Note: Several pre-release versions are tagged within the ldd-hst repo on GitHub. These were written between 2020 and 2024 by Mark Showalter and Mitch Gordon. version 1.0 2024-04-15 - Initial release version version 1.0.1 2024-05-31 - Update ldd_version_id value, pds4_versions, and current IM version Contains attributes related to the observation exposure. Contains parameters specific to the Hubble Space Telescope. Contains attributes related to the HST instrument(s) used. Contains attributes related to the commanding and operations of an instrument. Contains attributes related to pointing and the observation target. Contains attributes related to the processing of the data after receipt. Contains attributes describing the HST observing program. Contains attributes related to the instrument tracking. Contains attributes related to wavelengths, filters, and gratings. This section contains the simpleTypes that provide more constraints than those at the base data type level. The simpleTypes defined here build on the base data types. This is another component of the common dictionary and therefore falls within the common namespace. The name of the aperture used for the observation. For HST data files, this is generally the value of FITS keyword APERTURE. Note that these values are instrument-specific; see the relevant HST Instrument Handbooks and Data Handbooks for further details. For FOC data, this attribute should be nil with nilReason = "inapplicable". The approximate full width of the spectral bandpass, in microns. For WFPC2 and STIS data files, this is the value of FITS keyword BANDWID, divided by 10,000 to convert units from Angstroms to microns. The value is not provided for other HST instruments. For other HST instruments, this attribute should be nil with nilReason = "inapplicable". This attribute indicates how pixels have been combined on the detector during readout. A value of 2 indicates that pixels have been combined in 2x2 squares; A value of 1 indicates that the detector was read out at full resolution. For many HST products this is the value of BINAXIS1 or BINAXIS2, whichever is larger. (HST binning modes need not be square, so this attribute cannot fully capture all the possibilities. Nevertheless, in practice, BINAXIS1 and BINAXIS2 are almost always equal.) Note that, for some HST products, the values of BINAXIS1 and BINAXIS2 can be found in the global FITS header; for others, it is found in the second header, which is the first data header. For WFPC and WFPC2, this attribute is derived from the value of MODE: - MODE = FULL -> binning_mode = 1 - MODE = AREA -> binning_mode = 2 For instruments that do not support binning options, the value of this attribute is always 1. The approximate central wavelength of the filter bandpass, in microns. For WFPC2 and STIS data files, this is the value of FITS keyword CENTRWV, divided by 10,000 to convert units from Angstroms to microns. The value is not provided for other HST instruments. For other HST instruments, this attribute should be nil with nilReason = "inapplicable". An abbreviated name or acronym for the specific channel of the HST instrument used for this observation. Here, "channel" refers to a distinct optical path used by one or more of the instrument's detectors. For HST instruments that do not have multiple channels, such as WFPC2, this attribute has the same value as the instrument_id attribute. A Boolean flag (true, false) indicating whether a coronagraph was used for this observation. For HST products, this attribute is generally derived from the value of the FITS keyword APERTURE. For ACS/HRC products, the coronagraph is in use if APERTURE is HRC-CORON1.8, HRC-CORON3.0, or HRC-OCCULT0.8. This also corresponds to the FITS keyword OBSTYPE being set to CORONAGRAPHIC. For STIS products, a coronagraph is in use if APERTURE is 52X0.2F1, 52X0.2F1-R, 50CORON, or begins with either "BAR" or "WEDGE". For NICMOS/NIC2 products, a coronagraph is in use if APERTURE is NIC2-CORON. This attribute is always false for HST instruments that do not have a coronagraph. This is the number of "cosmic ray split" or "CR-split" exposures. CR-split exposures are used because otherwise identical images can be used to filter out the frequent but random bright spots in images associated with cosmic rays hitting the detector. In HST products, this is the value of FITS keyword CRSPLIT. For HST products that do not have a value of CRSPLIT, then the value of this attribute is 1. This identifier specifies which of the detectors of this instrument and channel obtained the data found in this HST product. This parameter