HST Phase II Proposal Instructions for Cycle 12 (RPS2)
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| HST Phase II Proposal Instructions for Cycle 12 (RPS2) | |||
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Tables and Figures
Table 4.1: Solar System Standard Targets
Table 4.2: Target Description Keywords
Table 4.3: Positional Parameters for TYPE = COMET
Table 4.4: Positional Parameters for TYPE = ASTEROID
Table 4.5: Parameters for TYPE = PGRAPHIC
Table 4.6: Parameters for TYPE = POS_ANGLE
Table 4.7: Parameters for TYPE = MAGNETO
Table 4.8: Parameters for TYPE = TORUS
Table 4.9: Parameters for TYPE = SAT
Table 4.10: Keywords for Observing Windows
Table 4.11: Operators for Observing Windows
Table 4.12: Formats for Specification of Target Flux Data
Table 4.1
Table 4.2
HST is able to point at and track solar system targets with sub-arcsecond accuracy. In order for target acquisition and tracking to succeed, planetary observers must specify positions for their targets in a precise and unambiguous manner. Therefore, it is imperative that the Solar System Target List (SSTL) be carefully and correctly completed. This section explains how to fill out the SSTL for any solar system target.
Ephemerides are generated using fundamental ephemeris information from NASA's Jet Propulsion Laboratory (JPL). Ephemerides can be generated for all known types of solar system targets, including planets, satellites, comets, asteroids, surface features on planets and satellites, and offset positions with respect to the centers of all the above bodies. The following instructions demonstrate how to define solar system targets in a way that allows accurate ephemeris generation.
The body-axes definitions, body dimensions, directions of rotation poles, rotation rates, and the definitions of cartographic coordinates used by STScI are normally identical to the values adopted in the report of the "IAU Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites: 1982" (Davies, M.E., et al., Celestial Mechanics, 29, 309-321, 1983). In a few instances, the latter data have been updated due to new results obtained from the flyby spacecraft. Also, some new bodies have been added which were unknown at the time of the IAU report. For Jupiter and Saturn, the lambda(III) coordinate system is assumed, but lambda(I) or lambda(II) can be used. For Uranus and Neptune, coordinates follow the "Report of the IAU/IAG/COSPAR Working Group on Cartographic Coordinates and Rotation Rates of the Planets and Satellites" (Celestial Mechanics and Dynamic Astronomy, 46, 197, 1989). If you need further information on these, please contact your Program Coordinator.
One exception exists to the requirements outlined above. Observers for solar system Targets of Opportunity (e.g. a "new" comet or asteroid, a solar-wind disturbance reaching the Jovian magnetosphere, etc.), should complete the Generic Target List (See "3.12" in chapter 3.) and the Visit and Exposure Specifications (to the extent possible) in time for the Phase II deadline. If and when a suitable target appears, the proposer must complete the Solar System Target List and update the Visit and Exposure Specifications. No target can be observed until the complete Phase II information is provided.
In this chapter, each heading has a description followed by a keyword in square brackets (e.g., Target Number [Target_Number]). The keyword must be used in your RPS2 form. Elsewhere, items in boldface (e.g., RA-OFF) show words or phrases to be used directly as RPS2 entries. Items in brackets (e.g., <value>) show entries you are to provide. Parameters listed in square brackets (e.g., [A1 = <value>]) are optional, whereas those not in square brackets are required.
4.1 Target Number [Target_Number]
Each target that will be observed must be assigned a unique target number. Target numbers must be positive, monotonically increasing (but not necessarily consecutive) integers. A different target should be defined whenever a different target position or timing description is required. For example, separate targets should be defined if you plan to take spectra of several different surface features on a planet, or if you plan to observe the same feature with different timing constraints.
If more than one type of Target List is used (if your program also requires filling out the Fixed Target List or the Generic Target List), the target numbers should continue consecutively from one list to the next. All target numbers within a proposal must be unique.
4.2 Target Name [Target_Name]
The name is used to identify a target; all target names within a proposal must be unique. The target name can be selected from the STScI list of standard targets (see Table 4.1; explanations of "Level 1" and "Level 2" are given below), or a name can be defined by the GO. The use of standard names is encouraged whenever it is possible.
