VaST [Variability Search Toolkit]

Contents

What is VaST?
Screenshots
Download
Usage
Output files
VaST mailing list
News/Release notes
Frequently Asked Questions
Publications using VaST
Other useful tools

VaST is a software tool for finding variable objects on a series of astronomical images. The images (CCD frames or digitized photographic plates) must be taken with the same instrument using the same filter and saved in the FITS format. CCD images should be calibrated (dark-subtracted and flat-fielded). The input images may be shifted and rotated with respect to each other, but they have to have the same scale (arcsec/pix). The images in a series should overlap by at least ~40% to ensure successful cross-identification. 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 sigma-magnitude, Stetson's L variability index, Robust Median Statistic (RoMS) and other plots may be used to visually identify variable star candidates. If data permit, period-search techniques may be employed to identify periodic variable stars among the candidates. All lightcurves are constructed in arbitrary magnitudes with zero magnitude corresponding to the background level on the reference image. 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 or with digitized wide-field photographic images). VaST is not tied up to any external catalog and WCS (if operated in its main "variable star search" mode), so it can be used on images taken with a telephoto lens as well as with a 2.6-m class telescope. If needed, absolute astrometric calibration may be performed through an interface to the Astrometry.net code allowing one to perform automatic magnitude scale calibration and variable star identification (however, this will work only if the input images are large enough to perform blind plate solution).

VaST is written in C (and partly in BASH scripting language) for GNU/Linux operating system. The latest versions are also tested on MacOS X and FreeBSD. The best practical way to run VaST under Windows is through Linux installed in a virtual machine (e.g. VirtualBox, see also a collection of pre-built VirtualBox images). The AAVSO forum thread mentions attempts to run VaST under Windows with Cygwin, but the results seem to be inconclusive. On all the supported systems VaST is able to utilize multiple processing cores to perform most of its computations in parallel.

VaST is free software: you can redistribute and/or modify it under the terms of the GNU General Public License. The program is in a continual, albeit slow, state of development. You are welcome to contribute bug reports, patches and feature requests: please write me at kirx[at]scan.sai.msu.ru

Screenshots

VaST (the main program) running in a terminal ./vast	The variability search window ./find_candidates
The lightcurve inspection program ./lc	VaST FITS image viewer ./pgfv

Getting VaST

• GNU/Linux or MacOS X or FreeBSD and some basic skills in using one of these operating systems through a command line interface (terminal)
• GCC (including Fortran and C++ compilers), 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. If SExtractor is not installed system-wide, VaST will use built-in SExtractor v2.5.

You can find at this page the latest version of VaST (download via ftp or http, ~9.5M) along with the sample data set (ftp or http, 24M).

You may download VaST with the command

If compilation fails, read the output carefully. Most probably it can't find some necessary libraries, header files or external programs. Please install the required programs and try to compile VaST again. If you are sure that the needed libraries and headers are installed in the system but the compiler cannot find them, try to open Makefile with a text editor and change the libraries locations to match your environment. Very old versions of VaST require PGPLOT, CFITSIO and GSL libraries to be installed in your system, but most likely you don't want to use such an old VaST version.

• Install these libraries from pre-compiled Ubuntu packages:
  sudo apt-get install build-essential gfortran g++ libX11-dev libXi-dev libXmu-dev libpng-dev curl wget
  If you want to install a newer SExtractor and PSFEx in order to perform PSF-fitting photometry with VaST, you'll need to install also
  sudo apt-get install libfftw3-dev libatlas-base-dev
  When compiling SExtractor and PSFEx from the source code, specify explicitly the location of ATLAS include files:
  ./configure --with-atlas-incdir=/usr/include/atlas && make && sudo make install
• Compile VaST as described above

• Install some basic development tools (login as root or use sudo):
  yum install gcc gcc-c++ gcc-gfortran libX11-devel libpng-devel
• Compile VaST as described above

Using VaST

To calibrate the magnitude scale using comparison stars with known magnitudes within the field of view use this script:

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, second degree polynome (parabola) or the Bacher et al. (2005, MNRAS, 362, 542) magnitude calibration relation a.k.a "photocurve". This option is suitable for processing digitized photographic plates. 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.

If the image field of view is large enough to be blindly solved with Astrometry.net code (as described below), one can automatically match stars detected on the image to the UCAC4/APASS catalog by running the magnitude calibration script with a command line argument specifying the observing band:

In order to save the current work, use the script

There is a tool to automatically identify variable stars detected with VaST. It requires a 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 plate solution 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:

A note on the graphical user interface

• To select a data point on a plot (or a given pixel of an image) - click on it with the left mouse button.
• To close a window - click the right mouse button anywhere in the window.
• To zoom in - use exactly the following sequence of actions: 1) put the cursor in one corner of the area you want to zoom on, 2) press 'Z' on keyboard and release the key, 3) specify the size of the area you want to zoom on by moving the mouse, 4) click the left mouse button to confirm your selection.
• To zoom out - press 'Z' key on a keyboard twice.

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:

Say, you have digitized photographic images in "photo_data" directory. To run VaST on them, change to the VaST directory and run the program

An example photographic dataset is available here. Beware, it's about 1G in size!

You may find some more details in the ArXiv:1403.5334 e-print "A search for new variable stars using digitized Moscow collection plates".

Search for transients with VaST

Apart from the standard "variable star search mode", where a long series of images is processed and lightcurves of detected stars are explored using the sigma-magnitude plot, VaST can be also used in the specialized "transient detection mode". In this mode VaST will process a series of four images: two first-epoch (reference) images and two second-epoch images. VaST will generate an HTML report containing a list of candidate transients. The transients are defined as either objects that were not visible on the reference images, or where at least 1 mag. fainter compared to the second-epoch images. Two first-epoch images are needed because image artifacts and star blending may cause VaST to miss a star on a single reference image, so it will appear as a false transient search mode is available. If there are two reference images - chances that the program will fail to detect a star at both of them is greatly reduced. Also note that two different reference images are needed: it would be impossible to "cheat" the program by feeding the same image to it twice.

An example dataset that allows one to test the transient search mode is available here.

