Announcement of Opportunity for Semester 97A
5000 x 8000 pixel Mosaic CCD Camera on WHT
The Mosaic CCD group (NAO Japan and University of Tokyo) invites
collaborative proposals for wide-field imaging observations with the
5000 x 8000 pixel mosaic CCD camera at the William Herschel Telescope
in the spring semester 1997.
The mosaic CCD camera (MCCD) is the one of largest cameras
available to the astronomical community today. At the WHT prime focus,
it can observe a 32.4 arcmin x 50.7 arcmin field with four shifted
exposures with a pixel size of 0.2 arcsec. The camera uses 40 of 1K x
1K pixel CCDs made by TI-Japan, which have virtual phase construction
and have 20\% QE in B-band. The 5 x 8 array has 90\% gaps between
each row and column of CCD chip. Thus a sequence of 4 images are
required to image a contiguous field.
Recent scientific results from a 4000 x 7000 camera are
described in Kashikawa et al
(1995,ApJ Letters, 452, 99) .
See also a
paper (Sekiguchi et al, 1992, PASP, 104 ,744) describing a 2000 x 8144
early version of the camera system.
How to Apply
MCCD is a private instrument, not supported by ING staff, and all
applications must be in collaboration with the mosaic CCD group, who
will assess the technical feasibility of programs before applications
are submitted. Applications will be made through PATT or CAT in the
normal way.
The key observing interests of the mosaic group are
Clusters of galaxies
QSO surveys
Interested astronomers should please contact Maki Sekiguchi. He can be
reached by e-mail at
maki@indy.mtk.nao.ac.jp
or by telephone at
+81-422-34-3638 or by fax at +81-422-34-3776.
Instrument Specifications and Sensitivities
The mosaic CCD camera can be used for wide-field imaging observations
at the WHT prime focus and is very well suited for observations of
cluster of galaxies or any kind of surveys. The instrument was used
at the WHT prime focus in Spring of 1996 for about 10 nights and
worked well.
This
Figure
shows a preliminary
B-band image of one of Coma cluster fields, covering 32.4 arcmin x
50.7 arcmin of cluster center. These observation required a total four
30 minutes exposures.
Two minor problems were observed. One is stray light from
LED-based position sensors in the camera shutter and another was an
unoptimized light-mask in front of CCDs, which created ghost lights
for very bright stars. The sensors will be replace by electromagnetic
ones and the new optimized light mask will be installed for any 1997
run.
The instrument specifications are listed below.
CCDs are organized in 5 x 8 array with 90\% gaps in between.
Four exposures are required to complete a contiguous field by filling
the gaps. Each CCD has 1K x 1K of 12 micron pixels. The picture of
the camera is shown in this
Figure
Spatial pixel scale 12micron pixels -- 0.20 arcsec at WHT Prime
Focus.
Available color filters: The MCCD needs dedicated large 25cm x 25cm
filters. Currently Johnson B, V, R, and I are available as well as
narrow I (710nm to 830nm) and Z (830nm to 1100 nm). Other color
filters including narrow band filters can be manufactured. The typical
cost of such filters, if manufactured by an experienced Japanese
company, is around US$ 10,000.
The quantum efficiency of the CCD is about 20% at 400nm, 35% at 500nm,
50% at 600-700nm, 40% at 800nm and 15% at 900nm.
This
Figure
shows the spectral response of CCD convolved with
+ B, V, R, narrow I and Z filters.
The limiting magnitude (magnitude that can be used for useful image
classification) is approximately 24 mag in B with 30 minutes exposure
and 23 mag in V band with 30 minutes exposure based on the preliminary
data analysis of 1996 spring data. The detection limit (s/n=10)
probably goes 1 mag deeper.
The readout time of whole array is 110 seconds. The entire frame data
are stored in local memory and the next exposure can start immediately
after the readout out. The amount of the data for one exposure is 80M
byte. The camera is remotely controlled by SPARCstation2 which
typically takes 3 minutes to transfer the 80M-byte data to its hard
disk. It is not possible to take exposures in cycle shorter than 3
minutes because of this data-transfer.
The image data from each CCD is saved as an IRAF binary file.
Typical amount of one night data ranges from 2Gbyte to 4Gbyte.
The minimum integration time is about 10 seconds due to the
the large shutter which can not move very fast.
Maki Sekiguchi
maki@indy.mtk.nao.ac.jp
Last modified: Wed Sep 11 18:25:36 1996