VLA Starting Conditions Editor Page

This panel allows you to set all of the global options and initial conditions for your observing program. These include the program name, the AIPS user number, the new source initial values, the calibrator naming convention, the array configuration, the starting position of the antennas and their subreflectors, and the date and time of the beginning of the observing program.

When all necessary values have been entered, hit the "Done" button on the button bar at the bottom to return to the List Editor. If you want to discard all changes you've made in this invocation of the Initial Conditions page hit the "Reset" button if you want to continue editing or "Cancel" to return to the List Editor. Note: if you select the "Set" button to invoke the Initial source values editor, this is equivalent to hitting the "Done" button.

Program Code

The Observing Program Identification. This is a code assigned to each successful observing proposal, generally of the form AX999. The code is also written on the archive tape to allow selective copying and filling of data into AIPS. This field is initialized to "ADA000", which is a project name for data that may be generally distributed.

AIPS Id

The AIPS Number of the observer. It is the number by which you will have to identify yourself when using a post-processing computer at the NRAO. The number is also written on the archive tape to allow selective copying and filling of data into AIPS. If you cannot remember your number, or you need to obtain one, call Gayle Rhodes (505) 835-7220, Tami Hale (505) 835-7221, or the Data Analysts (analysts@nrao.edu).

Beginning of Observation

Starting Local Sidereal Time and the Starting Position are used to determine the set-up time, antenna move time, etc. for the first source. The modified sidereal day number, together with the LST, is used to determine the coordinates of date and hence the azimuth and elevation of the antennas for the observations. These starting values should be set before scheduling the observations.

The date and time are specified as modified sidereal day number and LST. Hitting the Return (Enter) key on the keyboard will cause JObserve to read the entered values and display the equivalent local (Mountain) and GMT times.

To enter a value, type the digits of date or time, including the leading zeros of each field and blanks between fields. An incorrect entry will cause a message to appear in the status line. The modified sidereal day number is published down the right side of the VLA observing schedule.

IAT-UTC

The time system used by the VLA is International Atomic Time (IAT) which is continuous (no leap seconds) and is drifting away from UTC time which gives that actual orientation of the Earth. The box labeled "IAT-UTC" allows you to enter this value. It is safe to ignore this under most circumstances.

VLA Starting Position

The Starting Position represents the position of the antennas as they were left by the previous observing program. If it is not known, you may leave the default as a best guess. The Start Local Sidereal Time and the Starting Position are used to determine the set-up time, antenna move time, etc. for the first source. These starting values should be set before scheduling the observations.

The position may be specified in one of three ways:

azimuth and elevation;
hour angle and declination; and
right ascension and declination.

Entering one of values causes the program to compute the other dependent values. The calculation uses the Starting Date and Time from this Page.

The range of azimuth values, in degrees, for the VLA is -85 to +445. This represents the cable wrap for almost 1 1/2 turns. The range in elevation is +8 to +125. This allows the antenna to go "over the top" by 35 degrees.

Observer Name and Address

Enter your name and address in the Text Fields provided.

Office Phone number

Enter your office or normal daytime phone number.

Phone number during the observations

If you know a phone number where you can likely be reached during the observations enter it into this box.

Epoch calibrator names

Calibrator sources are listed in the Calibrator List on the List Editor Page. The sources are identified using the IAU naming convention referred either to the Besselian epoch of 1950 or the Julian epoch of 2000. At present, no common names (e.g. 3C numbers) are given in the table.

Set source initial values

Edit the New Source Initial Values. Hitting the "Set" button invokes the Scan Editor which allows you to set the initial values for each new source entry or "scan". When inserting a new scan in the User Defaults, Observe List, or Source List, the set of values defined here will be automatically entered. This includes entries created when using Find Nearby Calibrator, but does not include entries made from others using the Copy/Cut/Paste facility. Changing the Initial Values at any time does not change the values in any existing entry in one of these lists.

Note: After you finish editing the Initial Scan value you will need to select the "Starting Conditions" item on the Options menu to get back to this page.

Scan ending specification

The ending time of a Scan can be specified in the Observe VLA output schedule as either:

Stop LST or
duration (total scan time)

Note: this selection is independent of the stopping criterion used in each individual scan.

Observing modes

Various Observing modes can be selected by setting the associated Choice to "Yes". Note: some combinations are incompatable, e.g. Continuum and Spectral Line mode cannot both be selected. Possible modes are

Continuum - for continuum observations.
Spectral Line - to observe with multiple spectral channels.
Phased Array - a single summed output of all antennas in the subarray is desired. This is used for VLBI observations using the whole VLA.
Single dish - only a single antenna is used. This is used for VLBI observations using a single VLA antenna.

Array Configuration

Select the Array configuration. The VLA configuration is used during the scheduling operation to determine the shadowing of the antennas.

Reference Antenna

Enter the antenna number you want for a single dish or as the reference antenna for a phased array. Valid numbers are 1-28.

Starting Subreflector

The Starting Subreflector Position represents the position of the subreflector of the antennas as they were left by the previous observing program, i.e. the band at which the last observation was made. The time to rotate the subreflector for the first observation is taken into account in the initial move time. To select a band, type its band code. If the previous subreflector position is not known, you may leave this field blank. If this is done, no computation of subreflector rotation will be made. This is available here mostly for completeness. It will, in general, only be of any interest if your observations begin with the same source that ended the previous observing program.

Planet/Solar motion

Select yes if you want the Planetary Motion/Solar page to be displayed. JObserve doesn't typically display the planetary motion page since it's used only with solar system objects.

Phase tracking

Undocumented Observe feature.

Special instructions

Enter any special instructioins to the Array operators in the Text Fields.