The unpacked archive will contain two sub-directories with reference and second-epoch images. The search should be conducted in two steps:

Known limitations:

• The transient detection capability is still in the testing stage and is FAR FROM PERFECT, sorry...
• You'll need a reasonably high-speed Internet connection with unlimited traffic to efficiently use the transient-detection capability. An effort is made to reduce the Internet traffic to the necessary minimum. However, at the first start, the program will need to download ~200M of catalog data. During the routine work, the program will need to transmit a few 100K of data for every processed image (necessary for astrometric image calibration using the external server). The Internet connection is also needed to access external web-databases that would allow you to check the detected transient candidates.
• There are two transient-detection scripts for your to consider:
  util/transients/search_for_transients_single_field.sh is the simplified one that searches for transients in a single field.
  util/transients/transient_fatory_test30.sh is a more complex one, that is actually used to process NMW survey data. These scripts cannot cover all possible situations and should serve an example and inspiration for you to write your own script appropriate for your setup.
• Image field of view should be sufficiently large to allow automatic plate solution with Astrometry.net software. The default value is 180 arcmin, if your field of view is smaller - you should edit the transient detection script util/transients/search_for_transients_single_field.sh .
• The magnitude calibration is based on V magnitudes of Tycho-2 stars. If this is not appropriate for your system, please contact me and I'll try to develop an alternative calibration strategy for your setup.
• Reference images should be two different images obtained during one night. The reason behind using two reference images (instead of one) is the attempt to minimize the number of cases where SExtractor fails to deblend two stars on the reference image, but can successfully perform deblending on the second-epoch images. In this case, one of the two stars that "appeared" in the detection lists for the second epoch will be erroneously marked as a transient. The other measure that can minimize such errors is to try to use images with the best seeing as reference.
• There are two files controlling the star-detection behavior of SExtractor: default.sex and default.conv . You may refer to SExtractor documentation for a detailed description of these files. You may find a few examples of default.sex and default.conv files in the VaST directory. The default files are meant to work for a wide variety of CCD images, however they may not provide an optimal star detection efficiency for a particular instrument. The two files fine-tuned for the "transient_detection_test_Ceres" dataset are default.sex.telephoto_lens and default.conv.telephoto_lens . To use them instead of default files, just copy these files:
  cp default.sex.telephoto_lens default.sex
  cp default.conv.telephoto_lens default.conv
  You may want to edit these file to match your own setup.

Some switches that you may use with VaST

Description of output files produced by VaST

• Each "outNNNNN.dat" file contains an individual lightcurve of a star numbered NNNNN. This is a simple ASCII file that may be viewed in a text editor. The format is the following:
  - 1st column - JD(TT) (default) or JD(UTC) (if VaST was started with "-u" flag)
  - 2nd column - magnitude (with respect to the background level on the reference image if an absolute calibration was not done yet)
  - 3rd column - estimated magnitude error
  - 4th column - X position of the star on the current frame (in pixels)
  - 5th column - Y position of the star on the current frame (in pixels)
  - 6th column - diameter of the circular aperture used to measure the current frame (in pixels)
  - 7th column - file path corresponding to the current frame
  The extra columns specific to VaST may be easily removed as follows
  util/cute_lc out00183.dat > out00183_JD_mag_err.dat
  the output file out00183_JD_mag_err.dat will contain only three columns "JD", "mag" and "err". By default, util/cute_lc prints its output to stdout. If no lightcurve file name is provided as a command line argument, util/cute_lc will expect the input lightcurve to be sent to its stdin. You may easily change the number of digits returned by util/cute_lc by editing its source code file src/cute_lc.c and recompiling VaST (make).
• "data.m_sigma" file contains the information used to produce the sigma-magnitude plot. It has the following format:
  - 1st column - mean magnitude of a star
  - 2nd column - estimated sigma (standard deviation) of its lightcurve
  - 3rd column - X position of the star on the reference frame (in pixels)
  - 4th column - Y position of the star on the reference frame (in pixels)
  - 5th column - outNNNNN.dat file containing the lightcurve of this star
• "vast_summary.log" file summarizes the processing results. Its format is rather self-explanatory:
  Images processed 91
  Images used for photometry 91
  Ref. image: 2453192.38950 05.07.2004 21:18:19 ../sample_data/f_72-001r.fit
  First image: 2453192.38950 05.07.2004 21:18:19 ../sample_data/f_72-001r.fit
  Last image: 2453219.49141 01.08.2004 23:45:04 ../sample_data/f_72-091r.fit
  JD time system (TT/UTC/UNKNOWN): TT
  Transient candidates found: 34
  Number of SysRem iterations: 0
  Computation time: 14 seconds
  SExtractor parameter file: default.sex
  Total objects detected: 510
  Objects passed selection criteria: 174
  Measurements per detected object (mean, median, min, max): 34.2 16.0 2 91
  Measurements per selected object (mean, median, min, max): 78.3 84.0 40 91
  Average stars detected per image: 210.989
  Average stars matched: 203.89 (96.6354 %)
  Memory usage VmPeak: 745564 kB
  Software: VaST 1.0rc64 compiled with gcc (Gentoo 4.7.2-r1 p1.5, pie-0.5.5) 4.7.2
  SExtractor version 2.8.6 (2012-11-23)
  Processing completed on Sat Apr 13 07:04:41 UTC 2013
  
  Note however that the "Transient candidates found" line should be ignored in most cases. At this moment, transient detection is supported in the special four-image transient detection mode described above.
• "vast_image_details.log" file contains information about processing of individual images:
  exp_start= 05.07.2004 21:18:19 exp= 180 JD= 2453192.38950 ap= 7.2 rotation= 0.000 *detected= 334 *matched= 334 status=OK ../sample_data/f_72-001r.fit
  exp_start= 05.07.2004 21:21:30 exp= 180 JD= 2453192.39172 ap= 7.1 rotation= -0.106 *detected= 329 *matched= 310 status=OK ../sample_data/f_72-002r.fit
  exp_start= 05.07.2004 21:24:41 exp= 180 JD= 2453192.39393 ap= 7.0 rotation= -0.157 *detected= 337 *matched= 315 status=OK ../sample_data/f_72-003r.fit
  exp_start= 05.07.2004 21:27:52 exp= 180 JD= 2453192.39614 ap= 6.9 rotation= -0.020 *detected= 345 *matched= 330 status=OK ../sample_data/f_72-004r.fit
  exp_start= 06.07.2004 20:24:42 exp= 180 JD= 2453193.35227 ap= 6.2 rotation= -0.021 *detected= 416 *matched= 321 status=OK ../sample_data/f_72-005r.fit
  ...
  If an image could not be processed, this will be indicated by "status=ERROR".
• "vast_command_line.log" contains the command line with which VaST was started, so the exact processing parameters can be always figured out.
• "vast_sigma_selection_curve.log" contains the "sigma-selection curve" displayed on the sigma-magnitude plot.
• "vast_stars_with_large_sigma.log" contains the list of stars that are above the "sigma-selection curve" on the sigma-magnitude plot. The file format is identical to the one of "data.m_sigma" file. The stars listed in "vast_stars_with_large_sigma.log" have larger-than-average scatter of their lightcurves and may be investigated further, e.g., with period-search software.
• "vast_magnitude_calibration_details_log" is a directory containing details of the frame-to-frame magnitude calibration process. The details may be viewed as follows:
  cd vast_magnitude_calibration_details_log
  for i in *.calib ;do ../lib/fit_mag_calib "$i" "$i"_param ;done
  This is useful mostly for debugging purposes.
• "image*.cat" files are the raw SExtractor catalogs. Their format is defined in the "default.param" file (see SExtractor documentation). The correspondence between the catalogs and input images is given in the "vast_images_catalogs.log" file. These catalogs are useful mostly for debugging purposes.
• "image*.cat.aperture" files contain the aperture diameter (in pixels) used to produce a given SExtractor catalog.
• "vast_memory_usage.log" contains information about VaST usage of RAM.
• "vast_list_of_all_stars.log" contains pixel coordinates of all selected stars in the reference frame of the first (reference) image. Both stars actually detected on the first frame and the ones detected only on other frames are listed.
• "vast_list_of_all_stars.ds9" is the same as "vast_list_of_all_stars.log" except it is formatted as a DS9 region file (to be loaded into the DS9 FITS image viewer).

