The photometric calibration package PHOTCAL, contains a set of tasks for computing the transformation from the instrumental system to the standard photometric system, and applying the computed transformations to the observational data.
PHOTCAL distinguishes between two types of objects: standard stars, and program stars. Standard stars have known instrumental and standard photometric indices. Program stars have known instrumental photometric indices, but unknown standard photometric indices.
The standard indices of standard stars are contained in standard star catalogs known as catalog files. Each standard star catalog contains only a single entry for a given standard star. The instrumental indices of both standard and program stars are contained in observations catalogs, known as observations files. There may be any number of observations per star in an observations file.
PHOTCAL uses a setup file called the configuration file to specify the format of the input catalog and observations files and define the transformation equations to be fit.
Normally the user must perform the following logical steps to complete their photometric calibrations with PHOTCAL. However not all types of data require all the following steps.
[1]
Prepare a standard star catalog file using the MKCATALOG task.
[2]
Prepare a standard star observations file using the MKIMSETS and MKNOBSFILE
tasks or alternatively the MKOBSFILE task.
[3]
Create the configuration file using the MKCONFIG and CHKCONFIG tasks.
[4]
Fit the transformation equations with the FITPARAMS task.
[5]
Apply the transformations to the standard star observations file using
the EVALFIT or INVERTFIT tasks.
[6]
Prepare a program star observations file using the MKIMSETS and MKNOBSFILE
tasks or alternatively the MKOBSFILE tasks.
[7]
Apply the transformations to the program star observations file using the
EVALFIT or INVERTFIT tasks.
PHOTCAL catalog and observation files are simple text files containing any number of columns. Columns are delimited by whitespace. The first column is always reserved for the star id or matching name, and the rest contain actual data such as positions, magnitudes, colors, errors, air mass, or any other quantity of interest. Comments can be inserted as separate lines at any point in the catalog or observations files by beginning the comment line with the character "#".
The star id is used to match observations with catalog entries, and to determine which objects are standard and which are program stars. Star ids may contain any non-blank characters, but lower case letters are converted to upper case, and characters not in the set [A-Z,0-9,+,-,_] are removed before star id matching. Catalog files must contain only a single entry per star. Observations files may contain multiple entries per star. Missing or unknown data values should be set to INDEF not left blank.
Normal catalog and observations files records are restricted in length to the maximum size of a text file line in IRAF, currently 161 characters including the newline. The maximum record length can be extended by replacing the the star id in column 1 with the continuation character "*".
Several preprocessors are provided to convert data coming from other IRAF packages, such as APPHOT and DAOPHOT, into a format suitable for PHOTCAL. If a preprocessor for a specific type of data does not exist, then the user will have to use other IRAF facilities to convert it to into the appropiate format, or write their own.
A standard star catalog sutitable for input to PHOTCAL may be prepared in one of the following ways. The advantages and disadvantages of each method are briefly discussed.
[1]
Use one of the standard star catalogs supported by PHOTCAL and maintained in
the directory "photcal$catalogs/". Each supported standard star catalog has
an associated catalog format description file defining the format of the
standard star catalog. The catalog format description file may be used as
input to the MKCONFIG task. A list of currently supported standard star
catalogs and their format files can be found in the file
"photcal$catalogs/README".
The principal advantage of this option is that no data entry is required on the part of the user. The principal disadvantage is that PHOTCAL, in preparation for id matching, loads the entire standard star catalog into memory, even though the the number of observed standard stars may have been only a few dozen. For typical standard star catalogs containing a few hundred objects this is not a problem, but ver large standard star catalogs should be avoided.
[2]
Prepare a standard star catalog with the MKCATALOG task. MKCATALOG
prompts the user for the catalog title, the id column name and width, and the
names and widths of all the data columns.
When column definition is complete, MKCATALOG writes the catalog
definition information into the catalog header and the associated catalog
format file and prompts for data.
The catalog format description file created by MKCATALOG may be used
as input to MKCONFIG.