The following conventions should be followed in naming targets:
Table 4.1: Solar System Standard Targets
- The maximum allowable length of a target name is 31 characters.
- No blanks are permitted in target names. A hyphen should replace blanks that would normally be used to separate fields (e.g. IO-TORUS, COMET-BRADFIELD-1979X).
- Only letters and numerals are allowed in target names; punctuation (other than hyphens and + or -) is not permitted.
- Target names must begin with a letter, not a numeral.
- Construct target names so they make sense for your observing program. For example, if your program consisted of consecutive observations of three surface features on Mars, then three appropriate target names might be: MARS-FEATURE1, MARS-FEATURE2, and MARS-FEATURE3.
If you are uncertain whether or not your target can be referenced by name, contact your Program Coordinator for guidance.
Alternate names are given in parentheses for some bodies but these should not be listed in the RPS2 file. They are given here for identification purposes only.
4.3 Target Description [Description]
The target description is used to sort the solar system targets by class and will be useful to archival researchers. The first word in any target description must be one of the keywords listed below. The keyword is then followed with text that depends on the target class as described below.
Table 4.2: Target Description Keywords
4.4 Target Position
Target pointing Specification (TPS) and "Levels"
Three fields are used to describe the target's position, referred to here as the Target Pointing Specification (TPS). The TPS has been defined using a hierarchical structure.
- Level 1 refers to a target in orbit about the Sun. Examples of Level 1 targets include planets, asteroids, and comets. When a Level 1 object is the desired target for observation, complete the Level 1 field and leave the other two target position fields blank.
- Level 2 refers to a target whose motion is normally described with respect to a Level 1 object. Examples of Level 2 targets include planetary satellites, surface features on planets or asteroids, and non-nuclear positions in the coma of a comet. When a Level 2 object is the desired target for observations, the Level 1 field contains information on the parent body, and the Level 2 field gives positions relative to this body. In this case, leave the Level 3 field blank.
- Level 3 refers to a target whose motion is normally described with respect to a Level 2 object. Examples are a surface feature on a planetary satellite or a pointing which is offset from the center of a planetary satellite. When a Level 3 object is the desired target for observation, then all three fields must be completed, with Level 1 giving the parent of the body described in Level 2, and Level 3 giving the position of the observed target with respect to the body in Level 2.
No more than three levels are allowed. If you believe that your target cannot be described in this form, contact your Program Coordinator.
Describing Targets
The targets specified in the target position fields can be described in up to four ways:
- By a name selected from a list of targets
- By orbital elements
- By coordinates with respect to another object
- Via target selection during a real-time observing session
Table 4.1 gives the list of valid names for solar system targets. PIs are responsible for obtaining up-to-date orbital elements for bodies not in this table. Objects must be denoted by their IAU-adopted name. A good reference for object names can be found in the Astronomical Almanac, and in the Marsden comet catalog (Marsden, B. G., Catalog of Cometary Orbits, Enslow Publishers, Hillside, NJ, 1983). If you are uncertain whether or not your target can be referenced by name, contact your Program Coordinator.
In those cases where the target's position is given with respect to one of the standard objects, the latest available data from JPL on the bodies' physical dimensions, orientation, and rotation rates are used in calculating the target's position. In those cases where all or part of the TPS for your target can be described using standard names, we strongly recommend that you do so. Generally, this will result in the most accurate ephemeris generation for your target.
Specifying Time
Whenever there is an entry involving "time" (anywhere on the form), the format for that entry must be:
where DD is the day of the month, MMM is the first three letters of the month name, YYYY are the full four digits of the Gregorian calendar year, hh is the hour, mm is the minute, and ss.s are the decimal seconds. Only the necessary precision need be specified.
Two different systems of time are used in this document. TDB refers to Barycentric Dynamical Time and can be considered synonymous with ET (Ephemeris Time), which was used before 1984. UTC refers to Coordinated Universal Time. The precise interpretation of each time value depends on the context in which it is used.
