Director, WIYN Observatory
George after a WIYN Board meeting, near his home in the Hill Farm district in Tucson.
Areas of Interest
Galaxy Distances, Dynamics, and Chemical Compositions, Planetary Nebulae,
Local Group Galaxies, Instrumentation
Recent Research Results
- Nearby Galaxies
- Dwarf Galaxies --
Taft Armandroff , Jacoby and Johns Hopkins student James Davies
have found 2
new dwarf galaxies in the Local Group : And V, And VI around M31.
Previously, there were only 3 such dwarfs near M31. The first of these,
And V, is nearly as faint as any known dwarf galaxy. Both new galaxies
were found using the Digital Sky Survey and an innovative digital image
- Planetary Nebulae in M31 -- Jacoby and
Robin Ciardullo at Penn State have measured the chemical compositions
of 15 planetary nebulae in M31. From these measurements, it is clear that
the stars in M31 are derived from a complex history of chemical enrichment
because they span a very wide range of compositions, from 20 times lower
than the Sun to just slightly higher than the Sun.
- Planetary Nebulae in Globular Clusters --
Jacoby recently completed a survey for planetary nebulae in the Milky Way
globular cluster system. Earlier investigators have failed to find any
nebulae, but PN were found in NGC 6441 and Pal 6. The total number of
nebulae in the globular cluster system was doubled with the addition of
these two. Because the clusters are so poor in planetary nebulae, it
seems that the stars must find another path to becoming white dwarfs
other than through the PN phase. Since the Sun is only slightly more
massive than typical clusters stars (having 85% the mass of the Sun),
it is questionable whether the Sun will achieve its promised future of
going through a PN phase, as well.
- Planetary Nebulae in the Galactic Center --
Jacoby and Griet Van De Steene
have identified 95 candidate planetary
nebulae at the center of our Galaxy. They have obtained follow-up spectra
for ~65 of these to confirm all but a couple as bona fide nebulae. The
chemical compositions appear to be similar to those found in M31 by
Jacoby and Ciardullo.
- Planetary -- Special Cases -- Jacoby, Gary Ferland
of Kentucky, and Kirk Korista of Western Michigan studied the
ionization structure of Abell 39
in detail. This nebula is almost perfectly spherical - quite
- Sakurai's Star --
Jacoby, Orsola De Marco
and Dave Sawyer of WIYN have been following the stellar evolution gyrations
of Sakurai's star, a former PN central star that has ejected another shell
of material and dust.
See: IAU Circulars 7065 and 7155 .
- Distant Galaxy Systems
- Stars Between the Galaxies --
Robin Ciardullo and
John Feldmeier , Jacoby has been exploring the population of
stars between galaxies in the Fornax and Virgo clusters of galaxies.
Remarkably a significant fraction of the stars and light in a cluster
come from the regions between galaxies, perhaps as much as 50% of the
entire cluster light is NOT in galaxies.
Future Research Plans
- Stellar Dynamics
- Virgo Intracluster PN --
We have been using the WIYN observatory
and the ESO VLT
to obtain velocities of the PN between the galaxies in Virgo.
The observation and analysis of planetary nebula motions in galaxies is
of growing interest because there is no better way to measure the
stellar velocities, especially for these very faint stars in Virgo.
The velocities will map out the distribution and quantity of dark matter
in the Virgo cluster far better than the galaxies because there are hundreds
of thousands of PN and only a few hundred galaxies.
- M31 --
Jacoby, Holland Ford, Xaoihui Hui, and Robin Ciardullo
have accumulated velocities
for over 800 nebulae in the nearby Andromeda galaxy, and the analysis
is underway. Preliminary results show that the bulge of the galaxy is
rotationally supported. Also, there are about 10 times fewer stars in
the galaxy halo that produce planetary nebulae than initially thought,
possibly evidence for either a very low mass or a very old halo.
Nevertheless, there seem to be several times more halo PN in M31 than
in our own Galaxy.
- Galactic Center --
The observations of the Galactic center nebulae will help define the
motions of stars in the central "bar" of our Galaxy, as well as
flagging any nebulae that originated in the halo of our Galaxy but are
presently passing near the Galactic nucleus; already, two very fast
moving candidates have been identified as possible halo visitors.
- Chemical Compositions
- The Galactic Center --
Thus far, only ~12 of the new ~90 PN in the Galactic center have been
analyzed to derive their chemical compositions. In most of the remaining
cases, it will not be possible to make the measurements because the
nebulae are extremely faint, being extinguished by an enormous of
dust between the Galactic center and the Earth. Thus, each nebula that
can be studied is an important one. We are continuing our analysis
of the existing spectra.
- M31 Nebulae --
The PN in M31 generally have chemical compositions that are not as enriched
as the Sun, even relatively close to the nucleus of the galaxy. This result
is in conflict with estimates from spectra of the combined light from
the stars in M31 which suggest that the composition of the M31 stars
should be greater than that of the Sun. Are the differences in derived
compositions due to the methodologies (nebula vs stellar)? Is there some
physical reason why enriched stars cannot make planetary nebulae that
we then can study? These and other explanations have been explored
by Jacoby and Ciardullo, but their sample of 15 nebulae is not very exhaustive.
Future studies will target many more PN in M31.
- The Small Magellanic Cloud --
With Orsola De Marco, Jacoby is planning a significant search campaign for
the faintest planetary nebulae in the SMC. The stars in the SMC have
very low chemical compositions, nearly one-tenth that of the Sun. Thus,
those stars provide an excellent test area for processes that may depend
on the metallicities of stars. For example, we will measure the strengths
of the winds coming off the PN central stars to see if they are, in fact,
weaker than those in our Galaxy.
- Dwarf Galaxies --
Simulations predict that there should be ~1000 dwarf galaxies in our
Local Group. We know of about 20. Have the surveys been so poorly
executed that most of those galaxies have not been recovered? With Taft
Armandroff and summer student Jacqueline Chen, Jacoby will be surveying
more and more of the sky to look for the missing dwarfs.
- IRAF -- Image Reduction and Analysis Facility --
Jacoby is the project scientist for the IRAF
project, setting priorities and giving scientific direction to the
project, interfacing between the programmers and the users, NOAO
management, and outside organizations interested in the project (STScI,
AXAF, EUVE), and is the PI for the Open IRAF initiative being funded by
- CCD Mosaic --
Jacoby is one of the project scientists for the
CCD Mosaic Camera .
In addition, he was the scientist responsible for the new optical correctors
recently built for the 4-m and 0.9-m that are required to provide the very
wide fields of views (50' and 80', respectively) needed by the
- ADASS Conferences --
Jacoby serves as
a member of the scientific organizing committees for the annual
Astronomical Data Analysis and Software Systems conferences.
- IAU Symposia on Planetary Nebulae --
Jacoby is a member of
IAU Commission 34 (Interstellar Matter) and the
Planetary Nebula Working Group. He has been a member of the
scientific organizing committees for the Symposia for the past
SWIFT : The Spectroscopic WIde-Field Telescope --
With Arjun Dey, Joan Najita, Sam Barden, and Chuck Claver, Jacoby has
been developing the plans for a new national facility that will be able
to collect many thousands of spectra of stars and galaxies in each exposure.
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