and now the universe

From: Joe Patterson <*jop_at_astro.columbia.edu*> Date: Thu, 10 Oct 2002 15:41:28 -0400 (EDT) · jop_at_astro.columbia.edu

Dear CBAers,

     When we (Dave Skillman and I) started the CBA ~15 years ago, we
thought it would be a good research tool for many subject areas in
astronomy, not just CVs.  Personally I had in mind stars like Delta
Scuti variables - bright short-period pulsators.  But I have gotten
(and continue to be) so seduced by superhumps that they consume my
waking hours.  So we haven't spread out much to other areas, and our
observing techniques have effectively been fine-tuned for that one
topic.

     In some ways, it's odd.  The CBA is mainly amateur astronomers,
and amateurs are renowned for *discovery*... whereas professionals are
much more likely to spend years staring at one star to extract one
precious number from it.  Like we do.  While the CBA - of course! -
takes pride in being a ragtag cabal of misfits, I'm sure there are some
of you who'd like to do some of the discovery work too.  As well as
think about new scientific questions and technical challenges.

     I've been talking to Bohdan Paczynski about this.  He's interested
in the entire census of variable stars over the whole sky, for which
there is still no satisfactory data base.  The project he describes
below (ASAS) is a big step in that direction, but needs more stations
around the world to subdue the menaces of weather and longitude.  A
proper all-sky network should be all-earth and all-clear!

     So he wrote out a request for volunteers.  Note how different it
is from our usual thing: very small aperture and wide field, standard
filters, and the need for robotic operation eventually since it should
be running all night.  Looks mighty interesting to me.  See what you
think!

             joe
__________________________________

Joe,

Enclosed is a short text explaining the reason why monitoring the sky for 
variability is a new exciting frontier of astronomy, and references to
some Web sites.  I am more than happy to provide more information, and
a modest financial support.

Bohdan

============================================================================

    While most stars do not vary significantly in our lifetime, about 1% of
all stars vary on time scales of years, days, even hours, with amplitudes
from several percent to huge variations by a factor larger than one hundred.
Most variable stars have not been discovered yet, even among stars as bright
as those visible through ordinary binoculars.  In addition to variable stars
there are variable galactic nuclei (like quasars), exploding stars (like
supernovae and gamma-ray bursts), and moving objects (like asteroids).  Most
of them wait to be discovered.  Enclosed is the abstract of a paper with some
results of a pilot project: All Sky Automated Survey (ASAS).  The observations
were obtained with a fully robotic instrument located at the Las Campanas
Observatory in Chile.  This is a telephoto lens with the aperture of 75 mm and
a focal length of 135 mm.  It has a Meade/Pictor CCD camera with 512 x 768 
pixels attached to it.  A small equatorial mount is controlled by a computer.
This pilot project demonstrated that even among stars brighter than 13 mag
90% of variables have not been discovered yet.  The results may be viewed at
                 http://archive.princeton.edu/~asas/
Click on `Gallery' at the left margin, next click on any of about 100 pages,
each with a number of light curves.

    The ASAS project has expanded over the last several years, and all southern
sky is monitored every two nights.  More results will be available within
a week or two on the electronic preprint server:
                 http://arXiv.org/abs/astro-ph/

    ASAS hardware is very low cost.  The two most important elements are:
computer controlled equatorial mount and a CCD camera.  The most difficult
element is software.  I can provide software as used by the ASAS, but it
is not `industrial strength'.

    Note: there are very many ways in which ASAS type project may expand: the
sky may be monitored down to fainter stars, more frequently, with a variety
of filters.  It is essential to use standard filters to make the results
compatible with the results of other astronomers.  The most ambitious goal
is to develop a system which can detect any anomaly in the sky variability,
verify its reality automatically, and email an alert to the astronomical
community.  Enclosed is an abstract of my general review of the scientific
motivation for projects aimed at monitoring all sky for variability.  This
is highly underdeveloped area of astronomy, with new technology (CCD detectors
and computers) making a rapid progress possible at very modest cost.

                          Bohdan Paczynski
                       bp@astro.princeton.edu

------------------------------------------------------------------------------
\\
Paper: astro-ph/0005236
From: Pojmanski Grzegorz <gp@astrouw.edu.pl>
Date: Thu, 11 May 2000 18:00:15 GMT   (582kb)

Title: The All Sky Automated Survey. A Catalog of almost 3900 variable stars
Authors: Pojmanski, G
Comments: 14 pages, 6 figures, 4 tables
\\
  Results of the first two years of observations using the All Sky Automated
Survey prototype camera are presented. More than 140 000 stars in 50 Selected
Fields covering 300 sq. degrees were monitored each clear night in the I-band
resulting in the ASAS Photometric I-band Catalog containing over 50 x 10^6
individual measurements. Nightly monitoring over 100 standard stars confirms
that most of our data remains within sigma_I=0.03 of the standard I system.
Search for the stars varying on the time scales longer than a few days revealed
almost 4000 variables (mostly irregular, pulsating and binaries) brighter than
13 mag. Only 155 of them are known variables included in GCVS, 56 were observed
by Hipparcos satellite (46 were marked as variable). Among the stars brighter
than I ~ 7.5 (which are saturated on our frames) we have found about 50
variables (12 are in GCVS, 6 other in Hipparcos (Perryman etal 1997) catalog).
Because of the large volume of the data we present here only selected tables
and light-curves, but the complete ASAS Catalog of Variable Stars (currently
divided into Periodic and Miscellaneous sections) and all photometric data are
available on the Internet http://www.astrouw.edu.pl/~gp/asas/asas.html or
http://archive.princeton.edu/~asas/
\\ ( http://arXiv.org/abs/astro-ph/0005236 ,  582kb)

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http://arXiv.org/abs/astro-ph/9609073    = 
                   1997, Proceedings of 12th IAP Colloquium: "Variable Stars 
                   and the Astrophysical Returns of Microlensing Searches", 
                   Paris (Ed. R. Ferlet), p. 357

             The future of massive variability searches
                          Bohdan Paczynski 
                 Princeton University Observatory

     This is a personal review of various issues related to massive
     photometric and astrometric searches. A complete inventory of
     variable stars down to almost any magnitude limit will improve our
     understanding of the stellar evolution and the galactic structure.
     A search for detached eclipsing binaries will improve the distance
     scale, the value of the Hubble constant, and the age of the oldest
     stars. A search for supernovae will help the determination of
     cosmological parameters Omega and Lambda. A search for
     microlensing events will provide insight into the stellar mass
     function, dark matter, and may lead to a discovery of earth-mass
     planets.

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