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 3.1: Designations of Special Targets
Table 3.2: Target Categories
Table 3.3: Descriptive Keywords for STAR and EXT-STAR
Table 3.4: Descriptive Keywords for STELLAR CLUSTER and EXT-CLUSTER
Table 3.5: Descriptive Keywords for GALAXY
Table 3.6: Descriptive Keywords for CLUSTER OF GALAXIES
Table 3.7: Descriptive Keywords for ISM and EXT-MEDIUM
Table 3.8: Descriptive Keywords for UNIDENTIFIED
Table 3.9: Descriptive Keywords for CALIBRATION
Table 3.10: Discrete Features and Descriptors for All Categories
Table 3.11: Required Coordinate Accuracies
Table 3.12: Formats for Specification of Target Flux Data
Table 3.13: Bright-Object Constraints
The use of the RPS2 "FIXED_TARGETS" and "GENERIC_TARGETS" blocks are described in this chapter. To make the presentation of this material more concise, the section on solar system targets has been made into a separate chapter; see Chapter 4: "Solar System Targets List [Solar_System_Targets]".
The Target List tells us where you wish to point HST and so must be filled out with care, precision, and accuracy. The Target List also provides the information that defines and describe the targets, and which was used to determine exposure times. Three different kinds of Target Lists exist for the following three classes of targets, but only the Target List(s) required for your proposal need be submitted:
- Fixed targets (all targets outside the solar system whose positions can be defined by specific celestial coordinates);
- Solar-system targets (all moving targets);
- Generic targets (targets defined by certain properties, rather than by specific coordinates).
In this chapter, each heading has a description followed by a keyword in square brackets (e.g., Target_Number). The keyword must be used in your RPS2 form. Elsewhere, items in boldface (e.g., RA-OFF) show words or phrases that are 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.
3.1 Target Number [Target_Number]
Each target that will be observed must be assigned its own unique number. Target numbers must be positive and monotonically increasing (but not necessarily consecutive) integers. A different target must be defined whenever different coordinates or a different target description are required. Separate targets should be defined and listed if you plan to take observations at several points within an extended object. For example, if you were to take spectra at three different locations in the Crab Nebula, each point must have its own target number, name, and coordinates, such as CRAB1, CRAB2, and CRAB3.
If more than one type of Target List is used (such as both fixed and generic target lists), continue with the same numbering scheme used on the preceding Target List but start with a target number which is larger than the last target number on the preceding list.
All target numbers and names within a proposal must be unique (within that proposal).
3.2 Target Name [Target_Name and Alternate_Names]
Target names are used to provide unique designations for the targets that will be used throughout the proposal. These names will also be used to designate targets in the HST data archive. Prospective proposers and archival researchers will use these names to determine whether HST has observed a particular object. This facility will be most useful if consistent naming conventions are used.
The following conventions must be followed in naming targets:
- A new target name must be defined for each (celestial) target. For example, for several pointings within a galaxy, one might define target names such as NGC4486-NUC, NGC4486-JET, NGC4486-POS1, and NGC4486-POS2.
- The maximum allowable length of a target name is 30 characters.
- No blanks are permitted in target names. Blanks between a letter and a numeral must be suppressed (e.g., HD140283, NGC4378), but a hyphen (and not an underscore) must replace blanks between two letters or two numerals (e.g., ALPHA-CEN, NGC224-0040+4058). Also, a hyphen should be used where required for clarity (e.g., NGC4486-POS1).
- Only letters, numerals, hyphens, periods (.), and + or - are allowed in target names; other punctuation is not permitted (e.g., BARNARDS-STAR is valid, but BARNARD'S-STAR is not). Greek letters must be spelled out (e.g., ALPHA-ORI). Letters may be upper-case or lower-case, but will always be treated as if they are upper case (e.g. Alpha-Cen will be treated as if written ALPHA-CEN).
- Degree signs must be represented by an upper-case "D" (e.g., CD-42×14462 becomes CD-42D14462).
- Some special target names are reserved for calibrations and other purposes and may not be used for external pointings; see Table 3.1: Designations of Special Targets.
Whenever possible, two types of designations should be provided for each target. The first will be a "catalog name" (for example, HD124897), and the second will be at most two "common names" (e.g., ALPHA-BOO, ARCTURUS). The "catalog name" is entered in Target_Name and the "common names" are entered in Alternate_Names.
Only the catalog name is used when the target name is repeated in the Visit and Exposure Specifications. If the target is in the STScI Guide Star Catalog (GSC), the GSC name should be included as one of the common names (e.g., GSC5637-12345).
3.2.1 Catalog Name
The preferred order for catalogs to be used for the designation of various classes of objects is provided below. It is arranged in order of decreasing preference.
If a target is not contained in these catalogs, other catalog designations may be used (e.g., 4U X-ray catalog designation, Villanova white-dwarf catalog number, etc.). The use of positional catalogs (SAO, Boss, GC, AGK3, FK4, etc.) is discouraged.
For uncataloged targets, see3.2.2 "Uncataloged Targets".
Stars
- Henry Draper Catalog number (e.g., HD140283)is preferred. HDE numbers are discouraged, except in the Magellanic Clouds.
- Durchmusterung number (BD, CD, or CPD). In the southern hemisphere, adopt the convention of using CD north of -52 degrees and CPD south of there (e.g., BD+30D3639, CD-42D14462, CPD-65D7691).
- General Catalog of Variable Stars designation, if one exists (e.g., RR-LYR, SS-CYG).
- AFGL designation.
- IRC designation.
- IRAS designation.
Star Clusters and Nebulae
- New General Catalog (NGC) number (e.g., NGC6397, NGC7027).
- Index Catalog (IC) number (e.g., IC418).
- For planetary nebulae for which you do not have an NGC or IC designation, the Perek-Kohoutek designation (e.g., PK208+33D1) may be used.
- For H II regions for which you do not have an NGC or IC designation, the Sharpless catalog number (e.g., S106) may be used.
