The DETWCCDn packets

The DETWCCDn packets (where n is an integer from 1 to 8) each list header items which define the state of one CCD detector. The header records should be as follows:

UTSTART =  'hh:mm:ss.ss'     / UT at start of exposure
ELAPSED =  REAL              / Elapsed time (secs)
DARKTIME=  REAL              / Elapsed time (secs)
EXPOSED =  REAL              / Exposure time (secs)
EXPTIME =  REAL              / Exposure time (secs)
PREFLASH=  REAL              / Preflash time (secs)
BUNIT   =  'ADU'             / Physical units of data array
GAIN    =  REAL              / Electrons per ADU conversion factor 
READNOIS=  REAL              / Readout noise (electrons)
CCDSPEED=  CHAR              / Readout speed
CCDNCHIP=  INTEGER           / Number of chips in head
CCDCHIP =  INTEGER           / Name of this chip
CCDTYPE =  CHAR              / Type of CCD
CCDXSIZE=  INTEGER           / X dimension of digitized CCD frame 
CCDYSIZE=  INTEGER           / Y dimension of digitized CCD frame
CCDXIMSI=  INTEGER           / X dimension of useful image area
CCDYIMSI=  INTEGER           / Y dimension of useful image area
CCDXIMST=  INTEGER           / X start of useful image area
CCDYIMST=  INTEGER           / Y start of useful image area
CCDWMODE=  LOGICAL           / Windowing enabled ?
CCDWXO1 =  INTEGER           / X-offset of window 1
CCDWYO1 =  INTEGER           / Y-offset of window 1
CCDWXS1 =  INTEGER           / X-size of window 1
CCDWYS1 =  INTEGER           / Y-size of window 1
CCDWXO2 =  INTEGER           / X-offset of window 2
CCDWYO2 =  INTEGER           / Y-offset of window 2
CCDWXS2 =  INTEGER           / X-size of window 2
CCDWYS2 =  INTEGER           / Y-size of window 2
CCDWXO3 =  INTEGER           / X-offset of window 3
CCDWYO3 =  INTEGER           / Y-offset of window 3
CCDWXS3 =  INTEGER           / X-size of window 3
CCDWYS3 =  INTEGER           / Y-size of window 3
CCDWXO4 =  INTEGER           / X-offset of window 4
CCDWYO4 =  INTEGER           / Y-offset of window 4
CCDWXS4 =  INTEGER           / X-size of window 4
CCDWYS4 =  INTEGER           / Y-size of window 4
CCDXPIXE=  REAL              / Size of unbinned pixels in X (micron)
CCDYPIXE=  REAL              / Size of unbinned pixels in Y (micron)
CCDXBIN =  INTEGER           / Binning factor in X
CCDYBIN =  INTEGER           / Binning factor in Y
CCDSTEMP=  INTEGER           / Set temperature of CCD (K)
CCDATEMP=  INTEGER           / Actual temperature of CCD (K)
TRIMSEC =  CHAR              / Exposed area of the image
CCDSEC  =  CHAR              / Position of exposed area on CCD
BIASSEC =  CHAR              / Suggested bias region
DASMODE =  CHAR              / DAS data taking mode 
CCDCTEXP=  INTEGER           / Act no of integrations (CONTINUOUS mode only)
CCDCTSET=  INTEGER           / Set no of integrations (CONTINUOUS mode only)
CCDCTTYP=  CHAR              / Type of readout (CONTINUOUS mode only)
CCDCLSPD=  CHAR              / Speed of chip clearing

Notes:

• The UT at the start of the exposure is determined from the internal clock of the CCD controller. This is accurately synchronized with the opening of the shutter. It is normal practice to synchronize the CCD's clock with the time service at the beginning of a night and, at that time, values of UTSTART are accurate to the precision given. However, the CCD clock drifts out of synchronization with the time service on timescales of a few hours. Compare UTSTART with UTOBS to check for drift.

• The full CCD-frame includes both the useful image area and the overscan. The header information specifies the size of both the digitized frame and the useful image area, as well as the location of the useful image area. It is possible to window the CCD, so that the data array consists of only part of the full digitized CCD frame. The header information specifies the size and location of the window.

• The readout noise and electrons per ADU depends on the readout speed and output gain (not collected in these headers).

• All dimensions are in unbinned pixels

• The name of the cryostat ( e.g. EEV5) appears in the OBSVATON packet.

• ELAPSED and EXPOSED are preferred to TIMELAPS and TIMEXPOS for compatibility with AAO. EXPTIME and DARKTIME are also provided for use by IRAF.

• TRIMSEC, CCDSEC and BIASSEC should each define a rectangular region by giving the pixel bounds thus: [x1:x2,y1:y2]. Details of how these are derived are given in [2]

• Data are provided for all four of the windows that the user may set on the CCD. Any window with a size of zero has contributed no pixels to the image.

• DASMODE records the mode of data taking : NORMAL (for conventional exposures), CONTINUOUS (for continuous readout sequences) and TAURUS (planned for taurus exposures, but not used at time of writing, 8th Nov 1996).

• CCDCTEXP, CCDCTSET and CCDCTTYP are always collected, but are only valid where the DASMODE is CONTINUOUS.

• CCDCTTYP records the type of readout used in CONTINUOUS mode : NORMAL (repeated straight readouts), HSD (High Smear Drift), LSD (Low Smear Drift) and AUTO (Autoguider mode, not normally used).

• CCDCLSPD records the clear speed used : STANDARD, QUICK or FLASH .