| WFPC2 SYNPHOT TABLES: |
Jan 1999 (Previous Updates: August 1995, June 1996, May 1997)
S. Baggett
The SYNPHOT package in STSDAS has three primary uses: 1) to provide
photometric calibration information, which is inserted by the
calibration software into image headers: (keywords photflam, photbw,
etc), 2) to estimate exposure times for HST observations and, 3) to use
synthetic photometry to calibrate observations.
This readme file addresses:
The WFPC2 time-dependent photometric calibration tables (wfpc2_cont*)
in SYNPHOT have been updated. Note that the contamination tables are
not used by calwp2 but must be invoked manually in SYNPHOT.
Updates were based upon an analysis of the WFPC2 stellar photometric
monitoring data obtained over the last four years. The new analysis
showed that, for bright targets, (1) the long-term photometric
throughput continues to be quite stable: fluctuations are ~2% or less
peak-to-peak over 4 years in filters longwards of and including F336W,
(2) the UV throughput has gradually evolved, that is, the clean count
rates (immediately after the decons) have increased over the 4 years in
some filters, e.g., F160BW by ~12% in the PC, and F170W by ~9%, while
decreasing slightly in others, e.g., F255W by ~3% and, (3) the
contamination growth rates have slowed slightly for the UV filters,
e.g., ~1% per day to 0.5% per day in F160BW on the PC. More details on
the SYNPHOT contamination table update can be found in
ISR 98-03.
Based upon calibration data of grw+70d5824, all UV filters shortward of
F439W were updated as well as some of the more frequently-used
broadband filters redward of F439W (F450W, F555W, F606W, F675W, F702W,
F785LP, F791W, F814W, F850LP, and F1042M). Changes were installed in
the OPUS pipeline May 16,1997. The changes are described in detail in
ISR 97-10.
In addition, a couple of bugs in the tables (which had been effectively
canceling each other out) were corrected: the WFPC2 obstruction factor
and the aperture correction are now included in the wfpc2_optics table.
In previous versions, the SYNPHOT tables were intended to be for 0.5"
data, but due to the missing obscuration factor, mimicked data measured
at 3". The new wfpc2_optics table was generated by multiplying its
throughput by 0.9108 (WFPC2 obstruction) and dividing by the aperture
correction (10^(-apcorr/2.5). NOTE: aperture correction used at all
wavelengths was 10%.
With a few exceptions, changes to non-UV filter modes were relatively
minor: generally ~1-2% or less (F785LP, F850LP, and F1042M were more:
~1-4%, ~1-6$, and ~2-15% for them respectively, depending on the
chip.). The UV filters required somewhat larger changes to bring
SYNPHOT into agreement with the observations, ranging from ~2% (e.g.,
F255W and F300W) to ~5% (F170W, F218W) to 10% or more (F160BW, F375N).
Any filters not updated at this time will be checked with future
observations (planned for summer of 1997) and updated if necessary.
Based upon calibration data of grw+70d5824, the methane and [OII]
filter tables were updated to yield improved SYNPHOT countrate
predictions when compared to the observations.
Tables affected were: filter curves for fqch4p15, fqch4n15, and fquvn*.
Note that the unrotated methane quad (fqch4n) was not changed; it will
be updated when additional calibration data becomes available. The new
tables are available for ftp retrieval; changes will take effect in the
routine pipeline end of June 1996. Filter tables were multiplied by:
A major WFPC2-related update was done in July 1995 and all files are
available for ftp retrieval; the changes will take effect in the
routine PODPS pipeline in Aug 1995. The new tables bring SYNPHOT into
general agreement with the results presented in the WFPC2 Instrument Handbook
(Version 3.0, June 1995) and in Photometric Performance and Calibration
of WFPC2 by Holtzman et al.
(PASP 107,1065).
Tables affected include the wfpc2_optics, dqe curves, contamination
correction tables, and many, but not all, filter transmissions (see
Holtzman paper).
The pipeline calibration software calwp2
uses the wfpc2-related SYNPHOT tables to populate the photometric
keywords in the calibrated header (c0h); the data itself is not
changed. The keywords used are:
The graphtab/comptabs names used in the pipeline are based on the time
of installation; for the July 1995 update, the GRAPHTAB and COMPTAB
names should be f7* or later (f=year since 1980, 7 is month, d is day).