Type "help mkcatalog" for the details of task usage.
The principal advantages of using MKCATALOG are that the task always produces a PHOTCAL readable catalog and accompanying format description file, and that the standard star catalog contains values only for those objects that have actually been observed.
[3]
With a text file editor create or edit a standard star catalog which
conforms to the requirements of PHOTCAL as described in the previous section.
The principal advantage of this option is that the user can take advantage of any spread sheet capabilities that his/her favorite editor has. The principal disadvantage is that a format description file is not automatically created along with the catalog.
[4]
Reformat an existing standard star catalog until it conforms to the
requirements of photcal as described in the previous section. In some
case this may require writing a local preprocessor program. PHOTCAL users
should be aware of the PROTO package tasks JOIN and FIELDS, the LISTS
package tasks COLUMN, and the UTILITIES package task TRANSLIT.
The first few lines of a representative catalog file produced by MKCATALOG are listed below. V, BV, and UB stand for the V magnitude, B-V color, and U-B color respectively. The non-blank lines beginning with '#' at the beginning of the file are for the internal use of the MKCATALOG task only, and are ignored by other PHOTCAL tasks.
# CATALOG: ubv.cat # NCOLS: 7 # HDRLENGTH: 68 # # ID V error(V) BV error(BV) UB error(UB) # 8 8 8 8 8 8 8 105-307 12.050 0.020 0.690 0.020 0.220 0.020 105-405 8.309 0.004 1.521 0.001 1.905 0.007 105-411 10.620 0.014 0.950 0.010 0.620 0.008 105-256 11.820 0.013 0.610 0.012 0.180 0.022
The accompanying format description file produced by MKCATALOG is listed below. This file associates a column number with the column name and can be used as input to MKCONFIG. The comments opposite the column definitions were not produced by MKCATALOG but typed in later.
# Declare the catalog variables catalog V 2 # the V magnitude error(V) 3 # the error in the V magnitude BV 4 # the B-V color error(BV) 5 # the error in the B-V color UB 6 # the U-B color error(UB) 7 # the error in the U-B color
A standard star observations file suitable for input to PHOTCAL may be prepared in one of the following ways. APPHOT and DAOPHOT users should use options [1] or [2]. Other users must either enter their data by hand using options [3] and [4], or write a local program to prepare their data for input to PHOTCAL, option [5].
[1]
If the standard star magnitudes were computed with APPHOT or DAOPHOT
and consist of many individual and repeated observations of standard star
fields, then use MKIMSETS
followed by MKNOBSFILE to create an observations file. MKIMSETS creates
an image set definition file, telling MKNOBSFILE which images taken
in which filters belong to the same observation of a given stellar field.
For each observations file written, MKNOBSFILE
creates an associated format description file defining the format of
the new observations file and suitable for input to
MKCONFIG. MKNOBSFILE is set up to run automatically once the image set file
is defined. Type "help mknobsfile" for details.
[2]
If the standard star magnitudes in one or more colors were computed with
APPHOT or DAOPHOT and all the standard stars are in one stellar field,
use the MKOBSFILE task to create an observations file.
For each observations file created, MKOBSFILE
creates an associated format descriptin file defining the format of
the new observations file, and suitable for input to
MKCONFIG. MKOBSFILE prompts the user for all
the required input. Type "help mkobsfile" for details.
[3]
Prepare a standard star observations file with the MKCATALOG task. MKCATALOG
prompts the user for the observations file title, the id column name and
width, and the names and widths of all the data columns.
When column definition is complete, MKCATALOG writes the observations file
definition information into the observations file header and the associated
format description file and prompts for data.
The format description file created by MKCATALOG may be used as input
to MKCONFIG if the "catalog" keyword (see the example in the previous
section) is changed to "observations".
Type "help mkcatalog" for the details of task usage.
[4]
With the text editor create or edit a standard star observations file
which conforms to
the requirements of PHOTCAL as described in the previous section.
[5]
Write a local program to prepare the data for input to PHOTCAL.