- For IR nebulae, AFGL designation.
Galaxies and Clusters of Galaxies
- NGC number (e.g., NGC4536).
- IRAS designation.
- IC number (e.g., IC724).
- Uppsala Catalog number, only if an NGC or IC number is not available (e.g., UGC11810).
- For clusters of galaxies, the Abell catalog number, but only if an NGC or IC number is not available (e.g., ABELL2029).
Quasars and Active Galaxies
- The name defined in the compilation by Veron-Cetty and Veron (ESO Report No. 7, 1989) must be used (e.g., 3C273).
3.2.2 Uncataloged Targets
Objects that have not been cataloged or named must be assigned one of the following designations:
- Isolated objects must be designated by a code name (the allowed codes are STAR, NEB, GAL, STAR-CLUS, GAL-CLUS, QSO, SKY, FIELD, and OBJ), followed by a hyphen and the object's J2000 equatorial coordinates, if possible, rounded to seconds of time and seconds of arc (e.g., for a star at J2000 coordinates RA = 1H 34M 28S, DEC = -15D 31' 38", the designation would be STAR-013428-153138).
- Uncataloged objects within star clusters, nebulae, or galaxies must be designated by the name of the parent body followed by a hyphen and the rounded J2000 coordinates, if possible, of the object (e.g., for a target within NGC 224 with J2000 coordinates RA = 0H 40M 12S, DEC = +40D 58' 48", the designation would be NGC224-004012+405848).
- Positions within nebulae or galaxies may also be designated by the name of the parent object followed by a hyphen and a qualifier. The qualifier should be brief, but informative (e.g., the jet in NGC 4486 could be designated NGC4486-JET). Other examples are: NGC5139-ROA24, LMC-R136A, ABELL30-CENTRAL-STAR, NGC205-NUC.
3.2.3 Common Names
In addition to the catalog name, a target should be assigned at most two "common names," or aliases, if they exist. Examples of common names are the following:
- Stars: The Bayer (Greek-letter) designation or Flamsteed number with standard three-letter constellation abbreviation (e.g., ZETA-CAP, 22VUL, OMICRON2-ERI-B); the Bright Star Catalog number (e.g., HR5270); other names, if they exist (e.g., CYG-X1, BARNARDS-STAR, PROXIMA-CEN).
- Star clusters, nebulae, galaxies, and clusters of galaxies: Commonly used names (e.g., HYADES, OMEGA-CEN, CRAB-NEBULA, ABELL63, COMA-CLUSTER); Messier numbers (e.g., M13, M31, M67).
3.2.4 Special Targets
The names of certain types of targets must be designated by appending a code to the target name. For example, -CALIB should be appended to the name of a target that is being observed only as a calibration standard for other observations. These designations will assist in planning of the observing schedule. The possible codes are listed in Table 3.1.
Table 3.1: Designations of Special Targets
External calibration target -CALIB An astronomical target used for calibration (e.g., BD+28D4211-CALIB). Internal calibration sources (e.g., WAVE) and calibrations using the Earth must not be included in the Target List. Offset acquisition target -OFFSET A target that will be used for an offset acquisition; it is the object that will be acquired first, from which an offset will be applied to move to the target of interest (e.g., 3C273-OFFSET). Two separate exposures must be defined on the Visit and Exposure Specifications; an acquisition of the -OFFSET target, and a science exposure of the (target of interest) program target. The location of the latter target may be specified either by equatorial coordinates or by an offset (see 3.4 "Target Position [Position]"). For example: to observe the JET in 3C273, first acquire "stellar-like" source 3C273-OFFSET, then offset to program target 3C273-JET. Special designations These are reserved designations and may not be used as the names of external pointing in a target list: ANTI-SUN, ANY, BIAS, CCDFLAT, DARK, EARTH-CALIB, INTFLAT, KSPOTS, NONE, ORBIT-POLE, ORBIT-POLE-NORTH, ORBIT-POLE-SOUTH, UVFLAT, VISFLAT, WAVE
3.3 Target Description [Description]
A target description must be provided for each target. The Target Description will be one of the key fields used by archival researchers in searching through the HST data archive; thus it is extremely important that the information be filled out completely and accurately for each target.
Each target must be assigned a single primary category from Table 3.2, and at least one descriptive keyword, chosen from the appropriate Table 3.3 through Table 3.9 (see Table 3.2 for which table is appropriate for each category). The discrete features and descriptors in Table 3.10 may be used as descriptive keywords for any category. A maximum of five descriptive keywords may be specified.
It is possible, but not required, to specify a second category for a target, followed by one to five descriptive keywords from the appropriate tables, as described for the primary category.
Whether one or two categories are used, all values must be separated from each other by commas. For example, suppose the STAR category is chosen with the descriptive keywords Polar and Interacting Binary. This target description would be specified as STAR, Polar, Interacting Binary.
The categories in Table 3.2, and some of the descriptive keywords in Table 3.3 through Table 3.10, are followed by explanatory text in parentheses. This text is provided only for explanatory purposes and is not part of the category or keyword itself. Only the non-parenthesized portion, which appears in bold in the tables, should be entered into the RPS2 file.
