ASCAP

Photo-electric Photometry at CTIO, using PC/ASCAP

Instrument is retired and no longer available for use.

G. Schumacher
D. Geisler
Feb. 1991

some updates by A.R. Walker, Sept. 1998

 

INTRODUCTION

Photo-electric Photometry is only offered on the 1.5-m telescope, at f/13/5 (10 arcsec/mm). Unfortunately, there is at present no CTIO staff member carrying out scientific programs with this equipment, and so we may be a little slow at finding the answers to your questions. Sorry!

We have several photomultiplier tubes (GaAs, S20, S11) normally operating in a dry-ice cooled cold-box. We also have the last working Varian InGaAsP photomultiplier in the world (purchased in 1978!!) which has high sensitivity to almost 1.2 microns, we restrict access to this tube due to its fragility and uniqueness. The photometers are simple devices containing an aperture wheel, filter wheel, and TV viewing of the aperture, all under computer control. The pulses from the photomultipliers are amplified by either SSR or EMI amplifier- discriminators and then counted on hardware contained in a PC, which also operates the instrument, and has various facilities for displaying the data, manipulating and storing it, and doing reductions. The remainder of this document describes the program. Note that this PC is on the mountain ethernet, so you can transfer your data files home with ease, or else write them to floppy disk.

 

FILES

The files utilized by the PC-ASCAP program are ordinary text files consisting of one line records, which can be produced using any text editor which does not leave any special control character in the file. The records themselves consists of various fields separated by any number of spaces. Free format number decoding is used throughout. Therefore, it is important not to use a space within a field, for example in a star identification. We recommend using the "_" (underbar) or "-" (dash) characters instead.

User file.

This file is mandatory and contains the basic information for observation. We recommend calling it by your name, e.g. Jastronomer. The examples illustrate a typical set-up: using the 1.5m telescope with the Hamamatsu tube in cold box 71 and the filters VBURI in positions 1-5. The following record types are used in this file:

Name: this record identifies the observer. For example:

Name: Joe Astronomer

Telescope: this record identifies the telescope. The telescopes with encoders are the 4.0m, 1.5m, 1.0m, and 0.9m. Any other name is accepted, e.g. 0.6m, but the position information is then taken from the right ascension and declination of the object, as given with the 'ident' command (see below), instead of from the telescope encoders. For example:

Telescope: 1.5m

Tube: this record identifies the photomultiplier in use. The last field in the record contains the maximum recommended count rate for the tube.

Tube: Hamamatsu 71 200000

In order to prevent damage to the phototube, there is a maximum recommended count rate for each tube that should not be exceeded. In general, this maximum count rate is 200,000 counts/sec. This is true of all of the GaAs tubes (RCA, Hamamatsu) - see page IV-28 of the Facilities Manual for the maximum recommended count rate if you are using a different tube. If the count exceeds the number given in the user file in the first second of observation, the program will insert the TV mirror, warn you that you have exceeded the maximum count rate and ask if you wish to continue. To be safe, answer "NO" and observe a fainter star. You can force the integration to continue by typing "YES" but PLEASE be careful as excessive exposure to extreme light levels can fry the tube. If you must observe this star, use the minimum integration time necessary.

Dead time: this record gives the dead time in nanoseconds, needed to correct for coincidence losses.

Dead time: 35

Filters: this record initiates the description of the filters in use. The description consists of the filter position in the filter wheel, an identification label and optional comments. The identification label should start with an alphabetic character, not a number.

Filters:

 

  1. v
  2. b
  3. u
  4. r
  5. i

Precision: this record initiates the declaration of the precision value for each filter. You can omit this item if you are not using the automatic mode.

Precision:

 

  1. 1.5
  2. 0.7
  3. 0.7
  4. 0.7
  5. 0.7

Color equations: this record initiates the description of the color equations to be used in the quick look calculations. The equations are constructed utilizing the labels given in the filters record. You can omit this and following items if quick look is not desired.

Color equations:

U-B = 1.01*u - 1.01*b
B-V = 0.95*b - 0.95*v
V-R = 0.96*v - 0.96*r
R-I = 0.99*r - 0.99*i
V = 1.03*v - 0.03*b

NB - The order of these equations should be the same as that in the Standard file (see below).

Extinction coefficients: this record initiates the definition of the extinction coefficients.

Extinction coefficients:

v = 0.14
b = 0.23 - 0.024*b + 0.024*v
u = 0.50 - 0.024*b + 0.024*v
r = 0.085
i = 0.052 + 0.01*r - 0.01*i

Zero points: this record initiates the definition of zero point values.

