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FIELD: Field positions for each source

FIELD: Field positions for each source
Name	Format	Units	Measure	Comments
Columns
Key
Data
NAME	String			Name of field
CODE	String			Special characteristics of field
TIME	Double	s	EPOCH	Time origin for the directions and rates
NUM_POLY	Int			Series order
DELAY_DIR	Double(2, NUM_POLY+1)	rad	DIRECTION	Direction of delay center.
PHASE_DIR	Double(2, NUM_POLY+1)	rad	DIRECTION	Phase center.
REFERENCE_DIR	Double(2, NUM_POLY+1)	rad	DIRECTION	Reference center
SOURCE_ID	Int			Index in Source table
(EPHEMERIS_ID)	Int			Ephemeris id.
Flags
FLAG_ROW	Bool			Row flag

Notes:

The FIELD table defines a field position on the sky. For interferometers, this is the correlated field position. For single dishes, this is the nominal pointing direction.

NAME

Field name; user specified.

CODE

Field code indicating special characteristics of the field; user specified.

TIME

Time reference for the directions and rates. Required to use the same TIME Measure reference as in MAIN.

NUM_POLY

Series order for the *_DIR columns.

DELAY_DIR

Direction of delay center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type.

PHASE_DIR

Direction of phase center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type.

REFERENCE_DIR

Reference center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type. Used in single-dish to record the associated reference direction if position-switching has already been applied. For interferometric data, this is the original correlated field center, and may equal DELAY_DIR or PHASE_DIR.

SOURCE_ID

Points to an entry in the optional SOURCE subtable, a value of -1 indicates there is no corresponding source defined.

EPHEMERIS_ID

Points to an entry in the EPHEMERIS sub-table, which defines the ephemeris used to compute the field position. Useful for moving, near-field objects, where the ephemeris may be revised over time.

FLAG_ROW

True if data in this row are invalid, else False. Does not imply flagging in MAIN.