[vsnet-chat 1681] (fwd) THAPA report

[Taichi Kato <tkato>]

Date: Wed, 10 Mar 1999 15:52:52 +0100
From: Peter.Kroll@STW.TU-Ilmenau.DE (Peter Kroll)
Subject: [vsnet-chat 0] THAPA report

Dear all,

a couple of weeks ago this discussion group considered the THAPA
workshop held last week at Sonneberg Observatory. It was wondered, if
somebody could give a short report. Elizabeth Griffin (Oxford,
currently in Anwerp, Belgium) prepared such a report (for other
reasons) which I would like to forward to the VSNET community. Many
thanks to Elizabeth! 

With best regards
Peter Kroll
(Sonneberg Observatory)

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

Report given by Elizabeth Griffin (e.griffin1@physics.oxford.ac.uk)

             Treasure-Hunting in Astronomical Plate Archives
             -----------------------------------------------

    Workshop held at Sonneberg Observatory, Germany, March 4 - 6, 1999


In 1928 Sonneberg Observatory initiated a "sky patrol", an open-ended project
in which the whole of the night sky is recorded whenever conditions permit.
Observations since 1962 have also been made in two colours; limiting magnitudes
are 13 to 14.  During its 70+ years of operation so far, a collection of about
a quarter of a million records has thus been made, an invaluable and
unrepeatable element of astronomy's heritage.

The focus of the Workshop was to consider, by airing various experiences and
suggestions, (a) the technical feasibility of digitizing and reducing not only
the Sonneberg archive but at least some of the other direct-plate archives in
the world, including those which have now become "closed" and neglected, (b)
the scientific potential of such archives, and (c) specific scientific goals
for the Sonneberg archive.  Though my own work is entirely spectroscopic, with
but a small area of overlap in its occasional need for stellar photometry, I
have a strong affinity for those who struggle to preserve inherited data and I
am able to inject instances of my own experience in relation to "rescuing" the
world's heritage of photographic spectra.

Sonneberg Observatory has been through turbulent times of late, having been
closed for most of 1995 whilst political battles raged over its head.  Its
funding situation is still precarious and of a short-term nature only, so the
need to identify an international purpose for research from the Sonneberg 
resources has a particular and compelling acuity.

The meeting surveyed the plate-archiving activities within the experiences of
delegates, and described and discussed the various technical concepts of
digitizing large surveys and the local solutions that had been achieved (or
avoided).  It went on to identify astrophysical results that had come out of
investigations based on such surveys, and dealt with problems of both
photometry and astrometry.  Questions of data reduction were next addressed,
and were finally absorbed into discussions on large databases.

As is inevitable whenever a group of astronomers comes together from different
research backgrounds, all found common ground at first in the type of problems
they shared (lack of information about archives, lack of access to archives,
lack of machinery to measure plates either quickly or even at all, and a lack
of common-user software for suitable reductions).  Beyond that, however, all
found plenty of astrophysical achievements to illustrate from their own
individual efforts, and all clearly had enough of their own problems to solve.
One important purpose of the Workshop was in fact addressed "outside hours" by
an impromptu meeting of those interested, in a proposal to form a Pressure
Group to work out a plan for universal protection of plate archives.  The
proposal is to create an IAU Working Group for "Inherited Astronomical
Observations" (or similar title), which will be directly answerable to the
Executive Committee of the IAU; many different aspects of astronomy are
implicated: positional, solar-system and serendipitous astronomy, variable,
periodic and long-term phenomena, etc., and restricting such a Working Group
even to a Division could curtail its purpose and intended impact.

The action of airing many different ideas and experiences from databases of
different philosophies helped to propagate new propositions and to disseminate
important advice of varied hues.  One group, for instance, showed that details
of photographic-image properties can depend upon processing conditions, and are
such as to leave a 3-D effect; this can be important for astrometry, but would
be lost if all investigations used only 2-D digitized images rather than the
depth-dependent information present on the original plates.  Other groups could
recommend software tools for specific purposes which different delegates were
finding costly in some way.  All of this was rewarding for all concerned on the
wider scene.

However, the greatest impact, to my mind, was closer to home.  Patient
examination of the Sonneberg archive has already revealed instances of
near-earth approaches of objects, and has contributed very usefully (e.g. in
planning space missions) through global "skywatch" programmes for hazardous
objects.  But most significant of all were the results of photometric
measurements of selected region of sky-patrol plates and covering some 10,000
days.  Sonneberg photometry was illustrated for 4 stars for which Hipparcos
photometry was available.  The stars were not particularly faint: 9, 11, 12 and
13 magnitude, and all cited by Hipparcos as photometrically non-varying (at
least, not during the currency of the Hipparcos measurements).  Of the four,
the two of 11 and 13 magnitude also appeared, from the Sonneberg investigation,
to be constant to within an acceptable margin (a scatter amplitude of maybe a
couple of tenths of a magnitude), whereas the stars of 9 and 12 magnitude both
showed definite variations, with amplitudes of the order of 1 magnitude and
with larger-amplitude scatter than for the constant stars.  In both cases the
period of light variations was of the order of 20 years.  We may thus have here
our first evidence of long-term variations in stellar output, variations which
have never been addressed or even suspected before, and which can only possibly
be discovered through recourse to suitable archives.

+----------------------+----------------------+-----------------------+
| Dr. Peter Kroll      |                      |                       |
+----------------------+ Sternwarte Sonneberg |   S O N N E B E R G   |
| Tel. (49) 3675 81214 | Sternwartestr. 32    |                       |
| Fax. (49) 3675 81219 | D 96515 Sonneberg    | O B S E R V A T O R Y |
| pk@stw.tu-ilmenau.de | GERMANY              |                       |
+----------------------+----------------------+-----------------------+

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