Zero points:

U-B = 0.21
B-V = -0.38
V-R = -0.29
R-I = 1.20
V = 21.61

The next example shows a complete user file.

Name: Joe Astronomer
Telescope: 1.5m
Tube: Hamamatsu 71 200000
Dead time: 35
Filters:

  1. v
  2. b
  3. u
  4. r
  5. i

Precision:

  1. 1.5
  2. 0.7
  3. 0.7
  4. 0.7
  5. 0.7

Color equations:

U-B = 1.01*u - 1.01*b
B-V = 0.95*b - 0.95*v
V-R = 0.96*v - 0.96*r
R-I = 0.99*r - 0.99*i
V = 1.03*v - 0.03*b

Extinction coefficients:

v = 0.14
b = 0.23 - 0.024*b + 0.024*v
u = 0.50 - 0.024*b + 0.024*v
r = 0.085
i = 0.052 + 0.01*r - 0.01*i

Zero points:

U-B = 0.21
B-V = -0.38
V-R = -0.29
R-I = 1.20
V = 21.61

Macros file

The macros file contains the definitions of the automated observing sequences. The macros have the same format as the old Tolnet version. In order to distinguish one macro from another they are separated by a record containing the word 'macro' followed by a number. This number is then used to invoke the macro with the 'X' command. The macro may be extended to several lines and can have an unlimited number of commands. The file must be called ' macros '. The number of macros is also unlimited (unlike the old version where there were only 10 available). Within a macro, the format is : * (star) or / (sky), followed by filter number, then a comma, followed by the desired number of observations, then a space, and another 4-character command. For example:

 

macro 1
*1,1 *2,1 *3,1 *4,1 *5,1
/5,1 /4,1 /3,1 /2,1 /1,1

macro 2
*1,2 *2,2 *3,2 *4,2 *5,2 /5,1 /4,1 /3,1 /2,1 /1,1

After observing the star and before observing sky, the program will halt, move the TV mirror to the field position, and wait until you locate a sky patch and press the space key before observing sky.

Objects file

The objects file contains the positions of the objects to be observed. Remember that spaces are used to separate fields and should not be used within a field.

Within the data records, the following order is used:

- Record Identifier: The exact content of this record is up to the user. This identifier should be given with the 'ident' command. It can be up to 8 characters.

- right ascension: 3 numbers: HH MM SS.SS, e.g. 12 34 45.123

- declination: 3 numbers: DD MM SS.SS, e.g. -30 41 32.3

- epoch: a number in years., e.g. 1990.0

 

The rest of the line may be used for comments, identifiers, etc. PC-ASCAP does not use this information.

The following is an example of an object file:

 

1 17 05 05.431 -64 59 56.12 2000.0 Center of field
2 17 03 32 -65 00 53 1950 V= 18.24, B-V= 0.35

 

Standard file

This file contains the star id, standard magnitude and the color values for the standard stars. The order of the indices should be the same as that given in the user file. Also, the star id should be identical to that used in the objects file and

 

Star         U-B     B-V    V-R    R-I      V 

 E101      0.091   0.087   0.038   0.084  7.704
 E102      0.112   0.206   0.126   0.274  8.444 
 E103      0.098   0.086   0.037   0.085  9.657
 E104      0.001   0.362   0.213   0.427  7.455

Data file

The data file is called 'ppdata.dat'. The data is normally written to the hard disk but you can also select the floppy drive as a backup medium. The format of the data is the same card image format as the old version of People's Photometry, so you don't have to change your reduction program! At the end of the night, you can write out your data to floppy using the command PPCOPY. For example:

PPCOPY ppdata.dat a:dec2590.dat

The format of the data is:

 

 

Column(s)        Contents

   1        0 if normal data record or 1 if a comment, in which case the comment
            appears in columns 6-80.
   2-5      Record number.
   6-13     Identification.
   14       Standard flag: 1 if the star identification appears in your
            standard star (stand) file, 0 otherwise.
   15       Object flag: 0 if star, 1 if sky.
   16       Diaphram number (first diafram used =1, second =2, etc.).
   17       Filter number.
   20-21    Universal time hours.
   22-23    Universal time minutes.
   24-25    Universal time seconds.
   26-28    Hour angle hours.
   29-30    Hour angle minutes.
   31-32    Hour angle seconds.
   33-35    Declination degrees.
   36-37    Declination minutes.
   38-39    Declination seconds.
   40       Reject flag: blank if not rejected, 1 if rejected.
   41       Number of channels (=1).
   42-45    Integration time (sec).
   46-52    Counts.
   67-68    Month.
   69-70    Day.
   71-72    Year.
   73-74    Universal time tenths of seconds.