Table 3.2: Target Categories
SOLAR SYSTEM (Solar System Object) Chapter 4: "Solar System Targets List [Solar_System_Targets]" STAR (Galactic Stellar Object) Table 3.3 See Table 3.10 EXT-STAR (Star in an External Galaxy) Table 3.3 STELLAR CLUSTER (Galactic Star Cluster, Group, or Association) Table 3.4 EXT-CLUSTER (Star Cluster in an External Galaxy) Table 3.4 GALAXY (Galaxy or AGN) Table 3.5 CLUSTER OF GALAXIES (Galaxy Groupings, Clusters, Large-scale Structure) Table 3.6 ISM (Interstellar Medium of the Galaxy) Table 3.7 EXT-MEDIUM (Interstellar Medium of an External Galaxy) Table 3.7 UNIDENTIFIED (Unidentified Objects) Table 3.8 CALIBRATION (Calibration Observations) Table 3.9
Table 3.3: Descriptive Keywords for STAR and EXT-STAR
Table 3.4: Descriptive Keywords for STELLAR CLUSTER and EXT-CLUSTER
Globular Cluster OB Association Open Cluster T Association
Table 3.5: Descriptive Keywords for GALAXY
Table 3.6: Descriptive Keywords for CLUSTER OF GALAXIES
Table 3.7: Descriptive Keywords for ISM and EXT-MEDIUM
Table 3.8: Descriptive Keywords for UNIDENTIFIED
Radio Emitter Ultraviolet Emitter Blank Field Low Latitude Field Infrared Emitter X-ray Emitter Parallel Field Optical Emitter Gamma Ray Emitter High Latitude Field
Table 3.9: Descriptive Keywords for CALIBRATION
Table 3.10: Discrete Features and Descriptors for All Categories
3.4 Target Position [Position]
A position is required for each fixed target. The position may be expressed in any one of three different ways:
- By specifying the equatorial coordinates (RA and DEC) of the target;
- By specifying a positional offset from another target; or
- By specifying a region (area) of the sky.
It is also possible to specify that the coordinates were obtained using the Guide Star Selection System (GSSS; see3.4.5 "Determining Coordinates in the Guide Star Selection System (GSSS) Reference System"), or that they are currently uncertain or unknown, and that more accurate coordinates will be provided by the observer after an early acquisition exposure is taken, or in real time during the HST observations.
3.4.1 Required Accuracies of Target Positions
The HST Scientific Instruments (SIs) typically have very small apertures and fields of view. Target-acquisition apertures for several of the SIs are only a few seconds of arc in size. Since the HST has no analog to the video acquisition cameras common on many ground-based telescopes, it is essential to have accurate coordinates for targets. In many cases targets will be placed in the final observing aperture after a sequence of target-acquisition observations. This will only work, however, if the target coordinates are sufficiently accurate and precise to place the target in the first of these acquisition apertures.
HST uses two guide stars to stabilize the pointing of the telescope and to place the target in the desired aperture. The fundamental problem, then, is to determine the position of the target relative to the guide stars in the surrounding area with sufficient accuracy to place the target in the aperture. The specific pair of guide stars to be used cannot be determined in advance of the observation; several possible pairs will often be available for each target. The guide stars are chosen from the Guide Star Catalog (GSC). The uncertainty of the relative positions of a group of potential guide stars in the GSC is 0.33 arcsec (1 sigma) in the north and about 0.5 arcsec in the south.
The accuracies of positions typically needed for target acquisition with each of the SIs are shown in Table 3.11; these are predicated upon the positions being in the coordinate system of GSC, which is based upon the AGK3 and SAO reference systems. Note that several of the SIs have multiple acquisition apertures of different sizes that may be used. Be sure when selecting acquisition apertures to keep the coordinate uncertainties in mind. Furthermore, be sure to provide 1 sigma uncertainties with your positions so that STScI may check the appropriateness of your acquisition exposures. Inaccurate target coordinates can result in failed target acquisitions and can therefore waste valuable HST observing time. As indicated in Table 3.11, it is the observer's responsibility to provide accurate coordinates in all cases, but in particular they must be in the GSC reference frame when using STISwith the NIC1 and NIC2 detectors. Please contact your PC if you need additional information. Although GSC frame-based coordinates are not required for FGS and WFPC2 observations, it is still prudent to check the accuracy of your coordinates. All observers will be provided target confirmation charts by their PC to help them verify the target coordinates in the GSC reference frame. The Principal Investigator of a program is responsible for ensuring that target coordinates are accurate, both at the time of program submission, and later when target confirmation charts are provided. The following address has pertinent information on target confirmation charts:
Note: HST proposals executed before July 1991, as well as engineering proposals of type OV, SV, SMOV, and CAL, should not be used to derive target coordinates. Coordinates from such proposals may be unreliable owing to poor calibration and/or engineering-related pointing changes made during the observations.
Table 3.11: Required Coordinate Accuracies
WFPC2 (WFC) 10 No WFPC2 (PC) 5 No STIS 1 Yes FGS 1 No ACS/WFC 10 No ACS/HRC 4 No ACS/SBC 5 No ACS/HRC-OCCULT 1 Yes ACS/HRC-CORON 1 Yes NIC11 3 Yes NIC2 (2) 5 Yes NIC3 (2) 10 No
1If multiple NICMOS detectors are being used in parallel, the primary detector (the detector used for the exposures in the <primary-exp-list> of the PARallel WITH Special Requirement; see PARallel <parallel-exp-list> WITH <primary-exp-list>) determines the required coordinate accuracy for the observation and whether GSC frame-based coordinates are required.
3.4.2 Equatorial Coordinates
If you specify the target position directly in terms of equatorial coordinates (as opposed to specifying an offset or a region), then the right ascension and declination and their uncertainties are required, using the following format:
RA = <value> +/- <uncertainty>, DEC = <value> +/- <uncertainty>
- The comma following the right-ascension uncertainty is required.
- The uncertainties represent the accuracy (1 sigma) of the target coordinates, not the region within which a target could be observed (e.g., for a sky measurement). See3.4.4 "Region of Sky (Extended Targets)" for instructions on how to designate regions as targets.
- The right-ascension value must be expressed either in hours (H), minutes (M), and seconds (S) of time; or in decimal degrees (D). For example, RA = 108.14375D and RA = 7H 12M 34.5S are equivalent.
- The declination value must be expressed either in degrees (D), minutes ('), and seconds (") of arc; or in decimal degrees (D). Thus DEC = -12D 55M 33.3S and DEC = -12.92592D are equivalent.