Note: other instruments use the graph and comp tables as well, so there
may be new tables installed in the pipeline after July 1995 but these
will contain the same wfpc2-related data as the f7d* tables above. Any
future wfpc2 changes will be documented in this readme file.
The c0h header file from the pipeline contains HISTORY keywords which
provide a detailed list of the SYNPHOT table versions that were used to
populate the photometric keywords, for example, the SYNPHOT HISTORY
keywords for PC1 in an f300w observation:
If you've ascertained from the c0h file (via GRAPHTAB and COMPTAB names
or HISTORY records or getref ) that the most recent SYNPHOT tables were not
used, you may wish to recalibrate. This can be done by either using
calwp2 after editing the appropriate keywords (DOPHOTOM, GRAPHTAB,
COMPTAB) or by running SYNPHOT directly. If you're already planning on
executing calwp2 for other reasons, the first method may be easier; if
you don't need to run calwp2, the SYNPHOT task bandpar may be used in
conjunction with the PHOTMODE header keyword to obtain the values that
would have gone into the rest of the photometric keywords. For the
f300w example above, retrieve photmode keyword with hedit, then run
bandpar. To differentiate the iraf commands from output, we've
prefaced command lines with the IRAF prompt symbol ">".
If narrowband filters were used, we recommend you generate your own
wavetab (the default stepsize is sometimes not small enough for some of
the narrower filters). The wavelength table can be constructed with
the SYNPHOT task "genwave" and used as the wavetab in the bandpar
expression; for example:
The main SYNPHOT routine for estimating exposure times is calcphot,
which is a very powerful and versatile task; below is just one example
of the many ways in which it may be used. You will need to have the
SYNPHOT tables available as well as any spectra that you are interested
in using. All the tables in the cdbs directories are in the form of
binary STSDAS tables.
Some of the spectral directories are:
The Appendix B of the SYNPHOT User's
Guide discusses all the SYNPHOT tasks in more detail and the
Appendices discuss the available spectra in more detail.
If the online spectra aren't sufficient, you may also generate your
own, for example, by using the SYNPHOT calcspec task, which can create
blackbody, powerlaw, and rectangular, to name a few. Type "help
calcspec" at the iraf prompt or see the
SYNPHOT User's Guide for more
details about its capabilities.
Once you have the spectra, calcphot can be used to obtain a countrate:
To have calcphot include the contamination effect, you must add the
cont# keyword to the obsmode. The STSDAS epoch task converts date to
Modified Julian Date, MJD. For example, the June 1995 decon occurred
June 2; to compute the decrease in throughput 21 days after a typical
decon, run calcphot using MJD for June 24:
More details on exposure time estimation can be found in the
Frequently Asked Questions about WFPC2 Exposure Times. Also online
is the WFPC2 Exposure Time Calculator.
To run SYNPHOT for wfpc2-related observations, you will need the 2
general tables (graph and comp tables), the wfpc2-related tables, and
any necessary spectral data tables (discussed in section on Estimating
Exposure Times, above).
The graph and comp tables (tmg, tmc) can be found in:
The graphtab entries correlate keywords from the observation mode with
component table rootnames; generally these do not change much, unless
new observation modes are added. For example, the "f1042m" keyword in
an observation mode will point to a component table rootname:
"wfpc2_f1042m".
The comptab entries correlate the component table rootname from
graphtab with specific filenames; for the f1042m example, the component
table rootname "wfpc2_f1042m" points to the file
"crwfpc2comp$wfpc2_f1042m_003.tab", where the name preceding the '$'
refers to the directory, and the name after refers to the specific file
SYNPHOT will use for an f1042m observation.
WFPC2-related tables consist of:
Note that all SYNPHOT tables are in binary STSDAS format, readable only
with tasks in the IRAF/STSDAS ttools and SYNPHOT packages. The history
and version of each new table is included in the table header, which
can be viewed with, for example, tdump:
or from the direct link
www.stsci.edu/ftp/cdbs/cdbs2/comp/
and subdirectories therein (
wfpc2,
ota, etc).
