VaST [Variability Search Toolkit]

A software package for detection of variable objects
on a series of astronomical images

Contents: What is VaST?
Screenshots
Download
Short usage notices
VaST mailing list
Publications
Other useful tools

VaST is a program aimed to find objects of variable brightness on a series of astronomical images. The images (CCD frames or photographic plate scans) must be taken with the same instrument using the same filter and saved in FITS format. The images may be shifted and/or rotated with respect to each other, but they have to have the same scale (arcsec/pix). VaST performs object detection and aperture photometry using SExtractor on each image, cross-matches lists of detected stars, performs magnitude calibration with respect to the first (reference) image and constructs a lightcurve for each object. The simple sigma-magnitude plot may be used to visually identify variable star candidates. If data permit, period-search techniques ANOVA and BLS may also be employed to identify periodic variable stars among the candidates. All lightcurves are being constructed in an arbitrary magnitudes. If there are reference stars with known magnitudes in the field of view, all magnitudes can be later converted to the standard system.

Unlike software based on the image subtraction method, VaST can be used in case of unstable PSF (e.g., bad guiding, digitized wide-field photographic images). VaST is not tied up to any catalog and WCS, so it can be successfully used on images taken with a telephoto lens as well as with a 2.6-m class telescope.

VaST is written in C (and partly in BASH scripting language) for GNU/Linux operating system. It is in a continual, albeit slow, state of development. VaST is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License.

To compile and use VaST you'll need:

GNU/Linux and some basic skills in using it
GCC (including Fortran compiler), comes with your GNU/Linux distribution
BC calculator (can be found in your GNU/Linux distribution)
cURL (can be found in your GNU/Linux distribution)
SExtractor (local mirror)
GSL library (local mirror)
PGPLOT library (local mirror)
CFITSIO library (local mirror) needed only for versions before vast-1.0rc53!

You can find at this page the latest version of VaST (download via ftp or http, ~1.6M) along with some sample data (ftp or http, 24M)
and a short PowerPoint presentation in Russian (2M) which covers some aspects of variable star search with VaST (very, very, I mean VERY old!).

Files described here as well as older versions of VaST are available via our anonymous FTP.

Special note for Ubuntu users! The following installation procedure is recommended:

Install SExtractor (version 2.5 is recommended, DO NOT use the version of SExtractor supplied with Ubuntu, it is known not to work), GSL and CFITSIO libraries from the source code.
Install a number of additional libraries (including PGPLOT) from pre-compiled Ubuntu packages:
sudo apt-get install gfortran libX11-dev libXi-dev libXmu-dev libpng-dev pgplot5 curl
Compile VaST.

Screenshots

Different subroutines in VaST may be started automatically from the main program, or they may be started manually by user from a terminal. Names of the corresponding executable files are given under each screenshot. Click on images to see them in high resolution:

The variability search window ./find_candidates	The lightcurve inspection program ./lc

VaST (the main program) running in a terminal ./vast	VaST FITS image viewer ./pgfv

Video (screencast)
background comments in Russian only, sorry... I hope to prepare an English version soon...

Download, compile and test VaST download this video in full resolution (11M)	How to identify variable stars with VaST download this video in full resolution (29M)

How to remove trend from a lightcurve download this video in full resolution (29M)

Compiling VaST

First, make sure that you have PGPLOT, CFITSIO and GSL libraries installed in your system. Then unpack the program

tar -xvjf vast-latest.tar.bz2
cd vast-1.0rc48

And try to compile it by running

make

If compilation fails, read carefully compilers output. Most probably it can't find some necessary libraries. Explore the Makefile with your favorite text editor and change the libraries location to match your environment.

Using VaST

To try VaST, download the sample data set, unpack it

wget -c ftp://saistud.sai.msu.ru/pub/vast/sample_data.tar.bz2
tar -xvjf sample_data.tar.bz2

change to the VaST installation directory and run the program

cd vast-1.0rc48
./vast ../sample_data/*fit

cd vast-1.0rc48
./vast -p ../sample_data/*fit

After a brief computation the variability search window will be opened. Click on any star on the sigma-magnitude plot to inspect its lightcurve. Click on any point on the lightcurve plot to see an image from which this point comes. The star on the image will be marked with a red cross, a red circle around the star corresponds to the aperture used to measure this image.

