E.1 Scheduler Fields

This section describes the actions of all the buttons found in the web scheduler, as well as the purpose of all the scheduler fields. It is current as of 19 October 2010.

Figure E.1: The initial view of the CABB Web Scheduler

Source

The name of the source. If the name of a known calibrator is entered into this field, the scheduler will automatically fill the RA, Dec, Epoch and CalCode fields. The information in this field will be used by the correlator as the name of the source in the output FITS files. If observing a mosaic, this field should be set to the name of the mosaic file describing the mosaic pointings, without the .mos extension.

RA & Dec

These fields define where on the sky you want the array to point, ie. the phase centre. You must specify RA in hours, minutes and seconds separated by colons (:), and you must specify Dec in degrees, minutes and seconds separated by colons (:). The RA and Dec will be in the system defined by the Epoch field, thus they can also be used to represent Azimuth and Elevation.

Epoch

This defines the coordinate system used for the RA and Dec fields. Four epochs are recognised:

• J2000 (default)
• B1950
• Az/El (horizon coordinates)
• Galactic

CalCode

A flag used to specify if a certain source is used as a calibrator. It should either be C for a calibrator, or blank for a non-calibrator. For baseline solutions, the CalCode is set to B, a feature that should not be used by normal observers. When a calibrator is selected from the Search Cal screens, or matched from input to the Source field, this code will automatically be set to C. The CalCode field is rest to blank after a new scan is added to avoid inadvertantly calling a target source scan a calibrator scan.

The ASSISTANCE program makes use of the CalCode field to determine the level of on-line checking that is done. If a calibrator scan is indicated, the checks (for stable amplitude, small delays, closure phase, etc.) are more stringent. If a calibrator scan is not labelled with CalCode=C then these checks will not be performed. On the other hand, most target sources have structure and insufficient flux, so ASSISTANCE would sound alarms continuously if a source like that was marked as a calibrator scan.

ScanLength

This indicates the length of time to spend on the current scan. It is specified in time format and should be specified as HH:MM:SS, where HH,MM,SS is the number of hours, minutes and seconds to spend on the source respectively. Unless the ScanType is set to Dwell, the scan time includes the time to drive to the source. The scan must be at least four integration cycles long.

ScanType

This field specifies special scan characteristics:

• Normal: the scan will go for the length of time specified by ScanType, inclusive of all slewing/setup time to get on source.
• Dwell: the scan will go for the length of time specified by ScanType, in addition to any slewing/setup time incurred while moving to the source.
• Mosaic: this must be selected to indicate that this scan is a mosaic scan, and that the Source field should be interpreted as the name of a mosaic file.
• Point: indicates that this scan should be executed as a pointing pattern, which can be used to determine offsets for each antenna. This may be used for global pointing solutions as performed by local staff, or for reference pointing during observations.
• Paddle: indicates that the paddle should be inserted during 3mm observations; this scan type will have no effect during observations at other bands.
• Closefile: placing a scan with this scan type in a schedule causes the correlator to close the current file when it reaches this scan. No other scan parameters are interpreted when this scan type is specified. This is useful for keeping file sizes small, or for separating files based on the number of times the schedule has looped. The correlator will automatically start a new file when the next scan begins.
• OTFMos: this must be selected to indicate that this scan is an on-the-fly mosaic scan, and that the Source field should be interpreted as the name of a mosaic file.

Note that for any of the scan types, if the time taken to get on source is longer than the time specified in ScanLength, the scan will be skipped by the online system. For that reason, it is advisable to set the ScanLength of scans such as Point and Paddle to be much longer than the scan will actually take.

Pointing

This field specifies the pointing mode of the antenna. Options are:

• Global: the default pointing mode. It uses a global, all-sky pointing model determined at each reconfiguration.
• Offset: uses the offsets from the latest pointing solution (which should be determined on a nearby calibrator) to improve the pointing locally (near the calibrator) and for a limited time (offsets are time variable). For experiments that track only a single source and a nearby calibrator, this is the safest pointing mode to use.
• Offpnt: instructs CAOBS to find the best pointing solution for this scan by looking through all pointing solutions from the previous two hours, and selecting the one closest in az/el position and frequency. If no suitable pointing solution is found, it reverts to the global pointing model, which may cause serious problems, especially at 3mm wavelengths. This mode should be preferred over Offset pointing if many widely-separated sources are being observed together.
• Refpnt: determine new local pointing offsets by executing a pointing pattern on a calibrator. Using this Pointing mode causes the telescope to be put into global pointing mode before the new offsets are determined. This option only makes sense when combined with a ScanType of Point, and this should only be done while observing a calibrator.
• Update: determine new local pointing offsets by executing a pointing pattern on a calibrator. Using this Pointing mode causes the newly determined offsets to be added to the previously determined pointing solution. This option only makes sense when combined with a ScanType of Point, and this should only be done while observing a calibrator.