4.4.1 Target Position Level 1 [Level_1]
Specify your target in one of the following ways:
- STD = <object name>, where the name must be from Table 4.1, or
- 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.
- If COMET is chosen, then a set of 2-body orbital elements in the IAU Circular format must be supplied for the target.
- If ASTEROID is chosen, then a set of 2-body orbital elements in the Minor Planet Circular format must be supplied.
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 according to the rules given later.
COMET and ASTEROID Positional Parameters
Table 4.3: Positional Parameters for TYPE = COMET
Table 4.4: Positional Parameters for TYPE = ASTEROID
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 the "Example Target List Blocks" below for Example 3. However, notice in this example that the Level 1 target (Comet Halley) is a standard object and could have been listed on the form by name.
It is the responsibility of the observer to supply accurate orbital elements to STScI when specifying TYPE=COMET or TYPE=ASTEROID.
4.4.2 Target Position Level 2 [Level_2]
Five Target Reference Systems (TRSs) are described in the following paragraphs. Please pay careful attention to the definitions of each TRS. Specify your target in one of the following ways:
STD = <object name> or TYPE = <name>
In this case <object name> is from Table 4.1: Solar System Standard Targets, or the Type is:
PGRAPHIC
planetographic coordinates relative to Level 1 targetpolar coordinate offsets from Level 1 target
position in magnetic coordinate system
line-of-sight projected coordinate system
orbital elements of a satellite
For the PGRAPHIC, MAGNETO, and TORUS coordinate systems, the north pole is defined to be the rotational pole in the northern celestial hemisphere. For planets with direct rotation, the angular momentum vector coincides with the north pole. For planets with retrograde rotation, the angular momentum vector coincides with the south pole.
Planetographic Coordinate System
Table 4.5: Parameters for TYPE = PGRAPHIC
LONG = <value> planetographic longitude in degrees, LAT = <value> planetographic latitude in degrees; + or - are required to denote north and south latitude, respectively, [ALT = <value>] planetographic altitude above the reference ellipsoid, in kilometers, [R_LONG = <value>]1 rate of change of LONG, in degrees/day, [R_LAT = <value>]1 rate of change of LAT, in degrees/day, [R_RAD = <value>]1 rate of change of RAD, in kilometers/day, and [EPOCH = <value>] the reference time for the temporal variation, in UTC (4 digits).
1EPOCH must also be specified with this quantity.
The PGRAPHIC TRS is the IAU planetographic coordinate system. It is a non-spherical coordinate system aligned with and rotating about the rotation axis of the Level 1 body, positive north, whose origin lies at the center of the reference body. Locations within this TRS are specified by longitude, latitude, and altitude above the surface. (The lambda(III) coordinate system defines the prime meridian in this coordinate system; if lambda(I) or lambda(II) coordinate systems are desired, note this in the Comments field.)
Planetographic Latitude is defined as the angle between the equator and the normal to the surface of the reference ellipsoid at the point of interest.
By definition, the planetographic longitude of the sub-Earth point increases with time. For planets with direct rotation, the planetographic longitude increases in a left-handed direction. For planets with retrograde rotation, the planetographic longitude increases in a right-handed direction.
If ALT is omitted, then the surface of the reference ellipsoid is assumed.
If the coordinates are constant in time, then none of the other optional entries should be used. If any coordinate is given as a function of time, then EPOCH is required and the time-varying coordinate is interpreted in the following way.
For this example the longitude at any time, T, is given by:
longitude = LONG + R_LONG * (T - EPOCH)
longitude = 20 + 45 * (t - 5-JAN-1990:00:15:00)
The same interpretation for time-varying coordinates also applies to the other TRSs described below.
Position Angle Coordinate System
Table 4.6: Parameters for TYPE = POS_ANGLE
RAD = <value> Radius, in arcseconds ANG = <value> Position angle relative to the reference axis, in degrees REF = NORTH REF = SUN
REF = <value>1Reference axis is celestial north, or Reference axis is the apparent direction to the Sun as projected on the sky, or User specified position angle of the reference measured in degrees eastward from north. [R_RAD = <value>]1 Rate of change of RAD, in arcseconds/sec [R_ANG = <value>]1 Rate of change of ANG, in degrees/day [EPOCH = <value>] the reference time for the temporal variation, in UTC (4 digits).