VaST mailing list

Release notes

21 Feb 2016: version vast-1.0rc75:

 * Minor modifications to speed-up the star matching algorithm.

 * When manually opening a lightcurve file with './lc' it is now
possible to refer to the star only by its number without specifying
the full filename, i.e. './lc 12184' instead of './lc out12184.dat'.
The old way with the full file name still works, of course.

 * VaST can now properly handle the situation when DATE-OBS keyword
is present in the FITS image header, but does not specify the
observing time and a separate TIME-OBS keyword is not present.
In this case, VaST will try to get the observing date from JD
keyword.

 * Rewritten the SysRem algorithm implementation 
(Tamuz, Mazeh, Zucker, 2005, MNRAS, 356, 1466).
The new version should work faster and be less aggressive in
rejecting uncorrectable stars. The new implementation may be run as util/sysrem2
I'm keeping the old util/sysrem too for now.

 * Changed the way maximum trial period is set for the period search
in pokaz_laflerkinman.sh Now pmax=int(jd_range/3.0-0.5)

 * Fixed the experimental script that retrieves Catalina sky survey
data for a specified (small) sky area: util/catalina_search_area_TEST.sh

 * Added the interquartile range (IQR) 
as another measure of lightcurve scatter. In practice it turns out
to be very similar to the median absolute deviation (MAD)
that was added earlier.

 * Added a small tool that splits multi-extension FITS files into 
single-extension FITS images that can be processed with VaST:
util/split_multiextension_fits /path/to/my_multiextension.fits

 * Changed PSF extraction settings in default.psfex
The new settings are more appropriate for a wide-field instrument.
The old settings may be found in default.psfex.small_FoV
It may be a good idea to apply a few iterations of SysRem 
( util/sysrem2 ) to remove residual systematic effects arising
from imperfect PSF reconstruction that may degrade photometric
accuracy for bright stars.

 * Changes in util/solve_plate_with_UCAC4 to make it work faster.
The results of its work are not exactly the same as in the previous
version, but should be still acceptable.

 * Circumvent the mysterious gcc bug that refused to compile VaST with
the parameter "-march=native" set on some combination of gcc version
and CPU model. The new test is trying to compile the problematic
C-source file and does not set "-march=native" if this test
compilation fails.

 * Minor improvements in the Makefile to speed-up compilation. The
changes also allowed to fix problem with compilation on some Ubuntu
systems. Unfortunately, the changes rely on GNU make syntax, so if
you are on non-Linux system, it is now necessary to compile VaST
with 'gmake' instead of just 'make'.

 * Fixed the VaST testing script ( util/examples/test_vast.sh ) that
reported a failed test after the variable "NSV 11188" got its GCVS
name "V1451 Her" that was not previously recognized by the script.

 * Increased timeout for plate-solving (both remote and using a local
copy of Astrometry.net software).



24 Oct 2015: version vast-1.0rc74

 * VaST is now not trying to create a flag image in cases where there
are many zero-value pixels scattered across the image rather than being
grouped in specific areas (like along a frame edge). This makes it
possible again to process background-subtracted images with VaST.

 * Fixed the bug with incorrect observing time being set from "EXPSTART" keyword.
No problem appeared if other keywords ("DATE-OBS", "JD") were present in an image header.

 * By default, VaST now accepts stars having SExtractor flag set to 1:
"The object has neighbors, bright and close enough to significantly
bias the photometry, or bad pixels (more than 10% of the integrated area
affected)." It appears that in practice many stars that can be measured
well get this flag. As always, you may manually specify the maximum
acceptable SExtractor flag with '-x' option on the command line:
 # Accept blended stars
./vast -x3 /path/to/my/images*.fit
 # Accept everything including saturated stars
./vast -x99 /path/to/my/images*.fit

 * VaST now compiles with link time optimization (LTO) enabled 
by default on Linux systems. If this doesn't work for you - remove 
`lib/set_lto.sh` from OPTFLAGS in Makefile and re--compile with 'make'.

 * Further improvements to the automatic testing script
 util/examples/test_vast.sh
Beware, the script will download ~2Gb of test data and will need an hour to run!
If you have fast internet connection, you are welcome to run this
test script. Please write me if the test script reports any problems.

 * Added warning messages discouraging a user from running VaST on a small
number of images (and then be disappointed by the result).
Currently, the two 'proper' ways to run VaST are:

 1) Run VaST on a long (50-100-1000) series of images and inspect
lightcurves that show a large scatter.

 2) Run VaST in the 'transient detection' mode on *four* (4) images:
two reference and two second-epoch images. Then create an HTML
search report by running
 util/transients/search_for_transients_single_field.sh
VaST will run on a different number of images 2, 3, 5 (now printing
the warning message), but the results are unpredictable.

 * Added Median Absolute Deviation (MAD) as one of the displayed variability
indexes, see https://en.wikipedia.org/wiki/Median_absolute_deviation

 * Changed the "Modified sigma" index to the simple "Weighted sigma"

 * Stetson's J and L variability indexes computed using time-based
weighting are now displayed. For a detailed discussion of these indexes see
 http://adsabs.harvard.edu/abs/1996PASP..108..851S
and
 http://adsabs.harvard.edu/abs/2012AJ....143..140F

 * S_B variability detection statistic is now displayed, see
 http://adsabs.harvard.edu/abs/2013A&A...556A..20F
for a detailed discussion.

 * The variability index plots are now displayed in the following order:

 1) Standard deviation

 2) Weighted standard deviation

 3) Median Absolute deviation (MAD)

 4) Robust median statistic (RoMS) 

 5) Stetson's J with time-based weighting of pairs

 6) Stetson's L with time-based weighting of pairs

 7) S_B variability detection statistic

The first four indexes characterize the lightcurve scatter, 
Stetson's indexes (5 and 6) characterize the degree of correlation between
consecutive measurements, S_B statistic (7) combines information
about the correlation and the overall scatter. As before, you may
switch between these plots by pressing 'M' or 'N' on the keyboard
while in the variability search window (./find_candidates).

 * util/load.sh the script that loads work previously saved with
util/save.sh now checks if SExtractor configuration files that 
are to be loaded are the same as the ones currently present in VaST
directory. If the files are identical, the script doesn't bother   
user with the silly question "Do you want to rewrite a configuration
file?". The program md5sum should be installed in your system for   
this functionality to work.

 * The VaST settings header file src/limits.h is renamed to src/vast_limits.h
to avoid confusion with the standard C library header file also
called limits.h

 * Edited src/gsl/Makefile.in so GSL can compile without makeinfo (texinfo)
installed in the system.

 * Added timeout of 300 seconds to all network communications so the
program doesn't hang indefinitely if the connection fails at a critical moment.