If you quit the program without deleting any data, you can restart it without doing all the computations again by running:

./find_candidates aa

To calibrate the magnitude scale using comparison stars in the field of view use this script:

util/magnitude_calibration.sh

It will ask you to specify one or more comparison stars and their magnitudes. After the comparison stars have been specified, close the image window with the right mouse click and inspect the relation between instrumental and catalog magnitudes. This relation may be fitted by a linear function with the slope fixed to 1, linear function with a free slope or second degree polynome. Use (P) key on your keyboard to change the fitting function. For most CCD data sets, linear function with the fixed slope provides a good fit. The data points may be weighted according to their estimated errors or weighted equally. Use (W) key to change weighting. Close the dialog with the right mouse click to apply the calibration to all stars when you are satisfied with the fit.

In order to save the current work, use the script

util/save.sh my_favorite_field_name

If the field name was not provided, the script will ask for it. To restore previous work, use

util/load.sh my_favorite_field_name

or just copy all saved files from directory [my_favorite_field_name] back to the VaST directory.

To delete all files from the previous work, you can use:

util/clean_data all

New feature! There is a new tool to fully automatically identify variable stars detected with VaST. It requires working Internet connection at runtime. The tool may or may not work for your field depending on luck. If the field of view is greater than, say, 30' and the image quality is fine - the odds that the automatic identification will work for your field are pretty good. Here is how to use it... To identify the star number 00190 in the current dataset use the following command:

util/identify.sh out00190.dat 25

where "out00190.dat" is the lightcurve file of the star and "25" is the estimated field of view size in arcminutes. It is wise to set this value a little bit smaller than your best-guess field of view. If no field of value is given, the default value of 40' will be assumed. Note, that the field of view identification may take really long time (up to ~30 minutes), especially for small fields. Please, do not interrupt the process - just wait for a result. If the field identification failed, try to restart it with smaller estimated field of view size. On successful identification, the script will print the equatorial coordinates (J2000) of the star and will attempt to query popular databases to check if this star is already known as a variable. Note, that the coordinates returned by the identification script may be up to 10" off. We strongly advise to use the Aladin interactive sky atlas to verify the identification and obtain more precise star coordinates from some astrometric catalog (e.g., USNO-B1.0). The automatic identification function relies on tools provided by Astrometry.net. For more details visit http://astrometry.net/. Note, that according to the use conditions of the index files required to run the Astrometry.net code, you need to be ready to share the images solved using this software with any other interested party including the Astrometry.net team. According to the same use conditions: "If the indexes are used in any scholarly work, research grant proposals or other scientific or academic publications, the Astrometry.net project must be properly cited and acknowledged. The paper to cite is the Lang et al paper on our bibliography page http://astrometry.net/biblio.html. The acknowledgment text is "This research made use of tools provided by Astrometry.net." The VaST software developers assume, that this statement concerns the work which uses "util/identify.sh" script from the VaST package.

Using VaST with scanned photographic plates

If you have to deal with digitized photographic materials, you'll want first to convert TIFF images (which are typically produced by scanner software) to the FITS format. It can be easily done with the tiff2fits converter. Do not forget to change your images to positive (white stars on black sky). For example:

./tiff2fits -i input.tiff output.fits

Also, you'll have to enter the information about the date and time of observation in fits header. This can be done, among other ways, using the modhead program from the CFITSIO examples page, MissFITS or edhead from the WCSTools package. You may enter the observation date and time information in the image header by generating the usual "DATE-OBS" and "EXPTIME" header keys, or by simply putting the middle-of-exposure Julian Date into the "JD" key. You will most likely need to modify the default SExtractor settings stored in the "default.sex" file located in the VaST directory. Please use "default.sex.beta_Cas_photoplates" and "default.sex.PHOTO" as working examples (these files are also found in the VaST directory).
Say, you have digitized photographic images in "photo_data" directory. To run VaST on them, change to the VaST directory and run the program

cd vast-1.0rc54
./vast -o ../photo_data/*fit

The "-o" parameter tells VaST to use formulas (1) and (3) from Bacher et al. (2005, MNRAS, 362, 542) for magnitude calibration. This technique provide slightly better results for the aperture photometry on photographic data compared to the second-order polynome used in VaST by default for magnitude calibration. However, the standard calibration technique should also provide reasonably good results (see Figure 2 in this paper).

