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