is repeated if multiple detectors were used. For instruments that do not have multiple detectors, this attribute occurs just once and has the same value as the channel_id attribute. The total duration of the instrument's light integration time, in seconds. For most HST data files, this is the value of FITS keyword EXPTIME; however, for some data files, it is the value of keyword TEXPTIME. Note that, for HST products that are the result of merging multiple exposures, this is the sum of the exposure times of the individual source products. This keyword indicates how exposure time was calculated and whether it was interrupted. For HST data files, this is the value of FITS keyword EXPFLAG. Common values are NORMAL (the observation completed as requested), INTERRUPTED, INCOMPLETE, EXTENDED, UNCERTAIN, INDETERMINATE, and PREDICTED. The name of the filter(s), grating(s), polarizer(s), or other optical elements used for the observation. If two or more are combined, then both names are given, separated by a plus sign "+". For WFPC2 products, this is the name of either FITS keyword FILTNAM1 or FILTNAM2, whichever is not blank. If neither is blank, the two values are combined using "+", with the shorter-wavelength filter (the filter name containing the smaller three-digit number) appearing first. For ACS products: - if FILTER1 is CLEAR1S or CLEAR1L and FILTER2 is CLEAR2S or CLEAR2L, the value is "CLEAR"; - otherwise, if FILTER1 is CLEAR1S or CLEAR1L, the value of FILTER2 is used; - otherwise, if FILTER2 is CLEAR2S or CLEAR2L, the value of FILTER1 is used; - otherwise, the values of the two filters are combined with "+". If a polarizer is used (FILTER1 or FILTER2 starts with "POL"), the name of the polarizer appears second; otherwise, the filter with the shorter center wavelength (the three-digit number inside the filter name) appears first. For STIS products, wavelength response is defined by a grating (FITS keyword OPT_ELEM) and the filter (FITS keyword FILTER). If the FILTER name is "Clear", the grating name appears alone; otherwise, the two values are appended, separated by a "+". For FOC products, this is constructed from the values of the FITS keywords FILTNAM1, FILTNAM2, FILTNAM3, and FILTNAM4. After omitting "CLEAR" values, the remaining values are sorted and concatenated with "+". For FOS products, this is the value of FITS keyword SPEC_1, which is found in the _shf.fits file. For GHRS products, this is the value of FITS keyword GRATING. For other HST instruments, this is the value of FITS keyword FILTER. For instruments that do not use filters, the value is "Not applicable". The commanded lock of the Fine Guidance Sensor during the observation. For HST data files, this is the value of FITS keyword FGSLOCK. Common values are: - FINE: Fine lock on guide stars using two Fine Guidance Sensors. This is the most accurate pointing option, within 0.2 to 1 arcsec. - COARSE: Until new flight software (version 9.6) came online in September 1995, if the guide star acquisition failed, the guiding dropped to COARSE track. - GYRO: This mode produces the least accurate absolute and relative pointing. Absolute pointing accuracy is about 2-50 arcsec and drift is 1-5 mas/sec. - FINE/GYRO: Fine lock on a guide star using one FGS to control the pitch/yaw of the spacecraft, while roll control is handled by the gyros. Absolute accuracies can range from 0.5-5 arcseconds, while error due to roll drift about the guide star would be ~ 1-2 mas/sec. - UNKNOWN: Check the jitter files to find out what happened during the observation. The commanded gain of the CCD, typically in units of electrons per DN. For WFPC2 data products, this is the value of FITS keyword ATODGAIN, either 7 or 15. For ACS, STIS, and WFC3, it is the value of FITS keyword CCDGAIN. For FGS data files and for HST instruments that do not have gain settings, this attribute should be nil with nilReason = "inapplicable". The number of gyros scheduled for the observation, 2 or 3. For HST data files, this is derived from the value of FITS keyword GYROMODE. A value of "3" or "T" indicates that three gyroscopes were used; a value of "2" indicates that two gyroscopes were used. However, some earlier HST products do not contain the keyword GYROMODE; these observations were all obtained using three gyroscopes. The name of the principal investigator for this HST program, in the form "last, name, first name, optional middle initial". The numeric identifier of the proposal or observing program, as assigned by the Space Telescope Science Institute. In HST data files, this is the value of FITS keyword PROPOSID. Data quality