VaST mailing list

If you would like to receive updates about new versions of VaST, enter your e-mail address in the form below or just drop a line to kirx[at]scan.sai.msu.ru

Some switches which you can use with VaST

"-9" — use DS9 instead of VaST's own viewer pgfv to view FITS files.
"-n" — do NOT perform magnitude calibration. Useless for variable star search but good for doing differential photometry with util/differential_photometry.sh script.
"-u" — always assume UTC time system, don't perform conversion to TT.
"-e" — failsafe mode: only stars detected on the reference frame will be processed.
"-p" — tell VaST that it deals with linear detector. This flag is useful for well calibrated CCD images, but for some CCD images it is better not to use it. Test what works best for your particular dataset!
"-l" — perform sigma-filtering of lightcurves (can be extremely CPU-intensive)
"-r" — assume that images are not rotated with respect to one another by more than 3 degrees.
To get the full list of the available command line arguments use:

./vast -h

List of publications which make use of VaST

If you are aware of a publication which is not listed here, please, drop us a line to kirx[at]scan.sai.msu.ru so we can include it in the list!

K. V. Sokolovsky; "The Variability Type and Period of V348 Aql"
PZP, vol. 11, N 33 (17.11.2011) Available here.
V. Solovyov, A. Samokhvalov, B. Satovskiy; "New Variable Stars in the Field of V458 Vul"
PZP, vol. 11, N 31 (14.11.2011) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in the Field of V496 Aur"
PZP, vol. 11, N 28 (20.07.2011) Available here.
K. V. Sokolovsky, F. D'Ammando, S. Cutini, and J. M. Gelbord; "Swift observations of BL Lacertae"
2011 ATel #3377 Available here, also see the monitoring results page.
V. Solovyov, A. Samokhvalov, B. Satovskiy; "USNO-A2.0 1425-04252279: a New Eclipsing RS CVn Star with Spot Activity of Both Components"
PZP, vol. 11, N 21 (23.05.2011) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in the Field of the Globular Cluster NGC5466"
PZP, vol. 11, N 20 (11.05.2011) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in the Field of V651 Oph"
PZP, vol. 11, N 16 (22.04.2011) Available here.
V. Solovyov, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Perseus"
PZP, vol. 11, N 14 (7.04.2011) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in the Field of V2335 Oph"
PZP, vol. 11, N 13 (7.04.2011) Available here.
N. Virnina, S. V. Antipin, A. M. Zubareva; "Four New Eclipsing Variable Stars"
PZP, vol. 11, N 9 (14.03.2011) Available here.
T. Kryachko, A. Samokhvalov, S. A. Korotkiy, D. G. Lambas; "New Variable Stars in Two Fields in the Southern Hemisphere"
PZP, vol. 11, N 8 (11.03.2011) Available here.
Daniel J. Majaess, David G. Turner, David J. Lane, Tom Krajci; "Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars"
2011 JAVSO, 39, 219 Available here.
Natalia A. Virnina; ""Tsessevich" Project: an Attempt to Find the System YY Dra. I"
2011 OEJV, 133, 1 Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Auriga II"
PZP, vol. 11, N 4 (28.01.2011)Available here.
V. Solovyov, A. Samokhvalov, B. Satovskiy; "USNO-A2.0 1425-04279615 and USNO-A2.0 1425-04280420: Two New Short-Period Eclipsing RS CVn Variables"
2011 IBVS #5961 Available here.
T. Krajci, K. Sokolovsky, A. Henden; "griz photometry of 3C 454.3 following its extreme gamma-ray flare"
2010 ATel #3047 Available here, and see the monitoring results page.
D. M. Kolesnikova, L. A. Sat, K. V. Sokolovsky, S. V. Antipin, A. A. Belinskii, N. N. Samus'; "New variable stars on digitized Moscow collection plates. The field of 66 Ophiuchi"
2010, ARep, 54, 1000 The abstract is available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Aquila"