1EPOCH must also be specified with this quantity.
The POS_ANGLE TRS is a position-angle coordinate system (i.e. a two-dimensional polar-coordinate system). This TRS is useful for pointing at targets whose positions are known only in terms of an offset in projected celestial coordinates from another body. The origin of the system lies at the center of the Level 1 body. Locations are specified by giving the apparent distance from the origin (in projected celestial coordinates as viewed from the Earth) and the position angle from some reference axis to the target point. For REF = NORTH, angles are measured from celestial north (positive angles are measured in the same sense as rotating from celestial north through east). For REF = SUN, angles are measured from the direction to the Sun as projected on the sky (positive angles are measured in the same sense as rotating from celestial north through east). For REF = <value>, the proposer must specify the position angle of the reference axis, measured in degrees East of celestial north (once again, positive angles are measured in the same sense as rotating from celestial north through east).
Magnetic Coordinate System
Table 4.7: Parameters for TYPE = MAGNETO
The MAGNETO TRS is intended to support observations fixed with respect to a planetary magnetic field. It is a spherical coordinate system rotating with the Level 1 body around the rotation axis, with a specified offset of the coordinate origin and inclination of the coordinate pole. The MAGNETO coordinate system is defined in the following manner:
- Define a "cartographic" reference frame identical to the planetographic TRS, except use spherical latitudes.
- Rotate the new coordinate system relative to the cartographic frame so the new pole is located at POLE_LAT (latitude) and POLE_LONG (longitude).
- The final step is to translate the origin of the new system to the specified cartographic latitude, longitude, and radius (O_LAT, O_LONG, and O_RAD, respectively).
While the origin and coordinate axes may differ from those of the cartographic system, the rotation axis and rotation rate are identical to those of the cartographic system. Locations in the MAGNETO TRS are specified by longitude, latitude, and radius from the origin of the defined coordinate system.
Torus Coordinate System
Table 4.8: Parameters for TYPE = TORUS
If the optional fields above are left blank, the following default values are used:
The TORUS TRS is defined primarily to support observations of Jupiter's plasma torus and is closely related to the MAGNETO TRS. TORUS is also useful for observers who want to observe in a coordinate system that is fixed relative to the apparent disk of the Level 1 body, e.g. central meridian observations (see special instructions below). The difference between the two systems is in the definition of the prime meridian. For the TORUS TRS, the prime meridian is defined by the instantaneous longitude of the sub-Earth point. Therefore, the TORUS TRS does not rotate with the Level 1 body. A typical observation would be of the east or west ansa (point of maximum elongation) of an equatorial circle whose radius is roughly five times the equatorial radius of Jupiter (in this case, LONG = 270 (90 for the west ansa), LAT = 0, RAD = 3.57E05). As the planet rotates, the target moves up and down in celestial coordinates as Jupiter rotates. This coordinate system can also be used to support observations of a planetary ring ansa.
Satellite Elements Coordinate System
Table 4.9: Parameters for TYPE = SAT
When the target is a satellite of the object defined in the Level 1 field, but the satellite itself is not among the standard objects, then orbital elements must be specified. These elements refer to the motion of the satellite around the Level 1 object.
The "reference" axis for the angles defined above is the intersection of the Earth's equator at the standard epoch implied by the EQUINOX with the parent planet's equator at the EPOCH of the elements. The positive X-axis for the coordinate system used in the orbit calculation is obtained by taking the cross product of the Z-axis of the standard system (i.e. the system defined by the standard equator and equinox given by EQUINOX) with the pole of the planet. If E, I, O, W, O_RATE, and W_RATE are not supplied, then their values are assumed to be 0. If RAP and DECP are not supplied, then the standard IAU values are used. If RAP and DECP are supplied, then they should be referred to the standard equator and equinox given by EQUINOX. If EQUINOX is not provided, we will assume J2000.