To retrieve via FTP, for example:
Assuming that you already have IRAF and STSDAS running at your site (if
not, please see References), once back on your system, unpack the
tarfile:
SYNPHOT User's Guide from STSDAS Documentation page.
STSDAS FTP site for SYNPHOT tables.
Atlases of model and observed spectra for use in SYNPHOT.
WFPC2 Documentation for further information on exposure time estimations and WFPC2 Photometry
STSDAS homepage, for software, documentation, and user support.
WFPC2 Homepage for the top-level WFPC2 Instrument Page.
STSCI Homepage for the top-level STScI page.
The STSDAS SYNPHOT package currently contains the following tasks (type
"help synphot" at the iraf prompt):
hst_calib.synphot
Menu for the package stsdas.hst_calib.synphot:
from mtab
subdirectory (most recent table with wfpc2-related changes)
Introduction
History of WFPC2-Related SYNPHOT Updates
SYNPHOT Tables and Pipeline Processing
Updating Calibrated Pipeline Files with New SYNPHOT Results
Estimating Exposure Times
Summary of SYNPHOT Tables
Retrieving the Tables
Setting Up Your Environment to Run SYNPHOT
References
Appendix A: List of Tasks in the SYNPHOT Package
Appendix B: List of All WFPC2-related SYNPHOT Tables
History of SYNPHOT Table Updates
date reason for update
Jan 1999 UV contamination tables updated
May 1997 all UV modes updated, some redward ones as well
June 1996 minor update, affects fqch4p15, fqch4n15, fquvn* only
July 1995 major update, all obsmodes affected
End of 1993 prelaunch population of tables
Jan 1999 Update
May 1997 Update
June 1996 Update
filter+aperture FOV wavelength scaled by
fquvn,wf2 wf2 3986 0.913
fquvn,wf3 wf3 3916 0.865
fquvn,wf4 wf4 3839 0.938
fquvn33,fquvn33 wf2 3763 1.038
fqch4n33,fqch4n33 wf2/3 6193 0.949
fqch4n15,fqch4n15 pc1 6193 0.949
fqch4n,fqch4w3 wf3 8929 0.698
fqch4p15,fqch4p15 pc1 8929 0.698
July 1995 Update
SYNPHOT Tables and Pipeline Processing
keyword description example
PHOTMODE Photometry mode WFPC2,1,A2D7,F300W,,CAL
PHOTFLAM Inverse sensitivity 5.926793E-17
PHOTZPT Zero point -21.1 mag
PHOTPLAM Pivot wavelength 2990.016 Å
PHOTBW RMS bandwidth of the filter 324.5099 Å
GRAPHTAB HST graphtable used in pipeline f7d1401pm.tmg
COMPTAB HST comptable used in pipeline f7d1400mm.tmc
The PHOTFLAM is the flux conversion factor, the flux that produces 1
count/sec in the passband. These are all group keywords (accessible
via STSDAS task hedit or imhead, for example), so that there is a set
for each chip used.
HISTORY The following throughput tables were used:
crotacomp$hst_ota_005.tab,
HISTORY crwfpc2comp$wfpc2_optics_003.tab,
crwfpc2comp$wfpc2_f300w_003.tab,
HISTORY crwfpc2comp$wfpc2_dqepc1_002.tab,
crwfpc2comp$wfpc2_a2d7pc1_002.tab,
HISTORY crwfpc2comp$wfpc2_flatpc1_001.tab
If you are using STSDAS SYNPHOT software directly, the showfiles task
provides a quick check of the tables that would be used by SYNPHOT
tasks. For the example above:
> showfiles wfpc2,1,a2d7,f300w,cal
crotacomp$hst_ota_005.tab
crwfpc2comp$wfpc2_optics_003.tab
crwfpc2comp$wfpc2_f300w_003.tab
crwfpc2comp$wfpc2_dqepc1_002.tab
crwfpc2comp$wfpc2_a2d7pc1_002.tab
crwfpc2comp$wfpc2_flatpc1_001.tab
where "crotacomp" and "crwfpc2comp" are the directories containing the
named tables. Updating Calibrated Pipeline Files with New SYNPHOT Results
> hedit *101t.c0h[1] photmode .