A sample image set file produced by MKIMSETS is shown below. The labels STD1, STD2, ..., STD7 stand for standard star fields 1, 2, ..., 7 and the c0* labels are the names of images of each field taken through filters U, B, and V respectively.
STD1 : c023 c022 c021
STD2 : c024 c025 c026
STD3 : c029 c028 c027
STD4 : c033 c031 c032
STD5 : c061 c060 c059
STD6 : c064 c063 c062
STD7 : c069 c066 c065
The first few lines of the observations file produced by MKNOBSFILE using the above image set file both before and after the user has edited in the correct standard star ids is listed below. Note that there is usually more than 1 star in the field. In fact the data set above included 17 standard stars and 5 additional stars that the automatic star finding algorithm picked up. Note also that some known bad data points in the original observations file have been replaced with the undefined value INDEF.
before editing # FIELD FILTER OTIME AIRMASS XCENTER YCENTER MAG MERR STD1-1 1 INDEF 1.276 156.43 518.23 20.077 0.031 * 2 INDEF 1.270 155.37 521.12 17.712 0.053 * 3 INDEF 1.265 152.16 519.62 17.044 0.019 STD1-2 1 INDEF 1.276 481.39 357.19 18.683 0.009 * 2 INDEF 1.270 480.57 360.07 14.919 0.005 * 3 INDEF 1.265 477.07 358.62 13.292 0.002 STD1-3 1 INDEF 1.276 507.69 128.53 19.144 0.014 * 2 INDEF 1.270 507.06 131.44 16.612 0.020 * 3 INDEF 1.265 503.42 130.29 15.587 0.008 STD2-1 1 INDEF 1.305 719.59 399.17 19.863 0.097 * 2 INDEF 1.315 718.79 401.30 17.339 0.043 * 3 INDEF 1.320 715.47 402.55 16.601 0.033 STD2-2 1 INDEF 1.305 470.72 393.68 16.675 0.005 * 2 INDEF 1.315 469.71 396.22 14.743 0.004 * 3 INDEF 1.320 466.58 397.27 14.030 0.004 STD2-3 1 INDEF 1.305 498.75 204.35 19.413 0.057 * 2 INDEF 1.315 497.73 206.40 17.469 0.042 * 3 INDEF 1.320 494.55 207.64 16.662 0.032 STD2-4 1 INDEF 1.305 182.44 209.60 19.748 0.073 * 2 INDEF 1.315 181.10 211.95 18.056 0.074 * 3 INDEF 1.320 178.21 213.03 17.034 0.044 STD3-1 1 INDEF 1.251 397.57 200.65 19.060 0.007 * 2 INDEF 1.236 396.58 200.38 15.725 0.005 * 3 INDEF 1.231 393.53 200.51 14.237 0.007 after editing # FIELD FILTER OTIME AIRMASS XCENTER YCENTER MAG MERR STD1-1 1 INDEF 1.276 156.43 518.23 20.077 0.031 * 2 INDEF 1.270 155.37 521.12 17.712 0.053 * 3 INDEF 1.265 152.16 519.62 17.044 0.019 105-405 1 INDEF 1.276 481.39 357.19 18.683 0.009 * 2 INDEF 1.270 480.57 360.07 14.919 0.005 * 3 INDEF 1.265 477.07 358.62 13.212 0.002 105-411 1 INDEF 1.276 507.69 128.53 19.144 0.014 * 2 INDEF 1.270 507.06 131.44 16.612 0.020 * 3 INDEF 1.265 503.42 130.29 15.487 0.008 STD2-1 1 INDEF 1.305 719.59 399.17 19.863 0.097 * 2 INDEF 1.315 718.79 401.30 17.339 0.043 * 3 INDEF 1.320 715.47 402.55 16.601 0.033 105-257 1 INDEF 1.305 470.72 393.68 16.675 0.005 * 2 INDEF 1.315 469.71 396.22 14.743 0.004 * 3 INDEF 1.320 466.58 397.27 14.030 0.004 105-262 1 INDEF 1.305 498.75 204.35 INDEF 0.057 * 2 INDEF 1.315 497.73 206.40 17.469 0.042 * 3 INDEF 1.320 494.55 207.64 INDEF 0.032 STD2-4 1 INDEF 1.305 182.44 209.60 19.748 0.073 * 2 INDEF 1.315 181.10 211.95 18.056 0.074 * 3 INDEF 1.320 178.21 213.03 17.034 0.044 106-575 1 INDEF 1.251 397.57 200.65 19.060 0.007 * 2 INDEF 1.236 396.58 200.38 15.725 0.005 * 3 INDEF 1.231 393.53 200.51 14.237 0.007
The accompanying format description file produced by MKNOBSFILE is listed below. This file associated column numbers with column names. The filter numbers 1, 2, 3 were written into the image headers by the data taking program, and subsequently picked up by the APPHOT package tasks computed the magnitudes. They stand for filters U, B and V respectively.
