linear with time. Note that these data were plagged by other very
serious effects as documented on the news 0012 from this page.
The complete list of CFHTLS data suffering from that contamination,
and now cleaned from it, and delivered to CADC can be found
Oct. 06, 2004: 04BQ02 & 04BQ03 CCDs 27->35 problem
The failure of a video board in the South controller on the 5th of September 04 forced
us to shut down half the mosaic for two nights (CCDs 18 to 35). A new board was installed
and everything went back to normal on the evening of the 7th of September. However that
spare board failed somehow, though not completely, on the 8th of September and since then
the right amplifier of CCDs 27 to 35 have a saturation value of 32K instead of 65K (this
is due to the 16th bit being stuck at 0). The processed data (not RAW) will have the
MAXLINB (Level at 1% linearity departure) set to 32K on the Elixir processed data to
reflect this problem.
The file number for the images taken in half mosaic mode are 760630 to 760880. The
right amplifier saturation change effect started for the exposure 760956.
Sep. 28, 2004: The CFHTLS and the 25th anniversary of CFHT
The spotlight goes on the CFHTLS as CFHT celebrates its 25th year
of operation. A stunning image of the CFHTLS deep D1 field prepared
by Terapix is presented. Read all about it in the
CFHT Press Release. Other ressources include the
CNRS Press Release and the INSU
Aug. 25, 2004: 04BQ01 technical misfortunes
The first run of the 04B semester was unfortunately rich
in technical problems that altered the quality of the
data acquired on the sky. Fortunately, the problems
were not severe enough to the point of cancelling the observing
run, and data were taken at the usual rate for all three
components of the survey.
Due to the failure of a vaccum connector flange, some CCD pins were
pulled down (shortage to the ground) and this resulted with many
amplifiers ceasing to function normally. Most of them started
recovering right away though and by the middle of the run, only two amplifiers
were still non functional (A amplifier of CCD07 and CCD11, that
is the left amplifier). Some amplifiers were noisier than others
(A amplifier of CCD17, B amplifier of CCD16 and CCD14) in the
first days of the observing run but this
did not damage the data enough for having these sections masked
by the Elixir processing. Two masks have been built for the
Elixir processing: one for the period Aug. 6 to Aug. 14
(A amplifier of CCD00 and CCD11 off, and both amplifiers of
CCD07, CCD09, CCD10 off - left image below) and one for the
Aug. 14 to Aug. 24. period (A amplifier of CCD07 and CCD11 off
- right image below).
The Elixir masks for these two periods are 2004B.mask.0.36.00.fits
Internal light contamination:
A vacuum gauge of a new type was installed just prior the observing run
because of the repeated failures of the original model. Unfortunately,
the internal filament emits visible photons and this resulted in a
light contamination inside the cryostat. With all the focus going
on the CCD problem, it took us a few days to react on that one issue
since it was not very obvious (0.5 ADU per second in the brightest
areas). The raw data are salvageable by simply subtracting a master
dark frame. The gauge was shut down on the morning of the 10th of
Ice on the cryostat window:
The air flow venting the outside surface of the cryostat window
got contaminated with water twice during the run, which
resulted in an ice plug forming on the window. The data taken
in these conditions are totally useless in the areas occulted by
the ice. The CFHTLS data taken on the night it first happened
(from the 6th to the 7th) are mostly good with only a few patches
of ice left (the ice melted throughout the night fortunately
thanks to the ambient dry air of Mauna Kea). No CFHTLS data
were taken on the second night it happened (16th of August from
dusk until 1 AM of the 17th) while there was ice on the window
(the QSO team waited patiently for it to melt after clean
dry air was flowing again on the window and dissipated the
Aug. 23, 2004: All 2003 Deep data reprocessed
As announced on this page last June, new photometric superflats have been derived from
a data grid obtained in all 5 bands (u*, g', r', i', z') in October 2003, and
are now available at CADC. Following
a request from the SNLS groups, all the Deep survey data gathered in 2003 have been
reprocessed with a flat-field that includes that new map. The improvement in
photometric quality is significant with a zero point uniformity across the
mosaic of +-0.01 mag level for g', r', i'i, z', however the u* band still
shows residual up to +-0.05 mag offsets that need to be understood.
Chris Pritchet has studied the residuals from these grids processed by the
photometric superflat derived from them. His results can be found
All 2004 data available at CADC already include the improved photometric superflat
which was derived after the light baffle was installed on MegaPrime at the
beginning of the year.