STScI maintains its ephemeris data base with the best available elements, and you should use the STD = form for objects in Table 4.1: Solar System Standard Targets unless there is compelling scientific justification for specifying orbital elements. Note: It is the responsibility of the observer to supply accurate orbital elements to STScI when specifying TYPE=SAT.
4.4.3 Target Position Level 3 [Level_3]
The instructions for this field are identical to those for the Level 2 field except that "Level 3" should be substituted wherever "Level 2" occurs, and "Level 2" should be substituted wherever "Level 1" occurs.
4.5 Ephemeris Uncertainty [Ephem_Uncert]
The <value> for ephemeris uncertainty is the distance along its trajectory that the target is expected to be from its ephemeris position, in kilometers (KM), or seconds of time (S). The latter reflects the fact that in general, the least well known parameter in an ephemeris is the perihelion time. This parameter is required for any moving target used in an exposure with the REQuires EPHEMeris CORRection Special Requirement (see REQuires EPHEMeris CORRection <id>).
Note: A realistic estimate of ephemeris uncertainty is needed to schedule the time necessary to repoint the telescope to the improved position when it is known. It will not be possible for STScI to apply a correction larger than the specified uncertainty.
4.6 Acquisition Uncertainty [Acq_Uncert]
The <value> for acquisition uncertainty is the uncertainty in the position of the target in a direction perpendicular to the line of sight, in kilometers (KM) or arcsec (").
Note: A realistic estimate of acquisition uncertainty is needed to schedule the time necessary to repoint the telescope to the improved position when it is known. It will not be possible for STScI to apply a correction larger than the specified uncertainty.
4.7 Observing Windows [Window]
The observability of solar system targets is often constrained by various geometrical conditions (e.g. satellites observed at greatest elongation from their parent planet), or the desirability of coordinated observations (e.g. the observation of a planetary system at the same time as a spacecraft encounter with the system). The Window field is provided to allow the proposer to define geometric and timing constraints. The proposer should specify any constraints necessary to achieve the scientific objectives of the program. However, care should be taken in specifying constraints, since they can render the observations difficult or impossible to schedule.
In general, "windows" which define when the target is visible to HST need not be explicitly identified, since these windows will be calculated by the STScI. Windows in this category include:
- Times when the target is not occulted by the Earth.
- Times when the target is not too close to the Sun, Moon, or the bright Earth limb.
- If the target is a planetary satellite, the times when it is not occulted by any other object in the planetary system.
- If the target is a surface feature on a body, the times when the feature is within the field of view of the HST (i.e. the feature is on that part of the body "facing" HST).
If you require other specific conditions to be satisfied (e.g. to observe when a satellite is near elongation, to observe when the central meridian longitude lies in a particular range, etc.), then these conditions must be specified in the Window field. However, the proposer must recognize that proposer-supplied windows might not overlap with the "visibility" windows defined above (calculated by STScI), in which case the observation cannot be scheduled. Note that atmospheric drag and other effects make it difficult to predict the exact position of the HST in its orbit far in advance. This leads to uncertainty in the exact timing of the "visibility" windows more than two or three months in advance.
The various keywords used to define windows are given in the following table and described in detail below.
Table 4.10: Keywords for Observing Windows
Table 4.11: Operators for Observing Windows
The operator NOT, if present, should precede the keyword for the solar system target observing window, as in these examples:
NOT SEP OF IO JUPITER FROM EARTH GT 10
NOT A_VEL IO RELATIVE JUPITER FROM EARTH GT 10
SEP
SEP is short for "Separation" and is used to find the times when the apparent separation between two objects, as observed from a third object, satisfies certain conditions. The separation between two bodies is defined as the angle between the closest points on the observed limbs of the spheres representing the objects as viewed from the observer (the radius of the sphere is equal to the largest radius of the tri-axial ellipsoid representation of the object). The syntax is:
[NOT] SEP OF <object 1> <object 2> FROM <observer><condition> <angle>
where <object 1>, <object 2>, and <observer> must either be standard bodies, or objects that have been previously defined in the target position fields. The unit for "angle" must be chosen from one of D (degrees), ' (arc-minutes), or " (arc-seconds). The interpretation of the SEP keyword is as follows. When the <condition> is either LT, GT, or EQ then times are found when the separation of "objects 1 and 2", as viewed from <observer>, is less than <angle>, is greater than <angle>, or equals <angle>, respectively. When the <condition> is MAX (MIN), then times are found when "objects 1 and 2" are at maximum elongation (minimum separation), as viewed from <observer>.
