The rtcorr guide
rtcorr is a program for doing extinction correction on Real Time
photometry data.
The program is completely non-interactive. One input file is given and
a few options can be invoked. The output retains the format of the
rtp output files, adding a few header lines with information
on the processing steps applied.
The rtcorr program requires two additional files with information
to start the extinction correction; one file named TELESCOPE that gives
information about the observatory and instrument used (and which will be
the same for all targets of a given run), and one file named TARGET
which gives specifics for the current TARGET. See below for details on
how to create these files.
rtcorr execution
- In an xterm window, change directory to the data processing directory
for the run in question.
- Locate a file for extinction processing.
This can be any either the ".raw" file or the ".dat" output file from rtp.
- If the ".raw" file is given, the sky level is recomputed. In this case
it is possible to give the option -b [num], which will smooth the sky
values with a boxcar function of width [num] data points, before sky
subtraction. As with rtp the option -t [num] can be used to
specify a sky field different from the first.
- Normally the rtcorr program is executed simply like this;
rtcorr phot.dat
provided that the TELESCOPE and TARGET files have been properly set up.
- A -w [num] option can be given to get tapering of the light curve, where
num is the number of data points to taper on each end of the data set.
This produces an additional output file with the data tapering towards
zero at the ends. This is normally not recommended.
The TELESCOPE file
The TELESCOPE file should look something like this:
| Observatory: | "Nordic Optical Telescope"
| Longitude: | "-17d53m06.3s" # Negative for West / Positive for East |
| Latitude: | "+28d45m26.2s" |
| Altitude: | "2465.5m" |
| Instrument: | "ALFOSC" |
| Filters: | "XUBVRIWrX" # Filter in position 012345678 |
|
The longitude and latitude values are used for the extinction correction.
The observatory and instrument names used only read by rtp to
put in the data file headers, overriding the FITS keywords.
The filters sequence is important. It tells rtcorr what filter
correspond to which extinction coefficient in the TARGET file.
rtpextracts the filter number from the FITS header and puts this
in the output files. rtcorr then selects the filter letter
based on the position of the letters in the Filters string.
For standard filters the order is rarely changed.
The TARGET file
The TARGET file should look something like this:
# Target information:
| TARGET: | "PG 1336-013" |
| RA(B1950): | "13h36m13.3s" |
| DEC(B1950): | "-01d46m34s" |
| # Observation | run information: |
| DATE: | "2001-05-04" |
| TIME(UT): | "22:30:45" |
| # Extinction | coefficients |
| K_U: | "0.49" |
| K_B: | "0.30" |
| K_V: | "0.15" |
| K_R: | "0.09" |
| K_I: | "0.05" |
| K_W: | "0.15" |
The target name is only passed on to the output files for information
purposes, together with the coordinates and date/time of start.
The target coordinates and start time is of course used for
calculating the airmass. The extinction coefficients given here are
typical for La Palma, but may change significantly depending on
the conditions.
Copy the TELESCOPE and TARGET files
The easiest way to get started with rtcorr is simply to
copy the TELESCOPE and TARGET files from the ~fastphot
directory.
Output files
rtcorr normally produces three output files.
- A ".ext" file, containing the extinction corrected photometry.
- A ".edm" file, containing the extinction corrected differential photometry.
- A ".nma" file, containing the ".edm" data normalised in the same way as
rtft will do.
There is no difference between passing the .edm file or the .nma file to
rtft. The .nma file is provided only to show what the light curve
will look like after normalisation.
- A ".ras" file will be generated when giving a .raw file as input,
and it will contain the new sky subtracted data (with optional box average
processing) for comparison with the standard .dat file.
- A ".win" file can also be generated, if the -w option is applied,
containing the .nma data with tapered ends.
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Last modified: Tuesday, 31-Apr-2001 12:08:31 ACT