# Declare the observations file variables observations T1 3 # time of observation in filter 1 X1 4 # airmass in filter 1 x1 5 # x coordinate in filter 1 y1 6 # y coordinate in filter 1 m1 7 # instrumental magnitude in filter 1 error(m1) 8 # magnitude error in filter 1 T2 10 # time of observation in filter 2 X2 11 # airmass in filter 2 x2 12 # x coordinate in filter 2 y2 13 # y coordinate in filter 2 m2 14 # instrumental magnitude in filter 2 error(m2) 15 # magnitude error in filter 2 T3 17 # time of observation in filter 3 X3 18 # airmass in filter 3 x3 19 # x coordinate in filter 3 y3 20 # y coordinate in filter 3 m3 21 # instrumental magnitude in filter 3 error(m3) 22 # magnitude error in filter 3
The configuration file is a text file, created by the user, that specifies both the format of the input data and the form of the transformation equations. A detailed description of the grammar and syntax of the configuration file can be obtained by typing the following command.
ph> help configThe configuration file can be prepared in one of the following ways.
[1]
Run the MKCONFIG task using the output of MKCATALOG or direct terminal input to
define the catalog file format, the output of the MKNOBSFILE
or MKOBSFILE tasks or direct terminal input to define the observations file
format, and one of the standard template transformation section files or
direct terminal input to define the transformation equations.
Users are urged to use MKCONFIG if they are new to PHOTCAL,
if the catalog file is one of the supported catalogs, or if the observations
file was made with one of the standard preprocessors MKNOBSFILE or
MKOBSFILE.
[2]
Use the text editor to make small corrections to an existing functioning
configuration file. This is the recommended method if the transformation
equations have changed from a previous PHOTCAL reduction session but the
format of the standard star and observations catalogs has not, or if
the user has become familiar with the PHOTCAL configuration file format.
[3]
Use the text editor to create a configuration file from scratch.
The grammar and syntax of the configuration file can be checked with the CHKCONFIG task. If an error was found, the program will print the line and the word where the error was detected and the user must reedit the file until no errors are found.
A sample configuration file is shown below.
# Declare the catalog file variables catalog V 2 error(V) 3 BV 4 error(BV) 5 UB 6 error(UB) 7 # Declare the observations file variables observations T1 3 # time of observation in filter 1 X1 4 # airmass in filter 1 x1 5 # x coordinate in filter 1 y1 6 # y coordinate in filter 1 m1 7 # instrumental magnitude in filter 1 error(m1) 8 # magnitude error in filter 1 T2 10 # time of observation in filter 2 X2 11 # airmass in filter 2 x2 12 # x coordinate in filter 2 y2 13 # y coordinate in filter 2 m2 14 # instrumental magnitude in filter 2 error(m2) 15 # magnitude error in filter 2 T3 17 # time of observation in filter 3 X3 18 # airmass in filter 3 x3 19 # x coordinate in filter 3 y3 20 # y coordinate in filter 3 m3 21 # instrumental magnitude in filter 3 error(m3) 22 # magnitude error in filter 3 transformation fit u1 = 0.0, u2 = -.07, u3 = 0.70 UFIT : m1 = V + BV + UB + u1 + u2 * UB + u3 * X1 fit b1 = 0.0, b2 = -.06, b3 = 0.30 BFIT : m2 = V + BV + b1 + b2 * BV + b3 * X2 fit v1 = 0.0, v2 = 0.05, v3 = 0.20 VFIT : mv = V + v1 + v2 * BV + v3 * Xv
The heart of the PHOTCAL package is the parameter fitting task FITPARAMS. A detailed description of this task and its parameters can be obtained by typing the following command.