RANGE
RANGE is used to select windows based on the separation of objects in terms of distance (AU). The syntax is:
[NOT] RANGE <object 1> <object 2> <condition> <distance>
A_VEL
A_VEL is used to select windows based on the angular velocity of objects in terms of arcsec/sec. The syntax is:
[NOT] A_VEL <object 1> [RELATIVE <object 2>] FROM <object 3> <condition> <velocity>
<Velocity> is the angular velocity of <object 1> as observed from <object 3>. If RELATIVE is used, <velocity> is the apparent angular velocity of <object 1> relative to <object 2> as observed from <object 3>.
R_VEL
R_VEL is used to select windows based on the change in distance between two objects (i.e. the Radial Velocity) in km/sec. The syntax is:
[NOT] R_VEL <object 1> <object 2> <condition> <velocity>
Positive values of <velocity> mean that the objects are moving away from each other while negative values mean that the objects are moving closer to each other.
SIZE
SIZE is used to select windows based on the apparent angular diameter of an object in arc-seconds. The syntax is:
[NOT] SIZE <object> <condition> <angle>
PHASE
PHASE is used for solar phase angle, and is used to find times when the angular phase of one body as seen from another is within a specified range. The syntax is:
[NOT] PHASE OF <object> FROM <observer> BETWEEN <angle 1> <angle 2>
where <angle> is the observer-object-sun angle, in degrees.
OCC
OCC is short for "Occultation" and is used to find times when one body appears to pass behind another body as viewed from a third body. The syntax is:
[NOT] OCC OF <occulted object> BY <occulting object> FROM <observer>
The <occulted object>, <occulting object>, and <observer> must be standard bodies from Table 4.1: Solar System Standard Targets. An occultation is defined to begin when the limb of the sphere representing the <occulted object> first touches the limb of the sphere representing the <occulting object>, as seen from the vantage point of the <observer>.
TRANSIT
TRANSIT is used to find times when one body appears to pass across the disk of another body as viewed from a third body. The syntax is:
[NOT] TRANSIT OF <transiting object> ACROSS <transited object> FROM <observer>
The <transiting object>, <transited object>, and <observer> must be standard bodies from Table 4.1: Solar System Standard Targets. A transit is defined to begin when the disk representing the <transiting object> is entirely in front of the disk representing the <transited object>, as seen from the vantage point of the <observer>. The transit ends when the limbs of the two disks come into contact again. Thus at any time in the transit the <transiting object> is entirely surrounded by the <transited object>.
ECL
ECL is short for "Eclipse" and is used to find times when one body is in the shadow (cast in sunlight) of another body. The syntax is:
[NOT] ECL <type> OF <eclipsed object> BY <eclipsing object>
The <eclipsed object> and <eclipsing object> must be standard bodies from Table 4.1. An eclipse is defined to begin when the trailing limb of the <eclipsed object> enters the penumbra (<type> = P) or the umbra (<type> = U) of the <eclipsing object>. An eclipse is defined to end when the leading limb of the <eclipsed object> exits the penumbra (<type> = P) or the umbra (<type> = U) of the <eclipsing object>. One of the values P or U must be specified.
CML
CML is short for "Central Meridian Longitude" and is used to find times when the sub-observer meridian of an object lies within a particular range. The syntax is:
[NOT] CML OF <object> FROM <observer> BETWEEN <angle 1> <angle 2>
The <object> and <observer> must be standard bodies from Table 4.1: Solar System Standard Targets. The keyword specifies those times when the central meridian longitude lies between <angle 1> and <angle 2> (both in degrees) as seen by the <observer>.