comments found in the FITS header of the data product. This attribute is filled in by the HST pipeline is populated if there are problems with the exposure. This attribute may be missing from older data products. In such cases, this attribute should be nil with nilReason = "missing". Data quality summary found in the FITS header of the data product, which can be populated by the HST pipeline if there are problems with the exposure. Possible values include "OK", "GSFAIL", "EXPSHORT", and "TDF-DOWN". If multiple values are provided, they are separated by semicolons. This attribute may be missing from older data products. In such cases, this attribute should be nil with nilReason = "missing". The target of the observation as defined by the principal investigator. In HST data files, this is the value of FITS keyword TARGNAME. Note that targets can be named arbitrarily in HST observing programs, so the meaning of this character string might not be obvious to the user. An acronym for the HST instrument. This is the value of FITS keyword INSTRUME. The operating mode of the instrument. For most HST data products, this is the value of FITS keyword OBSMODE. Consult the relevant HST handbooks for details about each mode. For FGS data files, this attribute should be nil with nilReason = "inapplicable". A 9-character identifier used to specify data products, or sometimes sets of associated data products, in MAST (the Mikulski Archive for Space Telescopes). In HST data files, this is the value of FITS keyword ROOTNAME. The name ASN_ID, for "association identifier" is also sometimes used. Values are always converted to lower case, if necessary. In MAST, you can find these products by entering this ID into the search box on this page: archive.stsci.edu/cgi-bin/dataset_lookup/ The nine characters can generally be interpreted as follows: - the first letter indicates the instrument, 'u' for WFPC2, 'j', for ACS, etc.; - the next three characters are unique to each HST program; - the next two characters indicate the HST visit within the program; - two characters generally increment for successive observations during the visit, using "base 36" where the characters used are digits 0-9 plus letters a-z; - the last character indicates a transmission method, and is generally not important for scientific purposes. However, if it is a digit, this indicates that this particular file is the result of merging two or more other HST observations from this visit. The value of keyword "OPUS_VER" found in the FITS header, if any. It is updated when data files are re-calibrated. This attribute is often missing from older data products. In such cases, this attribute should be nil with nilReason = "missing". The detailed information used for targeting HST. This includes information about standard targets such as planets, satellites, and larger asteroids. It can also include information used to determine offsets from the center of these bodies. Here are some sample values of this attribute: STD = JUPITER STD = EUROPA TYPE=TORUS, LONG=90, LAT=0, RAD-3.98E05 They are obtained from the FITS header of an observation's associated _shf.fits or _spt.fits file. They are the values of FITS keywords MT_LV_1, MT_LV_2, etc. Consult with HST documentation for detailed interpretations. If no MT_LV keywords appear in the FITS header, this attribute should be nil with nilReason = "inapplicable". A Boolean flag (true, false) indicating whether or not the telescope pointing was based on tracking a moving target. For HST data files, this is derived from the value of FITS keyword MTFLAG, which can have values of 1 or "T" for true or 0, "F", or "" for false. Keyword values used in the HST planning software to define a moving target. These often provide easier-to-interpret information about a solar system target. Examples are "PLANET JUPITER", "TORUS JUPITER", "SATELLITE EUROPA", and "ASTEROID 216". These values are obtained from the FITS header of the _shf.fits or _spt.fits file, given as values of keywords TARKEY1, TARKEY2, etc. If no TARKEY keywords appear in the FITS header, this attribute should be nil with nilReason = "inapplicable". The type of the observation: one of IMAGING, SPECTROSCOPIC, or TIME-SERIES. IMAGING indicates that a 2-D image with two spatial axes was obtained. SPECTROSCOPIC indicates that one of the axes of the data array is related to wavelength. TIME-SERIES indicates that one of the axes is sampling time. For many HST data files, this is the value of FITS keyword OBSTYPE. Where OBSTYPE does not appear, this value depends on other information. - All ACS, NICMOS, WFC3, WFPC, and WFPC2 