Observer

This is an ASCII string up to 12 characters long that is used to identify who made the observations. It is not critical to any on-line system and is merely a label for reference.

Project

This is the project identification number (nnn) allocated to observing projects, and should be specified here as Cnnn. The Project field value is used by CAOBS to name the extension of the output RPFITS files. It is important that it is set correctly as it is used for record keeping and by the ATNF Online Archive. The default C999 code is used for system testing and test files; such files will not be considered as valuable when it comes to deleting data.

Time

The value of this field can only be set for source 1 in the schedule, and is used as the start time of the schedule. If TimeCode is set to LST, then this value is only used for calculation of slew times and elevations by the scheduler’s listing tab, and will be ignored by CAOBS. If TimeCode is set to UTC however, CAOBS will treat the schedule as an absolute time schedule, so each scan will only be executed between the time specified here (and the date specified in the Date field) and the time plus the value in ScanLength. This will usually only be useful when coordinating the activities of the ATCA with other telescopes (such as for VLBI).

TimeCode

The selection made here sets the type of time desired for the Time field above. It can be either local sidereal time (LST) or coordinated universal time (UTC). This field can only set for source 1 in the schedule. See the description of the Time field for the consequences of setting this field to UTC.

Date

The observing date can be set here to allow the scheduler to correctly determine the source positions and drive times. Of course, the date does not matter when setting LST, but is of vital importance when the TimeCode is set to UTC.

Config

This field is only displayed in the “Advanced View”. The value of this field may (eventually) be used to configure the correlator. Currently, there is only a few easily-usable correlator configurations, and this field should be left blank, or given the default value of null.

Averaging

This field is only displayed in the “Advanced View”. This parameter specifies the number of cycles to average together when writing the data out to an RPFITS file on disk. Averaging will restart on source and frequency changes.

Environment

This field is only displayed in the “Advanced View”. Setting this field requests CAOBS to record the attenuator and sampler settings assocated with each different field value, and recall those settings whenever a scan is encountered with the same value. Each frequency setting (modulo 1 MHz) allows for up to 128 such values. Valid Environment values are from 0 to 127.

PointingOffset1 & PointingOffset2

This field is only displayed in the “Advanced View”. Use these fields and the Offpnt Pointing type to make the telescope point away from the specified RA & Dec. PointingOffset1 is the offset in seconds to move in RA, and PointingOffset2 is the offset in arcseconds to move in Dec. Remember that the phase centre of the observation will always be at the position given in the RA and Dec fields. Therefore if you wish to use these offset pointing fields to avoid a potential DC offset issue, you must put an offset position in RA, Dec and then use PointingOffset1 and PointingOffset2 to shift the pointing centre to be on source again.

TVChan

This field is only displayed in the “Advanced View”. When switching between different observing frequencies, the usable range of correlator channels will also change, due to RFI or bandpass shape. The correlator uses only a certain subset of channels – called the TV channels – to determine system temperatures, and if the TV channels are not kept constant for each individual frequency config then you may encounter amplitude problems later in the reduction process. The TV channels setting also affects what is displayed by VIS. This parameter allows you to set the TV channels on a per scan basis, which makes frequency switching a far more automated process. This parameter should be either null to allow the current TV channel setting to be left as-is, or a set of four numbers, separated by commas, indicating (in order) the first and last TV channel for IF 1, and the first and last TV channel for IF 2.