ph> help fitparamsFITPARAMS takes the observation files, catalog files, and configuration file, and computes the value of the fit parameters for each of the transformation equations specified in the configuration file. Equations will be processed in the same order in which they occur in the configuration file. The output of FITPARAMS is a text database file containing one record, identified by the transformation equation label, for each equation fit. Successive fits are appended to the end of the database file. If more than one fit has the same label the last fit performed will be used by the evaluation tasks.
Only standard stars with known instrumental magnitudes and photometric indices are used to compute the parameters of each transformation equation. Standard stars are identified by matching the id in the observations catalog against the list of ids in the standard star catalog.
The fitting process can be either interactive or non-interactive. Interactive fitting is the default. In interactive mode, the user is presented with plots of the data and the fit, can reject points automatically using a k-sigma rejection algrotihm, delete points interactively with the cursor, change which parameters are to be fit and which are to be held constant, and so on. A detailed description of all the interactive options and colon commands can be obtained by typing the following command. .nf
ph> help inlfit
The database file produced by FITPARAMS for the catalog and observations files listed in sections III and IV and configuration file listed in section V is shown below.
# Mon 10:41:04 06-May-91 begin UFIT status 0 (Solution converged) variance 4.965303E-4 stdeviation 0.02228296 avsqerror 1. averror 1. avsqscatter 0. avscatter 0. chisqr 4.965303E-4 msq 3.901309E-4 rms 0.01975173 reference mu fitting V+BV+UB+u1+u2*UB+u3*Xu weights uniform parameters 3 u1 (fit) u2 (fit) u3 (fit) derivatives 3 0.1 0.1 0.1 values 3 6.108767 -0.04842735 0.7180178 errors 3 0.05704632 0.008730207 0.04209311 # Mon 10:41:14 06-May-91 begin BFIT status 0 (Solution converged) variance 0.002550806 stdeviation 0.0505055 avsqerror 1. averror 1. avsqscatter 0. avscatter 0. chisqr 0.002550806 msq 0.00207253 rms 0.04552504 reference mb fitting V+BV+b1+b2*BV+b3*Xb weights uniform parameters 3 b1 (fit) b2 (fit) b3 (fit) derivatives 3 0.1 0.1 0.1 values 3 4.826268 -0.08220235 0.275757 errors 3 0.1189408 0.02718129 0.08517767 # Mon 10:41:21 06-May-91 begin VFIT status 0 (Solution converged) variance 9.547584E-4 stdeviation 0.03089917 avsqerror 1. averror 1. avsqscatter 0. avscatter 0. chisqr 9.547584E-4 msq 7.501673E-4 rms 0.02738918 reference mv fitting V+v1+v2*BV+v3*Xv weights uniform parameters 3 v1 (fit) v2 (fit) v3 (fit) derivatives 3 0.1 0.1 0.1 values 3 4.632307 0.02190715 0.1877689 errors 3 0.07831987 0.01721398 0.0573602
This step is optional since the goodness of fit can be assessed more efficiently from within the FITPARAMS task. However in some cases the user may want a record of the fitted photometric indices for the standard stars and the residuals from the fit.
There are two tasks for evaluating the transformation equations and which one the user must select depends on how he/she has defined the transformations equations.
