Canada-France-Hawaii Telescope: A Progress
Report
by Pierre Martin
The Canada-France-Hawaii Telescope remains a key facility for the Canadian
astronomical community. With the recent arrival of new, unique and highly
efficient instruments, the pressure on the telescope from the main two
partners is very high: above 4 for France and 3 for Canada for the 2006A
semester. This
report presents some scientific highlights obtained at CFHT for the last
year as well as a brief description of the three main instruments now
offered to the community. Starting next semester, CFHT will be operated
in a queue mode for close to 85% of the telescope time available with
data pre-processed through the Elixir pipelines; the last section includes
comments on this mode of operation.
Scientific Highlights for 2005
The past year has been very rich in scientific
highlights for CFHT. With several unique instruments producing
large amounts of excellent quality data, CFHT continues to be a very
productive facility for all the communities it serves. Among those
results:
CFHTLS
The
CFHTLS is
a major undertaking from Canada and France, who have joined a significant
fraction (about 50%) of their dark and gray telescope time over five years,
starting in 2003, for a large survey using the 340 megapixels wide field
imager MegaCam. 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 (Deep, Wide Synoptic, Very Wide) and
the first scientific results have been published in 2005 . Among them:
SNLS Supernovae. A subset of the
Deep survey
is used by the
SuperNova Legacy
Survey collaboration (SNLS) to measure the distance of far supernovae
to derive the equation of state of Dark Energy. The SNLS is the largest
observational project of its kind. Many of the largest telescopes worldwide
are involved in this project; the imaging part of the program is carried
out at CFHT. During the first year alone, the SNLS team has measured
the distance to 71 supernovae that exploded between 2 and 8 billion
years ago. The team's first results is published in
a coming issue of Astronomy & Astrophysics (Astier
et al. 2005). The discovery of the accelerating Universe
expansion suggests the need for a cosmological constant that might,
among other models, explain the acceleration of the expansion. The
first results of the SNLS indeed show that the existence of a cosmological
constant is the best way to fit their observations. Once completed,
by the end of 2008, their Survey will bring even more restrictive constraints
to these cosmological models.
 |
Figure 1: Example of the science done in the SNLS. |
Weak Lensing. Covering 170 square
degrees in three patches of 49 to 72 square degrees through the whole
filter set (u*, g', r', i', z') down to i'=24.5, the
Wide Synoptic survey
allows the study of the large scale structures and matter distribution
in the Universe through weak lensing and galaxy distribution, as
well as the study of clusters of galaxies through morphology and
photometric properties of galaxies. Thanks to the sequencing of the
r' observations in two phases, early in the survey and three years
later, proper motions will be available for galactic structure studies. The
main science driver of the Wide survey is however to derive the dark
matter power spectrum and cosmological parameters. The images delivered
by the CFHT high-resolution wide-field imaging camera allows the
analysis of the light of hundred of thousands distant
galaxies, looking for distortions caused by intervening dark matter.
The results give cosmologists a viewing window into the possible
roles of dark matter in the evolution of the Universe. Preliminary
results based on the first year of data (articles submitted to ApJ
and A&A) already give constraints on some cosmological
parameters consistent with the SNLS findings. This is using just
20% of the data that will be accumulated by the end of the survey!
Kuiper Belt Objects. Covering a large fraction of the ecliptic
plane inside a band of +/-2 degrees for a total area of 410 square
degrees, the
Very Wide survey will provide an unprecedented sample
of the solar system population beyond Neptune. This data set will undoubtedly
provide discoveries that are sure to challenge the currently discussed
models of the solar system formation. One of the first results announced
late in 2005 from this survey is the exciting discovery of an unusual small
body orbiting the Sun beyond Neptune, in the region astronomers call the
Kuiper belt. This new object, nicknamed "Buffy". is twice as far from the
Sun as Neptune and is roughly half the size of Pluto (
http://www.cfeps.astrosci.ca/4b7/index.html).
The body's highly unusual orbit is difficult to explain using previous
theories of the formation of the outer Solar System. Currently
58 astronomical units from 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 Buffy 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 System....
|
Figure 2: Buffy's odd-ball orbit! |
Comet Tempel-1 and Deep Impact
CFHT was a key participant for the ground-based
observation campaign dedicated to the Comet Tempel-1 prior, during and
after the Deep Impact event. MegaCam was used to observe the comet every
minute for 3 consecutive hours during five nights centered around the
impact of the probe. Dramatic changes in the comet brightness and morphology
of the coma and ejecta material was seen and used by the PIs of the project
to better assess the magnitude and effects of the impact. Results were
published in Science (Meech et al. 2005).
|
Figure 3: Comet Tempel-1 (Click on image for full-screen
view) |
Magnetic Field in Accretion Disk
In 2005, ESPaDOnS has been frequently used to look
at stars in a search of their magnetic field. As shown with a publication
in Nature (Donati et al., 2005), the first detection of the magnetic
field inside a growing star's dusty disk has been made with this new instrument
which now offers a unique opportunity to study stars through the observation
of their magnetic activity.
