Many keywords derive their default values from the file ait.config which describes many of the properties of the particular telescope. (We recommend that you obtain a copy of this file before preparing observing requests.)
Strings which are delimited by single quotes:
Example: OBJECT = 'Orion Nebula'
By convention RA, DEC are specified as strings since they are expressed in Babylonian notation.
Numerical values are just specified after the equal sign:
Example: EXPTIME = 300.0
Boolean choices can be either true or false are specified by the single (upper case) values T or F. There are no quotes around these letters.
Example: SENDMAIL= F
Request files have several ways of putting in comments which are not read by programs: A pound sign # or slash / causes the text following up the the newline to be ignored. In addition the keyword COMMENT is accepted.
The last line of a request file must contain the END keyword.
For example to generate different exposures of the same target in the U, B, and V filters the following fragment can be used:
FILTERS= 'V' EXPTIME= 10.0 / object name, observer etc. specified above END / end of first stanza FILTERS= 'B' END EXPTIME= 35.0 / change exposure time FILTERS= 'U' ENDGroups are a powerful way to make sure that observations are performed together. However, if the observation of an early stanza fails, the rest of the observation is stopped, and the next request file is scheduled.
OBSERVER= 'Melissa Stevens' / astronomer's name - required SENDMAIL= T / T means send mail, F -don't -default:F MAILADDR= 'marsi@hopkins.com' / E-mail address to astronomer -depends PROCEDUR= 'photo_proc' / -default:'photo_proc' OBJECT = 'Orion Nebula' / name of object -required RA = ' 5:35:11.0 ' / Right Ascension - required DEC = '-5:23:16 ' / declination, not necessarily signed -required EPOCH = 2000 / epoch of position -required FILTERS = 'R' / the filter -required EXPTIME = 300.0 / the exposure time (seconds) -required NUM-OBS = 1 / -optional see below END / -requiredThe first keyword tells the system, who is requesting the observation. The next two keywords determine the disposition of the data: if the observer wishes to be informed when the observation has been made by setting SENDMAIL to T, then an Internet MAILADDR must be present.
The RA and declination must be specified in Babylonian format (hour minutes seconds format delimited by colons). You must fill in the values appropriate to your observation.
The declination should be between the limits found in ait.config, ,the ra should be observable in the near future, and the filter present in ait.config.
If you do not wish an image treated in this manner other PROCEDUR's are available (see below).
SEEING = 2.0 /max. FWHM of stellar images (arcsec) -default: 20 MOONPHAS= .3 /max phase of moon allowed (range 0-1) -default: 1.0 MOONDIST= 15. /minimum angular distance to moon -default: 15.0 degs. MOONWIDTH= 6. /specifies width of avoidance Lorentzian (see below) MAXAIRMA= 1.5 /max acceptable airmass -default: 3.0 EXTINCT= 0.3 /max acceptable extinction in mags -default: 1.0The default values are usually satisfactory. Set MOONDIST to a negative value if you are taking pictures of the moon.
The MOONWIDTH keyword can be used in conjunction with the MOONDIST keyword to specify an avoidance distance that varies with lunar phase. In particular observations will not be scheduled if the target is within MOONDIST/(1+(age/MOONWIDTH)^2) of the the moon. This means at full moon the avoidance will be MOONDIST and MOONWIDTH days before (or after) the avoidance will be one half MOONDIST.
DAYSTART= '20/01/1991' / start of period (UT) to observe -default:today DAYEND = '28/02/1991' / end of period (UT) - default:never UT-START ='8:12:45' / UT at which observation MUST be made -optional LSTSTART= ' 12:45:34' / start of LST window for object -optional LSTEND = '14:45:34' / end of LST window for object -optional JDSTART = 2448723.1989 / Julian Date of start -optional >NUM-OBS = 5 / number of obs to make during period -optional NUMPERNI= 3 / observe this many times per night -default:1 INTERVAL= 4 / how many days between observations -optionalNote: Dates are specified as day/month/year, and must be quoted. Times are specified as hours:minutes, and must be quoted.
If none of the above keywords are specified, one observation of the target will be made at the 'best' time with respect to it celestial coordinates.
There are two different ways of specifying the number of observations to be made. If NUM-OBS is specified that number of observations will be done. If an INTERVAL is specified, the scheduler will attempt to schedule them at the specified number of days apart. It is possible that they may occur more (or less) often. If an INTERVAL is specified and NUM-OBS is not, then observations will continue indefinitely (or till DAYEND). If an INTERVAL is not specified then NUM-OBS observations (default 1 for this situation) will be done as soon as possible.
