Padova and Asiago Observatories

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1 ISSN Padova and Asiago Observatories CCD DATA ACQUISITION SYSTEM FOR THE COPERNICO TELESCOPE Baruffolo A., D Alessandro M. Technical Report n. 3 March 1993 Document available at: Vicolo dell Osservatorio, Padova Tel Fax

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3 Abstract In this paper we describe the CCD data acquisition system, actually installed at the Copernico Telescope of the Asiago Astronomical Observatory. Particular attention is given to the hardware configuration and the operational guidelines of the system, whose detailed description is given in the Users' Manual. 1 Hardware configuration The CCD data acquisition system consists of one VME rack containing the following subsystems: master CPU, Eltec-E6, devoted to the global control of the system and to the user interface; slave CPU, TSVME 431, dedicated to the direct control of timings for CCD scanning; a Tecnint 32 MB memory card, for the temporary storage of images; True Color Display (TCD) graphic card, for image display and graphic plots; IPC digitizing card, for image acquisition from the guiding camera; one hard disk drive containing the PDOS real time operating system and all application programs; one hard disk drive dedicated to the permanent storage of images; one floppy disk drive; one alphanumeric terminal. The system is connected, through a twisted pairs cable, to the analog electronics relative to the CCD in use. The overall layout of the system is shown in Fig. 1. Fig. 1: Diagram of the CCD data acquisition system. 2 Control software All the software which controls the CCD images' acquisition, storage and quick-look was developed within the GATE environment (Ref. 1). Within this environment operate the tasks that control all devices connected to the system (disks, analog electronics, TV display, guiding camera). The acquisition system was designed so that it will be possible in the future to perform remote observing (Ref. 1). 1

4 At power on the PDOS operating system boots and the network software is started and initialized, if the boot is successful the system prompt 13:/> appears at the terminal. At this point it is possible to start one of the four programs provided for operation of the instruments actually in use at the telescope. Each program is started by typing respectively: b&c: for the Boller & Chivens spectrograph; camera: for the direct imaging camera; echelle: for the high resolution Echelle spectrograph; echelle1: for the high resolution Echelle spectrograph, with 22 binning; Each program initializes the instrument's CCD controller, sets the readout speed, the readout window size and the gain of the amplifier chain. The status command shows the values of these parameters. If the analog electronics was not powered on, during system initialization some errors are shown at the terminal. Immediately after initialization the control system's prompt (VMEK>>) appears at the terminal: now it is possible to issue all the commands listed and described in the Users' Manual (Ref. 2). Commands can be typed both in upper and lower cases and can be abbreviated, it is possible to edit the command string and to recall previously issued commands by using the arrow keys of the terminal. The last 20 commands issued by the user are stored in a memory buffer and can be displayed by the history command (which is not stored in the commands' buffer and cannot be abbreviated). On line help is available and is started by the help command. 3 Images acquisition The readout window's size can be modified by using either the ccdwindow or windowxy command, in the case the default settings do not match the observe r's needs. Once a proper readout window is set, it is possible to take science exposures with the command exptime. At the end of the exposure the slave CPU starts reading the CCD and signal the master CPU for the availability of the data. Data is read by the master CPU, stored in a memory buffer and displayed on the TCD's screen. At the time of this writing two memory buffers are available and it is possible to change the default setting of the destination memory buffer using the setdbuf command. Calibration frames are taken with the flat, dark, calib, bias commands. It is also possible to grab the guiding camera's display as it were a CCD exposure using the load command. All these commands automatically update the IMAGETYP field of the image's FITS header. The command focus was provided for telescope focusing: using this command it is possible to perform multiple exposures on the same frame, while varying focus parameters and moving the telescope. Two commands can be used to remove charge from the CCD: cwipe, which continuously reads the CCD at the fastest speed without data conversion and display, and cclear, which performs conversion and display and is therefore much slower. 4 Flux of the data All images are stored on the local hard disk and, if the Ethernet link is available, also on the disk of the data reduction Workstation. On the local system the disk devoted to permanent storage is PDOS 4.1 formatted, images are written in disk FITS format. It is thus possible to transfer images to the Workstation, outside the acquisition system, using the File Transfer Protocol (FTP). It is possible to store on disk images having different dimensions, i.e. corresponding to different readout windows, they are handled in a way completely transparent to the user. In the following sections the basic operations of images' input/output on disk in FITS format are discussed, a complete reference of the commands involved in these procedures is given in the Users' Manual (Ref. 2). The data flux within the acquisition system and the commands used for its control are shown in Fig. 2. 2