u2ou0101t.c0h[1],PHOTMODE = WFPC2,1,A2D7,F300W,,CAL
> bandpar wfpc2,1,a2d7,f300w,cal output="" photlist=all wavetab=""
# OBSMODE URESP PIVWV BANDW
wfpc2,1,a2d7,f300w,cal 5.9268E-17 2990. 324.5
# OBSMODE TPEAK EQUVW RECTW
wfpc2,1,a2d7,f300w,cal 0.0028794 2.4609 854.65
# OBSMODE EMFLX REFWAVE TLAMBDA
wfpc2,1,a2d7,f300w,cal 5.8289E-14 3010.7 0.0025022
The output is defined in detail in the online bandpar help and in the
SYNPHOT User's Guide; the bandpar output is related to the photometry
header keywords:
PHOTFLAM == URESP
PHOTPLAM == PIVWV
PHOTBW == BANDW
PHOTZPT == is always -21.1 mag
For record-keeping, if you wish to update your headers with the bandpar
results, the stsdas task hedit is best:
> hedit u2ou0101t.c0h[1] photflam value="5.9268E-17"
> hedit u2ou0101t.c0h[1] photplam value="2990."
etc.
> genwave output=wave.tab minwave=1000.
maxwave=10000. dwave=1.
> bandpar wfpc2,1,a2d7,f300w,cal output=""
photlist=all wavetab=wave.tab
None of the SYNPHOT tasks will change the wavetab in any way, so once
you've generated one, it can be used for all of your SYNPHOT
computations.Estimating Exposure Times
calspec spectra of HST flux calibration targets
bkmodels stellar flux spectra calculated by Kurucz and Buser
bpgs Bruzual et al. spectral (extension of Gunn/Stryker optical atlas)
bz77 Bruzual stellar spectra
gunnstryker from observations of Gunn and Stryker (ApJSupp 52,121)
jacobi from observations of Jacoby et al (ApJSupp 56,257)
All spectra are accessible via the CDBS
pages or via anonymous ftp to ftp.stsci.edu. Each of these
directories have README files, with short listings of table names,
objects, and spectral types. Before retrieving all tables, you may
wish to view these README files to select only certain spectra. For
example, after ftp'ing to stsci.edu anonymous:
cd cdbs/grid/bpgs
get README
!page README
shows:
# Spectral types are taken from Gunn and Stryker
# paper, ApJ Supplement 52:121-153, 1983 June
#Filename_________Target__________Type
bpgs_1.tab 9-SGR O5
bpgs_2.tab 9-SGE O8F
bpgs_3.tab HR8023 O6
bpgs_4.tab BD-01D935 B1V
...
Remember to type "binary" at the ftp prompt before retrieving any of
these tables, since these are STSDAS tables.
> calcphot wfpc2,1,a2d7,f300w spectrum="grw_70d5824_003.tab"
form=counts
Mode = band(wfpc2,1,a2d7,f300w)
Pivot Equiv Gaussian
Wavelength FWHM
2990.012 764.1473 band(wfpc2,1,a2d7,f300w)
Spectrum: /tib/cdbs/calspec/grw_70d5824_003.tab
VZERO (COUNTS s-1 hstarea-1)
0. 2275.741
Note that if you do not specify an a2d gain, the result is in
electrons; the output reads "(COUNTS s-1 hstarea-1)" regardless of
whether the result is in electrons or DN. Note, too, that the July
1995 SYNPHOT tables already contain the flatfield component in the
filter tables, so adding "cal" to the obsmode will not change the
countrate.
> epoch "june 24,1995" qual="" dmy_style=mdy printout=date,mjd
24 Jun 1995 00:00:00.00000 SAT
MJD 49892.0000000000
> calcphot wfpc2,1,a2d7,f300w,cont#49892.0
spectrum="grw_70d5824_003.tab" form=counts
Mode = band(wfpc2,1,a2d7,f300w,cont#49892.0)
Pivot Equiv Gaussian
Wavelength FWHM
2995.8 766.9841 band(wfpc2,1,a2d7,f300w,cont#49892.0)
Spectrum: /tib/cdbs/calspec/grw_70d5824_003.tab
VZERO (COUNTS s-1 hstarea-1)
0. 2202.372
Check the online iraf help (type "help calcphot") or the
SYNPHOT User's Guide for details on the variations possible with the calcphot task.