Cmd

This field is only displayed in the “Advanced View”. This field can be used to instruct CAOBS to issue one or more commands each time it starts this scan. Multiple commands may be specified, separated by semi-colons, although this field has an 80 character limit. Each command must be a recognised CAOBS command. For example, the tied-array configuration could be changed by specifying
corr catie ant 123456 123456; corr catie gain 0.2 0.2

The first command listed in this field will be executed as soon as the scan is started, and each subsequent command will be executed as soon as the previous has been processed. To allow more flexibility in the timing of the commands listed in this field, there is a special command WAIT n. This command (which cannot be used in manual CAOBS operation), waits for n integrations after the start of the scan. After this condition has been met, the commands after the WAIT command are executed. For example, to calibrate the phases after 5 cycles (to allow for data collection), specify
wait 5; corr pcal a

There are important caveats on the WAIT command. It does not guarantee on-source cycles will be waited: if the command wait 5 is specified, but it takes 5 or more cycles before the telescope gets on-source, the subsequent command will likely be executed before valid data is collected. To guard against this, consider putting a dummy scan before the scan with the command specification. The dummy scan should have a small (one or two cycles) amount of dwell time so that CAOBS will wait until the telescope is on-source before proceeding to the next schedule item.

The WAIT command is not a progression command either. Take for example the following command:
wait 5; corr dcal a; wait 4; corr pcal a
This command will fail, because after the dcal command is issued, it will immediately issue the pcal command. This is because the wait 4 command will immediately exit, as CAOBS has already waited for the fifth cycle to start, so it will no longer wait for the fourth cycle. Instead, this command should be:
wait 5; corr dcal a; wait 9; corr pcal a

CatVel

This field is only displayed in the “Advanced View”. The CatVel field can be set manually, or via the scheduler’s “Pick Source” function. This allows for rapid and reliable frequency calculation with the scheduler’s velocity calculator, as the information in this field is automatically propagated into the calculator. This field should be set as three values, separated by spaces as follows:

velocity velframe velconv

Here, velocity is the velocity of the source in km/s (recession is positive), velframe is the frame in which the velocity is measured (one of LSR or Bary), and velconv is the velocity convention (one of Radio, Optical or Z).

FreqConfig

This field is only displayed in the “Advanced View”. The FreqConfig field is used to create a number of frequency and zoom settings that can be shared between scans. Setting the continuum frequencies and specifying up to 8 zooms can be tedious and error prone if it has to be repeated for many scans. The FreqConfig field lets you select one or more scans as Master scans and then assign other scans to be Slave scans. Each Slave scan inherits the exact frequency and zoom settings of the corresponding Master scan. Using this you can ensure source and calibrator are observed with the same settings, even after recalculating velocities and frequencies for a different date. The default setting of null leaves the settings independent of other scans.

Figure E.2: The frequency and velocity calculator view of the CABB Web Scheduler.

Continuum (MHz)

Enter the central frequency (in MHz) of the 2 GHz wideband IF here. There is one of these fields in each of the Freq1 and Freq2 tabs, one for each available CABB wideband IF.

Chn. BW (MHz)

Select how wide (in MHz) each wideband channel will be for each IF. The channel width will also set the minimum bandwidth of each zoom band derived from this IF. There is one of these fields in each of the Freq1 and Freq2 tabs, one for each available CABB wideband IF.

Line

Enter a frequency (in MHz) that will appear within the zoom band. This will then fix the wideband channel that must be used. This frequency must be within 1 GHz of the frequency specified in the Continuum (MHz) field. There is currently a maximum of 16 such bands that can be specified in the scheduler for each IF when using a channel bandwidth of 1 MHz, and only 1 such band for each IF when using a channel bandwidth of 64 MHz.

Channel

Enter the wideband channel number to use for the zoom band. This will then restrict the frequencies available in the zoom band.

Width

This is the number of wideband channels to use for this zoom band. Note that a maximum of 16 wideband channels can be used for 1 MHz configurations, and 1 channel for 64 MHz configuration, so some of the Width boxes will be disabled if more than 1 wideband channel is assigned to any particular zoom band.

Fixed

Use this to select whether to keep the continuum frequency fixed or keep the frequency of the first zoom fixed when you change the Channel, Width or velocity.

Velo

This button brings up the velocity calculator that lets you specify the source velocity and rest frequency to calculate the sky frequency of the spectral line. The sky frequency is rounded to the nearest possible frequency setting of the telescope and entered in the schedule when you press the Apply button.

Fix

This tick box appears on the velocity calculator. When ticked, the same velocity setting will be used for all zooms on both frequencies. Use this to avoid having to enter the same information many times when the source has many spectral lines with more or less the same velocity.