 * Changed the way all VaST subroutines read lightcurve files - now they
use a dedicated function rather than simple 'scanf()'. This will
eventually allow VaST to natively handle lightcurve files in formats
other than the strict VaST format of "JD mag err X Y ap imagefilename".
The downside of this change is that lightcurve reading is noticeably slower than it used to be.
The support of multiple lightcurve formats is still in the experimental stage though. 
For now, in order to import ASCII lightcurve files in the format "JD mag err" into VaST     
use the script util/convert/three_column_ascii2vast.sh which will
convert them into the strict VaST format.



23 Jun 2015: vast-1.0rc73

 * Fixed the bug that caused VaST to fail if it tries to guess 
a saturation limit of an image that does not contain BUNIT key in
its header (sadly, the majority of ground-based images do not 
have this keyword).

 * Saturated pixels with values = 65535 are not flagged-out in the
flag image in order not to remove the saturated objects from the
list of detections. The brightest objects, even saturated ones, 
are useful for image matching and performing a blind plate solution
with the Astrometry.net code.

 * An additional aperture photometry run is performed for each image
processed in the PSF-fitting mode. The goal is, again, to have the
list of detections that includes the brightest stars. Under the
normal circumstances, saturated stars are omitted by VaST from the 
list of detections when working in the PSF-photometry mode.
The brightest stars are needed to perform blind plate solution with
the Astrometry.net code.

 * VaST is not attempting to create a flag image for input images
that contain many negative values as, in this case, zero-value pixels
are likely not the bad ones and should not be flagged.

 * Restored the partly-broken transient detection mode. See the
instructions at http://scan.sai.msu.ru/vast/#transientsearch
if you want to try it. The links to external resources in the HTML
transient search report located in transient_report/index.html 
(including MPChecker as well as CSS and NMW archives) are working again.

 * It is now possible to exit the catalog magnitude calibration plot
by pressing 'x' on a keyboard. Before the program was expecting only
the capital 'X' or right mouse click to exit.

 * Added timeout and retry attempts to util/solve_plate_with_UCAC4
subroutine in order to be able to recover from network connection
failures during communication with VizieR.

 * Further improvements to the automatic testing script util/examples/test_vast.sh
Beware, the script will download ~1.5Gb of test data!
If you have fast internet connection, you are welcome to run this
test script. Please write me if the test script reports any problems.

 * Updates and broken-link fixes on the VaST web page: http://scan.sai.msu.ru/vast/

 * The outdated README file is replaces by an HTML page in doc/ directory.



10 Jun 2015: vast-1.0rc72

 * Fixed the PSF photometry mode that was not working for images that
do not require creation of an external flag image.

 * VaST is now trying to explicitly set GAIN value if it is found in
the FITS header ("GAIN" keyword). You may also set the GAIN value
manually in default.sex file - VaST will not try to override it if
if it finds that the default gain value in default.sex is changed.
VaST will also try to recognize "count" and "countrate" images where 
the image units are "electrons" and "electrons/s" instead of ADUs
(electrons/gain) and set an appropriate gain value ("1" or equal to
exposure time in seconds, respectively). The correct gain value is 
needed to estimate Poisson noise contribution to photometric
measurement errors. See equation (61) in Section 10.4 of 
SExtractor documentation.
Note that SExtractor itself will try to override both GAIN and
SATUR_LEVEL values set in default.sex using FITS header keys
specified in default.sex as GAIN_KEY and SATUR_KEY.
Please set an appropriate gain value in default.sex if this
information is not available from FITS image header.

 * The plotting programs ./find_candidates, ./lc, ./pgfv
now ignore clicks outside the plotting area, so now one can easily
switch between multiple windows by left-clicking green area outside
the plot in each window.

 * The lightcurve viewer ./lc now marks the latest lightcurve point 
that was inspected by user.

 * The internal copy of CFITSIO library is updated to v3.370.

 * Introduced VaST testing script util/examples/test_vast.sh 
Beware, the script will download ~1.5Gb of test data!
If you have fast internet connection, you are welcome to run this
test script. Please write me if the test script reports any problems.



27 May 2015: vast-1.0rc71

* Restored the PSF photometry mode. It requires PSFEx 
and a recent SExtractor version 2.8 or later to work. 
Unfortunately, PSF fitting cannot be performed with the old
Sextractor-2.5 supplied with VaST, so you'll need to manually install a
newer SExtractor and PSFEx in your system. Please consult PSFEx manual to
learn about PSF extraction parameters set in default.psfex These
parameters will most likely require fine tuning for your images. 
To start VaST in the PSF photometry mode:
./vast -P ../sample_data/f_72-0*

* Instead of just displaying the familiar mag-sigma plot, ./find_candidates
can now also plot the following variability indexes as a function of magnitude:
 + Weighted sigma divided by the number of points in the lightcurve. The
idea is to artificially hide the lightcurves having large sigma but only a
small number of measurements. The weighting scheme follows Stetson (1996)
attempting to downweight outlier points in a lightcurve.
 + Stetson's L variability index as defined in the 1996 paper
 + Robust Median Statistic (RoMS) as defined by Enoch, Brown & Burgasser (2003)
 + The simple "peak-to-peak" variability index suggested by Aller, Aller & Hughes (1992)
 The peak-to-peak index is defined as 
v = ( ( M_max - error(M_max) ) - ( M_min + error(M_min) ) ) / ( ( M_max - error(M_max) ) + ( M_min + error(M_min) ) )
so it can be negative if the observed lightcurve scatter is lower than estimated errors.
Use 'M' and 'N' keys to switch between the plots.
For all the plots, a higher value generally indicates that an object is more
likely to be variable.

* The default SExtractor parameter files are changed to use "XWIN_IMAGE,
YWIN_IMAGE" star positions instead of "X_IMAGE, Y_IMAGE". It should result
in an improved astrometric accuracy at the cost of slightly longer
computing time. See Section 10.2 of the "official" SExtractor documentation for details.

* The internal FITS viewer ./pgfv now supports 32-bit images that lack BZERO
keyword in the header.

* The internal FITS viewer ./pgfv can now handle images with a narrow range
of pixel values like from 0.0 to 1.0.

* The internal FITS viewer ./pgfv can work with files having a white space in the name.

* The internal image viewer ./pgfv, if started from the lightcurve
inspection tool ./lc, will automatically zoom-in on the star of interest.
You may see the full image by pressing 'D' or 'Z'+'Z' to zoom-out.

* Renamed ds9 region file from vast_list_of_all_stars.ds9 to
vast_list_of_all_stars.ds9.reg in order to prevent ds9 from trying to open
it automatically each time it starts. The proper way to use this file would be
ds9 /path/to/reference/image.fits -region vast_list_of_all_stars.ds9.reg

* VaST now supports FreeBSD operating system. Tested on FreeBSD 10.1 with gcc.

Changes  are introduced in an attempt to allow VaST to handle HST Level 1
(exposure) images from the Hubble Legacy Archive:

* Image date can now be set from EXPSTART key containing MJD(UTC) of the exposure start.

* VaST is trying to guess the saturation limit for each image as
guessed_saturation_limit=maxval-SATURATION_LIMIT_INDENT*maxval
where maxval is the brightest image pixel and SATURATION_LIMIT_INDENT is set
in src/limits.h. By default SATURATION_LIMIT_INDENT=0.1. This behaviour may
be turned on by running ./vast with -g option or off by using -G option. If
none of the two options is specified explicitly, VaST will make a wild guess
if it should use SATUR_LEVEL specified in default.sex or if it should try to
guess it for each image individually.