For example, the calcspec/calphot step can be combined by giving a
filename to calcphot's spectrum parameter; the file should contain the
some function commands you would have given calcspec.Summary of SYNPHOT Tables
mtab$ (ie, h5g10115m.tmc,h5l1440cm.tmg)
The name is a timestamp for installation into the routine pipeline
processing system (f=year, 7=month, d is day).
hst_ota
wfpc2_optics
a2d (separate ones for each gain and chip)
dqe (efficiency tables, one for each chip)
flat (flatfield table; currently these are dummy tables
set to 1, as the flatfield information is already
contained in the wfpc2 optics table)
filter tables (one for each filter element, names like:
wfpc2_f300w_003, where 003 refers to version number
of table)
cont (contamination tables, invoked with "cont#" in the
obsmode, one per chip)
For a typical observation mode, you will normally see at least the ota,
optics, filter, dqe tables in the path; specifying "cal", "a2d7" (or
"a2d15"), and "cont#" followed by MJD, you will also see the flat, a2d,
and cont tables. For example:
> showfiles wfpc2,3,f555w
crotacomp$hst_ota_005.tab
crwfpc2comp$wfpc2_optics_003.tab
crwfpc2comp$wfpc2_f555w_003.tab
crwfpc2comp$wfpc2_dqewfc3_002.tab
> showfiles "wfpc2,3,f555w,a2d15,cal,cont#49943.0"
crotacomp$hst_ota_005.tab
crwfpc2comp$wfpc2_optics_003.tab
crwfpc2comp$wfpc2_f555w_003.tab
crwfpc2comp$wfpc2_dqewfc3_002.tab
crwfpc2comp$wfpc2_a2d15wf3_002.tab
crwfpc2comp$wfpc2_flatwf3_001.tab
crwfpc2comp$wfpc2_contwf3_005.tab[cont#]
Note that if you wish to include the contamination tables, you must
enclose the obsmode in quotes.Retrieving the Files
> tdump wfpc2_f555w_003.tab | page
The new tables are available via ftp to stsci.edu, in cdbs/cdbs2/comp/
ftp ftp.stsci.edu
anonymous - use your email address as password
binary - set retrievals for binary files
prompt - turn off prompt
cd /cdbs/cdbs2/comp/wfpc2
get wfpc2tar - fetch tarfile of wfpc2-related SYNPHOT files,
(includes the files from ota)
Note: the tarfile includes the recent May 1997 graph and comp tables,
which were the earliest tables to contain the most recent wfpc2-related
SYNPHOT update. If you intend to use SYNPHOT for other instruments as
well, you may wish to retrieve the most recent graph and comp tables,
that is:
cd /cdbs/mtab
mget *tmc
mget *tmg
ASCII tables are available at www.stsci.edu/ftp/cdbs/cdbs6/synphot_tables,
if you wish to retrieve only specific filters or observing modes.Setting Up Your Environment to Run SYNPHOT
tar xvf wfpc2tar
Set some logicals within IRAF:
> set mtab=localdir - for directory containing graph/comp tabs
> set crotacomp=localdir - dir containing ota file
> set crwfpc2comp=local - dir containing wfpc2 files
Point SYNPHOT to these new files, from within IRAF type:
> unlearn refdata
which will set refdata parameters to:
refdata.area = 45238.93416
refdata.grtbl = "mtab$*.tmg"
refdata.cmptbl = "mtab$*.tmc"
refdata.mode = "a"
where the graph and comptab pointers will choose the latest timestamp
file in the previously defined mtab directory; or, you can insert the
entire table name by:
> epar refdata
and editing in the appropriate names (ie, crcomp$hstgraph_950712a.tab
for grtbl, etc).References
help@stsci.edu (410-338-1082), for paper copies of the online documents.