- Units must be provided for both a value and its uncertainty. The uncertainty must be expressed in one and only one of the units used to express the related RA and/or DEC, with the additional units of minutes (') of arc or seconds (") of arc being allowed for right ascension. (In other words, the RA may be expressed as a combination of three units [H, M, S], but its uncertainty must be in terms of a single unit such as S or ".) To clarify:
RA: H-M-S timemin, timesec, arcmin, arcsec RA: Degrees degrees DEC: D-M-S degrees, arcmin, arcsec DEC: Degrees degrees
RA = 12H 7M 13.33S +/- 0.15S, DEC = +27D 3' 8.0" +/- 0.1" and RA = 181.80554D +/- 0.00063D, DEC = +27.05222D +/- 0.00003D are equivalent.
Note: If the sign of the declination is not indicated, a positive declination is assumed, but we urge you to always include the sign as a way of reducing errors.
3.4.3 Positional Offsets
The position of a target may alternatively be specified as an offset from a reference target. It is possible to specify offsets in equatorial coordinates, in rectangular coordinates, or in polar coordinates, all of which have their origin at the reference target. Note, however, that offsets larger than 30 arcsec may complicate the target acquisition procedure. If larger offsets are desired, please contact your Program Coordinator.
Equatorial and rectangular offsets are always in the sense offset = target-coordinates minus offset-reference-coordinates, while a polar offset is expressed as an angular separation and position angle of a line drawn from the offset reference target to the target. As with other similar quantities, we urge you to include the sign of the offset, even when it is positive, as a means of removing ambiguity.
Note that in the examples below, FROM 6, 3, and 4 are the target numbers which contain the equatorial coordinates of the reference targets, and that the reference-target names have -OFFSET appended (see Table 3.1).
Positional offsets are only a convenient method of specifying target coordinates, and do not automatically imply a particular method of target acquisition; observers must explicitly specify any target acquisitions on the Visit and Exposure Specifications via Special Requirements (see Chapter 7: "Special Requirements [Visit_Requirements and Special_Requirements]").
Warning: If your object has significant proper motion no correction may be applied. See 3.8 "Is Proper Motion or Parallax Relevant?", where it notes that the proper motion for the target is taken to be the same as for the offset object.
- The format for the specification of an offset as a difference in EQUATORIAL coordinates is:
RA-OFF =<value> +/- <uncertainty>, DEC-OFF = <value> +/- <uncertainty>, FROM <target number>Note the uncertainties and the commas separating the three items. The value for RA-OFF may be in units of seconds (S) of time or in decimal degrees (D), and the value for DEC-OFF may be in units of arcmin (') or arcsec ("), or in decimal degrees (D). The uncertainty must be expressed in one and only one of the units used to express the related RA and/or DEC.
In the following example, a target's right ascension is 1.1 seconds of time greater than, and its declination is 10 arcsec less than, the right ascension and declination of target number 6:
RA-OFF = +1.1S +/- 0.2S, DEC-OFF = -10" +/- 1", FROM 6- Offsets in RECTANGULAR coordinates are interpreted as displacements in the tangent plane whose origin is located at the reference target. For displacements of less than about one degree, they may be interpreted as the offsets that are measured on a photographic plate, without making errors larger than about 0.5 arcsec. The format for the specification of an offset in rectangular coordinates is:
XI-OFF = <value> +/- <uncertainty>, ETA-OFF = <value> +/- <uncertainty>, FROM <target number>
Note: North and east displacements are considered positive (+), south and west are negative (-).
The values of XI-OFF and ETA-OFF are required to both be expressed in arcmin (') or arcsec ("), and the uncertainties must be expressed in the same units (in other words, all four angular quantities must be in the same units). In the following example, a target has been measured on a sky-survey plate, with a scale of 67 arcsec/mm, to lie 0.5 mm west of, and 1 mm north of, target number 3, with an accuracy of 1 arcsec:
- The format for a POLAR offset specification is:
R = <value>, PA = <value>, FROM <target number>
Note that uncertainties must not be included in this type of specification. The separation is expressed in units of minutes (') or seconds (") of arc. The position angle of the target with respect to the reference target is measured east of north, and the unit of measurement (degrees) is required. In the following example, a target lies 10 arcsec from target number 4, at a position angle, measured at target 4 from north through east, of 60 degrees:
3.4.4 Region of Sky (Extended Targets)
Sometimes it is necessary to define a region of sky rather than a specific point. Examples are extended targets (such as emission nebulae and galaxies) and blank-sky regions for background measurements (if it is acceptable to make the observation anywhere within a region). It is possible to specify rectangular or circular regions. An Equinox value should be specified with the region coordinates (see3.5 "Equinox for Coordinates [Equinox]").
The units used for regions should be used in the same way as for coordinates; see3.4.2 "Equatorial Coordinates".
Rectangular Region
For a rectangular region, the format for equatorial coordinates must be used, followed by a comma and the word REGION; the values following +/- will then be interpreted as one-half the lengths of the sides of the rectangular area, rather than as uncertainties in the coordinates.
In the following example, a region 4 arcmin wide in right ascension by 2 arcmin high in declination is specified:
RA = 3H 51M 27S +/- 2', DEC = -37D 13' 25" +/- 1', REGION
Circular Region
If it is desired to specify a circular region, REGION must be followed by another comma and the radius of the region in the format R = <radius>; in this case, no uncertainties should be attached to the RA and DEC. Here is an example of a circular region with a radius of 2 arcmin:
RA = 3H 51M 27S, DEC = -37D 13' 25", REGION, R = 2'
Note that the units of R must be specified.
3.4.5 Determining Coordinates in the Guide Star Selection System (GSSS) Reference System
The HST reference frame is defined by the HST Guide Star Catalog (GSC) that STScI has created. For observations that require accurate coordinates, such as those listed as "GSC Coordinates Required" in Table 3.11, it is vital that you provide positions derived in the same reference frame as the original GSC plate material.