Jean-Francois Donati, who led the construction of ESPaDOnS
before its delivery to CFHT, and his colleagues used the instrument to study
visible light coming from the FU Orionis system, which contains a young star
that is being fed by a surrounding disk. The
magnetic field inside this disk helps to slow its rotation, causing material
to fall towards the central star. Although theoretical models predict this
crucial role, the magnetic field close to the star has not hitherto been
directly measured.
Light from FU Orionis is rotated, or polarized, by
magnetic fields in the disk. By measuring this polarization, the astronomers
found that the magnetic field slows down the disk material much more than
models predict. This may explain why the star does not spray out some of
the infalling material as a jet, a feature seen in other star-disk systems.
Instrumental Suite
In 2005, CFHT enters a new era where
most of the telescope time is used by three instruments: MegaCam, WIRCam,
and ESPaDOnS. Instruments like MOS, GECKO and AOB are still offered to
the community and visitor instruments are welcome. However, the bulk
of the observations are conducted with the instruments described below.
MegaCam
MegaPrime is a wide-field imaging facility (the
official first light took place in January 2003), and represents a major
upgrade of the telescope upper-end as well as the largest astronomical
CCD mosaic ever built. The wide-field imager, MegaCam (built by
CEA, France), consists of 40 2048 x 4612 pixel CCDs (a total of 340 megapixels),
covering a full 1 degree x 1 degree field-of-view with a resolution of
0.187 arcsecond per pixel to properly sample the 0.7 arcsecond median seeing
offered at Mauna Kea. The new prime focus upper end includes an image stabilization
unit and a guide/autofocus unit with two independent guide CCD detectors.
|
MegaPrime/MegaCam is an optical
instrument mounted on the telescope for periods centered on the New Moon.
It is using most of the telescope dark and gray time to conduct the typical
Principal Investigators scientific programs and the CFHT
Legacy Survey which represents by itself a total of 450 nights committed
over five years.
MegaPrime/MegaCam is operated exclusively through the CFHT New Observing
Process (NOP) (see section 4). Observations are carried out through Queued
Service Observing (QSO), the data are preprocessed (removal of the instrumental
signature) and calibrated (photometry and astrometry) by Elixir, and
eventually sent to the Principal Investigators on tapes or network by
the Data Archiving & Distribution System (DADS). The raw data are
archived at the Canadian Astronomy Data Centre (CADC) in Victoria, and
become public after a one year proprietary period (except for the CFHTLS
data). The Terapix data processing center based in Paris, primarily focused
on handling the CFHTLS data, also proposes its services to the whole
CFHT community with the data stacking, fine astrometric calibration and
catalogs generation.
|
Figure 4: MegaCam |
Very significant improvements to MegaCam have been
achieved during 2005. The most important regards the image quality issue,
which did not meet the original specifications during the first few semesters
of operations. A detailed investigation and reports can be found at http://www.cfht.hawaii.edu/News/Projects/MPIQ/. After
the unexpected flipping of the L3 lens in the wide-field corrector at the
end of 2004 and several adjustments made to the alignment and spacing of
the different optical systems, the image quality for MegaCam is now very
close from being optimized. On the operational side, the guide probe
motions were sped up by a large factor in May, resulting in a much improved
observing efficiency. By mid-2005, an auto-focus model based on telescope
truss temperature and position has been implemented. Focus sequences are
not necessary anymore, also improving significantly the observing efficiency.
ESPaDOnS
ESPaDOnS is a bench-mounted high-resolution echelle
spectrograph/spectropolarimeter fiber-fed from a Cassegrain module. This
module includes the calibration and guiding facilities, and an optional polarization
analyzer. The spectrograph is located in the 3rd floor Coude room, and is
housed in a thermal enclosure to minimize temperature and pressure fluctuations,
which affect the spectrograph's stability (see picture).
ESPaDOnS was designed to obtain a complete optical
spectrum (from 370 to 1,050 nm, with 3 very small gaps: 922.4-923.4
nm, 960.8-963.6 nm, 1002.6-1007.4 nm) in a single exposure with a resolving
power of about 68,000 (in spectropolarimetric and 'object+sky' spectroscopic
mode) and up to 81,000 (in 'object only' spectroscopic mode). With a 79 gr/mm
grating and a 2k x 4.5k CCD detector, the full spectrum spans 40 grating
orders (from order #61 in the blue to order #22 in the red). The total peak
throughput is between 15% and 20% (telescope and detector included). This
high throughput was obtained using the very efficient dual pupil design of
Baranne (along which many modern spectrographs such as UVES, FEROS and HARPS
were designed) as well as to the most recent advances in glass and coating
technologies (allowing to produce large dioptric optics with low reflectance
and absorption as well as high efficiency optical fibers and image slicers). ESPaDOnS
gives continuum subtracted linear and circular polarization spectra of the
stellar light (in polarimetric mode). The use of Fresnel rhombs instead of
standard crystalline plates suppresses the usual problems of interference
patterns in the collected spectra, with the additional advantage of being
much more achromatic.