* VaST will check how many pixels having the value of exactly zero are in
the input image and if there are more than
FRACTION_OF_ZERO_PIXEL_TO_USE_FLAG_IMG*total_number_of_pixels the program
will automatically produce a flag image for SExtractor to filter-out stars
overlapping with these bad pixels. The value of
FRACTION_OF_ZERO_PIXEL_TO_USE_FLAG_IMG can be changed in src/limits.h.
Make sure to run 'make' after updating src/limits.h for the changes to take effect.



11 Mar 2015: vast-1.0rc70

* Automatic choice of a VizieR mirror.

* VaST can now handle filenames with white spaces if they are specified in
the command line (but not in the vast_list_of_input_images_with_time_corrections.txt file, sorry).

* VaST is trying to guess the field of view of an image (for plate solving)
if it was not specified explicitly. The guess is based on a
previously-solved image of this same field or on the FOCALLEN key in the
FITS header (assuming it contains focal length of the telescope expressed in mm).

* If a blind plate solution failed with a specified (or guessed) field of
view, the program retries to solve the image assuming a larger or smaller field of view.



7 Mar 2015: vast-1.0rc69

* The program can now again work with VizieR.

* Astrometric calibration of images can now be performed using one of a few
plate-solving servers (the best one is be chosen automatically) or using a
local copy of Astrometry.net software (if it is installed in the system).

* Improvements in the plate solving algorithm.

* VaST FITS image viewer (./pgfv) now remembers image orientation (set by
pressing 'V' and 'B' on a keyboard) after changing zoom (keyboard 'Z').

* The magnitude-scatter plotter if started in the non-recompute mode
(./find_candidates aa) will now remember stars viewed by user earlier
(indicated as green points on the plot).

* While performing a manual magnitude scale calibration with
util/magnitude_calibration.sh it is now possible to cancel the input by
typing 99 instead of an actual star magnitude. This is useful in case one
selected a wrong comparison star.

* The magnitude calibration routine is now trying to guess if parabola or
the "photocurve" provide a better approximation of the "measured
mag."->alog mag." plot.elation. One can always override the automatic
choice by pressing 'P' while looking at the "measured mag."->"catalog mag." plot.

* Fixed the bug that prevented lib/vizquery from working properly if
cdsclient is not installed system-wide (wwwget was missing from $PATH).
Now VaST includes a fully self-contained copy of cdsclient.

* VaST now supports images obtained with the SBG camera of Kourovka
Astronomical observatory (Ural Federal University) that have a
non-standard FITS-like header.

* Updated tai-utc.dat file includes the leap second to be inserted at the
end of June 30, 2015 at 23:59:60 UTC. (This is needed for accurate UTC->TT
conversion after that date.)



17 Jun 2014: vast-1.0rc68

* The program can now again access VizieR. This feature was broken because
of the change in order of output columns printed by vizquery script.
Star identification scripts now work again. :)

* The Kwee - van Woerden (1956BAN....12..327K) minimum finding method built
into the VaST lightcurve viewer (./lc) now returns the full JD, not the one
relative to the lightcurve start. To activate the Kwee - van Woerden
algorithm, press 'K' in the lightcurve inspection window.

* The input images may now be specified not only as command line arguments,
but also listed in the file
vast_list_of_input_images_with_time_corrections.txt
located in the VaST directory. The file should have two columns:
absolute or relative path to the image file and time correction in seconds
that should be applied to the file (in most cases should be 0.0).
Full JD of the image may also be specified instead of the time correction.
That will override JD determined from the image FITS header. VaST will guess
what it is based on the specified value. See examples in
vast_list_of_input_images_with_time_corrections.txt_example

* Instead of specifying each image on the command line or in the
vast_list_of_input_images_with_time_corrections.txt file, it is now possible
to give a directory name as a command line argument. VaST will process all
FITS images found in the specified directory, but it will not look
recursively into sub-directories. Note that if only the directory name is
specified, user has no control over which image in this directory is
processed first and, therefore, used as the reference image. It is possible
to mix all three input methods (individual images specified in a command
line, vast_list_of_input_images_with_time_corrections.txt file and
directories specified in a command line) in a single VaST run, so one can
specify the first (reference) image explicitly on the command line.

* Fixed the bug causing segmentation fault when input images have different
size. Note that the input images may have different size in pixels, but
still have to have the same scale ("/pix) in order to be processed in a
single VaST run.

* Minor improvements in the image matching algorithm resulting in
a ~10% speed-up on a typical dataset.


13 May 2014: vast-1.0rc67

* Fixed the bug that caused "buffer overflow" crash on long image series (of
a few thousand images).

* New routine provides a locally-corrected astrometric position for each
object on an image. The astrometry is based on UCAC-4. The routine may be
called directly as

util/solve_plate_with_UCAC4 myfitsimage.fits 40

(here myfitsimage.fits is the FITS image file name, "40" is the approximate
field of view in arcminutes) to produce a list of sources on the given
image. A better way to benefit from it is by using the automated
identification script (util/identify.sh or 'U' key in the lightcurve
inspection window) and (hopefully) enjoying the much-improved astrometric
accuracy. This new astrometric routine needs Internet connection to work,
but the identification script needs it anyhow...

* It is now possible to use APASS magnitudes listed in UCAC-4 to calibrate
the instrumental magnitude scale. Use the script

util/magnitude_calibration.sh R 40

(where "R" is the observing band/filter and "40" is the approximate field of
view in arcminutes passed to the plate solution routine). The choice of
observing bands is the following:

+ "C" for "clear" are the unfiltered UCAC-4 magnitudes

+ "B" are the APASS B magnitudes

+ "V" are the APASS V magnitudes

+ "r" are the APASS r magnitudes

+ "i" are the APASS i magnitudes

+ "R" are Rc magnitudes computed from APASS V, r and i following Jester et
al. (2005), see http://www.sdss.org/dr4/algorithms/sdssUBVRITransform.html
Choose the scale that best matches your observing band. "R" is the usual
choice for unfiltered CCD chips, "V" may be appropriate for unfiltered
blue-sensitive CCD chips and green-channel of DSLRs, "B" may be good for
blue-sensitive photographic plates.
The old version of the magnitude calibration script is renamed to
util/magnitude_calibration_USNO-B1.0.sh

* Internal copies of libraries are updated to CFITSIO v3.360 and gsl-1.16.

* Plate solution details (such as field of view size and its center) are now
printed out in a terminal.

* Improved Aladin script that generated and launched if you have Aladin
installed locally. The script now displays both DSS and the original input
images. This may be useful to visually confirm identification of an
interesting object. The star suggested as a correct identification by the
automated procedure is clearly marked in the Aladin plot.

