DEEP2 DR3 Slitmask Info Primer

The information below is an attempt to document the DEIMOS slitmask design information that is housed in the "bintabs" files, as generated by the spec2d reduction pipeline and included in DR3. In addition to detailing the contents of each binary table (or bintab), some IDL code is provided to link the various tables.

The "bintabs" file for a given slitmask (e.g., 1243.bintabs.fits) details the position and dimension (PA, length, width, etc.) of each slitlet, the objects placed in each slitlet, and much more. This information is housed in the following binary tables:

(1) ObjectCat
(2) MaskDesign
(3) DesiSlits
(4) SlitObjMap
(5) MaskBlu
(6) BluSlits
(7) Observers
(8) PhotCat

With the exception of the PhotCat table, this slitmask information is provided as output on each DEIMOS science frame. The DEEP2 bintabs files are simply the manner in which the DEEP2 spec2d pipeline passes this info forward in the reduction process. For terse descriptions of each table, see below or follow the links above.

ObjectCat

The ObjectCat table gives info about the objects targeted on the slitmask. It can be read in IDL like so:

IDL> objcat = mrdfits('1243.bintabs.fits', 1)

The tags for the structure (objcat) follow the format:

OBJECTID	LONG	214942
OBJECT	STRING	'120101363 '
RA_OBJ	DOUBLE	214.21797
DEC_OBJ	DOUBLE	52.407818
RADECSYS	STRING	'FK5 '
EQUINOX	DOUBLE	2000.0000
MJD_OBS	DOUBLE	0.000000
MAG	FLOAT	22.1820
PBAND	STRING	'R '
RADVEL	DOUBLE	0.0000000
MAJAXIS	FLOAT	0.00000
OBJCLASS	STRING	'PROGRAM_TARGET '

with the following definitions:

OBJECTID:

an object id number assigned by the DEIMOS slitmask software (i.e., not the DEEP2 8-digit object ID). This tag is useful for linking this table to other tables in the "bintabs" file, such as the SlitObjMap.

OBJECT:

The 8-digit DEEP2 ID number as assigned in the DEEP2 photometry catalogs (or pcats).

RA_OBJ:

the RA for the object in decimal degrees.

DEC_OBJ:

the Dec for the object in decimal degrees.

RADECSYS:

the RA DEC system used.

EQUINOX:

the reference epoch for the RA, DEC info.

MJD_OBS:

an unutilized tag.

MAG:

the magnitude for the object in the CFHT R band, taken from the DEEP2 photometry catalog.

PBAND:

the passband corresponding to the magnitude (always the CFHT R band).

RADVEL:

an unused tag.

MAJAXIS:

not set.

OBJCLASS:

identifies the object (or slit) as being assigned to one of the following:

Program_Target -	a science target
Alignment_Star -	an alignment star

Note that DEEP2 uses sky-only slits, in which no object is positioned. These slits are still listed as Program_Targets, but they can be indentified based on their narrower slit widths (0.7" versus 1").

MaskDesign

The MaskDesign table gives general info about the DEIMOS slitmask:

DESID	LONG	1519
DESNAME	STRING	'DEEP2.1HS.1243 '
DESPID	LONG	5
DESCREAT	STRING	'Marc Davis (UC) via Dsim '
DESDATE	STRING	'2004-03-19T09:15:00'
DESNSLIT	LONG	156
DESNOBJ	LONG	269
PROJNAME	STRING	'DEEP2-1HS '
INSTRUME	STRING	'DEIMOS ;
MASKTYPE	STRING	10.04573
RA_PNT	DOUBLE	214.44726
DEC_PNT	DOUBLE	52.457268
RADEPNT	STRING	'FK5 '
EQUINPNT	FLOAT	2000.00
PA_PNT	DOUBLE	41.141777
DATE_PNT	STRING	'2004-04-11T00:00:00.000'
LST_PNT	FLOAT	-22.5000
UID	INT	13
STAMP	STRING	'2004-03-19T11:34:00'

with the following definitions:

DESID:	an ID number assigned to the slitmask design.
DESNAME:	a name given to the design (typically DEEP2.1HS. plus the 4-digit slitmask #).
DESPID:	not used.
DESCREAT:	the man (his institution) and the software responsible for the mask design.
DESDATE:	the date on whoch the mask was designed (i.e., submitted to the DEIMOS slitmask milling system).
DESNSLIT:	the number of slitlets on the slitmask.
DESNOBJ:	the number of objects in the source catalog that fall on the slitmask, although not necessarily targeted with slitlets??
PROJNAME:	the name of the project (here, DEEP2).
INSTRUME:	the instrument used --- this hopefully says DEIMOS!
MASKTYPE:	not used.
RA_PNT:	RA at which to point Keck II when observing the slitmask.
DEC_PNT:	DEC at which to point Keck II when observing the slitmask.
RADEPNT:	the RA/DEC system used.
EQUIPNT:	the epoch for the RA/DEC.
PA_PNT:	the position angle (E of N in degrees) for the slitmask.
DATE_PNT:	possibly the date that the slitmask was milled.
LST_PNT:	not really sure to what time this LST corresponds.
UID:	not used.
STAMP:	a stamp corresponding to the design date.

DesiSlits

The DesiSlits table gives useful info about each of the slitlets on the DEIMOS slitmask:

DESLITID	LONG	165128
DESID	LONG	1519
SLITRA	DOUBLE	214.21846
SLITDEC	DOUBLE	52.408156
SLITTYP	STRING	'P'
SLITLEN	FLOAT	8.74600
SLITLPA	FLOAT	41.1420
SLITWID	FLOAT	1.0000
SLITWPA	FLOAT	131.142
SLTINAME	STRING	'000 '

with the following definitions:

DESLITID:	an ID number assigned to the slitlet. Again, this is useful for linking this table with others such as the OobjectCat (i.e., allowing for matching of objects to their slitlets).
DESNAME:	an ID number assigned to the slitmask.
SLITRA:	the RA of the slitlets.
SLITDEC:	the DEC of the slitlets.
SLITTYP:	the type of slitlet: 'P' for program target and 'A' for alignment star.
SLITLEN:	the length of the slitlet in arcseconds.
SLITLPA:	the slitlet position angle (E of N in degrees). Note that this value is given in absolute terms and NOT relative to the PA of the slitmask.
SLITWID:	the width of the slitlet in arcseconds.
SLITWPA:	an unused tag.
SLITNAME:	the slit # (the same # as used by the DEEP2 spec2d reduction code and given in the filenames for the DR3 1-d and 2-d spectra).

SlitObjMap

The SlitObjMap table gives more useful info for each slitlet on the slitmask and is the key to linking the other tables to each other:

DESID	LONG	1519
OBJECTID	LONG	214942
DSLITID	LONG	165128
TOPDIST	FLOAT	5.99000
BOTDIST	FLOAT	2.75600

with the following definitions:

DESID:	an ID number assigned to the slitmask design.
OBJECTID:	the DEEP2 8-digit object ID number (as also given in the ObjectCat). Thus, this tag can be used to link the two tables.
DSLITID:	an ID number attached to the slitlets on the mask. This table is thus the one that links object to slit!!!
TOPDIST:	the projected position of the object given with respect to the top of the slitlet (in arcseconds).
BOTDIST:	same as TOPDIST, but from the bottom of the slitlet.

MaskBlu

The MaskBlu table gives general info about the DEIMOS slitmask:

BLUID	LONG	1519
DESID	LONG	1519
BLUNAME	STRING	'DEEP2.1HS.1243 '
BLUID	LONG	13
BLUCREAT	STRING	'DSIMULATOR -- 02Jul25 '
BLUDATE	STRING	'2004-03-19T09:15:00'
LST_USE	LONG	12.7910
DATE_USE	STRING	'2004-04-11T00:00:00'
TABLEID	LONG	1
REFID	LONG	0
ATMTEMPC	FLOAT	0.00000
ATMPRES	FLOAT	520.000
ATMHUMID	FLOAT	0.400000
ATMTLAP	FLOAT	0.00650000
REFWAVE	FLOAT	750.000
DISTID	LONG	0
GUINAME	STRING	'1243.E '
MILLSEQ	STRING	' '
STATUS	INT	2
LOC	STRING	' nbsp '
STAMP	STRING	'2004-03-19T11:34:00'

with the following definitions:

BLUID:	the ID number assigned to the slitmask design.
DESID:	the ID number assigned to the slitmask design.
BLUNAME:	a name given to the design (typically DEEP2.1HS. plus the 4-digit slitmask #).
BLUPID:	not used.
BLUCREAT:	the software used to create the mask design.
BLUDATE:	the date on which the mask design was submitted.
LST_USE:	the local sidereal time when used.
DATE_USE:	the date on which the mask was observed (or used).
TELEID:	a telescope ID #
REFRID:	not used.
ATMTEMPC:	the temperature --- not set.
ATMPRES:	the atmospheric pressure.
ATMHUMID:	the humidity.
ATMTLAP:	???
REFWAVE:	???
DISTID:	not used.
GUINAME:	the name that the slitmask was given within the milling system and the DEIMOS dashboard GUI.
MILLSEQ:	empty.
STATUS:	not used.
LOC:	empty.
STAMP:	a stamp corresponding to the design date.

BluSlits

The BluSlits table gives info about the position of the slitlets on the DEIMOS slitmask:

BSLITID	LONG	162706
BLUID	LONG	1519
DSLITID	LONG	165128
SLITX1	LONG	-355.26500
SLITY1	DOUBLE	63.745000
SLITX2	DOUBLE	-361.70000
SLITY2	DOUBLE	63.849000
SLITX3	DOUBLE	-361.69800
SLITY3	DOUBLE	64.580000
SLITX4	DOUBLE	-355.26400
SLITY4	DOUBLE	64.476000
BAD	LONG	0

with the following definitions:

BSLITID:	the ID number assigned to the slitmask design.
BLUID:	the ID number assigned to the slitmask design.
DSLITID:	a name given to the design (typically DEEP2.1HS. plus the 4-digit slitmask #).
SLITX1 - SLITX4:	the positions of the 4 corners (X1 - X4) of each slitlet in the x-direction.
SLITY1 - SLITY4:	the positions of the 4 corners (Y1 - Y4) of each slitlet in the y-direction.

Observers

The Observers table gives reference info for the observer/designer of the slitmask...no need to explain this one.

PhotCat

The PhotCat table gives info from the DEEP2 photometry catalog. The tags are explained in the DR1 photometry primer.

Linking the Bintabs...

The IDL routine link_bintabs is provided to link the various binary tables held within a bintabs file. The IDL function takes a single argument, a string specifying a bintabs file and returns an IDL structure containing much of the useful information from the bintabs file. The syntax is as follows:

out = link_bintabs('1243.bintabs.fits')

The output structure will should contain the following info:

IDL> help, out, /str
** Structure <22e918>, 33 tags, length=35248, data length=35232, refs=1:

OBJECTID	LONG	Array[nobj]
DSLITID	LONG	Array[nobj]
DESID	LONG	1519
OBJECT	STRING	Array[nobj]
RA_OBJ	SOUBLE	Array[nobj]
DEC_OBJ	DOUBLE	Array[nobj]
RADECSYS	STRING	Array[nobj]
RA_PNT	FLOAT	214.44726
DEC_PNT	FLOAT	52.457268
RADEPNT	STRING	'FK5 '
EQUIPNT	DOUBLE	Array[nobj]
PA_PNT	DOUBLE	41.141777
DATE_PNT	STRING	'2004-04-11T00:00:00.000'
SLITRA	DOUBLE	Array[nobj]
SLITDEC	DOUBLE	Array[nobj]
SLITTYP	DOUBLE	Array[nobj]
SLITLEN	DOUBLE	Array[nobj]
SLITLPA	DOUBLE	Array[nobj]
SLITWID	FLOAT	Array[nobj]
SLITNAME	STRING	Array[nobj]
TOPDIST	FLOAT	Array[nobj]
BOTDIST	FLOAT	Array[nobj]
SLITX1	DOUBLE	Array[nobj]
SLITY1	DOUBLE	Array[nobj]
SLITX2	DOUBLE	Array[nobj]
SLITY2	DOUBLE	Array[nobj]
SLITX3	DOUBLE	Array[nobj]
SLITY3	DOUBLE	Array[nobj]
SLITX4	DOUBLE	Array[nobj]
SLITY4	DOUBLE	Array[nobj]

where nobj is the number of objects on the slitmask. Note that the number of slitlets on the slitmask will often be less than nobj, since DEEP2 sometimes places two objects in a single slit. In the case of mask 1243, there are 157 objects (i.e., nobj = 157), with 156 slitlets. In this specific case, there are two repeated numbers in the SLITNAME entry in the linked IDL structure.

created by M. Cooper
last updated 2007aug01