 

COMMANDS

The $ level commands are those which accept parameters needed during data acquisition and logging. The commands are case insensitive and all responses require pressing the 'enter' key to be acted upon. A list of the available commands at any level appears on a window on the right-hand side of the screen. Following is a description of all implemented commands.

 

This command sets the clock to the Universal Time as given by the satellite receiver. In order to use this feature you need to be connected to the SUN computer named ctio1m (from the Sun, do "rlogin ctio1m"). Operation is as follows:

 

- Type the goes command at the PC terminal.

- Then type the goes command at the SUN terminal.

- On the PC screen you will see a time about 10 seconds ahead of the present time. When that time arrives the clock will be synchronized with the satellite time. There are ocassions when this command fails to terminate and the clock doesn't get synchronized at the shown time. In that case, strike any key at the PC terminal and repeat the operation again.

 

  • backup

    This command enables or disables backup of the data on a diskette. To enable backup type 'backup on'. To disable type 'backup off'. The backup status is permanently shown in the status window. For example:

    backup on

    It is a good idea to enable this feature, which will then cause the data to be written to floppy ~ every 10 records, naming the file something like a:dec2590.bck. However, since you may reject records during the night after they are written, you may also want to write the clean data to floppy at the end of the night using the PPCOPY feature (after you quit the program), naming the file a:dec2590.dat.

     

  • coord

    This command shows the present telescope coordinates on the screen. If printer logging is enabled they get typed on that medium too. The coordinates are presented in the order right ascension, declination and hour angle.

     

  • date.

    This command permits setting of the date. If no argument is given then the present date is shown on the screen. The format is month/day/year. For example:

    date 09/18/90

     

  • diaf

    With this command you give the program the size of the diafram (in mm) to be used. After given the command, the program positions the selected aperture inmediately. The acceptable arguments are: 0.7, 1.0, 1.4, 2.0, 2.8, 4.0, 5.6. See the Facilities Manual (Table IV-17) to determine the size of the apertures in arcseconds at your telescope. For example:

    diaf 1.4

     

  • dir

    This command permits examining a directory content. After you type the command, you are requested for the name of the directory to be shown. To return to the command level, just press 'ESC'.

     

  • edit

    This command permits editing of a file content. If the file doesn't exist it is created. Otherwise the file content is presented in an edit panel.

    The editor is a true screen editor (not a word processor) in that you use the arrows and pages keys to browse and insert text. To exit the editor press the ESC key. The following keys are supported:

     

    ESC       Quit editing
DEL       Delete character under cursor
BACKSPACE Delete character to the left of cursor
ALT-S     Search for a string
ALT-R     Search for a string and replace it
UP        Moves the cursor up one character
DOWN      Moves the cursor down one character
RIGHT     Moves the cursor right one character
LEFT      Moves the cursor left one character
HOME      Moves to beginning of the current line
END       Moves to the end of the current line
PGUP      Moves up one page
PGDN      Moves down one page
CTRL-PGUP Goes to the beginning of the text
CTRL-PGDN Goes to the end of the text
ALT-M     Turns marking mode on or off.
GRAY +    Copies the marked block to the cut buffer.
GRAY -    Cuts the marked block to the cut buffer.
INS       Pastes the cut buffer at the current cursor location.
DEL       Deletes the marked block if there is one.

    For example:

    edit jastronomer

    -Note. Be sure to use the "eq" command after editing your userfile to update the changes into the program, e.g. after changing the zero points at the beginning of the night.

     

  • eps

    This command is used to enter the limit of acceptable variability for the counts, C, according to:

    |C - Mean| / Sigma < Eps.

    If any count rate exceeds this criterion, integration will halt and an "Unstdy Counts" error message will appear. Check centering, etc. To continue, just press the space key. Be sure to reject the offending integration if appropriate.

    To suppress this feature enter a value of 0. For example:

    eps 10

     

  • eq

    This command permits rereading the equations for quick look contained in the user file. Normally you give this command after editing the user file, for example, after changing the zeropoints at the beginning of the night.

     

  • go

    This command transfers control to the section of the program where data acquisition actually occurs. The runtime window is placed on the screen. For example:

    go

    The GO level commands for actual data acquisition are virtually identical to the old People's Photometry commands. They are largely single key instructions requiring no 'enter' key to perform its action. However, 'enter' must still be used with those commands requiring parameters, such as setting an integration time. Following is a list of GO level commands.

