3.2.2 Solar System Targets Position Level 1

The Solar System Targets form is used to specify moving targets in some HST observations.  This article provides a description of the Level 1 specifications needed for the Astronomer’s Proposal Tool (APT).

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Format definitions

Boldface type indicates the name of an APT parameter or a value for a parameter.

(red star) Black text indicates an important note.

Magenta text indicates available but unsupported parameters (requires prior approval from STScI).

Red text indicates restricted parameters (for STScI use only).

Brown text indicates text file parameters.

Items in brackets - <value> - are required values.

Items in square brackets - [<value>] - are optional.

Target Position Level 1 [Level_1]

For the Level 1 position, specify your target in one of the following ways:

  1. STD = <object name>, where the name must be from the list in 3.2.1 Solar System Standard Targets, or
  2. TYPE = <name>.

The TYPE = <name> target description allows the specification of non-standard targets in a variety of formats and must be the first entry in the field if it is used.

For all cases, the required input data are described below. If the data are valid only over a specific period of time, then specify this time interval in the Window field.

Table 3.16: Positional Parameters for TYPE = COMET

ParameterDefinition
     Orbital Elements

Q = <value>

Perihelion distance, in AU

E= <value>

Eccentricity

I =<value>

Inclination, in degrees

O= <value>

Longitude of ascending node, in degrees

W = <value>

Argument of perihelion, in degrees

T = <value>

Time of perihelion passage, in TDB, TDT, or UTC

EQUINOX = <value>

either B1950, or J2000

EPOCH = <value>

Osculation date, in TDB, TDT, or UTC1

     Non-gravitational Model Parameters

[A1 = <value>]

Radial component of non-gravitational acceleration (AU/day2)

[A2 = <value>]

Component of non-gravitational acceleration lying in the orbital plane and parallel to the instantaneous velocity vector (AU/day2)

[A3 = <value>]

Component of non-gravitational acceleration directed perpendicular to the plane defined by A1 and A2 (AU/day2)

[R0 = <value>]Sublimation radius as normalizing radius (AU)
[ALN = <value>]Normalizing factor
[NM = <value>]Primary radial scaling law exponent
[NN = <value>]N distance exponent
[NK = <value>]K distance exponent
[DT = <value>]Delay parameter (days)
[AMRAT = <value>]Solar radiation pressure term (m2/kg)
SOURCE = <value>A comment describing the source of the orbital elements.

1 TDB (Barycentric Dynamical Time), TDT (Terrestrial Dynamic Time), UTC (Coordinated Universal Time)


Table 3.17: Positional Parameters for TYPE = ASTEROID

ParameterDefinition
     Orbital Elements

A = <value>

Semi-major axis, in AU

E = <value>

Eccentricity

I = <value>

Inclination, in degrees

O = <value>

Longitude of ascending node, in degrees

W = <value>

Argument of perihelion, in degrees

M = <value>

Mean anomaly at EPOCH, in degrees

EQUINOX = <value>

J2000

EPOCH = <value>

Osculation date, in TDB, TDT, or UTC2

     Non-gravitational Model Parameters

[A1 = <value>]

Radial component of non-gravitational acceleration (AU/day2)

[A2 = <value>]

Component of non-gravitational acceleration lying in the orbital plane and parallel to the instantaneous velocity vector (AU/day2)

[A3 = <value>]

Component of non-gravitational acceleration directed perpendicular to the plane defined by A1 and A2 (AU/day2)

[R0 = <value>]Scaling radius as normalizing radius (AU)
[ALN = <value>]Normalizing factor
[NM = <value>]Primary radial scaling law exponent
[NN = <value>]N distance exponent
[NK = <value>]K distance exponent
[AMRAT = <value>]Solar radiation pressure term (m2/kg)
SOURCE = <value>A comment describing the source of the orbital elements.

2 TDB (Barycentric Dynamical Time), TDT (Terrestrial Dynamic Time), UTC (Coordinated Universal Time)

The elements given above refer to the mean ecliptic and equinox of either B1950 or J2000 depending on which “value” is specified for EQUINOX. An example of TYPE = COMET is shown in Example 3.

(red star) It is the responsibility of the observer to supply accurate orbital elements to STScI when specifying TYPE=COMET or TYPE=ASTEROID.



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