* Server-side plate solution software is upgraded to astrometry.net-0.46
which (in a combination with new index files produced from Tycho-2 and 2MASS
catalogs) provides considerably better solutions of some badly distorted
images (think telephoto lenses and wide-field photographic plates). Silly
enough, it turned out that previous versions of the VaST plate solution
routine cannot handle the long FITS header produced by astrometry.net-0.46.
Please upgrade to vast-1.0rc67 if you conduct plate solutions from within
VaST.


27 Mar 2014: vast-1.0rc66

* Fixed the script performing absolute magnitude calibration
(util/magnitude_calibration.sh). It was broken by a change in the output
format of vizquery. To calibrate the magnitude scale using USNO-B1.0
B magnitudes as a reference you may execute:
util/magnitude_calibration.sh B
to do the same using R magnitudes from USNO-B1.0:
util/magnitude_calibration.sh R

* Fixed a problem preventing VaST from compiling on some virtual machines
when "gcc -march=native" cannot correctly recognize the processor
architecture.

* Fixed a problem preventing VaST from starting on a system that is low on
RAM. Now, if there is enough memory to process the data - VaST should be
able to use it efficiently.

* New log files vast_list_of_all_stars.log and vast_list_of_all_stars.ds9
contain pixel coordinates of all detected stars in thee list formated as a
region file that can be loaded into the ds9 FITS image view list wile
vast_list_of_all_stars.ds9 is the same list formated as a region file that
can be loaded into the ds9 FITS image view list wile
vast_list_of_all_stars.ds9 is the same list formated as a region file that
can be loaded into the ds9 FITS image viewer.


29 May 2013: vast-1.0rc65

* Added linear magnitude correction as a function of star position on
a frame. This is useful to correct extinction on very wide field (a few
degrees) images such as those obtained in the NMW survey
( http://scan.sai.msu.ru/nmw/ ). By default, the program will turn on this
correction if the reference image has more than 10000 stars on it. You may
manually turn this correction on (off) by starting VaST with "-j" ("-J")
flag. If you have wide field images, try to experiment with this option and
see what works best for your data.

* The star matching algorithm is now allowed to use saturated and blended
stars for image identification. This slightly degrades the quality of the
initial plate solution, but that is corrected for at a later stage. The good
thing is that this change makes the algorithm much more stable and it
typically requires less reference stars to match images.
The image matching process becomes faster.

* Fixed broken links to WISE-Atlas in the transient detection mode.

* Fixed the lightcurve viewer (./lc) crash when one tries to delete the
first point from a non-VaST-formatted lightcurve.


13 Apr 2013: vast-1.0rc64

* "Official" support of the transient detection mode. The code was there for
quite some time, but was lacking documentation and had to be tested
extensively. The code is still FAR from perfect, but I believe it may
already be useful. See the VaST home page for details.

* A major bug that prevented stars with very large sigma from appearing on
the sigma-magnitude plot is now fixed. Thanks to Fidrich Robert for
discovering it!

* "JD" keyword is read form a FITS header only if "DATE-OBS" keyword was not
found. Useful for FITS files that have both keywords in their headers.

* Fixed an issue that prevented VaST to compile on Mac OS after the latest
development environment update. Thanks to Alexei Alakoz for his valuable
help in testing!

* A new script util/catalina_search_area_TEST.sh is introduced that allows
to search Catalina Sky Survey data in a small area around a particular sky
position. The data may be processed using standard VaST tools. The current
implementation of the script is very slow and is meant only for testing and
feasibility studies, it is not ready for mass-processing of CSS data.

* An automatic-testing script lib/test_vast_release.sh is introduced. It
currently works only with a system-wide installation of SExtractor 2.8.6 and
consumes tens of megabytes of Internet traffic. But, if this is not a
problem - you are welcome to try it!

* Minor bug fixes.


16 Jan 2013: vast-1.0rc63

* Fixed the major bug that caused the new star matching algorithm
(introduced in vast-1.0rc62) to fail to match some stars in close pairs. The
problem was evident on large datasets when the program got swamped by
unidentified stars, while the older versions of VaST could handle these
datasets. I am deeply grateful to E. G. Lapukhin for spotting the problem.
Thank you! :)

* The program now uses internal versions of PGPLOT and GSL libraries, so
users do not have to worry about installing these libraries system-wide.

* VaST now comes with a built-in SExtractor v2.5. It is still recommended to
use a system-wide installation of a newer SExtractor version, but now, if
VaST fails to find "sex" executable in the $PATH, it will use the internal
one. This might be helpful for those who have problems compiling new
SExtractor or, more likely, ATLAS libraries on which the new SExtractor
depends.

* Individually processed images may now be viewed with DS9 instead of the
internal VaST image viewer: ./sextract_single_image -9 image.fits

* Fixed the bug that caused VaST not to create
vast_stars_with_large_sigma.log file when used with gsl-1.15.

* VaST was successfully tested on MacOS X 10.8.2 'Mountain Lion' + XQuartz,
Xcode, MacPorts -> gcc (including gfortran and g++), wget
(resolution is fine with a retina display).

* Internal CFITSIO library upgraded to Version 3.31.

Overall, if one has a Linux or Mac system with a working development
environment based on gcc, the new version of VaST is supposed to just
compile and work, with no need to manually install additional libraries and
programs. How well does it work in real life? Well... Bug reports and
success stories are welcome, as always! ;)


28 Oct 2012: vast-1.0rc62

* Improved star matching algorithm resulting in ~2x overall performance
increase on large datasets.

* The online period search interface ("L" in the lightcurve inspection
window) tries to set reasonable maximum and minimum trial periods
automatically.

* All lightcurves inspected with the online period search service are saved
locally in the "saved_period_search_lightcurves/" directory, so it's easier
to find them later.


28 May 2012: vast-1.0rc61

* The new experimental feature in vast-1.0rc61 is its integration with the
online period search service. You may try it by pressing 'L' key at the
lightcurve inspection window (./lc). The lightcurve will be sent to a remote
server for analysis and a browser window will open displaying the results.
Naturally, this feature requires an active Internet connection to work. You
are also welcome to try the period search service as a stand-alone
web-application by pointing your browser to http://scan.sai.msu.ru/lk/

* The bug is fixed which caused VaST to crash on images that have no comment
field for the DATE-OBS key in the FITS header.

* Improved stability of the magnitude calibration solution in "difficult
cases".

* The new version contains a local copy of the vizquery script from
cdsclient-3.7 package. No need to install cdsclient, for the automatic star
identification (e.g., "util/identify.sh out01234.dat") and magnitude
calibration (e.g., "util/magnitude_calibration.sh R") scripts to work.

* VaST correctly handles the situation when it cannot create child processes
(for example, because the system runs out of memory) during the execution of
the main program.

* vast-1.0rc61 compiles on the latest version of Ubuntu. Please check also
the updated instructions for Ubuntu users at the VaST homepage:
http://scan.sai.msu.ru/vast/#down

Frequently Asked Questions

How to set the aperture photometry parameters such as the aperture diameter, gap size, background region?

#------------------------------ Background -----------------------------------
BACK_SIZE       32              # Background mesh: size or width,height
BACK_FILTERSIZE 1               # Background filter: size or width,heigh
BACKPHOTO_TYPE  LOCAL           # can be "GLOBAL" or "LOCAL"

How to perform differential photometry with VaST?