OLG
OLG is short for "Orbital Longitude" and is used to select observation times based on a geocentric view (usually) of the object. OLG can be used on either a Level 1 or a Level 2 object. The syntax is:
[NOT] OLG OF <object 1> [FROM <object 2>] BETWEEN <angle 1> <angle 2>
where <angle 1> and <angle 2> are in degrees. OLG specifies those times when the orbital longitude lies between <angle 1> and <angle 2>. The default for <object 2> is the Earth. If <object 1> refers to a Level 2 body, usually a satellite, the orbital longitude is defined as follows (see Figure 4.1 Orbital Longitude for Satellites):
- Construct a vector from <object 2> (Earth) to the Level 1 parent (planet) of the <object 1> (satellite).
- Extend the vector "behind" the planet and project it onto the orbital plane of the satellite. This is the reference axis.
- The orbital longitude is the angle from the reference axis to the position of the satellite measured in the direction of motion of the satellite. Valid values for the orbital longitude lie in the range 0-360 degrees.
Orbital Longitude of 0 degrees corresponds to superior conjunction, Orbital Longitude of 180 degrees corresponds to inferior conjunction, and 90 degrees and 270 degrees correspond to greatest eastern and western elongation, respectively.
If "object 1" refers to a Level 1 body, e.g. a planet, asteroid, or comet, the orbital longitude is defined to be the angle between the Sun-Earth vector and the Sun-Planet vector, projected onto the planet's orbital plane, increasing in the direction of the planet's orbital motion (see Figure 4.2).
Orbital Longitude of 0 degrees corresponds to opposition, Orbital Longitude of 180 degrees corresponds to conjunction with the Sun. However, Orbital Longitude of 90 degrees or 270 degrees does not correspond with quadrature. Orbital Longitude is not synonymous with "elongation" or "separation" from the sun.
4.7.1 Default Target Windows
Please note that the following defaults apply for solar system targets:
SEP OF <target> SUN FROM EARTH GT 50D
All targets in the Martian system except Mars:
SEP OF <target> MARS FROM EARTH GT 10"
All targets in the Jovian system except Jupiter:
SEP OF <target> JUPITER FROM EARTH GT 30"
All targets in the Jovian system except Io:
SEP OF <target> IO FROM EARTH GT 10"
All targets in the Jovian system except Europa:
SEP OF <target> EUROPA FROM EARTH GT 10"
All targets in the Jovian system except Ganymede:
SEP OF <target> GANYMEDE FROM EARTH GT 10"
All targets in the Jovian system except Callisto:
SEP OF <target> CALLISTO FROM EARTH GT 10"
All targets in the Saturnian system except Saturn:
SEP OF <target> SATURN FROM EARTH GT 45"
All targets in the Saturnian system except Rhea:
SEP OF <target> RHEA FROM EARTH GT 10"
All targets in the Saturnian system except Titan:
SEP OF <target> TITAN FROM EARTH GT 10"
All targets in the Uranian system except Uranus:
NOT OCC OF <target> BY URANUS FROM EARTH
All targets in the Neptunian system except Neptune:
NOT OCC OF <target> BY NEPTUNE FROM EARTH
All TYPE=PGRAPHIC, and TYPE=MAGNETIC targets:
NOT OCC OF <target> BY <parent body> FROM EARTH
These default windows will be superseded by any similar windows specified in the solar system target list. For example, if the target is Io and an Io-Callisto separation window is specified by the observer, then the observer's Io-Callisto separation window will apply and the default will not.
4.8 Flux Data [Flux]
Flux information for all targets is required. There can be more than one entry for a given target. STScI will use this flux information to prevent over-illumination of sensitive detectors. Proposers should refer to 3.9 "Flux Data [Flux]"for instructions and guidelines on how to provide flux data for their targets. The flux data must be given in the format and units shown in Table 4.12: Formats for Specification of Target Flux Data. The units should not be entered on the Target List.
