7.5.3.5: Data dictionary for DEIMOS ASCII table extension file

Those keywords which apply to all fibers and/or all objects in the table are stored in regular FITS header cards.

7.5.3.5.1: Primary keys in the tables

OBJ_PKEY (I6) {TNULL = ' 0'}

An unique index assigned to each object entry in the catalog tables. OBJ_PKEY will typically be sequential in the order that the objects were read from the specified catalogs. It has no permanent significance. It serves merely to permit associations between entries in different tables.

SLITLID (I4)

An unique index assigned to each slitlet in the slitmask tables.

7.5.3.5.2: General keywords

CTIME (A28)

Local time of preparation of the FITS header as given by the Unix standard C library strftime(3) function with the format "%a %Y %b %d %T %Z". It duplicates the information in the FITS DATE keyword. This is included solely for human readability, but it also helps alleviate the century problem with the FITS DATE keyword until such time as the FITS community standardizes the use of MJD- keywords.

CTIMEPNT (A28)

Intended time of the observation (UT) as given by the Unix standard C library strftime(3) function with the format "%a %Y %b %d %T UT". It duplicates the information in the MJD_PNT keyword. This is included solely for human readability.

7.5.3.5.3: Astrometric keywords

Planetary motions will not be handled. General relativistic effects may be omitted. Precession, nutation, and annual aberration will be applied. This information permits a target selection algorithm to operate.

7.5.3.5.3.1: Header or Table Keywords

RADECSYS (A8) {TNULL = 'NULL '}

As in the WCS draft standard. The frame of reference for the equatorial coordinate system used below. Reference frame system which applies to all RAs, DECs. (The values of the keywords EQUINOX and/or MJD_WCS are also required to specify the WCS fully.) For the user input catalogs it will typically be 'FK4' or 'FK5'.

EQUINOX (F13.6) [annum]

Date of the precessional epoch which applies to RADECSYS. According to the FITS WCS draft standard its value depends upon RADECSYS. When RADECSYS = 'GAPPT' the EQUINOX keyword is not required and the keyword MJD-OBS is required. In practice, if RADECSYS = 'GAPPT' EQUINOX will generally be the Julian epoch of the date of the observation. If RADECSYS is one of the other possibilities then EQUINOX applies to the catalog reference frame.

The existing use of this keyword at Keck is consistent with the WCS draft.

EPOCH [ DEPRECATED ]

Because of its imprecise specification in the original FITS papers and because of widespread difference in its interpretation this keyword has been deprecated by the WCS draft. It should NOT appear in DEIMOS FITS headers. Its function is fulfilled by MJD_WCS.

DATE-OBS (A8)

As in the FITS standard: 'dd/mm/yy'. This keyword will soon suffer from a century ambiguity. Because it does not contain the time of observation within the same FITS card it is also possible to encounter conditions where the observation time wraps around a day boundary and refers to a different date. The WCS draft recommends that this keyword be supplemented by the MJD-OBS keyword, which see.

MJD-OBS (F17.9) [TAI diem]

The DEIMOS system should not use this keyword in the sense intended by the WCS draft. See MJD_WCS.
According to the FITS WCS draft this is technically the Modified Julian Date of the observation; however, as actually used by the WCS draft this is a required coordinate system keyword when RADECSYS is either 'GAPPT' or 'FK4'. MJD-OBS is not required if RADECSYS is 'FK5'.
The FITS draft WCS standard requires that this keyword serve these multiple meanings and that it be measured in International Atomic Time (TAI). Because such a requirement makes it impossible for FITS to encode data acquired before 1955 there remains some debate over this aspect of the draft standard.
At Keck there is an existing implementation for this keyword which appears to use UTC rather than TAI.

MJD_WCS (F17.9) [diem] {TNULL = '-999999.000000000'}

This keyword is used in place of MJD-OBS when it is necessary to define the epoch at which a coordinate system is valid. The time evolution of WCS is slow enough that it is not necessary to require a precise time scale such as TAI. In the case of catalog positions with proper motions this is also the epoch from which the motions are to be applied.

DEISKYPA (F11.7) [degree]

The position angle of DEIMOS on the sky measured from North towards East. The orientation of the PA coordinate system has been chosen such that typical slitlets are parallel to SKY_PA.

DEIMOSPA (F11.7) [degree]

The position angle of DEIMOS w.r.t. the Nasmyth platform. PA is as specified in the engineering drawings of DEIMOS. DEIMOSPA is zero when the slitlets are vertical, and increasing DEIMOSPA causes increasing SKY_PA

7.5.3.5.3.2: Header Keywords

RA_PNT (F11.7) [degree]

The Right Ascension towards which the Keck II telescope axis was (intended to be) pointed. This is used because the RA of the telescope axis is not contained within any FITS image array.

DEC_PNT (F11.7) [degree]

The Declination towards which the Keck II telescope axis was (intended to be) pointed. This is used because the Dec of the telescope axis is not contained within any FITS image array.

