University of Virginia Library

Observatory Dates Stars
With 50 Year-Old File

Photographic plates of stars
taken more than 50 years ago are
being pulled from files at the
University's Leander McCormick
Observatory for use in a new
project.

As part of research aimed at
identifying intermediate-age stars,
new photographs will be taken of
the same regions of the sky and
then compared with old plates to
observe the movement of the stars
over the past half-century.

The two-year study will be
funded by a $115,000 grant from
the National Science Foundation
and carried out by Charles Tolbert,
assistant professor of astronomy,
and Philip lanna, research associate,
in collaboration with Adriaan
Blaauw (cg), director of the European
Southern Observatory in Hamburg.
Germany, and former
member of the University's Center
for Advanced Studies.

"The University is one of the
few places in the world that can do
a study like this at this time," Mr.
Tolbert said. "Not only do we have
files of photographs taken over a
50-to 60-year span, but the same
telescope, built in 1881, is still in
use."

That telescope, a 26-inch refractor-type,
was the largest in the
world when installed at the University.

It is essential that the same
telescope be used for the new
photographs so that any difference
in a star's position will be due to
actual motion and not to variations
in equipment.

The star's motion will be one of
the factors in determining whether
the star is old, intermediate-age or
young. "In the beginning, our
galaxy was a sphere of rotating gas,
probably pure hydrogen," said Mr.
Tolbert.

"As stars began to form the
rotating sphere began to flatten
into an ellipsoid. It continued to
flatten, still rotating, into a disc
shape with a bulge in the middle,"
he continued. "We expect the
intermediate-age stars to have some
sort of ellipsoidal distribution, but
no evidence yet proves it."

The researchers will also analyze
the composition of stars in an
effort to determine their age. "The
oldest stars are made out of pure
hydrogen," said Mr. Tolbert. "Intermediate-age
stars will have a
small amount of heavier elements
such as helium, carbon and nitrogen,
and the youngest stars will be
rich in heavier elements."

A star's elements can be measured
through photoelectric techniques.
In the next two years Mr.
Tolbert will go to Kitt Peak
Observatory in Tucson, Ariz., and
Carro Tololo Interamerican Observatory
in La Serena, Chile, to make
photoelectric observations of 750
regions of the sky.