How to obtain a lightcurve of an individual object with VaST?

VaST doesn't detect my target source. What's wrong?

1  The object has neighbors, bright and close enough to
   significantly bias the photometry, or bad pixels
   (more than 10% of the integrated area affected).

2  The object was originally blended with another one.

VaST doesn't run complaining that no images are found.

Which Linux distribution is suitable for VaST?

Is there a Windows version of VaST?

Can VaST process DSLR images?

# capt0000.cr2 is the input RAW iamge

# Decode the RAW image and save as TIFF with 16 bits per color channel
dcraw -q 0 -f -4 -T -t 0 capt0000.cr2

# Get image info to insert it later in FITS header
DATEOBS=`identify -verbose capt0000.tiff 2>/dev/null | grep "date:create" | awk '{print $2}' | awk '{print $1}' FS='+'`
EXPTIME=`identify -verbose capt0000.tiff 2>/dev/null | grep "exif:ExposureTime:" | awk '{print $2}'`
FOCALLEN=`identify -verbose capt0000.tiff 2>/dev/null | grep "exif:FocalLength:" | awk '{print $2}'`

# Convert color TIFF image to monochrome FITS file extracting only green color chennel
/home/kirx/cod.old/tiff2fits/tiff2fits -c 1 capt0000.tiff test.fit

# Set FITS header info
sethead test.fit date-obs=$DATEOBS
sethead test.fit exptime=$EXPTIME 
sethead test.fit focallen=$FOCALLEN

VaST cannot match images in the input series.

#------------------------------- Extraction ----------------------------------
DETECT_MINAREA  2.0             # minimum number of pixels above threshold
DETECT_THRESH   2.0             # sigmas or threshold,ZP in mag.arcsec-2
ANALYSIS_THRESH 2.0             # sigmas or threshold,ZP in mag.arcsec-2

How to minimize the detection of stars near the edge of the field?

What exact metadata from the FITS image VaST needs, other than the image itself? Exposure time?

VaST calibrates the magnitude scale as a part of data processing... How exactly is this done?

How does the software compensate for differences between images, like different photographic plate types, exposure times, image quality etc.?

Is aperture photometry that VaST does enough in most cases, or should I do PSF-fitting photometry?

How to acknowledge VaST in a publication?