Access to the GSC, as well as lightly compressed versions of the plates used to construct the GSC, is available on the CASB WWW server. Begin at
http://www-gsss.stsci.edu/support/phase2.htmland follow the links under "General Guidelines." Coordinates produced using these facilities will be in the same reference frame as the GSC.Here are some more detailed guidelines for different categories of brightness and type:
- Stars with m(V) between about 9 and 14 (at high galactic latitude) or between about 9 and 13 (at low galactic latitude): Most of these are contained in the GSC. You can retrieve GSC coordinates using a form available on the CASB Web server listed above. When you have the GSC coordinates, enter them in the Position field of the Target List, followed by the plate identification number (not the region number) from the GSC, using the format PLATE-ID = <plate identifier>. This identifies the target coordinates as coming from the GSC. Also enter the GSC name as a target alias in Alternate_Names.
RA = 12H 13M 14.27S +/- 0.3", DEC = -13D 11' 03.3" +/- 0.3", PLATE-ID=00TB
For stars brighter than about m(V) = 9, coordinates from the Hipparcos Input Catalogue have been added to the GSC; these coordinates can be recognized as having a plate designation of +056. Enter the GSC name as a target alias, but do not include the PLATE-ID for coordinates derived from the Hipparcos Input Catalogue (but do indicate in the target-level Coordinate_Source field that the coordinates are from Hipparcos). Note that coordinates from the Hipparcos Output Catalog are on a different system from the GSC; but the differences are negligible in almost all instances.
- Stars fainter than about m(V) = 13 - 14, and extended sources: The plate material that was used to construct the GSC will generally allow identification of targets to magnitudes of V = 19 in the northern- and J = 22 in the southern hemisphere. Use the facility and instructions available on the CASB Web server listed above to determine coordinates of targets on the GSC plates.
Once coordinates have been obtained, Position should again contain the plate ID from GSC, using the PLATE-ID = <number> format. Contact your Program Coordinator if you need assistance.
- Stars fainter than about m(V) = 13 - 14, and extended sources (for which special plates or ground-based CCD images were obtained): You must transfer the GSC reference frame to your special plates or CCD images. You will need about ten stars from GSC as your reference stars when carrying out plate reductions. Enter the coordinates in Position, again with the PLATE-ID = <number> format, to indicate which GS plate provided the coordinates used for the plate reduction.
As part of preparing your observations, your Program Coordinator will provide, as a final check that the coordinates are correct, a Confirmation Chart showing the target coordinates (as entered in the proposal) overlaid on the field from the plate material used to construct the Guide Star Catalog. You are responsible for verifying that the coordinates are correct. (See3.4.1 "Required Accuracies of Target Positions".)
3.4.6 A Caution on Astrometry Prepared from STScI Plate Scans
Note that the set of plates used to construct the GSC is NOT the same one that is contained in the 102-volume set of CD ROMs distributed as the Digitized Sky Survey (DSS-I) and that is available elsewhere at the stsci.edu Web site. The DSS-I uses the 1950 epoch POSS-E plates for the north, whereas the GSC in the north is based on the 1982 epoch Palomar Quick V. Similarly, in a few cases, the southern plates used in the GSC are not the ones in the DSS-I. HST users may use the DSS-I CD ROMs to prepare their Phase II submissions only if they verify that the DSS-I plates are the same as those used in the GSC, i.e., the plate ID field must be identical.
3.4.7 Prohibition on the Use of GSC Version 1.2
Preliminary access to an improved (astrometrically recalibrated) GSC, version 1.2, has been provided via a WWW server. As this revision has significantly different astrometry from the GSC currently used by HST operations (version 1.1), GSC version 1.2 must not be used for Phase II target determinations. Note that all GSC CD ROMs in circulation are from version 1.1 or lower.
Uncertain or Unknown Coordinates
If it is impossible to obtain adequate plate material to measure coordinates to the required accuracy (e.g., a very crowded field which cannot be resolved using ground-based observations), it may be necessary to obtain an early acquisition image or to perform an acquisition that involves real-time interaction with the telescope (see7.3.1 "Target Acquisition"). In that case, coordinates as accurate as possible must be entered on the Target List.
3.4.8 Special Catalogs
The option PLATE-ID can be used to specify one of the special guide star catalogs which have been created by the STScI to accommodate special guide star requirements. These catalogs are primarily used for selecting guide stars from a subset of stars in the region which have certain properties or more accurate relative positions. This option is most commonly used when the relative accuracy of guide stars and target stars must be known with great precision.
The Special Catalogs currently available are:
ZZZZ NGC188 ZZZX Iota Carinae ZZZW HR6636 ZZZV HR6850 ZZZU HR6945 ZZZT NGC5617 ZZZR Omega Centauri ZZZQ Eta Carinae
Only a modest number of specific objects are listed in these catalogs; contact your PC. Note that any proper motion for objects on these plates has been applied through the year 2000, and so an Epoch of 2000 should be specified
3.5 Equinox for Coordinates [Equinox]
Specify the year of the equator and equinox to which the coordinates are referred, optionally preceded by a J or B to indicate the Julian or Besselian system. Integer or decimal values for the year may be used. If the year is given without a prefix (for example, 1975), the Besselian system is assumed for years prior to 2000 and the Julian system is assumed for the year 2000 and beyond. If a prefix is given, it must be B for years prior to 2000 and J for the year 2000 and beyond.
The values J2000 and B1950 correspond to commonly used catalogs; it is recommended that one of these be specified unless there is a good reason to use something else. It is not necessary to apply precession corrections to coordinates from positional catalogs. The Guide Star Catalog and the Hipparcos Input Catalogue both use the J2000 equinox. (Note, however, that the Hipparcos output catalogue is epoch 1991.25, which means proper motions can have significant effects if you are not careful.)
For some notes on Equinox, Epoch, and units, see3.13 "Getting Coordinates Coordinated".