If you wish observations to begin or cease on specific (Universal time) dates you may specify DAYSTART and DAYEND respectively. To specify observations on a given night only then DAYSTART should equal DAYEND.
If no other restrictions are made, the list generator will try to schedule the observations as close to meridian passage as possible and consistent with the sun at an altitude less than 10 degrees below the horizon.
In addition a window in local sidereal time can be constrained by the LSTSTART and LSTEND keywords; these will restrict the scheduling to within these times. Note: these keywords disable the constraints of MAXAIRMASS, the altitude of the sun, or even telescope limit checking.
To force observations at specific times, the UT-START or JDSTART keywords can be specified. These cause the list generator to schedule the group to within five minutes of that time (if space allows), without checking for telescope limits or whether the sky is dark. Use of these keywords is discouraged since they strongly constrain the scheduling.
The SUNALT keyword cause the observation to be scheduled within five minutes of the requested altitude of the setting sun.
The NUMPERNI keywords allows you to request the same target to be observed more than once per night. The list generator will divide the available observing window into NUMPERNI intervals and try to schedule the observations within each of these intervals. How uniform the intervals are depends on how busy the telescope is.
The following keyword can influence whether a request file is actually scheduled. We recommend the default value.
PRIORITY= 10 /* low numbers -> more important -default:10The values are limited to between 1 and 99.
GUIDEMOD= 'guide' / -default:'guide' GURA='12:12:12.3' / guide star coordinates -optional GUDEC='38:12:12.3' / guide star coordinates -optional GUEPOCH= 2000 / guide star coordinates -optionalThe default value of GUIDEMOD is 'guide' at which point the AIT will automatically select the guide star and acquire it. If it fails to acquire the star the observation will be aborted. Note: We define acquisition as the process of identifying and locking onto the guide star before the shutter is open. Once the shutter is open, the exposure will continue even if the guider looses track. The guider will leave a keyword GUSTAT in the data file describing its performance. IF GUIDEMOD = 'tryguide' is specified a guide star will be selected as before, however, in the event of acquisition failure, the observation will be completed. If GUIDEMOD='noguide' is specified, no attempt at guiding will be made.
It is usually best not to specify a guide star since a (hopefully) optimum one will be selected automatically (when GURA is not specified).
photo take a ccd image but don't process it further. photo_all take an image, process it, do photometry, and discard original. photo_proc take an image, process it (bias, dark, flat)
All these procedures needs to have the keywords: RA, DEC, EPOCH, FILTERS, and EXPTIME specified. Other values for PROCEDUR will be rejected. However we can develop new procedures customized for specific observers. Note: All the image files are stored and archived on tape and can be available at a later time. The procedures specify whether an image file or just the photometric results will be available on the Internet. Since we transmit these data by a slow phone line, not all image data are transferred.
TRACK = '0.23 -.0124'Where the two fields specify the ra and dec track rates in arc-seconds per second of time. Note the ra is specified not in angular units but is the change in Right Ascension.
The OBSTIME keyword can be used to notify the scheduler how long a given observation will take. It over-rides the EXPTIME and telescope estimates.
The USERID, and MAGNITUD keywords, if specified, will be transferred into the FITS header. One may used them to keep track of your own requests. They are not processed otherwise.
EASTLIM=-30. / default - TELLIME in ait.config -optional WESTLIM=+45. / default - TELLIMW in ait.config -optionalThe above keywords limit the hourangle to which observations can be made. The values should be specified in degrees with negative values for the EAST limit and positive values for the WEST.
The gain of the CCD can be changed from its default value of 1.0 to higher values by specifying the GAIN keyword.
The following keywords determine how an image is processed after it is observed.
ZEROCOR = 0 /* non-zero indicates zero correction -optional DARKCOR = 0 /* ditto dark -optional FIXPIX = 0 /* ditto bad pixels (not implemented yet) -optional CRFLAG = 0 /* ditto cosmic rays (not implemented yet)-optional FLATCOR = 0 /* ditto flat -optional FRINGCOR= 0 /* ditto fringes (not implemented yet) -optional
OBSERVAT= 'Leuschner' /observatory name -exact INSTRUME= 'B.A.I.T.' /instrument name -exact CCDSEC = '[1:512,1:512]' / what part of the chip is to be stored -exact
REQID = 'Jan34abd' / the filestem of the request file DATID = 'Feb3caabd' / the filestem of the data file DAYLAST = '12/22/1992' / the date of the last successful observation UTLAST = '01:24:59' / the ut of the last successful observation NUM-DONE= 3 / number of observations done successfully NUM-FAIL= 1 / number of observations that have errors