Automated Variable Star Observing
CCD photometry of variable stars can be used for fainter stars, provides a documentation through the image file and allows for a degree of magnitude increase in precision.
Productivity of CCD photometry, using an amateur telescope and camera, is relatively low because of the time needed to obtain images, store and then check and reduce them. Usually, the reduction step involves: visual identification of the variable star and of reference stars on the image by comparing it with a chart (such as an aavso chart), measurement of the flux of the variable and reference stars and estimation of the variable star magnitude. Then a record of the observation is made, for example by entering it in the aavso web form.
AVSOMAT is a project to automate the identification and photometry of variable stars on CCD images. It consists of a Linux command, avsomat which takes as arguments the name of a fits image, and the name of an electronic chart (another file) for the star supposedly on the image. avsomat produces the aavso observation report as a single line of text. Optionally, it can produce a picture with the reference and the variable stars, as it thinks it detected them, just for checking.
The electronic chart is a file with descriptions of the variable star, the reference stars and guide stars which are used to identify the field. See below for available examples. The electronic chart is also called a "recipe" and for this reason it is a text file with the extention .rcp
Download. The following files are available:
Installation and usage. avsomat works in Linux. Download the avsomat archive, untar it and make the executable:
tar xvzf avsomat-1.2-src.tgz
Now, download the rcp files, make a subdirectory, say rcp and untar it there:
Then download an example, say RZ-HER from above. Run:
gzip -d rzher.fits.gz
./avsomat -Przher.eps -NZZZ rzher.fits rcp/rzher.rcp
This should produce the aavso observation on your terminal, which you can then send, for example to firstname.lastname@example.org, to report the variable star magnitude (the example observations above have already been reported to aavso).
You must have default.cxr in the current directory. This form of the command line uses Radu's libccd library, distributed with avsomat, to extract star positions from the image and perform photometry. You can also use sextractor a free program which you must download and install first. After that, run:
sex rzher.fits ; avsomat -Przher.eps -NZZZ -Ctest.cat rzher.fits rcp/rzher.rcp
The call to sex will create the list of objects in test.cat which is then used by avsomat.
Use the -N option to indicate your aavso observer code (in place of "ZZZ"). Use the -P option to obtain an image of how the variable, reference and guide stars were detected.
The calls above use reference stars extracted from AAVSO chart sequences. Since version 1.1 you can use reference stars from the Tycho-2 catalog (VT references), which are available in the new recipes. Use the -t option and a new recipe to use Tycho references and the -tj option to use Tycho references corrected for the Johnson V filter.
Since avsomat V1.2 it is possible to generate a web page to contain the results and method of reducing a star. This is best accomplished using the new `avswork.lisp' binding, which is a CommonLisp library with functions for integrating avsomat and html and bitmap image generation. You need to be a bit familiar with CommonLisp though. To install edit the lisp file and adjust the directories at the beginning of the file. Then run CMU Commonlisp, for example by starting emacs and giving the command
Then load the binding with:
Then you can say, for example:
(run-avsomat "ssdel-v-001.fits.gz" 2911 1 'cua)
to run avsomat on the SS-Del image and then:
(do-obstar-obs 2911 'ss-del 1 'cua)
to assemble the results into a webpage. The webpage will be generated in *report-dir*/2911/SS-DEL/1.html, where *report-dir* is the value you established for this variable. The corresponding URL is included as a comment in the AAVSO observation report.
Examples of such observation results can be found here. This framework is still alpha software. Use with care.
Since version 3051 you can reduce all images from a directory (e.g. a CD) with a single command, also generating the web report during the process. Call, for example:
(avsomat-dir "/cdrom" 9999)
where 9999 a number or symbol identifying the observing session.
Cross-indexing all observations of a star
With V3051 and later, use:
to generate a directory containing one subdirectory for each constellation with one sub-subdirectory for each variable star in the constellation having star info from the gcvs catalog and links to each observation web bulletin of that particular star on your site. An optional argument can be a list of variable stars to actually build pages for. Otherwise, pages are built for all stars known to avsomat.
New version naming scheme. After version 1.2 we started naming versions by the day when they are released. The day is identified using the last 4 digits of the julian date. This is, for example, 3036 for January 31, 2004. More digits will not be necessary for the next 19 years or so.
Observations scheduler. This is a component which appeared in avsomat-3036. To install it, you need to install first the stardata-3036.tgz archive in the data subdirectory of avsomat home. Then start cmulisp as above (with the lisp command in Linux) and type:
to load the scheduler. Now you can obtain scripts for controlling GCX, the camera and the telescope by calling the function gcx-script. The function documentation is shown below. The default function value for WITH makes the gcx-controlled telescope to move to each star, take a control picture, correct position, then take two 10s pictures in sequence:
(gcx-script EXPR [WITH]) produces a GCX script to image the stars designated by EXPR, following an optimised path and going from west to east. Function WITH will be used to produce the script of each star designated by EXPR. It must return a string given a symbol. By variable stars, below, we understand the stars in the GCVS.lisp file, which was initially based on GCVS. EXPR may be a symbol, which could be: - a star name (example: RU-LYN) - a constellation TLA (three letter abbreviation)--variable stars in that constellation (example: LYN) - :IN-AAVSO stars having an aavso chart - :ERUPTIVE stars with an `eruptive' type of variability - :NEEDMORE stars `in need of more observations' If EXPR is a list, then it must have one of the following forms: (AND EXPR*) - stars designated simultaneously by all the EXPR's (OR EXPR*) - any of the stars designated by an expr (ANDNOT EXPR EXPR) - stars designated by the first EXPR without - those designated by the second EXPR Examples: (GCX-SCRIPT 'RU-LYN) ; returns a script to image RU-LYN (GCX-SCRIPT 'LYN) ; returns a script to image all variable stars known in LYN (GCX-SCRIPT 'LYN #'(lambda (star) (format nil \"~A~%\" star))) ; returns a string with the variable stars in LYN ; sorted aproximately from W to E and with optimisation ; of the path between them (GCX-SCRIPT '(AND LYN :IN-AAVSO)) ; returns a script to image all stars in LYN having aavso charts (GCX-SCRIPT '(AND :ERUPTIVE LYN)) ; returns a script to image all eruptive stars in LYN (GCX-SCRIPT '(ANDNOT (AND :ERUPTIVE LYN) :IN-AAVSO)) ; returns a script to image all eruptive star not in aavso
Related work. There are two reasons to have a command line variable star reduction program which uses premade recipies to reduce images:
[running on Linux]
[made in CommonLisp, C and Ada95]
[Copyright © 2003 A.D.Corlan]