PZP, vol. 10, N 25 (26.10.2010) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in the Field of V585 Lyr"
PZP, vol. 10, N 24 (26.10.2010) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Taurus"
PZP, vol. 10, N 17 (18.05.2010) Available here.
K. Sokolovsky, C. Maceroni, M. Hareter, C. Damiani, L. Balaguer-Nunez, I. Ribas; "A new eclipsing binary system with a pulsating component detected by CoRoT"
2010 CoAst, 161, 59 Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy, D. Denisenko; "New Variable Stars in Cygnus II"
PZP, vol. 10, N 10 (9.03.2010) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Auriga"
PZP, vol. 10, N 3 (2.02.2010) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy, D. Denisenko; "New Variable Stars in Cygnus"
PZP, vol. 10, N 2 (27.01.2010) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "The New UV-type Variable Star USNO-B1.0 1243-0454679"
PZP, vol. 9, N 33 (22.12.2009) Available here.
K. V. Sokolovsky; "NSVS 304708 is a High Amplitude Delta Scuti Star"
PZP, vol. 9, N 30 (5.11.2009) Available here.
T. Kryachko, A. Samokhvalov, S. A. Korotkiy; "New Variable Stars in the Field of Omicron Andromedae"
PZP, vol. 9, N 29 (5.11.2009) Available here.
Alex Golovin, Kirill Sokolovsky, Natalia Virnina, Javier Lopez Santiago; "Three New Variable Stars in Indus";
2009 OEJV, 111, 1 Available here.
T. Kryachko, A. Samokhvalov, D. Denisenko, B. Satovskiy; "New Variable Stars in the Field of GRB 080605"
PZP, vol. 9, N 24 (23.09.2009) Available here.
S. V. Antipin, A. M. Zubareva, D. Kolesnikova, N. N. Samus, L. A. Sat, K. V. Sokolovsky; "CCD Observations of Four Stars Suspected in Variability from Digitized Moscow Plates"
PZP, vol. 9, N 21 (19.06.2009) Available here.
K. V. Sokolovsky, L. Elenin, N. Virnina; "New Variable Stars Discovered Using the Tzec Maun Observatory Telescopes II"
PZP, vol. 9, N 20 (19.06.2009) Available here.
T. Kryachko, A. Samokhvalov, S. A. Korotkiy; "New Eclipsing Variable Stars in Canis Minor"
PZP, vol. 9, N 18 (17.06.2009) Available here.
T. Kryachko, A. Samokhvalov, D. Denisenko, B. Satovskiy; "New Variable Stars in Gemini"
PZP, vol. 9, N 10 (28.04.2009) Available here.
K. V. Sokolovsky; "Three New Eclipsing Binaries Near the Galactic Center"
PZP, vol. 9, N 9 (11.03.2009) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New variable stars in Andromeda II"
PZP, vol. 9, N 7 (13.02.2009) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New variable stars in the field of SGR0501+4516"
PZP, vol. 9, N 4 (11.02.2009) Available here.
T. Kryachko, A. Samokhvalov, D. Denisenko, B. Satovskiy; "New UV-type Variable Star USNO-A2.0 1350-05226717"
PZP, vol. 9, N 1 (3.02.2009) Available here.
T. Kryachko, A. Samokhvalov, S. A. Korotkiy; "New Variable Stars in Andromeda"
PZP, vol. 8, N 48 (8.12.2008) Available here.
T. Kryachko, A. Samokhvalov, D. Denisenko, B. Satovskiy; "New Variable Stars in Ophiuchus"
PZP, vol. 8, N 43 (24.11.2008) Available here.
K. V. Sokolovsky, L. Elenin; "New Variable Stars Discovered Using the Tzec Maun Observatory Telescopes"
PZP, vol. 8, N 42 (20.11.2008) Available here.
Kolesnikova, D. M.; Sat, L. A.; Sokolovsky, K. V.; Antipin, S. V.; Samus, N. N.; "New Variable Stars on Digitized Moscow Collection Plates. Field 66 Ophiuchi (Northern Half)"
2008, AcA, 58, 279 Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in the Field of Tau Aurigae"
PZP, vol. 8, N 29 (15.09.2008) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy; "New EW Variable Star GSC 0584-01373"
PZP, vol. 8, N 28 (15.09.2008) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy, A. V. Khruslov; "Variable Stars in the Field of GSC 4550-01669"