List of publications which make use of VaST

1. E. G. Lapukhin, S. A. Veselkov, A. M. Zubareva "New Variable Stars in Cepheus: Area of 2.3x2.3 deg., Centered at RA=22h00m, Dec=60d00' (2000.0). Part I"
   PZP, vol. 15, N 8 (2015) Available here.
2. T. Kryachko, A. Samokhvalov, B. Satovskiy; "Variability of TCP J04283707+3157578"
   PZP, vol. 15, N 3 (2015) Available here.
3. E. G. Lapukhin, S. A. Veselkov, A. M. Zubareva, E. D. Starovoit, I. V. Kolbasina; "New Variable Stars in Lacerta: Area of 2.3x2.3 deg., Centered at RA=22h50m, Dec=50d00' (2000.0). Part III."
   PZP, vol. 14, N 12 (2014) Available here.
4. E. G. Lapukhin, S. A. Veselkov, A. M. Zubareva, E. D. Starovoit, I. V. Kolbasina; "New Variable Stars in Lacerta: Area of 2.3x2.3 deg., Centered at RA=22h50m, Dec=50d00' (2000.0). Part II."
   PZP, vol. 14, N 11 (2014) Available here.
5. E. G. Lapukhin, S. A. Veselkov, A. M. Zubareva; "New Variable Stars in Ursa Major: Area of 2.3x4.6 deg., Centered at RA=12h00m, Dec=54d30'"
   PZP, vol. 14, N 8 (2014) Available here.
6. E. G. Lapukhin, S. A. Veselkov, A. M. Zubareva, E. D. Starovoit, I. V. Kolbasina; "New Variable Stars in Lacerta: Area of 2.3x2.3 deg., Centered at RA=22h50m, Dec=50d00' (2000.0). Part I"
   PZP, vol. 14, N 7 (2014) Available here.
7. K. V. Sokolovsky, S. A. Korotkiy; "New Variable Stars Discovered by the NMW Survey"
   PZP, vol. 14, N 6 (2014) Available here.
8. D. Majaess, G. Carraro, C. Moni Bidin, C. Bonatto, L. Berdnikov, D. Balam, M. Moyano, L. Gallo, D. Turner, D. Lane, W. Gieren, J. Borissova, V. Kovtyukh, Y. Beletsky; "Anchors for the cosmic distance scale: the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae"
   2013 Astronomy & Astrophysics, Volume 560, id.A22 Available here.
9. Kirill Sokolovsky, Sergei Antipin, Daria Kolesnikova, Alexandr Lebedev, Nikolai Samus, Lyudmila Sat, Alexandra Zubareva; "A search for new variable stars using digitized Moscow collection plates"
   in proceedings of the AstroPlate workshop, Prague, Villa Lanna, March 18-21, 2014 Available here.
10. E. G. Lapukhin, S. A. Veselkov, A. M. Zubareva; "New Variable Stars in Lacerta: Area of 2.3x2.3 deg, Centered at alpha=22h50m, delta=52d00' (2000.0)"
    PZP, vol. 13, N 12 (2013) Available here.
11. Kirill Sokolovsky, Stanislav Korotkiy, Alexandr Lebedev; "The New Milky Way: a wide-field survey of optical transients near the Galactic plane"
    in Stella Novae: Future and Past Decades, P. A. Woudt & V. A. R. M. Ribeiro (eds), ASPCS. (2013) Available here.
12. V. Solovyov, A. Samokhvalov, T. Kryachko, B. Satovskiy; "New Variable Stars at the Borderline of Ophiuchus and Serpens"
    PZP, vol. 13, N 10 (2013) Available here.
13. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Perseus"
    PZP, vol. 13, N 8 (2013) Available here.
14. E. G. Lapukhin, S. A. Veselkov, D. A. Yatmanov, A. M. Zubareva; "New Variable Stars in Lyra: Area of 2.3x2.3 deg., Centered at alpha=19h25m.0, delta=42d47' (2000.0)"
    PZP, vol. 13, N 4 (2013) Available here.
15. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Auriga III"
    PZP, vol. 13, N 2 (2013) Available here.
16. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Aquila II"
    PZP, vol. 12, N 21 (2012) Available here.
17. E. G. Lapukhin, S. A. Veselkov, S. V. Antipin, N. N. Samus; "New Variable Stars in Auriga: Area of 2.3x2.3 deg., Centered at alpha=06h00m, delta=29d15'";
    PZP, vol. 12, N 19 (2012) Available here.
18. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Ophiuchus III"
    PZP, vol. 12, N 17 (2012) Available here.
19. V. Solovyov, A. Samokhvalov, B. Satovskiy; "A Possible New FU Ori-type Variable Star"
    PZP, vol. 12, N 16 (2012) Available here.
20. V. Solovyov, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Ophiuchus II"
    PZP, vol. 12, N 15 (2012) Available here.
21. K. V. Sokolovsky, D. Gareeva, E. Gorbovskoy, A. Kuznetsov, V. Yurkov, E. Sinyakov; "New Semiregular Variable Star in Draco"
    PZP, vol. 12, N 14 (2012) Available here.
22. S. V. Antipin, A. M. Zubareva; "New Cepheid in Cygnus and Four New Eclipsing Variables"
    PZP, vol. 12, N 13 (2012) Available here.
23. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New UV-type Variable Star USNO-A2.0 0900-17250765"
    PZP, vol. 12, N 12 (2012) Available here.
24. E. G. Lapukhin, S. A. Veselkov, S. V. Antipin, N. N. Samus; "New Variable Stars in Ursa Major: Area of 9°.2â2°.3, Centered at alpha=13h38m, delta=53d30'"
    PZP, vol. 12, N 10 (2012) Available here.
25. A. C. Gupta et al. "Multiwavelength intraday variability of the BL Lacertae S5 0716+714"
    2012, MNRAS, 425, 1357 Available here.
26. K. V. Sokolovsky; "The Variability Type and Period of V348 Aql"
    PZP, vol. 11, N 33 (17.11.2011) Available here.
27. 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.
28. 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.
29. 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.
30. 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.
31. 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.
32. 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.
33. V. Solovyov, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Perseus"
    PZP, vol. 11, N 14 (7.04.2011) Available here.
34. 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.
35. N. Virnina, S. V. Antipin, A. M. Zubareva; "Four New Eclipsing Variable Stars"
    PZP, vol. 11, N 9 (14.03.2011) Available here.
36. 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.
37. 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.
38. Natalia A. Virnina; ""Tsessevich" Project: an Attempt to Find the System YY Dra. I"
    2011 OEJV, 133, 1 Available here.
39. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Auriga II"
    PZP, vol. 11, N 4 (28.01.2011) Available here.
40. 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.
41. 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.
42. 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.
43. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Aquila"
    PZP, vol. 10, N 25 (26.10.2010) Available here.
44. 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.
45. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Taurus"
    PZP, vol. 10, N 17 (18.05.2010) Available here.
46. 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.
47. T. Kryachko, A. Samokhvalov, B. Satovskiy, D. Denisenko; "New Variable Stars in Cygnus II"
    PZP, vol. 10, N 10 (9.03.2010) Available here.
48. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New Variable Stars in Auriga"
    PZP, vol. 10, N 3 (2.02.2010) Available here.
49. T. Kryachko, A. Samokhvalov, B. Satovskiy, D. Denisenko; "New Variable Stars in Cygnus"
    PZP, vol. 10, N 2 (27.01.2010) Available here.
50. 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.
51. K. V. Sokolovsky; "NSVS 304708 is a High Amplitude Delta Scuti Star"
    PZP, vol. 9, N 30 (5.11.2009) Available here.
52. 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.
53. Alex Golovin, Kirill Sokolovsky, Natalia Virnina, Javier Lopez Santiago; "Three New Variable Stars in Indus";
    2009 OEJV, 111, 1 Available here.
54. 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.
55. 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.
56. 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.
57. T. Kryachko, A. Samokhvalov, S. A. Korotkiy; "New Eclipsing Variable Stars in Canis Minor"
    PZP, vol. 9, N 18 (17.06.2009) Available here.
58. T. Kryachko, A. Samokhvalov, D. Denisenko, B. Satovskiy; "New Variable Stars in Gemini"
    PZP, vol. 9, N 10 (28.04.2009) Available here.
59. K. V. Sokolovsky; "Three New Eclipsing Binaries Near the Galactic Center"
    PZP, vol. 9, N 9 (11.03.2009) Available here.
60. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New variable stars in Andromeda II"
    PZP, vol. 9, N 7 (13.02.2009) Available here.
61. 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.
62. 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.
63. T. Kryachko, A. Samokhvalov, S. A. Korotkiy; "New Variable Stars in Andromeda"
    PZP, vol. 8, N 48 (8.12.2008) Available here.
64. T. Kryachko, A. Samokhvalov, D. Denisenko, B. Satovskiy; "New Variable Stars in Ophiuchus"
    PZP, vol. 8, N 43 (24.11.2008) Available here.
65. 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.
66. 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.
67. 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.
68. T. Kryachko, A. Samokhvalov, B. Satovskiy; "New EW Variable Star GSC 0584-01373"
    PZP, vol. 8, N 28 (15.09.2008) Available here.
69. 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.
70. 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.
71. 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.
72. 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.
73. T. Kryachko, K. Sokolovsky, B. Satovskiy; "Five New Variable Stars"
    PZP, vol. 8, N 8 (2008) Available here.
74. 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.
75. 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.
76. 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.
77. 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.
78. 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.
79. 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.
80. 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.
81. 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.
82. K. V. Sokolovsky; "Optical Variability of the Seyfert Galaxy FBQS J161047.7+330337"
    PZP, vol. 6, N 18 (30.06.2006) Available here.
83. 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.
84. 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.
85. 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.

Variable star search software not related to VaST

• C-Munipack/Muniwin - The C-Munipack is the software package which offers the complete solution for reduction of CCD observations of variable stars. It runs both on Windows and Linux. C-Munipack is free software licensed under the GPLv2.
• Astrokit - corrects for atmospheric transparency variations by selecting an optimal set of comparison stars for each object in the field. IRAF's PHOT/APPHOT task is meant to be used to generate input photometric data for Astrokit. Variable star candidates are selected with Robust Median Statistics. Astrokit is licensed under the GPL.
• VARTOOLS - is a powerful command line utility that provides tools for processing and analyzing astronomical time series data. It includes methods for calculating variability/periodicity statistics of light curves; for filtering, transforming, and otherwise modifying light curves; and for modeling light curves. It is intended primarily for batch processing a large number of light curves. The input photometric data should be generated by other software (or downloaded from an archive) and then converted to a VARTOOLS-friendly format. VARTOOLS is licensed under the GPL.
• HOTPANTS - High Order Transform of PSF ANd Template Subtraction is designed to photometrically align one input image with another, after they have been astrometrically aligned. This is an implementation of the Alard 1999 algorithm for image subtraction. The program is intended to be used as part of a transient detection or photometry pipeline.
• ISIS - is a complete package to process CCD images using the image subtraction method. It allows one to find variable objects in the subtracted images and build their light curves from a series of CCD images. The package includes a period search routine based on the Schwarzenberg-Czerny method.
• TraP - is a Python and SQL based system for detecting and responding to transient and variable sources in a stream of astronomical images. It primarily targets LOFAR radio astronomy data, but is also applicable to a range of other instruments (presumably, including the optical ones).

Other tools that might be useful

• Web-based lightcurve analysis tool - allows one to perform a period search using Lafler & Kinman (1965, ApJS, 11, 216) and Deeming (1975, Ap&SS, 36,137) methods.
• The New Milky Way survey image archive. A detailed description of the survey is available here.
• 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 digitized 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.
• Online FITS-to-ASCII lightcurve converters are available for INTEGRAL/OMC and SuperWASP data. The converters are based on the OMC2ASCII code.