ESPaDOnS transitioned very smoothly
to a fully operational CFHT instrument after engineering and commissioning
nights in November/December 2004. After a year of operations, ESPaDOnS
has proved to be a reliable and easy-to-use instrument, with quick and easy
data reduction thanks to software provided by the project PI (J.F. Donati:
Libre-Esprit) and CFHT. A complete description of the instrument can be found
at
http://www.cfht.hawaii.edu/Instruments/Spectroscopy/Espadons/
WIRCam
WIRCam is the newest wide-field imaging facility
at CFHT and represents one of the largest astronomical mosaic of infrared
detectors ever built. WIRCam contains four 2048 x 2048 pixel
HAWAII2-RG detectors, and covers a 20 arcminute x 20 arcminute field-of-view
with a sampling of 0.3 arcsecond per pixel (see picture). To properly sample
the 0.4 arcsecond infrared seeing often offered by the CFHT at Mauna Kea,
WIRCam uses its image stabilization unit to micro-step the image with 0.15
arcsecond sampling. The image stabilization signal will be obtained by
repeatedly reading out a small region of the detectors centered on a bright
star, while the exposure continues for the rest of the pixels. WIRCam
is a near infrared instrument, and is mounted at the prime focus of the
telescope.
WIRCam is operated exclusively through the CFHT New
Observing Process (NOP)(section 4). As with MegaCam, observations are carried
out through Queued Service Observing (QSO), the data are preprocessed (removal
of the instrumental signature) and calibrated (photometry and astrometry)
by Elixir, and eventually sent to the Principal Investigators on tapes or
network by the Data Archiving & Distribution System (DADS). The raw data
are archived at the Canadian Astronomy Data Centre (CADC) in Victoria, and
become public after a one year proprietary period (except for the CFHTLS
data). The Terapix data processing center also proposes its services to the
whole CFHT community with the data stacking, fine astrometric calibration
and catalogs generation.
During the semester 2005B, WIRCam was commissioned
and the first scientific observations were undertaken. On-chip guiding is
now operational, the image quality is excellent, and micro-dithering and
nodding modes have been successfully used. At the time of writing, efforts
concentrate in diminishing the operational overheads, stabilizing the performance
of the guiding, and decreasing the actual readout time to improve observing
efficiency. Information on WIRCam can be found at
http://www.cfht.hawaii.edu/Instruments/Imaging/WIRCam/
Operations: New Observing Process
Queued Service Observing
Since January 2001, CFHT wide-field imagers have
been used exclusively in Queued Service Observing (QSO) mode. QSO is the
front-end component of a broader ensemble of software, the New Observing
Process (NOP), which allow the acquisition, analysis and distribution of
high quality data. Since its commissioning in 2003, all of the observations
with the MegaCam mosaic camera were performed through the NOP at a rate of
about 10-15 Terabytes per year. With the improvements made on the camera
and with the minimization of some of the main operational overheads (guide
probe motion, auto-focus), observing efficiency has been steadily increasing.
In 2005B, overheads during good nights have been reduced to less than 10%,
contributing to very good statistics on programs, even if weather has been
worse than expected. Each night, about five queues created from observing
blocks extracted from several programs, as specified by the PIs in their
Phase 2, are prepared by the Queue Coordinator to cover diverse weather conditions.
At night, the Service Observer selects and executes the appropriate observations.
In general, grade A programs are completed at > 90% during a given semester.
The validation rate is close to 90%. Balance of the telescope time
allocated to the different Agencies, a strong constraint on scheduling, is
also achieved at a very good level. Complete information
on the queue mode at CFHT, including reports on previous semesters, statistics,
schedules and night reports, can be found here:
http://www.cfht.hawaii.edu/Instruments/Queue/
For WIRCam, a new version of the Phase 2 tool has been developed
in 2005. The tool allows the user to select options like micro-dithering and
nodding patterns. At the time of writing, scientific observations have been
started with WIRCam and have been very successful, although a lot of engineering
remains to be accomplished.
Elixir
A major component of the NOP is Elixir, an extensive
data assessment, calibration, and pre-processing system. The Elixir system
provides three types of services: 1) real-time data quality assessment, 2)
end-of-run detailed calibration analysis, 3) image pre-processing and meta-data
compilation for data distribution. Coupled with the data analysis pipelines
are various databases which store all of the necessary data products. Elixir
was first developed for CFH12K and then adapted and developed even further
for MegaCam observations since 2003.
Despite the large volume of data produced by MegaCam (~ 1 Tbytes per run),
data are fully pre-processed and ready for distribution within a week after
the end of an observing run. Since the arrival of MegaCam, several modifications
in the reduction "recipes" have been made to improve the end-results notably
on the reduction of the fringing pattern seen in the redder filters. When the
final recipes are implemented, CFHT plans to reprocess all of the MegaCam data
since first light.
CFHT will also provide pre-processed data for WIRCam. At the moment,
Elixir-WIRCam is a work in progress with recipes being developed on real science
images obtained at the end of the semester 2005B. It is expected that
a first version of Elixir for WIRCam will become implemented by the end of
the semester 2006A.
With the arrival of WIRCam, CFHT will be operated in a NOP mode
for about 85% of the time. Discussions on how to operate ESPaDOnS
also in a queue mode will take place during the next year. Those are challenging
but exciting times for CFHT!
