Fixed Targets
This article describes the parameters for Fixed Targets for the Roman telescope.
Introduction
A Roman Fixed Target consists of a specification of coordinates and other target parameters for use as the base pointing of an Observation.
- Fixed Targets specified in the Program may be referenced in multiple Pass Plans within the program.
- Before a program begins to be executed, any modifications to a fixed target specification will be used where ever that target is referenced.
- After a program is partially executed, changes to a fixed target specification will be used in elements of the newly generated execution plan and not in elements of the previous execution plans. This is an important difference that will be documented further when the change management process is fully implemented.
The Principal Investigator of a program is responsible for ensuring that Target Coordinate Parameters are accurate.
Figure of the Fixed Targets Form in APT
A screen capture of the Fixed Targets page for the demonstration program 960 which shows the parameters available to define a Fixed Target.
Fixed Target Identification Parameters
The Target Identification form for Fixed Targets includes a number of parameters described below.
Number
Number - Each target in your Program will be assigned its own unique number ranging from 1 TO 9999 by APT; note that these can be changed by the user.
Name
Name is a name you provide for the target within the Program. It provides a unique designation for a target for use throughout the Program. A name is required, must be 2 to 31 characters in length and only use letters, numbers, “.”, “+”, and “-”. No other characters are allowed including blanks.
Resolvable Name
Resolvable Name is a name you provide for use by the Archive. Using a common name for the target (e.g. CRABNEBULA instead of NGC1952) can make a program more readable. Annotating the name (e.g. CRAB1, CRAB2) may be useful when sampling parts of an extended object. But these names are not as helpful for people searching the Archive. So the Resolvable Name is an optional second target name. Proposers and archival researchers use these names to determine whether Roman has observed a particular object. This feature will be most useful if the names supplied are resolvable with standard name resolvers such as NED or SIMBAD.
Resolvable Name is not required, but if used must be 2 to 31 characters in length.
Category
Category - Each target must be assigned a single Category from the Table of Target Categories, and at least one descriptive keyword ( Description ), chosen from the appropriate tables.
Category is required and is selected from a list.
Table of Target Categories
Category | Descriptive Keywords |
|---|---|
| Cluster of Galaxies | Clusters of Galaxies table |
| Galaxy | Galaxy table |
| ISM | ISM table |
| Solar System | Solar System table |
| Star | Star table |
| Stellar Cluster | Stellar Cluster table |
| Unidentified | Unidentified table |
| Calibration | Calibration table |
Description
Description - One to five keywords must be selected for each target. Descriptions are selected from a table depending on the selected Category (see the Table of Target Categories). Description is one of the fields used by archival researchers in searching through the Roman data archive; thus it is extremely important that the information be supplied by the observer who knows the intention for each target.
Fixed Target Coordinates Parameters
Target Coordinates for Fixed Targets include a number of parameters described below.
ICRS Coordinates
The right ascension ( RA ) and declination ( Dec ) for the target are required and must be entered as ICRS coordinates (International Celestial Reference System). Coordinates are NOT required for Sample Targets.
- RA may be entered in HMS format (hh mm ss.ssss), or as decimal degrees (ddd.dddd). Decimal numbers will be converted to HMS.
- Dec may be entered in DMS format (dd mm ss.ssss) or as decimal degrees (ddd.dddd). Decimal degrees will be converted to DMS.
Proper Motion
Proper motion for the target may be specified with RA PM for right ascension and Dec PM for declination. The user must determine whether or not proper motion or parallax is significant.
At the time of the observation, the proper motion correction will be applied to the target coordinates (from the specified Epoch to the date of observation).
- RA PM units may be mas/yr, arcsec/yr, or seconds of time/yr.
- Dec PM units may be mas/yr or arcsec/yr.
- Both RA PM and Dec PM may be left blank but if either one is entered, both are required.
A warning is given if the proper motion entered is greater than the proper motion of Barnard's Star.
Epoch
Epoch is the the date of the target coordinates (either the date the target coordinates were measured or the date to which the target coordinates have been corrected using the proper motion).
- If proper motion has been specified for the target, Epoch of the target coordinates must also be specified.
- Epoch must be entered in a decimal year format (yyyy.nnn).
Allowed values are 1885.0 TO 3000.0
Annual Parallax
Parallax is the annual parallax of the target's position in arcsec/year. As with proper motion, the user must determine if parallax is significant. Parallax is applied to the target coordinates at the time of the observation.
- Parallax may be left blank. The allowed range is 0.00 TO 0.08 arcsec/year.
An ERROR will result if Parallax is less than 0.00 or greater than 0.08.
Target of Opportunity Sample Target
Select Target of Opportunity Sample Target to indicate this target is a placeholder for a target to be supplied when requesting an activation for a Target of Opportunity (ToO) observation.
When Sample Target is selected, ICRS Coordinates are not required.
Comments
Enter any comments about the target. Comments are stored with the target data within the program.
Target of Opportunity
A target of opportunity (ToO) refers to requested observations that are linked to a transient event, such as supernovae, that may occur at an unknown time.
To specify a ToO several steps are required:
- Create a Fixed Target designated as a Sample Target. This target is a placeholder for the actual target specification you will provide later when activating the ToO.
- Add a Target of Opportunity special requirement to all Survey Steps that use the Sample Target
- On the Program Information form, enter the total number of requested ToO activations in the program.
For additional questions not answered in this article, please contact the Roman Help Desk.