     

    space   continue integration after hold condition.
1-8     starts integration with selected filter.
*       group observations as star counts. 
/       group observations as sky counts.
-       group observations as dark counts.
!       force termination of present integration, and continue to next command
        if executing a macro.
a       selects automatic mode. (Integration terminates when the precision defined
        in the Precision Table is reached).
b       breaks integration or escapes from macro. Data is not recorded 
        for the interrupted integration.
c XXX   enters the comment XXX (up to 72 characters).
f       shows the field on the TV screen.
h       holds an integration. Continue by striking the space bar.
k       kills the previous sky readings.
m       selects manual mode.
n NN    sets the number of integrations to NN per filter.
r n-m   sets the reject flag on records n-m.
s       stop and return to $ level commands.
t n     sets the integration time to n seconds. Allowed values are 1 to 30,000.
v       view the area of the diafram on the TV screen.
x n     starts macro n.
z       zap (terminate) present macro command. Can reinitiate present macro 
        command with the Space bar.

     

  • goes
  • gonr

    This command transfers control to the section of the program where data acquisition actually occurs. The difference with the go command is that no data recording takes place.

     

  • i (ident)

    This command is used to identify an object using up to 8 characters. The command groups the observations belonging to one object together, and failure to use it negates internal housekeeping functions. After receiving the command, the program checks the standard file to see if the object is a standard star or not. If it is, the program tells you so.

    For telescopes lacking position encoders, or when the connection is disabled (see tcs command below) and if the id is not found in the objects file, then the program will ask for the coordinates of the object. The coordinates are requested in a formatted window. In order to escape from the window just press 'ESC'. For example:

    i LMC-0635

     

  • macros

    This command allows editting of the macros file. After the command is given the file content is presented in an edit window (see edit command above). For example:

    macros

     

  • object

    This command selects the objects file. The file should be prepared according to the description given in the 'files' section. For example:

    object obs24.coo

     

  • prec

    This command is used to change the precision values of any filter. After given the command you are presented with a window of precision values. To return to the command level press 'ESC'.

     

  • printer

    This command enables or disables logging of commands on the printer. To enable logging type 'printer on'. To disable logging type 'printer off'.

     

  • q (quick)

    This command requests the calculation of quick look reductions. If no argument is given then the last object observed is used. Otherwise, the argument is taken as the first record number of the object to be calculated. For example:

    q 274

     

  • quit

    This command terminates the program. After receiving the command, the program requests the user for confirmation. Respond 'yes' if you want to abandon the program. Use this command to terminate the program at the end of the night. If you quit the program during the night for whatever reason and then return, be sure to execute the "stand" command and set "backup" and "printer" on.

     

  • stand

    This command selects the standard stars file. The file should be prepared according to the description given in the 'files' section. Be sure to use this command again if, for whatever reason, you "Quit" the program and then return to it during the night. For example:

    stand ubvrimag

     

  • tcs

    This command enables or disables the connection to the telescope control system. Type 'tcs on' to enable. Type 'tcs off' to disable. For example:

    tcs on

     

  • time

    This command permits setting of the universal time into the computer. If no argument is given then the present time is shown on the screen. The format is hh:mm:ss. For example:

    time 06:35:40

Data Display

Figure 1 shows the run-time data display. It consists of a series of windows each showing specific pieces of information. Following is a description of each window.

Top left

This window displays the program name.

Top right

This window displays the date and universal time.

Middle left

This window displays the actual run-time information. Under 'object' it shows both '*' and '/', for star and sky respectively. Under 'filter' it shows the number of the actual filter being observed. Under 'time' it shows the total time of integration in seconds. Under 'counts/sec' it shows the rate for the present object being observed. Under 'counts' it shows the total counts already obtained for both star and sky for the selected filter. Under 'prec' it shows the present presicion obtained (in units of 0.1%), and finally under 'total (* - /)' is shown the total star counts minus the sky counts (=(Star count rate - Sky count rate)(both corrected for dead time) * ( total time observed on Star )). Thus, e.g., when this number reaches 10,000 you have achieved 1% accuracy from photon statistics.

Middle right

This window shows the status of the backup, printer and tcs options.

Bottom left

This is the actual command window.

Bottom right

This is the help window, where all possible commands available in the current task are shown. The window content changes as you select different levels of the program.

 

Next-day Reduction on the Mountain

A full photometry reduction program is available on the SUN computers, both on the mountain and in La Serena, enabling you to obtain final transformed magnitudes and colors for program stars. After a little practice, one can reduce a night's worth of data in about an hour.

 

G. Schumacher
D. Geisler
Feb. 1991