If all references to the catalog file variables are on the left-hand side of the transformation equations and the right-hand side is a function of the observations file variables only, then the user should use EVALFIT. The transformation equations used for reducing photoelectric photometry are often written in this manner.
If the left-hand side of the transformation equation is a function of the observations file variables and all references to the catalog files variables are on the right-hand side of the transformation equations then the user must use INVERTFIT. The transformation equations for reducing CCD photometry are usually written in this manner.
The full ouput of INVERTFIT for the partial catalog and observations files listed in section III and IV and the configuration file shown in section V are listed below. Only observations which were successively matched with objects in the standard star catalog files are shown. The fits for objects with undefined observational variables could not be successfully inverted producing a row of INDEF values.
# Tue 15:50:37 14-May-91 # List of observations files: # ubv.std # Number of catalog files: # ubv.cat # Config: ubv.cfg # Parameters: ubv.fit # # Computed indices for standard objects only # # Columns: # 1 object id # 2 V # 3 error(V) # 4 resid(V) # 5 BV # 6 error(BV) # 7 resid(BV) # 8 UB # 9 error(UB) # 10 resid(UB) 105-405 8.308 0.002 0.001 1.563 0.006 -0.042 1.878 0.011 0.027 105-411 10.597 0.008 0.023 0.913 0.024 0.037 0.639 0.027 -0.019 105-257 9.140 0.004 0.000 0.451 0.006 0.039 0.040 0.007 -0.020 105-262 INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF 106-575 9.345 0.007 -0.004 1.322 0.010 -0.014 1.457 0.009 0.026 106-728 INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF 107-998 10.399 0.010 0.041 0.602 0.018 0.028 0.217 0.020 -0.057 107-991 INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF 107-990 9.555 0.005 0.005 0.455 0.009 0.035 0.047 0.009 -0.047 114-473 8.514 0.004 0.006 1.005 0.007 0.005 0.832 0.008 -0.032 114-353 INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF 114-151 10.708 0.005 -0.048 0.748 0.011 0.002 0.221 0.014 0.069 114-236 10.446 0.005 0.034 0.687 0.010 -0.057 0.093 0.011 0.007 111-775 INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF INDEF 111-773 8.980 0.005 -0.017 0.270 0.006 -0.064 -0.258 0.005 0.047 111-1342 9.263 0.006 -0.043 1.702 0.009 -0.012 1.726 0.076 0.054 111-733 9.219 0.006 -0.039 0.262 0.007 0.038 0.172 0.007 0.008
A program star observations file is prepared in the identical manner to the standard star observations file as described in section IV. In fact there is no intrinsic reason why standard star and program star observations cannot occupy the same observations file since they can be separated later by the EVALFIT and INVERTFIT tasks. In the sample observations file shown in section IV objects with names like 105-411 are the actual standard stars and those with names like STD* can, for the purpose of illustration, be regarded as program stars.
The transformation equations are applied to the program stars in the same way they are applied to the standard stars ad described in section VII.
The ouput of INVERTFIT for the partial catalog and observations files listed in section III and IV and the configuration file shown in section V are listed below. Only observations which were not successfully matched with objects in the standard star files are shown. Note that the residuals from the fit cannot be computed for program objects and are therefore not output.
# Tue 16:17:11 14-May-91 # List of observations files: # ubv.obs # Number of catalog files: # ubv.cat # Config: ubv.cfg # Parameters: ubv.fit # # Computed indices for program objects only # # Columns: # 1 object id # 2 V # 3 error(V) # 4 BV # 5 error(BV) # 6 UB # 7 error(UB) STD1-3 12.165 0.019 0.403 0.063 0.508 0.069 STD2-2 12.136 0.045 0.796 0.096 -0.242 0.115 STD2-4 11.710 0.034 0.479 0.061 0.660 0.113 STD6-3 10.589 0.006 0.619 0.016 -0.069 0.022 STD7-5 11.852 0.059 0.406 0.069 0.981 0.129