observations are IMAGING. - All COS, FOS, and GHRS observations are SPECTROSCOPIC. - All HSP observations are TIME-SERIES. - For FOC, the observation_type depends on the value of FITS keyword OPMODE: IMAGING if OPMODE is "ACQ" or "IMAGE"; TIME-SERIES of OPMODE is "OCC"; SPECTROSCOPIC if OPMODE is "SPEC". Note that, for ACS/HRC, the FITS keyword OBSTYPE can have a value of CORONAGRAPHIC. In such cases, the value of this attribute is IMAGING and the coronagraph_flag attribute indicates whether the coronagraph was used. This attribute indicates approximate spatial size of one pixel in the data product, in units of arcseconds per pixel. For a few HST data products, this is the value of FITS keyword PLATESC. For other HST instruments, we provide the value if it can be readily determined. In cases where a product contains data from detectors with different plate scales, it is the smallest value. For non-imaging instruments, this attribute should be nil with nilReason = "inapplicable". The name of the proposed aperture used for the observation. For some data files, this is the value of FITS keyword PROPAPER. It is needed because the proposed aperture need not be the same as the aperture actually used. If the FITS keyword PROPAPER is missing or has a blank value, the value of FITS keyword APERTURE is used instead. For FOC data, this attribute should be nil with nilReason = "inapplicable". This is the number of repeated exposures as commanded for the HST instrument. For HST products, this is the value of FITS keyword NRPTEXP. For instruments that do not support repeated exposures, this attribute has a value of 1. The approximate spectral resolution of this data product, in microns. For STIS data files, this is the value of FITS keyword SPECRES, divided by 10,000 to convert units from Angstroms to microns. For other HST instruments, this attribute should be nil with nilReason = "inapplicable". A Boolean flag (true, false) indicating whether or not this data product was obtained using a subarray of the detector. For HST data files, this is derived from the value of FITS keyword SUBARRAY, which can have values of "T" or 1 for true or "F" or 0 for false. For instruments that do not support subarrays, the value of this attribute is always false. The identifier of the detector(s) used to define the targeting of this observation. For instruments with multiple detectors, this attribute indicates the one that is most likely to contain the intended target. When an observation was planned to employ more than one detector to encompass the target, this attribute will have multiple values. For instruments that do not have multiple detectors, this attribute will have a single value equal to that of channel_id and detector_id. For WFPC2, this attribute is derived from the value of the aperture: - PC1 for apertures PC1, PC1-FIX, POLQP15P, FQCH4P15; - WF2 for apertures WF2, WF2-FIX, FQUVN33, POLQN33, POLQN18, POLQP15W, FQCH4NW2, FQCH4N33; - WF3 for apertures WF3, WF3-FIX, FQCH4NW3, F160BN15; - WF4 for apertures WF4, WF4-FIX, FQCH4NW4; - All four for apertures WFALL, WFALL-FIX; - PC1 and WF3 for aperture FQCH4N15.** These are found in in Table 3.14 of the WFPC2 Instrument Handbook, Version 10.0. Note that they often appear in FITS lab (**Note: aperture FQCH4N15 was targeted relative to PC1, but was often used to position the methane 0.89 micron quad filter atop the WF3 chip as well.) For ACS/WFC, most aperture values begin with either "WFC1" or "WFC2", which indicates which of the detectors was used for targeting. Apertures WFCM, WFC, WFC-FIX, and WFCENTER are associated with both. For WFC3/UVIS, most aperture values begin with either "UVIS1" or "UVIS2", which indicates which of the detectors was used for targeting. Apertures UVIS, UVIS-CENTER, UVIS-FIX, UVIS-IR-FIX, G280, and G280-REF are associated with both detectors. The targeting of the UVIS-QUAD, UVIS-QUAD-FIX, and UVIS-QUAD-SUB apertures is are determined based on the value of the selected quad filter: UVIS1 for filters FQ378N, FQ387N, FQ437N, FQ492N, FQ508N, FQ619N, FQ674N, FQ750N, FQ889N, and FQ937N; UVIS2 for filters FQ232N, FQ243N, FQ422M, FQ436N, FQ575N, FQ634N, FQ672N, FQ727N, FQ906N, and FQ924N. (See Table 6.4 of the WFC3 Instrument Handbook.) For WFPC, this is derived from the aperture value: - WF1 for aperture W1; WF2 for aperture W2, etc. - PC5 for aperture P5; PC6 for aperture P6, etc. For COS/FUV, this attribute will always match the value(s) of detector_id. The two-digit "base 36" code identifying the visit number for this observations. An individual visit can comprise one or more orbits of HST around the Earth.