3.6 Source of Specified Coordinates
[Coordinate_Source]In this field please specify the source of the celestial coordinates that you list for each target. Most faint targets will use "Other_Source." Valid entries are:
Guide_Star_Catalog
To be used if the source is the HST Guide Star Catalog. Include the Plate ID (from the "Plt" column in the GSC) with your coordinates. Note: If the Plt value is 56, then the true source is the Hipparcos Input Catalogue, which should be listed (see below, and please note that Plate ID should not be specified).
GSC_Survey_Plate
To be used if coordinates were measured from a Guide Star Catalog survey plate. Include the Plate ID with your coordinates, taking it from the PLATEID keyword in the FITS header.
HST_Image
To be used if coordinates were measured from an existing HST image. Include the Plate ID, which can be determined from the guide star IDs listed in the observation's Standard Header Packet. All HST observations have at least one guide star ID in the Standard Header Packet (SHP). SHP data are in the _jif.fits file for WFPC2 observations, or in the .spt file for STIS data.
The guide stars that were used during any pointing of HST will be recorded in the SHP as character strings associated with specific header keywords. The primary, or dominant, guide star is given by the GSD_ID keyword, while SGESTAR lists the secondary, or sub-dominant, guide star. The guide star ID is a concatenation of the star number, the region number (from the Guide Star Catalog), and the particular FGS used in the pointing. For example, "0123406789F2" means guide star 01234 06789 was used with FGS2.
To find the Plate ID, go to the GSC web site:
The form will prompt you for the guide star ID (in two fields); you should use only the primary guide star. You should then be given the coordinates, estimated magnitude, associated errors, flags internal to the catalog structure, and the PLATE-ID. For most guide stars there will be multiple entries (and multiple PLATE-IDs because the fields of the plates overlapped. The first line of the output lists the primary plate, and this is the one you should list.
If the observation used only a single guide star then it is possible that a a secondary plate was used; contact your Contact Scientist.
Image_Tied_To_GSC_Frame
To be used if you measured several visible stars on a Guide Star Catalog survey plate and then used them to determine pseudo-GSC coordinates for a target imaged with another telescope. Include the Plate ID (from the PLATEID keyword in the FITS header) with your coordinates.
PPM_Star_Catalogue
To be used if coordinates are from the PPM (Catalog of Positions and Proper Motions).
Hipparcos_Input_Catalogue
To be used if coordinates are from the Hipparcos Input Catalogue, or, equivalently, they are from the Guide Star Catalog and the "Plt" column lists "56" (in this instance please do not specify plate ID). Because of systematic differences in coordinates, we urge you not to use the HIC as a coordinate source; the Hipparcos/Tycho Catalogue should be used instead.
Hipparcos/Tycho_Catalogue
To be used if the coordinates are from the Hipparcos/Tycho missions. Note that coordinates from the Hipparcos/Tycho_Catalogue have equinox J2000 but epoch 1991.25. This earlier epoch means that it is important to provide a proper motion for your target if it is at all significant. In some cases the Catalogue of Positions and Proper Motions (PPM) may be a better source for proper motions because of its longer time baseline.
Other_Source: <text>
To be used if none of the above apply to your coordinates. You must include a short description of where the coordinates are from, for example:
Coordinate_Source: Other_Source: HDF Catalog (Williams et al. 1996, AJ, 112, 1335)
The explanation cannot be very long, and so we recommend an entry like "Coordinate_Source: Other_Source: See comment" if you need more space.
3.7 Radial Velocity or Redshift [RV_or_Z]
Give, if known, the heliocentric radial velocity or redshift of the target. The format is V = <velocity in km/sec> or Z = <redshift>; examples are V = +1198 and Z = 1.95. The units must not be specified.
3.8 Is Proper Motion or Parallax Relevant?
If a small aperture or occulting spot is to be used, even a relatively small proper motion or parallax may cause difficulties in acquiring the target. In such cases, the Proper Motion/Parallax data must be provided. Note, however, that proper motion and parallax values may not be specified for a target which is specified by a positional offset. Such targets will be taken to have the same proper motion and parallax as the reference target. Offset targets have coordinates given with (RA-OFF, DEC-OFF), (ETA-OFF, XI-OFF), or (R, PA).
The observer must determine whether or not proper motion or parallax is relevant. In general, this will depend on the size of the acquisition aperture of the SI that will be used and the epoch of the coordinates that have been provided. For example, the STIS uses a target acquisition area of 5 arcsec square. For a star whose coordinates are given for the epoch 1950, and that will be observed in 1997, a proper motion of approximately 0.5*2.5/(1997-1950) = 0.027 arcsec per year would be "relevant," with a resulting offset of half the minimum center-to-edge distance.
If special plate catalogs are being used (see3.4.8 "Special Catalogs"), proper motions are probably not included (the HST Guide Star Catalog, for example, does not include proper motion). If the relative accuracy of the target and guide stars is essential, the proper motion should be included for the target star if the special catalog includes proper motions.
3.8.1 Proper Motion and Parallax Data
The following information is required for targets where proper motion and parallax are "relevant"; note that uncertainties for RA_PM, Dec_PM, and Annual_Parallax are not required. If a sign is not given for RA_PM or Dec_PM, a positive value will be assumed, but it is better to be explicit.
- RA_PM: For Proper Motion in RA, the value should be in units of seconds of time/year. To convert from arcsec/year to seconds of time/year, divide by 15 cos DEC.
- Dec_PM: For Proper Motion in DEC, the value should be in units of arcsec/year.
- Epoch: The "Epoch of position" is the date of the "Target Position" which was defined in the Target List (see3.4 "Target Position [Position]").
- The "Epoch of position" may or may not be the same as the date of "Equinox for Coordinates" in the Target List (see3.5 "Equinox for Coordinates [Equinox]"). Remember that the "Epoch of position" is the date the target position is referred to, whereas the "Equinox of Coordinates" is the date of orientation of the coordinate system in which the position is measured. For example, a star with a large proper motion may have its coordinates given in the J2000 system, but the numbers themselves are for epoch 1984, meaning that the star was at the specified position on January 1, 1984. Epoch should be of the form 20yy.y or 19yy.y.