Appendix A: List of Tasks in the SYNPHOT Package
bandpar - Calculate photometric parameters of a passband
calcband - Calculate a model passband.
calcphot - Calculate photometric quantities for spectra and passbands.
calcspec - Calculate a model spectrum.
countrate - Evaluate the photometric count rate of the HST.
fitband - Fit a passband model to data using Amoeba simplex method.
fitgrid - Fit a spectrum model to a grid of spectral data.
fitspec - Fit a spectrum model to data using Amoeba simplex method.
genwave - Interactively generate a wavelength set.
grafcheck - Check an instrument graph table for bad rows.
graflist - List the components downstream from a given component.
showfiles - Print filenames used in a SYNPHOT expression
grafplot - Plot the components downstream from a given component.
imspec - Convert an image to a SYNPHOT spectrum or vice versa.
plband - Plot a set of passbands.
plratio - Plot the ratio of observed to synthetic spectral or photometric data.
plspec - Plot spectral and photometric data.
pltrans - Plot photometric transformation diagrams (e.g., color-color or color-magnitude).
obsmode - Display observation mode keywords for an instrument
refdata - Pset to specify common SYNPHOT parameters.
Type "help synphot opt=sys" for a description of files used by these tasks.
Type "help" followed by taskname for details on a particular task.
Appendix B: List of all Most Recent WFPC2-related SYNPHOT Tables
ib615349m.tmg
j1c1553gm.tmc
from ota subdirectory (.tab files)
clear_001
dark_001
hst_ota_005
from wfpc2 subdirectory (.tab files)
wfpc2_a2d15pc1_002 wfpc2_a2d15wf2_002 wfpc2_a2d15wf3_002 wfpc2_a2d15wf4_002
wfpc2_a2d7pc1_002 wfpc2_a2d7wf2_002 wfpc2_a2d7wf3_002 wfpc2_a2d7wf4_002
wfpc2_contpc1_005 wfpc2_contwf2_005 wfpc2_contwf3_005 wfpc2_contwf4_005
wfpc2_dqepc1_003 wfpc2_dqewfc2_003 wfpc2_dqewfc3_003 wfpc2_dqewfc4_003
wfpc2_flatpc1_001 wfpc2_flatwf2_001 wfpc2_flatwf3_001 wfpc2_flatwf4_001
wfpc2_fqch4na_002 wfpc2_fqch4nb_003 wfpc2_fqch4nc_002 wfpc2_fqch4nd_003
wfpc2_fquvna_003 wfpc2_fquvnb_003 wfpc2_fquvnc_003 wfpc2_fquvnd_003
wfpc2_fr418n_001 wfpc2_fr533n_001 wfpc2_fr680n_001 wfpc2_fr868n_001
wfpc2_polq_par_002 wfpc2_polq_perp_002 wfpc2_polq_unp_001
wfpc2_lrf_002
wfpc2_optics_004
wfpc2_f1042m_004
wfpc2_f122m_004
wfpc2_f130lp_002
wfpc2_f157w_001
wfpc2_f160bw_004
wfpc2_f165lp_002
wfpc2_f170w_004
wfpc2_f185w_003
wfpc2_f218w_004
wfpc2_f255w_004
wfpc2_f300w_004
wfpc2_f336w_005
wfpc2_f343n_003
wfpc2_f375n_003
wfpc2_f380w_004
wfpc2_f390n_004
wfpc2_f410m_003
wfpc2_f437n_003
wfpc2_f439w_004
wfpc2_f450w_004
wfpc2_f467m_003
wfpc2_f469n_004
wfpc2_f487n_003
wfpc2_f502n_003
wfpc2_f547m_003
wfpc2_f555w_004
wfpc2_f569w_003
wfpc2_f588n_004
wfpc2_f606w_004
wfpc2_f622w_003
wfpc2_f631n_003
wfpc2_f656n_003
wfpc2_f658n_003
wfpc2_f673n_003
wfpc2_f675w_004
wfpc2_f702w_004
wfpc2_f785lp_004
wfpc2_f791w_004
wfpc2_f814w_004
wfpc2_f850lp_004
wfpc2_f953n_003
STScI Home Page
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WFPC2 Home Page.
WFPC2 Group.