HA_PNT (F11.7) [degree]

The hour angle towards which the Keck II telescope axis was (intended to be) pointed.

RADECPNT (A8) [as RADECSYS]

This keyword specifies the reference frame that applies to RA_PNT and DEC_PNT.

At Keck there is an existing keyword FRAME which is identical in spirit to RADECSYS. However, the permitted values for FRAME do not match those for RADECSYS. The DEIMOS software will have to translate these.

EQUINPNT (F13.6) [annum]

Date of precessional epoch appropriate for RADECPNT. This keyword specifies the reference frame that applies to RA_PNT and DEC_PNT.

MJD_PNT (F17.9) [diem]

MJD_PNT is included as an alternative to the WCS MJD-OBS keyword. This keyword is not required if RADECPNT = 'FK5', but is required to specify the epoch of the non-inertial coordinate systems when RADECPNT is 'FK4' or 'GAPPT'.

ASTR_LAT (F11.7) [degree]

The astrometric latitude of the telescope.

ASTRLONG (F11.7) [degree]

The astrometric longitude of the telescope.

ELEVAT (F7.1) [meter]

The elevation of the observatory above sea level.

GEOD_LAT (F11.7) [degree]

The geodetic latitude of the telescope.

GEODLONG (F11.7) [degree]

The geodetic longitude of the telescope.

GEODATUM (A20) [a list will have to be defined]

Name of the geodetic datum defining the terrestrial reference frame.

GEOIDHGT (F7.1) [meter]

The elevation of the local geoid above the geodetic reference ellipsoid.

REFWAVEL (F12.10) [meter]

The atmospheric refraction model is applied for a specific observation wavelength.

PRESSURE (F5.1) [mbar]

The atmospheric pressure at the observatory. This should be the actual pressure, not the pressure reduced to sea level.

TEMPERAT (F5.1) [Kelvin]

The ambient temperature at the observatory.

RELHUMID (F5.3)

The relative humidity at the observatory.

TROPTLAP (F7.5) [Kelvin/m]

The adiabatic temperature lapse rate in the troposphere above the observatory.

7.5.3.5.3.3: ASCII Table Column Keywords

SNAME (A32) [No embedded spaces]

A relatively short name of an object, preferably unique. Used to tag object in simulators and observation planning software -- names as short as possible reduce clutter.

RA_OBJ (F11.7) [degree]

Right Ascension of an object in the coordinate system specified by RADECSYS, EQUINOX, and MJD_WCS. The coordinate system keywords may be in the FITS header of the table or in other columns of the table.

HA_OBJ (F11.7) [degree]

Hour Angle of an object in the coordinate system specified by RADECSYS, EQUINOX, and MJD_WCS. The coordinate system keywords may be in the FITS header of the table or in other columns of the table.

DEC_OBJ (F11.7) [degree]

Declination of an object in the coordinate system specified by RADECSYS, EQUINOX, and MJD_WCS. The coordinate system keywords may be in the FITS header of the table or in other columns of the table.

PRIO (I4)

Priority of object. This is used in automated target assignment algorithms to determine the desirability of acquiring each object. The value 0 indicates an object potentially useful as a guide star. Values 1 through 98 indicates target objects in decreasing priority. The value 99 indicates an object intended to be used as the field center. Values other than these may take on special meanings to the assignment software.

MAG (F7.3) {TNULL = '-99.999'}

Magnitude of an object (in any consistent system). At present this is not used by the automated assignment algorithms.

NAME (A128)

Full name of an object including any commentary information

PM_RA (F9.4) [arcsec/(Julian annum)] {TNULL = '-999.9999'}

Proper motion in right ascension

PM_DEC (F7.3) [arcsec/(Julian annum)] {TNULL = '-999.9999'}

Proper motion in declination

PARALLAX (F7.4) [arcsec] {TNULL = '-9.9999'}

Parallax

RAD_VEL (F13.3) [m/s] {TNULL = '300000000.000'}

Radial velocity

CAT_FILE (A128)

Name of the file from which the data in the row were read

MAJAXIS (F10.7) [degree] {TNULL = '-9.9900000'}

Length of major axis of an extended object. May be used by the slitmask design process.

MINAXIS (F10.7) [degree] {TNULL = '-9.9900000'}

Length of minor axis of an extended object. May be used by the slitmask design process.

PA_AXIS (F11.7) [degree] {TNULL = '-99.9900000'}

Position angle of major axis of an extended object measured from North towards East. May be used by the slitmask design process.

7.5.3.5.4: DEIMOS hardware keywords

7.5.3.5.4.1: Header Keywords

[This list has not yet been specified]

7.5.3.5.4.2: ASCII Table Column Keywords

[keywords have not yet been defined]

7.5.3.5.5: Coordinate system transformation keywords

[These keywords have not yet been defined]