- Ordinarily the epoch of position is earlier than the present date. In the Guide Star Catalog (GSC), the equinox is J2000 while the epoch depends on the individual plate. Do not adjust your coordinates to be those that would be measured if the plate were taken in the year 2000. However, some catalogs contain coordinates already adjusted to an epoch of J2000: the Hipparcos Input Catalogue (often used in the GSC for stars brighter than m(V) ~= 9) and the PPM Star Catalog. When these catalogs are being used, it is appropriate to specify an epoch of J2000. (These remarks do not apply to the Hipparcos Output Catalog.)
- Annual_Parallax: The unit for parallax is arcsec.
The example below is for the object DM-9D697 (Epsilon Eridani), where the proper motion data are taken from the SAO Catalog.
RA_PM: Proper Motion in RA sec/yr -0.0662 DEC_PM: Proper Motion in DEC arcsec/yr 0.019 Epoch: Epoch of Position 20yy.y or 19yy.y 1984.5 Annual_Parallax: Annual parallax arcsec 0.30488
For some notes on proper motions and units, see3.13 "Getting Coordinates Coordinated".
3.9 Flux Data [Flux]
Flux information must be provided for all targets, and there can be more than one entry for a given target. All entries are values as observed at the Earth, rather than intrinsic values.
STScI uses flux information to test for over-illumination of sensitive detectors. In particular, STIS proposals cannot be implemented without flux information for all targets and other sources in the fields of view because of the critical requirements to protect its detectors from damage by excessively bright objects.
The first flux information given should generally be a broad-band magnitude or surface brightness. For stars, the spectral type and color index should also be included (when possible). As many additional flux values as appropriate for the requested exposures should be provided. For example, ultraviolet or emission-line fluxes should be given if the target is to be observed in the ultraviolet or through a narrow-band filter, or several magnitudes might be provided if the target is a variable star to be observed at various brightness levels. In some cases (Targets of Opportunity, variable objects, etc.) the estimated flux data may be very uncertain, but the best available estimates should nevertheless be given, along with appropriate uncertainties and comments.
It may be important to specify the flux of a background source as well as the target flux. For example, a globular cluster in M87 may be seen against the bright background of the galaxy. The keyword -BKG should be appended to a background flux specification in this case (see footnote 2 to Table 3.12). Use a comma to separate entries if more than one flux value is given.
Flux must be given as F(lambda) rather than F(nu). Recall that the conversion is:
where lambda is in Ångstroms and F(nu) is in erg/(cm^2 sec Hz). For example, if lambda = 1500Å, and F(nu) = 1.0 x 10^-26, then F(lambda) = 1.3 x 10^-14.
The flux data are to be expressed in the format shown in Table 3.12. Do not enter explicit units.
3.9.1 General Guidelines on What Flux Data to Include
The following summary provides general guidelines for what flux information must be included in five general cases. See the Instrument Handbooks for more detailed descriptions of how to make the exposure time calculations.
Point source, non-dispersive instrument
- Target flux: V magnitude, (B-V), E(B-V), spectral type.
Flux at specified wavelength may be substituted for V magnitude.
If no entry for E(B-V) is given, E(B-V) = 0 will be assumed.- Background (optional): Broad-band surface brightness or surface brightness at specified wavelength; -BKG must be specified in the name of the flux parameter.
- Flux in wavelength range of observation.
Extended source, non-dispersive instrument
- Target flux: V surface brightness, (B-V), E(B-V).
Flux at specified wavelength may be substituted for V surface brightness.
If no entry for E(B-V) is given, E(B-V) = 0 will be assumed.- Background (optional): Broad-band surface brightness or surface brightness at specified wavelength; -BKG must be specified in the name of the flux parameter.
- Surface flux at wavelength of observation and size of the region specified.
Point source, dispersive instrument
- Target flux: V magnitude, (B-V), E(B-V), spectral type.
Flux at specified wavelength may be substituted for V magnitude.
If no entry for E(B-V) is given, E(B-V) = 0 will be assumed.- Background (optional): Surface brightness of continuum; -BKG must be specified in the name of the flux parameter.
- Continuum flux in wavelength range of observation.
- Line flux and line width of brightest emission line in the wavelength range of observation.
Extended source, dispersive instrument
- Target flux: V surface brightness, (B-V), E(B-V).
Flux at specified wavelength may be substituted for V surface brightness.
If no entry for E(B-V) is given, E(B-V) = 0 will be assumed.- Background (optional): Surface brightness of continuum; -BKG must be specified in the name of the flux parameter.
- Surface flux at wavelength of observation and size of the region specified.
- Line surface flux and line width of brightest emission line in the wavelength range of observation.
Infrared source
- Target flux: J magnitude, (J-K). Flux at specified wavelength may be substituted for J magnitude.
- Background (optional): Broad-band surface brightness at specified wavelength; -BKG must be specified in the name of the flux parameter.
- Note that this refers to the astronomical background and not the thermal background.
- Flux in wavelength range of observation. Note that this must be in units of erg/(cm^2 sec Å). The
NICMOS units conversion toolon the STScI WWW pages can help you convert your source flux from J magnitude or flux in Janskys into this flux unit.Table 3.12: 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.
3.10 Bright-Object Constraints
Several of the Scientific Instruments must be protected against over-illumination. Table 3.13 summarizes the safety restrictions by instrument. You should not propose observations which violate these guidelines. Non-linearity, saturation, or other temporary effects which may occur at substantially fainter limits than those identified below are described in the Instrument Handbooks.
Table 3.13: Bright-Object Constraints
3.11 Comments [Comments]
Information that cannot be made to conform to the required formats may be entered in a "Comments" line. Comment lines are not interpreted by the software, but are maintained in the data base and do appear on printouts of the forms.