PZP, vol. 8, N 27 (27.06.2008) Available here.
T. Kryachko, A. Samokhvalov, B. Satovskiy, A. V. Khruslov; "Variable Stars in the Field of GSC 4329-01772"
PZP, vol. 8, N 26 (26.06.2008) Available here.
T. Kryachko, K. V. Sokolovsky, D. Denisenko, B. Satovskiy; "Low-Amplitude Eclipsing Binary Star GSC 04372-00066"
PZP, vol. 8, N 22 (22.05.2008) Available here.
T. Kryachko, K. V. Sokolovsky, D. Denisenko, B. Satovskiy; "New Eclipsing Binary Star GSC 04372-00577"
PZP, vol. 8, N 20 (13.05.2008) Available here.
T. Kryachko, K. Sokolovsky, B. Satovskiy; "Five New Variable Stars"
PZP, vol. 8, N 8 (2008) Available here.
K. V. Sokolovsky, D. O. Chekhovich, S. A. Korotkiy; "GSC 4232-02059 - a New Beta Lyrae System"
PZP, vol. 8, N 2 (2008) Available here.
S. V. Antipin, D. Kolesnikova, L. A. Sat, K. V. Sokolovsky, S. A. Korotkiy; "A New High Amplitude Delta Scuti Star on the Scanned Moscow Archive Plates"
PZ, vol. 27, N 8 (22.11.2007) Available here.
K. V. Sokolovsky, D. O. Chekhovich, S. A. Korotkiy; "GSC 4232-02515 - a New Eclipsing Binary Star"
PZP, vol. 7, N 26 (24.10.2007) Available here.
D. M. Kolesnikova, K. V. Sokolovsky, S. V. Antipin, N. N. Samus; "Moscow Digital Variables. III"
PZP, vol. 7, N 24 (19.10.2007) Available here.
D. M. Kolesnikova, K. V. Sokolovsky, N. N. Samus, S. V. Antipin; "Moscow Digital Variables. II"
PZP, vol. 7, N 3 (5.02.2007) Available here.
A. L. Manannikov, K. V. Sokolovsky, N. N. Samus, S. V. Antipin; "Moscow Digital Variables. I"
PZP, vol. 6, N 34 (22.12.2006) Available here.
K. V. Sokolovsky, E. P. Pavlenko; "USNO-B1.0 1381-0460341: a New Eclipsing Binary System Near V1500 Cyg"
PZP, vol. 6, N 33 (5.12.2006) Available here.
K. V. Sokolovsky, S. V. Antipin, S. A. Korotkiy; "Period Changes in the Algol-type Eclipsing Binary System TYC 1744 2329 1"
PZ, vol. 26, N 7 (20.10.2006) Available here.
K. V. Sokolovsky; "Optical Variability of the Seyfert Galaxy FBQS J161047.7+330337"
PZP, vol. 6, N 18 (30.06.2006) Available here.
K. V. Sokolovsky, V. R. Amirkhanyan; "USNO-B1.0 1323-0548678: a New EW Star in the Field of BL Lac"
PZP, vol. 6, N 1 (27.01.2006) Available here.
S. V. Antipin, K. V. Sokolovsky, A. A. Lebedev; "GSC 02050-00745: A New RR Lyrae Star with Blazhko Effect"
IBVS 5654 (2005) Available here.
K. V. Sokolovsky, A. A. Lebedev; "POISK - a SExtractor front-end for search of variable objects in series of CCD images"
12th Young Scientists' Conference on Astronomy and Space Physics, held in Kyiv, Ukraine, April 19-23, 2005, p. 79 Available here.

A few other (more or less) useful tools

Web-based World Coordinate System (WCS) image calibration - a tool based on the Astrometry.net engine that allows one to plate-solve a sky image using minimal a priori information about it. Please use the username vastuser and password vastpassword to access this page.
Web-based lightcurve analysis tool - allows one to perform a period search using Lafler & Kinman (1965, ApJS, 11, 216) method. Plase use the username vastuser and password vastpassword to access this page.
Times of minima calculator - a simple web-based tool to calculate times of minima from light elements.
TIFF2FITS - a simple C program (based on CFITSIO and libtiff) which converts TIFF images to 16-bit FITS format. May be useful for processing scanned photographic plates.
OMC2ASCII - a simple C program (based on CFITSIO) which converts INTEGRAL/OMC lightcurves from FITS table to simple ASCII table. May be useful if you don't want to install the Off-line Science Analysis (OSA) software just to get to INTEGRAL/OMC data.

If you have any questions fell free to contact authors via e-mail
kirx[at]scan.sai.msu.ru

Good luck in using VaST!
VaST developers team.

VaST developers team, 2005-2012