Table 4.12: Formats for Specification of Target Flux Data
Examples for Stars: Broad-band magnitude1 V=13.1 +/- 0.5 magnitude Spectral type TYPE=G5III Color Index1 B-V = 0.86 +/- 0.2 magnitude Color Excess E(B-V) = 0.3 +/- 0.2 magnitude Background Surface Brightness2 SURF-BKG(B) = 20 +/- 0.2 mag/arcsec2 Examples for Galaxies, Nebulae, and other extended sources: Surface Brightness1,2 SURF(V) = 25.0 +/- 1.0 mag/arcsec2 Surface Brightness1 SURF(B) = 24.5 +/- 0.5 mag/arcsec2 Color Excess E(B-V) = 2.5 +/- 0.2 mag Plus whatever other fluxes are relevant to your science program. Some other examples are listed below: Interstellar Extinction A(V) = 1.3 +/- 0.1 mag Flux at a specified wavelength F(5100) = 51 +/- 3 E-15 erg/(cm2 sec Å) Continuum Flux3 F-CONT(3500) = 57 +/- 3 E-15 erg/(cm2 sec Å) Line Flux3,4,5 F-LINE(3727) = 5 +/- 1 E-14 erg/(cm2 sec Å) Line Width6 W-LINE(3727) = 2.4 +/- 0.2 Å Surface Brightness at specified wavelength2 SURF(5100) = 11 +/- 2 E-15 erg/(cm2 sec Å arcsec^2) Surface Brightness at continuum wavelength2 SURF-CONT(5000) = 52 +/- 2 E-15 erg/(cm2 sec Å arcsec^2) Surface Brightness of line emission3,4,5 SURF-LINE(5007) = 52 +/- 2 E-15 erg/(cm2 sec arcsec^2) Size (FWHM of circular region)7 SIZE = 25 +/-5 arcsec
1The following broad-band magnitudes may be used: U,B,V,R,I,J,H,K.
2You may append "-BKG" to this reference (just before the wavelength designation) to indicate that it is a background flux value (e.g., SURF-BKG(V) = 18.2 +/- 0.5; SURF-CONT-BKG(5100) = 10 +/- 3 E-15).
3Give wavelength used in keyword in rest frame, but flux in observed frame.
4Line flux should be relative to the continuum, if specified, or relative to zero if not specified.
5Whenever the S/N refers to a spectral line, W-LINE must be given along with F-LINE or SURF-LINE. Values of F-LINE and SURF-LINE outside the Earth's atmosphere are required.
6W-LINE is the full width at half maximum (FWHM).
7SIZE should be included if the exposure time estimate assumed the flux was spread over an extended region; if omitted, the highest spatial resolution of the observing mode will be assumed.
4.9 Comments [Comments]
This field should include in words what you are trying to define by coordinates and windows in the other fields. For example, for Target No. 3 on the sample form the TPS and Window fields define mathematically the location of the target and the valid observation times, but the Comments field is probably much more useful in helping an observation planner determine the proposer's objectives. Use only alphanumeric characters and hyphens.
4.10 Illustrations of Orbital Longitude
Figure 4.1: Orbital Longitude for Satellites
Figure 4.2: Orbital Longitude for Planets
4.11 Examples of Target List Blocks
The sample targets defined in this section are provided as examples of completed blocks using the syntax described in these instructions. This collection does not provide an example for every type of keyword but does give a good overall representation of the types of target selections that can be accommodated. Numerical data in these examples is fictional.
- Example 1: In this example the proposer wants to perform spectroscopy of a volcano on Io. The position of the target is given in planetographic coordinates. The proposer also wants to observe the target when it lies close to the central meridian and, thus, uses CML to specify the allowable range of the central meridian longitude.
- Example 2: In this example the proposer wants to perform spectroscopy of the western ansa of the Io torus when Io is near greatest eastern elongation. The elongation condition is specified using the OLG keyword.
- Example 3: In this example the proposer wants to perform spectroscopy in the tail of comet Halley near the time of the Giotto spacecraft encounter. The latest orbital elements for the comet have been supplied by the proposer and these will be used for the ephemeris generation. The POS_ANGLE target reference system is used to specify the tailward pointing.
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