Aug. 04, 2004: Semester 2004A completed
The 2004A semester has just finished and the first MegaPrime
run of 2003B is only a few days away. More than a year after
starting the survey, the general statistics are:
Number of exposures (a very rough estimator to check on progress):
Deep Wide Very Wide
2003A 457 137 399
2003B 889 383 773
2004A 779 147 685
We see here, as announced earlier by the Steering Group, that the
Wide survey has taken the back seat during this past semester and
has accumulated little data. The Wide survey will be getting higher
priority for the coming semester in order to keep the three components
balanced. In terms of balance, here is the current ratio today at the end
Survey Component : Deep Wide Very Wide Pre-Survey
Total integration [validated exp.]: 166.4hr 55.8 hr 43.5 hr 2.7 hr
Current fraction of CFHTLS : 62.6 % 21.0 % 16.4 % n/a
Target fraction of CFHTLS : 44.0 % 34.0 % 22.0 % n/a
Starting 04Am06, CFHT has done its best to stick to its commitment
of providing the Elixir processed data to CADC within 7 to 10 days
after the end of the observing run. So far, this timescale seems
reasonable as CFHT has been able to deliver on time.
Jun. 29, 2004: CFHTLS Elixir data flow
Following a recommendation from the CFHTLS Steering Group,
the CFHT and CADC have commited to have the Elixir data
made available to the community within 3 weeks after the
end of an observing run. We are testing our capabilities
with the 04AQ06 run, expect these data to appear at CADC
mid-July as they will start transferring from CFHT early July.
Jun. 13, 2004: CFHTLS 04A (thus far) Elixir data ready
After the light baffle was installed on MegaPrime at the beginning
of the semester 04A, new photometric superflats had to be built.
We have now obtained these frames at a much higher quality
compared to the equivalent frames obtained early 2003 for the
semesters 03A & 03B. This was the primary reason for the delay
in releasing the CFHTLS Elixir 04A data (that's from January
to May included).
Note that new photometric grids were obtained just before
the light baffle was installed, and the new improved photometric superflats
for 03A & 03B will be used in the global reprocessing of the
CFHTLS data (since June 2003) which should take place later this
On the technical side, note that from now on the Elixir data are
transfered to CADC via network instead of SDLT tapes.
Jun. 02, 2004: MegaPrime image quality investigation
CFHT launches a project focused on investigating the image quality
issue in MegaPrime, which turned out to be not as good as expected
as the past year of operation has shown. All relevant information
and documents are presented here.
Mar. 18, 2004: CFHTLS 03B Elixir data ready
The last tapes including the remaining CFHTLS Elixir
data from the semester 03B were shipped this morning
to CADC. The complete 03B semester will be in consequence
fully available on line at CADC within a few days.
Mar. 15, 2004: Terapix CFHTLS performance pages
Terapix has released a collection of sophisticated pages
providing in depth analyses of the data quality of the
CFHTLS Terapix data products (products which will be very soon
available at CADC). These Terapix pages can be consulted
Mar. 03, 2004: Survey Depth Goals page updated
Based on actual sky data and comparison with DIET estimations,
the survey magnitude depth goals have been updated. Please keep
in mind that the images can be taken within a fairly large range
of airmass and sky brightness values for some filters and this
explains why some of the these numbers differ slightly from
the DIET output. Average values between various conditions
were taken to build up these numbers. For information on
exact depth based on the actual data, please refer to the
individual survey web sites.
Feb. 11, 2004: CFHTLS Primary Site at CFHT reshaped
To ease the cruising across the many pages focused on the CFHTLS
at CFHT, the primary CFHTLS web site based at CFHT ("CFHT Legacy Survey Home")
has been made "look&feel" compliant with the CFHTLS Data ("CFHTLS Observing Status Home")
and the MegaPrime/MegaCam pages.
This web site aims at proposing the large picture on the survey
with many pointers in particular to the sites developed by the CFHTLS community,
especially the web sites dedicated to each survey component
and run by the individual coordinators.
Feb. 05, 2004: CFHT's CFHTLS Observing Status site opening
CFHT is proposing this new web site ("CFHTLS Observing Status Home") focused on providing the scientists interested in the
CFHT Legacy Survey a large set of information to follow the progress of the survey from
the point of view of the data acquired at CFHT.
Jan. 15, 2004: CFHTLS Elixir data first release
The CFHT Elixir data released under the Elixir version 2.0 are now available to download from the CADC
for all registered CFHTLS users. The recipies aren't perfect yet, please consult
this page to find out about the limitations of that release.
All these data will be re-released later in 2004 using the
Elixir version 3.0 with improved recipes for the fringes in i' and z', the
sky background modes correction (all filters), the photometric superflats (all filters)
to name the three main areas left to be optimized.