3.12 Generic Targets List [Generic_Targets]
Generic targets are those that during Phase II can only be described in terms of astronomical characteristics or general location in the sky. This category is used only for Targets of Opportunity and parallel exposures.
For parallel exposures, both pure-parallel and coordinated-parallel (see Chapter 6: "Parallel Science Exposures"), the pointing is determined by the primary observation, and the specification of a generic target for the parallel exposure denotes a region within which the parallel aperture is expected to point. If the parallel pointing does not matter and the intent is simply to sample whatever the parallel aperture happens to detect, it is not necessary to define a generic target; instead the special target ANY should be used (see5.7 "Target Name [Target_Name]").
Note: Generic Target region coordinates are assumed to be in the J2000 reference frame.
3.12.1 Target Number(s) [Target_Number]
Generic targets should be given individual names and numbers just like fixed targets; however, it is possible to enter a range of target numbers associated with a single target name. If a range is specified, the number of targets must reflect the number of separate fields that will be observed. For example, if WFPC2 observations of 10 different fields, all named QSO-SURVEY-FIELD, are required for a quasar search, the value of the Target_Number keyword would be 1-10.
3.12.2 Target Name [Target_Name]
A descriptive name must be provided. If a name cannot be specified in advance, a provisional name should be supplied. When the actual observation is made, a more specific name will be added to the target designation. Either the provisional name or the updated name can then be used for archival searches (e.g., SN might be the provisional name, while SN-1995D might be the updated name). A unique target name must be assigned to each generic target.
3.12.3 Target Description [Description]
See 3.3 "Target Description [Description]".
3.12.4 Flux Data [Flux]
Flux data are not required for pure parallel observations of generic targets.
3.12.5 Comments [Comments]
See 3.11 "Comments [Comments]".
3.12.6 Generic Target Specifications
A way to specify generic celestial regions and target lists in a machine-readable fashion is described below, and should be used for the Generic Targets List. It is important that these instructions be followed in order for pure parallels with generic targets to be schedulable.
Two types of generic target specifications are permitted:
- Region generic targets: a celestial region specified in one of three coordinate systems
- Target Lists: lists of fixed or generic targets
The Selection Criteria column should use the syntax specified below whenever the selection criteria can be fully specified by a celestial region in one of the supported coordinate systems, or by a list of fixed or generic targets.
In all other cases a text description should continue to be provided after the "Other:" header.
Region Generic Targets
Three coordinate systems are supported:
- Equatorial: right ascension (RA) and declination (DEC)
- Galactic: Galactic longitude (LII) and Galactic latitude (BII)
- Ecliptic: ecliptic longitude (LAMBDA) and ecliptic latitude (BETA)
- "Rectangular" regions, i.e. bounded by latitude and longitude limits in the appropriate coordinate system
- Circular regions, specified as within some angular limit of a point specified in any of the three supported coordinate systems
- Polar caps or equatorial bands in any supported coordinate system
The following table provides examples of each of these types of region specifications. Note that the same rules for specifying RA and Dec apply as for fixed targets (See Equatorial Coordinates)
Note that for rectangular and circular regions, the syntax is identical to that of fixed target regions except that the indicator REGION is omitted, and galactic and ecliptic coordinates are allowed.
Target Lists
In some cases it may be desirable to specify as a Generic Target any of a list of Fixed Target positions or Generic Target regions. In this case the fixed targets should be provided as usual on the Fixed Target List, and the generic target regions should be specified as above on the Generic Target List. Then a new generic target can be defined with Selection Criteria specified by:
TARGETS = <target-number-list>
This will be taken to indicate that any of the targets in <target-number-list> are suitable as targets. Note that target numbers are required to be unique across all targets in a proposal, whether on the Fixed, Generic, or Solar System Target Lists.
This type of target is particularly useful when a known list of objects of interest is available, and it is desired to observe one of these objects with an imaging SI when a primary exposure with a spectrograph is positioned appropriately nearby.
3.13 Getting Coordinates Coordinated
Observers are responsible for the accuracy and appropriateness of the coordinates they supply and any changes made to them. Only you can determine where we should point HST.
Equinox is always a critical quantity when specifying coordinates. All astronomical coordinates change with time because of the precession of the Earth's rotation axis. Equinox specifies a time to which a coordinate system is tied. Thus J2000 refers to the location of an object in celestial coordinates for the coordinate reference frame of January 1, 2000.
Epoch is generally important only for objects that move. In particular, the epoch of a star's coordinates refers to a specific time at which the star is at that location. For example, the Hipparcos output catalogue lists coordinates of the brighter stars in the ICRS reference system (which is very nearly the same as J2000), and the coordinates themselves are for epoch 1991.25. The proper motions in the Hipparcos output catalogue are also epoch 1991.25, the midpoint of the mission. If you specify the epoch and equinox correctly, we can easily compute the location of an object at the time it will be observed with HST. (Note: An epoch is purely a time, and one of the form "J1991.25" is nonsensical.)
Proper motions sometimes cause problems. Units are especially crucial. The proper motion in Right Ascension (RA_PM) is to be listed in sec/yr, meaning seconds of time per year. If you have a value for RA_PM in arcsec per year, you need to divide it by 15 (to convert from arcsec to time sec), and to then divide by cos d because lines of constant RA converge in going to the poles. DEC_PM is almost always listed in arcsec/yr, which are the units needed for HST observing.
As we have emphasized above, we urge you to use signs on quantities, even when they are not required. A value of +0.060 for RA_PM, say, makes it clear that the sign has been considered. Just specifying 0.060 leaves ambiguity because sometimes observers forget a minus.
One more thing: be very careful if your target lies near a celestial pole. Many precession routines break down in this regime, and uncertainties in position can cause problems too. Also, patterns that you may execute with an instrument could cross the pole, leading to confusion in position. All these issues can be resolved, but careful attention is needed.
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