5 Fig. 2: Schematic view of the data flux in the acquisition system and of the commands used for its control. 5 Disk initialisation Before starting to store images on disk it is necessary to initialize it. This operation erases all files which eventually were already present on disk and initializes some parameters needed for a proper functionality of the storage subsystem. Since it is possible to mix images having different formats, the maximum number of images that can be stored on disk is not fixed in advance, the limit is ultimately the physical size of the disk. The initialization routine operates interactively and asks for confirmation before proceeding with the disk initialization. It is possible to stop the initialization procedure by hitting CTRL-C. 3

6 6 Data management The image currently stored in the default memory buffer can be written on disk using the store command. The user is asked for the insertion of some parameters (object name, filter and/or grating employed, comments) which will be inserted in the image's FITS header. Some keystrokes useful during editing are shown in the upper portion of the screen. Once all parameters were inserted the image is written on disk and eventually sent to the Workstation. The image is written on disk with the name IMAGEnnnn.FITS where nnnn is a increasing number which uniquely identifies the image. The number that will be associated to the next image that will be stored on disk can be displayed by the dwistack command and can be modified by the swiss command. The idir command displays a list of all images stored on disk, showing: order number of the image, exposure type, object name, telescope's coordinates at start exposure, Universal Time at start exposure, exposure time in seconds, image format (number of columns by number of rows). One image stored on disk can be read into memory in the default memory buffer, using the rdimage command, for display or inspection. It is possible to list at the terminal the header of an image stored on disk using the rdheader command. 7 Implemented FITS header The FITS header currently implemented contains the following cards: SIMPLE= always T; BITPIX= always 16; NAXIS= always 2; NAXIS1= number of columns in the CCD readout window (modified by the commands ccdwindow and windowxy); NAXIS2= number of rows in the CCD readout window (modified by the commands ccdwindow and windowxy); DATE-OBS= date of acquisition of the image (string of the form dd:mm:yy); DATE= date the file was written (always equal to DATE-OBS); EXPSTART= Universal Time at start exposure (string of the form hh:mm:ss); JD= JD at start exposure (floating point value); SID-TIME= Sidereal Time at start exposure (string of the form hh:mm:ss); EXPTIME= effective exposure time in seconds (floating point value), it is computed considering exposure interruption or suspensions (caused by using the pause or stop command), if any; RA= telescope's right ascension at start exposure (string of the form hh:mm:ss.cc); DEC= telescope's declination at start exposure (string of the form dd:mm:ss); AIRMASS= airmass at start exposure (floating point value); TELESCOP= telescope's identificative string; INSTRUME= employed instrument's name (string); ORIGIN= institution that originates the data (string); DETNAME= detector's name (string); OBJECT= user defined string which identifies the target; 4

7 OBSERVER= user defined string containing the observer's name; FILTER= user defined string which identifies the employed filter; IMAGETYP= exposure type string (flat field, object, bias, dark, calib); COMMENT= three user defined comment strings; COMMENT= six comment strings containing voltages, temperatures, gain and speed of the employed CCD at start exposure; END= end of the FITS header. User defined strings are inserted interactively when storing the image on disk. 8 Quick-look and image's analysis Some commands for data analysis, display and graphics plot were implemented in order to allow for images' quick-look The image currently stored in the default memory buffer can be displayed on the TCD screen using the tvdisplay command, it is possible to specify, as parameters, the low-cut and high-cut to be applied to the image before displaying it; the zoom factor (zero by default) can be varyied by the tvzoom command. The look-up-table (LUT) can be changed using the tvlut command, while the position of the image relative to the upper left corner of the screen can be modified by the fshift and tvshift commands. The plotrow and plotcol commands allow to obtain graphical plots of image's rows or columns, while by using the plotline command it is possible to plot image's values lying along a line whose extremes are fixed interactively. A graphical cursor is also available, it is activated by the gcursor command and allow to examine the plotted values and the respective positions. Image pixels' values can be inspected using the tvcursor command which draws a cursor on the TCD screen and displays its position (relative to the image upper left corner) along with the corresponding counts; the cursor can be moved around using the arrow keys of the terminal keyboard. When the command is terminated the cursor's position is stored and it is used by the sample command which computed statistics on the image in boxes centered on it, whose width is specified as parameters. Acknowledgements We wish to thank professor Favio Bortoletto who has partecipated to the design and implementation of the system. References Ref. 1: Bonoli, C., Fantinel, D., Baruffolo, A., Bortoletto, F., 1992, A distributed VME telescope control system for remote operations, TNG Technical Report n. 14 Ref. 2: Claudi, R.U., Cremonese, G., Fantinel, D., 1993, Manuale d'uso del nuovo sistema di acquisizione del Telescopio ``Copernico'', Osservatorio Astronomico di Padova Technical Report n. 2 5